
[Federal Register Volume 81, Number 191 (Monday, October 3, 2016)]
[Rules and Regulations]
[Pages 68216-68282]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2016-22983]



[[Page 68215]]

Vol. 81

Monday,

No. 191

October 3, 2016

Part V





Environmental Protection Agency





-----------------------------------------------------------------------





40 CFR Parts 50 and 51





Treatment of Data Influenced by Exceptional Events; Final Rule

  Federal Register / Vol. 81 , No. 191 / Monday, October 3, 2016 / 
Rules and Regulations  

[[Page 68216]]


-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2013-0572, EPA-HQ-OAR-2015-0229; FRL-9952-89-OAR]
RIN 2060-AS02


Treatment of Data Influenced by Exceptional Events

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule; notification to states with areas subject to 
mitigation requirements; final guidance.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency (EPA) is finalizing 
revisions to certain sections within the regulations that govern the 
exclusion of event-influenced air quality data from certain regulatory 
decisions under the Clean Air Act (CAA). The EPA's mission includes 
preserving and improving the quality of our nation's ambient air to 
protect human health and the environment, and the CAA and the EPA's 
regulations rely heavily on ambient air quality data. However, the CAA 
also recognizes that it may not be appropriate to use the monitoring 
data influenced by ``exceptional'' events that are collected by the 
ambient air quality monitoring network when making certain regulatory 
determinations. When ``exceptional'' events cause exceedances or 
violations of the national ambient air quality standards (NAAQS) that 
subsequently affect certain regulatory decisions, the normal planning 
and regulatory process established by the CAA may not be appropriate. 
This final rule contains definitions, procedural requirements, 
requirements for air agency demonstrations, criteria for the EPA's 
approval of the exclusion of event-influenced air quality data and 
requirements for air agencies to take appropriate and reasonable 
actions to protect public health from exceedances or violations of the 
NAAQS. It reflects the experiences of the EPA, state, local and tribal 
air agencies, federal land managers and other stakeholders in 
implementing this program over the past 10 years. These regulatory 
revisions, the EPA's commitment to improved communications, our focus 
on decisions with regulatory significance, and the expressed non-
binding guidance in the preamble regarding recommendations for 
demonstration narrative and analyses to include in demonstration 
packages, protect human health and the environment while providing 
needed clarity, increasing the administrative efficiency of 
demonstration submittal process, and removing some of the challenges 
associated with implementing the Exceptional Events Rule. As part of 
the EPA's mission to protect public health, this action promulgates new 
requirements for mitigation plans for areas with known, recurring 
events. We are simultaneously using this action to provide written 
notification to those states with areas that are initially subject to 
these new requirements. In addition to finalizing revisions to the 
Exceptional Events Rule, the EPA is also announcing the availability of 
the final version of the non-binding guidance document titled Guidance 
on the Preparation of Exceptional Events Demonstrations for Wildfire 
Events that May Influence Ozone Concentrations, which applies the rule 
revisions to wildfire events that could influence monitored ozone 
concentrations.

DATES: This final rule is effective on September 30, 2016.

ADDRESSES: The EPA established Docket ID No. EPA-HQ-OAR-2013-0572 for 
this action. All documents in the docket are listed in the http://www.regulations.gov Web site. Although listed in the index, some 
information is not publicly available, e.g., Confidential Business 
Information or other information whose disclosure is restricted by 
statute. Certain other material, such as copyrighted material, is not 
placed on the Internet and will be publicly available only in hard 
copy. Publicly available docket materials are available electronically 
in http://www.regulations.gov.
    The EPA also established Docket ID No. EPA-HQ-OAR-2015-0229 for the 
related guidance document titled Guidance on the Preparation of 
Exceptional Events Demonstrations for Wildfire Events that May 
Influence Ozone Concentrations. All documents in the docket are listed 
in the http://www.regulations.gov Web site. Although listed in the 
index, some information is not publicly available, e.g., Confidential 
Business Information or other information whose disclosure is 
restricted by statute. Certain other material, such as copyrighted 
material, is not placed on the Internet and will be publicly available 
only in hard copy. Publicly available docket materials are available 
electronically in http://www.regulations.gov.

FOR FURTHER INFORMATION CONTACT:  For general information regarding 
this rule, please contact Beth Palma, U.S. EPA, Office of Air Quality 
Planning and Standards, Air Quality Policy Division, Mail Code C539-04, 
Research Triangle Park, NC 27711, telephone (919) 541-5432, email at 
palma.elizabeth@epa.gov. For general information regarding the Guidance 
on the Preparation of Exceptional Events Demonstrations for Wildfire 
Events that May Influence Ozone Concentrations, please contact Lev 
Gabrilovich, U.S. EPA, Office of Air Quality Planning and Standards, 
Air Quality Policy Division, Mail Code C539-04, Research Triangle Park, 
NC 27711, telephone (919) 541-1496, email at gabrilovich.lev@epa.gov.

SUPPLEMENTARY INFORMATION: 

I. General Information

A. Executive Summary

    Pursuant to section 319(b) of the CAA, the EPA is taking action to 
finalize revisions to the Exceptional Events Rule (codified at 40 CFR 
50.1, 50.14 and 51.930), which governs the exclusion of these event-
affected air quality data. The CAA recognizes that it may not be 
appropriate to use monitoring data influenced by ``exceptional'' events 
collected by the ambient air quality monitoring network when making 
certain regulatory determinations. When ``exceptional'' events 
influence monitoring data and cause exceedances or violations of the 
NAAQS, air agencies can request the exclusion of event-influenced data, 
and the EPA can agree to exclude these data, from the data set used for 
certain regulatory decisions.
    This section summarizes the purpose of this regulatory action and 
its major provisions and provides an overview of the associated 
guidance. After considering the comments received during the public 
comment period, we are making several changes to the promulgated rule 
language and/or the preamble, in which we provide non-binding guidance 
to assist air agencies in implementing the rule. In accordance with 
section 553(d)(3) of the Administrative Procedures Act, good cause 
exists to expedite effectiveness of this final rule, therefore, we are 
also establishing the effective date of this action to be the date that 
it is published in the Federal Register. See 5 U.S.C. 553(d)(3). Good 
cause exists when urgency of conditions are coupled with demonstrated 
and unavoidable limitations in time; primary consideration is given to 
the convenience or necessity of the people affected. In this 
circumstance, prompt effectiveness of this final rule will allow state 
governors and tribes, if they wish, to consider the final rule 
revisions in advance of submitting recommendations for area 
designations for the 2015 Ozone NAAQS, which are due by October 1, 
2016, and which could include the consideration of exceptional events. 
The

[[Page 68217]]

deadline for states and tribes to submit recommendations for area 
designations for the 2015 Ozone NAAQS is a demonstrated and unavoidable 
time limitation. Prompt effectiveness of this final rule is in the 
public interest as it will ensure adequate time for states to develop 
their exceptional events demonstrations and time for the public to 
comment on those demonstrations. In addition, typically rules are 
effective at least 30 days after publication to provide time for 
affected parties to adjust their behavior and prepare before the final 
rule takes effect. That circumstance does not apply to this final rule 
because this rule does not require a behavior change. Rather, this 
final rule revises and provides additional clarity with respect to a 
previously existing opportunity.
    We are promulgating language to define those regulatory actions 
that comprise ``determinations by the Administrator with respect to 
exceedances or violations of the [NAAQS].'' In doing so, we apply the 
provisions in CAA section 319(b) to a specific set of regulatory 
actions (e.g., designations). The final rule language returns to the 
three core statutory elements and implicit concepts of CAA section 
319(b): (1) The event affected air quality in such a way that there 
exists a clear causal relationship between the specific event and the 
monitored exceedance or violation, (2) the event was not reasonably 
controllable or preventable, and (3) the event was caused by human 
activity that is unlikely to recur at a particular location or was a 
natural event. We clarify in the preamble the general types of analyses 
and narrative that the EPA expects to see in demonstrations to address 
each of these three core statutory elements. We also clarify how to 
apply these criteria in certain scenarios and to certain event types.
    In returning to the first of the three core statutory elements 
(i.e., the event affected air quality in such a way that there exists a 
clear causal relationship between the specific event and the monitored 
exceedance or violation), we are promulgating regulatory text that 
subsumes the ``affects air quality'' element into the ``clear causal 
relationship'' criterion. We are also removing from the rule language 
the requirement for air agencies to provide evidence that the event is 
associated with a measured concentration in excess of ``normal 
historical fluctuations including background'' and replacing it with a 
requirement for a comparison of the event-related concentration to 
historical concentrations. Additionally, we are removing the 2007 
Exceptional Events Rule language commonly referred to as the ``but 
for'' criterion and focus instead on the clear causal relationship 
criterion.
    With respect to the ``not reasonably controllable or preventable'' 
criterion, the EPA is promulgating a provision that enforceable control 
measures are ``reasonable controls'' with respect to all anthropogenic 
sources that have or may have contributed to event-related emissions if 
the controls are: (1) Implemented in accordance with an attainment or 
maintenance state implementation plan (SIP), a federal implementation 
plan (FIP) or a tribal implementation plan (TIP), (2) if the EPA 
approved the plan within 5 years of the date of an event, and (3) if 
the plan addresses the event-related pollutant and all sources 
necessary to fulfill the requirements of the CAA for the SIP, FIP or 
TIP.\1\ Also for the ``not reasonably controllable or preventable'' 
criterion, the EPA is codifying in regulatory text that air agencies 
generally have no obligation to specifically address controls if the 
event was due to emissions originating outside their jurisdictional 
(i.e., state or tribal) border. Of course, a submission based on 
emissions originating outside of the submitter's jurisdictional borders 
must demonstrate that the event also meets the other exceptional events 
criteria.
---------------------------------------------------------------------------

    \1\ If the air agency is required to revise its implementation 
plan as a result of a SIP Call action pursuant to CAA section 
110(k)(5), any deference to the implementation plan's enforceable 
control measures will be determined on a case-by-case basis.
---------------------------------------------------------------------------

    With respect to the ``human activity that is unlikely to recur at a 
particular location or was a natural event'' criterion, we present 
options in this preamble that air agencies and the EPA can use to 
determine whether the recurrence frequency of an event is ``unlikely to 
recur at a particular location.'' We expand on this concept with 
regulatory language that defines a specific approach to recurrence 
frequency applicable to prescribed fire on wildland. We also clarify in 
regulatory language that natural events can recur, sometimes 
frequently, without affecting the approvability of a demonstration for 
the identified natural event and that we consider reasonably controlled 
anthropogenic emissions sources to play little or no direct role in 
causing those emissions.
    The final rule preamble and rule text clarify that air agencies 
must address all of the core statutory elements and implicit concepts 
of CAA section 319(b) within an exceptional events demonstration. To 
facilitate early communications and coordination regarding the 
identification, development and review of these demonstrations, we are 
promulgating a regulatory requirement for an initial notification by 
the air agency to the EPA of a potential exceptional event for which 
the agency is considering preparing a demonstration as a preliminary 
step before submitting a demonstration. We further establish in rule 
language that the required demonstration elements include a narrative 
conceptual model, or narrative, describing the event(s) causing the 
exceedance or violation and a discussion of how emissions from the 
event(s) led to the exceedance at the affected monitor(s); a 
demonstration that the event affected air quality in such a way that 
there exists a clear causal relationship between the specific event and 
the monitored exceedance or violation supported, in part, by a 
comparison to historical concentrations; a demonstration that the event 
was both not reasonably controllable and not reasonably preventable; 
and a demonstration that the event was a human activity that is 
unlikely to recur at a particular location or was a natural event. 
Additionally, the rule revisions require documentation that the air 
agency conducted a public comment process.
    Because affected air agencies have provided feedback regarding the 
difficulty associated with meeting the regulatory timelines in the 2007 
rule associated with data flagging, initial event descriptions and 
demonstration submittals, the EPA is promulgating revisions that remove 
specific deadlines that apply in situations other than initial area 
designations following promulgation of a new or revised NAAQS. Also 
associated with demonstration timing, the EPA is promulgating a 
provision to terminate the EPA's obligation to review a demonstration 
following a 12-month period of inactivity by the air agency. In 
addition, although we are not promulgating timelines in rule language 
for the EPA's response to submitted demonstrations, we are identifying 
in this preamble the following intended response timelines: A formal 
response to the Initial Notification (see Section IV.G.5 of this 
preamble) within 60 days, initial review of an exceptional events 
demonstration with regulatory significance within 120 days of receipt 
(see Section IV.G.7 of this preamble), a decision regarding event 
concurrence/nonconcurrence within 12 months of receipt of a complete 
demonstration (see Section IV.G.7 of this preamble), and a

[[Page 68218]]

``deferral letter'' within 60 days of receipt of a demonstration that 
the EPA determined during the Initial Notification process to not to 
have regulatory significance (see Section IV.G.7 of this preamble).
    Among the questions stakeholders have raised since promulgation of 
the 2007 Exceptional Events Rule are those regarding fire-related 
components that the preamble to the 2007 Exceptional Events Rule 
discussed, but did not fully define or clarify. This final action 
promulgates in rule language several fire-related definitions and the 
conditions under which prescribed fires could qualify as exceptional 
events, which include the use of smoke management programs (SMP) and 
the application of basic smoke management practices (BSMP). We also 
discuss that while exceptional events demonstrations and data 
exclusions requests must be submitted by the affected state/tribal 
agency(ies), or with their concurrence, we support and encourage 
federal land managers (FLMs), other federal agencies and air agencies 
to work collaboratively to prepare and submit exceptional events 
demonstrations and data exclusion requests.
    In keeping with the EPA's mission to protect public health and 
after seeking comment on approaches ranging from retaining the existing 
``mitigation'' rule requirements to promulgating new mitigation-related 
rule components, we are promulgating in regulatory language the 
requirement to develop mitigation plans in areas with ``historically 
documented'' or ``known seasonal'' exceptional events. This action 
indicates those areas to which this requirement newly applies and makes 
clear that the EPA will not concur with certain exceptional events 
demonstrations if an air agency has not submitted the related required 
mitigation plan within 2 years of the effective date of this action.
    In addition to finalizing revisions to the 2007 Exceptional Events 
Rule, this action simultaneously announces the availability of a final 
non-binding guidance document titled Guidance on the Preparation of 
Exceptional Events Demonstrations for Wildfire Events that May 
Influence Ozone Concentrations (Wildfire Guidance), which applies the 
Exceptional Events Rule Revisions to wildfire events that may influence 
ozone levels. The EPA prepared this guidance document to further 
address specific stakeholder questions regarding the Exceptional Events 
Rule and further increase the efficiency of rule implementation.
    The Wildfire Guidance provides air agencies with information on how 
to prepare and submit evidence to meet the Exceptional Events Rule 
requirements for monitored ozone exceedances caused by wildfires. The 
document includes example analyses, conclusion statements, and 
technical tools that air agencies can use to provide evidence to 
satisfy the Exceptional Events Rule criteria. The Wildfire Guidance 
also identifies wildfire and monitor-based characteristics that might 
allow for a simpler and less resource-consuming demonstration. The 
Wildfire Guidance is not an EPA rule, and in specific cases the EPA may 
depart from the guidance for reasons that the EPA will explain at the 
time of the action. As noted by commenters, while many of the technical 
analyses included in the document may also be applied to prescribed 
fire events, the guidance document does not specify how demonstrations 
for prescribed fire events can address all promulgated rule 
requirements. The public comment period for the Draft Guidance on the 
Preparation of Exceptional Events Demonstrations for Wildfire Events 
that May Influence Ozone Concentrations ran simultaneously with the 
comment period on the proposed rule revisions and closed on February 3, 
2016. The EPA received 31 comments on the draft guidance during the 
public comment period. The EPA summarizes and discusses these comments 
in a document that accompanies the final guidance document. Both the 
public comments received on the draft guidance and the EPA's discussion 
document are available in the docket at http://www.regulations.gov 
(Docket ID No. EPA-HQ-OAR-2015-0229).
    Based on feedback from interested parties on the proposed rule 
revisions and the draft Wildfire Guidance, we intend to develop 
supplementary guidance to assist air agencies in addressing the 
Exceptional Events Rule criteria for prescribed fire on wildland. This 
guidance will focus on analyses and supporting documentation 
recommended to show that prescribed fire events on wildland were 
unlikely to recur at a particular location and were not reasonably 
controllable or preventable. We intend to post the draft guidance for 
prescribed fires and instructions for providing public comment on the 
exceptional events Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events shortly after 
finalizing these rule revisions.
    Also based on feedback from interested parties, we intend to 
develop supplementary guidance to describe satisfying the Exceptional 
Events Rule criteria for stratospheric ozone intrusions. In addition, 
as we discussed in the proposal and as discussed in more detail in 
Section IV.C of this preamble, we also intend to develop a 
supplementary guidance document, Draft Guidance for Excluding Some 
Ambient Pollutant Concentration Data from Certain Calculations and 
Analyses for Purposes Other than Retrospective Determinations of 
Attainment of the NAAQS, to describe the appropriate additional 
pathways for data exclusion for some ``predicted future'' monitoring 
data applications. Once available, the EPA intends to post both draft 
guidance documents on the exceptional events Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

B. Entities Affected by This Rule

    Entities potentially affected directly by this final rule and 
associated guidance include all state air agencies and local air 
quality agencies to which a state has delegated relevant 
responsibilities for air quality management, including air quality 
monitoring and data analysis. Tribal air agencies operating ambient air 
quality monitors that produce regulatory data may also be directly 
affected. Entities potentially affected indirectly by this final rule 
and related guidance include FLMs of Class I areas, other federal 
agencies and other entities that operate ambient air quality monitors 
and submit collected data to the EPA's Air Quality System (AQS) 
database.

C. Obtaining a Copy of This Document and Other Related Information

    In addition to being available in the docket, we will post an 
electronic copy of this Federal Register document and the final 
guidance at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.

D. Judicial Review

    Under CAA section 307(b)(1), judicial review of this final action 
is available only by filing a petition for review in the United States 
Court of Appeals for the District of Columbia Circuit by December 2, 
2016. Under CAA section 307(b)(2), the requirements established by this 
final rule may not be challenged separately in any civil or criminal 
proceedings brought by the EPA to enforce the requirements.

E. Organization of this Federal Register Document

    The information presented in this document is organized as follows:


[[Page 68219]]


I. General Information
    A. Executive Summary
    B. Entities Affected by This Rule
    C. Obtaining a Copy of This Document and Other Related 
Information
    D. Judicial Review
    E. Organization of this Federal Register Document
II. Glossary of Terms and Acronyms
III. Overview of Exceptional Events Statutory Authority, Regulation 
and Implementation
IV. Final Rule Revisions
    A. Applicability of the Exceptional Events Rule: Affected 
Entities and Pollutants
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    B. Definition and Scope of an Exceptional Event
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    C. Ambient Concentration Data and Data Uses Affected by the 
Exceptional Events Rule
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    D. Definition and Scope of a Natural Event
    1. Summary of Proposal
    2. Final Rule
    3. Comments and Responses
    E. Technical Criteria for the Exclusion of Data Affected by 
Events
    1. Human Activity Unlikely To Recur at a Particular Location or 
a Natural Event
    2. Not Reasonably Controllable or Preventable
    3. Clear Causal Relationship Supported by a Comparison to 
Historical Concentration Data
    F. Treatment of Certain Events Under the Exceptional Events Rule
    1. Transported Pollution
    2. Wildland Fires
    3. Stratospheric Ozone Intrusions
    4. High Wind Dust Events
    G. Other Aspects of Identifying Exceptional Events-Influenced 
Data and Demonstration Submittal and Review
    1. Aggregation of Events
    2. Demonstrations With Respect to Multiple NAAQS for the Same 
Pollutant
    3. Exclusion of Entire 24-hour Value Versus Partial Adjustment 
of the 24-Hour Value for Particulate Matter
    4. Flagging of Data
    5. Initial Notification of Potential Exceptional Event
    6. Submission of Demonstrations
    7. Timing of the EPA's Review of Submitted Demonstrations
    8. Dispute Resolution Mechanisms
V. Mitigation
    A. Summary of Proposal
    1. Defining Historically Documented or Known Seasonal Events
    2. Mitigation Plan Components
    3. Options for Implementing Mitigation Plans
    B. Final Rule
    1. Defining Historically Documented or Known Seasonal Events
    2. Mitigation Plan Components
    3. Implementing Mitigation Plans
    C. Comments and Responses
VI. Environmental Justice Considerations
VII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review and 
Executive Order 13563: Improving Regulation and Regulatory Review
    B. Paperwork Reduction Act (PRA)
    C. Regulatory Flexibility Act (RFA)
    D. Unfunded Mandates Reform Act (UMRA)
    E. Executive Order 13132: Federalism
    F. Executive Order 13175: Consultation and Coordination With 
Indian Tribal Governments
    G. Executive Order 13045: Protection of Children From 
Environmental Health and Safety Risks
    H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use
    I. National Technology Transfer and Advancement Act
    J. Executive Order 12898: Federal Actions To Address 
Environmental Justice in Minority Populations and Low-Income 
Populations
    K. Congressional Review Act (CRA)
VIII. Statutory Authority

II. Glossary of Terms and Acronyms

    The following are abbreviations of terms used in the preamble.

AQCR Air Quality Control Region
AQS Air Quality System
BACM Best Available Control Measures
BACT Best Available Control Technology
BLM Bureau of Land Management
BMP Best management practice(s)
BSMP Basic smoke management practices
CAA Clean Air Act
CASTNET Clean Air Status and Trends Network
CBI Confidential business information
CBSA Core based statistical area
CFR Code of Federal Regulations
CO Carbon monoxide
EPA Environmental Protection Agency
FIP Federal implementation plan
FLM Federal land manager responsible for management of a federally 
owned area that has been designated a Class I area as codified in 40 
CFR part 81, subpart D
FR Federal Register
LAER Lowest Achievable Emission Rate
[mu]g/m\3\ Micrograms per cubic meter
CH4 Methane
Mph Miles per hour
NAAQS National ambient air quality standard or standards
NEAP Natural Events Action Plan
NEI National Emissions Inventory
NH3 Ammonia
NO2 Nitrogen dioxide
NOAA National Oceanic and Atmospheric Administration
NOV Notice of violation
NOX Nitric oxides
NPRM Notice of proposed rulemaking
NPS National Park Service
NRCS Natural Resources Conservation Service
NRDC Natural Resources Defense Council
NWCG National Wildfire Coordinating Group
NWS National Weather Service
OAQPS Office of Air Quality Planning and Standards, U.S. EPA
OMB Office of Management and Budget
Pb Lead
PM Particulate matter
PM10 Particulate matter with a nominal mean aerodynamic 
diameter less than or equal to 10 micrometers
PM2.5 Particulate matter with a nominal mean aerodynamic 
diameter less than or equal to 2.5 micrometers
PRA Paperwork Reduction Act
PSD Prevention of significant deterioration
RACM Reasonably available control measures
RACT Reasonably Available Control Technology
RFA Regulatory Flexibility Act
SIP State implementation plan
SMP Smoke management program(s)
SO2 Sulfur dioxide
TAR Tribal Authority Rule
TIP Tribal implementation plan
Tpy Tons per year
UMRA Unfunded Mandates Reform Act
USB U.S. background
USDA U.S. Department of Agriculture
VOC Volatile organic compound or compounds

III. Overview of Exceptional Events Statutory Authority, Regulation and 
Implementation

    The EPA's mission includes preserving and improving, when needed, 
the quality of our nation's ambient air to protect human health and the 
environment as provided by the CAA. To accomplish this, the EPA 
develops the NAAQS for criteria pollutants and oversees the states' 
programs to improve air quality in areas where the current air quality 
is not in attainment with the NAAQS and to prevent deterioration in 
areas where the air quality meets or exceeds the NAAQS. The EPA then 
evaluates the status of the ambient air as compared to these NAAQS 
using data collected in the national ambient air quality monitoring 
network established under the authority of section 319(a) of the CAA.
    Congress recognized that it may not be appropriate for the EPA to 
use certain monitoring data collected by the ambient air quality 
monitoring network and maintained in the EPA's AQS in certain 
regulatory determinations. Thus, in 2005, Congress provided the 
statutory authority for the exclusion of data influenced by 
``exceptional events'' meeting specific criteria by adding section 
319(b) to the CAA. To implement this 2005 CAA amendment, the EPA 
promulgated the 2007 Exceptional Events Rule (72 FR 13560, March 22, 
2007).
    The 2007 Exceptional Events Rule created a regulatory process 
codified at 40 CFR parts 50 and 51 (sections 50.1,

[[Page 68220]]

50.14 and 51.930). These regulatory sections, which superseded the 
EPA's previous guidance on handling data influenced by events,\2\ 
contain definitions, procedural requirements, requirements for air 
agency demonstrations, criteria for the EPA's approval of the exclusion 
of event-affected air quality data from the data set used for 
regulatory decisions and requirements for air agencies \3\ to take 
appropriate and reasonable actions to protect public health from 
exceedances or violations of the NAAQS.\4\
---------------------------------------------------------------------------

    \2\ Previous guidance and policy documents that either implied 
or stated the need for special treatment of data affected by an 
exceptional event include:
    (i) Guideline for the Interpretation of Air Quality Standards, 
U.S. EPA, OAQPS No. 1.2-008, Revised February 1977. Available from 
the National Service Center for Environmental Publications through 
its document search, retrieval and download capabilities at https://www.epa.gov/nscep.
    (ii) Guideline on the Identification and Use of Air Quality Data 
Affected by Exceptional Events (the Exceptional Events Policy), U.S. 
EPA, OAQPS, EPA-450/4-86-007, July 1986.
    (iii) Areas Affected by PM-10 Natural Events (the 
PM10 Natural Events Policy), memorandum from Mary D. 
Nichols, Assistant Administrator for Air and Radiation, to the EPA 
Regional offices, May 30, 1996. Available at http://www.epa.gov/ttn/caaa/t1/memoranda/nepol.pdf.
    (iv) Interim Air Quality Policy on Wildland and Prescribed 
Fires, U.S. EPA. April 23, 1998. Available at http://www.epa.gov/ttn/oarpg/t1/memoranda/firefnl.pdf.
    (v) Guideline on Data Handling Conventions for the PM NAAQS, 
U.S. EPA, OAQPS, EPA-454/R-98-017, December 1998.
    \3\ References to ``air agencies'' include state, local and 
tribal air agencies responsible for implementing the Exceptional 
Events Rule. The regulatory text in the 2007 Exceptional Events Rule 
often uses ``State'' to apply to ``air agencies.'' In the context of 
flagging data and preparing and submitting demonstrations, the role 
of and options available to air agencies may also apply to federal 
land managers of Class I areas and other federal agencies managing 
federal land.
    \4\ Per the definition at 40 CFR 50.1(l), an exceedance with 
respect to a national ambient air quality standard means one 
occurrence of a measured or modeled concentration that exceeds the 
specified concentration level of such standard for the averaging 
period specified by the standard. Violations of a standard are 
standard-specific and are determined by applying the standard-
specific procedures for air quality data handling identified in the 
appendices to 40 CFR part 50. For example, per the requirements in 
40 CFR part 50, appendix N, an exceedance of the 2006 24-hour 
PM2.5 NAAQS of 35 [mu]g/m\3\ occurs when the 24-hour 
concentration is above 35 [mu]g/m\3\ on a single day. A violation of 
the 2006 24-hour PM2.5 NAAQS occurs when the 3-year 
average of the annual 98th percentile 24-hour concentrations is 
above 35 [mu]g/m\3\.
---------------------------------------------------------------------------

    Shortly after promulgation, the Natural Resources Defense Council 
(NRDC) brought a petition for judicial review challenging certain 
aspects of the 2007 rule, including the EPA's definition of a natural 
event and several statements in the preamble concerning the types of 
events that could qualify as being eligible for exclusion under the 
rule provisions.\5\ Regarding the definition of a natural event, the 
D.C. Circuit Court determined that NRDC did not identify its objection 
during the rulemaking process and, therefore, did not have standing 
under CAA section 307 to challenge the definition. NRDC also challenged 
the preamble language addressing high wind events. Because the EPA did 
not address the subject high wind preamble language in final rule text, 
the D.C. Circuit Court determined the high wind events section of the 
2007 preamble to be a legal nullity.
---------------------------------------------------------------------------

    \5\ NRDC v. EPA, 559 F.3d 561 (D.C. Cir. 2009).
---------------------------------------------------------------------------

    Air agencies affected by the 2007 rule also raised questions 
regarding interpretation and implementation. The EPA acknowledges that 
applying the provisions of the 2007 Exceptional Events Rule has been a 
challenging process both for the air agencies developing exceptional 
events demonstrations and for the EPA Regional offices reviewing and 
acting on these demonstrations. In response to these challenges, in May 
2013, after extensive outreach culminating in the EPA issuing a Federal 
Register Notice of Availability \6\ seeking broad public review, the 
EPA finalized the Interim Exceptional Events Implementation Guidance 
and made these documents publicly available on the exceptional events 
Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.\7\ The EPA simultaneously acknowledged 
the need to consider additional changes through a notice-and-comment 
rulemaking effort to revise the 2007 Exceptional Events Rule. Informed 
by feedback received during the development of the Interim Exceptional 
Events Implementation Guidance \8\ and feedback received during 
listening sessions and best practice conference calls,\9\ the EPA 
issued a notice of proposed rulemaking (NPRM) on November 20, 2015 (80 
FR 72840) titled ``Treatment of Data Influenced by Exceptional Events'' 
(proposed Exceptional Events Rule Revisions) to address certain 
substantive issues raised by state, local and tribal co-regulators and 
other stakeholders and to increase the administrative efficiency of the 
Exceptional Events Rule criteria and process.
---------------------------------------------------------------------------

    \6\ 77 FR 39959 (July 6, 2012).
    \7\ The Interim Exceptional Events Implementation Guidance 
includes: The Interim Guidance to Implement Requirements for the 
Treatment of Air Quality Monitoring Data Influenced by Exceptional 
Events, the Interim Exceptional Events Rule Frequently Asked 
Questions (the Interim Q&A document), and the Interim Guidance on 
the Preparation of Demonstrations in Support of Requests to Exclude 
Ambient Air Quality Data Affected by High Winds under the 
Exceptional Events Rule (the Interim High Winds Guidance document).
    \8\ See comments in Docket ID No. EPA-HQ-OAR-2011-0887.
    \9\ The EPA hosted exceptional events listening sessions in 
August and November of 2013 for interested air agencies, FLMs, other 
federal agencies, regional planning organizations, non-governmental 
organizations and other members of the public. The EPA also held 
conference calls with some air agencies between September 2014 and 
March 2015 to further discuss exceptional events implementation 
processes and practices. A summary of these implementation ``best 
practices'' is available at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.
---------------------------------------------------------------------------

    Although the EPA has undertaken this notice-and-comment rulemaking 
effort to provide clarity and increase the administrative efficiency of 
the Exceptional Events Rule demonstration submittal process, the EPA 
recognizes that developing some exceptional events demonstrations may 
still be challenging given the case-by-case nature of each event. For 
this reason, throughout the preamble to this final action, we provide 
recommendations for language and analyses to include in demonstration 
packages (see, for example, language in Sections IV.E of this preamble, 
Technical Criteria for the Exclusion of Data Affected by Events, and 
IV.F, Treatment of Certain Events Under the Exceptional Events Rule). 
Additional detail regarding specific recommendations is available in 
the EPA's guidance documents and on the EPA's exceptional events Web 
site, which the EPA will update to incorporate the finalized rule 
changes concurrently with or shortly after promulgating the final rule. 
The EPA also intends to maintain and update the exceptional events 
submissions table on its Web site with examples of approved 
submissions. These examples may help air agencies develop demonstration 
packages; however, they may not contain the minimum level of data or 
case-specific analyses necessary for all exceptional events 
demonstrations of the same event type. The EPA encourages air agencies 
to consult with their EPA Regional office for further guidance on 
specific demonstrations.

IV. Final Rule Revisions

    This final action supersedes the 2007 Exceptional Events Rule and 
all natural events and exceptional events data handling guidance 
developed prior to the 2007 Exceptional Events Rule. This final action 
also supersedes the 2013 Interim Exceptional Events Implementation 
Guidance until such time as the EPA can revise these documents to 
reflect the revisions contained in these Exceptional Events

[[Page 68221]]

Rule Revisions. This final action accomplishes the objectives 
identified in the proposed Exceptional Events Rule Revisions by 
promulgating rule language accompanied by explanation/interpretation in 
the preamble and/or presenting non-binding guidance in the preamble.
    The public comment period for the proposed revisions to the 
Exceptional Events Rule closed on February 3, 2016. The EPA received 94 
unique, timely comments on the proposed rule revisions. The preamble to 
this final rule discusses the most significant comments received on the 
proposal and how the EPA considered them in developing the agency's 
final revisions to the Exceptional Events Rule. The Response to 
Comments document that accompanies this final rule provides more 
detailed responses to comments. The public comments received on the 
proposal and the EPA's Response to Comments document are available in 
the docket at http://www.regulations.gov (Docket ID No. EPA-HQ-OAR-
2013-0572).
    As a result of feedback received during the public comment period, 
we have changed the proposed regulatory text and/or non-binding 
guidance in the preamble in the following ways:
     Modified the provision for FLMs and other federal agencies 
to prepare and submit exceptional events demonstrations to include a 
step for the concurrence of the affected state/tribal air agency(ies);
     Modified the definition of an exceptional event to more 
clearly address drought conditions;
     Modified the list of regulatory actions included within 
the scope of the Exceptional Events Rule;
     Revised the provision for reliance on controls in an EPA-
approved SIP to satisfy the not reasonably controllable or preventable 
criterion by also including reliance on controls in FIPs and TIPs;
     Modified the required demonstration elements to support 
the clear causal relationship criterion by moving the table of analyses 
from the rule text to the preamble where it will serve as guidance;
     Added regulatory text requiring air agencies, federal land 
managers and burn managers \10\ to collaborate and document a process 
for working together to protect public health and manage air quality 
during the conduct of prescribed fires on wildland. Such discussions 
must include outreach and education regarding general expectations for 
the selection and application of appropriate BSMP and goals for 
advancing strategies and increasing adoption and communication of the 
benefits of appropriate basic smoke management practices;
---------------------------------------------------------------------------

    \10\ Throughout this preamble and the associated final rule 
text, we use the terminology ``burn manager'' to mean the party 
responsible for supervising a prescribed fire from ignition through 
fire extinguishing and cleanup, or another party in the same 
organization who represents, supervises or is supervised by said 
party and can be a communications pathway to and from such person. 
Different organizations, states, local agencies and tribes may use 
the terms burn manager, burn boss, fire manager or another similar 
term to describe the party with this responsibility. Regardless of 
the terminology, the actions of the party responsible for prescribed 
fire management must conform to and be consistent with any 
applicable local, state or federal laws and regulations, where these 
laws and regulations exist.
---------------------------------------------------------------------------

     Identified intended timelines for the EPA's response in 
this preamble; and
     Added required regulatory elements for mitigation plans 
for areas with known, recurring events.
    We discuss all of these changes in more detail in this preamble.

A. Applicability of the Exceptional Events Rule: Affected Entities and 
Pollutants

1. Summary of Proposal
    As noted in the proposal, the Exceptional Events Rule applies to 
all states, to local air quality agencies to whom a state has delegated 
relevant responsibilities for air quality management including air 
quality monitoring and data analysis, and to tribal air quality 
agencies operating ambient air quality monitors that produce regulatory 
data. The proposal also included new provisions to allow FLMs and other 
federal agencies to prepare and submit exceptional events 
demonstrations and data exclusion requests directly to the EPA. We 
included these provisions for the following reasons, which we expressed 
in the proposal. First, the CAA language at section 319(b)(3)(B)(i) 
provides authority for FLMs to initiate and submit such demonstrations 
and data exclusion requests in the language that reads, ``the 
occurrence of an exceptional event must be demonstrated by reliable, 
accurate data that is promptly produced and provided by Federal, State, 
or local government agencies.'' Second, FLMs and other federal agencies 
may operate regulatory monitors \11\ and submit collected data to the 
EPA's AQS database,\12\ and emissions from exceptional events could 
affect these same monitors. Third, allowing FLMs to prepare and submit 
demonstrations directly to the EPA could expedite the exceptional 
events demonstration development and submittal process. The EPA 
solicited comment on our proposal to allow FLMs and other federal 
agencies to prepare and submit exceptional events demonstrations and 
data exclusion requests directly to the EPA. In addition, the proposal 
explained that the final rule might modify the provision that provided 
for FLMs and other federal agencies preparing and submitting 
exceptional events demonstrations and data exclusion requests directly 
to the EPA (see 80 FR 72848).
---------------------------------------------------------------------------

    \11\ The Ambient Air Quality Surveillance provisions in 40 CFR 
part 58 include, among other elements, the requirements for 
monitoring data certification and data submittal and archive in AQS. 
40 CFR 58.3 provides that these data reporting requirements 
specifically apply to state air pollution control agencies and any 
local air pollution control agency to which the state has delegated 
authority to operate a portion of the state's monitoring network.
    \12\ For a description of one network of monitoring sites 
operated by federal agencies, see the 2014 CASTNET (Clean Air Status 
and Trends Network) Annual Network Plan, available at https://www3.epa.gov/castnet/docs/CASTNET_Plan_2014_Final.pdf, which applies 
to National Park Service (NPS) and Bureau of Land Management (BLM) 
site managers operating CASTNET monitors.
---------------------------------------------------------------------------

    The proposal also reiterated the EPA's interpretation that the 
Exceptional Events Rule applies to all criteria pollutant NAAQS \13\ 
based on the language in CAA section 319(b)(3)(B)(iv), which applies to 
exceedances or violations of ``the national ambient air quality 
standards.'' The EPA did not specifically request comment on this 
statement.
---------------------------------------------------------------------------

    \13\ There are NAAQS for carbon monoxide (CO), lead (Pb), 
nitrogen dioxide (NO2), ozone, particle pollution and 
sulfur dioxide (SO2). This applicability includes the 
primary and secondary NAAQS. At present, most of the secondary NAAQS 
are identical to the primary NAAQS for the same pollutant, so there 
is no distinction in how the Exceptional Events Rule applies. To 
date, the EPA has not encountered an exceptional event situation 
with respect to a non-identical secondary NAAQS.
---------------------------------------------------------------------------

2. Final Rule
    The Exceptional Events Rule continues to apply to all state air 
agencies and to local air quality agencies to which a state has 
delegated relevant responsibilities for air quality management, 
including air quality monitoring and data analysis. The Exceptional 
Events Rule also continues to apply to tribal air quality agencies 
operating ambient air quality monitors that produce regulatory data. 
All affected air agencies, including tribal air quality agencies, 
should use the Initial Notification of Potential Exceptional Event 
process described in more detail in Section IV.G.5 of this preamble, to 
discuss with their EPA Regional office the most appropriate approach to 
implementing the provisions of the Exceptional Events Rule.

[[Page 68222]]

    After considering the public comments, as explained in subsequent 
paragraphs and the response to comments below, we are finalizing a 
modified version of our proposal, under which FLMs and other federal 
agencies could prepare and submit exceptional events demonstrations and 
data exclusion requests directly to the EPA if the affected state/
tribal air agency(ies) concurs.\14\ Presumably, demonstrations and 
requests for exclusion prepared and submitted by FLMs or other federal 
agencies would address prescribed fires or wildfires occurring on 
federally-owned and managed land that influence concentrations at 
regulatory monitors either on federally-owned and managed land or at 
state, local, or tribal regulatory monitors. Although the EPA is 
deferring the appropriate mechanism for concurrence to the affected 
state or tribal air agency(ies) in accordance with 40 CFR 
50.14(a)(1)(ii)(A)(2), the EPA can envision several acceptable 
approaches, some of which follow.
---------------------------------------------------------------------------

    \14\ We note that any agency, group or individual could submit 
an exceptional events demonstration. However, the EPA is obligated 
to consider only those submittals that meet the requirements of this 
final rule and come from authorized agencies (i.e., all states; 
local air quality agencies to whom a state has delegated relevant 
responsibilities for air quality management including air quality 
monitoring and data analysis; tribal air quality agencies operating 
ambient air quality monitors that produce regulatory data; and FLMs 
or other federal agencies to whom the relevant state has granted 
approval). Further, the EPA cannot take action on material submitted 
by an unauthorized party.
---------------------------------------------------------------------------

     An air agency could provide written authorization to the 
FLMs or other federal agencies owning land or operating air quality 
monitoring stations to prepare and directly submit exceptional events 
demonstrations to the EPA. Any such authorization must conform to and 
be consistent with any applicable state laws and regulations. The 
written authorization (i.e., letter from the air agency official 
responsible for preparing demonstrations) would specify the conditions 
under which the FLM could submit a demonstration directly to the EPA 
and whether the FLM could initiate the Initial Notification of 
Potential Exceptional Event (either with or without including the 
affected air agency(ies) in this process). The affected air agency 
would submit a copy of the authorization to the reviewing EPA Regional 
office either in advance of the demonstration submittal and/or with the 
Initial Notification of Potential Exceptional Event process associated 
with a specific event or events. An air agency selecting this option 
would need to provide the submitting FLM or other federal agency with a 
case-by-case concurrence in accordance with 40 CFR 
50.14(a)(1)(ii)(A)(2), which requires that a demonstration-specific 
concurrence from the air agency accompany each submittal. The FLM would 
include the concurrence with its submission to the EPA.
     An air agency could agree, on a case-by-case basis, to 
allow an FLM or other federal agency to develop and submit a complete 
demonstration for an event or events directly to the EPA. Under this 
scenario, the air agency could notify the EPA during the Initial 
Notification of Potential Exceptional Event process that an FLM will 
submit demonstration(s) for a particular event(s) or particular types 
of events, specifying the event type(s), pollutant(s) and date(s). An 
air agency selecting this option would need to provide the submitting 
FLM or other federal agency with a case-by-case concurrence, in 
accordance with 40 CFR 50.14(a)(1)(ii)(A)(2), which the FLM would 
include with its submission to the EPA.
     The air agency could ask the FLM to prepare the agreed-
upon demonstration for submittal to the affected air agency. The FLM 
would then independently prepare the demonstration and submit it to the 
affected air agency. The air agency, in turn, could submit the 
demonstration to the EPA with a cover letter indicating that the FLM or 
federal agency prepared the demonstration, that the affected state/
tribal air agency agrees with the content and the affected state/tribal 
air agency requests that the EPA review and take action on the 
submitted demonstration.
     Another option might consist of the air agency and the 
affected FLM collaboratively developing demonstrations for submittal by 
the affected air agency. In this scenario, the air agency and the FLM 
would likely agree to a division of responsibilities for specific 
analyses or sections of a demonstration.
    If an air agency agrees that FLMs or other federal agencies may 
prepare and submit exceptional events demonstrations and data exclusion 
requests directly to the EPA, then the FLM-prepared demonstrations must 
meet all of the provisions in the Exceptional Events Rule, including 
the requirement for a public comment period on a prepared demonstration 
\15\ and the requirements related to schedules and procedures for 
demonstration submittal that apply to state agencies that operate the 
affected monitors. Regardless of the approach selected, the EPA 
encourages discussions between the FLM and the affected state/tribal 
air agency(ies) similar to those described in the Initial Notification 
of Potential Exceptional Event process (see Section IV.G.5 of this 
preamble) to ensure that the FLM and the air agency(ies) share a common 
understanding regarding the potential event, share relevant information 
and data, and understand the timeline for flagging data in AQS and 
submitting the demonstration. A number of areas have established local 
or regional collaboratives whose goals include improving the health of 
local ecosystems (e.g., wildlands), increasing community resiliency to 
wildfire, communicating air quality and public health impacts and 
communicating the results and benefits of prescribed fire management 
and implementation programs.\16\
---------------------------------------------------------------------------

    \15\ A public comment opportunity is important prior to 
submission to the EPA because under the Exceptional Events Rule, the 
EPA is not required to provide a public comment opportunity prior to 
concurring or non-concurring with an air agency's request to exclude 
data. The EPA generally provides a public comment opportunity before 
using air quality data, with or without such exclusions, in a final 
regulatory action. States typically provide an opportunity for 
public comment by posting draft demonstrations on a Web site. 
Federal agencies could do the same.
    \16\ See, for example, the Fire Memorandum of Understanding 
(MOU) Partnership, consisting of multiple state and federal forestry 
agencies, prescribed fire councils and conservation agencies, who 
work collaboratively with air agencies in California to resolve 
issues related to managed fire and protection of public health. 
Additional information available at http://www.sierraforestlegacy.org/CF_ManagingFire/FireMOU.php and in 
comment number EPA-HQ-OAR-2013-0572-0138.
---------------------------------------------------------------------------

    Also related to the entities affected by the Exceptional Events 
Rule, the proposal asserted that, as the single actor responsible for 
administering air quality planning and management activities within its 
jurisdictional boundaries, the state, exclusive of tribal lands, is 
ultimately responsible for submitting exceptional events demonstrations 
for exceedances that occur at all regulatory monitoring sites within 
the boundary of the state. While the state can request that FLMs or 
other federal agencies or local agencies to which a state has 
authorized relevant responsibilities develop and submit exceptional 
events demonstrations for events that influence concentrations at 
regulatory monitors operated by these entities, the state can always 
submit demonstrations for events that meet the requirements of the 
Exceptional Events Rule for any regulatory monitor within its 
jurisdictional bounds, including those operated by FLMs, other federal 
agencies and delegated local agencies. The state retains the authority 
to decide

[[Page 68223]]

whether to concur with and forward an exceptional events submittal 
generated by another agency. For example, if a state does not concur 
with the local agency's, FLM's, other federal agency's or other 
entity's exceptional events claim, the state can decide not to forward 
the submittal to the EPA even if the state has authorized the federal 
or local government agencies (who are also authorized by the CAA to 
produce and provide data) to prepare and submit demonstrations directly 
to the EPA. At the suggestion of several commenters, the EPA is adding 
regulatory language to 40 CFR 50.14(a)(1)(ii) to clarify this point. 
Where questions arise, the reviewing EPA Regional office can provide 
assistance and direction as part of the Initial Notification of 
Potential Exceptional Event process. In addition to requesting that 
FLMs, other federal agencies or delegated local agencies prepare or 
assist in the preparation of demonstration analyses, a state can also 
request the same of industrial facilities operating regulatory monitors 
experiencing event-influenced exceedances. The EPA cannot act on 
demonstrations submitted directly by industrial facilities. The 
authorizing state is responsible, at its discretion, for submitting 
demonstrations prepared by industrial entities.
    Consistent with our proposal, we are also promulgating regulatory 
language at 40 CFR 50.14(a)(1)(i) that the Exceptional Events Rule 
applies to the treatment of data showing exceedances or violations of 
any criteria pollutant NAAQS. AQS retains the capability for air 
agencies to flag all criteria pollutant data and for the EPA to concur, 
as appropriate, on requests for exclusion.
3. Comments and Responses
    Although three commenters agreed with the EPA's proposal to allow 
FLMs and other federal agencies to initiate a request for data 
exclusion if the FLM either operates a regulatory monitor that has been 
affected by an exceptional event or manages land on which an 
exceptional event occurred that influenced a monitored concentration at 
a regulatory monitor, the large majority of commenters disagreed with 
this proposed provision. State and local air agencies, as well as 
several regional planning organizations, commented that it is 
inappropriate for the EPA to allow agencies that are not directly 
responsible and accountable for managing and/or assuring air quality to 
submit exceptional event demonstrations or data exclusion requests. 
Several commenters noted that FLMs and other federal agencies may have 
different functions and priorities and that the protection of air 
quality and public health may not be a primary objective. Some of these 
same commenters noted that while the proposed rule language at 40 CFR 
50.14(a)(l)(ii)(A)(2) allowed another agency to initiate a request 
``only after discussing such submittal with the State in which the 
affected monitor is located,'' ``discussing'' does not require 
``agreement'' from the state or a requirement that the FLM incorporate 
the state's feedback into its submittal. These commenters stated that, 
under the proposed requirements, an FLM could submit a request to 
exclude data over the objections of the state with primary 
responsibility to regulate air quality, which could potentially create 
legal conflicts between agencies. Another commenter suggested allowing 
FLMs to submit demonstrations only for regulatory monitors owned by the 
FLM or located on FLM-managed land rather than for state-owned and 
operated monitors influenced by an event (e.g., fire) on FLM-managed 
land. Two states and one industry association commenter suggested 
following an approach allowing, on a case-by-case basis, FLMs to submit 
demonstrations and requests for data exclusion if the affected state/
tribal air agency(ies) agrees and if the FLM works with the affected 
state/tribal air agency(ies) through the demonstration development and 
submittal process.
    The EPA continues to believe that allowing FLMs to prepare and 
submit demonstrations directly to the EPA could expedite the 
exceptional events demonstration development and submittal process 
because, in many cases, the lands managed and/or owned by federal 
entities are not entirely within the jurisdictional boundary of a 
single state or local government and because federal entities may 
either initiate prescribed fires or fight wildfires on lands managed 
and/or owned by federal entities. We also recognize that under the CAA, 
states, exclusive of tribal lands, are primarily responsible for the 
administration of air quality management programs within their borders, 
which includes monitoring and analyzing ambient air quality, submitting 
monitoring data to the EPA, which are then stored in the EPA's AQS 
database, and identifying measurements that may warrant special 
treatment under the Exceptional Events Rule. As commenters have noted, 
and as the EPA recognizes, FLM submittal of exceptional events 
demonstrations and air agency objectives for air quality management may 
conflict. Federal land managers do play an important role in helping 
states and tribes improve the air quality in those areas that do not 
meet the NAAQS. The General Conformity Rule requires that federal 
agencies work with state, tribal and local governments in nonattainment 
and maintenance areas to ensure that federal actions conform to any 
applicable SIP, FIP or TIP. However, because states and tribes are 
ultimately responsible for administering air quality management 
programs within their borders, which could include addressing air 
quality and health impacts from wildfire emissions, the EPA is 
finalizing a modified version of our proposal, under which FLMs and 
other federal agencies could prepare and submit exceptional events 
demonstrations and data exclusion requests directly to the EPA with the 
agreement of the affected state/tribal air agency(ies). We believe that 
this approach, which requires the agreement of the affected state/
tribal air agency(ies), could encompass all of the alternative 
approaches noted by commenters representing state, local and regional 
planning organizations. Deferring the approach to achieve agreement to 
the affected air agencies provides individual air agencies with the 
flexibility to account for any state/tribal-specific authorities that 
may limit an agency's ability to regulate certain types of air quality 
concerns. Fire plays a critical role in restoring resilient ecological 
conditions in our wildlands. In addition, the increased use of 
prescribed fire and managed wildfire can reduce the effects of 
catastrophic wildfire. The EPA strongly encourages collaboration 
between the FLMs and other federal agencies and the appropriate state/
tribal air agency(ies) during the event identification and 
demonstration development process regardless of who ultimately submits 
the demonstration.
    Also concerning the entities affected by the Exceptional Events 
Rule, one commenter asked for clarification regarding whether 
industrial facilities operating regulatory monitors can submit 
demonstrations directly to the EPA. Other commenters asked that the EPA 
clarify whether states and tribes can always submit demonstrations for 
any monitors within their jurisdictional bounds. These commenters also 
asked whether the EPA would allow and/or evaluate ``competing'' 
demonstrations.
    The EPA notes in the final rule section of this preamble that while 
industrial facilities may operate regulatory monitors that experience 
event-influenced exceedances and, at the request of the state, such 
facilities may prepare demonstrations for these exceedances, the EPA 
cannot act on

[[Page 68224]]

demonstrations submitted directly by industrial facilities. The CAA 
language at section 319(b)(3)(B)(i) reads, ``the occurrence of an 
exceptional event must be demonstrated by reliable, accurate data that 
is promptly produced and provided by Federal, State, or local 
government agencies.'' Additionally, the CAA language at 
319(b)(3)(B)(iv) requires that the EPA's implementing regulations 
provide that ``there are criteria and procedures for the Governor of a 
State to petition the Administration to exclude air quality monitoring 
data. . . .'' Under the CAA, states, exclusive of tribal lands, are 
primarily responsible for the administration of air quality management 
programs within their borders. States can delegate relevant 
responsibilities for air quality management to local agencies, but the 
CAA does not provide for delegation of these responsibilities to 
industrial facilities. Where industrial facilities operate regulatory 
monitors, the state is ultimately responsible for ensuring that 
collected data are uploaded into AQS and for verifying the accuracy of 
these data. Thus, the authorizing state, at its discretion, is 
responsible for submitting any demonstrations prepared by industrial 
entities. The EPA has also clarified in the preamble that a state (or 
tribe) can always submit demonstrations for events that meet the 
requirements of the Exceptional Events Rule for any regulatory monitor 
within its jurisdictional bounds, including those operated by FLMs, 
other federal agencies, delegated local agencies, and industrial 
facilities. We have added regulatory language to 40 CFR 50.14(a)(1)(ii) 
to clarify this point.
    Another commenter noted that CAA section 319(b)(3)(B)(i) provides 
that ``the occurrence of an exceptional event must be demonstrated by 
reliable, accurate data that is promptly produced and provided by 
Federal, State, or local government agencies.'' The commenter maintains 
that this provision allows federal, state or local government agencies 
to produce and provide data, but not to prepare and submit 
demonstrations.
    The EPA agrees that the identified CAA language grants specific 
authority to state, federal and local government agencies to produce 
and provide data. The EPA also notes, however, that nothing in the CAA 
language at 319 explicitly restricts federal and local government 
agencies from submitting demonstrations if the state agrees. Section 
319(b)(3)(B)(iv) of the CAA directs the EPA to develop criteria and 
procedures for the ``Governor of a State to petition the Administrator 
to exclude air quality monitoring data. . . .'' The EPA's implementing 
regulatory language at 40 CFR 50.14(b)(1) says that the EPA shall 
exclude data from use in determinations of exceedances and NAAQS 
violations where a state demonstrates to the EPA's satisfaction that an 
exceptional event caused a specific air pollution concentration in 
excess of one or more NAAQS. The language ``where a State 
demonstrates'' has historically been interpreted to mean that only 
states can initiate the exceptional events process and submit 
demonstrations. A state may delegate the authority for preparing and 
submitting demonstrations to local government agencies that are 
authorized by the CAA to produce and provide data. In this action, the 
EPA is promulgating regulatory language that authorizes federal 
agencies to prepare and submit demonstrations if the affected state 
concurs, on a case-by-case basis, on the preparation and submission of 
demonstrations by those federal agencies. Submissions by delegated 
local agencies and/or state-concurred demonstrations by federal 
agencies have the effect of a state ``demonstration.'' Additionally, 
the state maintains the ultimate responsibility for submitting 
exceptional events demonstrations for events influencing concentrations 
at any regulatory monitor within its jurisdictional bounds.
    Two tribal commenters asked the EPA to clarify how the provisions 
in the Exceptional Events Rule apply to tribes. One of these commenters 
asked that this clarification include regulatory text to define 
``state'' and ``tribe.'' The EPA is not adding regulatory text to 
define ``state'' and ``tribe,'' but instead intends to apply the 
definitions set forth in the Tribal Authority Rule (TAR) at 40 CFR 
49.2. At 40 CFR 49.2(c), an Indian tribe or tribe is defined as ``any 
Indian tribe, band, nation, or other organized group or community, 
including any Alaska Native village, which is federally recognized as 
eligible for the special programs and services provided by the United 
States to Indians because of their status as Indians.'' Section 40 CFR 
49.2(e) defines a state as ``a State, the District of Columbia, the 
Commonwealth of Puerto Rico, the Virgin Islands, Guam, and American 
Samoa and includes the Commonwealth of the Northern Mariana Islands.''
    We further clarify the applicability to tribes by reiterating the 
language that appears in Section IV.A.1 of this preamble, which states 
that the Exceptional Events Rule applies to all states; to local air 
quality agencies to whom a state has delegated relevant 
responsibilities for air quality management including air quality 
monitoring and data analysis; and to tribal air quality agencies 
operating ambient air quality monitors that produce regulatory data. 
Throughout the preamble and regulatory language associated with this 
final action, we use the terminology ``state,'' ``tribe'' and ``air 
agency'' somewhat interchangeably. Footnote 3 in this document 
clarifies that references to ``air agencies'' are meant to include 
state, local and tribal air agencies responsible for implementing the 
Exceptional Events Rule. The regulatory text in the 2007 Exceptional 
Events Rule often uses ``State'' to apply to ``air agencies.'' To be an 
affected entity for purposes of this rule, the air agency must first 
operate one or more ambient air quality monitors that produce 
regulatory data. The provisions of this rule apply uniformly to state 
and tribal air agencies (and to authorized federal and local agencies) 
that meet this condition. Tribal air quality agencies that operate air 
quality monitoring networks that produce regulatory data that are 
affected by emissions from exceptional events should consult with the 
EPA Regional office prior to addressing the procedures and requirements 
associated with excluding data that have been influenced by exceptional 
events. As we have in the past, the EPA will continue to work with 
tribes in implementing the provisions of the Exceptional Events Rule, 
including these rule revisions.
    We neither solicited nor received comment regarding applying the 
provisions of the Exceptional Events Rule to the treatment of data 
showing exceedances or violations of any criteria pollutant NAAQS and 
we are making no changes to the rule with respect to this issue.

B. Definition and Scope of an Exceptional Event

1. Summary of Proposal
    The EPA proposed and solicited comment on the following generally 
applicable changes to the 2007 Exceptional Events Rule with respect to 
clarifying what constitutes an exceptional event:
     Revising the definition of exceptional event by including 
the concept of considering the combined effects of an event and the 
resulting emissions.
     Removing the ``but for'' element.
     Moving the ``clear causal relationship'' element into the 
list of criteria that explicitly must be met for data to be excluded.

[[Page 68225]]

     Subsuming the ``affects air quality'' element into the 
``clear causal relationship'' element.
     Removing the requirement to provide evidence that the 
event is associated with a measured concentration in excess of ``normal 
historical fluctuations including background'' and replacing it with a 
requirement for a comparison of the event-related concentration to 
historical concentrations.

The proposal provided a detailed rationale for each of these proposed 
changes, which we summarize here.

    With respect to revising the definition of an exceptional event by 
including the combined effects of an event and the resulting emissions, 
the proposal noted that a physical event may or may not generate 
emissions and these emissions may or may not reach a regulatory monitor 
and result in an exceedance or violation of a NAAQS. Each of these 
components (i.e., a physical event that generates emissions, transport 
of event-generated pollution to a monitor, and an exceedance or 
violation at a regulatory monitor) is necessary for an event to qualify 
as an exceptional event. The EPA would not consider the physical event 
(e.g., a high wind or the wildfire) to be an exceptional event unless 
the resulting event-generated pollution (e.g., particulate matter (PM) 
or ozone) reached and caused an exceedance or violation at a monitoring 
location or locations.
    The EPA elaborated on this concept by providing several examples, 
one of which was drought. The proposal stated that while the CAA 
definition of an exceptional event excludes ``a meteorological event 
involving high temperatures or lack of precipitation,'' the EPA 
recognizes that high temperatures and drought conditions can contribute 
to exceedances and violations caused by other exceptional events, such 
as high wind dust events. The proposal further noted that if an air 
agency submits evidence showing that a severe drought that resulted in 
arid conditions (e.g., lower than typical soil moisture content, 
decreased vegetation) was combined with an event (e.g., a high wind 
event) that falls within the CAA definition of an exceptional event and 
meets all of the requirements, provisions and criteria in the 
Exceptional Events Rule, then these data could be considered eligible 
for exclusion under the provisions of the Exceptional Events Rule. The 
proposal also stated that high temperatures, stagnations and inversions 
alone would not be eligible for exclusion under the Exceptional Events 
Rule by the very clear provisions of the CAA. The proposal stated the 
EPA's belief that Congress intended air agencies to compensate for the 
effects of high temperature, stagnation and inversions through the 
development of SIPs.
    In our November 2015 action, the EPA proposed to rely more directly 
upon the statutory requirement at CAA section 319(b)(3)(B)(ii) by 
removing the regulatory requirement at 40 CFR 50.14(c)(3)(iv)(D) that 
``there would have been no exceedance or violation but for the event'' 
(i.e., the ``but for'' criterion). The proposal explained that in the 
2007 Exceptional Events Rule, the EPA derived the ``but for'' criterion 
from the language at CAA section 319(b)(3)(B)(ii), which requires ``a 
clear causal relationship . . . between the measured exceedances . . . 
and the exceptional event to demonstrate that the exceptional event 
caused a specific air pollution concentration at a particular air 
quality monitoring location'' \17\ and the requirement that there be 
``criteria and procedures for the Governor of a State to petition the 
Administrator to exclude. . .data that is directly due to the 
exceptional events.'' \18\ Air agencies and the EPA have, in some 
cases, historically interpreted the ``but for'' criterion as implying 
the need for a strict quantitative analysis of the estimated air 
quality impact from the event. To clarify the intended approach, the 
EPA proposed removing the ``but for'' regulatory language and focusing 
on the ``clear causal relationship'' statutory criterion applied to the 
specific case, using a weight of evidence approach.
---------------------------------------------------------------------------

    \17\ The EPA believes that the terminology ``specific air 
pollution concentration'' refers to the identified exceedance or 
violation rather than a specific increment in the measured 
concentration, which implies quantitative source attribution and a 
supporting quantitative analysis.
    \18\ CAA section 319(b)(3)(B)(iv) (emphasis added).
---------------------------------------------------------------------------

    The proposal also modified the regulatory language in 40 CFR 
50.14(c)(3)(iv) to more clearly indicate, consistent with the CAA 
directive, the requirement to ``demonstrate'' versus to merely 
``provide evidence'' that a clear causal relationship must exist 
between the specific event and the monitored exceedance. Also 
consistent with Congressional intent and air agencies' and the EPA's 
experience in implementing the 2007 Exceptional Events Rule, the EPA 
proposed to integrate the phrase ``affected air quality'' into the 
clear causal relationship criterion. The proposal explained that 
separately requiring an air agency to provide evidence to support a 
conclusion that an event ``affects air quality'' is unnecessary in 
light of a mandatory clear causal relationship showing. The proposal 
expressed that if an air agency demonstrates that an event has a clear 
causal relationship to an exceedance or violation of a NAAQS, then the 
event has certainly affected air quality.
    Finally, the EPA proposed to remove the requirement for air 
agencies to provide evidence that the event is associated with a 
measured concentration in excess of ``normal historical fluctuations 
including background'' and replace it with a requirement to compare the 
event-influenced concentration to historical concentrations. The 
proposal clarified that an air agency does not need to prove a specific 
``in excess of'' fact in developing these comparisons to historical 
concentrations. The EPA proposed these comparisons to support the clear 
causal relationship criterion.
    The proposal stressed that making these changes would result in 
returning to the following three core statutory elements of CAA section 
319(b) that air agencies must meet when requesting that the EPA exclude 
event-related concentrations from regulatory determinations:
     The event affected air quality in such a way that there 
exists a clear causal relationship between the specific event and the 
monitored exceedance or violation,
     The event was not reasonably controllable or preventable, 
and
     The event was a human activity that is unlikely to recur 
at a particular location or was a natural event.

We proposed to include these core statutory elements in the revised 
regulatory definition of an exceptional event.
2. Final Rule
    As proposed, and as supported by numerous commenters, we are 
finalizing and incorporating into the regulatory definition of an 
exceptional event the following three core statutory elements of CAA 
section 319(b) that air agencies must meet when requesting that the EPA 
exclude event-related concentrations from regulatory determinations:
     The event affected air quality in such a way that there 
exists a clear causal relationship between the specific event and the 
monitored exceedance or violation,
     The event was not reasonably controllable or preventable, 
and
     The event was a human activity that is unlikely to recur 
at a particular location or was a natural event.
    This section of the final rule preamble focuses on the definition 
of an

[[Page 68226]]

exceptional event particularly as it incorporates these three elements. 
We discuss additional detail surrounding the individual criteria (i.e., 
clear causal relationship, not reasonably controllable or preventable 
and human activity/natural event) in Section IV.E of this preamble, 
Technical Criteria for the Exclusion of Data Affected by Events.
    While we are incorporating the previously identified elements into 
the definition of an exceptional event, after considering the public 
comments, as discussed more fully in the following paragraphs, we are 
finalizing the following slightly modified version of our proposed 
definition of an exceptional event: Exceptional event means an event(s) 
and its resulting emissions that affect air quality in such a way that 
there exists a clear causal relationship between the specific event(s) 
and the monitored exceedance(s) or violation(s), is not reasonably 
controllable or preventable, is an event(s) caused by human activity 
that is unlikely to recur at a particular location or a natural 
event(s), and is determined by the Administrator in accordance with 40 
CFR 50.14 to be an exceptional event. It does not include air pollution 
relating to source noncompliance. Stagnation of air masses and 
meteorological inversions do not directly cause pollutant emissions and 
are not exceptional events. Meteorological events involving high 
temperatures or lack of precipitation (i.e., severe, extreme or 
exceptional drought) also do not directly cause pollutant emissions and 
are not considered exceptional events. However, events involving high 
temperatures or lack of precipitation may promote occurrences of 
particular types of exceptional events, such as wildfires or high wind 
events, which do directly cause emissions. We presented this concept in 
the proposal (see 80 FR 72848), and the EPA is codifying it in the 
final rule to prevent confusion, as explained below.
    After considering the public comments received, as discussed as 
follows, we have included in the revised regulatory definition the 
concept of ``event'' or ``events'' to convey that one or more events 
and their resulting emissions could be eligible for consideration in 
the aggregate under the provisions in 40 CFR 50.14. We have also 
revised the definitional language to ``monitored exceedance(s) or 
violation(s)'' to indicate that a single event can cause multiple NAAQS 
exceedances or violations either occurring on the same day at multiple 
monitors or occurring at one or more monitors on multiple days. The 
revised definition also clarifies, at the suggestion of a commenter, 
our position with respect to ``meteorological events involving high 
temperatures or lack of precipitation'' (i.e., severe, extreme or 
exceptional drought). We include the qualifiers ``severe, extreme or 
exceptional drought'' to distinguish drought categories from abnormally 
dry conditions. In using this language, we incorporate by reference the 
conditions described in the U.S. Drought Monitor available at http://droughtmonitor.unl.edu/ and produced through a partnership between the 
National Drought Mitigation Center at the University of Nebraska-
Lincoln, the United States Department of Agriculture (USDA) and the 
National Oceanic and Atmospheric Administration (NOAA).
3. Comments and Responses
    In considering the three core statutory elements of CAA section 
319(b), we note that both the not reasonably controllable or 
preventable criterion and the human activity/natural event criterion 
are from the statutory language defining the term ``exceptional event'' 
at CAA section 319(b)(1)(A). The criterion that the event affected air 
quality in such a way that there exists a clear causal relationship 
between the specific event and the monitored exceedance or violation 
combines the statutory ``affects air quality'' definitional element at 
CAA section 319(b)(1)(A) with the ``clear causal relationship'' 
statutory requirement at CAA section 319(b)(3)(B) and removes the 
regulatory-only ``but for'' language. Because this section of the final 
rule preamble focuses on the definition of an exceptional event 
particularly as it incorporates the statutory elements, we address 
comments related to the statutory elements here and discuss the 
application of each of these elements in Section IV.E of this preamble.
    Numerous commenters supported, and one commenter representing 
several environmental groups opposed, the EPA's incorporating the 
``affects air quality'' criterion into the clear causal relationship 
element. Commenters supporting this approach agreed with the EPA's 
position that if an air agency demonstrates that an event has a clear 
causal relationship to an exceedance or violation of a NAAQS, then the 
event has certainly affected air quality and that a submitting air 
agency does not need to address ``affects air quality'' as a distinct 
component. The commenter opposing this approach noted that the EPA 
cannot escape the plain language of the CAA that ``affects air 
quality'' and ``clear causal relationship'' are two requirements and 
must be addressed individually. The EPA does not disagree that in the 
definition of exceptional event, the CAA language at section 
319(b)(1)(A)(i) specifically identifies ``affects air quality'' as a 
defining term. CAA section 319 does not, however, provide any 
indication regarding how an air agency should demonstrate that an event 
``affects air quality.'' Rather, the requirements set forth at CAA 
section 319(b)(3)(B) indicate that the EPA's implementing regulations 
shall provide that (i) the occurrence of an exceptional event must be 
demonstrated by reliable, accurate data that are promptly produced and 
provided by federal, state or local government agencies; (ii) a clear 
causal relationship must exist between the measured exceedances of a 
NAAQS and the exceptional event to demonstrate that the exceptional 
event caused a specific air pollution concentration at a particular air 
quality monitoring location; (iii) there is a public process for 
determining whether an event is exceptional; and (iv) there are 
criteria and procedures for the Governor of a state to petition the 
Administrator to exclude air quality monitoring data that are directly 
due to exceptional events from use in determinations by the 
Administrator with respect to exceedances or violations of the NAAQS. 
In subsuming the ``affects air quality'' element into the ``clear 
causal relationship'' criterion we are simply defining the approach by 
which an air agency must show that the event affected air quality.
    Similarly, the large majority of commenters supported, and three 
commenters representing environmental groups opposed, the EPA's 
proposal to remove the ``but for'' criterion. The commenters opposing 
the removal of the ``but for'' criterion explain that the EPA correctly 
acknowledged in the 2007 rule that the ``but for'' criterion was 
derived from the following two statutory requirements: (1) CAA section 
319(b)(3)(B)(ii), which requires ``a clear causal relationship . . . 
between the measured exceedances . . . and the exceptional event to 
demonstrate that the exceptional event caused a specific air pollution 
concentration at a particular air quality monitoring location'' and (2) 
CAA section 319(b)(3)(B)(iv), which requires that the EPA develop 
``criteria and procedures for the Governor of a State to petition the 
Administrator to exclude . . . data that is directly due to the 
exceptional events.'' (Emphasis added.) The commenters argue that the 
EPA's proposal to rely more directly upon the ``clear causal 
relationship'' statutory

[[Page 68227]]

element effectively ignores the statutory requirement that excluded 
data be ``. . . directly due to the exceptional events.'' The EPA 
disagrees with the commenters on this point. While we are finalizing 
our proposal to remove the ``but for'' regulatory requirement, we are 
retaining the ``direct causal'' statutory language in the regulatory 
definition of exceptional event. This revised regulatory language, 
along with our provided example analyses in this preamble (see Section 
IV.E.3 of this preamble) and in our associated guidance documents, more 
clearly conveys the strength and robustness of our intended weight of 
evidence approach \19\ and removes some of the challenges associated 
with implementing a strict ``but for'' demonstration.\20\ Further, the 
``directly due'' concept is represented through the totality of the 
requirements in the revisions to the Exceptional Events Rule that we 
are promulgating, including that a demonstration show a ``clear causal 
relationship'' between ``an event(s) and its resulting emissions'' and 
``the monitored exceedance(s) or violation(s).''
---------------------------------------------------------------------------

    \19\ As we indicated in our November 2015 proposal and in the 
preamble to the 2007 Exceptional Events Rule, an air agency's ``but 
for'' analysis does not necessarily need to be precise. Rather, we 
indicated that the EPA would use a holistic ``weight of evidence'' 
approach in analyzing submitted demonstration packages. The 2007 
preamble further explained that a ``weight of evidence demonstration 
can present a range of possible concentrations, which is not as 
technically demanding as justifying a specific adjustment to a 
measured value.'' (See 72 FR 13570, March 22, 2007).
    \20\ Since promulgation of the 2007 rule, the ``but for'' 
criterion has often been interpreted as implying the need for a 
strict quantitative analysis to show a single value, or at least an 
explicitly bounded plausible range, of the estimated air quality 
impact from the event. As a result, some air agencies began using 
burdensome approaches to provide quantitative analyses in their 
exceptional events demonstrations to show that the event in question 
was a ``but for'' cause of a NAAQS exceedance or violation in the 
sense that without the event, the exceedance or violation would not 
have occurred. In many cases, the ``but for'' role of a single 
source or event is difficult to determine with certainty and it is 
more often the case that the impact of emissions from events and 
other sources cannot be separately quantified and distinguished.
---------------------------------------------------------------------------

    Part of promulgating rule text that is consistent with the core 
statutory element that ``the event affected air quality in such a way 
that there exists a clear causal relationship between the specific 
event and the monitored exceedance or violation'' involves removing the 
regulatory requirement in 40 CFR 50.14(c)(3)(iv)(C) that a state must 
submit evidence that the event is associated with a measured 
concentration in excess of normal historical fluctuations, including 
background. We are finalizing our proposal to remove this language and 
replace it with regulatory text requiring a comparison of the event-
influenced concentration to historical concentrations. We discuss 
comments associated with this revision in Section IV.E.3.c of this 
preamble.
    Multiple commenters supported the EPA's proposal to revise the 
definition of an exceptional event to include the event and resulting 
emissions. We have also incorporated the suggestion of one commenter to 
indicate in regulatory text, through the plural word ``events,'' that 
an aggregation of events and their resulting emissions could be 
eligible for consideration under the provisions in 40 CFR 50.14. We 
discuss the aggregation of events in more detail in Section IV.G.1 of 
this preamble. We believe that this concept also applies to exceedances 
and violations, so we extended the use of plural terminology to this 
part of the exceptional events definition to more clearly acknowledge 
that an event may cause multiple exceedances (e.g., exceedances at 
multiple monitors or multiple exceedances at a single monitor) or 
violations.
    Regarding exceedances and violations, one commenter asked the EPA 
to clarify whether values that are not themselves exceedances or 
violations, but raise the design value such that the design value 
exceeds the NAAQS can be considered as exceptional events. The EPA 
recognizes that events can make an air concentration significantly 
higher than it would have been in the absence of the event contribution 
and elevate the 3-year design value for a NAAQS pollutant. However, the 
concentration values used in calculating a violating 3-year design 
value could be considered for exclusion under the Exceptional Events 
Rule only if the concentration itself is an exceedance or results in a 
violating design value. If the elevated concentration is not itself an 
exceedance nor does it result in a violating design value, then the 
value in question could not be considered as an exceptional event. As 
we explained in the proposal and restate here, while not an exceptional 
event, retaining such data in the calculation of a design value can 
elevate the design value and, for a nonattainment area seeking the 
EPA's approval of an attainment demonstration, make it seem that the 
area needs more emissions reduction to attain the NAAQS than is 
actually the case. Because these data are not exceptional events, we do 
not address exclusion under this rule. We do, however, discuss this 
scenario in more detail in Section IV.C of this preamble.
    Another commenter suggested that, for regulatory clarity, we 
incorporate our interpretation of ``meteorological events involving 
high temperatures or lack of precipitation'' (i.e., drought) into 
regulatory text. We agree with the commenter and have clarified, 
through the regulatory definition of an exceptional event, the position 
that we expressed in the proposal preamble, which is that drought alone 
does not create emissions and therefore does not meet the definition of 
an exceptional event. Rather, drought can result in arid conditions 
that can combine with or exacerbate the effects of events that meet the 
requirements, provisions and criteria of the Exceptional Events 
Rule.\21\ Because there may be many definitions of drought, we also 
clarify that we are referring to ``severe, extreme or exceptional 
drought'' as defined by the U.S. Drought Monitor. We are not including 
other drought categories in this discussion, nor would other drought 
categories alone be considered exceptional events.
---------------------------------------------------------------------------

    \21\ Drought can also exacerbate the air quality impact of 
activities that do not meet the criteria of the Exceptional Events 
Rule, such as dust from vehicular travel on unpaved roads.
---------------------------------------------------------------------------

    Also related to the definition of an exceptional event, one 
commenter asked the EPA to include within the definition of an event 
both short-term and long-term contributors to elevated pollutant 
concentrations. The commenter further asked the EPA to address the 
applicability of the Exceptional Events Rule to ``background'' ozone 
and background pollutant concentrations in general. The EPA does not 
agree with the commenter's suggestion to add the language or concept of 
``short-term and long-term contributors'' to the regulatory definition 
of an exceptional event. The EPA believes that the definition that we 
are promulgating could include both short- and long-term contributors 
provided the contributors meet the operative provisions in the rule. 
The EPA will review each request under the Exceptional Events Rule on a 
case-by-case basis using a weight of evidence approach.
    With respect to addressing rule applicability to ``background'' 
ozone, the EPA refers to the recent Implementation of the 2015 Primary 
Ozone NAAQS: Issues Associated with Background Ozone White Paper for 
Discussion.\22\ As defined in this white paper, U.S. background (USB) 
ozone is

[[Page 68228]]

any ozone formed from sources or processes other than U.S. manmade 
emissions of nitrogen oxides (NOX), volatile organic 
compounds (VOC), methane (CH4), and CO.\23\ USB ozone does not include 
intrastate or interstate transport of manmade ozone or ozone 
precursors. While some sources that contribute to USB (e.g., wildfires, 
stratospheric intrusions) may be eligible for treatment as exceptional 
events, other sources of USB would not meet the Exceptional Events Rule 
criteria. For example, routine or long-term international manmade 
emissions are not exceptional events because they are caused by human 
activity that is likely to recur at a given location; likewise, routine 
biogenic VOC emissions are not exceptional events because they are not 
deviations from normal or expected conditions. Thus despite being 
natural, they are not ``events.'' The EPA provides additional 
information regarding the treatment of certain events under the 
Exceptional Events Rule in Section IV.F of this preamble.
---------------------------------------------------------------------------

    \22\ Implementation of the 2015 Primary Ozone NAAQS: Issues 
Associated with Background Ozone White Paper for Discussion, U.S. 
EPA, December 2015. Available at https://www.epa.gov/sites/production/files/2016-03/documents/whitepaper-bgo3-final.pdf.
    \23\ 80 FR 65292 (October 26, 2015).
---------------------------------------------------------------------------

C. Ambient Concentration Data and Data Uses Affected by the Exceptional 
Events Rule

1. Summary of Proposal
    In our November 2015 document, the EPA proposed in regulatory 
language to interpret the CAA section 319(b) phrase ``determinations by 
the Administrator with respect to exceedances or violations of national 
ambient air quality standards'' to encompass determinations of current 
\24\ or historical NAAQS exceedances/violations or non-exceedances/non-
violations and determinations of the air quality ``design value'' at 
particular receptor sites when made as part of the basis for any of the 
following five types of regulatory actions: \25\
---------------------------------------------------------------------------

    \24\ The term ``current'' denotes the determination at issue in 
the current analysis. In actual practice, such determinations are 
based on historical data and thus reflect a past actual condition.
    \25\ The proposal noted that when one of these determinations is 
based on a combination of monitoring data and air quality modeling, 
the criterion requiring that there be a clear causal relationship 
between the event and a NAAQS exceedance or violation will apply to 
the combined estimate of air pollution levels rather than on the 
directly monitored background air quality data. That is, the event 
would not be required to have caused an actual exceedance or 
violation at the background ambient monitoring site, but rather to 
have made the critical difference in the combined estimate of air 
pollution levels (background plus source impact) resulting in a 
NAAQS exceedance or violation, because the event increased the 
background levels that are added to the air quality modeling output.
---------------------------------------------------------------------------

     An action to designate or redesignate an area as 
attainment, unclassifiable/attainment, nonattainment or unclassifiable 
for a particular NAAQS. Such designations rely on the existence or lack 
of a violation at a monitoring site in or near the area being 
designated.
     The assignment or re-assignment of a classification 
category (marginal, moderate, serious, etc.) to a nonattainment area to 
the extent this is based on a comparison of its ``design value'' to the 
established framework for such classifications.
     A determination regarding whether a nonattainment area has 
attained a NAAQS by its CAA deadline.
     A determination that an area has had only one exceedance 
in the year prior to its deadline and thus qualifies for a 1-year 
attainment date extension, if applicable.
     A finding of SIP inadequacy leading to a SIP call to the 
extent the finding hinges on a determination that the area is violating 
a NAAQS.
    In proposing this language, the EPA effectively applied the 
exceptional events process to these related types of determinations and 
across the NAAQS, which we believe is an appropriate interpretation of 
the CAA 319(b) phrase ``determinations by the Administrator with 
respect to exceedances or violations of national ambient air quality 
standards.'' For the identified types of determinations, the EPA 
proposed to exclude event-affected data only if an air agency satisfies 
the procedural (e.g., event identification, opportunity for public 
comment, demonstration submission) and substantive (i.e., clear causal 
relationship, not reasonably controllable or preventable, and human 
activity not likely to recur or natural event) requirements of the 
exceptional events process. The proposal also repeated the EPA's 
previous position that once data are excluded under the Exceptional 
Events Rule, these same data also should be excluded from (i) design 
value estimates and AQS user reports (unless the AQS user specifically 
indicates that they should be included), (ii) selecting appropriate 
background concentrations for prevention of significant deterioration 
(PSD) air quality analyses and transportation conformity hot spot 
analyses, and (iii) selecting appropriate ambient data for projecting 
future year concentrations as part of a modeled attainment 
demonstration.\26\
---------------------------------------------------------------------------

    \26\ See Question 14a in the Interim Exceptional Events Rule 
Frequently Asked Questions. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf.
---------------------------------------------------------------------------

    The proposal also noted that while data exclusion associated with 
the five actions in the previously noted bulleted list must follow the 
provisions in the Exceptional Events Rule, there are other actions for 
which it may be appropriate to exclude data using mechanisms other than 
the Exceptional Events Rule. The proposal differentiated between these 
five actions and other actions based on ``past'' versus ``predicted'' 
exceedances and/or violations. The proposal explained that the five 
identified actions involve determinations of whether a NAAQS exceedance 
or violation occurred at an ambient monitoring site at a particular 
time in the past. We characterized these exceedances or violations as 
occurring in the ``past'' because the process of determining whether an 
actual exceedance or violation occurred involves reviewing the ambient 
air monitoring data collected at monitoring sites over some historical 
timeframe (e.g., the data have already been collected at the monitors, 
verified for quality assurance purposes, submitted to AQS, and used in 
various regulatory calculations). In short, the collected monitoring 
data provide evidence that an exceedance or violation actually 
happened. This scenario is different than predicted future NAAQS 
violations. The proposal explained that predictions of future NAAQS 
violation(s) generally involve reviewing the historical ambient 
concentration data that are the evident focus of CAA section 319(b), 
estimating expected future emissions, and then using both of these data 
sets as inputs to an air quality modeling tool or other analytical 
approach that extrapolates these data to predict a future outcome. 
While science supports, and the EPA relies on, predictions of future 
NAAQS violations in several parts of the clean air program, such as in 
the EPA's approval of attainment demonstrations in SIPs, in PSD air 
permitting programs and in actions to reclassify a moderate 
PM10 or PM2.5 nonattainment area to serious,\27\ 
the fact that these predicted future values rely only in part on 
historical monitoring data implies that a different standard for data 
exclusion may be appropriate.
---------------------------------------------------------------------------

    \27\ Projection of future NAAQS exceedances or violations do not 
necessarily play a role in reclassification of an ozone 
nonattainment area to a higher classification level.
---------------------------------------------------------------------------

    For these reasons, the EPA proposed requiring that the five types 
of determinations that involve data exclusion associated with ``past'' 
exceedances or violations must follow the provisions in the Exceptional 
Events Rule. The EPA also indicated our intent

[[Page 68229]]

to develop a supplementary guidance document, Draft Guidance for 
Excluding Some Ambient Pollutant Concentration Data from Certain 
Calculations and Analyses for Purposes Other than Retrospective 
Determinations of Attainment of the NAAQS, to describe the appropriate 
additional pathways for data exclusion for some ``predicted future'' 
monitoring data applications (e.g., predicting future attainment that 
is the basis for approval of an attainment demonstration in the SIP for 
a nonattainment area, preparing required air quality analyses in an 
application for a PSD permit or preparing required air quality analysis 
for the purposes of transportation conformity).
2. Final Rule
    After considering the public comments we received, as explained 
more fully in the following paragraphs, we are finalizing language that 
applies the provisions in the Exceptional Events Rule to the treatment 
of data showing exceedances or violations of any NAAQS for purposes of 
the following types of regulatory determinations by the Administrator.
     An action to designate or redesignate an area as 
attainment, unclassifiable/attainment, nonattainment or unclassifiable 
for a particular NAAQS. Such designations rely on a violation at a 
monitoring site in or near the area being designated.
     The assignment or re-assignment of a classification 
category (marginal, moderate, serious, etc.) to a nonattainment area to 
the extent this is based on a comparison of its ``design value'' to the 
established framework for such classifications.
     A determination regarding whether a nonattainment area has 
attained a NAAQS by its CAA deadline. This type of determination 
includes ``clean data determinations.''
     A determination that an area has data for the specific 
NAAQS that qualify the area for an attainment date extension under the 
CAA provisions for the applicable pollutant.
     A finding of SIP inadequacy leading to a SIP call to the 
extent the finding hinges on a determination that the area is violating 
a NAAQS.
     Other actions on a case-by-case basis if determined by the 
EPA to have regulatory significance based on discussions between the 
air agency and the EPA Regional office during the Initial Notification 
of Potential Exceptional Event process.
    After considering comments from multiple state and local air 
agencies, regional planning organizations and industrial commenters 
that requested an option for using the Exceptional Events Rule for 
other regulatory determinations, we have added the sixth bullet in the 
preamble and in the regulatory text to acknowledge that it may be 
appropriate to use the provisions in the Exceptional Events Rule to 
exclude data for regulatory determinations not specifically articulated 
in the first five bullets. We expect that air agencies and the 
appropriate EPA Regional offices will discuss these case-by-case 
scenarios as part of the Initial Notification of Potential Exceptional 
Event process, described in more detail in Section IV.G.5 of this 
preamble.
    Upon further review of the identified determinations by the 
Administrator, we also realized that the fourth bullet, formerly ``A 
determination that an area has had only one exceedance in the year 
prior to its deadline and thus qualifies for a 1-year attainment date 
extension, if applicable'' applies to attainment date extensions only 
for PM10 as indicated in CAA section 188(d)(2) because 
``only one exceedance'' is specific to PM10. Attainment date 
extensions for other NAAQS have other CAA conditions. Our intent was 
that this determination would apply to attainment date extensions for 
all NAAQS and these NAAQS have CAA conditions other than ``only one 
exceedance.'' As a result, we have revised the language as follows to 
better convey this concept: ``A determination that an area has data for 
the specific NAAQS, which qualify the area for an attainment date 
extension under the CAA provisions for the applicable pollutant.'' 
Using this approach, a state would be required to demonstrate that a 
given area had data with respect to the statistical form of that 
particular standard in the calendar year prior to the applicable 
attainment date for the area (i.e., for the 1997 24-hour 
PM10 NAAQS, no more than one exceedance of the 24-hour NAAQS 
and the annual mean concentration of PM10 in the area for 
such year is less than or equal to the standard level). Revising this 
language also accounts for potential future revisions to the form and 
level of the NAAQS, data handling provisions and regulatory changes to 
state implementation plan requirements.
    As we indicated in the proposal, we still intend to develop a 
supplementary guidance document, Draft Guidance for Excluding Some 
Ambient Pollutant Concentration Data from Certain Calculations and 
Analyses for Purposes Other than Retrospective Determinations of 
Attainment of the NAAQS, which will describe the appropriate additional 
pathways for data exclusion for some ``predicted future'' monitoring 
data applications. We have delayed the release of this guidance, 
however, to allow us to incorporate the content of the final 
Exceptional Events Rule revisions. We intend to post the draft guidance 
and instructions for providing public comment on the exceptional events 
Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events shortly after finalizing these rule 
revisions. As we noted in the proposal, we intend this guidance to do 
the following:
     Clarify that data excluded under the procedural and 
substantive provisions of the Exceptional Events Rule will also be 
excluded from (i) design value estimates and AQS user reports (unless 
the AQS user specifically indicates that they should be included), (ii) 
selecting appropriate background concentrations for PSD air quality 
analyses and transportation conformity hot spot analyses, and (iii) 
selecting appropriate ambient data for projecting future year 
concentrations as part of a modeled attainment demonstration.
     Identify potential pathways for data exclusion for 
determinations based on ``predicted'' future NAAQS exceedances or 
violations (e.g., PSD, transportation conformity).
     Identify the scenarios in which the EPA would not exclude 
data, such as when setting priority classifications for emergency plans 
under 40 CFR 51.150. The EPA believes that implementing the CAA 
principle at section 319(b)(3)(A) that ``protection of public health is 
the highest priority'' may necessitate that an air agency address in 
its emergency plan the appropriate planned response for any elevated 
concentration known to be possible because it has already been observed 
even if that elevated concentration is associated with an exceptional 
event.
3. Comments and Responses
    While the majority of commenters agreed with the EPA's proposal 
that the provisions in the Exceptional Events Rule apply to the 
enumerated five actions, many of these same commenters urged the EPA 
not to limit the scope of the Exceptional Events Rule to the five 
actions that we identified in the proposal as comprising 
``determinations by the Administrator with respect to exceedances or 
violations of national ambient air quality standards.'' Commenter 
suggestions ranged from adding a sixth element to capture other case-
by-case actions deemed to be of regulatory significance to specifically 
listing other potential actions (that is, they suggested adding the 
following to list of

[[Page 68230]]

specifically covered actions: Design value estimates, PSD background 
determinations, transportation hot spot analyses, future year 
projections for modeled attainment determinations, clean data 
determinations (which are included within the third bullet identifying 
the types of regulatory determinations by the Administrator included 
within the scope of the Exceptional Events Rule), other actions that 
rely on design values, monitoring network plans, etc.). The EPA agrees 
that the list of actions identified in the regulatory text should allow 
for a case-by-case determination in certain circumstances (e.g., such 
as when an event is determined during the Initial Notification of 
Potential Exceptional Events process to have regulatory significance 
for an action not otherwise identified in the regulatory text) and has 
added this language to the final regulatory text. The EPA believes that 
this language could include any of the specific actions identified by 
other commenters. However, as we noted in the proposal, the CAA does 
not clearly apply the statutory criteria of section 319(b) to all of 
the other actions identified by the commenters. Therefore, under 
certain circumstances, we believe that it may be appropriate to exclude 
data for some of the other specific actions. Hence, we are not 
identifying these actions in the regulatory text. Rather, we intend to 
address them in the additional guidance previously mentioned and 
discussed further in the following paragraphs.
    As indicated, the majority of commenters agreed with the EPA's 
approach to define those actions that constitute ``determinations by 
the Administrator.'' A few other commenters, however, indicated that 
the EPA cannot narrow the scope of the Exceptional Events Rule nor 
agree to exclude event-affected data from other types of regulatory 
determinations using another mechanism without first undertaking 
notice-and-comment rulemaking. The EPA disagrees with this comment. 
First, neither the CAA language at section 319(b)(3)(B)(iv), which 
requires regulations allowing a state to petition the Administrator to 
exclude air quality monitoring data that is directly due to exceptional 
events from use in determinations by the Administrator with respect to 
exceedances or violations of the national ambient air quality 
standards, nor the implementing language in the 2007 Exceptional Events 
Rule at 40 CFR 50.14(a)(1), which allows air agencies to request 
exclusions for data showing exceedances or violations of the NAAQS that 
are directly due to an exceptional event from use in determinations, 
identify the scope of the word ``determinations.'' Second, identifying 
the Exceptional Events Rule as the only mechanism by which data may be 
excluded from regulatory actions may result in unintended consequences. 
As we have noted previously, an event may make a past air concentration 
significantly higher than it would have been in the absence of the 
event contribution. If the event-influenced data do not result in an 
exceedance or violation, they are not eligible for exclusion under the 
Exceptional Events Rule. CAA section 319(b) is ambiguous with respect 
to how to treat an exceptional event that contributed to a past air 
concentration being higher than it would have been without the event, 
but the air concentration did not result in an exceedance or violation. 
The EPA's decision to not apply the Exceptional Events Rule to data 
that does not exceed or violate a NAAQS is consistent with how the rule 
has been applied and interpreted and is not inconsistent with CAA 
section 319(b). However, we acknowledge that retaining the event-
influenced data could have regulatory implications that seem contrary 
to the purpose of CAA section 319(b). For example, retaining such data 
in the calculation of background concentrations used in air quality 
analysis for a PSD permit may suggest that there will be a NAAQS 
violation after construction of a new source and thus could prevent the 
permitting authority from issuing the permit.\28\
---------------------------------------------------------------------------

    \28\ If a similar event were to occur after completion of 
construction, the event-affected data could be excluded and thus 
there would be no ``official'' violation.
---------------------------------------------------------------------------

    As previously noted, we intend our Draft Guidance for Excluding 
Some Ambient Pollutant Concentration Data from Certain Calculations and 
Analyses for Purposes Other than Retrospective Determinations of 
Attainment of the NAAQS to describe the appropriate additional pathways 
for data exclusion for some ``predicted future'' monitoring data 
applications. Multiple commenters expressed interest in this guidance 
and called for its quick release. The EPA recognizes that this guidance 
is an important supplement to the revisions to the Exceptional Events 
Rule that we are promulgating and we will work towards the quick 
release of this document.
    Throughout this preamble and in our proposal, we use the term 
``weight of evidence'' to describe the process by which we evaluate 
individual exceptional events demonstrations and air agency requests 
for data exclusion. Several commenters asked for additional 
clarification regarding this terminology, either in preamble or in 
regulatory text. Several other commenters asked that we use the ``more 
commonly understood'' terminology of ``preponderance of the evidence.'' 
Another commenter objects to the use of a weight of evidence approach 
noting that it could lead to incorrectly granted requests for data 
exclusion.
    While we are not adding language to the regulatory text, we are 
clarifying in this preamble to the final rule that in applying a 
``weight of evidence'' approach to reviewing individual exceptional 
events demonstrations, the EPA believes it is appropriate to consider 
all relevant evidence and qualitatively ``weigh'' this evidence based 
on its relevance to the Exceptional Events Rule criterion being 
addressed, the degree of certainty, its persuasiveness, and other 
considerations appropriate to the individual pollutant and the nature 
and type of event. Courts have found that it is reasonable for the EPA 
to use a ``weight of evidence'' analysis when implementing the CAA. 
See, e.g., Envtl. Def. v. EPA, 369 F.3d 193 (2d Cir. 2004) (upholding 
the EPA's approval of a state's attainment demonstration using 
photochemical grid modeling and a weight of evidence analysis) and BCCA 
Appeal Group v. EPA, 355 F.3d 817 (5th Cir. 2003) (finding that the 
EPA's conclusion that the weight of evidence approach to approving 
attainment demonstrations was consistent with the CAA, reasonable and 
entitled to deference). In this context, ``weight'' refers to the 
relevance of the evidence to the determination and its technical merit, 
and not to the amount of documentation. The language ``weight of 
evidence'' is consistent with this approach and consistent with the 
terminology used in other EPA regulatory actions. ``Preponderance of 
the evidence'' conveys many of the same concepts as ``weight of 
evidence,'' but because it is a legal term of art, we are not using 
that term as part of this rulemaking action. The weight of evidence 
approach is an appropriate and reasonable approach, which has been used 
historically and successfully under key CAA programs. The commenter did 
not present any information showing that this approach is more likely 
to yield ``incorrect'' decisions than any other evidentiary approach 
that might be applicable to exceptional events demonstrations.

[[Page 68231]]

D. Definition and Scope of a Natural Event

1. Summary of Proposal
    In the 2007 Exceptional Events Rule, the EPA defined a natural 
event as an event in which human activity plays little or no direct 
causal role (see 72 FR 13580). In our 2015 action, the EPA proposed to 
revise this definition to include the concept of an event and its 
resulting emissions and to acknowledge that natural events can recur. 
The EPA also proposed to include language in the regulatory definition 
to clarify that anthropogenic emission sources that contribute to the 
event emissions (and subsequent exceedance or violation) that are 
reasonably controlled do not play a ``direct'' role in causing 
emissions. The proposal elaborated on the ``direct causal'' concept by 
repeating language that first appeared in the preamble to the 2007 
Exceptional Events Rule but not in rule text.
    In the 2007 rule preamble and the November 2015 proposal, the EPA 
explained that we generally consider human activity to have played 
little or no direct role in causing an event-related exceedance or 
violation if anthropogenic emission sources that contribute to the 
exceedance are reasonably controlled at the time of the event (see 72 
FR 13563-4 and 80 FR 72844). This is the case regardless of the 
magnitude of emissions generated by these reasonably controlled 
anthropogenic sources and regardless of the relative contribution of 
these emissions and emissions arising from natural sources in which 
human activity has no role.\29\ Thus, the event could be considered a 
natural event by applying the reasonable interpretation that the 
anthropogenic source had ``little'' direct causal role. To further 
illustrate this concept, as we have noted previously, the EPA considers 
wildfires to be natural events even though some accidental human 
actions initiate some wildfires and, to some degree, prior land 
management practices can influence the frequency and scale of 
wildfires. The EPA believes the interpretation that wildfires are 
natural events best implements the Congressional intent and is a more 
appropriate approach than expecting air agencies to determine the 
initial cause of each wildfire of interest and classifying it as 
natural or anthropogenic based on that cause. In addition, landowners 
and managers and government public safety agencies are strongly 
motivated to reduce the frequency and severity of human-caused 
wildfires. Our proposal further explained that if anthropogenic 
emission sources that contribute to the event emissions can be 
reasonably controllable but reasonable controls were not implemented at 
the time of the event, then the event would not be considered a natural 
event.
---------------------------------------------------------------------------

    \29\ For example, if an area affected by a high wind dust event 
has adequate rules or ordinances for sources of windblown dust 
(e.g., rules that establish restrictions for operating vehicles on 
unpaved property, rules that control windblown dust emissions 
associated with lands disturbed by construction, earthwork and land 
development) and the air agency can provide evidence of 
implementation and enforcement, then the EPA would generally 
consider human activity to have played little or no direct causal 
role in causing the monitored exceedance or violation.
---------------------------------------------------------------------------

2. Final Rule
    After consideration of the public comments and as supported by many 
commenters, we are finalizing the following definition: ``natural event 
means an event and its resulting emissions, which may recur at the same 
location, in which human activity plays little or no direct causal 
role. For purposes of the definition of a natural event, anthropogenic 
sources that are reasonably controlled shall be considered to not play 
a direct role in causing emissions.'' In the final regulatory 
definition that we are promulgating, we are adding the language ``at 
the same location'' to more clearly indicate that natural events can 
recur in the same area or at the same location and still be considered 
as exceptional events. The language we are adding in the definition 
contrasts the recurrence frequency of natural events with human 
activities that must be ``unlikely to recur at a particular location'' 
to be considered to be an exceptional event (see CAA section 
319(b)(1)(A)(iii)). Although several commenters disagreed with our 
approach, and stated that a natural event must have no human activity 
component at all, we are retaining in the regulatory definition the 
concept that we consider reasonably controlled anthropogenic sources to 
not play a direct role in causing emissions. We are, however, adding 
the language ``[f]or purposes of the definition of a natural event'' 
prior to the language ``anthropogenic sources that are reasonably 
controlled shall be considered to not play a direct role in causing 
emissions'' to clarify that the ``direct causal'' language applies to 
reasonably controlled anthropogenic sources when considering whether 
the event is natural. As we have previously stated, we believe that if 
reasonable controls were implemented on contributing anthropogenic 
sources at the time of the event and if, despite these efforts and 
controls, an exceedance occurred, then we would consider the human 
activity to have played little or no direct causal role in causing the 
event-related exceedance. Rather, in those cases in which the 
anthropogenic source has ``little'' direct causal role, we would 
consider the high wind and the emissions arising from the contributing 
natural sources (in which human activity has no role) to cause the 
exceedance or violation. Additionally, the event would not be natural 
if all of the event-related emissions originated from anthropogenic 
sources or if anthropogenic emission sources that contributed to the 
event-related emissions could have been reasonably controllable but 
reasonable controls were not implemented at the time of the event.\30\ 
We discuss the concept of reasonable control in more detail in Section 
IV.E.2 of this preamble.
---------------------------------------------------------------------------

    \30\ As we clarify in the final rule discussion in Section 
IV.F.2.a of this preamble, when considering prevention/control for 
purposes of exceptional event categorization, a prescribed fire 
effectively becomes like a wildfire when, for example, the 
prescribed fire escapes secure containment due to unforeseen 
circumstances (e.g., a sudden shift in prevailing winds). In these 
instances, the burn manager would no longer control the path of the 
fire. Thus, the fact that the initial fire was deliberately ignited 
should not result in the entire burn (e.g., the duration and extent 
of the burn) needing to follow the rule requirements for prescribed 
fires on wildland.
---------------------------------------------------------------------------

3. Comments and Responses
    Commenters providing feedback on the natural events section of the 
proposal generally focused on one of the following concepts: The 
language in the proposed revised definition of natural event, those 
event types considered to be natural events and the concept of 
reasonable controls as it relates to contributing anthropogenic 
emissions. We address in the explanation of the final rule language in 
Section IV.D.2 of this preamble those comments related to the 
definition of natural event. We address the types of natural events in 
this section and we discuss reasonable controls in Section IV.E.2 of 
this preamble.
    Several commenters asked that we clarify those types of events that 
could be considered natural events eligible for data exclusion under 
the Exceptional Events Rule. Commenters specifically asked for clarity 
regarding earthquakes, lightning and biological emissions. Through our 
experience implementing the Exceptional Events Rule, we have come to 
realize that it may be helpful to think of an event in terms of the 
source of its emissions. If the underlying source is natural and the 
generated emissions influence a regulatory monitor, then the ensuing 
event (i.e., event and resulting

[[Page 68232]]

emissions) could be considered a ``natural event'' under the 
Exceptional Events Rule. Applying this rationale, as we expressed in 
the 2007 rule and the November 2015 proposal (see 72 FR 13565 and 80 FR 
72854-72858), the EPA generally considers wildfires, stratospheric 
ozone intrusions, volcanic and seismic (e.g., earthquake) activities, 
natural disasters (e.g., hurricanes and tornados) and windblown dust 
from natural, undisturbed landscapes to be natural events. Natural 
events, including, but not limited to, those previously identified, and 
their resulting emissions could be considered under the provisions of 
the Exceptional Events Rule. Also, as explained in this section, events 
that include emissions from both natural and anthropogenic sources, 
such as high wind dust events, can be considered natural events only if 
reasonable controls have been applied to the contributing anthropogenic 
sources. Lightning storms occurring close to a regulatory monitor, such 
that the particular storm notably affects the monitor close in time to 
the storm might qualify as natural events that could also be 
exceptional events. However, the ongoing and delayed aggregate impact 
of many lightning storms that are not proximate to the monitor is not a 
deviation from normal or expected conditions and thus would not be an 
exceptional event. Also, routine biological emissions (e.g., including, 
but not limited to, emissions from vegetation, microbes and/or animals) 
are not deviations from normal or expected conditions. Thus despite 
being natural, they are not ``events'' and would not qualify as 
exceptional events. As is true for all exceptional events 
determinations, the EPA will consider these events, and other event 
types not identified here, on a case-by-case basis.

E. Technical Criteria for the Exclusion of Data Affected by Events

    As described in Section IV.B of this preamble, the EPA is 
finalizing provisions to return to the core statutory elements and 
implicit concepts of CAA section 319(b): That the event affected air 
quality in such a way that there exists a clear causal relationship 
between the specific event and the monitored exceedance or violation, 
the event was not reasonably controllable or preventable, and the event 
was caused by human activity that is unlikely to recur at a particular 
location or was a natural event. See, e.g., 42 U.S.C. 7619(b)(1). All 
exceptional events demonstrations, regardless of event type or relevant 
NAAQS, must address each of these technical criteria. The EPA has 
posted examples of acceptable demonstrations for various event and 
pollutant combinations on its Web site at https://www.epa.gov/air-quality-analysis/exceptional-events-submissions-table. We will update 
this Web site as additional examples become available. This section 
summarizes the EPA's proposed revisions, final regulatory language and 
public comments regarding each of these technical criteria. Section 
IV.G of this preamble discusses additional process-related components 
of exceptional events demonstrations.
1. Human Activity Unlikely To Recur at a Particular Location or a 
Natural Event
    Because Section IV.D of this preamble addresses the definition of a 
natural event and those event types that can be considered natural 
events under the Exceptional Events Rule, we focus this section of the 
preamble on the ``human activity unlikely to recur at a particular 
location'' portion of the ``human activity unlikely to recur at a 
particular location or a natural event'' technical criterion. In the 
final rule description section in this part of the preamble, we provide 
example conclusory language that air agencies can use in the portion of 
their exceptional events demonstration that addresses this criterion. 
This example language applies to both human activity and natural 
events.
a. Summary of Proposal
    Our proposal stated that according to both the statutory and 
regulatory definitions, an exceptional event must be ``an event caused 
by human activity that is unlikely to recur at a particular location or 
a natural event'' (emphasis added, see CAA section 319(b)(1)(A)(iii) 
and 40 CFR 50.1(j)). As we noted in the discussion of a natural event 
in Section IV.D of this preamble, we have come to realize that it may 
be helpful to think of an event in terms of the source of its 
emissions. If the underlying source is natural and the generated 
emissions influence a regulatory monitor, then the ensuing event (i.e., 
event and resulting emissions) could be considered a ``natural event'' 
under the Exceptional Events Rule. Under this particular criterion, if 
the underlying source of emissions is anthropogenic, then the event can 
only be ``exceptional'' if the original source is ``unlikely to recur 
at a particular location.'' The proposal noted that neither the CAA nor 
the 2007 Exceptional Events Rule defined ``unlikely to recur'' or ``at 
a particular location.'' Therefore, the proposal sought to clarify both 
of these phrases. In addition to proposing a generally applicable 
approach for ``unlikely to recur,'' we also proposed specific 
approaches for wildland fires, notably prescribed fires on wildland 
(which we discuss in Section IV.F.2 of this preamble), and high wind 
dust events (which we discuss in Section IV.F.4 of this preamble). The 
proposal also clarified that under CAA section 319(b) and a provision 
of the 2007 Exceptional Events Rule that we did not propose to change, 
air pollution related to source noncompliance is not an exceptional 
event regardless of its frequency.
    We proposed, as guidance, to interpret the unlikely to recur 
language as follows. If an event type has not previously occurred 
within a given air quality control region (AQCR) \31\ in the 3 years 
preceding the submittal of an exceptional events demonstration for an 
event that has occurred recently, the EPA will consider this recent 
event to be a ``first'' event and will generally consider that event 
type to be unlikely to recur in the same location.\32\ Similarly, if 
there was one prior event (for which a demonstration may or may not 
have been submitted) within the 3 years preceding the submittal of an 
exceptional events demonstration for the recent event, that event type 
would also generally be considered unlikely to recur in the same 
location. However, if there have been two prior events of a similar 
type within a 3-year period in an AQCR, that would generally indicate 
the third event, for which the demonstration is being prepared (or 
would be prepared), does not satisfy the ``human activity that is 
unlikely to recur at a particular location'' criterion and, thus, would 
not qualify as an exceptional event. The terms ``one prior event'' and 
``two prior events'' refer to events that affect the same AQCR, even if 
they have not affected the same monitor.\33\ This proposed guidance is 
consistent with the approach taken to recurrence in our Interim High 
Winds Guidance document in which we identified non-recurring events as 
being less than one event per year in a given area.\34\ In the Interim 
High Winds

[[Page 68233]]

Guidance, we did not define ``area'' other than to differentiate areas 
by attainment status or jurisdiction (i.e., intrastate versus 
interstate or international). The EPA solicited comment on using an 
AQCR to define the bounds for an area subject to event recurrence and 
on whether to incorporate into rule text the benchmark of three events 
in 3 years.
---------------------------------------------------------------------------

    \31\ 40 CFR part 81, subpart B, Designation of Air Quality 
Control Regions, defines Air Quality Control Regions.
    \32\ While we proposed to define event recurrence as occurring 
in the 3 years preceding the submittal of an exceptional events 
demonstration, the proposal language should have read in the 3 years 
preceding the event that is the subject of an exceptional events 
demonstration. We clarify this 3-year timeframe in the final rule 
section.
    \33\ The EPA will consider previously flagged exceedances within 
AQS with their associated descriptions to be ``events'' regardless 
of whether the EPA has received or acted on event demonstrations. 
The EPA also notes that a single event could influence 
concentrations on multiple days.
    \34\ See footnote 27 in table 2 of Interim Guidance on the 
Preparation of Demonstrations in Support of Requests to Exclude 
Ambient Air Quality Data Affected by High Winds Under the 
Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf.
---------------------------------------------------------------------------

b. Final Rule
    As a result of the feedback from numerous commenters, we are 
providing clarifications to the ``unlikely to recur at a particular 
location'' language as guidance in this preamble and not regulatory 
text. We note here, as guidance, the benchmark of three events in 3 
years to define recurrence. We measure the 3-year period backwards from 
the date of the most recent event (e.g., for an event occurring on May 
1, 2016, the 3-year period would be May 1, 2013, through May 1, 2016). 
As described previously, if there have been two prior events of a 
similar type (i.e., a similar event type generating emissions of the 
same pollutant whether flagged or the subject of a demonstration) 
within a 3-year period in ``a particular location,'' the third event, 
for which the demonstration is being prepared (or would be prepared), 
would generally not satisfy the ``human activity that is unlikely to 
recur at a particular location'' criterion and, thus, would not qualify 
as an exceptional event. Although under this approach, the third event 
essentially confirms that the first two events are ``routine,'' an air 
agency would not likely recognize the routine nature of the first two 
events until the third occurrence. Also as noted in our proposal, the 
EPA will consider previously flagged exceedances within AQS with their 
associated descriptions to be ``events'' regardless of whether the 
affected air agency has submitted or the EPA has acted on these 
``recurring'' event demonstrations. We also note in this final action 
that the benchmark of three events in 3 years generally applies 
regardless of an area's designation status with respect to the NAAQS 
that is the focus of the event demonstration. The EPA could grant 
exceptions to the benchmark of three events in 3 years benchmark on a 
case-by-case basis. Several commenters supported, and no commenters 
opposed, this generally applicable approach.
    With regard to the frequency, several commenters asked the EPA to 
clarify how the concept of recurrence applies to a single event 
spanning multiple days. First, the EPA notes that for purposes of 
exceptional events eligibility, the concept of recurrence only applies 
to ``human activity unlikely to recur at a particular location'' and 
not to natural events. Natural events can recur. That said, a single 
event, natural or caused by human activity, can span multiple days and 
result in an air agency flagging multiple monitor-day values in AQS 
(i.e., multiple exceedances of a given NAAQS at a single monitor in a 
single day or multiple NAAQS exceedances at multiple monitors on 
multiple days). The EPA considers a single discrete event to be one 
occurrence even if it extends over more than one day. Applying our 
benchmark of three events in 3 years, for an area experiencing three 
authorized and deliberately set structural fires in 2 years, the EPA 
would not consider a third such structural fire in the third year to be 
an exceptional event.\35\ Because prescribed fires on wildland eligible 
for exceptional events consideration involve igniting and managing the 
fire according to the provisions set forth in either a Smoke Management 
Program or using basic smoke management practices, we discuss the 
unique circumstances associated with the recurrence of prescribed fires 
on wildland in IV.F.2.
---------------------------------------------------------------------------

    \35\ A deliberately set structural fire that has been authorized 
by a responsible government agency is clearly not a natural event. 
We are not offering guidance at this time on whether accidentally 
set structural fires or arson-set structural fires should be 
considered natural or anthropogenic events. We do note, however, 
that wildfires on wildland initiated by accident or arson are 
considered natural events, and on a case-by-case basis this 
treatment for wildfires may bear on the appropriate treatment of 
accidental and arson-set structural fires.
---------------------------------------------------------------------------

    While we proposed, as guidance, to use an AQCR to define the bounds 
for an area subject to recurrence, in light of the comments received 
and issues raised therein, we agree that using AQCRs as the only way in 
which to define the bounds for an area subject to recurrence is not 
appropriate. Commenters identified the following reasons why an AQCR 
may not be suitable: AQCRs can be antiquated and inconsistent with 
current jurisdictional boundaries; AQCRs may be too large (particularly 
in some areas of the West) for effective analysis of event recurrence; 
AQCRs could be subdivided by terrain (e.g., mountains or valleys) that 
could affect the transport and/or chemical interactions of pollutants; 
pollutant sources and monitors may not fall within the bounds of the 
same AQCR. Rather than prescribe an approach to define ``a particular 
location,'' commenters suggested that the EPA Regional offices and the 
affected air agencies could agree to the bounds of ``a particular 
location'' as part of regular, on-going conversations and/or as part of 
the Initial Notification of Potential Exceptional Event process. 
Commenters suggested that while an AQCR might appropriately define ``a 
particular location'' in some areas of the country, other areas may 
determine one of the following to be more suitable: Counties or other 
political boundaries, core based statistical areas (CBSAs), 
nonattainment or unclassifiable area boundaries (if applicable), a 
density metric (i.e., number of events per thousand square miles 
calculated using the radius around the subject monitor), and/or 
distance to the monitor as indicated by a defined radius from the 
subject monitor. We agree that some of the commenters' suggestions may 
be appropriate in particular cases and we leave it to the EPA Regional 
offices and to the affected air agencies to consult on how to 
characterize ``a particular location.''
    As stated previously, all exceptional events demonstrations, 
regardless of event type or relevant NAAQS, must address each of the 
three technical criteria. We proposed conclusory language associated 
with the ``human activity that is unlikely to recur at a particular 
location or a natural event'' criterion and repeat it here as part of 
the preamble to the final Exceptional Events Rule revisions. When 
addressing this criterion as part of an exceptional events 
demonstration, the EPA recommends that the submitting air agency 
document and discuss the following in a distinct ``human activity/
natural event'' section of the demonstration: The type/source of event 
(e.g., a particular type of chemical spill or other industrial 
accident, fire in a particular type of structure, lightning-ignited 
wildfire, etc.), clearly identify whether the event is natural or was a 
human activity that is unlikely to recur at a particular location, the 
resulting emissions (e.g., characterized in terms of the pollutant and 
magnitude, if applicable/available), and the documented frequency of 
the event in the prior 3 years (or other appropriate timeframe as 
agreed with the reviewing EPA Regional office).\36\

[[Page 68234]]

The air agency should then affirmatively state that in characterizing 
the event, it has satisfied the ``human activity unlikely to recur at a 
particular location or a natural event'' criterion.
---------------------------------------------------------------------------

    \36\ The frequency of event recurrence is important for both 
natural and anthropogenic events. For anthropogenic events, 
frequency can determine whether the event satisfies the ``human 
activity unlikely to recur at a particular location or a natural 
event'' criterion. For a natural event, the frequency can determine 
whether a mitigation plan is necessary (see Section V of this 
preamble).
---------------------------------------------------------------------------

2. Not Reasonably Controllable or Preventable
    As noted in the proposal, because CAA section 319(b) does not 
restrict the applicability of the not reasonably controllable or 
preventable criterion to certain types of events, this CAA criterion, 
and the implementing Exceptional Events Rule language, applies to both 
events caused by human activity and to natural events. This section 
discusses the criterion in general terms. We discuss the criterion's 
specific applicability to fire events on wildland in Section IV.F.2 of 
this preamble and to high wind dust events in Section IV.F.4 of this 
preamble.
a. Summary of Proposal
    The EPA proposed to codify in regulatory language key aspects of 
the ``not reasonably controllable or preventable'' criterion to reduce 
uncertainty for air agencies and other parties. Specifically, we 
proposed and solicited comment on the following revisions to the 
Exceptional Events Rule to indicate that:
     The not reasonably controllable or preventable criterion 
has two prongs, prevention and control. An air agency must demonstrate 
that an event was both not reasonably preventable and not reasonably 
controllable.
     An event is not reasonably preventable if reasonable 
measures to prevent the event were applied at the time of the event.
     An event is not reasonably controllable if reasonable 
measures to control the impact of the event on air quality were applied 
at the time of the event.
     The reasonableness of measures is case-specific and is to 
be evaluated in light of information available at the time of the 
event.
     Air agencies do not need to provide case-specific 
justification to support the ``not reasonably controllable or 
preventable'' criterion for remote, large-scale, high-energy and/or 
sudden high wind dust events, such as ``haboobs.''
     Provided the air agency is not under an obligation to 
revise the SIP, the EPA would consider (i.e., give deference to) 
enforceable control measures implemented in accordance with a state 
implementation plan, approved by the EPA within 5 years of the date of 
a demonstration submittal, that address the event-related pollutant and 
all sources necessary to fulfill the requirements of the CAA for the 
SIP to be reasonable controls with respect to all anthropogenic sources 
that have or may have contributed to event-related emissions.
     Air agencies do not need to provide case-specific 
justification to support the ``not reasonably controllable or 
preventable'' criterion for emissions-generating activity that occurs 
outside of the boundaries of the state (or tribal lands) within which 
the concentration at issue was monitored.

In addition to the identified revisions, the proposal also discussed 
and solicited feedback on the role of an EPA-approved SIP in 
nonattainment, maintenance, unclassifiable and attainment areas; prior 
communications regarding expectations for reasonable controls; 
prospective agreements regarding assessments of reasonable controls; 
and components of a not reasonably controllable or preventable showing 
within a demonstration. We summarize our proposed positions on these 
topics in the following paragraphs.
    The proposal stated that while we would defer to the enforceable 
control measures in attainment plan SIPs applying to maintenance and 
nonattainment areas, we would not give this same deference to 
infrastructure SIPs developed for attainment, unclassifiable/attainment 
and unclassifiable areas. We differentiated attainment plan SIPs and 
infrastructure SIPs by the fact that attainment plan SIPs must include 
an attainment demonstration and reasonably available control measures 
(RACM), best available control measures (BACM),\37\ and other 
requirements,\38\ which together constitute an assessment of reasonable 
controls. Infrastructure SIPs typically rely on maintenance and 
attainment SIPs to demonstrate compliance with the key infrastructure 
elements. Therefore, the EPA proposed that the underlying SIPs, which 
would themselves include the control measures, be the relevant SIPs for 
exceptional events demonstrations.
---------------------------------------------------------------------------

    \37\ BACM applies to attainment plans for serious 
PM10 or PM2.5 areas.
    \38\ Marginal ozone nonattainment areas are exceptions because 
they are not required to submit attainment demonstrations.
---------------------------------------------------------------------------

    The proposal also recognized that regulations and an area's 
planning status are often evolving and changing, that these changes can 
span several years and involve multiple rounds of formal and informal 
communications between the affected air agency and the EPA, and that 
these changes could ultimately result in an air agency's adoption of 
new control measures, which, for exceptional events purposes, could 
constitute ``reasonable'' controls. Acknowledging that these 
conversations could inform what the air agency knew at the time of the 
event and thus could influence a case-specific assessment of the not 
reasonably controllable or preventable criterion, the EPA solicited 
comment on methods to definitively identify the status of 
communications and planning efforts (e.g., formal correspondence or 
other documentation, timelines for responding) and whether this 
approach would be more appropriately addressed through rule language.
    First appearing in the Interim High Winds Guidance, the proposal 
repeated the suggestion that an air agency could prospectively assess 
and determine that the controls in place for a particular type of 
event, or a planned enhancement of those controls, are sufficient to 
meet the not reasonably controllable or preventable criterion, and then 
obtain the EPA's review and concurrence of this assessment prior to 
more events of that type occurring. The proposal expressed the EPA's 
belief that this prospective approach would reduce disagreements that 
might otherwise occur over later retrospective assessments.
    The proposal also solicited comment on recommending as either 
guidance or rule the following components that an air agency should 
include within the not reasonably controllable or preventable showing 
in a demonstration: (1) Identify the natural and anthropogenic sources 
of emissions causing and contributing to the event emissions, including 
the contribution from local sources, (2) identify the relevant SIP or 
other enforceable control measures in place for these sources and the 
implementation status of these controls, and (3) provide evidence of 
effective implementation and enforcement of reasonable controls, if 
applicable.\39\ In identifying natural and anthropogenic sources, we 
clarified that the air agency should assess both

[[Page 68235]]

potentially contributing local/in-state and upwind sources.
---------------------------------------------------------------------------

    \39\ The EPA generally expects evidence that the controls 
determined to be reasonable, if any, were effectively implemented 
and appropriately enforced. This assessment of local sources should 
include a review and description of any known nearby facility upsets 
or malfunctions that could have resulted in emissions of the 
relevant pollutant(s) that influenced the monitored measurements on 
the day(s) of the claimed events. In the case of a high wind dust 
event, for example, for the identified potentially contributing 
local sources, the analysis should explain how significant dust 
emissions occurred despite having reasonable controls in place 
(e.g., that controls were overwhelmed by high wind), if appropriate.
---------------------------------------------------------------------------

b. Final Rule
    After considering the public comments we received, we are 
finalizing the following not reasonably controllable or preventable 
elements, all of which contain associated regulatory language.
     The not reasonably controllable or preventable criterion 
has two prongs, prevention and control. An air agency must demonstrate 
that an event was both not reasonably preventable and not reasonably 
controllable.
     An event is not reasonably preventable if reasonable 
measures to prevent the event were applied at the time of the event.
     An event is not reasonably controllable if reasonable 
measures to control the impact of the event on air quality were applied 
at the time of the event.
     The reasonableness of measures is case-specific and is to 
be evaluated in light of information available as of the date of the 
event.
     Air agencies do not need to provide case-specific 
justification to support the ``not reasonably controllable or 
preventable'' criterion for emissions-generating activity that occurs 
outside of the boundaries of the state (or tribal lands) within which 
the concentration at issue was monitored.\40\
---------------------------------------------------------------------------

    \40\ Under the CAA, the EPA generally considers a state (not 
including areas of Indian country) to be a single responsible actor. 
Accordingly, neither the EPA nor the 2007 Exceptional Events Rule 
provides special considerations for intrastate scenarios when an 
event in one county affects air quality in another county in the 
same state, assuming that the event occurs on land subject to state 
authority (versus tribal government authority). The EPA expects 
controls appropriate for the designation status of the county (or 
portion of the county) in which the emissions originate.
---------------------------------------------------------------------------

    In addition, as a result of commenter feedback as explained more 
fully in subsequent paragraphs, we are promulgating in regulatory text 
the following revised versions of elements that we proposed for the not 
reasonably controllable or preventable criterion:
     Provided the appropriate federal, state or tribal air 
agency is not under an obligation to revise the SIP or FIP or TIP for 
an attainment or maintenance area for the event-related pollutant, the 
EPA would consider (i.e., give deference to) enforceable control 
measures implemented in accordance with such a SIP or FIP or TIP, 
approved by the EPA within 5 years of the date of the event, that 
address the event-related pollutant and all sources necessary to 
fulfill the requirements of the CAA for the SIP or FIP or TIP to be 
reasonable controls with respect to all anthropogenic sources that have 
or may have contributed to the monitored exceedance or violation.\41\ 
If the appropriate air agency is under an obligation to revise its 
implementation plan with respect to the specific enforceable control 
measures applicable to the exceptional events demonstration due to a 
SIP call pursuant to CAA section 110(k)(5), the EPA will evaluate on a 
case-by-case basis the control measures in place to determine whether 
emissions were reasonably controlled at the time of the event.
---------------------------------------------------------------------------

    \41\ Under CAA section 110(c), the EPA is required to issue and 
enforce a federal implementation plan if a state fails to develop, 
adopt and implement an adequate SIP. States may also choose to adopt 
the federal plan as an alternative to developing their own plan. If 
a federal plan is implemented in a state, the state may still, at a 
later date submit a plan to replace the federal plan either in whole 
or in part. States may take over the administrative and enforcement 
aspects of a federal plan rather than leaving it to the EPA. 
Similarly, under the TAR at 40 CFR 49, tribes can develop their own 
plans (i.e., tribal implementation plans) to implement the CAA 
provisions. Rather than develop their own TIPs, tribes can request 
that the EPA develop a FIP.
---------------------------------------------------------------------------

     When addressing the ``not reasonably controllable or 
preventable'' criterion within an exceptional events demonstration, air 
agencies should: (1) Identify the natural and anthropogenic sources of 
emissions causing and contributing to the monitored exceedance or 
violation, including the contribution from local sources,\42\ (2) 
identify the relevant SIP, FIP or TIP or other enforceable control 
measures in place for these sources and the implementation status of 
these controls, and (3) provide evidence of effective implementation 
and enforcement of reasonable controls, if applicable.\43\
---------------------------------------------------------------------------

    \42\ In specifying ``local'' sources, we mean those sources that 
are both within the jurisdiction of the state or tribe and that are 
in the vicinity of or are located upwind of the monitor with the 
recorded exceedance or violation. ``Local'' sources could include, 
but are not limited to, large point sources (e.g., large industrial 
sources, electric power plants, airports, etc), nonpoint sources 
(e.g., residential heating, asphalt paving, etc.), mobile sources 
(e.g., both on- and off-road vehicles, construction equipment, 
trains, and vessels), natural sources or biogenic sources (e.g., 
off-gassing from soil, animals and vegetation).
    \43\ The EPA recognizes that air agencies have various methods 
of ensuring source compliance and various methods of permitting and 
enforcement. We do not expect nor would all agencies necessarily 
need to have enforcement records for all events. However, agencies 
should make a general showing that they are enforcing controls to a 
reasonable degree (not necessarily on the particular day of the 
event). If an air agency identifies several categories of 
anthropogenic sources as significant or likely contributors to an 
event, the air agency should also describe in the demonstration the 
means used to determine compliance with reasonable control 
requirements for each category.
---------------------------------------------------------------------------

     Air agencies do not need to provide case-specific 
justification to support the ``not reasonably controllable or 
preventable'' criterion for large-scale and high-energy high wind dust 
events, such as ``haboobs.'' (We discuss the characteristics of these 
events in Section IV.F.4 of this preamble.)
    In addition, we repeat in this final action our suggestion that an 
air agency can prospectively assess and determine that the controls in 
place for a particular type of event, or a planned enhancement of those 
controls, are sufficient to meet the not reasonably controllable or 
preventable criterion, and then obtain the EPA's review and concurrence 
of this assessment prior to the occurrence of similar events (i.e., a 
similar event type generating emissions of the same pollutant). This 
prospective approach would reduce disagreements that might otherwise 
occur over later retrospective assessments. Although air agencies have 
not historically pursued this option, it is our intent going forward to 
work with any air agency expressing an interest in pursuing this 
approach. Air agencies interested in this process should contact their 
reviewing EPA Regional office.
c. Comments and Responses
    While some commenters supported the EPA's stated position in the 
proposal that the not reasonably controllable or preventable criterion 
consists of two prongs (i.e., control and prevention), other commenters 
asserted that the statutory criterion and the implementing language in 
the 2007 rule is ``not reasonably controllable or preventable'' 
(emphasis added). Commenters disagreeing with the EPA's position claim 
that the EPA's interpretation is contrary to the CAA and that the EPA 
lacks authority to contravene the precise statutory language in the 
implementing regulatory language by interpreting the CAA to mean that 
an exceptional event must be both not reasonably controllable and not 
reasonably preventable.
    As previously noted, we maintain that the criterion consists of two 
factors: Prevention and control and that to qualify as an exceptional 
event, the event must satisfy both factors. CAA section 
319(b)(1)(A)(ii) is ambiguous regarding whether ``not reasonably 
controllable or preventable'' requires a demonstration to show both 
criteria, or one or the other. In adopting our interpretation, we have 
applied a valid rule of inference known as De Morgan's law, which 
recognizes that the negation of a disjunction is the conjunction of the 
negations. Stated simply, ``not (A or B)'' is the same as ``(not A) and 
(not B).'' See, e.g., State v. Nelson, 842 NW.2d 433, at 440-41 (Minn. 
2014) (finding it reasonable to apply De Morgan's law to

[[Page 68236]]

statutory interpretation); Schane v. Int'l Bhd. Of Teamsters, 760 F.3d 
585, 589-92 (7th Cir. 2014) (applying De Morgan's law to address a 
pension plan dispute, focusing on the context in which the ``not . . . 
or'' phrase was used). Applied to CAA section 319(b)(1)(A)(ii), an 
exceptional event means an event that is both not reasonably 
controllable and not reasonably preventable. The legislative history 
supports this logical reading of the statutory language. Congress 
provided the following rationale for promulgating the exceptional 
events provisions: ``Events such as forest fires or volcanic eruptions, 
should not influence whether a region is meeting its Federal air 
quality goals.'' S. Rep. No. 109-53, at Sec. 1618 (2005) and S. Rep. 
No. 108-222, at Sec. 1618 (2004). The examples used in the legislative 
history--forest fires and volcanic eruptions--are both not reasonably 
controllable and not reasonably preventable.
    This interpretation is also supported by the intent of CAA section 
319(b), which identifies the limited circumstances in which it is 
appropriate to exclude from certain regulatory decisions air monitor 
data clearly caused by an exceptional event balanced with the CAA's 
goal of protecting human health and the environment. The language ``not 
reasonably controllable'' clearly implicates controls, as does 
``preventable,'' since an event may be ``preventable'' by mitigating 
the conditions under which the event occurs--i.e., by applying 
controls. Thus, consideration of the circumstances of the event and 
possible application of controls is appropriate in both contexts, and a 
separate analysis is required for ``not reasonably controllable'' and 
``not reasonably preventable.''
    We note that the commenters who disagree with the EPA's 
interpretation failed to identify any scenarios or provide any examples 
of why it is problematic for the EPA to require that an exceptional 
event must be both not reasonably controllable and not reasonably 
preventable. While some air agencies that have submitted demonstrations 
have argued that the ``or'' in this criterion allows them to choose 
between showing either prevention or control of the event-related 
emissions, this type of ``or'' selection is contrary to the emphasis of 
CAA section 319(b) on the protection of public health and the exclusion 
of data associated with emissions from ``exceptional events.'' The CAA 
as a whole, and section 319(b) in particular, is premised on the idea 
that states should undertake reasonable actions to control emissions 
and protect public health. Exemptions and exceptions apply in addition 
to, rather than in place of, reasonable controls. The CAA does not 
allow air agencies to avoid applying reasonable controls to address 
emissions simply because other factors also contribute to those 
emissions. For example, for a high wind event, applying ``or'' might 
suggest that because the wind is not preventable, the agency has no 
obligation to address reasonable controls (e.g., the application of 
water to stockpiles of wood chips) that could reduce emissions in the 
case of such an event. For prescribed fire, the use of ``or'' could 
allow an air agency to argue that a fire is not reasonably preventable 
because of the safety or ecosystem benefits that would be foregone if 
the fire were not applied, so the emissions and air quality impacts 
from the fire do not need to be reasonably controlled through the 
application of basic smoke management practices. Another example of 
when applying ``or'' would be problematic is a situation in which a 
developer could intentionally set fire to forested land to clear it for 
development, as that event would be preventable but possibly not 
controllable; such an event should not be considered an exceptional 
event. In contrast, elsewhere in the preamble to these final rule 
revisions we explain that some events may be neither preventable nor 
their air quality impacts to be controllable to any degree, such as 
potential increases in SO2 concentrations associated with 
volcanic eruptions, and thus would qualify as exceptional events.
    These final rule revisions present that what is ``reasonable'' for 
purposes of ``not reasonably controllable or preventable'' should 
consider the technical knowledge available to the air agency at the 
time of the event. While this concept was supported by some commenters, 
others maintain that ``controllable'' is forward looking rather than 
backward looking and that air agencies should anticipate future events 
and implement controls and measures to account for potential future 
impacts.
    We agree with the commenters that a prospective approach to 
assessing what might constitute ``reasonable controls'' could be 
helpful in some cases, particularly for areas experiencing recurring 
events. Therefore, we have modified our proposal as it relates to 
mitigation for areas experiencing historically documented or known 
seasonal events. We discuss these concepts in Section V of this 
preamble. We disagree, however, with the commenters' forward-looking 
approach as it applies to other situations. As we noted in the 
proposal, an air agency ``caught by surprise'' by an event of a given 
type (or by an unexpected number of such events in a period over which 
NAAQS compliance is evaluated, typically 3 years) should not be 
expected to have implemented the same controls prior to an event as an 
air agency that has been aware that events of a certain type occur with 
regularity and cause NAAQS exceedances or violations. The EPA 
anticipates that nonattainment (or maintenance) areas have technical 
information needed to understand those measures that constitute 
reasonable control of anthropogenic sources in their jurisdiction for 
recurring events of the type(s) that cause or contribute to 
nonattainment (or that did previously). In contrast, the EPA generally 
does not expect areas identified as attainment, unclassifiable/
attainment or unclassifiable for a NAAQS to have the same understanding 
or to have adopted the same level of event-relevant controls as areas 
that are nonattainment (or maintenance) for the same NAAQS. Also, if an 
area has been recently designated to nonattainment but is still 
developing its SIP and has not yet reached a deadline to implement 
controls, the EPA expects the level of controls that is appropriate for 
that planning stage.\44\
---------------------------------------------------------------------------

    \44\ The CAA provides different timeframes for developing and 
implementing SIPs depending on the NAAQS and the nonattainment 
area's classification (e.g., severity of the nonattainment problem). 
The EPA recognizes that within the SIP development and 
implementation process, some measures may be implemented relatively 
quickly (e.g., transportation conformity, new source review) whereas 
other programs, such as development or rules for particular source 
types, can take time and involve state legislative processes.
---------------------------------------------------------------------------

    As noted previously, the EPA proposed, and is finalizing in rule 
language, that an air agency does not need to provide case-specific 
justification to support the ``not reasonably controllable or 
preventable'' criterion for emissions-generating activity that occurs 
outside the boundaries of the state (or tribal lands) within which the 
concentration at issue was monitored. While the majority of commenters 
supported this provision, other commenters noted that it is 
inconsistent with the plain language of CAA section 319, which requires 
that an event be not reasonably controllable or preventable and does 
not distinguish based on the origin of emissions associated with the 
event.
    A review of the legislative history, and the language of section 
319, as well as the purpose and intent of the CAA as a whole, reveals 
that Congress did not likely intend to deny a downwind state

[[Page 68237]]

or tribe relief in the form of data exclusion within the context of the 
Exceptional Events Rule for emissions that state or tribe has no 
authority to control. See, e.g., H.R. Rep. No. 109-203 (2005) and CAA 
section 319(b)(1). As we expressed in the proposal, it is not 
reasonable to expect the downwind air agency (i.e., the state or tribe 
submitting the demonstration) to have required or persuaded the upwind 
state, tribe, or foreign country to have implemented controls on 
sources sufficient to limit event-related air concentrations in the 
downwind state or tribal lands. In fact, Congress explicitly addressed 
interstate pollution transport in CAA sections 110(a)(2)(D)(i) and 
(ii), which we discuss in more detail in Section IV.F.1 of this 
preamble. There is no evidence that Congress intended for such efforts 
to be repeated in the context of exceptional events. We note, however, 
that we do expect the submitting (downwind) air agencies to assess 
potential contribution from local/in-state sources within their 
jurisdiction and submit evidence and statements supporting the other 
exceptional events criteria (i.e., clear causal relationship and human 
activity unlikely to recur or a natural event) in their demonstrations 
for events that originate outside of their jurisdictional bounds.
    Regarding the origin of emissions, several commenters asked that 
the EPA clarify how ``outside of jurisdiction'' applies to emissions 
from ocean-going vessels (e.g., container ships and large tankers that 
are regulated by international treaties) and international natural and 
anthropogenic emissions. Although the EPA would consider emissions from 
ocean-going vessels regulated by international treaties as well as 
other international emissions (regardless of whether they are natural 
or anthropogenic in origin) to be emissions originating outside of the 
jurisdiction of the affected air agency and these emissions would 
therefore satisfy the not reasonably controllable or preventable 
criterion, these same emissions would only qualify for treatment under 
the Exceptional Events Rule if they also satisfy the clear causal 
relationship criterion and the human activity unlikely to recur at a 
particular location or a natural event criterion. In these scenarios, 
emissions from ships regulated by international treaty and 
international emissions from routine anthropogenic activity would not 
satisfy the human activity unlikely to recur at a particular location 
criterion because they are both routine and occur frequently in the 
same area (e.g., the port or coastline). International emissions 
originating from a natural, event-based sources (e.g., wildfire, 
volcanic activity) or from human activities unlikely to recur at a 
particular location (e.g., industrial explosions) are more likely to 
qualify as exceptional events. As we have stated multiple times in this 
preamble, to qualify for data exclusion under the provisions of the 
Exceptional Events Rule, an event must satisfy all of the technical and 
administrative requirements under the rule.
    The proposed rule revisions contained regulatory language allowing 
air agencies to defer to the control measures included in an attainment 
or maintenance SIP, approved by the EPA within 5 years of the date of a 
demonstration submittal, that addresses the event-related pollutant and 
contributing sources, to satisfy the requirement for reasonable 
controls. While the overwhelming majority of commenters, representing 
state, local, regional planning organizations and industry, supported 
this presumption, a few commenters disagreed with this provision noting 
that the EPA should not universally defer to SIP measures, but rather 
should assess the not reasonably controllable or preventable criterion 
on a case-by-case basis. Commenters supporting deference asked the EPA 
to consider the following revisions: (1) Measure the sufficiency of SIP 
requirements from the date of the event rather than the date of 
demonstration; (2) include reliance on measures in FIPs and/or TIPs in 
addition to those in SIPs; (3) include reliance on BACMs in air quality 
permits that are designed to control anthropogenic industrial sources; 
and (4) expand the reliance to include infrastructure SIPs (with or 
without Natural Events Action Plans (NEAP) or other mitigation plans).
    We individually address these general comments and specific 
suggestions for revision in the following paragraphs. We maintain, as 
supported by many commenters and as opposed by a few, that deference to 
enforceable control measures implemented in accordance with an 
attainment or maintenance SIP (or FIP or TIP), is appropriate provided 
the timeframe for deference is limited and provided the SIP addresses 
the pollutant and the sources potentially contributing emissions to the 
exceedance or violation that is the subject of the exceptional events 
demonstration. SIPs demonstrate that the state has the basic air 
quality management program components in place to implement a new or 
revised NAAQS by identifying the emission control requirements that 
state will rely on to attain/maintain these NAAQS. In developing its 
SIP according to the provisions of CAA section 110(a), a state must 
identify and assess those sources of emissions that are contributing to 
the state's air pollution problem, identify appropriate controls, 
identify contingency measures, address provisions for demonstrating 
reasonable further progress, identify permitting requirements, and 
satisfy other requirements. When a nonattainment area reaches 
attainment, it may be redesignated to maintenance area status if it has 
implemented all applicable nonattainment area requirements and obtains 
the EPA's approval for a maintenance plan for a 10-year period. Thus, 
in both maintenance and nonattainment areas with approved attainment 
plan SIPs, the air agency and the EPA, with input from the public, will 
have considered what controls are necessary and reasonable to provide 
for attainment, based on information available at the time of plan 
development and approval. Because the attainment/maintenance SIP 
development process includes the identification and assessment of those 
sources of emissions that are contributing to the state's air pollution 
problem, which could include event-related emissions, it is appropriate 
to rely on the measures in the SIP as constituting reasonable controls 
for purposes of exceptional events demonstrations just as it is 
reasonable to rely on the measures in the SIP as constituting 
reasonable controls for emissions sources. We do, however, agree with 
the commenters that deference to the control measures in an attainment 
or maintenance SIP should not be open-ended. We discuss limitations to 
this deference in the following paragraphs, including deference for a 
limited timeframe (i.e., 5 years).
    As suggested by commenters, we have changed the language in this 
provision to be 5 years from the date of the ``event'' rather than the 
date of ``demonstration submittal'' as we proposed. We believe that it 
is reasonable and appropriate to make this change to ensure that the 
exceptional events process is implemented in a manner consistent with 
the CAA. We also agree with commenters that ``5 years from the date of 
the event'' is the more appropriate time-frame given that we are 
promulgating requirements in 50.14(b)(8)(i)-(iv), which also rely on 
the date of the event.
    As we noted in this preamble, we also agree with commenter 
recommendations that we defer to enforceable control measures

[[Page 68238]]

implemented in accordance with an attainment or maintenance SIP, FIP or 
TIP. We have included these implementation plans in the regulatory 
text. We agree that FIPs and TIPs provide the same level of assessment 
of control measures during the development and approval process as 
attainment/maintenance SIP process previously described and that the 
only difference between these plans lies in the agency developing the 
plan and the agency to whom the plan applies, neither of which impact 
whether the measures contained in the plans constitute reasonable 
controls for purposes of exceptional events demonstrations. For several 
reasons, however, we do not agree that we should universally extend 
this same deference to BACM or fugitive dust control plans contained in 
air quality permits. First, control measures in air quality permits may 
or may not be EPA-approved and evaluated using the same rigor as 
controls in a SIP, FIP or TIP. Second, the best available control 
measures in an air quality permit apply to the permit holder and not to 
all sources potentially contributing emissions to a monitored 
exceedance or violation. While we are not deferring to BACM controls in 
air quality permits, we encourage air agencies to identify these 
measures in the collection of controls that they determine constitute 
``reasonable'' controls for purposes of addressing the not reasonably 
controllable or preventable criterion.
    The EPA disagrees with the suggestion from a few other commenters 
to defer to provisions in infrastructure SIPs to satisfy the not 
reasonably controllable or preventable criterion. CAA sections 
110(a)(1) and 110(a)(2) require every state to develop and submit to 
the EPA an ``infrastructure SIP'' for each NAAQS within 3 years of the 
promulgation of a new or revised NAAQS. While infrastructure SIPs 
address a number of CAA requirements, including the requirement to 
identify emission limits for specific pollutants, infrastructure SIPs 
are not required to include attainment or maintenance demonstrations 
and are not required to demonstrate that the controls on particular 
sources are ``reasonable.'' Thus, the EPA-approved infrastructure SIPs 
do not necessarily constitute an assessment of those controls that are 
reasonable to have in place to address air quality impacts from 
particular types of events that may become the focus of exceptional 
events demonstrations. As with measures in air quality permits, while 
we are not deferring to measures identified in infrastructure SIPs to 
universally satisfy the not reasonably controllable or preventable 
criterion, we encourage air agencies to identify measures in 
infrastructure SIPs, NEAPs, mitigation plans, SMP and prospective 
assessments of reasonable controls in the collection of controls that 
they determine constitute ``reasonable'' controls for purposes of 
addressing the not reasonably controllable or preventable criterion. We 
note that provisions in these plans could, on a case-by-case basis with 
the proper showing, satisfy the not reasonably controllable or 
preventable criterion.
    We are promulgating rule language that the timeframe for 
attainment/maintenance SIP deference is 5 years from the date of the 
SIP approval measured to the date of an event at issue. We solicited 
comment on whether and what other timeframes might be appropriate for 
this deference. In responding to this specific solicitation for 
feedback, commenters provided a range of options for SIP deference 
including 3 years, 5 years, 10 years, reliance on the SIP until a new 
NAAQS is adopted or until the EPA disapproves or calls the SIP, and, as 
previously noted, no reliance on the SIP because any such deference is 
inappropriate. One commenter noted that a deference timeframe of 3 
years is more consistent with design value averaging and the timeframe. 
We previously suggested in the 2013 Interim Exceptional Events 
Implementation Guidance, and other commenters argued, that 10 years is 
consistent with the timeframe for maintenance plan updates. The EPA 
considered this information and is now promulgating, as proposed, a 
deference timeframe of 5 years. After reviewing feedback received 
during the comment period, we retain our proposed language that 5 years 
represents a reasonable timeframe during which (1) the control measures 
in a current SIP (or FIP or TIP) address all event-relevant sources of 
current importance, (2) the control measures that were considered by 
the air agency and the EPA at the time the EPA last approved the SIP 
(or FIP or TIP) are the same measures that are known and available at 
the time of a more recent event, and (3) the conditions in the area 
have not changed in a way that would affect the approvability of the 
same SIP (or FIP or TIP) if it newly needed the EPA's approval. 
Additionally, as we discuss in Section IV.E.3 of this preamble, we 
encourage the use of 5 years of data when developing analyses to 
support the clear causal relationship criterion because we believe that 
5 years of ambient air data represent the range of ``normal'' air 
quality. Using a 3-year period of deference might mask (or accentuate) 
the range of ``normal'' air quality, while using a 10-year deference 
timeframe could overlook new emissions sources, relevant control 
measures and control measure technologies, and other changes in the 
affected area that could influence the approvability of a SIP (or FIP 
or TIP).
    We also note that in establishing a period of deference of 5 years, 
we are not implying that in periods longer than 5 years, the controls 
in a SIP automatically become inappropriate or insufficient. Rather, we 
are saying that in cases where the SIP was approved more than 5 years 
prior to the date of the event (and the air agency is not under an 
obligation to revise the SIP), because of the passage of time, the SIP 
controls should not be presumed to satisfy the not reasonably 
controllable or preventable criterion. In such a case, the air agency 
should complete a case-specific assessment of the reasonableness of 
controls to satisfy the not reasonably controllable or preventable 
criterion. This case-by-case assessment would include the following 
components, which we are promulgating as rule text: (1) Identify the 
natural and anthropogenic sources of emissions causing and contributing 
to the monitored exceedance or violation, including the contribution 
from local sources, (2) identify the relevant SIP or other enforceable 
control measures in place for these sources and the implementation 
status of these controls, and (3) provide evidence of effective 
implementation and enforcement of reasonable controls, if applicable. 
As we identified earlier in this preamble, when we specify ``local'' 
sources, we mean those sources that are both within the jurisdiction of 
the state or tribe and that are also in the vicinity of or are located 
upwind of the monitor with the recorded exceedance or violation. 
``Local'' sources could include, but are not limited to, large point 
sources (e.g., large industrial sources, electric power plants, 
airports, etc), nonpoint sources (e.g., residential heating, asphalt 
paving, etc.), mobile sources (e.g., both on- and off-road vehicles, 
construction equipment, trains, and vessels), natural or biogenic 
sources (e.g., off-gassing from soil, animals and vegetation).
    We identified in the proposal these three components of a case-by-
case assessment of the not reasonably controllable or preventable 
criterion and solicited comment on including these components as 
regulatory language. One commenter supported this suggestion, and, as a 
result, we are promulgating associated rule text. Although no

[[Page 68239]]

commenters opposed including the components as rule text, a number of 
commenters asked that we clarify our expectations with respect to these 
components. We do so here.
    When identifying the sources of emissions causing and contributing 
to the monitored exceedance or violation, the air agency should first 
discuss the scope of the analysis with the reviewing EPA Regional 
office. This scope will be determined on a case-by-case basis 
considering the specifics of the individual event. For example, if an 
air agency claims that an event was regional in nature, then the area 
of focus for the not reasonably controllable or preventable criterion 
would likely be the county or counties involved in the ``region.'' If 
an affected air agency claims that an exceedance or violation was 
caused by an event originating in a nearby state, then the air agency 
would include in its assessment the area and the potentially 
contributing sources located between the subject upwind source and the 
affected monitor. Once the air agency and the EPA determine the 
appropriate area of analysis, the air agency should identify, within 
the area of analysis, those stationary, mobile (if applicable) and area 
sources and any other natural sources that emit the pollutant or 
precursors that are the subject of the demonstration.\45\ In doing 
this, the air agency should include, for ``major'' point sources,\46\ 
the facility name, the distance of the facility to the affected 
monitor, and emissions in terms of tons per year (tpy) of the pollutant 
in question. Air agencies may identify other point sources and area 
sources by category.
---------------------------------------------------------------------------

    \45\ A recent emissions inventory could serve as a starting 
point when identifying sources of emissions within a given area of 
analysis. Air agencies should also consider other sources that 
potentially contribute to event-related emissions that may not be 
the focus of routine annual inventories, which are often required by 
federal, state or local rules for only a specific set of sources or 
pollutants.
    \46\ The term ``major'' can vary by pollutant and NAAQS and 
affected air agencies should discuss the expectation during the 
initial notification of a potential exceptional event process. 
Generally, however, we would consider ``major'' to be the thresholds 
used in the initial area designations process for the NAAQS in 
question. For example, for PM2.5, major point sources are 
those whose sum of PM precursor emissions (PM2.5 + 
NOX + SO2 + VOC + NH3) are greater 
than 500 tpy based on the most recent National Emissions Inventory 
(NEI) or SIP inventory.
---------------------------------------------------------------------------

    For each source category and/or individual source, if appropriate, 
the air agency should identify applicable control measures in the SIP 
or in other state rules or ordinances and provide a statement as to why 
these controls are reasonable.\47\ In addition to the SIP, state rules 
or local ordinances, air agencies could also identify control measures 
in individual permits, NEAPs, SMP, other mitigation plans, or USDA/
Natural Resources Conservation Service (NRCS)-approved Best Management 
Practices (BMPs) (discussed in more detail in Section IV.F.2.b of this 
preamble). The air agency may also consider recent Reasonably Available 
Control Technology (RACT)/Best Available Control Technology (BACT)/
Lowest Achievable Emission Rate (LAER) determinations in the affected 
area or in another area with similar sources or other appropriate 
measures. This assessment should include a review and description of 
any known instances of source noncompliance (e.g., nearby facility 
upsets or malfunctions, failure to comply with applicable rules such as 
vacant lot stabilization or moisture requirements for area sources) 
that could have resulted in emissions of the relevant pollutant(s) that 
influenced the monitored measurements on the day(s) of the claimed 
events. The air agency would then identify the implementation status of 
these controls and provide evidence of enforcement. As we indicated 
earlier, the EPA generally expects evidence that the controls 
determined to be reasonable, if any, were effectively implemented and 
appropriately enforced.
---------------------------------------------------------------------------

    \47\ To clarify, the EPA does not need to formally approve an 
air agency's rules and SIP before reasonable controls are officially 
in place for an exceptional events determination. These final rule 
revisions and final rule preamble indicate that we will defer to 
controls in a SIP/FIP/TIP approved by the EPA within 5 years of the 
date of the event provided the controls are specific to the 
pollutant and contributing anthropogenic sources. Thus, a SIP/FIP/
TIP approved within 5 years of an event satisfies reasonable 
controls, but an area could also satisfy the not reasonably 
controllable or preventable criterion a number of other ways as 
discussed in this preamble. We also note that if an air agency has a 
record of other controls that are not yet part of a SIP/FIP/TIP (as 
could be the case for an attainment, unclassifiable/attainment or 
unclassifiable area or for a nonattainment or maintenance area 
undergoing SIP planning or revision process) but that are 
implemented and enforced and not just contemplated, that we would 
consider these controls to be SIP/FIP/TIP controls.
---------------------------------------------------------------------------

    After addressing these components and in concluding that they have 
shown that reasonable measures to control the impact of the event on 
air quality were applied at the time of the event and that the event 
was therefore not reasonably controllable, the air agency should then 
apply the concept that if a set of control measures should reasonably 
have been in place for emission sources that contribute to the event 
emissions, then those controls must have been in place for the event to 
satisfy the not reasonably controllable or preventable criterion. To do 
this, the air agency should ask the following questions: (1) Do the 
control measures in the current SIP (or other programs) address all 
event-relevant sources of current importance? (2) Are the control 
measures that were considered by the air agency and the EPA at the time 
the EPA last approved the SIP the same measures that are known and 
available at the time of the more recent event? and (3) Have the 
conditions in the area changed in a way that would affect the 
approvability of the same SIP if it newly needed the EPA's approval? In 
our view an event is ``not reasonably controllable'' if an exceedance 
or violation occurs even when reasonable controls were actually in 
place and any further control would have been beyond what was 
reasonable. As indicated in these rule revisions, the EPA intends to 
consider these aspects when applying the concept of ``reasonable 
controls'' on anthropogenic sources.
    The EPA notes that there are several instances in which this step-
wise approach to addressing the not reasonably controllable or 
preventable criterion is not necessary. This analysis is not required 
when an air agency can rely on deference to control measures contained 
in a SIP (or FIP or TIP). It is also not required for exceedances or 
violations caused by events whose emissions are solely from natural 
sources (e.g., wildfire; stratospheric ozone intrusions; windblown dust 
from natural, undisturbed landscapes; large-scale and high-energy high 
wind dust events, volcanic activity) as demonstrated by satisfying the 
clear causal relationship (discussed in more detail in Section IV.E.3 
of this preamble). In these cases, after addressing the clear causal 
relationship criterion, the air agency should affirmatively state that 
the not reasonably controllable or preventable criterion is satisfied 
by the fact that the natural event was of a character that could not 
have been prevented and could not have been controlled and that there 
were no contributions of event-related emissions from anthropogenic 
sources as demonstrated in the clear causal relationship showing. To 
clarify, once an air agency has satisfied the clear causal relationship 
criterion and has shown that the subject exceedance or violation was 
caused by an event whose emissions are solely from natural sources, 
then the not reasonably controllable criterion applies only to 
emissions from natural sources/event and not to local sources. And, for 
natural sources, air agencies can satisfy

[[Page 68240]]

the criterion with a statement similar to that in the following 
example.
    Consider, as an example, a stratospheric ozone intrusion event. 
Stratospheric intrusions are by nature not reasonably controllable or 
preventable. If an air agency has shown in the clear causal portion of 
its demonstration that ozone transported from the stratospheric ozone 
intrusion overwhelmingly caused each of the identified exceedances, 
then it has shown these are natural, intrusion events and controls on 
anthropogenic sources are irrelevant. The air agency can include the 
following statements in its demonstration:

    The analysis shows that ozone transported via a stratospheric 
ozone intrusion caused each of the identified exceedances in 
[Section A] of this demonstration. We conclude that the event 
identified should be considered a natural, stratospheric ozone 
intrusion event. (An air agency may include this type of conclusory 
language in the natural events section of the demonstration.)
    The analysis shows that ozone transported via a stratospheric 
ozone intrusion caused each of the identified exceedances in 
[Section A] of this demonstration. We conclude that the event in 
question was a stratospheric ozone intrusion event and thereby an 
unpreventable and uncontrollable natural event, and therefore not 
reasonably controllable or preventable. (An air agency may include 
this type of conclusory language in the not reasonably controllable 
or preventable portion of the demonstration.)

    The proposal also discussed and solicited feedback on the role of 
prior communications regarding expectations for reasonable controls. 
The proposal indicated that the EPA would consider communications 
between the EPA and the air agency when assessing ``reasonableness'' as 
part of assessing the technical information available to the air agency 
at the time the event occurred and what should reasonably have been in 
place at the time of the event for anthropogenic emission sources that 
contribute to the event emissions. We noted that because regulations 
and an area's planning status are often evolving and changing and 
because these changes and iterative discussions often include issues 
regarding appropriate controls, including what controls would 
constitute ``reasonable'' controls for exceptional events purposes, we 
solicited comment on what form of communication would be most effective 
in conveying the EPA's views to the affected air agency and whether 
this approach would be most appropriately addressed through guidance or 
regulatory text. Although one commenter responding to this specific 
solicitation for comment indicated that our decision should be 
promulgated in rule text, the majority of commenters indicated that 
expectations in guidance were appropriate. These commenters suggested 
that any formal communication notifying an air agency of specific 
expectations regarding reasonable controls that should be, but are not 
yet, included in the SIP (or FIP or TIP) would be sufficient to 
override the deference to existing SIP (or FIP or TIP) controls. 
Commenters noted that such communications, either electronic or in hard 
copy, come from an authorized person within the EPA and be transparent 
and publicly available. One commenter suggested that the ``authorized'' 
person be the Regional Administrator. The EPA agrees with commenters 
that we would consider as sufficient any formal communication notifying 
the affected air agency of SIP (or FIP or TIP) deficiencies with 
respect to those controls that constitute reasonable controls for the 
sources and pollutants that are contained within the SIP (or FIP or 
TIP) and are the subject of an exceptional events demonstrations.\48\ 
These communications can be conveyed electronically or in hard copy and 
come from any person within the EPA who is authorized to make such 
decisions. Generally, these authorized persons could be branch chiefs, 
air program managers, air division directors or the equivalent highest 
manager who exclusively oversees air programs, or regional 
administrators.
---------------------------------------------------------------------------

    \48\ The EPA acknowledges that not all SIP (or FIP or TIP)-
related communications would negatively impact deference to the 
control measures contained within the SIP (or FIP or TIP). For 
example, if the EPA issued a letter notifying an air agency that its 
existing SIP (or FIP or TIP)-approved controls appear to meet a new 
SIP (or FIP or TIP) requirement (i.e., BACM for the 2008 Ozone NAAQS 
would also be BACM for 2015 Ozone NAAQS), this same correspondence 
could support continued use of those controls as ``reasonable'' for 
exceptional events purposes.
---------------------------------------------------------------------------

    Related to these communications regarding expectations for 
reasonable controls, the proposal invited comment on whether there 
should be a grace or grandfathering period before a SIP (or FIP or TIP) 
call involving a relevant NAAQS that would effectively end the 
deference that applied prior to the SIP (or FIP or TIP) call. If an 
event were to occur during such a grace period, the existing SIP (or 
FIP or TIP) controls would still be given the deference. Several 
commenters supported, and no commenters opposed, incorporating this 
concept into regulatory language, noting that agencies should be given 
time to enact appropriate control measures after the EPA has identified 
this need. Commenters also noted that the timeframe for enacting these 
measures often depends on the widely-varying state/area-specific 
administrative requirements. In many cases, state and local agencies 
are prohibited by state law from enacting ``stricter than federal'' 
controls unless required by a federal action such as a nonattainment 
designation or SIP call. Therefore, in most circumstances, when a SIP 
(or FIP or TIP) revision is required, such as when new regulations must 
be incorporated or when an area receives a new designation, we think it 
is reasonable that agencies be given time to enact appropriate control 
measures after the need to do so has been identified and justification 
is in place to satisfy state laws. However, in some circumstances, the 
requirement to revise particular emission control measures in an 
implementation plan might be pursuant to a SIP call under CAA section 
110(k)(5), which represents a determination by the EPA that the control 
measures in the existing implementation plan are substantially 
inadequate. In the proposal, the EPA acknowledged that such SIP calls 
might necessitate different treatment and took comment on that issue 
(see 80 FR 81878). After fully considering the issue, including 
comments received, we have determined that in such cases involving a 
SIP call, we do not think it would be reasonable for an air agency to 
continue to rely on those deficient measures in an exceptional events 
demonstration. Accordingly, we are including regulatory text that 
extends the deference to emission control measures contained in a SIP 
that is subject to a revision requirement to the due date for a 
required SIP revision. However, the regulatory text also explains that 
when the control measures applicable to the exceptional events 
demonstration are subject to a SIP call under CAA section 110(k)(5), 
the EPA will evaluate on a case-by-case basis the control measures in 
place to determine whether emissions were reasonably controlled at the 
time of the event.
3. Clear Causal Relationship Supported by a Comparison to Historical 
Concentration Data
a. Summary of Proposal
    The EPA proposed to revise the 2007 Exceptional Events Rule 
language related to the clear causal relationship criterion as follows:

 To move the ``clear causal relationship'' element into the 
list of criteria that explicitly must be met for data to be excluded

[[Page 68241]]

 To subsume the ``affects air quality'' element into the 
``clear causal relationship'' element
 To remove the ``but for'' element
 To remove the term ``historical fluctuations'' and replace it 
with text referring to a comparison to historical concentrations,
 To clarify that the comparison to historical concentrations is 
not a fact that must be proven
 To clearly identify in regulatory language the types of 
analyses that are necessary and sufficient in a demonstration to 
address the comparison to historical concentrations

    As noted in the proposal, CAA section 319(b)(3)(B)(ii) requires 
that ``a clear causal relationship must exist between the measured 
exceedances of a national ambient air quality standard and the 
exceptional event to demonstrate that the exceptional event caused a 
specific air pollution concentration at a particular air quality 
monitoring location.'' The clear causal relationship criterion 
establishes causality between the event and a measured exceedance or 
violation of a NAAQS. If the actual effect of the event were small, it 
may be very difficult to distinguish the effect of the event with 
sufficient confidence because many other factors could have produced 
similar effects. As with the other exceptional events criteria, the EPA 
has used a weight of evidence approach when reviewing analyses to 
support a causal relationship between an event and a monitored 
exceedance or violation.
    Showing that an event and elevated pollutant concentrations 
occurred simultaneously may not establish causality. The clear causal 
relationship section of an exceptional events demonstration should 
include analyses showing that the event occurred and that emissions of 
the pollutant of interest resulting from the event were transported to 
the monitor(s) recording the elevated concentration measurement(s). The 
last three of the bullets, summarized here, relate to analyses 
associated with demonstrating that a clear causal relationship exists 
between the event-related emissions and the monitored exceedance or 
violation (i.e., they relate to the technical treatment of data, which 
is the subject of this section of the preamble). We discussed our 
proposed rationale for the first three bullets in Section V.B.1 of this 
preamble, Definition and Scope of an Exceptional Event.
    The EPA proposed to remove the regulatory language in the 2007 
Exceptional Events Rule that ``[t]he event is associated with a 
measured concentration in excess of normal historical fluctuations, 
including background'' and replace it with text referring to a 
comparison to historical concentrations. Our intent with the original 
language in the 2007 rule was to require air agencies to present event-
influenced concentration data along with historical data and to 
quantify the difference, if any, between the event and the non-event 
concentrations thus supporting the weight of evidence within the clear 
causal relationship determination. We indicated in our November 2015 
proposal that the phrase ``in excess of normal historical fluctuations, 
including background'' is vague and provides no additional value to 
historical concentration comparisons. Rather than use this language, we 
proposed that every exceptional events submittal must include a 
demonstration of a clear causal relationship between the event-related 
emissions and the monitored exceedance or violation as supported by a 
comparison to historical concentration data.
    To support the clear causal relationship generally, we proposed 
example analyses and guidance, shown in Table 1, as being appropriate 
for most event types.\49\
---------------------------------------------------------------------------

    \49\ For purposes of summarizing example clear causal 
relationship analyses in one place, the EPA has included an entry 
for the comparison to historical concentrations showing in Table 1. 
The EPA notes that although the Interim High Winds Guidance and the 
Interim Q&A document discussed the comparison to historical 
concentrations showing, neither of these guidance documents 
presented this showing as part of the clear causal relationship. See 
specifically Interim Guidance on the Preparation of Demonstrations 
in Support of Requests to Exclude Ambient Air Quality Data Affected 
by High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. 
Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf and Interim 
Exceptional Events Rule Frequently Asked Questions. U.S. EPA. May 
2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf.

    Table 1--Example Clear Causal Relationship Evidence and Analyses
------------------------------------------------------------------------
   Example of clear causal      Types of analyses/information to support
    relationship evidence                     the evidence
------------------------------------------------------------------------
Comparison to Historical       Analyses and statistics showing how the
 Concentrations.                observed event concentration compares to
                                the distribution or time series of
                                historical concentrations of the same
                                pollutant.
Occurrence and geographic      Special weather statements, advisories,
 extent of the event.           news reports, nearby visibility
                                readings, measurements from regulatory
                                and non-regulatory (e.g., special
                                purpose, emergency) monitoring stations
                                throughout the affected area, satellite
                                imagery.
Transport of emissions         Wind direction data showing that
 related to the event in the    emissions from sources identified as
 direction of the monitor(s)    part of the ``not reasonably
 where the measurements were    controllable or preventable''
 recorded.                      demonstration were upwind of the
                                monitor(s) in question, satellite
                                imagery, monitoring data showing
                                elevated concentrations of other
                                pollutants expected to be in the event
                                plume.
Spatial relationship between   Map showing likely source area, wind
 the event, sources,            speed/direction and pollutant
 transport of emissions and     concentrations for affected area during
 recorded concentrations.       the time of the event, trajectory
                                analyses.
Temporal relationship between  Hourly time series showing pollutant
 the event and elevated         concentrations at the monitor in
 pollutant concentrations at    question in combination with wind speed/
 the monitor in question.       direction data in the area where the
                                pollutant originated/was entrained or
                                transported.
Chemical composition and/or    Chemical speciation data from the
 size distribution (for PM2.5   monitored exceedance(s) and sources,
 to PM10) of measured           size distribution data.
 pollution that links the
 pollution at the monitor(s)
 with particular sources or
 phenomenon.
Comparison of event-affected   Comparison of concentration and
 day(s) to specific non-event   meteorology to days preceding and
 days.                          following the event, comparison to high
                                concentration days in the same season
                                (if any) without events, comparison to
                                other event days without elevated
                                concentrations (if any), comparison of
                                chemical speciation data.
------------------------------------------------------------------------


[[Page 68242]]

    We noted that we do not expect nor would all air agencies 
necessarily need to include all of the evidence and analyses identified 
in Table 1, but rather to use available information to build a weight 
of evidence showing. The proposal also noted that the EPA expects 
nonattainment areas to have more sophisticated air quality prediction 
tools, in some cases these tools include photochemical or regression 
models and modeling experience. Depending on the case-by-case nature of 
the event, these tools may be beneficial, particularly in situations 
where the causality between the event and a measured exceedance of a 
NAAQS is not clearly established with evidence and analyses identified 
in Table 1.
    As we have noted previously, the EPA's mission includes preserving 
and improving, when needed, the quality of our nation's ambient air to 
protect human health and the environment. The EPA accomplishes this by 
developing the NAAQS for criteria pollutants, evaluating the status of 
the ambient air as compared to these NAAQS using data collected in the 
national ambient air quality monitoring network established under the 
authority of section 319(a) of the CAA, and by overseeing the states' 
programs to improve air quality, as needed. Thus, ambient air quality 
data are fundamental to the CAA and the protection of public health. 
Data exclusions must also be consistent with the CAA. The ``comparison 
to historical concentration'' portion of the clear causal relationship 
criterion shows how the event-influenced data compare to other non-
event related air quality data.
    To clarify our expectations for the ``comparison to historical 
concentrations'' portion of the clear causal relationship showing, we 
proposed the evidence and analyses shown in Table 2 as rule text to 
indicate types of statistics, graphics and explanatory text regarding 
comparisons to past data. The proposed rule language also indicated 
that the analyses described in Table 2 are sufficient to satisfy the 
rule's requirement regarding the comparison to historical concentration 
data and that the submitting air agency does not need to prove any 
specific threshold or ``in excess of'' fact.
    As with other evidence in an exceptional events demonstration 
submittal, the EPA will use a weight of evidence approach in reviewing 
submitted demonstrations and will consider the ``clear causal 
relationship'' information, including the comparison to historical 
concentrations showing, along with evidence supporting the other 
Exceptional Events Rule criteria.
b. Final Rule
    After considering the public comments as described in the following 
text, many of which supported our proposed approach, we are finalizing 
as proposed and revising the regulatory requirement that the 
demonstration to justify data exclusion must include a demonstration 
that the event affected air quality in such a way that there exists a 
clear causal relationship between the specific event and the monitored 
exceedance or violation. We are also finalizing a modified version of 
our proposal that the demonstration include analyses comparing the 
claimed event-influenced concentration(s) to concentrations at the same 
monitoring site at other times to support the clear causal relationship 
criterion. The modification to the language within 40 CFR 
50.14(c)(3)(iv)(C) retains the statement that the Administrator shall 
not require an air agency to prove a specific percentile point in the 
distribution of data. We note, in response to comments, that 
``proving'' a specific percentile point is different than 
``determining'' a specific percentile point. Also in response to 
commenter feedback, we have removed the regulatory table identifying 
the specific analyses associated with the comparison to historical 
concentrations and included a revised version of the proposed table 
(see Table 2) in this preamble as guidance. Although the table includes 
several changes and clarifications suggested by commenters, we have 
retained the proposed analysis that involves ``determining'' the 
percentile ranking of the concentration in question because this 
assessment provides perspective for the clear causal showing.

     Table 2--Evidence and Analyses for the Comparison to Historical
                             Concentrations
------------------------------------------------------------------------
   Historical concentration     Types of analyses/supporting information
           evidence                               \a\
------------------------------------------------------------------------
1. Compare the concentrations   Provide the data in the form
 on the claimed event day       relevant to the standard being
 with past historical data.     considered for data exclusion.
                                Present monthly maximums of the
                                NAAQS relevant metric (e.g., maximum
                                daily 8-hour average ozone or 1-hr SO2)
                                vs presenting monthly or other averaged
                                daily data as this masks high values for
                                the most recent 5-year period that
                                includes the event(s).\b\
                                Alternatively, if informative,
                                include separate plots for each year (or
                                season).\c\
                                See examples at https://www.epa.gov/sites/production/files/2015-05/documents/ideasforshowingeeevidence.pdf and
                                Question 3 in the Interim Q&A document
                                provides additional detail.\d\
2. Demonstrate spatial and/or   Prepare one or more time series
 temporal variability of the    plots showing the concentrations of the
 pollutant of interest in the   pollutant of interest at the affected
 area.                          monitor and nearby monitors.
                                Compare concentrations on the
                                claimed event day with a narrower set of
                                similar days by including neighboring
                                days at the same location (e.g., a time
                                series of two to three weeks) and/or
                                other days with similar meteorological
                                conditions (possibly from other years)
                                at the same or nearby locations with
                                similar historical air quality along
                                with a discussion of the meteorological
                                conditions during the same timeframe.\e\
3. Determine percentile         Determine 5-year percentile of
 ranking.                       the data requested for exclusion on a
                                per monitor basis.
                                Determine the annual ranking of
                                the data requested for exclusion. This
                                assessment may be potentially helpful to
                                show when the non-event concentrations
                                during the year with the exclusion
                                request were lower than surrounding
                                years.
4. Plot annual time series to   Prepare a time series plot
 show the range of ``normal''   covering 12 months (or all months in
 values (i.e., Display          which the data were collected)
 Interannual Variability) \f\.  overlaying at least 5 years of
                                monitoring data from the event-
                                influenced monitor to show how monitored
                                concentrations compare at a given time
                                of year and/or coincide with the subject
                                event. This plot will display the non-
                                event variability over the appropriate
                                seasons or number of years.
                                For annual comparisons, use the
                                daily statistic (e.g., maximum daily 8-
                                hour average, or maximum 1-hour)
                                appropriate for the form of the standard
                                being considered for data exclusion.

[[Page 68243]]

 
5. Identify all ``high''        Label ``high'' data points as
 values in all plots.           being associated with concurred
                                exceptional events, suspected
                                exceptional events, other unusual
                                occurrences, or high pollution days due
                                to normal emissions (provide evidence to
                                support the identification when
                                possible).
                                Include comparisons omitting
                                known or suspected exceptional events
                                points, if applicable.
6. Identify historical trends   Describe how pollutant
 (optional if this trends       concentrations have decreased over the 5-
 analysis provides no           year window, if applicable.
 additional ``weight'').        Identify and discuss trends due
                                to emission reductions from planning
                                efforts and/or implementing emission
                                control strategies.
                                Identify and discuss trends or
                                other variability due to meteorology or
                                economics of an area.
                                If appropriate, create a plot to
                                show how a downward trend in pollutant
                                concentrations over the 5-year
                                historical data record obscures the
                                uniqueness of the event-related
                                concentration.
7. Identify diurnal or          Show how the diurnal or seasonal
 seasonal patterns.             pattern differs due to the event, if the
                                event causes a change from typical
                                diurnal/seasonal patterns.
------------------------------------------------------------------------
\a\ While the EPA recommends using 5 years of data in analyses to
  support the comparison to historical concentrations, we recognize that
  there may be exceptions to using 5 years of data such as when 5 years
  of data are not available for a given monitor or in case-by-case
  analyses such as those for prescribed fire on wildlands.
\b\ Section 8.4.2.e of appendix W (proposed revisions at 80 FR 45374,
  July 29, 2015) recommends using 5 years of adequately representative
  meteorology data from the National Weather Service (NWS) to ensure
  that worst-case meteorological conditions are represented. Similarly,
  for exceptional events purposes, the EPA believes that 5 years of
  ambient air data, whether seasonal or annual, better represent the
  range of ``normal'' air quality than do data from shorter periods.
\c\ ``Season'' can be pollutant and area specific. For example, the EPA
  defines ozone monitoring seasons in Table D-3 to Appendix D of Part
  58: ``Ozone Monitoring Season by State.'' These seasons include, but
  may be longer than, an area's typical photochemical ozone season. For
  exceptional events purposes, an area may want to include both the
  typical photochemical ozone season and the ``season'' in which the
  event happened (if they are different). Similarly, the ``season'' for
  PM may be in the winter (for areas influenced by wood smoke). The
  general concept behind ``seasonal'' analyses is to compare the season
  of anthropogenic pollutant generation to the season in which the event
  occurred.
\d\ Interim Exceptional Events Rule Frequently Asked Questions. U.S.
  EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf.
\e\ If an air agency compares the concentration on the claimed event day
  with days with similar meteorological conditions from other years, the
  agency should provide information regarding any changes in wind
  patterns or sources of emissions of the pollutant(s) of concern in the
  area, including increases or reductions in the emissions inventory, or
  other known source of emissions information, that could affect the
  concentration of the pollutant(s) of concern during the exceptional
  event. If an air agency compares the concentration on the claimed
  event day to days immediately preceding and following the event day,
  the air agency should discuss and compare the meteorology on those
  days.
\f\ The EPA does not intend to identify a particular historical
  percentile rank point in the seasonal or annual historical data that
  plays a critical role in the analysis or conclusion regarding the
  clear causal relationship.

    In summarizing the clear causal relationship section of its 
demonstration, the air agency should conclude with this type of 
statement: ``On [day/time] an [event type] occurred which generated 
pollutant X or its precursors resulting in elevated concentrations at 
[monitoring location(s)]. The monitored [pollutant] concentrations of 
[ZZ] were [describe the comparison to historical concentrations 
including the percentile rank over an annual (seasonal) basis]. 
Meteorological conditions were not consistent with historically high 
concentrations, etc.'' and ``In addition to the comparison to 
historical concentrations showing, analyses X, Y and Z support Agency 
A's position that the event affected air quality in such a way that 
there exists a clear causal relationship between the specific event and 
the monitored exceedance or violation and thus satisfies the clear 
causal relationship criterion.''
c. Comments and Responses
    As indicated previously, numerous commenters supported revising the 
regulatory language from ``event is associated with a measured 
concentration in excess of normal historical fluctuations, including 
background'' to ``a comparison to historical concentrations.'' 
Commenters supportive of the proposal agreed with the EPA's position 
that the phrase ``in excess of normal historical fluctuations, 
including background'' is vague and provides no additional value to 
historical concentration comparisons. Commenters representing the 
environmental community urged the EPA to maintain the ``in excess of 
normal historical fluctuations, including background'' language 
included in the 2007 rule, arguing that removing this language simply 
because it is unclear effectively weakens clean air protections. The 
EPA does not see this change to the rule text as weakening the CAA 
protections. An analysis of measured concentrations, which inherently 
includes background, and evidence that supports a comparison to 
historical concentrations is still required to support the 
demonstration of the clear causal criterion for the data exclusion 
request to qualify as an exceptional event. Thus, the ``comparison to 
historical concentrations'' showing is not less stringent than the ``in 
excess of normal historical fluctuations, including background'' 
showing because the technical analysis remains robust.
    Commenters generally supported requiring a historical 
concentrations showing as part of the clear causal relationship 
criterion. Several of these commenters suggested that the EPA include 
the proposed regulatory table identifying these historical 
concentrations analyses as guidance in the preamble rather than in 
regulatory text. Commenters offering this suggestion stated that 
because some of the identified analyses are required and others are 
optional, they are not universally applicable and are therefore best 
presented as guidance. As indicated in the final rule discussion, the 
EPA agrees with this approach and is removing the table from the final 
rule language and retaining it as guidance, with changes, in this 
preamble.
    A number of other commenters provided feedback regarding the 
details of the clear causal relationship criterion, particularly asking 
that we lessen or remove certain analyses. Although we address these 
comments here and/or in the Response to Comments document that 
accompanies this final rule, we note that CAA section 319(b)(3)(B) 
requires the EPA to promulgate regulations, which ``at a minimum'' 
provide that exceptional events must be ``demonstrated by reliable, 
accurate

[[Page 68244]]

data.'' The requirement for a ``demonstration'' necessarily imposes 
data-driven analyses.
    One commenter requested that the EPA eliminate what is now Table 2 
in this preamble from both rule and guidance because the EPA did not 
provide an acceptable range of percentiles or a process/methodology to 
determine whether the historical concentrations showing had been 
satisfied. In response to this commenter, the EPA notes that 
comparisons to historical concentrations help build a weight of 
evidence showing for the clear causal relationship criterion and add 
perspective to other analyses that air agencies may use in their clear 
causal showing. A demonstration may be less compelling if some evidence 
is inconsistent with the description of how the event caused the 
exceedance. For example, if an air agency describes an event as a 
regional dust storm or wildfire, then the EPA anticipates that most or 
all monitors within the same regional scale would be similarly affected 
by the event. That is, the EPA expects that the demonstration elements 
and factors (e.g., clear causal relationship, reasonable controls, 
meteorology, wind speeds) would also support the case for a regional 
event. Comparison of concentrations and conditions at other monitors 
could thus be very important for the demonstration of a clear causal 
relationship. Alternatively, eliminating plausible non-event causes may 
also support a causal relationship between the event and the elevated 
concentration. In response to the commenter's request to eliminate the 
showing based on a lack of information about an acceptable range of 
percentiles or a process/methodology to determine whether the criterion 
has been satisfied, the EPA points to language in this section of the 
preamble and rule text that provides such criteria by indicating that 
the analyses described in Table 2 are sufficient to satisfy the rule's 
requirement regarding the comparison to historical concentration data 
and that the submitting air agency does not need to prove any specific 
threshold or ``in excess of'' fact (see 40 CFR 50.14(c)(3)(iv)(C)).
    In response to other specific comments regarding the analyses in 
Table 2, two commenters noted that a comparison involving 5 years of 
data is an inappropriate time for the comparison to historical 
concentrations. As we note in footnote ``a'' to Table 2, we believe 
that 5 years of ambient air data, whether seasonal or annual, better 
represent the range of ``normal'' air quality than do data from shorter 
periods. We recognize, however, that some monitors do not have 5 years 
of data and/or may have periods of invalid data. The EPA recognizes 
that there may be exceptions to using 5 years of data. One commenter 
suggested that an appropriate comparison to historical concentrations 
for prescribed fires may involve ``visual observations and/or modeled 
impacts based on biomass consumption or other ecological parameters'' 
rather than comparisons using 5 years of monitoring data. The commenter 
explains that while we were not measuring air quality impacts 100 years 
ago, current fuel models may be used to estimate the area's fire 
history and, thus, historical concentrations influenced by smoke. The 
EPA agrees that the commenter's comparative analysis for prescribed 
fire on wildland could supplement the comparison to historical 
concentrations using monitoring data as part of the clear causal 
relationship showing. The EPA acknowledges that current fuel models 
could incorporate a timeframe for comparison that is longer than 5 
years and could incorporate contributions from both prescribed fire and 
wildfire. We further note that such modeling could support the clear 
causal relationship by showing that a given observed ambient 
concentration is similar to concentrations associated with past 
fires.\50\ Such modeling, however, is not a substitute for the 
comparison to historical concentrations using monitoring data. The 
title of CAA section 319(b) is ``Air quality monitoring data influenced 
by exceptional events.'' The language at section 319(b)(3)(B)(ii) 
requires that ``a clear causal relationship must exist between the 
measured exceedances of a national ambient air quality standard and the 
exceptional event to demonstrate that the exceptional event caused a 
specific air pollution concentration at a particular air quality 
monitoring location.'' Monitoring data are at the core of the rule. 
Generally, the form of most primary NAAQS (carbon monoxide and lead 
excluded) relies on 3 years of data. Regulatory determinations 
associated with these NAAQS employ data from regulatory monitors. 
Therefore, if an exceptional event influences a regulatory monitor that 
produces data, which will be used for a regulatory decision, 3 years of 
data will be available. Comparisons of monitored event-influenced data 
to modeled data, which are inherently predicted or estimated, do not 
carry the same weight under a weight of evidence approach. 
Additionally, because these monitoring data are readily available and 
accessible, these analyses are also relatively easy to produce.
---------------------------------------------------------------------------

    \50\ While this comparison contributes to plausibility, it does 
not necessarily mean that in the subject case, the exceedance or 
violation was not caused by some other source or factor. The 
comparison to actual historical concentrations on days not affected 
by fire can make this point.
---------------------------------------------------------------------------

    In the same table, commenters asked for clarification regarding 
``seasonal'' analyses. In response to this comment, the EPA has added a 
new footnote clarifying that ``season'' can be pollutant and area 
specific. For example, the EPA defines ozone monitoring ``seasons'' in 
40 CFR part 58, appendix D, Table D-3, ``Ozone Monitoring Season by 
State.'' These seasons include, but may be longer than, an area's 
typical photochemical ozone season. For exceptional events purposes, an 
area may want to include both the typical photochemical ozone season 
and the ``season'' in which the event happened (if they are different). 
Similarly, the ``season'' for PM may be in the winter (for areas 
influenced by wood smoke). The general concept behind ``seasonal'' 
analyses is to compare the season of anthropogenic pollutant generation 
to the season in which the event occurred.
    Continuing with additional requested clarifications regarding Table 
2, another commenter asked that we clarify the language ``time 
horizon.'' As a result of the modifications to this table, we no longer 
use this term. Another commenter asks that we revise the language in 
footnote ``e'' to Table 2, which reads ``. . . the agency should also 
verify and provide evidence that the area has not experienced 
significant changes in wind patterns, and that no significant sources 
in the area have had significant changes in their emissions of the 
pollutant of concern'' to ``. . . the agency should provide information 
regarding any changes in wind patterns or sources of emissions of the 
pollutant(s) of concern in the area, including increases or reductions 
in the emissions inventory that could affect the pollutant 
concentration during the exceptional event.'' The EPA agrees that the 
suggested language better conveys our intent to require details of any 
changes rather than evidence of lack of changes. We have incorporated 
the commenter's suggested language with the following revision into the 
footnote in Table 2 of this preamble: ``. . . the agency should provide 
information regarding any changes in wind patterns or sources of 
emissions of the pollutant(s) of concern in the area, including 
increases or reductions in the emissions inventory, or other known 
source of emissions information, that could affect the concentration of 
the

[[Page 68245]]

pollutant(s) of concern during the exceptional event.''
    In response to a commenter's request to clarify that the burden on 
the air agency does not change with moving the ``clear causal 
relationship'' element into the list of criteria that explicitly must 
be met for data to be excluded, we affirm that the burden does not 
increase. In our rule revisions, we have clarified that air agencies 
must address all three of the core statutory elements and implicit 
concepts of CAA section 319(b) (i.e., the event affected air quality in 
such a way that there exists a clear causal relationship between the 
specific event and the monitored exceedance or violation, the event was 
not reasonably controllable or preventable and the event was caused by 
human activity that is unlikely to recur at a particular location or 
was a natural event) in an exceptional events demonstration. Prior to 
these rule revisions, the elements ``affects air quality,'' ``not 
reasonably controllable or preventable,'' and ``human activity unlikely 
to recur at a particular location or a natural event'' were included in 
the definition of an exceptional event, while the requirement at 40 CFR 
50.14(c)(3)(iv) that a ``demonstration to justify data exclusion shall 
provide evidence'' included addressing the exceptional events 
definitional requirements, ``clear causal relationship,'' ``historical 
fluctuations'' and ``but for.'' Based on our experience implementing 
the rule, it is more clear to explicitly include all of the elements in 
a single place in the regulatory language.

F. Treatment of Certain Events Under the Exceptional Events Rule

    The preamble of the November 2015 proposal stated that air quality 
data affected by the following event types are among those that could 
meet the definition of an exceptional event and qualify for data 
exclusion provided all requirements of the rule are met: (1) Chemical 
spills and industrial accidents, (2) structural fires, (3) terrorist 
attacks, (4) volcanic and seismic activities, (5) natural disasters and 
associated cleanup, and (6) fireworks.\51\ We did not propose any 
changes to the definition of exceptional event to address these event 
types nor did we intend to imply that these are the only event types 
that could be considered for data exclusion under the Exceptional 
Events Rule. We simply repeated these event categories because they 
were specifically identified and discussed in the preamble to the 2007 
Exceptional Events Rule and we wanted to acknowledge our continued 
belief that the identified events could be considered ``exceptional.'' 
The AQS database contains a more detailed list of other events that may 
also be identified for consideration. The EPA will consider other types 
of events on a case-by-case basis.
---------------------------------------------------------------------------

    \51\ Of these noted event types, the regulatory language at 40 
CFR 50.14 only specifically addresses fireworks. We did not propose 
any revisions to the exclusion at 40 CFR 50.14(b)(2) for fireworks 
that are demonstrated to be significantly integral to traditional 
national, ethnic or other cultural events.
---------------------------------------------------------------------------

    Based on our implementation experience, our proposal, and commenter 
feedback, the following sections clarify details for other potential 
exceptional events categories: Transported pollution, wildland fires 
(including wildfires and prescribed fires), stratospheric ozone 
intrusions, and high wind dust events. We discuss each of these event 
categories in the following sections of this preamble.
    Several commenters provided feedback on the EPA's list of 
identified, but not discussed, potential exceptional events. One 
commenter noted that fireworks cannot be an exceptional event. This 
comment is beyond the scope of this rulemaking because we did not 
propose to change our consideration of fireworks under the Exceptional 
Events Rule and did not open this issue for comment (see additional 
explanation in footnote 51).
    Another commenter asked why the EPA added as an explanation for the 
``chemical spills and industrial accidents'' event type the following 
footnote: ``A malfunction at an industrial facility could be considered 
to be an exceptional event if it has not resulted in source 
noncompliance, which is statutorily excluded from consideration as an 
exceptional event, see CAA 319(b)(1)(b)(iii), and if it otherwise meets 
the requirements of the Exceptional Events Rule.'' While we are 
deleting the footnote in this final action, we note that we added the 
footnote to the proposal to clarify the position stated in previous EPA 
guidance \52\ that limited noncompliance of local sources can be 
expected from time to time as a result of process upsets or 
malfunctioning control equipment. These events are usually classified 
as ``upsets'' or ``malfunctions'' as defined by the applicable State or 
local agency regulations, or they may be considered a violation of 
applicable emission or opacity limits. If these events are caused by 
upsets or malfunctions, they should be so noted and reported to the 
appropriate control agency. If they constitute a violation, legal 
remedies are available to relevant parties. In summary, if a 
malfunction is caused by or results in source noncompliance, then the 
resulting emissions cannot be considered for exclusion under the 
Exceptional Events Rule in light of the plain language of CAA section 
319(b)(1)(B)(iii). However, if the malfunction was not caused by nor 
did it result from source noncompliance (e.g., it resulted from an act 
of nature, such as a lightning strike) AND if the resulting emissions 
caused a NAAQS exceedance or violation AND if it otherwise meets the 
requirements of the Exceptional Events Rule, then the emissions from 
the malfunction could be considered for exclusion under the provisions 
of 40 CFR 50.14.
---------------------------------------------------------------------------

    \52\ Guideline on the Identification and Use of Air Quality Data 
Affected by Exceptional Events (the Exceptional Events Policy), U.S. 
EPA, OAQPS, EPA-450/4-86-007, July 1986.
---------------------------------------------------------------------------

1. Transported Pollution
    We did not propose any new guidance or specific regulatory language 
addressing the transported pollution that could be considered for 
exclusion under the Exceptional Events Rule. Rather, the proposal 
discussed the provisions within the CAA that provide regulatory relief 
for, or otherwise regulate, transported pollution and identified the 
circumstances under which air agencies can use these provisions. While 
our focus in this action is the Exceptional Events Rule (CAA section 
319(b)), we also discuss transport under other CAA sections for context 
(i.e., 179B (International Transport), 182(h) (Rural Transport Areas), 
110(a)(2)(D)(i)(I) (Interstate Transport) and 126 (Interstate 
Transport)). We are finalizing the language from our proposal with 
additional clarifications resulting from commenter feedback as guidance 
in this preamble.
a. Transported Pollution Within the Exceptional Events Rule
    To be considered for data exclusion, transported pollution must 
meet all of the Exceptional Events Rule criteria. Specifically, 
transported pollution must be event-related AND be either natural or 
caused by a human activity unlikely to recur at a particular location 
(see 40 CFR 50.14(c)(3)(iv)(E)). Human activities unlikely to recur at 
a particular location could include some of the event types mentioned 
in the introduction to this section of this preamble, such as chemical 
spills, industrial accidents, or terrorist activities. Routine 
emissions generated by and transported from anthropogenic sources are 
not

[[Page 68246]]

exceptional events.\53\ Additionally, transported emissions from 
natural sources must be event-related (e.g., wildfires, stratospheric 
ozone intrusion, Saharan dust) versus ongoing on a daily basis to 
qualify for data exclusion under the Exceptional Events Rule. Natural 
emissions that occur every day and contribute to background levels, 
such as routine biogenic emissions of ozone precursors from vegetation 
and soils, do not meet the definition of an exceptional event because 
they are not deviations from normal or expected conditions. Despite 
being natural, they are not ``events.''
---------------------------------------------------------------------------

    \53\ An example of routine emissions generated by and 
transported from anthropogenic sources might include emissions of 
ozone precursors or directly emitted particulate matter (or PM 
precursors) from one state or foreign country's power plants 
transported into another state or the U.S. The CAA provides other 
mechanisms like 179B (for international transport) or 110(a)(2)(D) 
and/or 126 (for interstate transport) to address these types of 
emissions.
---------------------------------------------------------------------------

    In most cases, of the previously identified CAA sections, the 
mechanisms in the Exceptional Events Rule provide the most regulatory 
flexibility in that air agencies can use these provisions to seek 
relief from designation as a nonattainment area.\54\ Because the 
Exceptional Events Rule may be used during the initial area 
designations process and may make a difference in an attainment versus 
a nonattainment decision, the EPA believes that the Exceptional Events 
Rule will often be the most appropriate mechanism to use when 
addressing transported emissions from out-of-state natural events or 
events due to human activity that is unlikely to recur at a particular 
location.
---------------------------------------------------------------------------

    \54\ The CAA section 179B (International Transport) and CAA 
section 182(h) (Rural Transport Areas) apply following, or 
concurrent with, the initial area designations process.
---------------------------------------------------------------------------

    If an air agency determines that the Exceptional Events Rule is the 
most suitable approach to address contributions from event-related 
transported emissions, then the air agency must consider the source(s) 
of emissions contributing to the exceedance or violation to determine 
how to address individual Exceptional Events Rule criteria, 
specifically the not reasonably controllable or preventable criterion 
and the human activity unlikely to recur or a natural event criterion.
    Under the CAA, the EPA generally considers a state (not including 
areas of Indian country) to be a single responsible actor. Accordingly, 
neither the EPA nor the 2007 Exceptional Events Rule provides special 
considerations for intrastate scenarios when an event in one part of a 
state, such as a county or air district, affects air quality in another 
part of the same state, assuming that the event occurs on land subject 
to state authority (versus tribal government authority). For cases 
involving intrastate transport, the state or local air agency should 
evaluate whether contributing event emissions from those parts of the 
state located between the subject upwind source and the affected 
monitor were not reasonably controllable or preventable. Section IV.E.2 
of this preamble discusses the not reasonably controllable or 
preventable criterion in more detail. Because there may be special 
considerations regarding air agencies' authority to regulate activity 
on federally-owned and managed lands (e.g., national parks within the 
state), states and tribes should discuss with the appropriate FLM or 
other federal agency and their EPA Regional office early in the 
development of an exceptional events demonstration if they believe that 
sources on federally-owned and managed land contributed event-related 
emissions to a degree that raises issues of reasonable control.
    Interstate and international transport events are different than 
intrastate events. As noted in Section IV.E.2 of this preamble and in 
the final regulatory language at 40 CFR 50.14(b)(8)(vii), the EPA 
maintains that it is not reasonable to expect the downwind air agency 
(i.e., the state or tribe submitting the demonstration) to have 
required or persuaded the upwind foreign country, state or tribe to 
have implemented controls on sources sufficient to limit event-related 
emissions in the downwind state. As with any demonstration, the 
submitting (downwind) state should identify all natural and 
anthropogenic contributing sources of emissions (both local/in-state 
and out-of-state) to show the causal connection between an event and 
the monitored exceedance or violation. Although the downwind state must 
still assess potential contribution from in-state sources as discussed 
in Section IV.E.2 of this preamble, we are finalizing regulatory 
language at 40 CFR 50.14(b)(8)(vii) that the event-related emissions 
that were transported in the downwind state are ``not reasonably 
controllable or preventable'' for purposes of data exclusion. If the 
event-related emissions are international in origin and affect monitors 
in multiple states or regions, the EPA may assist affected agencies in 
identifying approaches for evaluating the potential impacts of 
international transport and determining the most appropriate 
information and analytical methods for each area's unique situation.
    As with all exceptional events demonstrations, the EPA will 
evaluate the information on a case-by-case basis based on the facts of 
a particular exceptional event including any information and arguments 
presented in public comments received by the state in its public 
comment process or by the EPA in a notice-and-comment regulatory action 
that depends on the data exclusion.
b. Other Transport Mechanisms Within the CAA
    In the following paragraphs, we discuss other provisions within the 
CAA that provide regulatory relief for, or otherwise regulate, 
transported pollution and identify the circumstances under which air 
agencies can use these provisions.
     CAA section 179B, International Transport--CAA section 
179B allows states to consider in their attainment demonstrations 
whether a nonattainment area might have met the NAAQS by the attainment 
date ``but for'' emissions contributing to the area originating outside 
the U.S. This provision addresses sources of emissions originating 
outside of the U.S. and provides qualifying nonattainment areas some 
regulatory relief from otherwise-applicable additional planning and 
control requirements should the area fail to reach attainment by its 
deadline. It does not provide a pathway for regulatory relief from 
designation as a nonattainment area; rather, CAA section 179B applies 
following the initial area designations process.
     CAA section 182(h), Rural Transport Areas--CAA section 
182(h) authorizes the EPA Administrator to determine that certain ozone 
nonattainment areas can be treated as rural transport areas, which 
provides relief from more stringent requirements associated with higher 
nonattainment area classifications (i.e., ozone classifications above 
Marginal). Under CAA section 182(h), a nonattainment area may qualify 
as a Rural Transport Area if it does not contain emissions sources that 
make a significant contribution to monitored ozone concentrations in 
the area or in other areas, and if the area does not include and is not 
adjacent to a Metropolitan Statistical Area. Generally, an area 
qualifies as a Rural Transport Area because it does not contribute to 
its own or another area's nonattainment problem; rather, ozone 
exceedances are due to transported emissions, which could be 
international, interstate or

[[Page 68247]]

intrastate in origin. The Rural Transport Area determination can be 
made during or after the initial area designations and classifications 
process.
     CAA section 110(a)(2)(D)(i)(I), Interstate Transport--CAA 
section 110(a)(2)(D)(i)(I) requires states to develop and implement 
SIPs to address the interstate transport of emissions from sources 
within their jurisdiction. Specifically, this provision requires each 
state's SIP to prohibit ``any source or other type of emissions 
activity within the State from emitting any air pollutant in amounts 
which will significantly contribute to nonattainment'' of any NAAQS in 
another state, or which will ``interfere with maintenance'' of any 
NAAQS in another state. When the EPA promulgates or revises a NAAQS, 
each state is required to submit a SIP addressing this interstate 
transport provision as to that NAAQS within 3 years. The EPA interprets 
this interstate transport provision to address anthropogenic sources of 
emissions from other states, and not to address natural sources of 
emissions.
     CAA section 126, Interstate Transport--CAA section 126 
provides states \55\ and political subdivisions with a mechanism to 
petition the Administrator for a finding that ``any major source or 
group of stationary sources emits or would emit any air pollution in 
violation of the prohibition of CAA 110(a)(2)(D)(i).'' \56\ Where the 
EPA grants such a petition, an existing source may operate beyond a 3-
month period only if the EPA establishes emissions limitations and 
compliance schedules to bring about compliance with CAA section 
110(a)(2)(D)(i) as expeditiously as practicable, but no later than 3 
years after such finding. Similar to our interpretation for CAA section 
110(a)(2)(D)(i), the EPA interprets the reference to ``major source or 
group of stationary sources'' in CAA section 126 to refer to 
anthropogenic sources of emissions from other states. The EPA's 
interpretation is that this provision is not intended to address 
natural sources of emissions.
---------------------------------------------------------------------------

    \55\ Tribes with treatment as a state authority (under the TAR) 
for CAA section 126 could also use this CAA provision.
    \56\ The text of CAA section 126 codified in the United States 
Code cross references CAA section 110(a)(2)(D)(ii) instead of 
section 110(a)(2)(D)(i). The courts have confirmed that this is a 
scrivener's error and the correct cross reference is to section 
110(a)(2)(D)(i), See Appalachian Power Co. v. EPA, 249 F.3d 1032, 
1040-44 (D.C. Cir. 2001).
---------------------------------------------------------------------------

c. Comments and Responses
    Several commenters asked that the EPA clarify how the provisions in 
the Exceptional Events Rule apply to background ozone concentrations 
and longer duration emissions sources such as biogenics, lightning and 
international transport. We provide some clarification in this section 
of the preamble, but also refer to the discussion in Section IV.B.3, 
which discusses rule applicability to background ozone.
    Commenters also asked for clarification regarding assessing 
``event-related emissions that originate outside of the boundaries of 
the state within which the concentration at issue was monitored'' for 
purposes of the not reasonably controllable or preventable criterion. 
As discussed in Section IV.E.2 of this preamble, the state or local air 
agency should evaluate whether contributing event emissions from those 
parts of the state located between the subject upwind source and the 
affected monitor were not reasonably controllable or preventable.
    Another commenter suggests that where meteorological conditions 
play a pronounced role in transporting extra-jurisdictional emissions, 
those emissions would not prevent classification as a natural event. 
The commenter notes that because recurring natural events may qualify 
as exceptional events under the Exceptional Events Rule, international 
event-related emissions, because they are transported by recurring 
natural meteorological mechanisms, could also be exceptional events 
even if the source of emissions in another country is anthropogenic. 
The commenter continued that if the EPA does not consider all 
international emissions to be ``natural events,'' then the data 
associated with international emissions could still qualify for 
exclusion under the Exceptional Events Rule in those instances in which 
the magnitude of transported emissions or the resulting concentrations 
are ``unusual.'' As we have noted, over the course of implementing the 
Exceptional Events Rule, we have come to realize that an event needs to 
be defined by the source of the emissions. If the underlying source is 
a natural event (e.g., wildfire) and the emissions influence a 
regulatory monitor, then it can be considered for exclusion under the 
Exceptional Events Rule. If the underlying source is anthropogenic then 
it can only be considered under the Exceptional Events Rule if the 
emissions from the original source is unlikely to recur at a particular 
location. The meteorological processes that result in pollutant 
transport are ongoing and thus not an event, even though their 
influence on ambient concentrations at a particular time and location 
may be observed only occasionally and thus seem ``event-like.''
2. Wildland Fires
    The proposal noted that fires on wildland can play an important 
ecological role across the nation, benefiting those plant and animal 
species that depend upon natural fires for propagation, habitat 
restoration and reproduction. The proposed rule also noted the large 
contribution that wildfire can make to air pollution (including 
periodic high PM2.5 and PM10, and VOC and 
NOX, which are precursors to PM2.5, 
PM10 and ozone) and wildfire's potential threat to public 
safety. The proposal further recognized that these adverse effects can 
be mitigated through management of wildland vegetation, including 
planned prescribed fires and letting some wildfires proceed naturally 
(typically those with lower fire intensity and severity).
    The proposal also recognized, consistent with the EPA's past 
practice, that both wildfires and prescribed fires, under certain 
circumstances, can be considered exceptional events. The preamble to 
the 2007 Exceptional Events Rule, however, used unclear or undefined 
fire-related terminology, making the preparation of some fire-related 
demonstrations particularly challenging. Recognizing some of these 
unique challenges associated with fires on wildland, we proposed a 
number of fire-related revisions to the Exceptional Events Rule for 
wildfires and prescribed fires that occur on wildland.\57\
---------------------------------------------------------------------------

    \57\ While we proposed, and are finalizing, provisions only for 
fires that occur predominantly on wildland, we did not intend to 
restrict wildfires on other types of land from receiving similar 
treatment as wildfires on wildland. In addressing the not reasonably 
controllable or preventable criterion in a demonstration for a 
wildfire that is not on wildland, air agencies should state that 
available resources were reasonably aimed at suppression and 
avoidance of loss of life and property and that no further efforts 
to control air emissions from the fire would have been reasonable.
---------------------------------------------------------------------------

    These revisions included proposed regulatory language for certain 
fire-related definitions, clarification and associated regulatory text 
related to using SMP and BSMP to satisfy exceptional events 
demonstration and program implementation elements, and new Exceptional 
Events Rule provisions to specifically address prescribed fire 
exceptional events issues. We provide additional detail in the separate 
sections on wildfires (Section IV.F.2.a of this preamble) and 
prescribed fire (Section IV.F.2.b of this preamble).
    As we implement the changes we are promulgating in this regulatory 
action,

[[Page 68248]]

we remain committed to working with federal, state, local, tribal and 
private land owners/land managers and state, tribal and local air 
quality agencies to effectively manage prescribed fire use to reduce 
the impact of catastrophic wildfire-related emissions on ozone, 
PM10 and PM2.5.
a. Wildfires
    Summary of Proposal. The EPA proposed the following guidance, 
clarifications and rule revisions to assist air agencies preparing 
exceptional events demonstrations for wildfires.
    (i) Definition of wildland and wildfire. The EPA proposed to codify 
in regulatory language the definition of ``wildland'' by using the 
October 2014 National Wildfire Coordinating Group (NWCG) Glossary of 
Wildland Fire Terminology \58\ definition that a wildland is ``an area 
in which human activity and development is essentially non-existent, 
except for roads, railroads, power lines, and similar transportation 
facilities. Structures, if any, are widely scattered.'' As noted in the 
proposal, wildland can include forestland,\59\ shrubland,\60\ grassland 
\61\ and wetlands.\62\ This proposed definition of wildland includes 
lands that are predominantly wildland, such as land in the wildland-
urban interface.63 64
---------------------------------------------------------------------------

    \58\ National Wildfire Coordinating Group. Glossary of Wildland 
Fire Terminology, PMS 205. October 2014. We are retaining our 
proposed definition of the wildland although the NWCG has revised 
its October 2014 glossary. The October 2015 glossary, which became 
available after the November 2015 exceptional events proposal, is 
available at http://www.nwcg.gov/glossary-of-wildland-fire-terminology.
    \59\ Forestland is land on which the vegetation is dominated by 
trees or, if trees are lacking, the land shows historic evidence of 
former forest and has not been converted to other uses. Definition 
available at https://globalrangelands.org/glossary.
    \60\ Shrubland is land on which the vegetation is dominated by 
shrubs. Definition available at https://globalrangelands.org/glossary/.
    \61\ Grassland is land on which the vegetation is dominated by 
grasses, grass like plants, and/or forbs. This definition has 
changed since the EPA proposed the definition of grassland. We are 
retaining the proposed definition. The current Global Rangelands 
definition is available at https://globalrangelands.org/glossary.
    \62\ Wetlands, as defined in 40 CFR 230.3(t), means those areas 
that are inundated or saturated by surface or ground water at a 
frequency and duration sufficient to support, and that under normal 
circumstances do support, a prevalence of vegetation typically 
adapted for life in saturated soil conditions. Wetlands generally 
include swamps, marshes, bogs and similar areas.
    \63\ The wildland-urban interface is the line, area or zone 
where structures and other human development meet or intermingle 
with undeveloped wildland or vegetative fuels. The term describes an 
area within or adjacent to private and public property where 
mitigation actions can prevent damage or loss from wildfire. See, 
Glossary of Wildland Fire Terminology, PMS 205. October 2014. We are 
retaining our proposed definition of the wildland and our proposed 
description of the wildland-urban interface although the NWCG has 
revised its October 2014 glossary. The October 2015 glossary, which 
became available after the November 2015 exceptional events 
proposal, is available at http://www.nwcg.gov/glossary-of-wildland-fire-terminology.
    \64\ We would generally treat a large prescribed fire in a 
wildland-urban interface area as a prescribed fire on wildland, 
subject to the prescribed fire provisions described in this 
document. We do not expect a small prescribed fire in an interface 
area (e.g., a prescribed fire ignited by a single landowner on his/
her personal property) to generate emissions that would raise 
exceptional events issues.
---------------------------------------------------------------------------

    The proposed definition for wildland considered the types of human 
intervention that could affect whether a land is considered a 
``wildland'' and stated that the presence of fences to limit the 
movement of grazing animals, or of infrastructure to provide water to 
grazing animals, would not prevent a land area from being wildland. The 
proposal further clarified that cultivated cropland (i.e., a field that 
is plowed or disked or from which crops are removed on an annual or 
more frequent basis) is not wildland and land areas on which nursery 
stock is grown to marketable size (e.g., Christmas tree farms) are 
generally not wildland unless they are ``wild'' in terms of a having 
only limited human entrance and intervention for management or removal 
purposes thereby resulting in a complex ecosystem. The proposed rule 
indicated that managed timberlands \65\ could be considered wildland if 
they have a complex ecosystem affected by only limited human entrance 
and intervention. We invited comment on incorporating these examples of 
land use types into the regulatory definition of wildland.
---------------------------------------------------------------------------

    \65\ Timberland is land on which the natural potential 
vegetation is forest. It may be managed primarily for the production 
and harvest of timber. Definition available at https://globalrangelands.org/glossary/.
---------------------------------------------------------------------------

    We also proposed in regulatory text, the following definition of 
``wildfire,'' a ``wildfire is any fire started by an unplanned ignition 
caused by lightning; volcanoes; other acts of nature; unauthorized 
activity; or accidental, human-caused actions; or a prescribed fire 
that has been declared to be a wildfire. A wildfire that predominantly 
occurs on wildland is a natural event.''
    (ii) Not reasonably controllable or preventable. As proposed and as 
with other natural events, the ``not reasonably controllable or 
preventable'' criterion applies to wildfires. The proposed rule 
articulated that because wildfires on wildland are unplanned, fire 
management agencies generally have either no advanced notice or limited 
and uncertain notice of wildfire ignition and location. In addition, 
many areas of wildland are very remote and rugged, and thus not easily 
reached and traversed. These factors generally limit preparation time 
and on-site resources to prevent or control the initiation, duration or 
extent of a wildfire. Also, by their nature, catastrophic wildfires 
typically present some risk of property damage, ecosystem damage and/or 
loss of life (of the public or firefighters), which is a strong 
motivation for appropriate suppression and control efforts. The EPA 
believes that land managers and other fire management entities have the 
motivation and the best information for taking action to reasonably 
prevent and limit the extent of wildfires on wildland, thus also 
controlling the resulting emissions. Therefore, the EPA believes that 
it is not useful to require air agencies to include in their individual 
wildfire exceptional events demonstrations descriptions of prevention 
and control efforts employed by burn managers/wildfire responders to 
support a position that such efforts were reasonable. The EPA therefore 
proposed in regulatory language a rebuttable presumption that every 
wildfire on wildland satisfies the ``not reasonably controllable or 
preventable'' criterion unless evidence in the record demonstrates 
otherwise and that satisfying this criterion for wildfires on wildland 
would involve referencing the appropriate regulatory citation in the 
demonstration. The proposal further indicated that in situations in 
which a fire manager could have suppressed or contained a wildfire but 
allowed the fire to continue burning through an area with a current, 
in-place land management plan calling for restoration through natural 
fire or mimicking the natural role of fire, that we would expect the 
fire manager to employ appropriate BSMP as described in Section 
IV.F.2.b of this preamble when possible.
    (iii) Coordinated communications. As stated in the proposal, 
regardless of the considerations for wildfires, the EPA urges land 
managers and air agencies to coordinate, as appropriate, in developing 
plans and appropriate public communications regarding public safety and 
reducing exposure in instances where wildfires are potential 
exceptional events and contribute to exceedances of the NAAQS. 
Coordinated efforts can help air agencies satisfy the Exceptional 
Events Rule obligation at 40 CFR 51.930 that air agencies must provide 
public notice and public education and must provide for implementation 
of reasonable measures to protect public health when an event

[[Page 68249]]

occurs.\66\ Also, when wildfire impacts are frequent and significant in 
a particular area, land managers, land owners, air agencies and 
communities may be able to lessen the impacts of wildfires by working 
collaboratively to take steps to minimize fuel loading in areas 
vulnerable to fire.\67\ Fuel load minimization steps can consist of 
both prescribed fire and mechanical treatments, such as using 
mechanical equipment to reduce accumulated understory.
---------------------------------------------------------------------------

    \66\ 72 FR 13575 (March 22, 2007).
    \67\ One example of this collaborative approach is the evolving 
interagency Wildland Fire Air Quality Response Program, which has 
developed resources to help address and predict smoke impacts from 
wildfires to reduce public exposure to wildfire smoke. Additional 
information is available in the docket for this action (see EPA-HQ-
OAR-2013-0572, Wildland Fire Air Quality Response Program).
---------------------------------------------------------------------------

    Final Rule. We are finalizing, as proposed, for the reasons 
discussed in our proposal and herein, and as supported by several 
commenters, the following definition of wildland: ``Wildland means an 
area in which human activity and development are essentially non-
existent, except for roads, railroads, power lines, and similar 
transportation facilities. Structures, if any, are widely scattered.'' 
In finalizing this definition, we are retaining, as guidance, the 
proposed examples of land use types and types of human intervention 
that are considered wildland (or not) in the preamble of this final 
rule. Many commenters supported this approach while others preferred 
incorporating land use types and specifically allowable types of 
structures (e.g., fences to limit the movement of grazing animals) into 
the regulatory definition. We have determined that because the 
presented land use types and clarifications regarding allowable 
structures and human intervention are only examples, and not an all-
inclusive list of all lands that could be considered ``wildland,'' 
guidance is more appropriate for these details than rule. We also 
clarify, at the request of one commenter, that we would generally 
consider lands like state and national parks and wildlife refuges 
(provided they are primarily wild and natural and provided hunting, if 
allowed, is limited) to be wildland. We are not including the 
modifications suggested by several commenters that would change the 
phrase ``development is essentially non-existent'' to ``development is 
limited in scope.'' First, the language ``limited in scope'' in the 
phrase ``development is limited in scope'' is subjective and would 
create additional uncertainty and ambiguity, which is not intended in 
this action. Additionally, when considering the term ``wildland,'' the 
word ``wild,'' by definition, implies a natural, uncultivated or 
uninhabited region. Conversely, ``development'' implies growth, 
construction and, potentially, groupings of buildings. Modifying the 
definition as proposed by the commenters could be interpreted to mean 
that parcels of land with some empty space between groupings of 
buildings (e.g., cultivated and inhabited areas) could be wildland. 
This is not our intent. Another commenter suggested that because 
``wild'' implies minimal ongoing ecological impacts from human activity 
and not an infrequent presence of humans and their structures that we 
change the regulatory definition to ``wildland means an area where the 
impact on the ecosystem from human development and agriculture is 
essentially nonexistent, except for widely separated roads, railroads 
and power lines.'' While we agree with the commenter's perspective 
regarding very limited human impact on the ecosystem, we believe that 
the definition we are promulgating conveys similar intent and will have 
the same practical effect.
    Also related to the definition of wildland, several states asked 
that we specifically address prescribed fires on cultivated cropland 
and other agricultural lands. As we proposed and as we are finalizing 
in this rule, the fire-related provisions apply specifically to fires 
that occur predominantly on wildland. Air agencies contemplating 
preparing fire-related exceptional events demonstrations for fires not 
on wildland, should consult with their reviewing EPA Regional office. 
The EPA will review submitted demonstrations on a case-by-case basis 
considering the specific merits of each event.
    Comments and Responses. After consideration of the public comments, 
we are finalizing a modified version of our proposed definition of 
wildfire: ``Wildfire is any fire started by an unplanned ignition 
caused by lightning; volcanoes; other acts of nature; unauthorized 
activity; or accidental, human-caused actions, or a prescribed fire 
that has developed into a wildfire. A wildfire that predominantly 
occurs on wildland is a natural event.'' The final revised definition 
includes ``a prescribed fire that has developed into a wildfire'' 
instead of the proposed language ``a prescribed fire that has been 
declared to be a wildfire.''
    Some commenters supported the original proposed definition, but 
others recommended deleting the phrase ``a prescribed fire that has 
been declared to be a wildfire'' from the definition because they 
disagree with allowing burners to ``declare'' a prescribed fire to be a 
wildfire. Commenters noted that burn managers might make such a 
declaration for reasons other than their unanticipated inability to 
control the deliberately ignited fire. We note that the proposed 
definition of wildfire did not require that the objective be to put out 
such a fire for it to meet the definition. When an unplanned fire on 
wildland does not threaten catastrophic consequences (e.g., 
consequences to public health, safety or property) and when the 
wildfire is burning on land that would otherwise be identified for 
ecosystem management (e.g., fuels management through prescribed 
burning), it may be appropriate to allow the fire to continue burning 
under managed conditions. This fire management scenario was not our 
intended focus in proposing the ``declaration'' language. Rather, as 
stated in the proposal, ``a prescribed fire that has been declared to 
be a wildfire'' refers to specific instances in which the conditions of 
a particular prescribed fire have developed in an unplanned way such 
that its management challenges are essentially the same as if it were a 
wildfire. The federal, state and tribal wildland fire management 
community uses the terminology ``prescribed fire declared wildfire'' to 
describe the infrequent and significant instances when meteorological 
and/or other environmental conditions, resource availability, or other 
unforeseen circumstances lead the burn manager to make such a 
declaration to protect the health and safety of fire management staff 
and the public. For example, if the prescribed fire has escaped secure 
containment lines and requires suppression along all or part of its 
boundary or if it no longer meets the resource objectives (e.g., smoke 
impact, flame height). It was not our intention to allow categorical 
re-definition of some types of prescribed fire to be wildfires. Our 
intent was to clearly identify those fires that could be considered 
wildfires and those that would be considered prescribed fires. In doing 
this, we also identified the applicable demonstration requirements 
under the Exceptional Events Rule. That is, wildfires and prescribed 
fires on wildland have different requirements for exceptional events 
demonstrations based on the practicality of prevention/control (i.e., 
the approach to addressing the not reasonably controllable or 
preventable criterion) and on the natural versus anthropogenic origin 
of the fire (i.e., the human activity that is unlikely

[[Page 68250]]

to recur or a natural event). When considering prevention/control for 
purposes of exceptional event categorization, a prescribed fire 
effectively becomes like a wildfire when, for example, the prescribed 
fire escapes secure containment due to unforeseen circumstances (e.g., 
a sudden shift in prevailing winds). In these instances, the burn 
manager would no longer control the path of the fire. Thus, the fact 
that the initial fire was deliberately ignited should not result in the 
entire burn (e.g., the duration and extent of the burn) needing to 
follow the rule requirements for prescribed fires on wildland. Given 
these potential circumstances, we proposed to rely on the burn 
manager's (or another individual familiar with the circumstances of the 
fire) declaration that the prescribed fire has become a wildfire. 
Because many commenters expressed concern with the ``declaration'' 
language, we have changed the phrase to ``a prescribed fire that has 
developed into a wildfire,'' by which we mean that has developed in an 
unplanned way such that its management challenges are essentially the 
same as if it had been initiated by an unplanned ignition.'' We believe 
that this revised language conveys our original intent. In showing that 
a prescribed fire ``hasdeveloped into a wildfire,'' air agencies should 
include the following documentation when addressing the ``human 
activity unlikely to recur at a particular location or a natural 
event'' criterion in their demonstration: (1) News reports or 
notifications to the public characterizing the nature of the fire and 
(2) the demonstration submitter's explanation of the origin and 
evolution of the fire.
    All commenters providing feedback on the EPA's proposal to grant a 
rebuttable presumption that every wildfire on wildland satisfies the 
``not reasonably controllable or preventable'' criterion unless 
evidence in the record demonstrates otherwise agreed with the EPA's 
proposed regulatory language. We have therefore finalized the provision 
at 40 CFR 50.14(b)(4) that the ``Administrator shall exclude data from 
use in determinations of exceedances and violations where a State 
demonstrates to the Administrator's satisfaction that emissions from 
wildfires caused a specific air pollution concentration in excess of 
one or more national ambient air quality standard at a particular air 
quality monitoring location and otherwise satisfies the requirements of 
this section. Provided the Administrator determines that there is no 
compelling evidence to the contrary in the record, the Administrator 
will determine every wildfire occurring predominantly on wildland to 
have met the requirements . . . regarding the not reasonably 
controllable or preventable criterion.''
b. Prescribed Fires
    The proposal stated, and this final rule repeats, the EPA's 
recognition that use of prescribed fire on wildland can influence the 
occurrence, severity, behavior and effects of catastrophic wildfires 
and benefit the plant and animal species that depend upon natural fires 
for propagation, habitat restoration and reproduction, as well as a 
myriad of ecosystem functions (e.g., carbon sequestration, maintenance 
of water supply systems and endangered species habitat maintenance). 
The EPA formally recognized in the 1998 Interim Air Quality Policy on 
Wildland and Prescribed Fires \68\ that federal, state, local, tribal 
and private land owners/land managers use prescribed fire on wildland 
to achieve some of these resource benefits, to correct the undesirable 
conditions created by past wildfire suppression management strategies 
and to reduce the risk of catastrophic wildfires to the public.
---------------------------------------------------------------------------

    \68\ Interim Air Quality Policy on Wildland and Prescribed 
Fires. U.S. EPA. April 23, 1998. Available at http://www.epa.gov/ttn/oarpg/t1/memoranda/firefnl.pdf.
---------------------------------------------------------------------------

    Summary of Proposal. The EPA proposed the following guidance, 
clarifications and rule revisions to assist air agencies preparing 
exceptional events demonstrations for prescribed fire on wildland.
    (i) Definition of a prescribed fire. We proposed to adopt in rule 
language a modified version of the then-current NWCG-recommended 
definition of a prescribed fire: ``[A]ny fire intentionally ignited by 
management actions in accordance with applicable laws, policies and 
regulations to meet specific land or resource management objectives.'' 
In this definition, ``management'' refers to the owner or manager of 
the land area to which prescribed fire is applied. The proposal 
replaced the original NWCG language ``specific objectives'' with 
``specific land or resource management objectives.''
    (ii) Events caused by human activity. We proposed regulatory 
language stating that prescribed fires are events caused by human 
activity and, therefore, to be considered an exceptional event, every 
prescribed fire demonstration must address the ``human activity 
unlikely to recur at a particular location'' criterion.
    (iii) Unlikely to recur at a particular location. The proposed rule 
set forth generally applicable guidelines to clarify both ``unlikely to 
recur'' and ``at a particular location.'' In this action, we discussed 
these guidelines for most events caused by human activity in Section 
IV.E.1 of this preamble, but we also clarified that specific approaches 
apply for prescribed fires on wildland, which we discuss here.
    Our proposed rule indicated that when characterizing the ``human 
activity that is unlikely to recur at a particular location'' 
criterion, a demonstration for a prescribed fire on wildland could use 
one of two benchmarks to describe the expected frequency of prescribed 
fires on wildland: \69\ (1) The natural fire return interval as 
articulated in the 2007 preamble or (2) the prescribed fire frequency 
needed to establish, restore and/or maintain a sustainable and 
resilient wildland ecosystem. The proposal also stated that multi-year 
land or resource management plans prepared by the land management 
agency or any private property owner generally include documentation of 
these established fire intervals. Considering these two concepts, we 
proposed rule text that considered a demonstration's referencing of a 
multi-year land or resource management plan \70\ (and including either 
a copy or an internet link to the plan) with a stated objective to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem and/or to preserve endangered or threatened species that also 
identifies the subject area as a candidate for prescribed fire to be 
dispositive evidence that a particular fire conducted in accordance 
with such a plan satisfies the ``unlikely to recur at a particular 
location'' criterion. The proposal noted that referencing a fire 
management plan for tribal or private lands that has been reviewed and 
certified by the appropriate fire and/or resource management 
professionals and agreed to and followed by the land owner/manager can 
also satisfy the ``unlikely to recur at a particular location'' 
criterion.
---------------------------------------------------------------------------

    \69\ The EPA will assess benchmarks for the expected frequency 
of prescribed fires not on wildland on a case-by-case basis.
    \70\ These plans could also include fire management plans, 
prescribed fire on wildland management plans, landscape management 
plans or equivalent public planning documents.
---------------------------------------------------------------------------

    (iv) Not reasonably controllable or preventable. The proposed rule 
stated that, consistent with current practice and 2007 preamble and 
rule language, the EPA considers it appropriate for air agencies to 
rely on an in-place and implemented state-certified SMP or on a burn 
manager's use of BSMP that

[[Page 68251]]

minimize emissions and control impacts, in lieu of a state-certified 
SMP, to satisfy the controllability prong of the ``not reasonably 
controllable or preventable'' criterion. We also proposed that, 
provided there is no compelling evidence to the contrary in the record, 
an air agency could rely upon, comply with and reference a multi-year 
land or resource management plan for a wildland area with a stated 
objective to establish, restore and/or maintain a sustainable and 
resilient wildland ecosystem and/or to preserve endangered or 
threatened species through a program of prescribed fire to satisfy the 
preventability prong of the ``not reasonably controllable or 
preventable'' criterion. We provide further context from our proposed 
action in the paragraphs that follow.
    Because the 2007 Exceptional Events Rule used the terms SMP and 
BSMP without defining them, our proposed rule provided clarity. With 
respect to a SMP, the proposal noted that at a minimum, a state-
certified SMP would include provisions for (i) authorization to burn, 
(ii) minimizing air pollutant emissions, (iii) smoke management 
components of burn plans, (iv) public education and awareness, (v) 
surveillance and enforcement, and (vi) program evaluation. We also 
indicated that ``certification'' requires that a responsible state or 
delegated local agency certify in a letter to the Administrator of the 
EPA, or a Regional Administrator, that it has adopted and is 
implementing a SMP. We solicited comment on incorporating these SMP 
elements into rule text language.
    The proposal continued the discussion of SMP by noting that states 
with certified SMP typically have robust communications between 
officials concerned with air quality impacts and officials and members 
of the public who use prescribed fire. These groups communicate during 
the development of the SMP, during the day-to-day burn authorization 
process and in the periodic review and potential revision of the SMP. 
For these reasons, the EPA proposed to accept the testimony of the air 
agency submitting the exceptional events demonstration that the SMP is 
being implemented, provided that prior to the EPA's acting on a 
demonstration, the record contains no clear evidence to the contrary.
    The proposed rule provided similar detail for BSMP by identifying 
in the rule text six BSMP as being generally appropriate, and generally 
endorsed and followed by federal, state and local agencies and private 
landowners, for exceptional events purposes for prescribed fires on 
wildland as well as for other prescribed fires. The six BSMP (i.e., 
evaluating smoke dispersion conditions, monitoring effects on air 
quality, recordkeeping/maintaining a burn or smoke journal, 
communicating, considering emission reduction techniques, and sharing 
the airshed) came from guidance on BSMP for prescribed fires provided 
by the USDA Forest Service and USDA NRCS.\71\ The proposal noted that 
while the BSMP are broadly stated, burn managers use site-specific 
considerations to select the exact actions of each type and apply them 
to specific burn projects. The EPA proposed to accept as evidence of 
the use of BSMP the burn manager's statement that he or she employed 
applicable BSMP for a prescribed fire. The proposal noted that 
documentation of evidence could consist of a copy of the routine post-
burn report or a letter prepared by the burn manager. While the EPA 
asserted in the proposal that we would work collaboratively with other 
federal agencies to make post-burn reports available to the air 
agencies that need them, we also encouraged land managers and other 
organizations employing prescribed fire to work with states and tribes 
to develop an efficient process to coordinate fire planning activities, 
issue public health advisories, if needed, and share relevant fire-
related documentation, including pre-and post-burn reports.
---------------------------------------------------------------------------

    \71\ USDA Forest Service and Natural Resources Conservation 
Service, Basic Smoke Management Practices Tech Note, October 2011, 
http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1046311.pdf.
---------------------------------------------------------------------------

    The proposal provided similar detail with respect to addressing the 
``prevention'' prong of the ``not reasonably controllable or 
preventable'' criterion stating that because prescribed fires are 
intentionally ignited, clarifying preventability is particularly 
relevant. The proposal noted that because both SMP and BSMP generally 
apply to the planning, execution and follow-up once the decision has 
been made to ignite a burn, they, therefore, do not specifically 
address prevention or deciding not to burn. The proposal stated that an 
affected agency should conclude a prescribed fire to be not reasonably 
preventable based on the benefits that would be foregone if the fire 
were not conducted. We articulated ``forgone benefits'' as those 
objectives in a multi-year fire management plan that establish, restore 
and/or maintain a sustainable and resilient wildland ecosystem. The 
proposed regulatory text intended to rely on the benefits in these 
plans as satisfying the not reasonably preventable prong of the not 
reasonably controllable or preventable criterion provided there is no 
compelling evidence to the contrary in the record when the EPA approves 
the associated exceptional events demonstration. The proposal provided 
additional detail regarding the development of these multi-year land or 
resource management plans.
    The proposal also removed the phrase ``and must include 
consideration of development of a SMP'' from the sentence of the 
existing text of 40 CFR 50.14(b)(3) that in the 2007 Exceptional Events 
Rule read, ``If an exceptional event occurs using the basic smoke 
management practices approach, the State must undertake a review of its 
approach to ensure public health is being protected and must include 
consideration of development of a SMP.''
    Final Rule. We are finalizing in regulatory language, as proposed 
and for the reasons discussed in our proposal and herein, the following 
definition of prescribed fire: A ``prescribed fire is any fire 
intentionally ignited by management actions in accordance with 
applicable laws, policies, and regulations to meet specific land or 
resource management objectives.''
    We are also finalizing our proposal that a prescribed fire can 
satisfy the human activity unlikely to recur at a particular location 
criterion if certain requirements are met and provided there is no 
compelling evidence to the contrary in the record. Specifically, the 
air agency must describe the actual burn frequency, but may rely on 
either the natural fire return interval or the prescribed fire 
frequency needed to establish, restore and/or maintain a sustainable 
and resilient wildland ecosystem contained in a multi-year land or 
resource management plan \72\ with a stated objective to establish, 
restore and/or maintain a sustainable and resilient wildland ecosystem 
and/or to preserve endangered or threatened species through a program 
of prescribed fire. As we noted in the proposal, the EPA understands 
that multi-year plans incorporate factors relevant to identifying and 
selecting the areas and times under which management will

[[Page 68252]]

initiate a specific prescribed fire. We also recognize that evaluating 
the behavior and results of prior prescribed fires aids in determining 
the frequency and need for future prescribed fire in a given area. 
Thus, we acknowledge that a multi-year plan with a stated objective to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem and/or to preserve endangered or threatened species may 
include general targets for the frequency of prescribed fire use and 
that management may deviate from the general plan due to unexpected 
differences between planned and actual fire behavior, landscape or 
ecosystem characteristics, fuel loading patterns and weather patterns. 
As a result, when the EPA reviews an exceptional events demonstration 
for a prescribed fire conducted under a wildland management plan, we 
intend to compare the actual time pattern of prescribed fires on the 
land with the pattern described in the applicable multi-year plan in a 
general way, rather than treating the multi-year plan as containing a 
specific schedule to which management must adhere. For example, if the 
wildland management plan identified an approximate 5-year burn 
interval, the EPA would not disapprove a demonstration if the burn 
occurred on a 4-year or a 6-year interval, provided, of course, that 
the demonstration met all other Exceptional Events Rule criteria. Also, 
as we discussed in more detail in the proposal and consistent with our 
recognition of the ecosystem benefits of prescribed fire, ``sustainable 
and resilient wildland ecosystem'' could include maintaining a 
regenerated forest in a healthy condition able to withstand and/or 
diminish the effects of catastrophic wildfire.
---------------------------------------------------------------------------

    \72\ On a case-by-case basis, in the absence of a multi-year 
plan, the EPA would also consider a prescribed fire on wildland 
conducted on a fire return interval established according to 
scientific literature to satisfy the not reasonably controllable or 
preventable criterion provided the prescribed fire was also 
conducted with the objective to establish, restore and/or maintain a 
sustainable and resilient wildland ecosystem and conducted in 
compliance with either a state-certified SMP or BSMP. This case-by-
case approach is similar to the approach currently used under the 
2007 Exceptional Events Rule.
---------------------------------------------------------------------------

    We are finalizing our proposed regulatory language that a 
prescribed fire must be conducted under an adopted and implemented 
certified SMP or must have used appropriate BSMP to satisfy the 
controllable prong of the not reasonably controllable or preventable 
criterion. As we indicated in the proposal, ``certification'' requires 
that a responsible state or delegated local agency certify in a letter 
to the Administrator of the EPA, or a Regional Administrator,\73\ that 
it has adopted and is implementing a SMP.\74\ Past certifications 
provided to the EPA through this process are sufficient to meet the 
``certified'' SMP language in this final action. An air agency with a 
current SMP that has not been certified according to this process could 
pursue certification of its existing SMP. SMPs that have been 
incorporated into a SIP are ``certified.'' We are retaining Table 3, 
which identifies generally appropriate BSMP, in the regulatory text. To 
the proposed version of the table, we have added a footnote to indicate 
that the listing of BSMP is not intended to be all-inclusive. Burn 
managers can consider other appropriate BSMP as they become available 
due to technological advancement or programmatic refinement. While not 
in regulatory text, we also incorporate into this final rule preamble, 
as guidance, Table 4, which includes example content for a burn report. 
The preamble to this final rule identifies burn reports as one example 
of documentation that air agencies can use in their exceptional events 
demonstrations for prescribed fires to show the implementation of BSMP. 
After incorporating commenter feedback into the descriptions of some of 
these components, we are retaining in the preamble, as guidance, the 
following components of a certified SMP: \75\
---------------------------------------------------------------------------

    \73\ As discussed in more detail in Section IV.G.7 of this 
preamble, concurrent with these rule revisions, the EPA has revised 
the delegation of authority for exceptional events decision making 
to allow for redelegation from the EPA Regional Administrator to the 
Regional Air Division Director or equivalent highest manager who 
exclusively oversees air programs. If an EPA Regional office elects 
to pursue redelegation, then a state could ``certify'' its SMP by 
sending a letter to the delegated official in the EPA Regional 
office.
    \74\ The EPA anticipates that any person within an air agency 
responsible for submitting exceptional events demonstrations or SIP 
revisions could also be responsible for certifying a Smoke 
Management Program.
    \75\ The EPA is adapting the language associated with the six 
basic components of a certifiable SMP from the 1998 Interim Air 
Quality Policy on Wildland and Prescribed Fires. Although states may 
have developed and implemented a certified SMP that addresses 
prescribed fire not on wildland, this regulatory action focuses on 
the elements of a certified SMP as applied to managing smoke from 
prescribed fires on wildland. In this context, the EPA expects burn 
managers to consider actions and approaches where appropriate.
---------------------------------------------------------------------------

     Authorization to Burn--Includes a process for authorizing 
or granting approval to manage prescribed fires on wildland within a 
region, state or on Indian lands and identifies a central authority 
responsible for implementing the program. The authorization process 
could, but is not required to, include burn permits or other forms of 
instruction for conducting burns that consider air quality and the 
ability of the airshed to disperse emissions.
     Minimizing Air Pollutant Emissions--Encourages wildland 
owners/managers to consider and evaluate alternative treatments to 
fire, but if fire is the selected approach to follow appropriate 
emission reduction techniques.
     Smoke Management Components of Burn Plans--If the smoke 
management program requires burn plans, then the burn plan should 
include the following components: Actions to minimize fire emissions, 
approaches to evaluate smoke dispersion, public notification and 
exposure reduction procedures, and air quality monitoring.
     Public Education and Awareness--Establishes the criteria 
for issuing health advisories when necessary and procedures for 
notifying potentially affected populations.
     Surveillance and Enforcement--Includes procedures to 
ensure compliance with the terms of the SMP.
     Program Evaluation--Provides for periodic review by 
interested stakeholders of the SMP effectiveness and program revision 
as necessary. A review of effectiveness should consider the role of 
prescribed fire in meeting the goals in a multi-year or resource 
management plan with a stated objective to establish, restore and/or 
maintain a sustainable and resilient wildland ecosystem and/or to 
preserve endangered or threatened species. Effectiveness reviews should 
also consider air quality impacts as well as any received post-burn 
reports, which may describe implemented contingency plans due to smoke 
impacts or use of BSMP and recommendations for future improvements. SMP 
procedures for re-evaluation should address a frequency of review 
(e.g., every 3 to 5 years, or as needed); participants in the review 
process (e.g., original program developers to include land owners/
managers, air quality managers, the public, etc.); and program 
objectives over the review period (e.g., acres burned, anticipated/
desired future acres burned, needed modifications).

[[Page 68253]]



 Table 3--Summary of Basic Smoke Management Practices, Benefit Achieved
                With the BSMP, and When It Is Applied \a\
------------------------------------------------------------------------
                                                        When the BSMP is
    Basic smoke management      Benefit achieved with   applied--before/
         practice \b\                  the BSMP         during/after the
                                                              burn
------------------------------------------------------------------------
Evaluate Smoke Dispersion       Minimize smoke         Before, During,
 Conditions.                     impacts.               After.
Monitor Effects on Air Quality  Be aware of where the  Before, During,
                                 smoke is going and     After.
                                 degree it impacts
                                 air quality.
Record-Keeping/Maintain a Burn/ Retain information     Before, During,
 Smoke Journal.                  about the weather,     After.
                                 burn and smoke. If
                                 air quality problems
                                 occur, documentation
                                 helps analyze and
                                 address air
                                 regulatory issues.
Communication--Public           Notify neighbors and   Before, During.
 Notification.                   those potentially
                                 impacted by smoke,
                                 especially sensitive
                                 receptors.
Consider Emission Reduction     Reducing emissions     Before, During,
 Techniques.                     through mechanisms     After.
                                 such as reducing
                                 fuel loading can
                                 reduce downwind
                                 impacts.
Share the Airshed--             Coordinate multiple    Before, During,
 Coordination of Area Burning.   burns in the area to   After.
                                 manage exposure of
                                 the public to smoke.
------------------------------------------------------------------------
\a\ The EPA believes that elements of these BSMP could also be practical
  and beneficial to apply to wildfires for areas likely to experience
  recurring wildfires.
\b\ The listing of BSMP in this table is not intended to be all-
  inclusive. Not all BSMP are appropriate for all burns. Goals for
  applicability should retain flexibility to allow for onsite variation
  and site-specific conditions that can be variable on the day of the
  burn. Burn managers can consider other appropriate BSMP as they become
  available due to technological advancement or programmatic refinement.


   Table 4--Elements That May Be Included in Burn Plans and Post-Burn
      Reports for Prescribed Fires Submitted as Exceptional Events
------------------------------------------------------------------------
             Element                   Burn plan       Post-Burn report
------------------------------------------------------------------------
Fire Name a.....................  Include...........  Include.
Permit number (if appropriate)..  Include...........  Include.
Latitude/longitude and physical   Include...........  Include.
 description.
Date of burn, ignition time and   Include...........  Include.
 completion time (duration of
 burn).
AQI status on burn day, if        Predicted.........  Actual.
 available (both in the vicinity
 of the fire and in the affected
 upwind area).
Acres burned....................  Planned...........  Actual
                                                       (blackened).
Description of fuel loading.....  Estimated.........  Actual (tons
                                                       consumed).
Meteorological data (weather      Predicted           Actual conditions
 conditions, wind speed and        conditions          (including actual
 direction, dispersion).           (including          dispersion).
                                   predicted
                                   dispersion).
Smoke Impacts...................  Anticipated smoke   Observed or
                                   impacts.            reported smoke
                                                       impacts (include
                                                       nature, duration,
                                                       spatial extent
                                                       and copies of
                                                       received
                                                       complaints).
BSMP actions to reduce impacts..  Expected BSMP       Actual BSMP
                                   actions.            actions.
Recommendations for future burns  ..................  Include.
 in similar areas.
Analytics (modeled/actual fire    ..................  Include.
 spread, satellite imagery and
 analysis, webcam/video, PM/
 ozone concentrations over the
 course of the fire).
------------------------------------------------------------------------
\a\ The ``Fire Name'' should be unique and referenced, to the greatest
  extent possible, in all exceptional events-related documentation,
  including the event name in AQS. The fire name could simply consist of
  the county, state, and date in which the burn occurred (e.g., County
  X, State Y Prescribed Fire on Date Z) if no other name has been
  assigned.

    Also as proposed, and for the previously summarized reasons, we are 
removing the phrase ``and must include consideration of development of 
a SMP'' from the sentence that in 40 CFR 50.14(b)(3) of the 2007 
Exceptional Events Rule that read, ``If an exceptional event occurs 
using the basic smoke management practices approach, the State must 
undertake a review of its approach to ensure public health is being 
protected and must include consideration of development of a SMP.''
    With respect to the not reasonably preventable prong of the not 
reasonably controllable or preventable criterion, after considering 
public comments, we are finalizing our reliance on a multi-year land or 
resource management plan for a wildland area with a stated objective to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem and/or to preserve endangered or threatened species through a 
program of prescribed fire.
    While our proposal encouraged all agencies and managers/owners 
involved in land, air quality and fire management to communicate and 
collaborate regarding fire use practices in general and plans for 
specific prescribed fires with use of BSMP, we did not propose to 
require this communication. Commenters provided both general and 
specific feedback related to the EPA's encouragement of these 
collaborative fire communications. From a holistic perspective, 
commenters noted that a shared understanding regarding the goals of a 
specific prescribed fire helps both air quality and land managers meet 
their respective air quality objectives and land and resource 
management objectives. Some state and regional planning organization 
commenters also responded that it is inappropriate to allow federal 
land managers, who are not directly accountable for managing air 
quality, to independently make decisions for which air agencies are 
responsible. As we have noted previously in this preamble, federal land 
managers do play an important role

[[Page 68254]]

in helping states and tribes improve the air quality in those areas 
that do not meet the NAAQS. Regardless of whether the provisions in the 
General Conformity Rule \76\ apply, commenters specifically asked the 
EPA to ensure that burn managers using BSMP consult with the air agency 
or air agencies within whose jurisdiction the burn is being conducted 
regarding the selection and use of BSMP to ensure that those BSMP are 
appropriate and address local air quality and public health issues. 
Some land managers have offered the counter-perspective that pre-burn 
approval on a fire-by-fire basis could consume resources from all 
parties and have no practical effect regarding actual measures taken 
before, during or after a fire. These same land managers also 
articulated that requiring extensive pre-burn discussions between 
burners and air agencies could have the unintended result of burners 
not using BSMP.
---------------------------------------------------------------------------

    \76\ The General Conformity Rule requires that federal agencies 
work with state, tribal and local governments in nonattainment and 
maintenance areas to ensure that federal actions conform to any 
applicable SIP, FIP or TIP.
---------------------------------------------------------------------------

    The EPA must balance the concerns raised by the states during the 
comment period on the NPRM with the concerns identified by other 
federal agencies with which we have consulted in the development of 
this action. To effect this balance, the EPA is incorporating preamble 
language and rule text that requires that air agencies, federal land 
managers and other agencies as appropriate, periodically discuss with 
the burn managers operating within their jurisdiction and document the 
process by which air agencies and land managers will work together to 
protect public health and manage air quality impacts during the conduct 
of prescribed fires on wildland. Consistent with operational protocols 
within the fire management community, these discussions must include 
outreach and education regarding general expectations for the selection 
and application of appropriate BSMP and goals for advancing strategies 
and increasing adoption and communication of the benefits of 
appropriate BSMP. As with other components of this final rule, we are 
not defining the mechanism by which air agencies and land managers will 
conduct and document these discussions nor are we prescribing the full 
scope of these discussions. Rather, we are finalizing regulatory text 
that, after an initial implementation period, the EPA will not concur 
with a request to exclude data that have been influenced by a 
prescribed fire on wildland if the air agency(ies), federal land 
managers and burn managers have not discussed and documented a process 
that includes outreach and education regarding general expectations for 
the selection and application of appropriate BSMP and goals for 
advancing strategies and increasing adoption and communication of the 
benefits of appropriate BSMP. The initial implementation period is 
defined as 2 years from the effective date of this action. This time 
will allow air agencies and land managers to develop and incorporate 
the collaboration process into operational management.
    The EPA expects that the mechanism under which these discussions 
are conducted and documented could be formal, such as a Memorandum of 
Understanding or an Interagency Agreement, or it could be a letter 
agreement. Similarly, in indicating that discussions occur 
``periodically,'' we mean that discussions could occur annually at the 
beginning of a burn season, prior to initiating burns on identified 
tracts of land, or on some other identified frequency. We do not expect 
discussions prior to each prescribed fire on wildland. The EPA also 
expects that discussions will include outreach and education regarding 
general expectations for the selection and application of appropriate 
BSMP and goals for advancing strategies and increasing adoption and 
communication of the benefits of appropriate BSMP and not the 
initiation or timing of the prescribed fire (except in those cases 
where a BSMP specifies certain factors related to the timing). Not all 
BSMP are appropriate for all burns. Goals for applicability should 
remain flexible to allow for onsite variation and site-specific 
conditions that can be variable on the day of the burn. Where states 
have an existing, documented process or program under which air 
agencies, federal land managers, state fire agencies and other entities 
engage with burn managers regarding the protection of public health and 
air quality and general expectations for the selection, application and 
benefits of appropriate BSMP, they may rely upon and reference this 
process or program when addressing the not reasonably controllable or 
preventable criterion for an exceptional events demonstration for a 
prescribed fire.
    Also related to air agency and land manager collaboration, we have 
clarified the regulatory language at 40 CFR 50.14(b)(3)(ii)(A) to 
require that when a NAAQS exceedance or violation occurs when a 
prescribed fire is employing an appropriate BSMP approach that the air 
agency and the burn manager conduct a retrospective review of the 
prescribed fire event and the employed BSMP to ensure the protection of 
air quality and public health and progress towards restoring and/or 
maintaining a sustainable and resilient wildland ecosystem. Either the 
air agency or the burn manager could initiate such a retrospective 
review. This regulatory language previously indicated that the ``State 
must undertake a review of its approach. . . .'' The added regulatory 
text clarifies our intent in using the term ``approach.'' We are also 
requiring that if the prescribed fire becomes the subject of an 
exceptional events demonstration, the demonstration must include 
documentation of the post-burn review. The EPA may be unable to concur 
on a demonstration that does not include documentation of the post-burn 
review. Together, the regulatory language at 40 CFR 50.14(b)(3)(ii) now 
requires both proactive discussions focused on education and outreach 
regarding BSMP and a ``lessons learned'' review of events that occur 
with the use of BSMP. We note that this required collaborative 
proactive and retrospective approach does not affect any land manager's 
ability to conduct a prescribed fire, only whether a prescribed fire 
conducted after the effective date of this action is eligible for 
consideration as an exceptional event. The mandatory provisions for 
these required discussions do not apply where a burner is operating 
under a developed and implemented certified SMP.
    Comments and Responses. The EPA received many comments expressing 
agreement with the EPA's recognition of the importance of prescribed 
fire on wildland and welcoming continued dialogue among state, tribal 
and local air agencies, the EPA and other federal agencies to ensure 
that land managers have adequate available tools to manage ecosystem 
development and restoration and manage wildland vegetation, including 
use of planned prescribed fires and letting some wildfires proceed 
naturally, and to ensure that use of these tools is protective of 
public health and does not result in unhealthy air. No commenters 
disagreed with this objective, but, as described in the following 
paragraphs, some commenters provided feedback regarding applying the 
specific aspects of prescribed fire on wildland to the exceptional 
events process.
    Some commenters supported the proposed definition of prescribed 
fire, while others offered suggestions for revision. Several commenters 
recommended that we include within the regulatory definition the 
concept

[[Page 68255]]

that prescribed fire on wildland must be conducted using either SMP or 
BSMP principles. While we agree that either a SMP or BSMP are required 
for a prescribed fire to be eligible for consideration under the 
Exceptional Events Rule, as indicated in this preamble and in the 
regulatory text at 40 CFR 50.14(b)(3)(ii)(A), we have not added either 
SMP or BSMP to the regulatory definition of a prescribed fire because 
to do so would have the effect of excluding from the definition of 
prescribed fire those deliberately ignited fires that do not use BSMP 
or SMP. That is, we would not have terminology to define intentionally 
ignited fires not using BSMP or SMP, which the land management 
community refers to as prescribed fires. We believe that promulgating a 
regulatory definition that is substantively different than the common 
usage would create confusion. Moreover, the definition of prescribed 
fire that we are promulgating combined with the specific exceptional 
events provisions for prescribed fire on wildland (e.g., the 
requirement that the fire must have been conducted under a SMP or have 
BSMP applied) will achieve the same goal as the suggested revision to 
the definition of prescribed fire.
    Another commenter suggested that the definition of prescribed fire 
also include the caveat that that ``applicable laws, policies, and 
regulations'' (1) actually exist (2) are enforceable by or through 
delegated authority from the state air quality management entity, and 
(3) are intended to adequately control emissions and impacts at all 
downwind locations. We have not incorporated the commenter's suggested 
language. Under the CAA, states, exclusive of tribal lands, are 
primarily responsible for the administration of air quality management 
programs within their borders. As the responsible entity, states 
promulgate laws and regulations, where needed, and ensure they are 
followed and are enforceable (states also develop policies, but 
policies are generally not enforceable). We note that in some states, 
legislation gives the leadership of fire management to a forestry or 
public safety agency rather than to an air agency. As pointed out by 
one commenter, the EPA cannot mandate that states grant air agencies 
the authority or purview to regulate or enforce public health and 
safety. We can, however, require coordination as a condition for the 
EPA's approval for the exclusion of event-influenced ambient data, 
which is what we have done with the regulatory language at 40 CFR 
50.14(b)(3)(ii)(A).
    As previously noted, after considering public comments, we are 
finalizing that to satisfy the human activity unlikely to recur at a 
particular location criterion, the air agency may rely on either the 
natural fire return interval or the prescribed fire frequency needed to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem contained in a multi-year land or resource management plan 
with a stated objective to establish, restore and/or maintain a 
sustainable and resilient wildland ecosystem and/or to preserve 
endangered or threatened species through a program of prescribed fire. 
While a few commenters agreed with the language as proposed, several 
commenters asked for clarification regarding recurrence and the 
development of land management plans. Specifically, commenters asked 
how the recurrence frequency identified in land management plans as 
being needed to achieve land management goals or defined by the natural 
fire return interval compares to the recurrence frequency generally 
established for the human activity unlikely to recur at a particular 
location criterion. In discussing the concept of recurrence in Section 
IV.E.1 of this preamble, we note that the general benchmark for 
recurrence (i.e., three events in 3 years) does not apply to prescribed 
fires. Rather than using this general benchmark for prescribed fire on 
wildland, we are promulgating in 40 CFR 50.14(b)(3)(iii), that 
recurrence for prescribed fires is defined by either the natural fire 
return interval or the prescribed fire frequency needed to establish, 
restore and/or maintain a sustainable and resilient wildland ecosystem 
contained in a multi-year land or resource management plan with a 
stated objective to establish, restore and/or maintain a sustainable 
and resilient wildland ecosystem and/or to preserve endangered or 
threatened species through a program of prescribed fire. Thus, the 
recurrence frequency for prescribed fire is specific to the ecosystem 
and resource needs of the affected area. Several additional commenters 
requested that we codify language allowing either the natural fire 
cycle or the fire frequency needed to meet ecological objectives to be 
defined by scientific literature. We are not codifying the concept that 
recurrence can be defined by scientific literature, but we are 
including this clarification in the final rule preamble.\77\ Two 
additional commenters asked that we clarify how an event spanning 
multiple days counts towards recurrence. As we discuss in Section 
IV.E.1 of this preamble, the EPA recognizes that a single event, 
natural or caused by human activity (to include prescribed fire 
events), can span multiple days and result in an air agency flagging 
multiple monitor-day values in AQS (i.e., multiple exceedances of a 
given NAAQS at a single monitor in a single day or multiple NAAQS 
exceedances at multiple monitors on multiple days). The EPA considers a 
single discrete event to be one occurrence.
---------------------------------------------------------------------------

    \77\ As a general matter, this preamble provides non-binding 
guidance and recommendations for satisfying specific rule criteria. 
This does not mean that these recommendations are the only way to 
address a given issue. The preamble guidance only precludes other 
approaches when the rule language identifies a specific condition as 
being necessary to satisfy a given requirement.
---------------------------------------------------------------------------

    Commenters also asked for clarification regarding the development 
of land and resource management plans. Specifically, commenters note 
that while the description and content of the plans identified in the 
preamble to our proposed rule may be appropriate for federal agencies, 
the description and content of land and resource management plans was 
not appropriate for private landowners who burn at the landscape level. 
Commenters asked that we clarify that prescribed fires undertaken by 
private landowners or on lands managed by multiple parties that are 
consistent with their management plans be considered under the 
exceptional events process. We disagree with the commenters on this 
point. The existence of identified objectives in a state or private 
management plan may not be sufficient under the exceptional events 
process. Rather, the stated objectives must include those identified in 
this rule. The EPA is promulgating regulatory provisions that describe 
the process and requirements by which emissions from prescribed fires 
on wildland causing an exceedance or violation of a NAAQS can be 
considered for exclusion under the Exceptional Events Rule. In 
finalizing these rule revisions, our intent is to clearly articulate 
the components needed to satisfy the statutory requirements under CAA 
section 319(b) and the Exceptional Events Rule. It is not our intent to 
exclude specific event types or scenarios from consideration. Rather, 
the EPA will review each event on a case-by-case basis considering the 
merits of each specific case. We recognize that addressing the 
prescribed fire-related components may be more difficult in some states 
than others (or more difficult for some land areas within a state than 
other land areas within the same state) because of the

[[Page 68256]]

state legislative authority for fire management or because of the 
nature and management/ownership of lands considered to be wildland. We 
further recognize that successfully implementing these rule revisions 
will require the coordination, cooperation and compromise of all 
involved parties, including federal, state, local, tribal, and private 
land owners/land managers; state, tribal and local air quality 
agencies; and the EPA.
    Commenters provided a similar level of detailed feedback regarding 
the not reasonably controllable or preventable criterion. Most 
commenters agreed with the EPA's now final provision that, to be 
considered under the provisions of the Exceptional Events Rule, 
prescribed fires must be conducted under an adopted and implemented 
certified SMP or using appropriate BSMP. One commenter asked that we 
clarify in rule text that if a certified SMP is in place for an area, 
then all prescribed fires conducted in the area must first comply with 
the provisions in a SMP. In response to the commenter's suggestion, we 
note in this preamble that if a state has adopted and implemented a 
certified SMP, then a prescribed fire on lands included within the 
scope of the SMP should be conducted under the terms of the SMP. We 
note, however, that some SMP may allow individual burners to 
voluntarily adhere to the terms of the SMP. If this is the case, or in 
situations in which a state has developed, but not implemented, a SMP, 
then burn managers may use BSMP to address the provisions of the 
Exceptional Events Rule. States are responsible for implementing and 
ensuring conformance with the terms of their SMP.
    Our proposal solicited comment on whether to include SMP elements 
in the final rule revisions as rule text. We received comments 
supporting retaining the SMP elements in the preamble as guidance, and 
we received other comments supporting including the SMP elements in 
regulatory language. As previously noted in this preamble, we are 
retaining the SMP elements in the preamble as guidance. When the SMP 
elements were developed for the 1998 Interim Air Quality Policy on 
Wildland and Prescribed Fires, the language reflected actions 
consistent with addressing three types of wildland fire (i.e., 
wildfire, prescribed fire and wildland fire use fire). Fire terminology 
now recognizes two types of wildland fire: Wildfire and prescribed 
fire. We chose not to include provisions in regulatory text that do not 
reflect current terminology. Additionally, in the 1998 Interim Air 
Quality Policy on Wildland and Prescribed Fires, we recommended that 
all state-certified SMP include the six identified elements. However, 
because the elements were only recommended versus being required, not 
all states adopted all six elements. Requiring the six SMP elements in 
the rule text could result in some states needing to revise their SMP. 
Where a state has incorporated the SMP into a SIP, the effects of 
including the SMP elements in the final rule text could include 
revising the SIP if the state intends to rely on the SMP path to 
address the controllable prong of the not reasonably controllable or 
preventable criterion. As we note in this preamble, based on commenter 
feedback, we have slightly modified the descriptions of some of these 
components. For example, several commenters noted that the 
authorization to burn component appears to attempt to require burn 
permits. We have clarified that while this component must include a 
process for authorizing or granting approval to manage prescribed fires 
on wildland, this authorization process may or may not include burn 
permits.\78\ Also in response to commenter feedback, we have clarified 
the program evaluation component including ``periodic review'' by 
interested stakeholders of the SMP effectiveness and program revision 
as necessary.
---------------------------------------------------------------------------

    \78\ By ``burn permit,'' we mean a document or communication 
saying that a particular party may conduct a prescribed fire in a 
particular area on a particular day or range of days. Acceptable 
alternative approaches to burn permits include communicating more 
broadly where and when landowners may conduct prescribed fires. 
However, we do not consider a program that authorizes prescribed 
fire across broad areas throughout an entire season with no regard 
for meteorological or pollution conditions on specific days to be a 
SMP.
---------------------------------------------------------------------------

    Several commenters expressed support for our proposal to remove the 
phrase ``and must include consideration of development of a SMP'' from 
the sentence that in 40 CFR 50.14(b)(3) of the 2007 Exceptional Events 
Rule that read, ``If an exceptional event occurs using the basic smoke 
management practices approach, the State must undertake a review of its 
approach to ensure public health is being protected and must include 
consideration of development of a SMP.'' As we noted in the proposal, 
while the EPA supports states considering the development of a SMP when 
an event occurs while using BSMP, we believe states have had many 
opportunities to develop SMP since 2007. The language in the 2007 rule 
effectively requires an ongoing consideration to develop a SMP every 
time a prescribed fire causes a NAAQS exceedance or violation that 
merits exclusion as an exceptional event. We do not believe Congress 
intended this ongoing consideration to be a requirement under CAA 
section 319(b). We maintain that when air agencies observe NAAQS 
exceedances or violations attributed to a prescribed fire, air agencies 
should consider a wide range of alternatives including, but not limited 
to, the development of a SMP or more frequent or intensive use of BSMP 
to minimize smoke impacts. In addition, we believe that a SMP is most 
appropriate when multiple parties wish to employ prescribed fire at 
about the same time in the same airshed, which is a more narrow 
situation than specified in the sentence we proposed to remove. For 
these reasons, as supported by commenter feedback, we are removing the 
language from the rule text.
    Four states and one national organization agreed with our proposal 
to include BSMP in rule text. One national forestry association 
indicated its preference to include BSMP in the preamble as guidance. 
As noted, we are including the table identifying BSMP in regulatory 
text. While not in regulatory text, we are also incorporating into this 
final rule, as guidance in the preamble, Table 4, which includes 
example content in a burn report. Although one commenter asked that 
this table be included in regulatory text, we are not doing this 
because the table provides example content of a burn report, which is 
only a single example of the type of documentation that air agencies 
can use in their exceptional events demonstrations for prescribed fires 
to show the implementation of BSMP. It is not our intent to convey as 
required documentation either burn reports or the identified content.
    Several commenters supported, and no commenters opposed, the 
presumption that a prescribed fire should be considered not reasonably 
preventable based on the benefits that would be foregone if the burn 
did not take place. As we have noted, we have incorporated this concept 
into the final rule preamble and finalized associated regulatory text, 
which allows states to rely on a multi-year land or resource management 
plan for a wildland area with a stated objective to establish, restore 
and/or maintain a sustainable and resilient wildland ecosystem and/or 
to preserve endangered or threatened species through a program of 
prescribed fire to satisfy the preventability prong of the not 
reasonably controllable or preventable criterion.
3. Stratospheric Ozone Intrusions
    The section of the proposal addressing exceedances due to

[[Page 68257]]

stratospheric ozone intrusions did not propose any new guidance or 
specific regulatory language. Rather, it provided a general 
(meteorological) description of stratospheric ozone intrusions, 
indicated that stratospheric ozone intrusions are purely natural 
events, and provided general guidance on applying the Exceptional 
Events Rule criteria when preparing demonstrations for stratospheric 
ozone intrusion events. Because we intend to develop a supplementary 
guidance document, Draft Guidance on the Preparation of Exceptional 
Events Demonstrations for Stratospheric Ozone Intrusions, which will 
apply the final rule provisions to the development of demonstrations 
for stratospheric ozone intrusion events and will include example 
analyses, conclusion statements and technical tools that air agencies 
can use in their demonstrations, we are not repeating in this final 
action the language that appeared as guidance in the proposal. We 
intend to post the draft guidance and instructions for providing public 
comment on the exceptional events Web site at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events shortly 
after finalizing these rule revisions.
    After consideration of the public comments, as discussed more fully 
in the paragraph that follows, we are finalizing a rule provision 
related to satisfying the not reasonably controllable or preventable 
criteria for stratospheric ozone intrusions. While the not reasonably 
controllable or preventable criterion applies to natural events, the 
EPA has stated that air agencies generally have no obligation to 
specifically address reasonable controls if the event was natural. We 
applied this concept when proposing (and, in this action, finalizing) a 
categorical presumption of not reasonably controllable for wildfires 
that would involve referencing the appropriate regulatory citation in 
the demonstration. The proposal preamble repeatedly acknowledges that, 
similar to wildfires, stratospheric ozone events are purely natural 
events. The proposal also stated in the not reasonably controllable or 
preventable section that ``In these cases [volcanic releases of 
SO2 and stratospheric ozone intrusions], the air agency 
should affirmatively state that the not reasonably controllable or 
preventable criterion is satisfied by the fact that the natural event 
was of a character that could not have been prevented or controlled and 
that there were no contributions of event-related emissions from 
anthropogenic sources.'' As a natural outgrowth of our proposal, and as 
specifically suggested by one commenter, we are extending this 
categorical presumption to satisfying the not reasonably controllable 
or preventable criterion to stratospheric ozone intrusion events by 
promulgating regulatory language at 40 CFR 50.14(b)(6).
4. High Wind Dust Events
a. Summary of Proposal
    The EPA proposed as guidance in the preamble and/or as changes to 
regulatory text concepts and language that first appeared in the 
Interim High Winds Guidance document. These changes included adding 
regulatory definitions for high wind dust events and a high wind 
threshold, determining the scenarios under which a high wind dust event 
could be considered ``natural'' for purposes of the Exceptional Events 
Rule, identifying that remote, large-scale, high-energy and/or sudden 
high wind dust events, such as ``haboobs,'' would generally satisfy the 
not reasonably controllable or preventable criterion with streamlined 
documentation, and incorporating best management practices (i.e., soil 
conservation management practices) as reasonable controls. We solicited 
comment on all of these concepts and discuss each in more detail in the 
following paragraphs.
    Definition of an Event. Consistent with the EPA's proposed revision 
of the regulatory definition of an exceptional event to include both 
the event and its associated resulting emissions, the EPA proposed to 
define a high wind dust event as an event that includes the high-speed 
wind and the dust that the wind entrains and transports to a monitoring 
site. We also proposed, consistent with the nullified language in the 
2007 Exceptional Events Rule preamble, the PM10 Natural 
Events Policy and the Interim High Winds Guidance, to define high wind 
dust events in the rule text as ``natural events'' in cases where 
windblown dust is entirely from natural sources or where all 
significant anthropogenic sources of windblown dust have been 
reasonably controlled.
    High Wind Threshold. To facilitate clearer expectations regarding 
the level of evidence needed to demonstrate not reasonably controllable 
or preventable, the EPA proposed to codify in rule language the 
definition of ``high wind threshold'' as the minimum threshold wind 
speed capable of causing particulate matter emissions from natural 
undisturbed lands in the area affected by a high wind dust event. The 
EPA proposed to accept a threshold of a sustained wind of 25 mph for 
areas in the western U.S. provided this value is not contradicted by 
evidence in the record when we reviewed a demonstration. The proposal 
noted that if we received specific information based on relevant 
studies that suggest a different high wind threshold for an identified 
area, the EPA would notify the affected air agency so that the agency 
may consider basing its demonstration on that threshold value. The 
proposal also indicated that the EPA would consider such information as 
part of the weight of evidence analysis for a submitted demonstration. 
As we had previously articulated in the Interim High Winds Guidance, 
the proposal stated that air agencies could, as an alternative to the 
25 mph high wind threshold, identify and use an area-specific high wind 
threshold that is more representative of local/regional conditions.
    The proposal explained that we would use the high wind threshold 
concept when assessing the not reasonably controllable or preventable 
criterion for all high wind dust exceptional events demonstrations 
except for those events in which the source of the emissions is 
entirely natural (i.e., windblown dust from natural undisturbed lands) 
or where a large-scale and high-energy high wind dust event generates 
emissions that cause an exceedance or violation. In the case of a 
large-scale and high-energy high wind dust event, no assessment of 
reasonable controls is needed to satisfy the controllability prong of 
the ``not reasonably controllable or preventable'' criterion.
    Large-Scale and High-Energy High Wind Dust Events. The EPA proposed 
rule language to apply a general approach when considering 
reasonableness of controls for remote, large-scale, high-energy and/or 
sudden high wind dust events, such as ``haboobs'' in the southwest 
where sustained wind speeds can exceed 40 mph and generate walls of 
dust several miles wide and more than a mile high. The proposed rule 
text provided that if an event met the criteria for a large-scale and 
high-energy event, then it would be considered not reasonably 
preventable or controllable. Therefore, a demonstration limited to such 
event(s) will not need to substantively address this criterion.
    Best Management Practices. The EPA solicited comment on whether, as 
part of the assessment of local sources and reasonable controls, USDA/
NRCS-approved BMPs constitute sufficient reasonable controls in any or 
in all high wind event-affected areas and whether these measures should 
therefore be

[[Page 68258]]

specifically and categorically identified in preamble or rule language 
as constituting reasonable controls. The preamble repeated the EPA's 
previous guidance that USDA/NRCS-approved BMPs designed to effectively 
reduce fugitive dust emissions and prevent soil loss in agricultural 
applications could be included in the collection of controls determined 
to constitute reasonable controls for wind-blown dust events in areas 
in which they have been implemented.\79\ Although the EPA has addressed 
the sufficiency of BMPs in decisions on individual exceptional events 
demonstrations when the BMPs were part of a SIP-approved BACM 
determination, we have not previously addressed whether or not BMPs 
individually or in some combination with each other constitute 
sufficient reasonable controls nationally or in any particular types of 
areas.
---------------------------------------------------------------------------

    \79\ Interim Guidance on the Preparation of Demonstrations in 
Support of Requests to Exclude Ambient Air Quality Data Affected by 
High Winds Under the Exceptional Events Rule. U.S. EPA. May 2013. 
Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf and Interim 
Guidance to Implement Requirements for the Treatment of Air Quality 
Monitoring Data Influenced by Exceptional Events. U.S. EPA. May 
2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_guidememo_130510.pdf.
---------------------------------------------------------------------------

b. Final Rule
    After consideration of the public comments received, and for the 
reasons discussed in our proposed rule section and response to such 
comments, we are finalizing regulatory language defining high wind dust 
events and high wind threshold; determining the scenarios under which a 
high wind dust event could be considered ``natural'' for purposes of 
the Exceptional Events Rule; identifying that large-scale and high-
energy high wind dust events, such as ``haboobs,'' would generally 
satisfy the not reasonably controllable or preventable criterion with 
streamlined documentation; and providing guidance related to 
incorporating best management practices (i.e., conservation management 
practices) as reasonable controls.
    Definition of an Event. We are promulgating, as proposed, that a 
high wind dust event is an event that includes the high-speed wind and 
the dust that the wind entrains and transports to a monitoring site. No 
commenters opposed this definition.
    Also as proposed, we are promulgating regulatory text that we 
consider high wind dust events as ``natural events'' in cases where 
windblown dust is solely from natural sources or where all significant 
anthropogenic sources of windblown dust have been reasonably 
controlled.\80\ While we discuss this concept (and related comments and 
responses) in more detail in Section IV.D of this preamble, we note 
here that this long-standing policy was first established in the 
PM10 Natural Events Policy, which provided that:
---------------------------------------------------------------------------

    \80\ As identified in Section IV.D of this preamble, the EPA 
will generally consider human activity to have played little or no 
direct role in causing emissions of the dust generated by high wind 
for purposes of the regulatory definition of ``natural event'' if 
contributing anthropogenic sources of the dust are reasonably 
controlled, regardless of the amount of dust coming from these 
reasonably controlled anthropogenic sources, and thus the event 
could be considered a natural event. In such cases, the EPA believes 
that it would generally be a reasonable interpretation to find that 
the anthropogenic source had ``little'' direct causal role. If 
anthropogenic sources of windblown dust that are reasonably 
controllable but that did not have those reasonable controls applied 
at the time of the high wind event have contributed significantly to 
a measured concentration, the event would not be considered a 
natural event.

    Ambient PM10 concentrations due to dust raised by 
unusually high winds will be treated as due to uncontrollable 
natural events under the following conditions: (1) The dust 
originated from nonanthropogenic sources, or (2) the dust originated 
from anthropogenic sources controlled with best available control 
measures (BACM).\81\
---------------------------------------------------------------------------

    \81\ Areas Affected by PM-10 Natural Events (the PM10 
Natural Events Policy), memorandum from Mary D. Nichols, Assistant 
Administrator for Air and Radiation, to the EPA Regional offices, 
May 30, 1996.

    High Wind Threshold. We are also promulgating, as proposed, that 
the definition of a high wind dust threshold is the minimum threshold 
wind speed capable of causing particulate matter emissions from natural 
undisturbed lands in the area affected by a high wind dust event. No 
commenters opposed this definition. In concert with this definition, we 
are also finalizing a modified version of our proposed regulatory text 
that we will accept a threshold of a sustained wind of 25 mph for areas 
in the western U.S. provided this value is not contradicted by evidence 
in the record when we review a demonstration. Several commenters 
supported this definition either as proposed or with the clarification 
that air agencies could develop as an alternative to the 25 mph high 
wind threshold, their own area-specific high wind threshold that is 
more representative of local/regional conditions. Although we included 
this language in the proposal preamble, we did not include this 
language in the proposed regulatory text. We are including this 
language in the final regulatory text as a result of commenter 
feedback.
    We also repeat language from the proposal that any area-specific 
high wind threshold should be representative of conditions (i.e., 
sustained wind speeds \82\) that are capable of overwhelming reasonable 
controls (whether RACM, BACM or other) on anthropogenic sources and/or 
causing emissions from natural undisturbed areas. The threshold was not 
intended to represent the minimum wind speed at which any level of 
emissions could occur (e.g., aerodynamic entrainment), but rather the 
wind speed at which significant emissions begin to occur due to 
reasonable controls on disturbed soil or the natural wind resistance of 
undisturbed areas becoming overwhelmed. We further note that we 
included guidance on both threshold development and determining wind 
speeds in the Interim High Winds Guidance.\83\ While we believe this 
guidance is still appropriate with respect to determining wind speed 
characteristics and developing a wind speed threshold, we intend to 
revise the guidance to incorporate the provisions of this final action. 
We note that areas with Natural Events Action Plans that include a high 
wind threshold that meets the criteria identified in the Interim High 
Winds Guidance may be able to use the previously developed threshold as 
an area-specific high wind threshold. The proposal also accepted 
information on different high wind thresholds for identified areas (see 
80 FR 72878). After evaluating comments advocating that the EPA 
consider area-specific high wind thresholds, the EPA is codifying this 
provision in the final rule. The EPA recognizes, however, that there 
are likely to be limited situations in those areas in the western 
U.S.\84\ where this threshold applies in which exceptional events occur 
at wind speeds

[[Page 68259]]

less than 25 mph.\85\ Air agencies should consult with their EPA 
Regional office when developing alternate high wind thresholds for a 
particular area.
---------------------------------------------------------------------------

    \82\ Section 6.3.2.2 in the Interim Guidance on the Preparation 
of Demonstrations in Support of Requests to Exclude Ambient Air 
Quality Data Affected by High Winds Under the Exceptional Events 
Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf for details on the 
calculation of sustained wind speed. Generally, the EPA will accept 
that high winds could be the cause of a high 24-hour average 
PM10 or PM2.5 concentration if there was at 
least one full hour in which the hourly average wind speed was above 
the area-specific high wind threshold.
    \83\ See Appendices A2 and A3 in the Interim Guidance on the 
Preparation of Demonstrations in Support of Requests to Exclude 
Ambient Air Quality Data Affected by High Winds Under the 
Exceptional Events Rule. U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_highwinds_guide_130510.pdf for additional information 
on the development of a high wind threshold.
    \84\ See rule language that we are promulgating at 40 CFR 
50.14(b)(5)(iii).
    \85\ The default threshold of 25 mph was based on extensive 
windblown dust emissions research performed by the Department of 
Civil and Environmental Engineering at the University of Nevada, Las 
Vegas under contract to the Clark County Department of Air Quality 
and Environmental Management. See Appendix A1 in the Interim 
Guidance on the Preparation of Demonstrations in Support of Requests 
to Exclude Ambient Air Quality Data Affected by High Winds Under the 
Exceptional Events Rule. U.S. EPA. May 2013, and Refined PM10 
Aeolian Emission Factors for Native Desert and Disturbed Vacant Land 
Areas. Final Report, June 30, 2006.
---------------------------------------------------------------------------

    The EPA will continue to consider an area's high wind threshold 
when reviewing demonstrations for events in a nonattainment or 
maintenance area where the EPA has approved a SIP, TIP or FIP within 5 
years of the date of the event. For a demonstration in such a case, the 
not reasonably controllable criterion hinges only on implementation of 
the control measures in the SIP, TIP or FIP, not on the content of 
those measures. For events with sustained wind speeds above the high 
wind threshold that occur simultaneously with high monitored PM 
concentrations, it is very plausible that SIP, TIP or FIP controls were 
being implemented and the high PM concentrations resulted from 
emissions generated by sources in the area despite implementation of 
those controls. Conversely, for events with sustained wind speeds below 
the high wind threshold, it becomes more plausible that there may be 
noncompliance with control measures or that anthropogenic sources 
unrelated to the event (e.g., dust from traffic for a special event) 
are contributing to the exceedance. Therefore, the comparison of 
sustained wind speeds during an event to the high wind threshold will 
help the EPA Regional offices determine what evidence must be included 
in a demonstration. Specifically, it will inform the evidence required 
for the not reasonably controllable or preventable criteria, the 
possibility of noncompliance, or emissions from non-event sources.
    Similarly, the high wind threshold also aids in determining whether 
a high wind dust event that includes emissions from anthropogenic 
sources can be considered a natural event. We have clarified that 
natural events can recur, sometimes frequently, and that we consider 
reasonably controlled anthropogenic emissions sources to play little or 
no direct role in causing emissions. For high wind dust events, if 
sustained wind speeds are above the high wind threshold and the 
anthropogenic emissions sources are reasonably controlled, it is more 
likely that human activity plays little or no direct role in causing 
emissions. Conversely, if sustained wind speeds are below the high wind 
threshold it is more likely that human activity does have a direct role 
in causing emissions because significant emissions under low wind 
conditions only occur if the area has been disturbed by human activity 
and those sources have not been reasonably controlled.
    As noted in the proposed rule preamble and in the Interim High 
Winds Guidance, as part of an exceptional events demonstration for high 
wind dust events, the EPA expects air agencies to provide relevant wind 
data (e.g., wind speed and direction). Wind speed data consist of 
analyses and statistics showing how the observed sustained wind speed 
compares to the established high wind threshold and demonstrates a 
relationship between the sustained wind speeds and measured PM 
concentrations at a particular monitoring location. The EPA has 
recommended that air agencies show these analyses as part of the clear 
causal relationship criterion discussed in Section IV.E.3 of this 
preamble. The EPA has encouraged air agencies to discuss wind direction 
in the narrative and to present wind direction data graphically in 
maps/plots in the clear causal relationship section of the high wind 
dust events demonstration.
    The EPA will review any demonstration for a high wind dust event 
not meeting the criteria for a ``large-scale and high-energy'' 
described in the next paragraph on a case-by-case basis. In doing so, 
the EPA will consider what controls are reasonable in light of an 
area's attainment status and associated CAA control requirements, the 
frequency, and range of typical high wind dust events known (at the 
time of the particular event that is the subject of the demonstration) 
to occur in the area.
    Large-Scale and High-Energy High Wind Dust Events. Many commenters 
supported the EPA's proposed rule language to apply a case-specific 
approach when considering reasonableness of controls for remote, large-
scale, high-energy and/or sudden high wind dust events, such as 
``haboobs,'' where sustained wind speeds can exceed 40 mph and generate 
walls of dust several miles wide and more than a mile high. As a 
result, we are finalizing this provision with several clarifying 
changes to the proposed language at 40 CFR 50.14(b)(5)(vi), which read, 
``For remote, large-scale, high-energy and/or sudden high wind dust 
events, such as ``haboobs'' in the southwest, the Administrator will 
generally consider a demonstration documenting the nature and extent of 
the event to be sufficient with respect to the not reasonably 
controllable criterion of paragraph (c)(3)(iv)(D) of this section.'' We 
have changed this terminology to ``a large-scale and high-energy high 
wind dust event.'' We have removed the phrase ``such as haboobs in the 
southwest'' as a result of commenter feedback identifying that 
``haboobs'' occur in places other than the ``southwest.'' We agree with 
the commenter. We removed the descriptive terms ``remote'' and 
``sudden'' because we found that these words do not effectively change 
the characteristics of the type of event that we intend to include as 
``a large-scale and high-energy'' high wind dust event. Thus, provided 
the event meets the identified criteria for a ``large-scale and high-
energy'' high wind dust event, it could qualify for case-specific 
treatment with respect to the not reasonably controllable or 
preventable criterion.
    Some areas of the country may claim that, because of local 
topography and meteorology, each PM exceedance that occurs in their 
jurisdiction would qualify as a ``large-scale and high-energy'' high 
wind dust event. While we acknowledge that large-scale and high-energy 
high wind dust events in a particular area may be associated with 
meteorological conditions unique to that area, we also believe that to 
qualify for the specific exclusion at 40 CFR 50.14(b)(5)(vi), a large-
scale and high-energy high wind dust event must: Be associated with a 
dust storm,\86\ have sustained wind speeds greater than or equal to 40 
mph, have reduced visibility equal to or less than 0.5 miles,\87\ be 
the focus of a ``Dust Storm Warning'' issued by the NWS (or a similar 
scientifically-based government entity) and include NWS (or a similar 
scientifically-based government entity) observations of dust storms and 
blowing dust. In addition, the event must be associated with measured 
exceedances occurring at multiple monitoring sites over a large 
geographic area unless the area has only a single PM monitor or if the 
area has monitors operating on a sampling frequency that does not 
coincide with the timing of the event.
---------------------------------------------------------------------------

    \86\ The NWS defines a dust storm as a severe weather condition 
characterized by strong winds and dust-filled air over an extensive 
area. See definition at http://w1.weather.gov/glossary/.
    \87\ Many NWS distributed alerts and advisories include 
visibility estimates. In addition, many airports provide estimates 
of surface visibility. Air agencies may also be able to use 
nephelometers to determine visibility.

---------------------------------------------------------------------------

[[Page 68260]]

    Best Management Practices. After consideration of the public 
comments, as discussed more fully in this paragraph, we are finalizing 
here as guidance that, on a source or area-specific basis, we would 
accept as ``reasonable controls'' for purposes of satisfying the not 
reasonably controllable or preventable criterion for a particular 
potentially contributing source, those USDA/NRCS-approved BMPs designed 
to effectively reduce fugitive dust air emissions and prevent soil loss 
in agricultural applications in cases where these measures have been 
incorporated into an EPA-approved SIP, FIP or TIP or incorporated into 
state laws, regulations or local ordinances and where those measures 
consist of controls specific to the pollutant and potentially 
contributing source.
    As we discuss in Section IV.E.2.b of this preamble, when addressing 
the not reasonably controllable or preventable criterion within an 
exceptional events demonstration, air agencies should: (1) Identify the 
natural and anthropogenic sources of emissions causing and contributing 
to the monitored exceedance or violation, including the contribution 
from local sources, (2) identify the relevant, enforceable control 
measures in place for these sources and the implementation status of 
these controls, and (3) provide evidence of effective implementation 
and enforcement of reasonable controls, if applicable. For example, 
applying this approach to farm- and operation-specific BMPs for a high 
wind dust event that occurs during harvest time, an air agency would 
identify the potentially contributing agricultural source (e.g., 
harvesting operations of crop X), identify the relevant BMP (e.g., 
baling, which reduced PM emissions from residue burning and chopping) 
and provide evidence of penetration, scale and intensity (e.g., baling 
applied at X of Y acres).
c. Comments and Responses
    We noted in the final rule portion of the High Winds Dust Events 
section of this preamble that we did not receive comments related to 
the definition of either high wind dust event or high wind threshold. 
We further noted in the previous discussion that commenters did provide 
feedback regarding establishing, in rule, a high wind threshold of 25 
mph. Several commenters supported this definition either as proposed or 
with the clarification that air agencies could develop as an 
alternative to the 25 mph high wind threshold, their own area-specific 
high wind threshold that is more representative of local/regional 
conditions. As already indicated, we have included this clarification 
in the regulatory text. Several of the commenters suggesting this 
revision also asked that the regulatory language include a provision 
that exceptional events can still occur at wind speeds less than 25 
mph. We have not included this change as we believe that allowing areas 
to establish their own threshold will largely address this potential 
issue. Additionally, as stated in the proposal and in this final 
action, the EPA will review other events on a case-by-case basis 
considering the merits of each specific case. Still more commenters 
recommended keeping the high wind threshold as guidance rather than 
rule as it is ``overly restrictive.'' The EPA believes these revisions 
provide sufficient additional flexibility to address this concern.
    Another commenter asked that we include in this final action 
language from our Interim High Winds Guidance, which stated ``high 
winds could be the cause of a high 24-hour average PM10 or 
PM2.5 concentration if there was at least one full hour in 
which the hourly average wind speed was above the area-specific high 
wind threshold.'' We still believe this is an accurate statement, and 
we are noting this point in this final action.
    As we noted previously, many commenters supported the EPA's 
proposed rule language to apply a case-specific approach when 
considering reasonableness of controls for large-scale and high-energy 
high wind dust events, such as ``haboobs.'' Another commenter noted 
that haboobs should not have special treatment under the rule 
revisions. This same commenter asked that we define large-scale and 
high-energy events, which we have done in the discussion of the final 
rule. Regarding special treatment of these types of events, we maintain 
that some events are of a scale and intensity that they would have 
overwhelmed all reasonable controls and other efforts to minimize wind-
blown dust emissions. We maintain that such events warrant different 
treatment under the Exceptional Events Rule. We do, however, note that 
air agencies will need to provide evidence that the claimed event 
satisfied all of the other Exceptional Events Rule criteria.
    We have incorporated relevant commenter feedback regarding BMP into 
our discussion of BMP in the final rule section of this action. We note 
that one additional commenter asked that we clarify whether the 
fugitive dust control plans included in approved air quality permits 
are or can represent reasonable controls for permitted sources. While 
we are not addressing this comment here, we note that we discuss the 
relationship between BACM or fugitive dust control plans and reasonable 
controls in our comments and responses section of the not reasonably 
controllable or preventable portion of this final action (see Section 
IV.E.2.c of this preamble).

G. Other Aspects of Identifying Exceptional Events-Influenced Data and 
Demonstration Submittal and Review

    This portion of the proposed rule discussed the eight topics 
identified in the following sections, as well as a ninth topic 
addressing who may submit a demonstration for data exclusion. Because 
we identify, discuss and respond to questions regarding those entities 
that are allowed to submit a demonstration in Section IV.A of this 
preamble and because the proposal contained no additional items needing 
clarification, we omit that topic in this part of the final action.
1. Aggregation of Events
a. Summary of Proposal
    The EPA proposed and solicited comment on guidance in the preamble 
and rule text allowing 24-hour concentrations of any NAAQS pollutant to 
be compared to a NAAQS level defined for a longer period as part of a 
weight of evidence showing for the clear causal relationship with 
respect to the NAAQS with the longer period and the NAAQS with the 
shorter period. This proposed approach allowed for examining one day at 
a time. For example, if an event were demonstrated to have caused a 24-
hour concentration of SO2 to exceed the level of the annual 
SO2 NAAQS, the air agency and the EPA would consider this to 
be a demonstration that the event caused an ``exceedance or violation'' 
with respect to the 24-hour NAAQS and the annual NAAQS. This would 
avoid the need to determine if the 1-day effect of the event was enough 
to cause the annual average concentration of SO2 to exceed 
the level of the annual SO2 NAAQS. It would also allow the 
data from a day to be excluded from calculation of the design value for 
the 24-hour SO2 NAAQS even if the event did not cause an 
exceedance of the level of the 24-hour SO2 NAAQS. However, 
such exclusion would be unlikely to be material to compliance with the 
24-hour SO2 NAAQS if there was no such exceedance of the 
level of the 24-hour SO2 NAAQS.
    The EPA also proposed to allow air agencies to aggregate either 
similar or dissimilar events (e.g., stratospheric ozone intrusion 
followed by a wildfire

[[Page 68261]]

or two distinct wildfires) that influence the same NAAQS but that occur 
on different days for the purpose of determining whether their 
collective effect has caused an exceedance or violation. The proposed 
event aggregation process would apply only for NAAQS with averaging or 
cumulative periods longer than 24 hours. Although we proposed this 
approach to event aggregation, we also indicated that it may be 
difficult to implement if the effects of the individual events on their 
individual days are not fully quantified. We proposed rule text and 
solicited comment on this approach.
b. Final Rule
    After consideration of the public comments, as discussed more fully 
in the subsequent section, we are finalizing, as proposed and as 
supported by several commenters, rule language that will allow an air 
agency to compare a 24-hour concentration of any NAAQS pollutant to the 
NAAQS for the same pollutant with a longer averaging period as part of 
a weight of evidence showing for the clear causal relationship with 
respect to the NAAQS with the longer period. As we discussed in the 
proposal, the EPA's AQS database houses ambient air quality monitoring 
and related data. The data in AQS are maintained as individual reported 
measurements, which can range from 5-minute maximum concentrations per 
hour for SO2, to hourly data for ozone, CO, NO2, 
SO2 and some PM measurements, to 24-hour measurements for 
lead and other PM measurements. Under the 2007 Exceptional Events Rule, 
air agencies identify individual measurements in AQS and compare these 
measurements to the subject NAAQS to determine whether an exceedance or 
violation occurred. When the averaging period for the NAAQS is the same 
as the measurement duration period, this comparison is relatively 
straightforward. For example, air agencies and the EPA can directly 
compare 1-hour ozone, 1-hour CO, 1-hour SO2, and 1-hour 
NO2 measurements to the respective 1-hour NAAQS. This 
comparison becomes more complicated, however, when there is a 
difference between the pollutant measurement duration and the averaging 
time of the NAAQS, which is the case when comparing a 1-hour 
measurement to an 8-hour, 24-hour, 3-month or annual NAAQS (or in the 
case of 1-hour ozone, the previously existing NAAQS, which may still 
apply in certain areas). The provision that we are finalizing allows an 
air agency to compare a 24-hour concentration of any NAAQS pollutant to 
the NAAQS for the same pollutant with a longer averaging period as part 
of the clear causal relationship showing. Using Table Q30-2 in the 
Interim Q&A document \88\ as a guide, this rule revision will allow an 
air agency to compare a 24-hour averaging period for PM2.5 
to either the 24-hour PM2.5 NAAQS or the annual NAAQS. 
(Note: If air agencies desire to exclude the identified concentration 
for both the 24-hour and the annual PM2.5 NAAQS, they need 
to specifically request exclusion for both NAAQS, assuming regulatory 
significance for both standards.) Air agencies could also compare a 24-
hour lead measurement to the rolling 3-month averaging period. A number 
of commenters supported the provision as proposed. One commenter, 
however, indicated that comparing a 24-hour concentration of any NAAQS 
pollutant to the NAAQS for the same pollutant with a longer averaging 
period is an ``apples to oranges'' analysis that could increase 
uncertainty and decrease the quality of the demonstration. The EPA 
acknowledges the commenter's perspective, but believes that 
clarification is needed regarding the comparison of measured 
concentrations to ambient air quality standards because, as we have 
explained, the measurement time frames do not often agree with the 
averaging period of the NAAQS. In preparing demonstrations, air 
agencies have often asked the EPA Regional offices whether such 
comparisons are allowed under the Exceptional Events Rule, and, if they 
are, how to present such comparisons in a demonstration. Our preamble 
discussion about these comparisons and our promulgation of associated 
rule language responds to these comments and provides clarity. We also 
note that the 2007 rule preamble discussed and allowed this type of 
comparison for the specific case of the PM2.5 annual NAAQS 
and the 24-hour PM2.5 NAAQS. We are extending this concept 
to all similar NAAQS comparisons.\89\
---------------------------------------------------------------------------

    \88\ Interim Exceptional Events Rule Frequently Asked Questions. 
U.S. EPA. May 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/eer_qa_doc_5-10-13_r3.pdf.
    \89\ 72 FR 13570 (March 22, 2007).
---------------------------------------------------------------------------

    We are also finalizing regulatory language allowing air agencies to 
aggregate either similar or dissimilar events (e.g., stratospheric 
ozone intrusion followed by a wildfire or two distinct wildfires) that 
influence the same NAAQS but that occur on different days for the 
purpose of determining whether their collective effect has caused an 
exceedance or violation of a NAAQS with an averaging or cumulative 
period longer than 24 hours.\90\ That is, when considered individually, 
each event would not separately need to result in an exceedance or 
violation of a given NAAQS. The collective effect of the aggregated 
events would, however, need to cause an exceedance or violation of a 
NAAQS with an averaging or cumulative period longer than 24 hours. 
Also, as part of this aggregation approach, the air agency must show 
that each identified event separately satisfies each of the three 
technical rule criteria (i.e., human activity/natural event, not 
reasonably controllable or preventable, and clear causal relationship). 
For the clear causal relationship showing, the air agency would need to 
definitively show that each discrete event contributed to the elevated 
concentrations and that, together, the cumulative effect of the events 
caused the exceedance or violation of a NAAQS with an averaging or 
cumulative period longer than 24 hours. We do not intend our approach 
for event aggregation to allow for the aggregation of unnamed events or 
events that occur over the course of an extended timeframe. Two 
commenters urged the EPA to remain silent on this provision and not 
include it in rule language, while several other state, local, tribal 
and association commenters supported the provision as proposed. To 
clarify, the final rule text also includes a statement that air 
agencies may aggregate events occurring on the same day and compare the 
cumulative effects to a NAAQS with an averaging period of 24 hours or 
less. As previously noted, for the clear causal relationship showing, 
the air agency would need to definitively show that each discrete event 
contributed to the elevated concentrations and that, together, the 
cumulative effect of the events caused the exceedance or violation of 
the NAAQS and that each identified event separately satisfies each of 
the three technical rule criteria (i.e., human activity/natural event, 
not reasonably controllable or preventable, and clear causal 
relationship).
---------------------------------------------------------------------------

    \90\ See 80 FR 72882, which proposed allowing event aggregation 
occurring on different days for NAAQS with averaging or cumulative 
periods longer than 24 hours. It is not appropriate to aggregate the 
effects of events occurring over more than a 24-hour period to a 
standard that is less than or equal to 24 hours.
---------------------------------------------------------------------------

    We provide a specific approach to aggregating wildfire-related 
events that occur in different locations on the same day in the 
Wildfire Guidance, which we are releasing concurrently with this 
action. The aggregation methodology in the Wildfire Guidance applies 
for purposes of determining whether a given wildfire could use a tiered

[[Page 68262]]

approach to satisfy the clear causal relationship criterion in a 
demonstration for an ozone standard (i.e., either a 1-hour or an 8-hour 
standard). The current ozone NAAQS do not meet the pre-conditions for 
the aggregation approach discussed here, which requires the averaging 
or cumulative period of the standard to be longer than 24 hours. 
Additionally, use of the aggregation approach in the Wildfire Guidance 
would occur only after an exceedance or violation of the relevant ozone 
NAAQS versus the aggregation approach that we are finalizing in rule 
text that would allow aggregation to determine whether an exceedance or 
violation occurred. For these reasons, the regulatory approach to 
aggregation and the specific approach for wildfires that may influence 
ozone concentrations cannot be interchanged.
c. Comments and Responses
    We address any additional comments received on this topic in the 
Response to Comments document found in the docket for this action.
2. Demonstrations With Respect to Multiple NAAQS for the Same Pollutant
a. Summary of Proposal
    The proposal solicited comment on whether a successful 
demonstration with respect to any NAAQS for a given pollutant would 
suffice to qualify the data in question for exclusion with respect to 
all NAAQS for that pollutant. For example, the ``approved for one NAAQS 
approved for all NAAQS for the same pollutant'' concept would have 
allowed an air agency to prepare a demonstration for a 1-hour NAAQS 
and, if concurred, exclude data for both a 1-hour and an 8-hour NAAQS 
for the same pollutant.
b. Final Rule
    Several commenters supported promulgating rule text for the 
proposed concept that a successful demonstration with respect to any 
NAAQS for a given pollutant would suffice to qualify the data in 
question for exclusion with respect to all NAAQS for that pollutant, 
but one commenter noted that this pathway is unlawful and would allow 
air agencies an easier path to exclude unfavorable data. After 
considering the feedback, we are retaining our current approach to 
excluding data on a NAAQS-specific basis with the previously identified 
clarifications for certain measurements and certain NAAQS. CAA section 
319(b)(3)(B)(ii) refers to ``the measured exceedances of a national 
ambient air quality standard'' (emphasis added); CAA section 
319(b)(3)(B)(iv) references excluding data from use in determinations 
with respect to ``exceedances or violations of the national ambient air 
quality standards.'' These passages do not clearly say that the EPA 
must or may allow data to be excluded for the purposes of all NAAQS for 
a given pollutant if the conditions for exclusion are satisfied for one 
of the NAAQS but not all of them. Even assuming arguendo that that the 
passages permit the EPA to allow such exclusions, we believe that we 
would be undermining the public health and welfare purpose of the NAAQS 
if we were to allow such broad exclusion. One public commenter provided 
a cogent statement of this fact. The CAA also directs that protection 
of public health is the highest priority. The commenters in favor of 
broad exclusion did not provide a legal or public health protection 
basis for their recommendations. Therefore, neither the final rule nor 
the preamble to the final rule includes language or guidance for the 
proposed ``approved for one NAAQS approved for all NAAQS for the same 
pollutant'' concept.
c. Comments and Responses
    We address any additional comments received on this topic in the 
Response to Comments document found in the docket for this action.
3. Exclusion of Entire 24-Hour Value Versus Partial Adjustment of the 
24-hour Value for Particulate Matter
a. Summary of Proposal
    Citing Question 29 of the Interim Q&A document, the proposal 
articulated the EPA's current recommendation that air agencies 
preparing demonstrations to support requests to exclude 
PM2.5 and PM10 data obtained via monitor 
instruments that provide 1-hour measurements should flag all 24 1-hour 
values within a given event-affected day and consider the effect of the 
event on the 24-hour average concentration, even if the event did not 
last all these hours. If concurred upon, flagging all 1-hour values and 
considering the effect of the event on the 24-hour average 
concentration relative to the level of the 24-hour NAAQS ultimately 
results in the same available remaining data for regulatory analysis 
and calculation as would be the case had the 24-hour PM2.5 
or PM10 measurement data been collected from filter-based 
(24-hour) monitoring instruments.\91\ We further recommended that 
flagging all 24 1-hour values is appropriate because flagging only peak 
or selected hours could result in the remaining 1-hour values still 
meeting the data completeness requirements, even though there may be 
very few remaining 1-hour measurements, because flagged and excluded 
data do not count against completeness even though they cannot be used 
in calculating an average concentration for a 24-hour period. Under the 
rules for data interpretation, exclusion of only the event-affected 1-
hour concentrations could result in AQS calculating a seemingly valid 
24-hour concentration that is actually highly uncertain because it is 
based on only a few hours and thus may be biased relative to the actual 
24-hour concentration or the 24-hour concentration that would have 
existed in the absence of the event.\92\ The proposal solicited comment 
on codifying this approach in rule text to eliminate any regulatory 
uncertainty.
---------------------------------------------------------------------------

    \91\ Filter based instruments typically record a single value 
within a 24-hour period while continuous monitors typically collect 
24 1-hour measurements. Because AQS can calculate a valid 24-hour 
average concentration with as few as 18 hours, it may be necessary 
to exclude hours not actually affected by the event to ensure the 
same data exclusion outcome as if the measurement had been made with 
a 24-hour filter.
    \92\ The form of the 24-hour PM2.5 NAAQS of 35 [mu]g/
m\3\ is 98th percentile averaged over 3 years. The form of the 
primary annual PM2.5 NAAQS of 12 [mu]g/m\3\ is an annual 
mean averaged over 3 years. The form of the 24-hour PM10 
NAAQS of 150 [mu]g/m\3\ is not to be exceeded more than once per 
year on average over 3 years. Biased concentrations can potentially 
skew the determination of the 98th percentile and/or the annual mean 
for PM2.5 and the averages for PM2.5 or 
PM10 calculated to determine compliance with the relevant 
NAAQS.
---------------------------------------------------------------------------

b. Final Rule
    After considering the public comments we received, and for the 
reasons discussed in our proposed rule section, we are finalizing 
regulatory language, supported by a number of commenters, to exclude 
all 24 1-hour values within a given event-affected day for 
PM2.5 and PM10 data obtained via monitor 
instruments that provide 1-hour measurements. We believe that the 
exclusion of all hours in a given event-affected day is appropriate, 
consistent with the approach for filter based analyzers, and will 
eliminate the calculation of uncertain and potentially biased daily 
values for PM2.5 and PM10 NAAQS. We also agree 
with three commenters who suggested that the EPA modify the programming 
in AQS to automatically flag all remaining hourly values in the 24-hour 
period if an air agency flags only the event-influenced hours within 
AQS. The EPA will program the identified changes within AQS.
c. Comments and Responses
    We address any additional comments received on this topic in the 
Response

[[Page 68263]]

to Comments document found in the docket for this action.
4. Flagging of Data
a. Summary of Proposal
    The EPA proposed to revise the ``general'' schedule language 
contained within 40 CFR 50.14(c)(2) by removing the timelines 
associated with initial event flagging. We also proposed to modify the 
associated data flagging process within AQS to correspond with the 
proposed regulatory changes.\93\ Specifically, the revisions proposed 
to modify the flagging of exceptional event data by defining 
``flagging'' as the application of the one- or two-character event type 
and event description text as described in the following paragraph, 
along with a concurrent or subsequent request for data exclusion 
communicated to the EPA through the Initial Notification of Potential 
Exceptional Event process.
---------------------------------------------------------------------------

    \93\ ``Flag'' is the common terminology for a data qualifier 
code in the EPA's AQS. Unless explicitly noted, the process of 
``flagging'' data refers to adding Request Exclusion (R) data 
qualifier codes (R flags) to selected data in AQS. R flags are the 
only AQS flags that satisfy the 2007 Exceptional Events Rule 
requirement for initial data flagging. The current design of the AQS 
software is such that the EPA can act/concur only on an R flag.
---------------------------------------------------------------------------

    The proposal noted that because the flagging of data necessarily 
begins with the identification of an event, the EPA proposed to retain, 
with modifications, the AQS free-form text field for an initial event 
description. As is currently the practice, we would request that air 
agencies use the ``initial event description'' to identify a unique, 
real-world event. We proposed to expand this ``initial event 
description'' to contain a unique event name; the type of the event 
(e.g., high wind dust, volcanic eruption, other); a brief description 
of the event; and, to the extent known, the scope of the event in terms 
of geography and time (e.g., likely affected area using latitude and 
longitude and a radius of influence and beginning day/time and ending 
day/time).\94\ We proposed to simplify the process in AQS to allow the 
air agency to associate specific AQS sites and potentially affected 
monitors and specific data points with a given event as so described. 
We noted that this would enable air agencies and the EPA to ``flag'' or 
add qualifier codes to selected data in a single step rather than 
adding this information or the necessary codes on a per entry basis. 
Historically, when events have influenced the concentrations at 
multiple monitors for multiple days, the air agency has added initial 
event descriptions and set flags on each monitored concentration, 
sometimes resulting in hundreds of identical individual entries. The 
proposal noted that ``associating'' monitors with an event defined in 
time and space will save resources.
---------------------------------------------------------------------------

    \94\ The EPA is proposing that air agencies select the ``type of 
event'' from a pre-set list of event types, which would likely 
consist of those event types currently identified by existing 
Informational and R flags within AQS.
---------------------------------------------------------------------------

    The proposal noted that the process of requesting exclusion for 
identified data would consist of two discrete operations: (1) 
Indicating in a separate communication to the EPA that specific ambient 
air quality measurements are affected by a defined event (see Section 
IV.G.5 of this preamble related to Initial Notification of Potential 
Exceptional Event), and (2) requesting that these identified ambient 
air quality measurements be excluded from regulatory actions according 
to the Exceptional Events Rule and/or the EPA's guidance for other 
applications of air quality data. The proposal indicated that AQS would 
retain a field to allow the EPA to concur or not concur with a given 
request for exclusion for one or more of the data points associated 
with a described event, once review of the air agency's request and 
demonstration is completed.
    As noted previously, we proposed to remove the ``general'' flagging 
schedule in 40 CFR 50.14(c)(2)(iii), which requires that air agencies 
submit R flags and an initial description of the event by July 1 of the 
calendar year following the year in which the flagged measurement 
occurred or by the other deadlines identified with individual NAAQS. 
The proposal noted that an air agency may not know that data influenced 
by an exceptional event caused a violation of a NAAQS until after the 
initial event flagging deadline has passed. We proposed to remove the 
current language at 40 CFR 50.14(c)(2)(iii) and reserve that section 
number.
b. Final Rule
    As proposed, and as supported by numerous commenters, we are 
removing the ``general'' flagging schedule in 40 CFR 50.14(c)(2)(iii), 
which requires that air agencies submit request exclusion flags and an 
initial description of the event by July 1 of the calendar year 
following the year in which the flagged measurement occurred or by the 
other deadlines identified with individual NAAQS. We are making this 
change because flagging data by the previously indicated deadlines can 
be difficult in the case of an annual standard where an air agency 
needs all 12 months of data to calculate an annual average and then 
needs 3 years of annual averages to identify whether or not the event-
influenced data results in a violation of a 3-year design value. An air 
agency may not know that data influenced by an exceptional event caused 
the design value to become a NAAQS violation until 3 years after the 
event occurred. No commenters disagreed with this proposal.
    One commenter requested that AQS retain the ability to incorporate 
informational flags in the data identification process. This commenter 
noted that informational flagging has uses beyond the exceptional 
events process. We are retaining informational flags in AQS.
c. Comments and Responses
    We address any additional comments received on this topic in the 
Response to Comments document found in the docket for this action.
5. Initial Notification of Potential Exceptional Event
a. Summary of Proposal
    As part of the best practices for communications \95\ during the 
exceptional events process and to aid all agencies in resource planning 
and prioritization, the EPA proposed that air agencies and the EPA 
engage in regular communications to identify those data that have been 
potentially influenced by an exceptional event, to determine whether 
the identified data affect a regulatory determination, and to discuss 
whether an air agency should develop and submit an exceptional events 
demonstration. The proposal indicated that most of these discussions 
would be between individual air agencies and the reviewing EPA Regional 
office, but some discussions could involve a group discussion between 
the EPA Regional office and all air agencies in the region followed by 
individual discussions, as needed. In still other cases, such as where 
large events cross state lines and when two or more states are pursuing 
exclusion for the same event(s), the EPA region or regions may initiate 
discussions with all potentially affected states/agencies to assist in 
coordinating states affected by regional events.
---------------------------------------------------------------------------

    \95\ Between September 2014 and March 2015 the EPA held 
conference calls with some air agencies to ask about exceptional 
events implementation concerns and to better understand currently 
employed exceptional events implementation processes and practices. 
As a result of these discussions, the EPA developed a list of best 
practices for communication and collaboration between the EPA and 
air agencies, a summary of which is available at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.
---------------------------------------------------------------------------

    The EPA referred to these communications as the ``Initial

[[Page 68264]]

Notification of Potential Exceptional Event'' (Initial Notification) 
process and described the purpose of the Initial Notification process 
as initiating conversations between an air agency and the EPA if not 
already on-going, or engaging in more detailed discussions if a process 
is currently in place, regarding specific data and whether the 
identified data are ripe for submittal as exceptional events. As 
stakeholders have repeatedly expressed and as the EPA acknowledges, the 
identification of data affected by exceptional events and the 
subsequent preparation, submittal and review of demonstrations is a 
resource intensive process both for the preparing air agency and the 
reviewing EPA Regional office.
    The proposal also noted that if these data do not have regulatory 
significance, then engaging in the development and review of an 
exceptional events demonstration is generally not an efficient use of 
an air agency's or the EPA's limited resources. As described in the 
proposal, the Initial Notification process would focus efforts on the 
relevant data and provide the EPA with the opportunity to convey to the 
affected air agency our initial thoughts regarding the identified event 
and analyses that may or may not be appropriate for inclusion in a 
demonstration, and, with respect to regulatory significance, which 
demonstrations the EPA will consider for review.
    The proposal indicated that the Initial Notification could include 
any form of communication (e.g., letter, email, in-person meeting with 
an attendees list and discussion summary or phone conversation with 
follow-up email) that ultimately identifies the potential need to 
develop an exceptional events demonstration and communicates key 
information related to the data identified for potential exclusion. 
Where an air agency independently identifies event-affected data and 
the need to submit an exceptional events demonstration outside of its 
regular, on-going communications with the EPA Regional office, the air 
agency could prepare a letter or email communicating its Initial 
Notification. Generally, the EPA anticipates that air agencies would 
develop and provide an Initial Notification as soon as the agency 
identifies event-influenced data that potentially influence a 
regulatory decision or when an agency wants the EPA's input on whether 
or not to prepare a demonstration.\96\ The EPA further proposed that 
each Initial Notification would include the following components:
---------------------------------------------------------------------------

    \96\ The EPA recognizes that air agencies can immediately 
identify those events that result in an exceedance of a NAAQS with a 
short averaging time (e.g., 1-hour, 8-hour or 24-hour standards) but 
may need additional time for an annual average standard. An air 
agency could also submit an annual Initial Notification if annual 
submittal makes sense for resource planning or for recurring 
seasonal events.
---------------------------------------------------------------------------

     Unique event name (field in AQS)--facilitates future 
communication and understanding between the submitting air agency and 
the reviewing EPA Regional office, particularly if an air agency has 
submitted multiple exceptional events demonstrations.
     Initial event description (field in AQS)--provides a brief 
narrative of the event that could also include maps or graphs similar 
to what an air agency might include in the narrative conceptual model 
discussed in Section IV.G.6 of this preamble; the event description 
would include a qualitative description of the event and, at a minimum, 
briefly describe the air agency's current understanding of interaction 
of emissions with the event, transport and meteorology (e.g., wind 
patterns such as strength, convergence, subsidence, recirculation) and 
pollutant formation in the area.
     Affected regulatory decision--provides a description of 
the regulatory action or actions potentially affected by the claimed 
event-influenced data and the anticipated timing of this action.
     Proposed target date for demonstration submittal--
identifies the proposed target date by which the air agency would 
submit a demonstration to the reviewing EPA Regional office.
     Most recent design value including and excluding the 
event-affected data--the air agency's assessment of the most recent 
design value both with and without the identified event(s) is helpful 
when assessing regulatory significance. The EPA cannot accurately 
calculate this value (and therefore may not be able to determine 
significance) if the air agency has flagged more data than it intends 
to include in an exceptional events demonstration.
     Information specific to each monitored day--see Table 5 
for an example of the type of table that could be used, which would be 
developed by the submitting air agency and generated from the initial 
event description in AQS (see discussion in Section IV.G.4 of this 
preamble).
[GRAPHIC] [TIFF OMITTED] TR03OC16.001

    The proposal indicated that, after one or more informal phone 
discussions with the air agency, the EPA would acknowledge an air 
agency's Initial Notification and then formally respond within 90 days 
of receipt of the Initial Notification via letter, email or in-person 
meeting with an attendees list and discussion summary. The response 
would provide the EPA Regional office's best assessment of the priority 
\97\ that can be given to the submission once received, any case-
specific advice the EPA may have to offer for the preparation of the 
demonstration, and the target date for demonstration submittal. Where 
the data are to be used in initial area designations, the EPA

[[Page 68265]]

proposed to rely on the documentation submission schedule that, at the 
time of the proposal, appeared as Table 1 at 40 CFR 
50.14(c)(2)(vi).\98\ Where the data would influence another near-term 
regulatory decision, the EPA proposed to rely on the case-by-case 
timelines by which the air agency should submit the demonstration. For 
case-by-case demonstrations, the EPA's recommended date for 
demonstration submittal would consider the nature of the event and the 
anticipated timing of the regulatory decision, and would allow time for 
both an air agency's preparation of the demonstration and the EPA's 
review. Additionally, the EPA would request in its response that, if 
the submitting air agency has not already identified the affected data 
within AQS, that it undertake this effort according to the process 
described in Section IV.G.4 of this preamble. If the data identified in 
the Initial Notification do not have regulatory significance as 
discussed in Section IV.B of this preamble, then the EPA would indicate 
this in its correspondence back to the air agency and would discourage 
the air agency from devoting resources to developing a demonstration 
because the EPA would likely not review or act upon the submittal.
---------------------------------------------------------------------------

    \97\ ``Priority'' refers to those exceptional events 
determinations that affect near-term regulatory decisions. 
``Regulatory decisions'' include findings as to whether the area has 
met the applicable NAAQS, classification determinations, attainment 
demonstrations (including clean data findings), attainment date 
extensions, findings of SIP inadequacy and other actions on a case-
by-case basis determined to have regulatory significance. See 
discussion in Section IV.B of this preamble for additional detail.
    \98\ This table appears as Table 2 at 40 CFR 50.14(c)(2)(vi) in 
the Exceptional Events Rule revisions that we are promulgating in 
this action.
---------------------------------------------------------------------------

    The proposal further noted that if the EPA has acknowledged as part 
of the Initial Notification process that identified data have 
regulatory significance (or some other compelling reason for excluding 
data), then the air agency should proceed with the development of a 
technical demonstration that satisfies the requirements in 40 CFR 50.14 
and accounts for any case-specific advice from the EPA and additional 
information in the EPA's guidance documents.\99\ The proposal specified 
that although air agencies could submit demonstrations for events that 
do not affect a regulatory action, the EPA would likely not review or 
act on such submittals.
---------------------------------------------------------------------------

    \99\ Interim Guidance to Implement Requirements for the 
Treatment of Air Quality Monitoring Data Influenced by Exceptional 
Events. Memorandum from Stephen D. Page, U.S. EPA Office of Air 
Quality Planning and Standards, to Regional Air Directors, Regions 
I-X. May 10, 2013. Available at http://www2.epa.gov/sites/production/files/2015-05/documents/exceptevents_guidememo_130510.pdf.
---------------------------------------------------------------------------

    To support the previously summarized process, the EPA proposed to 
revise the language in 40 CFR 50.14(c)(2)(i) as follows: ``A State 
shall notify the [EPA] of its intent to request exclusion of one or 
more measured exceedances of an applicable national ambient air quality 
standard as being due to an exceptional event by creating an initial 
event description and flagging the associated data that have been 
submitted to the AQS database and by engaging in the Initial 
Notification of Potential Exceptional Event process . . . .'' The EPA 
solicited comment on the proposed rule text revision (in 40 CFR 
50.14(c)(2)) to require an Initial Notification of Potential 
Exceptional Event, with a provision that the EPA could waive the 
Initial Notification requirement on a case-by-case basis. We also 
solicited comment on making the Initial Notification of Potential 
Exceptional Event a voluntary process.
    The proposal also included the associated revisions to rule text at 
(ii): ``The data shall not be excluded from determinations with respect 
to exceedances or violations of the national ambient air quality 
standards unless and until, following the State's submittal of its 
demonstration pursuant to paragraph (c)(3) of this section and the 
Administrator's review, the Administrator notifies the State of its 
concurrence by placing a concurrence flag in the appropriate field for 
the data record in the AQS database.''
b. Final Rule
    In response to our solicitation for comment, several commenters 
indicated their desire for a voluntary Initial Notification of 
Exceptional Event process, while others indicated their desire that the 
Initial Notification process be promulgated in rule text as a 
requirement. To provide more regulatory certainty for all involved 
parties, we are finalizing the Initial Notification process as 
proposed, which includes a requirement for air agencies to engage in 
communications with the EPA once they identify a potential event; for 
air agencies to flag data within AQS, if appropriate; for the EPA to 
identify a demonstration submittal date that considers the nature of 
the event and the anticipated timing of the regulatory decision that 
may be affected by the exclusion of the flagged data; and an option for 
the appropriate EPA official to waive the Initial Notification 
process.\100\ We also intend to formally respond (via email or letter) 
to an air agency's Initial Notification within 60 days of receipt of 
the Initial Notification.\101\ We discuss the EPA's response timeframes 
in more detail in Section IV.G.7 of this preamble.
---------------------------------------------------------------------------

    \100\ As discussed in Section IV.A.2 of this preamble, if an air 
agency authorizes an FLM or other federal agency to prepare and 
submit exceptional events demonstrations directly to the EPA, the 
air agency should also indicate in this authorization whether an FLM 
can initiate the Initial Notification of Potential Exceptional Event 
process and whether this process would include or exclude the 
authorizing air agency.
    \101\ As previously indicated, the Initial Notification could 
include any form of communication (e.g., letter, email, in-person 
meeting with an attendees list and discussion summary or phone 
conversation with follow-up email) that ultimately identifies the 
potential need to develop an exceptional events demonstration and 
communicates key information related to the data identified for 
potential exclusion. The EPA's timeline for formally responding to 
an agency's Initial Notification is based on the date of receipt of 
the identified communication.
---------------------------------------------------------------------------

    When the EPA promulgated the revised ozone NAAQS in 2015,\102\ we 
revised the flagging, initial event description and demonstration 
submittal deadlines for data influenced by exceptional events for use 
in the initial area designations process. We did not propose any 
changes to this schedule as part of the proposed revisions to the 
Exceptional Events Rule. However, because we are finalizing the Initial 
Notification process in this action, which includes a requirement for 
air agencies to flag data within AQS, if appropriate, and characterize 
the identified event, we are revising the ``flagging and initial event 
description'' language in Table 2 to 40 CFR 50.14 that we promulgated 
with the ozone NAAQS to read ``Initial Notification.'' We are not 
changing the schedules for event-influenced data that may affect 
decisions associated with the initial area designations process.
---------------------------------------------------------------------------

    \102\ 80 FR 65292 (October 26, 2015).
---------------------------------------------------------------------------

c. Comments and Responses
    Other than the comments related to the ``voluntary'' versus 
``required'' nature of the Initial Notification process, the majority 
of the remaining comments on this topic pertained to the content of the 
Initial Notification and to the mechanics of communications between the 
EPA and affected air agencies. Two state commenters agreed with the 
proposed content of the Initial Notification to include: A unique event 
name, an initial event description, the affected regulatory decision, a 
proposed target date for demonstration submittal, the most recent 
design value (including and excluding the event-affected data), and 
basic information specific to each monitored day. Other commenters 
indicated that the content of the Initial Notification should not be 
specified. While we are not specifying required content in regulatory 
language, we are providing example content of an Initial Notification 
in this preamble. We also note that individual EPA Regional offices may 
implement procedures within their regions to assist with event

[[Page 68266]]

identification, prioritization and processing.
    Regarding communications between the EPA and affected air agencies, 
one commenter encouraged the EPA to ensure communication is formalized 
in writing and clarify that the EPA should initiate conversations 
regardless of the ``completeness'' of the notification to avoid 
confusion about whether the EPA has received the notification. Another 
commenter asked that we include regulatory language requiring that the 
EPA negotiate a timeline for demonstration submittal based on the 
available (and sometimes very limited) resources of the affected air 
agency. We interpret this comment to mean that the ``negotiation'' 
requirement would be a requirement for air agency agreement on the 
timeline for submittal rather than a consultation on timing.
    The EPA agrees with the commenter that decisions or specific 
direction provided or agreed to between the EPA Regional office and the 
affected air agency should be communicated in writing either by letter 
or email. By decisions or direction, we generally mean decisions 
regarding whether a potential event has regulatory significance 
(including the EPA's intent with respect to review), direction 
regarding specific event day(s) to pursue and/or information to include 
in a demonstration and decisions related to target dates for 
demonstration submittal. The EPA also agrees that we should acknowledge 
receipt, in writing, of any submitted written Initial Notification. We 
do not, however, agree with the other commenter's suggestion to include 
regulatory language requiring a negotiated timeline for demonstration 
submittal based on the available resources of the affected air agency. 
First, such a regulatory requirement would not provide for an outcome 
should the negotiations between the air agency and the EPA Region 
office fail to reach agreement. Also, an air agency's failure to meet a 
regulatory deadline could have different consequences than an air 
agency's failure to meet an EPA-identified target date. As we noted in 
the proposal and this preamble, the EPA will establish a target date 
for demonstration submittal, which the EPA will communicate in writing, 
after discussing the specifics of the potential event with the affected 
air agency and after considering the nature of the event, the 
anticipated timing of the regulatory decision, the target date for 
demonstration submittal proposed by the air agency as part of its 
Initial Notification (if provided), and the available time for both the 
air agency's preparation of the demonstration and the EPA's review. We 
believe this process adequately addresses the commenter's concerns 
without the need for regulatory text.
6. Submission of Demonstrations
a. Summary of Proposal
    With respect to the submission of demonstrations, the EPA proposed 
to make the following changes to the regulatory language in 40 CFR 
50.14(c)(3):
     Remove the general schedule provisions in 40 CFR 
50.14(c)(3)(i) for submitting demonstrations.
     Move the language requiring an air agency to include the 
comments it received during the public comment period for the subject 
demonstration from 40 CFR 50.14(c)(3)(i) to (v).
     Modify the language at 40 CFR 50.14(c)(3)(iv) to more 
clearly identify the required elements of an exceptional events 
demonstration to include (1) a narrative conceptual model and (2) 
demonstrations and analyses that address the core statutory technical 
criteria.
     Modify the language at 40 CFR 50.14(c)(3)(v) to identify 
that a demonstration submittal must include (1) documentation that the 
air agency conducted a public comment process on its draft exceptional 
events demonstration that was a minimum of 30 days, which could be 
concurrent with the EPA's review, (2) any public comments received 
during the public comment period and (3) an explanation of how the air 
agency addressed the public comments.
    As described in more detail in the proposed rule, the EPA proposed 
to remove the provision in 40 CFR 50.14(c)(3)(i) that requires air 
agencies to submit a demonstration ``not later than the lesser of 3 
years following the end of the calendar quarter in which the flagged 
concentration was recorded or 12 months prior to the date that a 
regulatory decision must be made by EPA.'' In place of this language, 
the EPA proposed to rely on the documentation submission schedule that, 
at the time of the proposal, appeared as Table 1 at 40 CFR 
50.14(c)(2)(vi) in those cases where the data are to be used in initial 
area designations. If the data could influence a regulatory 
determination other than an initial area designation, the EPA proposed 
to rely on the case-by-case timelines established by the reviewing EPA 
Regional office as part of the Initial Notification of Potential 
Exceptional Event process. As we noted when discussing removing the 
deadlines associated with initial event flagging in Section IV.G.4 of 
this preamble, air agencies have previously expressed concern that the 
timelines for event flagging and demonstration submittal are not always 
appropriate because an air agency may not know that data influenced by 
an exceptional event caused the design value exceedance until 3 years 
after the event occurred.\103\ The EPA has previously acknowledged that 
this scenario can and does occur, particularly for annual standards and 
when a regulatory decision is based on a design value that is averaged 
over 3 years.
---------------------------------------------------------------------------

    \103\ Responses to Significant First-Round Comments on the Draft 
Guidance Documents on the Implementation of the Exceptional Events 
Rule, U.S. EPA, June 2012. Available in Docket No. EPA-HQ-OAR-2011-
0887.
---------------------------------------------------------------------------

    With respect to the public comment provisions for a developed 
demonstration, the EPA proposed to move the language requiring an air 
agency to include the comments it received during the public comment 
period for the subject demonstration from 40 CFR 50.14(c)(3)(i) to (v) 
to consolidate the required elements of the public comment process for 
exceptional events demonstrations within a single regulatory provision. 
The proposal noted that the language at 40 CFR 50.14(c)(3)(i) requires 
that ``A State must submit the public comments it received along with 
its demonstration to EPA.'' The ``public comments it received'' refer 
to those obtained when the air agency follows the process outlined in 
40 CFR 50.14(c)(3)(v), which requires the air agency to document, and 
submit with its demonstration, evidence that it followed the public 
comment process.
    Because the public comment process described in the 2007 rule did 
not identify a duration for the public comment process, the EPA also 
proposed to specify a minimum 30-day public comment process, which 
provides sufficient time for exchange between the reviewing public and 
the air agency. We noted that shorter comment periods may not provide 
necessary time for the public to research the identified event and 
associated supporting data while longer timeframes may not be possible 
where a near-term regulatory decision relies on an exceptional events 
decision. The proposal stated that in very limited cases where the air 
agency is relying on exceptional events claims as part of a near-term 
regulatory action, such as an initial area designation decision for a 
new or revised NAAQS under a 2-year designation schedule, the public 
comment period could be concurrent with the EPA's review provided the 
submitting air agency sends any received public comments and

[[Page 68267]]

responses to the EPA by a specified date. If an air agency receives 
public comment disputing the technical elements of a demonstration 
during a comment period that runs concurrent with the EPA's review and 
these comments result in the air agency's need to reanalyze or reassess 
the validity of a claimed event, a second public comment period may be 
necessary.
    The EPA also proposed to revise the language at 40 CFR 
50.14(c)(3)(iv) so that it more clearly identifies the required 
elements of an exceptional events demonstration. The EPA proposed that 
each demonstration begin with a narrative conceptual model supported by 
summary tables or maps, which summarizes the event in question and 
provides context for required statutory technical criteria analyses. 
The EPA further proposed, consistent with other proposed changes, that 
an air agency include in its demonstration to justify data exclusion 
evidence that the following statutory technical criteria are satisfied:
     The event was a human activity that is unlikely to recur 
at a particular location or was a natural event.
     The event was not reasonably controllable or preventable.
     The event affected air quality in such a way that there 
exists a clear causal relationship between the specific event and the 
monitored exceedance or violation (supported in part by the comparison 
to historical concentrations and other analyses).
    The EPA sought comment on the identified proposed changes to the 
language at 40 CFR 50.14(c)(3)(i), (iv) and (v), which more clearly 
identify the required elements of an exceptional events demonstration.
b. Final Rule
    As with our proposal to remove the general schedule deadlines 
associated with initial event flagging, the overwhelming majority of 
commenters supported our proposal to remove the general schedule 
demonstration submittal deadlines contained within 40 CFR 
50.14(c)(3)(i). Therefore, upon consideration of those comments and for 
the reasons previously explained, we are promulgating this provision as 
proposed. One commenter expressed general support for this concept 
provided the deadline for demonstration submittals is not extended. In 
response, we note that while the deadline for demonstration submittal 
might be longer than it would have been under the previous deadline of 
``the lesser of 3 years following the end of the calendar quarter in 
which the flagged concentration was recorded or 12 months prior to the 
date that a regulatory decision must be made by EPA,'' we are not 
changing the timing of the regulatory actions in which the affected 
data may be used. Many of these deadlines are statutorily established 
and cannot be changed by regulation. Because the EPA is also 
accountable for these statutory deadlines, the effect of this now 
finalized exceptional events scheduling revision is compressing the 
timeline for the EPA's review.
    The final rule will provide limited flexibility regarding the 
deadline for submitting exceptional events demonstrations that are 
otherwise due October 1, 2016. Given the close proximity of the Federal 
Register publication date of this revised rule with the demonstration 
submittal deadline for data influenced by exceptional events that could 
be used in the initial area designation decisions for the 2015 Ozone 
NAAQS, we are intentionally adjusting the deadline for those 
demonstrations in Table 2 to Sec.  50.14 and intend for this deadline 
to apply to submissions that would otherwise be due October 1, 2016. 
This rule is being promulgated in advance of the October 1, 2016 
deadline for the 2015 Ozone NAAQS designations, providing stakeholders 
with sufficient notice of this updated submission deadline. As set 
forth in Table 2 to Sec.  50.14, exceptional events demonstrations must 
be submitted to the EPA on the later of (1) sixty days after the 
effective date of this rule or (2) the date that state and tribal 
recommendations are due to the Administrator. Going forward, 
exceptional events demonstrations will be due no later than the date 
that state and tribal designation recommendations are due to the 
Administrator.
    We received no significant comments regarding the proposed 
revisions associated with the public comment process. Therefore, for 
the previously explained reasons, we are finalizing, as proposed, the 
repositioning of the requirement that an air agency include any 
received public comments from 40 CFR 50.14(c)(3)(i) to (v). We are also 
promulgating the revised language at 40 CFR 50.14(c)(3)(v) to identify 
that a demonstration submittal must include (1) documentation that the 
air agency conducted a public comment process on its draft exceptional 
events demonstration that was a minimum of 30 days, which could be 
concurrent with the beginning of the EPA's initial review period, (2) 
any public comments received during the public comment period and (3) 
an explanation of how the air agency addressed the public comments. As 
indicated in 40 CFR 50.14(c)(3)(v)(A), we have also finalized 30 days 
as the minimum duration for a public comment period.
    We are promulgating revisions to the submission and required 
elements of an exceptional events demonstration at 40 CFR 
50.14(c)(3)(iv), as proposed, for the previously stated reasons and as 
supported by commenters. Regarding the requirement that components of a 
demonstration include a narrative conceptual model, one commenter asked 
that we use the terminology ``narrative'' or ``executive summary'' 
rather than ``conceptual model.'' We have retained the use of narrative 
conceptual model because we believe this best conveys our intent, which 
is the ``story'' or ``executive summary'' of the event that provides an 
overview of the technical information in the demonstration and helps 
identify relevant quantitative information critical in satisfying the 
Exceptional Events Rule criteria. In most cases, air agencies will 
support the discussion in the narrative conceptual model with tables 
and maps.
c. Comments and Responses
    We address any additional comments received on this topic in the 
Response to Comments document found in the docket for this action.
7. Timing of the EPA's Review of Submitted Demonstrations
a. Summary of Proposal
    The proposal summarized and clarified some of the EPA's previous 
statements regarding the prioritization and submittal of 
demonstrations, and proposed regulatory language to increase the 
efficiency of preparing, submitting and reviewing exceptional events 
demonstrations. We did not propose any changes to regulatory language 
pertaining to the timing of the EPA review process. Rather the proposal 
discussed processes, expectations and communications concerns, which 
are at the center of timing-related issues.
    The proposal articulated the EPA's previously expressed commitment 
to work collaboratively with air agencies as they prepare complete 
demonstrations. As we have previously communicated, demonstrated and 
summarized in our best practices for communications,\104\ we encourage 
ongoing discussions between the

[[Page 68268]]

reviewing EPA Regional office and the submitting air agency through the 
duration of the exceptional events process beginning with the Initial 
Notification of Potential Exceptional Event. Implementing the 
approaches identified by air agencies has generally improved the 
exceptional events process by improving relationships between air 
agencies and the EPA Regional office, clarified expectations, and 
resulted in decreased instances of submissions containing insufficient 
or unnecessary information.
---------------------------------------------------------------------------

    \104\ Best Communication Practices for Preparation of 
Exceptional Event Demonstrations, U.S. EPA, OAQPS, 2015. Available 
at http://www2.epa.gov/air-quality-analysis/treatment-data-influenced-exceptional-events.
---------------------------------------------------------------------------

    The proposal clarified our continued efforts to improve the 
exceptional events process, in part through improved communications but 
also through regulatory changes and workload prioritization. On this 
last point, the proposal identified that in reviewing submitted 
demonstrations, the EPA will generally give priority to exceptional 
events determinations that may affect near-term regulatory decisions, 
such as the EPA's action on SIP submittals, NAAQS designations and 
clean data determinations (see discussion in Section IV.C of this 
preamble). The proposal stated the EPA's intent to make a decision 
regarding event status expeditiously following submittal of a complete 
demonstration if required by a near-term regulatory action. If during 
the review process the EPA identifies the need for additional 
information to determine whether the exceptional events criteria are 
met, the EPA will notify the submitting air agency and encourage the 
agency to provide the supplemental information. If the information 
needed is minor and a natural outgrowth of what was previously 
submitted, the EPA will not require the air agency to undergo an 
additional public notice-and-comment process. However, if the needed 
information is significant, the EPA may request that the air agency re-
notice the demonstration before resubmitting it to the EPA, thus 
requiring an additional EPA review following resubmittal. The EPA will 
work with air agencies on supplemental timeframes; however, the 
mandatory timing of the EPA actions may limit the response time the EPA 
allows. The EPA proposed to include as rule text a requirement for the 
air agency to submit additional information within 12 months. If 
additional information is not received in 12 months, then the EPA would 
consider the submitted demonstration inactive, and would not continue 
the review or take action. In effect, an air agency's lack of response 
within a 12-month period would ``void'' the submittal. The proposal 
stated that in these cases, the EPA would not intend to issue a formal 
notice of deferral. If the air agency later decided to pursue the 
exceptional events claim after a 12-month period of inactivity, it may 
re-initiate the exceptional events process by submitting a new Initial 
Notification of Potential Exceptional Event followed by a new 
demonstration, which could simply be revising the original submittal to 
include the additional information previously requested by the EPA.
    The proposal explained that at the conclusion of the EPA's review, 
the EPA would make a determination regarding the status of a submitted 
exceptional events demonstration. The EPA's decision could result in 
concurrence, nonconcurrence or deferral.\105\ In acting on a submitted 
demonstration covering multiple event days and/or multiple flags, the 
EPA could concur with part of a demonstration and nonconcur or defer 
other flagged values. If the EPA determined that the events addressed 
in an exceptional events demonstration are not anticipated to affect 
any future regulatory decision, the EPA could defer review of these 
events and notify the submitting agency if a subsequent review results 
in a determination that the events would affect a regulatory 
decision.\106\ The proposal stated that formal mechanisms for deferral 
could include the EPA's indicating this decision by letter, by email to 
a responsible official or during a high-level meeting with an attendees 
list and discussion summary.
---------------------------------------------------------------------------

    \105\ The EPA anticipates a reduced number of deferrals and/or 
nonconcurrences for demonstrations associated with the Initial 
Notification of Potential Exceptional Event process as discussed in 
Section IV.G.5 of this preamble because the EPA and the affected air 
agency would have discussed issues/concerns prior to the EPA's 
decision on a submitted demonstration.
    \106\ Routine status calls between the reviewing EPA Regional 
office and air agencies could include an agenda item to review the 
status of all submitted demonstrations, including those that the EPA 
has deferred.
---------------------------------------------------------------------------

b. Final Rule
    For the previously explained reasons and as supported by one 
commenter, the EPA is finalizing with some clarification to the 
proposed language, the regulatory provision at 40 CFR 50.14(c)(3)(vi) 
to cease review of a demonstration following a 12-month period of 
inactivity by the submitting air agency. This finalized provision would 
apply when the air agency has submitted a demonstration for which the 
EPA has requested additional information, as indicated in writing by 
letter or email. The air agency will have 12 months from the date of 
the EPA's request to respond with the requested information. The EPA 
intends to track progress on demonstrations with regulatory 
significance and this 12-month period will ensure air agency 
accountability for its demonstrations and will allow the EPA to 
appropriately prioritize resources. Although the EPA anticipates 
ongoing discussions with the air agency, if the EPA has not received 
information from the air agency in response to the EPA's request for 
additional information, then least a month before the expiration 
period, the EPA will remind the air agency in writing (e.g., a letter 
or email) of the upcoming deadline. The EPA will work with individual 
air agencies to address those situations where a response is 
insufficient or where an air agency needs additional time to prepare 
needed analyses or assemble identified information. If the air agency 
has not responded within this 12-month timeframe, then the EPA's review 
of the demonstration will terminate. The EPA can provide notification 
of such termination by sending written notification (e.g., a letter or 
email) to the affected air agency.
    Although we are not promulgating timelines in rule language for the 
EPA's response to demonstrations, we are identifying here the response 
timelines that we intend to follow during the Initial Notification and 
demonstration review processes. As we stated in Section IV.G.5.b of 
this preamble, the EPA intends to acknowledge receipt shortly after 
receiving an air agency's Initial Notification and then formally 
respond to the Initial Notification within 60 days. The EPA response 
will provide the EPA Regional office's best assessment of the priority 
that can be given to the submission once received, any case-specific 
advice the EPA may have to offer for the preparation of the 
demonstration, and the target date for demonstration submittal.
    The EPA generally intends to conduct its initial review of an 
exceptional events demonstration with regulatory significance within 
120 days of receipt. This initial review could be extended in certain 
circumstances, such as if the EPA is reviewing a demonstration 
concurrent with an air agency's public comment period. Following this 
initial review, the EPA will generally send a letter or email to the 
submitting air agency that includes a completeness determination and/or 
a request for additional information, a date by which the supplemental 
information should be submitted (if applicable), and an indicator of 
the timing of the EPA's final review. The EPA intends to make a 
decision regarding event concurrence as

[[Page 68269]]

expeditiously as necessary if required by a near-term regulatory 
action, but no later than 12 months following submittal of a complete 
demonstration.
    In addition, if an air agency submits a demonstration for an event 
not discussed in the Initial Notification process or that the EPA has 
determined during the Initial Notification process to not to have 
regulatory significance (and there is no other compelling reason for 
excluding data), then the EPA will ``close out'' a submitted 
demonstration with a ``deferral letter'' within 60 days of receipt of 
the demonstration.
c. Comments and Responses
    Numerous commenters asked that the EPA promulgate deadlines by 
which the EPA must act on exceptional events demonstrations. We are 
accountable for many statutorily-established deadlines for regulatory 
action. We also note that promulgating timelines for action might not 
have the intended result of expediting the EPA's action because it 
could force both the air agencies and the EPA to focus their efforts 
and limited resources on demonstrations that ultimately have no 
regulatory significance. Or, promulgated timelines could cause the EPA 
to act on determinations in the order in which they were received 
instead of allowing the EPA to prioritize demonstrations for nearer-
term regulatory actions or mandated regulatory actions.
    Establishing regulatory deadlines also implies consequences for 
missing such deadlines. Three commenters have suggested that the EPA's 
failure to act on a submitted demonstration within a promulgated 
timeframe should result in automatic approval of the subject 
demonstration. The EPA's inaction cannot be assumed to be approval of a 
demonstration. By statute in CAA section 319(b), exceptional events 
must satisfy certain definitional and procedural requirements, 
including a determination by the Administrator. These CAA criteria 
cannot be presumed to be satisfied unless the Administrator 
concurs.\107\ Inaction is not concurrence. Additionally, approval by 
default is not appropriate because it would not ensure that air 
agencies and the EPA are upholding the principles and requirements of 
CAA section 319(b). Specifically, automatic approval of a demonstration 
without adequate review would not ensure that air agencies are taking 
appropriate and reasonable actions to protect public health from 
exceedances or violations of the NAAQS. Another consequence of missing 
a promulgated deadline could be the opportunity for an air agency, or, 
potentially, another interested party, to file a lawsuit. This action 
is also not likely to expedite a decision on a given demonstration.
---------------------------------------------------------------------------

    \107\ As discussed in more detail in Section IV.G.7 of this 
preamble, concurrent with these rule revisions, the EPA has revised 
the delegation of authority for exceptional events decision making. 
These authorities were previously delegated to the EPA Regional 
Administrators and, under the revised delegation, may be redelegated 
from the EPA Regional Administrator to the Regional Air Division 
Director or equivalent highest manager who exclusively oversees air 
programs.
---------------------------------------------------------------------------

    While we are not promulgating timelines in rule language for EPA's 
action, this preamble identifies the response timelines that we intend 
to follow during the Initial Notification and demonstration review 
process. Further, we have finalized provisions that focus on 
exceptional events demonstrations that have regulatory significance, 
which means that the demonstrations affect the outcome of a regulatory 
action. We are committed to taking action on all submitted 
demonstrations that have regulatory significance.
    Two commenters expressly supported the EPA's approach to 
prioritizing exceptional events demonstrations to focus on those that 
affect regulatory determinations. Several other commenters indicated 
their belief that the EPA should act on all submitted demonstrations. 
Regarding acting on all demonstrations, we have taken numerous steps in 
this action and otherwise to improve the exceptional events process and 
we maintain that, given limited resources, both the air agencies' and 
the EPA's efforts should focus on the development and review of those 
demonstrations that affect regulatory determinations. Expending time 
and energy on demonstrations that will not influence the outcome of a 
regulatory action is generally not an efficient use of resources. As we 
have indicated in numerous passages in this final action, we will 
consider exceptional events demonstrations on a case-by-case basis and 
air agencies will have an opportunity to state their position during 
the Initial Notifications process. Unless there is a compelling reason, 
we will ``close out'' those demonstrations that we receive, which were 
not discussed in the Initial Notification process or those which the 
EPA has determined during the Initial Notification process do not have 
regulatory significance.
    Another commenter asks that the EPA ``grandfather'' or otherwise 
respond to those demonstrations that have been previously submitted but 
on which the EPA has not yet acted. In promulgating these final rule 
revisions, we are taking no actions with respect to previously 
submitted and unprocessed demonstrations that otherwise remain 
``open.'' To request a response for an inactive demonstration, we ask 
that the affected air agency contact the reviewing EPA Regional office 
and inquire as to the most appropriate next steps.
    Two commenters supported, and several opposed, the EPA's regulatory 
provision to terminate the EPA's obligation to review a demonstration 
following a 12-month period of inactivity by the air agency. One of 
these supporters asked that, to facilitate transparency, that the EPA 
develop a publicly-accessible and transparent tracking system or 
otherwise provide status updates. The EPA agrees that a national 
tracking system could be valuable. We intend to explore this concept 
further as we implement these rule revisions.
8. Dispute Resolution Mechanisms
    In the November 2015 proposal, the EPA discussed currently 
available dispute resolution mechanisms but neither proposed any 
associated regulatory language nor solicited comment on the dispute 
resolution process. Rather, the proposal explained that there is no 
need for a formal dispute resolution mechanism for exceptional events 
for the following reasons: (1) The existing dispute resolution 
mechanisms are sufficient, (2) the EPA is committed to focusing on 
communication and collaboration with the submitting air agency through 
the exceptional events demonstration process, and (3) this final action 
includes useful clarifications that should reduce disagreements between 
air agencies and the EPA regarding the adequacy of demonstrations.
    Despite our statement that we were not soliciting comment of the 
topic of dispute resolution, numerous commenters requested that the EPA 
promulgate a dispute resolution process. Although commenters specified 
that the process be ``judicially appealable,'' ``include an independent 
third party with technical expertise'' and/or ``involve multiple EPA 
decision makers,'' no commenters provided substantive suggestions as to 
the mechanism by which a dispute resolution process could be 
implemented. In this action, we are not promulgating a dispute 
resolution mechanism. We are, however, restating currently available 
elevation measures and the EPA's internal mechanisms that ensure 
regional consistency.
    As noted in the proposal, several mechanisms currently exist that 
air agencies can use at various points in the

[[Page 68270]]

exceptional events process. These mechanisms include engaging in early 
dialogue with the reviewing EPA Regional office, submitting requests 
for reconsideration to the official who made the determination if a 
request identifies a clear error or if the reviewing EPA Regional 
office overlooked information submitted by the affected air agency, 
and/or elevating the concern within the EPA's chain of command. 
Additionally, air agencies can raise any unresolved event-related 
issues during the regulatory process that relies upon the claimed 
event-influenced data by participating in related public notice-and-
comment processes and/or challenging in an appropriate court the 
regulatory decision subsequently made based in part on the EPA's 
exceptional events determination.
    The EPA did not specifically identify in the proposal some of the 
internal steps we have taken to improve our ability to act on 
exceptional events activities and actions in a timely and efficient 
manner. First, we have expanded the number of officials within the EPA 
who can make exceptional events decisions. While the language of CAA 
section 319(b) states that decision making on exceptional events is a 
process undertaken by the Administrator, our promulgation of the 2007 
Exceptional Events Rule was accompanied by a delegation of authority 
delegating the decision making for exceptional events from the 
Administrator to the Assistant Administrator for Air and to the EPA 
Regional Administrators. However, this delegation did not allow for 
final decision making below the EPA Regional Administrator level. As 
part of this rule revision process, we revised the delegation of 
authority for exceptional events to allow for redelegation from the EPA 
Regional Administrator to the EPA Regional Air Division Director or 
equivalent highest manager who exclusively oversees air programs. If an 
EPA Regional Administrator elects to pursue redelegation, then the EPA 
Regional Air Division Director (or equivalent manager) would make 
exceptional events decisions and the EPA Regional Administrator would 
be an additional resource available within the elevation process for an 
air agency wishing to elevate concerns regarding an exceptional events-
related decision.
    The proposal also did not explain the role of the EPA's National 
Exceptional Events Work Group. This work group consists of technical 
and policy staff within the EPA's Office of Air Quality Planning and 
Standards (OAQPS), each of the EPA's Regional offices and the EPA's 
Office of General Counsel. The work group typically meets once each 
month and discusses technical and policy issues regarding exceptional 
events, including best practices implemented within the regions, new or 
evolving tools and technologies to help identify events and assess 
their impacts, upcoming regulatory decisions that could be influenced 
by event determinations and opportunities for outreach. In addition, at 
each meeting, regional participants report on the status of exceptional 
events actions in their respective states. This event report out also 
includes a discussion of new event types and/or novel policy issues and 
provides an opportunity for regional and OAQPS review of and input on 
specific demonstrations. These collaborative reviews are particularly 
relevant for new events (such as for the 2012 Wyoming Stratospheric 
Ozone Intrusion).\108\
---------------------------------------------------------------------------

    \108\ Wyoming Department of Environmental Quality, Air Quality 
Division. Big Piney and Boulder, Wyoming Ozone Standard Exceedance, 
June 14, 2012. Available at http://www2.epa.gov/air-quality-analysis/exceptional-events-submissions-table.
---------------------------------------------------------------------------

    As noted in the proposal, with exceptional events decisions, the 
air agency has opportunities to elevate concerns during two processes: 
The exceptional events determination and the subsequent regulatory 
action that relies on the exceptional events decision.

V. Mitigation

    Section 319(b)(3)(A) of the CAA identifies five principles that the 
EPA must follow in developing implementing regulations for exceptional 
events:

    (i) Protection of public health is the highest priority;
    (ii) Timely information should be provided to the public in any 
case in which the air quality is unhealthy;
    (iii) All ambient air quality data should be included in a 
timely manner in an appropriate federal air quality database that is 
accessible to the public;
    (iv) Each state must take necessary measures to safeguard public 
health regardless of the source of the air pollution; and
    (v) Air quality data should be carefully screened to ensure that 
events not likely to recur are represented accurately in all 
monitoring data and analyses.

    The regulatory requirements implementing (iii) and (v) of this part 
of the statute are found in 40 CFR 50.14 while the regulatory 
requirements implementing (i) and (iv) are found in 40 CFR 51.930, 
Mitigation of Exceptional Events. Both Sec. Sec.  50.14(c)(1) and 
51.930(a)(1) implement (ii) of this part by requiring states to provide 
notice of events to the public.
    The EPA promulgated the ``mitigation'' measures \109\ at 40 CFR 
51.930 when we finalized the Exceptional Events Rule in 2007, but we 
did not incorporate these measures into the criteria and processes by 
which data are excluded from use in regulatory determinations. The 
provisions at 40 CFR 51.930 require air agencies requesting data 
exclusion to take appropriate and reasonable actions to protect the 
public health from exceedances or violations of the NAAQS, promptly 
notify the public when the air exceeds or is expected to exceed the 
NAAQS, and educate the public regarding steps they can take to minimize 
exposure. These requirements apply whenever an air agency requests data 
exclusion, regardless of whether the EPA approves the exclusion. 
Although air agencies submitting demonstrations must meet the 
requirements at 40 CFR 51.930, the provisions do not require air 
agencies to submit their identified measures to the EPA or to notify 
the EPA of the measures an air agency plans to take or has taken. The 
mitigation measures that the EPA has seen air agencies practicing most 
commonly are those related to the requirement that air agencies 
``provide for prompt public notification whenever air quality 
concentrations exceed or are expected to exceed the NAAQS.'' Often, 
these public notifications have included public health alerts for high 
wind dust events or wildfires. Other aspects of mitigation, including 
implementing appropriate measures to protect public health beyond 
notification, are also important in implementing the CAA guiding 
principle that ``each State must take necessary measures to safeguard 
public health regardless of the source of the air pollution.''
---------------------------------------------------------------------------

    \109\ The term ``mitigation'' does not appear in CAA section 
319(b). It appears in the title but not the text of 40 CFR 51.930.
---------------------------------------------------------------------------

A. Summary of Proposal

    The proposal identified several possible changes to the mitigation-
related rule components and solicited comment on approaches ranging 
from retaining the existing rule requirements at 40 CFR 51.930 to 
including several new components. The proposal indicated that as a 
result of commenter feedback, we might make no changes, adopt all of 
the presented components, or adopt some of the described features. The 
proposal also indicated that, if finalized, the identified mitigation 
components, which would be an obligation for an affected air agency and

[[Page 68271]]

serve as criteria for the EPA's approval of future exceptional events 
demonstrations, would only apply to those air agencies with areas 
subject to ``historically documented'' or ``known seasonal'' 
exceptional events.
1. Defining Historically Documented or Known Seasonal Events
    The proposal accepted comment on whether to define ``historically 
documented'' or ``known seasonal'' exceptional events to include events 
of the same type and pollutant (e.g., high wind dust/PM or wildfire/
ozone) that recur on an annual or seasonal basis and meet any of the 
following criteria: An event for which an air agency has previously 
submitted exceptional events demonstrations; an event that an air 
agency has previously flagged for concurrence in AQS (regardless of 
whether the air agency submitted a demonstration); or an event that has 
been the subject of public health alerts or published scientific 
journal articles. The proposal indicated that the EPA would not require 
an air agency to develop a mitigation plan for the first event of a 
given type (e.g., if an area is prone to wildfires but has never 
experienced a high wind dust event, then it would not be expected to 
develop a mitigation plan for its first high wind dust event, but it 
would be expected to develop a mitigation plan for wildfires). A second 
event of a given type within a 3-year period would subject the area to 
``having a history'' and, therefore, needing a mitigation plan.\110\ 
This option avoids plan development following a one-of-a-kind 
occurrence.\111\ In defining ``first'' and ``second'' events, the EPA 
indicated that it could consider events that affect the same AQCR, but 
not necessarily the same monitor.\112\ We also solicited comment on 
whether it would be appropriate to consider a season of multiple events 
of a common type as one of three required seasons, so that a mitigation 
plan would be required only when an event type persists across several 
years.
---------------------------------------------------------------------------

    \110\ A 3-year period is measured backwards from the date of the 
most recent event.
    \111\ Because the form of the NAAQS varies by pollutant, it is 
possible that multiple events in a 3-year period may not cause a 
NAAQS violation. An air agency that identifies multiple events of 
the same type (e.g., wildfire/ozone) in AQS, but prepares and 
submits a demonstration for only one of these events, would trigger 
the proposed requirement to develop a mitigation plan.
    \112\ 40 CFR part 81, subpart B, Designation of Air Quality 
Control Regions, defines Air Quality Control Regions.
---------------------------------------------------------------------------

2. Mitigation Plan Components
    The proposal also identified and solicited comment on the following 
three plan components that could be recommended or required to 
implement the mitigation principles found in CAA section 319(b)(3)(A): 
Public notification and education; steps to identify, study and 
implement mitigating measures; and provision for periodic revision of 
the mitigation plan (to include public review of plan elements). Given 
the identified components, the proposal solicited comment on 
appropriate timelines for submitting a plan.
3. Options for Implementing Mitigation Plans
    Because the 2007 Exceptional Events Rule did not tie the mitigation 
elements at 40 CFR 51.930 to the EPA's review of exceptional events 
demonstrations, we proposed and solicited feedback on the following 
options: Option 1 included the EPA's review for completeness but not 
substantive approval or disapproval, while Option 2 included the EPA's 
approval of the substance of the mitigation plan. The proposal noted 
that neither option would require a mitigation plan to be included in a 
SIP or to be otherwise federally-enforceable. Regarding the submittal 
of a mitigation plan to the EPA, the EPA proposed that air agencies 
with historically documented or known seasonal exceptional events could 
submit the mitigation plan to the EPA in advance of an event, or submit 
a mitigation plan along with an exceptional events demonstration. For 
both options, the proposal explained that if the EPA otherwise 
concurred with an exceptional events demonstration for a type of event 
that is also the subject of the mitigation plan, the EPA would only 
concur with such a demonstration for the relevant event type if a 
mitigation plan passed the type of review described in the option 
(i.e., completeness review for Option 1 or approval of content for 
Option 2).

B. Final Rule

    In keeping with the EPA's mission to protect public health and 
consistent with the principles included at CAA section 319(b)(3)(A), 
and after consideration of the public comments, we are promulgating new 
mitigation-related regulatory language at 40 CFR 51.930 requiring the 
development of mitigation plans in areas with ``historically 
documented'' or ``known seasonal'' exceptional events. As part of these 
promulgated requirements, we have decided to follow the review option 
identified as Option 1 in the proposal, which includes the EPA's review 
and a completeness determination, but not the EPA's ``approval'' of the 
plan content (identified as Option 2 in the proposal), as discussed in 
the comments and responses section below. We believe this option 
maximizes the flexibility of the air agency while providing for the 
protection of public health through the EPA's review of the required 
plan content and through the required public review process. We further 
believe that Option 2, which required the EPA's approval of mitigation 
plan content, could have the unintended effect of imposing additional 
administrative burden (e.g., multiple rounds of review and revision) 
without corresponding additional public health and air quality benefit. 
Other regulatory mechanisms are already available to address public 
health and air quality, as needed (e.g., SIP revisions or the 
regulatory action that is the focus of an event of the type that is the 
subject of the mitigation plan and an exceptional events 
demonstration). We are also adding a provision to clarify that, after 
an initial implementation period (as discussed in Section V.B.3 of this 
preamble), the EPA will not concur with an air agency's request to 
exclude data that have been influenced by an event of the type that is 
the subject of a required mitigation plan if an air agency has not 
submitted the related required mitigation plan. The EPA could, however, 
either nonconcur or defer action on a demonstration for such event-
influenced data. The EPA's action would likely depend on the timing of 
the associated regulatory action. We are promulgating this regulatory 
language after seeking comment on approaches ranging from retaining the 
existing ``mitigation'' rule requirements to promulgating new 
mitigation-related rule components.
1. Defining Historically Documented or Known Seasonal Events
    We are defining ``historically documented'' or ``known seasonal'' 
events to include events of the same type and pollutant (e.g., high 
wind dust/PM or wildfire/ozone) that recur every year, either 
seasonally or throughout the year. For purposes of identifying the 
bounds of ``a particular area'' for those areas that are initially 
subject to the requirement to develop a mitigation plan (as discussed 
later in this section), we are using nonattainment area boundaries or 
county boundaries for those areas not in a nonattainment area. After 
these initial areas for which we have identified boundaries, the EPA 
Regional office and the affected air

[[Page 68272]]

agencies should consult regarding how to characterize ``a particular 
location.'' Ultimately, the EPA will determine the bounds for ``a 
particular location.''
    Regarding recurrence, we are using the benchmark of three events in 
3 years, which applies regardless of an area's designation status with 
respect to the NAAQS that could be the focus of a potential 
demonstration for a recurring event and regardless of whether the event 
type is the focus of specific recurrence circumstances within this rule 
for the ``human activity unlikely to recur at a particular location or 
a natural event'' criterion. We measure the 3-year period backwards 
from the date of the most recent event. Similar to our discussion of 
recurrence for the ``human activity unlikely to recur'' criterion in 
Section IV.E.1 of this preamble, if there have been two prior events of 
a similar type (i.e., a similar event type generating emissions of the 
same pollutant) within a 3-year period in ``a particular location,'' 
the third event constitutes recurrence. While we are using the 
benchmark of three events in a 3-year period, for purposes of 
``historically documented'' or ``known seasonal'' events, we will treat 
a season with multiple events as one event such that a mitigation plan 
will be required only when an event type persists across several years. 
For example, an area may not have previously experienced wildfires in 
the past 10 years, but then experiences multiple wildfires and multiple 
exceedances in a single wildfire season. If these multiple wildfires 
affect the same general geographic area and monitors in a relatively 
short period of time (e.g., 2-3 months), then they could be considered 
a single event for purposes of developing a mitigation plan and would 
not trigger the requirement for a mitigation plan. Also, for purposes 
of counting a season towards the limit of three seasons in 3 years, we 
mean a season containing one or more events for which an air agency has 
previously submitted exceptional events demonstrations or a season of 
events that is the subject of an Initial Notification of Potential 
Exceptional Event as discussed in Section IV.G.5 of this preamble 
(regardless of whether the air agency submitted a demonstration).\113\ 
Where an area experiences multiple event seasons in a given year (e.g., 
a spring season and a fall season of events), then each season will 
count towards the benchmark of three recurrences in 3 years. Under this 
scenario, an area could experience a single season of events in year 
one, no events in year two, and multiple seasons of events in year 
three. Using the benchmark of three event-containing seasons in 3 years 
would subject the area to ``having a history'' and, therefore, needing 
a mitigation plan. The requirements of this section will apply 
regardless of the event/pollutant combination and regardless of whether 
the event type is the focus of specific recurrence circumstances within 
this rule for the ``human activity unlikely to recur at a particular 
location or a natural event'' criterion. We note, however, a 
demonstration for an event (or event season) for which the EPA 
nonconcurs (or previously nonconcurred) will not count towards 
recurrence.
---------------------------------------------------------------------------

    \113\ Because the Initial Notification of Potential Exceptional 
Event is a new requirement in this action, we cannot use it to 
define recurrence for those areas that are initially subject to the 
requirement to develop a mitigation plan. For these areas, we are 
defining recurrence as three events or event seasons for which an 
air agency submitted a demonstration within a 3-year period or three 
events or event seasons in a 3-year period that resulted in a NAAQS 
exceedance(s) or violation(s) for which an air agency has previously 
flagged events for concurrence in AQS (regardless of whether the air 
agency submitted a demonstration).
---------------------------------------------------------------------------

    Applying this framework of three events (or three seasons with 
multiple events of a common type) in a 3-year period, we identify in 
Table 6 those areas that have experienced recurring events during the 
timeframe from January 1, 2013, through December 31, 2015. Per the 
requirements set forth in 40 CFR 51.930(b)(1)(ii), we are using this 
action to provide written notice that the areas identified in Table 6 
need to submit mitigation plans according to the requirements of the 
rule provisions in 40 CFR 51.930(b).

                  Table 6--Areas Subject to the Mitigation Requirements in 40 CFR 51.930(b) \a\
----------------------------------------------------------------------------------------------------------------
                                                         AQS Flag                          Nonattainment area,
            Pollutant               AQS Flag \b\        description          State       county or city boundary
----------------------------------------------------------------------------------------------------------------
Ozone...........................  RO                Stratospheric       CO               Denver-Boulder-Greeley-
                                                     Ozone Intrusion.                     Ft. Collins-Loveland,
                                                                                          CO Ozone Nonattainment
                                                                                          Area
Ozone...........................  RT                Wildfire-U. S.....  CO               Denver-Boulder-Greeley-
                                                                                          Ft. Collins-Loveland,
                                                                                          CO Ozone Nonattainment
                                                                                          Area
Ozone...........................  RT                Wildfire-U. S.....  NV               Clark County
PM10............................  RJ                High Winds........  AZ               Phoenix, AZ PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  AZ               Rillito, AZ PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  AZ               West Pinal, AZ PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  AZ               Yuma, AZ PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  AZ               Gila River Indian
                                                                                          Community
PM10............................  RJ                High Winds........  AZ               Salt River Pima-
                                                                                          Maricopa Indian
                                                                                          Community
PM10............................  RJ                High Winds........  CA               Coso Junction, CA PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  CA               Imperial Valley, CA
                                                                                          PM10 Nonattainment
                                                                                          Area
PM10............................  RJ                High Winds........  CA               Coachella Valley, CA
                                                                                          PM10 Nonattainment
                                                                                          Area
PM10............................  RJ                High Winds........  CA               San Joaquin Valley PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  CA               Los Angeles South Coast
                                                                                          Air Basin PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  CO               Alamosa County
PM10............................  RJ                High Winds........  CO               Prowers County
PM10............................  RJ                High Winds........  NM               Anthony, NM PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  NM               Luna County
PM10............................  RJ                High Winds........  NV               Nye County
PM10............................  RJ                High Winds........  NV               Clark County PM10
                                                                                          Nonattainment Area
PM10............................  RJ                High Winds........  WA               Wallula PM10
                                                                                          Maintenance Area
PM2.5...........................  RA                African Dust......  TX               Harris County
PM2.5...........................  RJ                High Winds........  TX               El Paso County
PM2.5...........................  RS                Volcanic Eruptions  HI               Hawaii County
PM2.5...........................  RT                Wildfire-U. S.....  CA               Nevada County
PM2.5...........................  RT                Wildfire-U. S.....  CA               Sacramento, CA PM2.5
                                                                                          Nonattainment Area

[[Page 68273]]

 
PM2.5...........................  RT                Wildfire-U. S.....  MT               Missoula County
PM2.5...........................  RT                Wildfire-U. S.....  MT               Ravalli County
PM2.5...........................  RT                Wildfire-U. S.....  NV               Carson City (City)
PM2.5...........................  RT                Wildfire-U. S.....  NV               Douglas County
PM2.5...........................  RT                Wildfire-U. S.....  NV               Washoe County
SO2.............................  RS                Volcanic Eruptions  HI               Hawaii County
----------------------------------------------------------------------------------------------------------------
\a\ The areas noted in this table were identified using monitoring data in AQS for the January 1, 2013, through
  December 31, 2015, timeframe. The EPA downloaded data with request exclusion flags in May 2016, matched these
  data to exceedance days and then identified those areas with three seasons of events within a 3-year period.
\b\ The complete list of AQS qualifier codes and descriptions is available at https://aqs.epa.gov/aqsweb/documents/codetables/qualifiers.html.

    An area that appears in Table 6 for multiple NAAQS and/or event 
types could have a single mitigation plan, provided the plan components 
and actions address the multiple NAAQS and events. For example, a few 
areas have recurring high wind dust events for both PM10 and 
PM2.5. These areas could develop a single high wind dust 
mitigation plan that addresses both PM10 and 
PM2.5.
    Within 2 years of the effective date of this action, air agencies 
responsible for ensuring air quality for the identified areas shall 
submit mitigation plans to the applicable EPA Regional Administrator. 
After this 2-year timeframe, the EPA will not concur with an air 
agency's request to exclude data that have been influenced by an event 
of the type that is the subject of a required mitigation plan if an air 
agency has not submitted the related required mitigation plan. The EPA 
could, however, either nonconcur or defer action on a demonstration for 
such event-influenced data. The EPA's action would likely depend on the 
timing of the associated regulatory action. As other areas become 
subject to the mitigation requirements identified in this action, the 
EPA will notify such areas in writing of the need for a mitigation 
plan. We discuss the timing associated with implementing a mitigation 
plan in more detail in Section V.B.3 of this preamble.
2. Mitigation Plan Components
    After considering the public comments we received, we are 
finalizing the following three required plan components to help 
implement the mitigation principles found in CAA section 319(b)(3)(A). 
Unless otherwise specified, each mitigation plan should address actions 
that would be taken within an air agency's own jurisdiction for events 
that happen within its own jurisdiction or within the jurisdiction of 
another air agency.
    a. Public notification to and education programs for affected or 
potentially affected communities. Air agencies are required to include 
in their mitigation plans steps to activate public notification and 
education systems whenever air quality concentrations exceed or are 
expected to exceed an applicable short-term NAAQS.\114\ If possible, 
air agencies would notify the public of the actual or anticipated event 
at least 48 hours in advance of the event using methods appropriate to 
the community being served. (The EPA recognizes that for some event 
types, a 48-hour advance notice may not be possible.) Outreach 
mechanisms could include: Web site alerts, National Weather Service 
alerts, telephone or text bulletins, television or radio campaigns or 
other messaging campaigns. Public notification and education programs 
should include some or all of the following actions to support the 
outreach system: Adoption of methods for forecasting/detection, 
consultation with appropriate health department personnel regarding 
issuing health advisories and suggested actions for exposure 
minimization for sensitive populations (e.g., remain indoors, avoid 
vigorous outdoor activity, avoid exposure to tobacco smoke and other 
respiratory irritants and, in extreme cases, evacuation or public 
sheltering procedures).
---------------------------------------------------------------------------

    \114\ By short-term, we mean NAAQS with averaging times that are 
24-hours or less. We do not believe it is appropriate to notify the 
public when the pollutant concentrations exceed or violate a 3-month 
rolling average or an annual average as these violations reflect 
cumulative effects and in many cases the cause of the exceedance or 
violation is long past.
---------------------------------------------------------------------------

    b. Steps to identify, study and implement mitigating measures, 
including approaches to address each of the following:
    (i) Mandatory or voluntary measures to abate or minimize 
contributing controllable sources of identified pollutants that are 
within the jurisdiction of the affected air agency. An air agency is 
encouraged to consider full-time or contingent controls on event-
related sources as well as non-event related sources. For example, 
these measures might include continuously operating control measures 
during an extreme event for identified sources that normally operate 
these same controls on an intermittent basis. It could also involve 
including work practices (e.g., water spray for dust suppression) or 
contingent limits during extreme events on emissions from non-event 
related sources that, under non-event periods, have no or less 
stringent emissions limits or work practices.
    (ii) Methods to minimize public exposure to high concentrations of 
identified pollutants.
    (iii) Processes to collect and maintain data pertinent to the event 
(e.g., to identify the data to be collected, the party responsible for 
collecting and maintaining the data and when, how and to whom the data 
will be reported).
    (iv) Mechanisms to consult with other air quality managers in the 
affected area regarding the appropriate responses to abate and minimize 
impacts. Consultation could include collaboration between potentially 
affected local, state, tribal and federal air quality managers and/or 
emergency response personnel.
    c. Provisions for review and evaluation of the mitigation plan and 
its implementation and effectiveness by the air agency and all 
interested stakeholders (e.g., public and private land owners/managers, 
air quality, agriculture and forestry agencies, the public). During the 
initial development of the mitigation plan, this public review process 
would follow a process similar to that required for the public review 
of an exceptional events demonstration. That is, to solicit feedback 
from interested parties, an air agency subject to the mitigation 
requirements would conduct a public comment process on a draft 
mitigation plan for a minimum of 30 days. The air agency would then 
submit the public comments received to the EPA with the air agency's 
submission of its final

[[Page 68274]]

mitigation plan. With this submission and for each public comment 
received, the air agency would explain the changes made to the 
mitigation plan or explain why the air agency did not make any changes 
to the mitigation plan. We believe that public feedback will inherently 
strengthen the mitigation plans and focus the air agency action in the 
areas most needing the attention. Air agencies and the affected public 
are better suited than the EPA to determine effective mitigation 
measures.
    The EPA expects that once an area becomes subject to these 
mitigation requirements, it will always have a mitigation plan in 
effect, although the plan would be periodically revised and evaluated 
for effectiveness. The process by which the air agency accomplishes 
this periodic review and evaluation of plan effectiveness after the 
initial development of the plan must also be identified in the plan. 
The review and evaluation would necessarily include a public process to 
solicit feedback from interested stakeholders (e.g., public and private 
land owners/managers, air quality, agriculture and forestry agencies, 
the public). Periodic review could follow a process similar to the one 
identified for initial plan development. Although the air agency can 
determine the review timeframe for a mitigation plan, we offer the 
following guidance. For example, within this section of a mitigation 
plan, the air agency could specify review and revision, if appropriate, 
and recertification of the mitigation plan every 3 years. The air 
agency could also identify that review, revision, and recertification 
would occur after a season of implementing the plan, which could result 
in annual review if events continued to recur with such a frequency. 
Or, if the subject event did not recur for 5 years, then plan 
reassessment would follow a longer timeframe.
    Because evaluating the effectiveness of a mitigation plan includes 
actions and responses from a variety of interested stakeholders, the 
air agency should consider submitting a summary and response to the 
comments received during the public plan review process to the EPA 
along with the recertification statement and/or revised mitigation 
plan. While we are requiring an air agency to submit any received 
public comments to the EPA after the air agency initially develops a 
mitigation plan, we are not requiring that the air agency summarize and 
submit public comments for subsequent reviews and plan reassessments.
    If the historically documented or known seasonal exceptional events 
continue to result in elevated pollutant concentrations above the 
relevant NAAQS, thus showing that the combination of the existing SIP 
and the existing mitigation plan does not effectively safeguard public 
health, the air agency should consider whether to strengthen the 
mitigation plan.
    In adopting these revisions, it is possible that all affected air 
agencies may not need to prepare new plans. If an air agency has 
developed and implemented a contingency plan under 40 CFR part 51, 
subpart H, Prevention of Air Pollution Emergency Episodes, that meets 
the requirements of 40 CFR 51.152, and that includes provisions for 
events that could be considered ``exceptional events'' under the 
provisions in 40 CFR 50.14, then the subpart H contingency plan would 
likely satisfy the mitigation requirements. If the identified basic 
elements are included and addressed, including the element for public 
comment, then other types of existing mitigation or contingency plans 
may satisfy the mitigation plan requirements. For example, if an area 
has developed a natural events action plan or a high wind action plan 
covering high wind dust events, this plan likely would satisfy 
mitigation elements for high wind dust events. Smoke management 
programs and/or forest management plans might also satisfy the 
mitigation elements for prescribed fires and wildfires. Most air 
agencies likely have sufficient, established processes that meet the 
public notification and education element, and which can be easily 
adapted or modified to meet the mitigation elements proposed in this 
action.
3. Implementing Mitigation Plans
    The EPA is finalizing implementation provisions that provide for 
the EPA's review and verification of the mitigation plans' inclusion of 
the required elements and to ensure that the development of the 
mitigation plan included a public comment process. We would not 
formally review the substance of the plan in the sense of approving the 
details of the specific measures and commitments in the plan. We will, 
however, review each submitted plan and verify that it includes the 
required elements. Within 60 days of receipt of such a plan, the EPA 
plans to notify the submitting air agency that we have reviewed the 
mitigation plan and verified that it contains the required elements. 
Mitigation plans developed under 40 CFR 51.930 are not required to be 
included in a SIP or to be otherwise federally-enforceable.
    Commenters asked that we allow air agencies 2 years from the date 
that they become subject to any mitigation plan requirements to develop 
their mitigation plan. We note that developing an effective mitigation 
plan that includes the required elements may require input from and 
coordination with numerous stakeholders, including, but not limited to, 
air agencies, public health officials, local governments, 
representatives serving potentially affected minority and low-income 
populations, if applicable, and the media. Additionally, air agencies 
must make the mitigation plan available for public comment, and respond 
and revise the mitigation plan in response to those comments, as 
appropriate. Upon consideration, we believe 2 years is a reasonable 
amount of time to ensure that air agencies have adequate time to 
prepare comprehensive mitigation plans that respond to the public 
health threat presented by historically documented or known seasonal 
events. Therefore, we are incorporating the commenters' suggestion into 
this preamble and into the final regulatory language. Thus, air 
agencies with historically documented or known seasonal exceptional 
events that we are formally identifying in this action as being subject 
to the requirements of this section will have 2 years from the 
effective date of this action to submit a mitigation plan to their 
applicable EPA Regional office. The EPA will process events of the type 
and pollutant that are the subject of the mitigation plan that occur 
during this 2-year period following the general provisions outlined in 
40 CFR 50.14. During this interim period, the EPA's concurrence on 
demonstrations will not be contingent upon the affected air agency's 
submittal of a mitigation plan because air agencies should have 
sufficient time to develop their newly required mitigation plans. It is 
not reasonable to delay acting on demonstration submittals while air 
agencies prepare these plans. However, for events of the type subject 
to the mitigation plan requirement that occur after this 2-year window, 
the EPA's action on demonstrations will be contingent on the submittal 
of a mitigation plan that meets the requirements of this action. As the 
EPA identifies other areas subject to the mitigation requirements in 
this final rule, we provide such notice to the affected air agencies. 
Notified air agencies will then have a 2-year period to develop a 
mitigation plan. During this period of development, the EPA's 
concurrence on demonstrations for events of the type and pollutant that 
are

[[Page 68275]]

the subject of the mitigation plan will not be contingent upon the 
affected air agency's submittal of a mitigation plan.
    All areas subject to these mitigation plan requirements can submit 
the mitigation plan to the EPA in advance of an event, or submit a 
mitigation plan along with an exceptional events demonstration. The EPA 
expects that mitigation plans developed according to this section will 
assist agencies in satisfying the not reasonably controllable or 
preventable criterion discussed in Section IV.E.2 of this preamble.

C. Comments and Responses

    While the majority of commenters provided feedback indicating their 
preference to retain the existing mitigation requirements in 40 CFR 
51.930 without revision, several other commenters supported the 
development of mitigation plans either for areas with ``historically 
documented'' or ``known seasonal'' events or all events. Of those 
commenters providing feedback on the EPA's review of mitigation plans, 
many commenters supported the ``review'' versus ``approval'' option. As 
previously noted, we have implemented the review option, which we 
proposed as Option 1. We believe that Option 1 maximizes the 
flexibility of the air agency while providing for the protection of 
public health through the EPA's review to ensure inclusion of required 
plan content and through the required public review process. Also 
consistent with commenter feedback, we have identified required program 
components, but have not specified the required content. Rather, it is 
appropriate to allow air agencies to develop mechanisms that are 
tailored to their unique situations and events.
    Also regarding specific recommendations on plan content, one 
commenter did not support public notification for exceedances of an 
annual standard. The EPA agrees with the commenter that public 
notification is not necessary when the pollutant concentrations exceed 
or violate a 3-month rolling average or an annual average as these 
exceedances/violations reflect cumulative effects and in many cases the 
cause of the exceedance or violation is long past. We have clarified 
this point by adding regulatory language requiring public notification 
for exceedances or anticipated exceedances of short-term NAAQS. We also 
added regulatory text and a footnote in this preamble to define 
``short-term'' as a NAAQS with an averaging time that is less than or 
equal to 24-hours.

VI. Environmental Justice Considerations

    The Exceptional Events Rule provides the criteria by which state, 
local and tribal air agencies identify air quality data they believe 
have been influenced by exceptional events, which by statutory 
definition are not reasonably controllable or preventable. Because it 
is not reasonable to control or prevent these events, they can affect 
all downwind populations including minority and low-income populations. 
For this reason, in adding CAA section 319(b), Congress identified as a 
guiding principle in developing regulations, ``the principle that 
protection of public health is the highest priority.'' The Exceptional 
Events Rule at 40 CFR 50.14 requires air agencies to seek public 
comment on prepared exceptional events demonstrations prior to 
submitting them to the reviewing EPA Regional office. The public can 
also comment on rulemakings that include decisions related to the 
exclusion of event-influenced data. The mitigation of exceptional 
events language at 40 CFR 51.930 also requires that air agencies 
provide public notification and education programs related to events.
    To protect all people and communities, notably minority and low-
income populations, air agencies should ensure that notifications and 
education programs are communicated using the language (e.g., English 
and Spanish) and media (e.g., radio and postings in local community 
centers) best suited to the target audience(s). Furthermore, this 
action requires states to develop mitigation plans for recurring event 
types. Additionally, these revisions to the Exceptional Events Rule are 
being made as part of a public notice-and-comment rulemaking effort, 
which included a public hearing. These opportunities for public input 
in the rulemaking process, and the resulting requirements regarding 
public input and education ensure that all those residing, working, 
attending school or otherwise present in areas affected by exceptional 
events, regardless of minority and economic status, are protected.

VII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive 
Order 13563: Improving Regulation and Regulatory Review

    This action is a significant regulatory action that was submitted 
to the Office of Management and Budget (OMB) for review because it 
raises novel policy issues. Any changes made in response to OMB 
recommendations have been documented in the docket.

B. Paperwork Reduction Act (PRA)

    This action does not impose any new information collection burden 
under the PRA. OMB has previously approved the information collection 
activities for ambient air monitoring data and other supporting 
measurements reporting and recordkeeping activities associated with the 
40 CFR part 58 Ambient Air Quality Surveillance rule and has assigned 
OMB control number 2060-0084. The information being requested under 
these proposed rule revisions is consistent with current requirements 
related to information needed to verify the authenticity of monitoring 
data submitted to the EPA's AQS database, and to justify exclusion of 
data that have been flagged as being affected by exceptional events.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action will not impose any requirements on small entities. Instead, the 
rule revisions provide the criteria and increase the efficiency of the 
process by which state, local and tribal air agencies identify air 
quality data they believe have been influenced by an exceptional event. 
The rule revisions also clarify those actions that state, local and 
tribal air agencies should take to protect public health during and 
following an exceptional event. Because affected air agencies would 
have discretion to implement controls on sources that may need to be 
regulated due to anthropogenic contribution in the area determined to 
be influenced by an exceptional event, the EPA cannot predict the 
indirect effect of the rule on sources that may be small entities.

D. Unfunded Mandates Reform Act (UMRA)

    This action does not contain an unfunded mandate of $100 million or 
more as described in UMRA, 2 U.S.C. 1531-1538, and does not 
significantly or uniquely affect small governments. The action imposes 
no enforceable duty on any state, local or tribal governments or the 
private sector.

E. Executive Order 13132: Federalism

    This action does not have federalism implications. The EPA 
believes, however, that this action may be of significant interest to 
states and to local air quality agencies to whom a state has delegated 
relevant responsibilities for air quality management. Consistent with

[[Page 68276]]

the EPA's policy to promote communications between the EPA and state 
and local governments, the EPA consulted with representatives of state 
and local governments early in the process of developing this action to 
permit them to have meaningful and timely input into its development. A 
summary of the concerns raised during that consultation is provided in 
Section IV of this preamble.

F. Executive Order 13175: Consultation and Coordination with Indian 
Tribal Governments

    This action does not have tribal implications as specified in 
Executive Order 13175. It would not have a substantial direct effect on 
one or more Indian tribes. Furthermore, these regulation revisions do 
not affect the relationship or distribution of power and 
responsibilities between the federal government and Indian tribes. The 
CAA and the TAR establish the relationship of the federal government 
and tribes in characterizing air quality and developing plans to attain 
the NAAQS, and these revisions to the regulations do nothing to modify 
that relationship. Thus, Executive Order 13175 does not apply to this 
action.
    Although Executive Order 13175 does not apply to this action, the 
EPA held public meetings attended by tribal representatives and 
separate meetings with tribal representatives to discuss the revisions 
proposed in this action. The EPA also provided an opportunity for all 
interested parties to provide oral or written comments on potential 
concepts for the EPA to address during the rule revision process. 
Summaries of these meetings are included in the docket for this rule. 
The EPA received comments on this action from multiple tribal 
organizations, requesting clarification on how this action includes and 
protects federal tribal communities. The Exceptional Events Rule 
addresses these concerns through the public comment process for both 
the rule revision and the exceptional events demonstrations, outreach 
efforts, and notification requirements.

G. Executive Order 13045: Protection of Children From Environmental 
Health & Safety Risks

    The EPA interprets Executive Order 13045 as applying only to those 
regulatory actions that concern environmental health or safety risks 
that the EPA has reason to believe may disproportionately affect 
children, per the definition of ``covered regulatory action'' in 
section 2-202 of the Executive Order. This action is not subject to 
Executive Order 13045 because it does not concern an environmental 
health risk or safety risk.

H. Executive Order 13211: Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution or Use

    This action is not a ``significant energy action'' because it is 
not likely to have a significant adverse effect on the supply, 
distribution or use of energy. The purpose of this proposed rule is to 
provide the criteria, and increase the efficiency of the process, by 
which state, local and tribal air agencies may identify air quality 
data they believe have been influenced by an exceptional event. The EPA 
does not expect these activities to affect energy suppliers, 
distributors or users.

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

J. Executive Order 12898: Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations

    The EPA believes that this action does not have disproportionately 
high and adverse human health or environmental effects on minority 
populations, low-income populations and/or indigenous peoples, as 
specified in Executive Order 12898 (59 FR 7629, February 16, 1994). The 
documentation for this decision is contained in the Section VI of the 
preamble titled ``Environmental Justice Considerations.'' This action 
provides the criteria and increases the efficiency of the process by 
which state, local and tribal air agencies identify air quality data 
they believe have been influenced by exceptional events, which, by 
statutory definition, are not reasonably controllable or preventable. 
These regulatory provisions do, however, provide information concerning 
actions that state, local or tribal air agencies might take to 
uniformly protect public health once the EPA has concurred with an air 
agency's request to exclude data influenced by an exceptional event. 
The mitigation component of the rule could ultimately provide 
additional protection for minority, low income and other populations 
located in areas affected by recurring exceptional events. Therefore, 
the EPA finds that this action would not adversely affect the health or 
safety of minority or low-income populations, and that it is designed 
to protect and enhance the health and safety of these and other 
populations.

K. Congressional Review Act (CRA)

    This action is subject to the CRA, and the EPA will submit a rule 
report to each House of the Congress and to the Comptroller General of 
the United States. This action is not a ``major rule'' as defined by 5 
U.S.C. 804(2).
Page 225 of 247--Treatment of Data Influenced by Exceptional Events

VIII. Statutory Authority

    The statutory authority for this action is provided by 42 U.S.C. 
7401, et seq.

List of Subjects

40 CFR Part 50

    Environmental protection, Air pollution control, National parks, 
Wilderness areas.

40 CFR Part 51

    Environmental protection, Air pollution control, National parks, 
Wilderness areas.

    Dated: September 16, 2016.
Gina McCarthy,
Administrator.

    For the reasons set forth in the preamble, parts 50 and 51, title 
40, chapter I of the Code of Federal Regulations are amended as 
follows:

PART 50--NATIONAL PRIMARY AND SECONDARY AMBIENT AIR QUALITY 
STANDARDS

0
1. The authority citation for part 50 continues to read as follows:

    Authority:  42 U.S.C. 7401, et seq.


0
2. Amend Sec.  50.1 by:
0
a. Revising paragraphs (j) and (k).
0
b. Adding paragraphs (m), (n), (o), (p), (q) and (r).
    The revisions and additions read as follows:


Sec.  50.1  Definitions.

* * * * *
    (j) Exceptional event means an event(s) and its resulting emissions 
that affect air quality in such a way that there exists a clear causal 
relationship between the specific event(s) and the monitored 
exceedance(s) or violation(s), is not reasonably controllable or 
preventable, is an event(s) caused by human activity that is unlikely 
to recur at a particular location or a natural event(s), and is 
determined by the Administrator in accordance with 40 CFR 50.14 to be 
an exceptional event. It does not include air pollution relating to 
source noncompliance. Stagnation of air masses and meteorological 
inversions do not directly cause pollutant emissions and are not 
exceptional events. Meteorological events involving

[[Page 68277]]

high temperatures or lack of precipitation (i.e., severe, extreme or 
exceptional drought) also do not directly cause pollutant emissions and 
are not considered exceptional events. However, conditions involving 
high temperatures or lack of precipitation may promote occurrences of 
particular types of exceptional events, such as wildfires or high wind 
events, which do directly cause emissions.
    (k) Natural event means an event and its resulting emissions, which 
may recur at the same location, in which human activity plays little or 
no direct causal role. For purposes of the definition of a natural 
event, anthropogenic sources that are reasonably controlled shall be 
considered to not play a direct role in causing emissions.
* * * * *
    (m) Prescribed fire is any fire intentionally ignited by management 
actions in accordance with applicable laws, policies, and regulations 
to meet specific land or resource management objectives.
    (n) Wildfire is any fire started by an unplanned ignition caused by 
lightning; volcanoes; other acts of nature; unauthorized activity; or 
accidental, human-caused actions, or a prescribed fire that has 
developed into a wildfire. A wildfire that predominantly occurs on 
wildland is a natural event.
    (o) Wildland means an area in which human activity and development 
are essentially non-existent, except for roads, railroads, power lines, 
and similar transportation facilities. Structures, if any, are widely 
scattered.
    (p) High wind dust event is an event that includes the high-speed 
wind and the dust that the wind entrains and transports to a monitoring 
site.
    (q) High wind threshold is the minimum wind speed capable of 
causing particulate matter emissions from natural undisturbed lands in 
the area affected by a high wind dust event.
    (r) Federal land manager means, consistent with the definition in 
40 CFR 51.301, the Secretary of the department with authority over the 
Federal Class I area (or the Secretary's designee) or, with respect to 
Roosevelt-Campobello International Park, the Chairman of the Roosevelt-
Campobello International Park Commission.

0
3. Revise Sec.  50.14 to read as follows:


Sec.  50.14  Treatment of air quality monitoring data influenced by 
exceptional events.

    (a) Requirements--(1) Scope. (i) This section applies to the 
treatment of data showing exceedances or violations of any national 
ambient air quality standard for purposes of the following types of 
regulatory determinations by the Administrator:
    (A) An action to designate an area, pursuant to Clean Air Act 
section 107(d)(1), or redesignate an area, pursuant to Clean Air Act 
section 107(d)(3), for a particular national ambient air quality 
standard;
    (B) The assignment or re-assignment of a classification category to 
a nonattainment area where such classification is based on a comparison 
of pollutant design values, calculated according to the specific data 
handling procedures in 40 CFR part 50 for each national ambient air 
quality standard, to the level of the relevant national ambient air 
quality standard;
    (C) A determination regarding whether a nonattainment area has 
attained the level of the appropriate national ambient air quality 
standard by its specified deadline;
    (D) A determination that an area has data for the specific NAAQS, 
which qualify the area for an attainment date extension under the CAA 
provisions for the applicable pollutant;
    (E) A determination under Clean Air Act section 110(k)(5), if based 
on an area violating a national ambient air quality standard, that the 
state implementation plan is inadequate under the requirements of Clean 
Air Act section 110; and
    (F) Other actions on a case-by-case basis as determined by the 
Administrator.
    (ii) A State, federal land manager or other federal agency may 
request the Administrator to exclude data showing exceedances or 
violations of any national ambient air quality standard that are 
directly due to an exceptional event from use in determinations 
identified in paragraph (a)(1)(i) of this section by demonstrating to 
the Administrator's satisfaction that such event caused a specific air 
pollution concentration at a particular air quality monitoring 
location.
    (A) For a federal land manager or other federal agency to be 
eligible to initiate such a request for data exclusion, the federal 
land manager or other federal agency must:
    (1) Either operate a regulatory monitor that has been affected by 
an exceptional event or manage land on which an exceptional event 
occurred that influenced a monitored concentration at a regulatory 
monitor; and
    (2) Initiate such a request only after the State in which the 
affected monitor is located concurs with the federal land manager's or 
other federal agency's submittal.
    (B) With regard to such a request, all provisions in this section 
that are expressed as requirements applying to a State shall, except as 
noted, be requirements applying to the federal land manager or other 
federal agency.
    (C) Provided all provisions in this section are met, the 
Administrator shall allow a State to submit demonstrations for any 
regulatory monitor within its jurisdictional bounds, including those 
operated by federal land managers, other federal agencies and delegated 
local agencies.
    (D) Where multiple agencies within a state submit demonstrations 
for events that meet the requirements of the Exceptional Events Rule, a 
State submittal shall have primacy for any regulatory monitor within 
its jurisdictional bounds.
    (2) A demonstration to justify data exclusion may include any 
reliable and accurate data, but must specifically address the elements 
in paragraphs (c)(3)(iv) and (v) of this section.
    (b) Determinations by the Administrator--(1) Generally. The 
Administrator shall exclude data from use in determinations of 
exceedances and violations identified in paragraph (a)(1)(i) of this 
section where a State demonstrates to the Administrator's satisfaction 
that an exceptional event caused a specific air pollution concentration 
at a particular air quality monitoring location and otherwise satisfies 
the requirements of this section.
    (2) Fireworks displays. The Administrator shall exclude data from 
use in determinations of exceedances and violations where a State 
demonstrates to the Administrator's satisfaction that emissions from 
fireworks displays caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise satisfies the 
requirements of this section. Such data will be treated in the same 
manner as exceptional events under this rule, provided a State 
demonstrates that such use of fireworks is significantly integral to 
traditional national, ethnic, or other cultural events including, but 
not limited to, July Fourth celebrations that satisfy the requirements 
of this section.
    (3) Prescribed fires. (i) The Administrator shall exclude data from 
use in determinations of exceedances and violations, where a State 
demonstrates to the Administrator's satisfaction that emissions from 
prescribed fires caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise

[[Page 68278]]

satisfies the requirements of this section.
    (ii) In addressing the requirements set forth in paragraph 
(c)(3)(iv)(D) of this section regarding the not reasonably controllable 
or preventable criterion:
    (A) With respect to the requirement that a prescribed fire be not 
reasonably controllable, the State must either certify to the 
Administrator that it has adopted and is implementing a smoke 
management program or the State must demonstrate that the burn manager 
employed appropriate basic smoke management practices identified in 
Table 1 to Sec.  50.14. Where a burn manager employs appropriate basic 
smoke management practices, the State may rely on a statement or other 
documentation provided by the burn manager that he or she employed 
those practices. If an exceedance or violation of a NAAQS occurs when a 
prescribed fire is employing an appropriate basic smoke management 
practices approach, the State and the burn manager must undertake a 
review of the subject fire, including a review of the basic smoke 
management practices applied during the subject fire to ensure the 
protection of air quality and public health and progress towards 
restoring and/or maintaining a sustainable and resilient wildland 
ecosystem. If the prescribed fire becomes the subject of an exceptional 
events demonstration, documentation of the post-burn review must 
accompany the demonstration.
    (B) If the State anticipates satisfying the requirements of 
paragraph (c)(3)(iv)(D) of this section by employing the appropriate 
basic smoke management practices identified in Table 1 to Sec.  50.14, 
then:
    (1) The State, federal land managers, and other entities as 
appropriate, must periodically collaborate with burn managers operating 
within the jurisdiction of the State to discuss and document the 
process by which air agencies and land managers will work together to 
protect public health and manage air quality impacts during the conduct 
of prescribed fires on wildland. Such discussions must include outreach 
and education regarding general expectations for the selection and 
application of appropriate basic smoke management practices and goals 
for advancing strategies and increasing adoption and communication of 
the benefits of appropriate basic smoke management practices;
    (2) The State, federal land managers and burn managers shall have 
an initial implementation period, defined as being 2 years from 
September 30, 2016, to implement the collaboration and outreach effort 
identified in paragraph (b)(3)(ii)(B)(1) of this section; and
    (3) Except as provided in paragraph (b)(3)(ii)(B)(2) of this 
section, the Administrator shall not place a concurrence flag in the 
appropriate field for the data record in the AQS database, as specified 
in paragraph (c)(2)(ii) of this section, if the data are associated 
with a prescribed fire on wildland unless the requirements of paragraph 
(b)(3)(ii)(B)(1) of this section have been met and associated 
documentation accompanies any applicable exceptional events 
demonstration. The Administrator may nonconcur or defer action on such 
a demonstration.
    (C) With respect to the requirement that a prescribed fire be not 
reasonably preventable, the State may rely upon and reference a multi-
year land or resource management plan for a wildland area with a stated 
objective to establish, restore and/or maintain a sustainable and 
resilient wildland ecosystem and/or to preserve endangered or 
threatened species through a program of prescribed fire provided that 
the Administrator determines that there is no compelling evidence to 
the contrary in the record and the use of prescribed fire in the area 
has not exceeded the frequency indicated in that plan.
    (iii) Provided the Administrator determines that there is no 
compelling evidence to the contrary in the record, in addressing the 
requirements set forth in paragraph (c)(3)(iv)(E) of this section 
regarding the human activity unlikely to recur at a particular location 
criterion for demonstrations involving prescribed fires on wildland, 
the State must describe the actual frequency with which a burn was 
conducted, but may rely upon and reference an assessment of the natural 
fire return interval or the prescribed fire frequency needed to 
establish, restore and/or maintain a sustainable and resilient wildland 
ecosystem contained in a multi-year land or resource management plan 
with a stated objective to establish, restore and/or maintain a 
sustainable and resilient wildland ecosystem and/or to preserve 
endangered or threatened species through a program of prescribed fire.

  Table 1 to Sec.   50.14--Summary of Basic Smoke Management Practices,
         Benefit Achieved With the BSMP, and When it is Applieda
------------------------------------------------------------------------
                                                        When the BSMP is
    Basic Smoke Management      Benefit achieved with   applied--before/
         Practice \b\                  the BSMP         during/after the
                                                              burn
------------------------------------------------------------------------
Evaluate Smoke Dispersion       Minimize smoke         Before, During,
 Conditions.                     impacts.               After.
Monitor Effects on Air Quality  Be aware of where the  Before, During,
                                 smoke is going and     After.
                                 degree it impacts
                                 air quality.
Record-Keeping/Maintain a Burn/ Retain information     Before, During,
 Smoke Journal.                  about the weather,     After.
                                 burn and smoke. If
                                 air quality problems
                                 occur, documentation
                                 helps analyze and
                                 address air
                                 regulatory issues..
Communication--Public           Notify neighbors and   Before, During.
 Notification.                   those potentially
                                 impacted by smoke,
                                 especially sensitive
                                 receptors.
Consider Emission Reduction     Reducing emissions     Before, During,
 Techniques.                     through mechanisms     After.
                                 such as reducing
                                 fuel loading can
                                 reduce downwind
                                 impacts.
Share the Airshed--             Coordinate multiple    Before, During,
 Coordination of Area Burning.   burns in the area to   After.
                                 manage exposure of
                                 the public to smoke.
------------------------------------------------------------------------
\a\ The EPA believes that elements of these BSMP could also be practical
  and beneficial to apply to wildfires for areas likely to experience
  recurring wildfires.
\b\ The listing of BSMP in this table is not intended to be all-
  inclusive. Not all BSMP are appropriate for all burns. Goals for
  applicability should retain flexibility to allow for onsite variation
  and site-specific conditions that can be variable on the day of the
  burn. Burn managers can consider other appropriate BSMP as they become
  available due to technological advancement or programmatic refinement.

    (4) Wildfires. The Administrator shall exclude data from use in 
determinations of exceedances and violations where a State demonstrates 
to the Administrator's satisfaction that emissions from wildfires 
caused a

[[Page 68279]]

specific air pollution concentration in excess of one or more national 
ambient air quality standard at a particular air quality monitoring 
location and otherwise satisfies the requirements of this section. 
Provided the Administrator determines that there is no compelling 
evidence to the contrary in the record, the Administrator will 
determine every wildfire occurring predominantly on wildland to have 
met the requirements identified in paragraph (c)(3)(iv)(D) of this 
section regarding the not reasonably controllable or preventable 
criterion.
    (5) High wind dust events. (i) The Administrator shall exclude data 
from use in determinations of exceedances and violations, where a State 
demonstrates to the Administrator's satisfaction that emissions from a 
high wind dust event caused a specific air pollution concentration in 
excess of one or more national ambient air quality standards at a 
particular air quality monitoring location and otherwise satisfies the 
requirements of this section provided that such emissions are from high 
wind dust events.
    (ii) The Administrator will consider high wind dust events to be 
natural events in cases where windblown dust is entirely from natural 
undisturbed lands in the area or where all anthropogenic sources are 
reasonably controlled as determined in accordance with paragraph (b)(8) 
of this section.
    (iii) The Administrator will accept a high wind threshold of a 
sustained wind of 25 mph for areas in the States of Arizona, 
California, Colorado, Kansas, Nebraska, Nevada, New Mexico, North 
Dakota, Oklahoma, South Dakota, Texas, Utah, and Wyoming provided this 
value is not contradicted by evidence in the record at the time the 
State submits a demonstration. In lieu of this threshold, States can 
identify and use an Administrator-approved alternate area-specific high 
wind threshold that is more representative of local or regional 
conditions, if appropriate.
    (iv) In addressing the requirements set forth in paragraph 
(c)(3)(iv)(D) of this section regarding the not reasonably preventable 
criterion, the State shall not be required to provide a case-specific 
justification for a high wind dust event.
    (v) With respect to the not reasonably controllable criterion of 
paragraph (c)(3)(iv)(D) of this section, dust controls on an 
anthropogenic source shall be considered reasonable in any case in 
which the controls render the anthropogenic source as resistant to high 
winds as natural undisturbed lands in the area affected by the high 
wind dust event. The Administrator may determine lesser controls 
reasonable on a case-by-case basis.
    (vi) For large-scale and high-energy high wind dust events, the 
Administrator will generally consider a demonstration documenting the 
nature and extent of the event to be sufficient with respect to the not 
reasonably controllable criterion of paragraph (c)(3)(iv)(D) of this 
section provided the State provides evidence showing that the event 
satisfies the following:
    (A) The event is associated with a dust storm and is the focus of a 
Dust Storm Warning.
    (B) The event has sustained winds that are greater than or equal to 
40 miles per hour.
    (C) The event has reduced visibility equal to or less than 0.5 
miles.
    (6) Stratospheric Intrusions. Where a State demonstrates to the 
Administrator's satisfaction that emissions from stratospheric 
intrusions caused a specific air pollution concentration in excess of 
one or more national ambient air quality standard at a particular air 
quality monitoring location and otherwise satisfies the requirements of 
this section, the Administrator will determine stratospheric intrusions 
to have met the requirements identified in paragraph (c)(3)(iv)(D) of 
this section regarding the not reasonably controllable or preventable 
criterion and shall exclude data from use in determinations of 
exceedances and violations.
    (7) Determinations with respect to event aggregation, multiple 
national ambient air quality standards for the same pollutant, and 
exclusion of 24-hour values for particulate matter.
    (i) Where a State demonstrates to the Administrator's satisfaction 
that for national ambient air quality standards with averaging or 
cumulative periods less than or equal to 24 hours the aggregate effect 
of events occurring on the same day has caused an exceedance or 
violation, the Administrator shall determine such collective data to 
satisfy the requirements in paragraph (c)(3)(iv)(B) of this section 
regarding the clear causal relationship criterion. Where a State 
demonstrates to the Administrator's satisfaction that for national 
ambient air quality standards with averaging or cumulative periods 
longer than 24 hours the aggregate effect of events occurring on 
different days has caused an exceedance or violation, the Administrator 
shall determine such collective data to satisfy the requirements in 
paragraph (c)(3)(iv)(B) of this section regarding the clear causal 
relationship criterion.
    (ii) The Administrator shall accept as part of a demonstration for 
the clear causal relationship in paragraph (c)(3)(iv)(B) of this 
section with respect to a 24-hour NAAQS, a State's comparison of a 24-
hour concentration of any national ambient air quality standard 
pollutant to the level of a national ambient air quality standard for 
the same pollutant with a longer averaging period. The Administrator 
shall also accept as part of a demonstration for the clear causal 
relationship in paragraph (c)(3)(iv)(B) of this section with respect to 
a NAAQS with a longer averaging period, a State's comparison of a 24-
hour concentration of any national ambient air quality standard 
pollutant to the level of the national ambient air quality standard for 
the same pollutant with a longer averaging period, without the State 
having to demonstrate that the event caused the annual average 
concentration of the pollutant to exceed the level of the NAAQS with 
the longer averaging period.
    (iii) Where a State operates a continuous analyzer that has been 
designated as a Federal Equivalent Method monitor as defined in 40 CFR 
50.1(g) that complies with the monitoring requirements of 40 CFR part 
58, Appendix C, and the State believes that collected data have been 
influenced by an event, in following the process outlined in paragraph 
(c)(2) of this section, the State shall create an initial event 
description and flag the associated event-influenced data that have 
been submitted to the AQS database for the affected monitor. Where a 
State demonstrates to the Administrator's satisfaction that such data 
satisfy the requirements in paragraph (c)(3)(iv)(B) of this section 
regarding the clear causal relationship criterion and otherwise satisfy 
the requirements of this section, the Administrator shall agree to 
exclude all data within the affected calendar day(s).
    (8) Determinations with respect to the not reasonably controllable 
or preventable criterion. (i) The not reasonably controllable or 
preventable criterion has two prongs that the State must demonstrate: 
prevention and control.
    (ii) The Administrator shall determine that an event is not 
reasonably preventable if the State shows that reasonable measures to 
prevent the event were applied at the time of the event.
    (iii) The Administrator shall determine that an event is not 
reasonably controllable if the State shows that reasonable measures to 
control the impact of the event on air quality were applied at the time 
of the event.
    (iv) The Administrator shall assess the reasonableness of available 
controls for

[[Page 68280]]

anthropogenic sources based on information available as of the date of 
the event.
    (v) Except where a State, tribal or federal air agency is obligated 
to revise its state implementation plan, tribal implementation plan, or 
federal implementation plan, the Administrator shall consider 
enforceable control measures implemented in accordance with a state 
implementation plan, tribal implementation plan, or federal 
implementation plan, approved by the EPA within 5 years of the date of 
the event, that address the event-related pollutant and all sources 
necessary to fulfill the requirements of the Clean Air Act for the 
state implementation plan, tribal implementation plan, or federal 
implementation plan to be reasonable controls with respect to all 
anthropogenic sources that have or may have contributed to the 
monitored exceedance or violation.
    (vi) Where a State, tribal or federal air agency is obligated to 
revise its state implementation plan, tribal implementation plan, or 
federal implementation plan, the deference to enforceable control 
measures identified in paragraph (b)(8)(v) of this section shall remain 
only until the due date of the required state implementation plan, 
tribal implementation plan, or federal implementation plan revisions. 
However, where an air agency is obligated to revise the enforceable 
control measures identified in paragraph (b)(8)(v) of this section in 
its implementation plan as a result of an action pursuant to Clean Air 
Act section 110(k)(5), the deference, if any, to those enforceable 
control measures shall be determined on a case-by-case basis.
    (vii) The Administrator shall not require a State to provide case-
specific justification to support the not reasonably controllable or 
preventable criterion for emissions-generating activity that occurs 
outside of the State's jurisdictional boundaries within which the 
concentration at issue was monitored. In the case of a tribe treated as 
a state under 40 CFR 49.2 with respect to exceptional events 
requirements, the tribe's jurisdictional boundaries for purposes of 
requiring or directly implementing emission controls apply. In the case 
of a federal land manager or other federal agency submitting a 
demonstration under the requirements of this section, the 
jurisdictional boundaries that apply are those of the State or the 
tribe depending on which has jurisdiction over the area where the event 
has occurred.
    (viii) In addition to the provisions that apply to specific event 
types identified in paragraphs (b)(3)(ii) and (b)(5)(i) through (iii) 
of this section in addressing the requirements set forth in paragraph 
(c)(3)(iv)(D) of this section regarding the not reasonably controllable 
or preventable criterion, the State must include the following 
components:
    (A) Identification of the natural and anthropogenic sources of 
emissions causing and contributing to the monitored exceedance or 
violation, including the contribution from local sources.
    (B) Identification of the relevant state implementation plan, 
tribal implementation plan, or federal implementation plan or other 
enforceable control measures in place for the sources identified in 
paragraph (b)(8)(vii)(A) of this section and the implementation status 
of these controls.
    (C) Evidence of effective implementation and enforcement of the 
measures identified in paragraph (b)(8)(vii)(B) of this section.
    (D) The provisions in this paragraph shall not apply if the 
provisions in paragraph (b)(4), (b)(5)(vi), or (b)(6) of this section 
apply.
    (9) Mitigation plans. (i) Except as provided for in paragraph 
(b)(9)(ii) of this section, where a State is subject to the 
requirements of 40 CFR 51.930(b), the Administrator shall not place a 
concurrence flag in the appropriate field for the data record in the 
AQS database, as specified in paragraph (c)(2)(ii) of this section, if 
the data are of the type and pollutant that are the focus of the 
mitigation plan until the State fulfills its obligations under the 
requirements of 40 CFR 51.930(b). The Administrator may nonconcur or 
defer action on such a demonstration.
    (ii) The prohibition on placing a concurrence flag in the 
appropriate field for the data record in the AQS database by the 
Administrator stated in paragraph (b)(9(i) of this section does not 
apply to data that are included in an exceptional events demonstration 
that is:
    (A) submitted in accordance with paragraph (c)(3) of this section 
that is also of the type and pollutant that is the focus of the 
mitigation plan, and
    (B) submitted within the 2-year period allowed for mitigation plan 
development as specified in 40 CFR 51.930(b)(3).
    (c) Schedules and procedures--(1) Public notification. (i) In 
accordance with the mitigation requirement at 40 CFR 51.930(a)(1), all 
States and, where applicable, their political subdivisions must notify 
the public promptly whenever an event occurs or is reasonably 
anticipated to occur which may result in the exceedance of an 
applicable air quality standard.
    (ii) [Reserved]
    (2) Initial notification of potential exceptional event. (i) A 
State shall notify the Administrator of its intent to request exclusion 
of one or more measured exceedances of an applicable national ambient 
air quality standard as being due to an exceptional event by creating 
an initial event description and flagging the associated data that have 
been submitted to the AQS database and by engaging in the Initial 
Notification of Potential Exceptional Event process as follows:
    (A) The State and the appropriate EPA Regional office shall engage 
in regular communications to identify those data that have been 
potentially influenced by an exceptional event, to determine whether 
the identified data may affect a regulatory determination and to 
discuss whether the State should develop and submit an exceptional 
events demonstration according to the requirements in this section;
    (B) For data that may affect an anticipated regulatory 
determination or where circumstances otherwise compel the Administrator 
to prioritize the resulting demonstration, the Administrator shall 
respond to a State's Initial Notification of Potential Exceptional 
Event with a due date for demonstration submittal that considers the 
nature of the event and the anticipated timing of the associated 
regulatory decision;
    (C) The Administrator may waive the Initial Notification of 
Potential Exceptional Event process on a case-by-case basis.
    (ii) The data shall not be excluded from determinations with 
respect to exceedances or violations of the national ambient air 
quality standards unless and until, following the State's submittal of 
its demonstration pursuant to paragraph (c)(3) of this section and the 
Administrator's review, the Administrator notifies the State of its 
concurrence by placing a concurrence flag in the appropriate field for 
the data record in the AQS database.
    (iii) [Reserved]
    (iv) [Reserved]
    (v) [Reserved]
    (vi) Table 2 to Sec.  50.14 identifies the submission process for 
data that will or may influence the initial designation of areas for 
any new or revised national ambient air quality standard.

[[Page 68281]]



     Table 2 to Sec.   50.14--Schedule for Initial Notification and
 Demonstration Submission for Data Influenced by Exceptional Events for
                    Use in Initial Area Designations
------------------------------------------------------------------------
 Exceptional events/Regulatory                       Exceptional events
            action                  Condition      deadline schedule \d\
------------------------------------------------------------------------
(A) Initial Notification        If state and       then the Initial
 deadline for data years 1, 2    tribal initial     Notification
 and 3.\a\.                      designation        deadline will be the
                                 recommendations    July 1 prior to the
                                 for a new/         recommendation
                                 revised national   deadline.
                                 ambient air
                                 quality standard
                                 are due August
                                 through January,
(B) Initial Notification        If state and       then the Initial
 deadline for data years 1, 2    tribal             Notification
 and 3.\a\.                      recommendations    deadline will be the
                                 for a new/         January 1 prior to
                                 revised national   the recommendation
                                 ambient air        deadline.
                                 quality standard
                                 are due February
                                 through July,
(C) Exceptional events          None.............  no later than the
 demonstration submittal                            later of November
 deadline for data years 1, 2                       29, 2016 or the date
 and 3 \a\.                                         that state and
                                                    tribal
                                                    recommendations are
                                                    due to the
                                                    Administrator.
(D) Initial Notification and    None.............  by the last day of
 exceptional events                                 the month that is 1
 demonstration submittal                            year and 7 months
 deadline for data year 4 \b\                       after promulgation
 and, where applicable, data                        of a new/revised
 year 5.\c\.                                        national ambient air
                                                    quality standard,
                                                    unless either
                                                    paragraph (E) or
                                                    paragraph (F)
                                                    applies.
(E) Initial Notification and    If the             the deadline is 2
 exceptional events              Administrator      years and 7 months
 demonstration submittal         follows a 3-year   after promulgation
 deadline for data year 4 \b\    designation        of a new/revised
 and, where applicable, data     schedule.          national ambient air
 year 5.\c\.                                        quality standard.
(F) Initial Notification and    If the             the deadline is 5
 exceptional events              Administrator      months prior to the
 demonstration submittal         notifies the       date specified for
 deadline for data year 4 \b\    state/tribe that   final designations
 and, where applicable, data     it intends to      decisions in such
 year 5.\c\.                     complete the       Administrator
                                 initial area       notification.
                                 designations
                                 process
                                 according to a
                                 schedule between
                                 2 and 3 years,.
------------------------------------------------------------------------
\a\ Where data years 1, 2, and 3 are those years expected to be
  considered in state and tribal recommendations.
\b\ Where data year 4 is the additional year of data that the
  Administrator may consider when making final area designations for a
  new/revised national ambient air quality standard under the standard
  designations schedule.
\c\ Where data year 5 is the additional year of data that the
  Administrator may consider when making final area designations for a
  new/revised national ambient air quality standard under an extended
  designations schedule.
\d\ The date by which air agencies must certify their ambient air
  quality monitoring data in AQS is annually on May 1 of the year
  following the year of data collection as specified in 40 CFR
  58.15(a)(2). In some cases, however, air agencies may choose to
  certify a prior year's data in advance of May 1 of the following year,
  particularly if the Administrator has indicated intent to promulgate
  final designations in the first 8 months of the calendar year.
  Exceptional events demonstration deadlines for ``early certified''
  data will follow the deadlines for ``year 4'' and ``year 5'' data.

    (3) Submission of demonstrations. (i) Except as provided under 
paragraph (c)(2)(vi) of this section, a State that has flagged data as 
being due to an exceptional event and is requesting exclusion of the 
affected measurement data shall, after notice and opportunity for 
public comment, submit a demonstration to justify data exclusion to the 
Administrator according to the schedule established under paragraph 
(c)(2)(i)(B).
    (ii) [Reserved]
    (iii) [Reserved]
    (iv) The demonstration to justify data exclusion must include:
    (A) A narrative conceptual model that describes the event(s) 
causing the exceedance or violation and a discussion of how emissions 
from the event(s) led to the exceedance or violation at the affected 
monitor(s);
    (B) A demonstration that the event affected air quality in such a 
way that there exists a clear causal relationship between the specific 
event and the monitored exceedance or violation;
    (C) Analyses comparing the claimed event-influenced 
concentration(s) to concentrations at the same monitoring site at other 
times to support the requirement at paragraph (c)(3)(iv)(B) of this 
section. The Administrator shall not require a State to prove a 
specific percentile point in the distribution of data;
    (D) A demonstration that the event was both not reasonably 
controllable and not reasonably preventable; and
    (E) A demonstration that the event was a human activity that is 
unlikely to recur at a particular location or was a natural event.
    (v) With the submission of the demonstration containing the 
elements in paragraph (c)(3)(iv) of this section, the State must:
    (A) Document that the State followed the public comment process and 
that the comment period was open for a minimum of 30 days, which could 
be concurrent with the beginning of the Administrator's initial review 
period of the associated demonstration provided the State can meet all 
requirements in this paragraph;
    (B) Submit the public comments it received along with its 
demonstration to the Administrator; and
    (C) Address in the submission to the Administrator those comments 
disputing or contradicting factual evidence provided in the 
demonstration.
    (vi) Where the State has submitted a demonstration according to the 
requirements of this section after September 30, 2016 and the 
Administrator has reviewed such demonstration and requested additional 
evidence to support one of the elements in paragraph (c)(3)(iv) of this 
section, the State shall have 12 months from the date of the 
Administrator's request to submit such evidence. At the conclusion of 
this time, if the State has not submitted the requested additional 
evidence, the Administrator will notify the State in writing that it 
considers the demonstration to be inactive and will not pursue 
additional review of the demonstration. After a 12-month period of 
inactivity by the State, if a State desires to pursue the inactive 
demonstration, it must reinitiate its request to exclude associated 
data by following the process beginning with paragraph (c)(2)(i) of 
this section.

PART 51--REQUIREMENTS FOR PREPARATION, ADOPTION, AND SUBMITTAL OF 
IMPLEMENTATION PLANS

0
4. The authority citation for part 51 continues to read as follows:


[[Page 68282]]


    Authority:  23 U.S.C. 101; 42 U.S.C. 7401-7671q.

0
5. Revise Sec.  51.930 to read as follows:


Sec.  51.930  Mitigation of Exceptional Events.

    (a) A State requesting to exclude air quality data due to 
exceptional events must take appropriate and reasonable actions to 
protect public health from exceedances or violations of the national 
ambient air quality standards. At a minimum, the State must:
    (1) Provide for prompt public notification whenever air quality 
concentrations exceed or are expected to exceed an applicable ambient 
air quality standard;
    (2) Provide for public education concerning actions that 
individuals may take to reduce exposures to unhealthy levels of air 
quality during and following an exceptional event; and
    (3) Provide for the implementation of appropriate measures to 
protect public health from exceedances or violations of ambient air 
quality standards caused by exceptional events.
    (b) Development of mitigation plans for areas with historically 
documented or known seasonal events--(1) Generally. All States having 
areas with historically documented or known seasonal events shall be 
required to develop a mitigation plan with the components identified in 
paragraph (b)(2) of this section and submit such plan to the 
Administrator according to the requirements in paragraph (b)(3) of this 
section.
    (i) For purposes of the requirements set forth in this section, 
historically documented or known seasonal events shall include those 
events of the same type and pollutant that recur in a 3-year period and 
meet any of the following:
    (A) Three events or event seasons for which a State submits a 
demonstration under the provisions of 40 CFR 50.14 in a 3-year period; 
or
    (B) Three events or event seasons that are the subject of an 
initial notification of a potential exceptional event as defined in 40 
CFR 50.14(c)(2) in a 3-year period regardless of whether the State 
submits a demonstration under the provisions of 40 CFR 50.14.
    (ii) The Administrator will provide written notification to States 
that they are subject to the requirements in paragraph (b) of this 
section when the Administrator becomes aware of applicability.
    (2) Plan components. At a minimum, each mitigation plan developed 
under this paragraph shall contain provisions for the following:
    (i) Public notification to and education programs for affected or 
potentially affected communities. Such notification and education 
programs shall apply whenever air quality concentrations exceed or are 
expected to exceed a national ambient air quality standard with an 
averaging time that is less than or equal to 24-hours.
    (ii) Steps to identify, study and implement mitigating measures, 
including approaches to address each of the following:
    (A) Measures to abate or minimize contributing controllable sources 
of identified pollutants.
    (B) Methods to minimize public exposure to high concentrations of 
identified pollutants.
    (C) Processes to collect and maintain data pertinent to the event.
    (D) Mechanisms to consult with other air quality managers in the 
affected area regarding the appropriate responses to abate and minimize 
impacts.
    (iii) Provisions for periodic review and evaluation of the 
mitigation plan and its implementation and effectiveness by the State 
and all interested stakeholders.
    (A) With the submission of the initial mitigation plan according to 
the requirements in paragraph (b)(3) of this section that contains the 
elements in paragraph (b)(2) of this section, the State must:
    (1) Document that a draft version of the mitigation plan was 
available for public comment for a minimum of 30 days;
    (2) Submit the public comments it received along with its 
mitigation plan to the Administrator; and
    (3) In its submission to the Administrator, for each public comment 
received, explain the changes made to the mitigation plan or explain 
why the State did not make any changes to the mitigation plan.
    (B) The State shall specify in its mitigation plan the periodic 
review and evaluation process that it intends to follow for reviews 
following the initial review identified in paragraph (b)(2)(iii)(A) of 
this section.
    (3) Submission of mitigation plans. All States subject to the 
provisions of paragraph (b) of this section shall, after notice and 
opportunity for public comment identified in paragraph (b)(2)(iii)(A) 
of this section, submit a mitigation plan to the Administrator for 
review and verification of the plan components identified in paragraph 
(b)(2) of this section.
    (i) States shall submit their mitigation plans within 2 years of 
being notified that they are subject to the provisions of paragraph (b) 
of this section.
    (ii) The Administrator shall review each mitigation plan developed 
according to the requirements in paragraph (b)(2) of this section and 
shall notify the submitting State upon completion of such review.

[FR Doc. 2016-22983 Filed 9-28-16; 4:15 pm]
 BILLING CODE 6560-50-P


