

[Federal Register: March 10, 2006 (Volume 71, Number 47)]
[Proposed Rules]               
[Page 12591-12610]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr10mr06-23]                         


[[Page 12591]]

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Part V





Environmental Protection Agency





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40 CFR Parts 50 and 51



The Treatment of Data Influenced by Exceptional Events; Proposed Rule


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50 and 51

[EPA-HQ-OAR-2005-0159; FRL-8042-5]
RIN 2060-AN40

 
The Treatment of Data Influenced by Exceptional Events

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Today, EPA is proposing a rule to govern the review and 
handling of air quality monitoring data influenced by exceptional 
events. Exceptional events are events for which the normal planning and 
regulatory process established by the Clean Air Act (CAA) is not 
appropriate. In this rulemaking action, EPA is proposing to: Implement 
section 319(b)(3)(B) and section 107(d)(3) authority to exclude air 
quality monitoring data from regulatory determinations related to 
exceedances or violations of the National Ambient Air Quality Standards 
(NAAQS) and avoid designating an area as nonattainment, redesignating 
an area as nonattainment, or reclassifying an existing nonattainment 
area to a higher classification if a State adequately demonstrates that 
an exceptional event has caused an exceedance or violation of a NAAQS. 
Also, EPA is proposing four options with respect to whether, and to 
what extent, States should be required to take additional actions to 
address public health impacts related to the event.

DATES: Comments must be received on or before May 9, 2006. Comments 
must be postmarked by the last day of the comment period.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-HQ-
OAR-2005-0159, by one of the following methods:
     http://www.regulations.gov. Follow the on-line 

instructions for submitting comments.
     E-mail: Comments may be sent by electronic mail (e-mail) 
to A-and-R-Docket@epa.gov, Attention Docket ID No. EPA-HQ-OAR-2005-
0159.
     Fax: Fax your comments to: 202-566-1741, Attention Docket 
ID no. EPA-HQ-OAR-2005-0159.
     Mail: Send your comments to: Air and Radiation Docket and 
Information Center, U.S. Environmental Protection Agency, Mail Code: 
6102T, 1200 Pennsylvania Ave., NW., Washington, DC 20460, Attention 
Docket ID No. EPA-HQ-OAR-2005-0159.
     Hand Delivery: Air and Radiation Docket and Information 
Center, U.S. Environmental Protection Agency, 1301 Constitution Avenue, 
NW., Room B102, Washington, DC, Attention Docket ID No. EPA-HQ-OAR-
2005-0159. Such deliveries are only accepted during the Docket's normal 
hours of operation, and special arrangements should be made for 
deliveries of boxed information.
    Instructions: Direct your comments to Docket ID No. EPA-HQ-OAR-
2005-0159. The EPA's policy is that all comments received will be 
included in the public docket without change and may be made available 
online at http://www.regulations.gov, including any personal 

information provided, unless the comment includes information claimed 
to be Confidential Business Information (CBI) or other information 
whose disclosure is restricted by statute. Do not submit information 
that you consider to be CBI or otherwise protected information through 
http://www.regulations.gov, or e-mail. The http://www.regulations.gov 
Web site is an ``anonymous access'' system, which means that EPA will 
not know your identity or contact information unless you provide it in 
the body of your comment. If you send an e-mail comment directly to EPA 
without going through http://www.regulations.gov, your e-mail address 

will be automatically captured and included as part of the comment that 
is placed in the public docket and made available on the Internet. If 
you submit an electronic comment, EPA recommends that you include your 
name and other contact information in the body of your comment and with 
any disk or CD-ROM you submit. If EPA cannot read your comment due to 
technical difficulties and cannot contact you for clarification, EPA 
may not be able to consider your comment. Electronic files should avoid 
the use of special characters, any form of encryption, and be free of 
any defects or viruses. For additional instructions on submitting 
comments, go to SUPPLEMENTARY INFORMATION.
    Docket: All documents in the docket are listed in the http://www.regulations.gov
 index. Although listed in the index, some 

information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available either electronically 
in http://www.regulations.gov or in hard copy at the Office of Air and 

Radiation Docket and Information Center, EPA West, Room B102, 1301 
Constitution Ave., NW., Washington, DC. The Public Reading Room is open 
from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal 
holidays. The telephone number for the Public Reading Room is (202) 
566-1744, and the telephone number for the Office of Air and Radiation 
Docket and Information Center is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT: General questions concerning this 
proposed rule should be addressed to Mr. Larry D. Wallace, Ph.D., 
Office of Air Quality Planning and Standards, Air Quality Policy 
Division, Mail Code C539-01, Research Triangle Park, NC 27711; 
telephone (919) 541-0906, and e-mail address wallace.larry@epa.gov.
    Questions concerning technical and analytical issues related to 
this proposed rule should be addressed to Mr. Neil Frank, Office of Air 
Quality Planning and Standards, Air Quality Assessment Division, Mail 
Code C304-04, Research Triangle Park, NC 27711; telephone (919) 541-
5560, and e-mail address frank.neil@epa.gov.

SUPPLEMENTARY INFORMATION: 

Public Hearing

    The EPA will hold two public hearings on today's proposal during 
the comment period. The details of the public hearings, including the 
times, dates, and locations will be provided in a future Federal 
Register notice. The public hearings will provide interested parties 
the opportunity to present data, views, or arguments concerning the 
proposed rule. The EPA may ask clarifying questions during the oral 
presentations, but will not respond to the presentations or comments at 
that time. Written statements and supporting information submitted 
during the comment period will be considered with the same weight as 
any oral comments and supporting information presented at the public 
hearings. Under CAA section 307(d)(1)(A), the procedural requirements 
of section 307(d) apply to this proposal. In addition, under section 
307(d)(1)(U), the Administrator determines that this action is subject 
to the provisions of section 307(d). Section 307(d)(1)(U) provides that 
the provisions of section 307(d) apply to ``such other actions as the 
Administrator may determine.'' The EPA is including the proposals in 
today's proposed rulemaking under sections 307(d)(1)(A) and (U).

Comments

    1. Submitting CBI. Do not submit this information to EPA through 
http://www.regulations.gov or e-mail. Clearly mark the part or all of 

the information that you claim to be CBI. For CBI information in a disk 
or CD-ROM that

[[Page 12593]]

you mail to EPA, mark the outside of the disk or CD-ROM as CBI and then 
identify electronically within the disk or CD-ROM the specific 
information that is claimed as CBI. In addition to one complete version 
of the comment that includes information claimed as CBI, a copy of the 
comment that does not contain the information claimed as CBI must be 
submitted for inclusion in the public docket. Information so marked 
will not be disclosed except in accordance with procedures set forth in 
40 CFR part 2.
    2. Tips for Preparing Your Comments. When submitting comments, 
remember to:
     Identify the rulemaking by docket number and other 
identifying information (subject heading, Federal Register date and 
page number).
     Follow directions--The agency may ask you to respond to 
specific questions or organize comments by referencing a Code of 
Federal Regulations (CFR) part or section number.
     Explain why you agree or disagree; suggest alternatives 
and substitute language for your requested changes.
     Describe any assumptions and provide any technical 
information and/or data that you used.
     If you estimate potential costs or burdens, explain how 
you arrived at your cost estimate in sufficient detail to allow for it 
to be reproduced.
     Provide specific examples to illustrate your concerns, and 
suggest alternatives.
     Explain your views as clearly as possible, avoiding the 
use of profanity or personal threats.
     Make sure to submit your comments by the comment period 
deadline identified.
    In addition, please send a copy of your comments to: Mr. Larry D. 
Wallace, Ph.D., U.S. Environmental Protection Agency, by one of the 
means listed below:
    1. E-Mail: wallace.larry@epa.gov.
    2. Fax: (919) 541-5489, Attention: Mr. Larry D. Wallace, Ph.D.
    3. Mail: Mr. Larry D. Wallace, Ph.D., U.S. Environmental Protection 
Agency, Office of Air Quality Planning and Standards, Mail Code: C539-
01, Research Triangle Park, NC 27711.
    4. Hand Delivery: Mr. Larry D. Wallace, Ph.D., U.S. Environmental 
Protection Agency, Office of Air Quality Planning and Standards, 109 
T.W. Alexander Drive, Research Triangle Park, NC 27709.

Table of Contents

    The following is an outline of the preamble.

I. Preamble Glossary of Terms and Acronyms
II. Background and Purpose of Today's Rulemaking
    A. Legislative Requirements
    B. Historical Experience Concerning Exceptional and Natural 
Events
III. Today's Proposed Action
    A. To Whom and to What Pollutants Does Today's Proposed Rule 
Apply?
    B. How Does This Rule Relate to Indian Tribes?
    C. What Is an Exceptional Event?
    D. Examples of Exceptional Events
    1. Chemical Spills and Industrial Accidents
    2. Structural Fires
    3. Exceedances Due to Transported Pollution
    4. Exceedances Due to a Terrorist Attack
    5. Natural Events
    a. Volcanic and Seismic Activities
    b. Natural Disasters and Associated Clean-up Activities
    c. High Wind Events
    d. Unwanted Fires
    e. Stratospheric Ozone Intrusions
IV. The Management of Air Quality Data Affected by Exceptional 
Events
    A. Flagging of Data in the AQS Database
    B. What Does It Mean for an Event To ``Affect Air Quality''?
    1. Option 1: 95th Percentile Criterion
    2. Option 2: 75th Percentile/95th Percentile Tiered Approach
    3. Option 3: Case-by-Case Approach Based On Weight of Evidence
    C. Use of a ``But For'' Test
    D. Schedules and Procedures for Flagging and Requesting 
Exclusion of Data
    1. Option 1: Early Data Flagging and Demonstration Submission
    2. Option 2: Early Data Flagging and Delayed Demonstration 
Submission
    3. Option 3: Delayed Data Flagging and Demonstration Submission
    E. Exclusion of Entire 24-Hour Value as Opposed to a Partial 
Adjustment of the 24-Hour Value
    F. What Should States be Required To Submit in Their Exceptional 
Events Demonstrations?
    G. Special Considerations Relevant to Proposed Standards for 
PM10-2.5
    H. Public Availability of Air Quality Data and Demonstrations 
Related to Exceptional Events
V. Additional Requirements
    A. Option 1: Proposed Option: Require Public Notification, 
Education and Appropriate and Reasonable Measures
    B. Option 2: The Development of a Mitigation Plan by States 
Under Section 110 of the CAA
    C. Option 3: The Development of a Mitigation Plan for Episodic 
Events
    D. Option 4: Do Not Require States To Adopt and Implement 
Specific Mitigation Plans or Measures Under This Rule
VI. Special Treatment of Certain Events Under This Rule
    A. Volcanic and Seismic Activities
    B. High Wind Events
    C. Stratospheric Ozone Intrusion
VII. Treatment of Fireworks Displays
VIII. Statutory and Executive Order Reviews
    A. Executive Order 12866: Regulatory Planning and Review
    B. Paperwork Reduction Act
    C. Regulatory Flexibility Act
    D. Unfunded Mandates Reform Act
    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 that Significantly Affect 
Energy Supply, Distribution, or Use
    I. National Technology Transfer Advancement Act

I. Preamble Glossary of Terms and Acronyms

    The following are abbreviations of terms used in the preamble.

AQS Air Quality System
BACM Best Available Control Measures
CAA Clean Air Act
CAAA Clean Air Act Amendments
EPA Environmental Protection Agency
FIP Federal Implementation Plan
FMP Fire Mitigation Plan
NAAQS National Ambient Air Quality Standards
NEAP Natural Event Action Plan
OAQPS Office of Air Quality Planning and Standards
PM10 Particles with a nominal mean aerodynamic diameter less 
than or equal to 10 micrometers
PM10-2.5 Particles with a nominal mean aerodynamic diameter 
greater than 2.5 micrometers and less than or equal to 10 micrometers
PM2.5 Particles with a nominal mean aerodynamic diameter 
less than or equal to 2.5 micrometers
RACM Reasonably Available Control Measures
SIP State Implementation Plan
SAFE-TEA-LU Safe Accountable Flexible Efficient-Transportation Equity 
Act--A Legacy for Users
SMP Smoke Management Plan
TAR Tribal Authority Rule
TIP Tribal Implementation Plan

II. Background and Purpose of Today's Rulemaking

A. Legislative Requirements

    Today, EPA is proposing a rule to govern the review and handling of 
air quality monitoring data influenced by exceptional events. As 
discussed below, these are events for which the normal planning and 
regulatory process established by the CAA is not appropriate. Section 
319 of the CAA, as amended by section 6013 of the Safe Accountable 
Flexible Efficient-Transportation Equity Act: A Legacy for Users (SAFE-
TEA-LU) of 2005, requires EPA to publish this rule in the Federal

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Register no later than March 1, 2006.\1\ Further, EPA is required to 
issue the final rule no later than 1 year from the date of proposal.
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    \1\ All subsequent references to section 319 of the CAA in this 
proposal are to section 319 as amended by SAFE-TEA-LU unless 
otherwise noted.
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    The EPA is proposing to establish procedures and criteria related 
to the identification, evaluation, interpretation, and use of air 
quality monitoring data related to any NAAQS where States petition EPA 
to exclude data that are affected by exceptional events. Section 319 
defines an event as an exceptional event if the event affects air 
quality; is a natural event or an event caused by human activity that 
is unlikely to recur at a particular location; and is determined by the 
Administrator to be an exceptional event. The statutory definition of 
exceptional event specifically excludes stagnation of air masses or 
meteorological inversions; a meteorological event involving high 
temperature or lack of precipitation; or air pollution relating to 
source noncompliance.
    Section 319(b)(3)(B)(i) requires a State air quality agency to 
demonstrate through ``reliable, accurate data that is promptly 
produced'' that an exceptional event occurred.\2\ Section 
319(b)(3)(B)(ii) requires that ``a clear causal relationship'' be 
established between a measured exceedance of a NAAQS and the 
exceptional event demonstrating ``that the exceptional event caused a 
specific air pollution concentration at a particular location.'' In 
addition, section 319(b)(3)(B)(iii) requires a public process to 
determine whether an event is an exceptional event. Finally, section 
319(b)(3)(B)(iv) requires criteria and procedures for a Governor to 
petition the Administrator to exclude air quality monitoring data that 
is directly due to exceptional events from use in determinations with 
respect to exceedences or violations of the NAAQS.
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    \2\ While this document refers primarily to States as the entity 
responsible for flagging data impacted by exceptional events, other 
agencies, such as local or Tribal government agencies, may also have 
standing to flag data as being affected by these types of events, 
and the criteria and procedures that are discussed in this 
rulemaking also apply to these entities.
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    Section 319 also contains a set of five principles for EPA to 
follow in developing regulations to implement section 319:
    (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 data base 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 (42 U.S.C. 7619(b)(3)(A)).
    In adopting revisions to section 319, EPA believes that Congress 
sought to provide statutory relief to States to allow them to avoid 
being designated as nonattainment or to avoid continuing to be 
designated nonattainment as a result of exceptional events in 
appropriate circumstances. In addition, Congress indicated that States 
should not have to prepare and implement regulatory strategies when 
their air quality is affected by events beyond their reasonable 
control. To accomplish this goal, Congress enumerated certain minimum 
requirements for this rulemaking. In addition, Congress provided 
certain statutory principles for EPA to follow in promulgating 
regulations to exclude data affected by exceptional events.
    Section 319 also includes an interim provision, section 319(b)(4), 
that addresses the transition period between the present and the date 
that a final regulation governing the treatment of data related to 
exceptional events is promulgated. The provision indicates that 
following EPA guidance documents continues to apply until the effective 
date of a final regulation promulgated under section 319(b)(2): 
``Guidance on the Identification and Use of Air Quality Data Affected 
by Exceptional Events'' (July 1986); ``Areas Affected by 
PM10 Natural Events,'' May 30, 1996; and appendices I, K, 
and N to 40 CFR part 50, which describe how air quality monitoring data 
are to be used and interpreted to determine compliance with the 
applicable NAAQS. The statute requires the promulgation of the final 
rule no later than 1 year following the publication of this proposed 
rule.

B. Historical Experience Concerning Exceptional and Natural Events

    Since 1977, EPA guidance and regulations have either implied or 
documented the need for a flagging system for data affected by an 
exceptional event. The first EPA guidance related to the exclusion or 
discounting of data affected by an exceptional event was an Office of 
Air Quality Planning and Standards (OAQPS) guidance document entitled, 
``Guidelines for the Interpretation of Air Quality Standards,'' 
Guideline No. 1.2-008 (revised February 1977).\3\
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    \3\ ``Guideline for Interpretation of Air Quality Standards,'' 
U.S. Environmental Protection Agency, Office of Air Quality Planning 
and Standards, Research Triangle Park, N.C. OAQPS No. 1.2-008 
(Revised February 1977). The guidance indicated the need for a data 
flagging system which would require the submittal of detailed 
information establishing that a violation was due to uncontrollable 
natural sources and that the information could be used in decision-
making related to the feasibility of modifying control strategies.
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    In July 1986, EPA issued the guidance entitled, ``Guideline on the 
Identification and Use of Air Quality Data Affected by Exceptional 
Events'' (the Exceptional Events Policy). The Exceptional Events Policy 
provided criteria for States to use in making decisions related to 
identifying data that have been influenced by an exceptional event.
    In addition to the Exceptional Events Policy, on July 1, 1987, EPA 
promulgated the NAAQS for PM10 (particulate matter with an 
aerodynamic diameter of 10 micrometers or less) which also addressed 
the issue of excluding or discounting data affected by exceptional 
events.\4\ Appendix K of that rule allows for special consideration of 
data determined to be affected by an exceptional event. Section 2.4 of 
appendix K authorizes EPA to discount from consideration in making 
attainment or nonattainment determinations for air quality data that 
are attributable to ``an uncontrollable event caused by natural 
sources'' of PM10, or ``an event that is not expected to 
recur at a given location.'' Section 2.4 of appendix K, together with 
EPA guidance contained in the Exceptional Events Policy, describes the 
steps that should be taken for flagging PM10 data that a 
State believes are affected by an exceptional or natural event.
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    \4\ Federal Register (52 FR 24667), July 1, 1987.
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    In 1990, section 188(f) was added to the CAA. This section of the 
CAA provided EPA authority to waive either a specific attainment date 
or certain planning requirements for serious PM10 
nonattainment areas that were affected by nonanthropogenic sources. In 
response to section 188(f), and in consideration of the CAA 
consequences for areas affected by elevated concentrations caused by 
natural events, in 1996 EPA issued a policy to address data affected by 
natural events entitled, ``Areas Affected by PM10 Natural 
Events,'' (the PM10 Natural Events Policy).\5\
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    \5\ Memorandum from Mary D. Nichols, Assistant Administrator for 
Air and Radiation, to EPA Regional Offices entitled, ``Areas 
Affected by PM10 Natural Events,'' May 30, 1996.

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    On July 18, 1997, EPA issued revised NAAQS for ozone and a new 
NAAQS addressing PM2.5. For ozone, the revised NAAQS 
provided for an 8-hour averaging period (versus 1 hour for the previous 
NAAQS), and the level of the standard was changed from 0.12 ppm to 0.08 
ppm (62 FR 38856). For the PM2.5 NAAQS, EPA established both 
a new 24-hour standard and a new annual standard. In that Federal 
Register, EPA also promulgated appendices I and N to 40 CFR part 50. 
Appendices I and N provided the methodologies for determining whether 
an area is in attainment of the 8-hour ozone and PM2.5 NAAQS 
respectively, using ambient air quality data. Section 1.0 of appendix 
I, and section 1.0(b) of appendix N provide the authority for EPA to 
give special consideration to data determined to be affected by an 
exceptional or natural event.
    Appendices K, I, and N, which are a part of the NAAQS for the 
affected pollutants as described above, provide that, while States must 
submit all valid ambient air quality data to EPA's Air Quality System 
(AQS) data base for use in making regulatory decisions, in some cases 
it may be appropriate for the Regional Administrator to exclude, 
discount, weight, or make adjustments to data that have been 
appropriately flagged from calculations in determining whether or not 
an area has attained the standard. These decisions are to be made on a 
case-by-case basis using all available information related to the event 
in question, and are required to be made available to the public for 
review. It should also be noted that, while it would be desirable to be 
able to adjust the daily value to exclude only those portions of the 
data that are attributable to the exceptional event, due to technical 
limitations, such subtraction has not been possible, and EPA's 
historical practice has been to exclude a daily measured value in its 
entirety when that value is found to be largely caused by an 
exceptional event.
    Following the promulgation of the 8-hour ozone and the 
PM2.5 NAAQS, EPA provided additional guidance to States on 
how to address data affected by exceptional and natural events.\6\ That 
guidance directed the States to follow three specific EPA guidance 
documents in making determinations related to data influenced by 
exceptional and natural events: (1) The Exceptional Events Policy; (2) 
The PM10 Natural Events Policy; and (3) The Interim Air 
Quality Policy on Wildland and Prescribed Fires, Memorandum from 
Richard D. Wilson, Acting Assistant Administrator for Air and 
Radiation, to EPA Regional Administrators, May 15, 1998. The Interim 
Air Quality Policy on Wildland and Prescribed Fires addressed the 
treatment of air quality monitoring data that are affected by wildland 
and prescribed fires that are managed for resource benefits.\7\ The EPA 
will continue to use these policies to address issues related to the 
existing and/or revised PM2.5 NAAQS pending EPA's final 
action on today's proposed rulemaking. Similarly, issues related to 
exceptional and natural events affecting the ozone standard will 
continue to be addressed under the 1986 Exceptional Events Policy until 
EPA issues a final exceptional events rule.
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    \6\ ``Guideline on Data Handling Conventions for the PM NAAQS,'' 
United States Environmental Protection Agency, Office of Air Quality 
Planning and Standards, Research Triangle Park, N.C. 27711, EPA-454/
R-99-008, April 1999.
    ``Guideline on Data Handling Conventions for the 8-hour Ozone 
NAAQS,'' United States Environmental Protection Agency, Office of 
Air Quality Planning and Standards, Research Triangle Park, N.C. 
27711, EPA-454/R-99-008, April 1999.
    \7\ Following the promulgation of this rule, EPA will revise the 
``Interim Air Quality Policy on Wildland and Prescribed Fires'' to 
be consistent with current policies related to wildland and 
prescribed fires as well as the final rulemaking on exceptional 
events.
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III. Today's Proposed Action

A. To Whom and to What Pollutants Does Today's Proposed Rule Apply?

    Under the statutory scheme established by the CAA, States are 
primarily responsible for the administration of air quality management 
programs within their borders. This includes the monitoring and 
analysis of ambient air quality and submission of monitoring data to 
EPA, which are then stored in EPA's AQS data base. The EPA retains an 
important oversight responsibility for ensuring compliance with CAA 
requirements. With respect to the treatment of air quality monitoring 
data, States are responsible for ensuring data quality and validity and 
for identifying measurements that they believe warrant special 
consideration, while EPA is responsible for reviewing and approving or 
disapproving any requests for such consideration. Therefore, if 
adopted, today's proposed rule would apply 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, as discussed below, to Tribal air 
quality agencies where appropriate. This proposed rule would also 
govern EPA's actions in reviewing and approving or disapproving the 
relevant actions taken or requested by States. Where EPA implements air 
quality management programs on Tribal lands, this proposed rule would 
govern those actions as well.
    At present, only the NAAQS for ozone and PM contain provisions 
which allow for the special handling of air quality data affected by 
exceptional events (40 CFR part 50, appendices K, I, and N). The 
language of section 319 of the CAA is broad in terms of making its 
provisions applicable to events that ``affect air quality'' and to 
exceedances or violations of ``the national ambient air quality 
standards'' (42 U.S.C. 7619(b)(1)(A)(i), (b)(3)(B)(iv)). Thus, its 
provisions can apply to the NAAQS for any criteria pollutant. Because 
the NAAQS established for other criteria pollutants do not currently 
contain provisions permitting the discounting or exclusion of data due 
to exceptional events, we are proposing to only apply the provisions of 
this rule initially to ozone and PM. As we review and consider the need 
for revisions to the NAAQS for other pollutants, we will include 
provisions to address exceptional events in those NAAQS in accordance 
with section 319, as appropriate at that time. Because issuance of a 
new or revised NAAQS will necessitate the initiation of the designation 
process, EPA believes that the NAAQS rules are an appropriate place to 
make provision for exceptional events in the evaluation of air quality 
data. In the interim, where exceptional events result in exceedances or 
violations of NAAQS that do not currently provide for special treatment 
of the data, we intend to use our discretion as outlined under section 
107(d)(3) not to redesignate affected areas as nonattainment based on 
these events.

B. How Does This Rule Relate to Indian Tribes?

    Under the CAA and the Tribal Authority Rule (TAR), eligible Indian 
Tribes may develop and submit Tribal Implementation Plans (TIPs) for 
EPA approval, to administer requirements under the CAA on their 
reservations and other areas under their jurisdiction. However, Tribes 
are not required to develop TIPs or otherwise implement relevant 
programs under the CAA. The EPA has stated that it will continue to 
ensure the protection of air quality throughout the nation, including 
in Indian country, and will issue Federal Implementation Plans (FIPs) 
as necessary or appropriate to fill gaps in program implementation in 
affected areas of Indian country (63 FR 7254, 7265; February 12, 1998).

[[Page 12596]]

    In cases where a Tribal air quality agency has implemented an air 
quality monitoring network which is affected by emissions from 
exceptional events, the criteria and procedures identified in this 
proposed rule may be used to exclude or discount data for regulatory 
purposes. Certain Tribes may implement all relevant components of an 
air quality program for purposes of meeting the various requirements of 
this proposed rule. In some cases, however, a Tribe may implement only 
portions of the relevant program and may not be in a position to 
address each of the procedures and requirements associated with 
excluding or discounting emissions data (e.g., a particular Tribe may 
operate a monitoring network for purposes of gathering and identifying 
appropriate data, but may not implement relevant programs for the 
purpose of mitigating the effects of exceptional events required under 
this proposed rule). The EPA intends to work with Tribes on the 
implementation of this proposed rule, which may include appropriate 
implementation by EPA of program elements ensuring that any exclusion 
or discounting of data in Indian country areas with air quality 
affected by exceptional events comports with the procedures and 
requirements of this proposed rule.

C. What Is an Exceptional Event?

    In accordance with the language in section 319, EPA is proposing to 
define the term ``exceptional event'' to mean an event that:
    (i) Affects air quality;
    (ii) Is not reasonably controllable or preventable;
    (iii) Is an event caused by human activity that is unlikely to 
recur at a particular location or a natural event; and
    (iv) Is determined by the Administrator through the process 
established in these regulations to be an exceptional event.

It is important to note that natural events, which are one form of 
exceptional events according to this definition, may recur, sometimes 
frequently (e.g., western wildfires). For purposes of this rule, EPA is 
proposing to define ``natural event'' as an event in which human 
activity has no substantial or direct causal connection to the event in 
question. We recognize that over time, certain human activities may 
have had some impact on the conditions which later give rise to a 
``natural'' air pollution event. However, we do not believe that small 
historical human contributions should preclude an event from being 
deemed ``natural.''
    In this proposed rule, EPA also defines the term ``exceedance'' 
with respect to compliance with the NAAQS and establishes criteria for 
determining when an event can be said to ``affect air quality.'' We are 
not proposing more detailed requirements for determining when an event 
is ``not reasonably controllable or preventable'' because we believe 
that such determinations will necessarily be dependent on specific 
facts and circumstances that cannot be prescribed by rule. In adopting 
section 188(f) of subpart 4 of the 1990 amendments to the CAA, Congress 
recognized and provided for distinctions between these types of 
activities, while discussing circumstances under which events should or 
should not be considered natural (see Public Law 101-549, CAA 
Amendments of 1990 House Report No. 101-290(l), May 17, 1990; and 
discussion of Mono Lake, California therein).

D. Examples of Exceptional Events

    The EPA believes that the following types of events meet the 
definition of exceptional events, as defined above. This means that air 
quality data affected by these types of events may qualify for 
exclusion under this proposed rule if all other requirements of the 
rule are met. The AQS data base also contains a more detailed list of 
other similar events that may be flagged for special consideration 
(http://www.epa.gov/ttn/airs/airsaqs/manuals/ codedescs.htm).

1. Chemical Spills and Industrial Accidents
    Emissions that result from accidents such as fires, explosions, 
power outages, train derailments, vehicular accidents, or combinations 
of these may be flagged as an exceptional event.
2. Structural Fires
    Structural fires include any accidental fire involving a manmade 
structure.
3. Exceedances Due to Transported Pollution
    Transported pollution, whether national or international in origin 
and whether from natural or anthropogenic sources, may cause 
exceedances which are eligible for exclusion under this rule as long as 
the other criteria and requirements for exceptional events under this 
rule are met. For example, States may flag, and EPA may exclude, data 
associated with fires occurring outside of the borders of the United 
States, such as forest fires in Mexico, Central America, and Canada; or 
transport events such as African dust and Asian dust which contribute 
significantly to ambient concentrations of a pollutant, leading to 
exceedances or violations of the NAAQS. An example of interstate 
transported emissions which may be flagged as due to an exceptional 
event would be emissions due to smoke from wildland fires which cause 
exceedances or violations at monitoring sites in other States. Other 
types of events may be considered on a case-by-case basis.
4. Exceedances Due to a Terrorist Attack
    Emissions that result from a terrorist attack such as smoke from 
fires, dust, explosions, power outages, train derailments, vehicular 
accidents, or combinations of these may be flagged as an exceptional 
event.
5. Natural Events
    The natural events addressed by this proposed rule are: (1) 
Volcanic and seismic activities; (2) natural disasters and associated 
cleanup activities; (3) high wind events; (4) unwanted fires; and (5) 
stratospheric ozone intrusions. The EPA will consider other types of 
natural events on a case-by-case basis.
    a. Volcanic and Seismic Activities. Ambient concentrations of 
particulate matter for which volcanic eruptions or seismic activity 
caused or contributed to high levels of particulate matter in an 
affected area will be treated as natural events. While not occurring 
frequently, volcanic and seismic activity can affect air quality data 
related to the particulate matter NAAQS for an extended period of time 
after an event. Volcanic eruptions contribute to ambient concentrations 
in two ways; concentrations due to primary emissions (e.g., ash); and 
emissions of precursor pollutants (e.g., sulfur dioxide) that 
contribute to the secondary formation of particulate matter. Seismic 
activity (e.g., earthquakes) can also contribute to ambient particulate 
matter concentrations by shaking the ground, causing structures to 
collapse and otherwise raising dust.
    b. Natural Disasters and Associated Clean-up Activities. For the 
purpose of flagging, major natural disasters, such as hurricanes and 
tornados for which State, local, or Federal relief has been granted, 
and clean-up activities associated with these events may be considered 
exceptional events.
    c. High Wind Events. High wind events are events that affect 
ambient particulate matter concentrations through re-entrainment of 
material, i.e., by raising dust. Concentrations of coarse particles, 
i.e., PM10-2.5 and PM10 in some locations, are 
most likely affected by these types of events, although 
PM2.5

[[Page 12597]]

standards may be exceeded under such circumstances as well.
    d. Unwanted Fires. Ambient particulate matter concentrations caused 
by smoke from wildland fires will be treated as due to natural events 
if the fires are determined to be unwanted fires, designated wildland 
fire use fires, not designated or managed as prescribed fires, or 
requiring appropriate suppression action by a wildland manager.\8\
---------------------------------------------------------------------------

    \8\ It should be noted that this rule does not cover 
agricultural burning. To the extent that it is necessary for EPA to 
address this issue, we will do so in the future via separate 
guidance or rulemaking.
---------------------------------------------------------------------------

    The question of what is a natural versus an anthropogenic fire has 
particular significance in considering the impacts of wildland fires on 
air quality and how they should be regarded under today's proposed 
rule. Federal land managers have given recognition to several different 
types of wildland fires, depending on their causal circumstances and 
the role that such fires play in the affected ecosystems. ``Wildfires'' 
are described as unplanned, unwanted wildland fires, and include 
unauthorized burns (such as arson or acts of carelessness by campers), 
prescribed burns that escape control due to unforeseen circumstances, 
or other wildland fires where the primary objective is to suppress the 
fire as quickly as possible.
    In contrast, ``wildland fire use'' fires are those which were 
ignited naturally or unintentionally (e.g., as the result of lightning) 
and are allowed to continue burning without suppression efforts in 
locations that have been designated in fire management plans as areas 
where fires are necessary and desirable to accomplish specific resource 
management objectives. ``Prescribed fires'' are those ignited purposely 
to accomplish specific management objectives, and have been subject to 
written, approved prescribed fire plans (``Interagency Strategy for 
Directives Task Group,'' Memorandum from National Fire and Aviation 
Executive Board to Agency Personnel: Bureau of Indian Affairs, Bureau 
of Land Management, National Park Service, U.S. Fish and Wildlife 
Service, USDA Forest Service, April 18, 2005). Under these 
classifications, we believe that wildfires due to whatever causes them 
clearly fall within the meaning of ``natural events'' as that term is 
used in section 319. Similarly, we believe that wildland fire use fires 
qualify as ``natural events'' by virtue of their natural origins.
    Prescribed fires, however, cannot be classified as ``natural,'' 
given their clearly anthropogenic origins. Nonetheless, we believe that 
prescribed fires are not automatically excluded from the definition of 
exceptional events. If a prescribed fire meets the statutory criteria 
of being ``unlikely to recur at the same location'' or ``not reasonably 
controllable or preventable,'' and the measures specified below, it may 
qualify as an exceptional event.
    Prescribed fires carried out for resource management objectives are 
frequently designed to restore the role of wildland fires as they once 
occurred under natural conditions. As such, their expected frequency 
can vary widely, depending on the fire regenerative cycle of a 
particular landscape or wildland ecosystem. The natural fire cycle can 
range from once every year to less frequently than once in 35-60 years. 
Thus in many, though not all, cases it may be demonstrated that the 
likelihood of recurrence is sufficiently small that these events should 
be accorded special consideration under the rule.
    Since a prescribed fire is being deliberately ignited, it does not 
qualify as ``natural,'' and one view is that it cannot qualify as ``not 
reasonably controllable or preventable.'' However, a different 
interpretation of this provision of section 319 examines whether there 
are any reasonable alternatives to the use of fire in light of the 
needs and objectives to be served by it. For instance, there may be a 
sufficient build-up of forest fuels in a particular area that if left 
unaddressed would pose an unacceptable risk of catastrophic wildfire, 
which result in adverse impacts of much greater magnitude and severity 
than would result from the careful use of prescribed fires. A 
particular ecosystem may also be highly dependent on a natural fire 
cycle to maintain a sustainable natural species composition. 
Alternatively, pest or disease outbreaks in an area may be such that 
there are no reasonable alternatives to fire. In some cases, other 
legal requirements may preclude the use of mechanical fuel reduction 
methods such as in designated wilderness or National Parks. Where such 
ecological conditions exist, or where mechanical or other treatments 
are not reasonably feasible for reasons that include, but are not 
limited to, a lack of access or severe topography, we believe that it 
would be appropriate to exclude the impacts from well-managed 
prescribed fires to address them. Well-managed prescribed fires are 
those that consider smoke impacts prior to and during the burn, barring 
unforeseen circumstances, and when the prescribed fire is in compliance 
with a Smoke Management Plan (SMP).
    The EPA is proposing in this action that States continue to follow 
the smoke management provisions described in the ``Interim Air Quality 
Policy on Wildland and Prescribed Fires,'' issued May 15, 1998 
(Wildland and Prescribed Fire Policy). This policy provides that EPA 
will allow exceedances to be discounted that have been flagged by a 
State as having been caused by prescribed fires used for purposes of 
resource management provided that the State certifies that it has 
adopted and is implementing a certified SMP as described in our policy. 
Under our proposal, if a State, local, or Tribal air quality agency 
does not certify that a basic SMP is being implemented, or that basic 
smoke management practices are being employed by burners, EPA would not 
exclude data related to exceedances or violations attributed to 
prescribed fires managed for resource benefits.
    We request comments on the interpretation of prescribed fire 
described above on the proposed requirements for SMPs, and on any 
additional criteria or conditions that should be considered in 
determining whether and under what circumstances prescribed fires 
should be considered to be exceptional events.
    e. Stratospheric Ozone Intrusions. Stratospheric ozone intrusion is 
considered to be a natural event. A stratospheric ozone intrusion 
occurs when a parcel of air originating in the stratosphere, which is 
at an average height of 20 km or 12.4 miles, is re-entrained directly 
to the surface of the earth. Stratospheric ozone intrusions are very 
infrequent, localized events of short duration. They are typically 
associated with strong frontal passages and, thus, may occur primarily 
during the spring season.

IV. The Management of Air Quality Data Affected by Exceptional Events

    The EPA is proposing that, in order to exclude air quality data 
from consideration for regulatory purposes, States must follow the 
procedures, timelines, and other requirements described in this 
proposed rule. Specifically, States must clearly identify, or ``flag,'' 
data they believe to be influenced by such events; they must show that 
they have flagged days on which air quality has been ``affected'' by 
exceptional events according to EPA criteria; and they must submit 
appropriate documentation demonstrating that the exceptional event 
caused the exceedance or violation of the NAAQS in question. Each of 
these steps is described in detail below.

[[Page 12598]]

A. Flagging of Data in the AQS Data Base

    Air quality data are required, pursuant to 40 CFR part 58.35, to be 
submitted to EPA by each State on a calendar quarterly basis, with 
submissions due not later than 90 days after the end of a quarterly 
reporting period. Once air quality data have been submitted to EPA, it 
is possible to ``flag'' specific values for various purposes. ``Data 
flagging'' refers to the act of making a notation in a designated field 
of an electronic data record. The principal purpose of the data 
flagging system in the AQS data base is to identify those air quality 
measurements for which special attention or handling is warranted. 
These include, but are not limited to, those measurements that are 
influenced by exceptional events. In the case of exceptional events, 
States place the initial flag on the data in the AQS data base. 
Following an evaluation of the supporting documentation, EPA will 
decide whether to concur with the flag; concurrence will be marked by 
the placement of a second flag in the AQS data base by EPA. Once EPA 
has concurred on the flag, the data will be excluded from regulatory 
decisions such as determinations of attainment or nonattainment.
    While the flagging of data by the State is the first step in an 
exceptional events demonstration, it is insufficient by itself to allow 
for the exclusion of data. In order to have EPA concur on a flag, 
States must meet the additional requirements described below. As 
explained, the State has the responsibility to document both the 
occurrence of the event and the causal connection to the monitoring 
data under consideration. Because the initial step of flagging the data 
is a relatively simple one, States may flag many more days than the 
number of days for which they ultimately submit documentation to 
support exclusion.

B. What Does It Mean for an Event To ``Affect Air Quality''?

    It is important to recognize that any emissions-producing event has 
the potential to have some influence on downwind air quality. Indeed, 
on any given day, measured air quality at any given location will 
reflect the influences of a variety of activities, including both 
natural and anthropogenic emissions from both local and remote upwind 
sources. The EPA believes that it would be unreasonable to exclude data 
affected by an exceptional event simply because of a trivial 
contribution of the event to air quality. Furthermore, we also believe 
that it would be unreasonable to exclude more significant, but routine 
background air quality impacts, as this would disregard an important 
part of the public's exposure to air pollution upon which EPA's air 
quality standards are based. The effect of such exclusion would be an 
inappropriate reduction in the stringency of the NAAQS, rather than 
providing specific relief under the circumstances provided in section 
319 for which States should not be designated nonattainment or be 
required to prepare control strategies.
    Neither section 319 nor its legislative history provides precise 
guidance on what should be considered when determining whether an event 
``affects air quality'' and thus qualifies to be considered for 
exclusion or special treatment. However, section 319(b)(3)(B)(ii) and 
(iv) provide that there must be a ``clear causal relationship'' between 
a measured exceedance of a standard and the event to show that the 
event ``caused a specific air pollution concentration;'' and it must be 
shown that the data in question are ``directly due'' to an exceptional 
event. Moreover, one of the principles provided by section 319(b)(3)(A) 
indicate that the protection of public health is the highest priority. 
For these reasons, we are proposing that for an event to qualify as 
``exceptional'' for purposes of special regulatory consideration, its 
air quality impact must fall both above the level of the applicable 
standard (i.e., must be an ``exceedance'' as required by section 319) 
and significantly beyond the normal fluctuating range of air quality, 
including background air quality concentrations, and should be large 
enough so that without it there would have been no exceedance. We next 
provide several alternative approaches to determining whether and when 
air quality is ``affected by'' exceptional events, and request comment 
on which of these approaches is most suitable for demonstrating such 
impacts.
1. Option 1: 95th Percentile Criterion
    The first proposed approach is essentially a test for statistical 
deviations from the norm. For measurement days on which the event can 
be shown to have an air quality impact, the measurement would be 
compared to the 95th percentile of measurements typical of days in the 
particular calendar quarter that are not influenced by exceptional 
events (``non-event days''). The typical days could be based on a 3-5 
year period of record which exclude days influenced by exceptional 
events. Under this option, only an event whose resulting concentrations 
meet or exceed the 95th percentile criterion, along with meeting the 
other criteria in this proposed rule would qualify for exclusion from 
regulatory consideration.
    In evaluating available air quality data, we have found that by 
limiting consideration to those concentrations above the 95th 
percentile, only those concentrations that fall approximately two 
standard deviations above the mean of concentrations for that quarter 
would generally be excluded (See memo from Mark Schmidt, OAQPS, to 
docket entitled ``Analysis of Flagged Particulate Matter Data,'' 
February 10, 2006). Excluding days on which concentrations caused by 
exceptional events exceed the 95th percentile threshold employs a 
general test of statistical significance and has the effect of ensuring 
that such concentrations would clearly fall beyond the range of normal 
expectations for air quality during a particular time of year.
    In our analysis of flagged and excluded air quality data for the 
period 1999-2004, we found that application of the 95th percentile 
criterion would result in the exclusion of approximately 85 percent of 
data previously flagged by States and concurred on by EPA. Thus, this 
approach would result in a somewhat more rigorous qualification 
requirement than is reflected in EPA's past case-by-case approach. 
Previously, EPA did not have a concentration threshold or other 
quantitative criteria to determine which days would be eligible for 
exclusion due to exceptional events. As indicated above, approximately 
15 percent of the flags that were concurred on were concentrations that 
were not necessarily statistically distinguishable from routine levels. 
The 95th percentile approach could also help to eliminate some of the 
variability from State to State and Region to Region: as described in 
Schmidt (2006), rates of flagging and the severity of pollution on 
flagged days have varied significantly among States and regions in the 
past. For PM2.5, for example, many States flagged no days 
between 1999-2004, while Puerto Rico flagged 15 percent of all of its 
PM2.5 data. Also, while most PM2.5 flags during 
this period were above the 95th percentile, some States flagged data at 
the 75th percentile or lower. (See memo from Mark Schmidt, OAQPS, to 
docket entitled ``Analysis of Flagged Particulate Matter Data,'' 
February 10, 2006.)
2. Option 2: 75th Percentile/95th Percentile Tiered Approach
    Under this approach, we propose to retain flexibility to determine 
whether concentrations less than the 95th percentile but above the norm 
should

[[Page 12599]]

qualify for exclusion as ``affecting air quality.'' In particular, 
multiple measurement values over time with relatively small individual 
event impacts may collectively affect an annual average concentration 
to a significant degree. States may wish to consider whether to exclude 
such impacts if the average concentration is close to the level of the 
annual NAAQS. Therefore, we are soliciting comment on a second approach 
whereby measured values are compared both to the historical 95th 
percentile of non-event days and to the 75th percentile of such days.
    Where concentrations caused by an exceptional event meet or exceed 
the 95th percentile criterion, they would be conclusively determined to 
qualify for exclusion subject to the other requirements of this 
proposed rule. Where concentrations caused by an exceptional event do 
not meet the 95th percentile criterion, we would provide a further 
opportunity for States to make demonstrations which satisfy the other 
criteria in this proposed rule, so long as values exceeded the 75th 
percentile of non-event days. This approach would provide for a more 
flexible approach and would rely on a weight-of-evidence demonstration 
that would permit States to make other sorts of showings that the 
concentrations caused by the event were in some way unusual or not 
representative of normal air quality and thus should not result in 
additional regulatory requirements.
    When we applied the 75 percent percentile criterion to our analysis 
of flagged and excluded air quality data for the period 1999-2004, we 
found that this criterion would make nearly all of the data previously 
flagged by States and concurred on by EPA eligible for exclusion. Thus, 
we expect this approach would have a result that is roughly consistent 
with EPA's past case-by-case approach.
3. Option 3: Case-by-Case Approach Based on Weight of Evidence
    The third option is to permit the more general case-by-case 
evaluation, without threshold criteria, that may be guided by the 
magnitude of the measured concentration on days affected by exceptional 
events relative to historical, seasonally adjusted air quality levels. 
This approach is most nearly analogous to our historical treatment of 
exceptional events but, in contrast to Options 1 and 2, provides the 
least definitive guidance to assist States in their evaluations. 
Nevertheless, the case-by-case approach allows for consideration of 
days with ambient concentrations which are not necessarily among the 
highest concentrations that have been historically observed. In fact, 
25 percent of days have concentrations greater than the median value 
but less than the 75th percentile. While such days are unlikely to 
impact short-term standards, discounting such days can certainly have 
an impact on an annual average concentration. In general, however, 
demonstration that an event caused a concentration which is essentially 
indistinguishable from routine air quality would be very difficult to 
document, and this approach may make it difficult for EPA regions to be 
consistent when determining whether to concur on a flag.
    We request comment on which of these proposed options should be 
included in the final rule, including the appropriateness of proposed 
statistical criteria, the period of record on which to base the 95th 
and 75th percentile and conclusions about normal air quality 
expectations (e.g., 3 years, 5 years, or some longer period of record), 
and any other criteria or procedures we should consider adopting along 
with one of these options.

C. Use of a ``But For'' Test

    There may be instances in which exceptional events may have a 
significant impact on air quality on days when concentrations are 
already above the applicable standard in the absence of the influence 
of such events. In such cases, it is important to preserve and consider 
all valid air quality data influenced by activities which properly fall 
within the responsibilities of States to manage for purposes of air 
quality attainment and maintenance. For this reason, we are proposing 
to require that air quality data may not be excluded except where 
States show that exceedances or violations of applicable standards 
would not have occurred ``but for'' the influence of exceptional 
events. In other words, to the extent it is possible to determine that 
the resulting air quality concentrations and appropriate design values 
for an area would be above the level of the standards even without the 
influence of the exceptional event, the air quality data for the day(s) 
in question should not be excluded. However, consideration of the 
impacts of exceptional events on air quality values for control 
strategy planning purposes may be appropriate, and States are 
encouraged to consult with the appropriate EPA regional offices to 
further discuss this issue.

D. Schedules and Procedures for Flagging and Requesting Exclusion of 
Data

    In establishing procedures and timetables for States to request, 
and EPA to grant, exclusion of data affected by exceptional events, we 
are guided by two competing considerations: ensuring States have 
adequate time and opportunity to compile and evaluate all relevant and 
available information in support of such requests; and making 
determinations in a timely manner so that all pertinent and valid air 
quality data would be appropriately considered in regulatory 
determinations. To assist EPA in determining the best approach to 
managing the data flagging process and submissions of demonstrations 
for the final rule, we are proposing three alternatives for public 
review and comment.
1. Option 1: Early Data Flagging and Demonstration Submission
    The first approach would establish a two-step process for 
identification of data and submission of demonstrations. This process 
provides for the early flagging of data and the notification of the 
appropriate EPA Regional Office concerning the State's intention to 
seek exclusion of data, followed by a longer timeframe for States to 
prepare and submit their demonstrations.
    Under this approach, we would require a State to flag the data that 
they believe to be affected by exceptional events at the time of 
submission of the air quality data to EPA's AQS data base, in 
accordance with the schedule described in 40 CFR part 50.35, which is 
generally no later than 90 days after the end of the calendar quarter. 
This approach would ensure that the flagging process remains consistent 
with the timeline set forth in rules governing data submission 
requirements.
    Just as the scope and substance of demonstrations in support of 
requests for exclusion will vary depending on facts and circumstances 
(see section IV.F. below), so, too, will the time required for such 
demonstrations. Where air quality in an area is influenced by a 
relatively small set of emission sources with well-defined emission 
profiles and limited pollutant species, a demonstration that an air 
quality measurement influenced by a particular event merits exclusion 
may be relatively simple to make. In other cases, such as where the 
number and types of sources contributing to measured air quality 
concentrations are extremely complex and varied, making it more 
difficult to distinguish between the effects of routine activities and

[[Page 12600]]

unusual ones, more time and effort will be needed for a State to 
provide an adequate demonstration in support of its request.
    For these reasons, we are proposing under this option to require 
States to notify the appropriate EPA Regional Office of their intent to 
seek exclusion of data due to exceptional events at the time of 
submission of quarterly air quality data to the AQS data base. We are 
also proposing to require the State to consult with the EPA Regional 
Office as soon as reasonably possible after notification about the 
event, its suspected air quality impact, and the demonstration needed 
to justify a decision to exclude the data from regulatory 
consideration. This is intended to enable the State and EPA to work 
together during the process of data analysis and documentation to 
ensure that a complete and well-supported demonstration is submitted in 
a timely manner.
    With respect to demonstrations in support of requests for exclusion 
of data, we are proposing under this option to provide States with more 
time to submit the necessary demonstration. We propose that States 
submit complete demonstrations to EPA not later than 180 days following 
the close of the quarter in which the event occurred. Based on past 
experience with exceptional events and associated data analyses, we 
believe that this will provide adequate time in most cases for States 
to identify, compile, and evaluate all relevant factors pertaining to 
an exceptional event and its impacts. However, in special circumstances 
where additional time is required to make a complete submission, and 
where the outcome of such additional efforts is likely to have a 
substantial impact on the demonstration, we are proposing to allow 
States to request extensions of up to 90 additional days. We expect 
that such extensions under this option would be the exception, rather 
than the rule, and that they will be limited to special circumstances 
necessitating more complex and sophisticated analyses, such as where 
the collection and analysis of species-specific data in urban areas may 
be needed in order to characterize and quantify an event's contribution 
to air quality at a particular location. Under this option, as well as 
the options addressed below, once EPA receives a State's demonstration, 
EPA will then have a 30-day period to review the demonstration and 
provide a concurrence or nonconcurrence on the flag in the AQS data 
base. The EPA expects that, in most cases, a period of 30 days will be 
enough time to review and provide a concurrence related to a State's 
request to exclude data affected by an exceptional event. However, for 
more complex demonstrations, EPA may require more time for its review. 
In such cases, EPA may extend the time for its review by not more than 
an additional 30 days.
2. Option 2: Early Data Flagging and Delayed Demonstration Submission
    Under this option, we are proposing the same requirements for the 
flagging of data and notification of the appropriate EPA Regional 
Office as described in Option 1. However, under Option 2, we propose to 
allow up to 3 years following the quarter in which the event occurred 
for the submission of exceptional events demonstrations. The reason for 
providing more time under this option is that for most existing air 
quality standards, decisions regarding whether or not an area is 
attaining the applicable standard are based on the most recent 3 years 
of air quality data. Providing 3 years for submission of demonstrations 
would provide States with an opportunity to evaluate whether the 
influence of one or more exceptional events will be relevant to 
determinations of attainment or nonattainment before undertaking the 
effort of preparing and submitting demonstrations.
3. Option 3: Delayed Data Flagging and Demonstration Submission
    Under this option, we are proposing to decouple the process of 
flagging and demonstrations from the regular submission of air quality 
data to the AQS data base and to require instead that data be flagged 
and exceptional events demonstrations be submitted not later than 6 
months prior to the date when regulatory decisions using the air 
quality data must be made. This option is based on the recognition that 
while data flagging itself may not be a particularly burdensome 
exercise, it triggers a more extensive process of collection and 
analysis of other information to determine and demonstrate whether, in 
fact, an exceptional event has occurred which affects air quality data 
in a way that justifies exclusion of the data. It may be that although 
certain events occurred which do indeed affect air quality in 
significant ways, their impact on regulatory decisions may not be known 
for a significant period of time, i.e., until a relevant 3-year period 
of record is compiled and the need for a regulatory decision is 
identified. Thus under this option, it would be less burdensome for the 
States and EPA if demonstrations were not required unless and until it 
became apparent that potentially affected measurements would be used in 
making regulatory findings of attainment or nonattainment (e.g., where 
a State with an existing area designated as nonattainment seeks to have 
that area redesignated as attainment and the existence of one or more 
exceptional events may affect its ability to provide the requisite 3 
years of clean air quality data).
    We request comment on which of the above three proposed options EPA 
should promulgate and on what, if any, modifications to these options 
we should make prior to the final rule.

E. Exclusion of Entire 24-Hour Value as Opposed to a Partial Adjustment 
of the 24-Hour Value

    The EPA's historical practice has been to exclude a daily measured 
value in its entirety when that value is found to be largely caused by 
an exceptional event, and we are proposing to retain this approach in 
today's proposed rule. With this approach, a determination is made that 
emissions from the event are largely responsible for the resultant 
ambient air pollutant concentration. For example, if the observed 
concentration is 200 [mu]g/m3 PM2.5 and is 
associated with a nearby forest fire, then EPA would concur with the 
claim that the event was responsible for the ambient concentration. The 
measured value would be excluded in its entirety from the data used to 
judge attainment (as per 40 CFR 50, appendix N), although the 
measurement day would still count towards meeting minimum data capture 
requirements.
    We believe it would be desirable to adjust the daily value to 
exclude only those portions of the data that are attributable to the 
exceptional event in question, and to retain the remainder of the day's 
measurement if appropriate and accurate methods were available to make 
such adjustments. For example, if an area affected by a forest fire had 
a measured 24-hour PM2.5 concentration of 50 [mu]g/
m3 and the estimated event impact was 30 [mu]g/
m3, then the expected value which would have occurred but 
for the event would have been 20 [mu]g/m3. Normal air 
quality for this location might be 16 [mu]g/m3 and, 
therefore, the ``but-for'' concentration of 20 [mu]g/m3 is 
above average. Discounting the entire event day could, therefore, 
inappropriately bias a determination of nonattainment with the annual 
PM2.5 NAAQS (currently set at 15 [mu]g/m3). We 
are currently seeking to develop and evaluate new analytical methods 
that would allow us to discount only the portion of the daily value 
attributable to the exceptional event. However, at present, we are not 
aware of the existence of adequate and universally

[[Page 12601]]

applicable techniques that are administratively and technically 
feasible and that could support partial adjustment of air quality data 
except perhaps in limited cases, such as where the number and type of 
pollutant species and contributing sources are relatively less complex 
or potentially, when sufficient spatial, temporal, meteorological and 
chemical data are available [See memo to docket, Husar et al. 2006, 
(http://www.regulations.gov, Epa-HQ-Oar-2003-0061-0733 thru 0733.5)]. 

When we determine that techniques for adjustment of air quality data 
are sufficiently well-demonstrated for use in exceptional events 
determinations, we will publish a notice of proposed rulemaking to seek 
comment on the appropriateness and scope of such use.

F. What Should States Be Required To Submit in Their Exceptional Events 
Demonstrations?

    Section 319 requires that, in order to have a flagged value 
excluded from regulatory determinations, a State must make an 
affirmative demonstration that an event occurred (as shown by reliable 
and accurate data that is promptly produced) and that there is a clear 
causal relationship between measured exceedances or violations of a 
standard and the exceptional event in question to ``demonstrate that 
the exceptional event caused a specific air pollution concentration.'' 
(42 U.S.C. 7619(b)(3)(B)(ii), (iv)). Section 319 also indicates that 
regulations promulgated under the section should provide for criteria 
and procedures to exclude air quality monitoring data ``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.''
    Therefore, after flagging data in the AQS data base, States are 
expected to develop appropriate documentation to support each 
individual flag. As a general matter, we believe that such 
demonstrations should include documentation showing that the event in 
fact occurred and that emissions related to the event were transported 
in the direction of the monitor(s) where measurements were recorded; 
the size of the area affected by the transported emissions; the 
relationship in time between the event, transport of emissions, and 
recorded concentrations; and, as appropriate, pollutant species-
specific information supporting a causal relationship between the event 
and the measured concentration. The latter information could be based 
on available data provided by routine speciation, monitoring networks, 
or from selective laboratory analysis of archived particulate matter 
filters for the day thought to be impacted by specific events. In 
certain situations, such data might be useful for evaluation of impacts 
from exceptional events, e.g., to distinguish between impacts caused by 
natural fires versus impacts caused by industrial sources. Depending on 
which option is finalized pursuant to section V below, States may also 
need to show that appropriate mitigation actions were taken at the time 
that the event occurred, or after an event occurred in order to protect 
public health.
    The following examples are intended to further illustrate the kinds 
of information that States could consider in preparing their 
demonstrations:
    1. Information demonstrating the occurrence of the event and its 
subsequent transport to the affected monitors. This could include, for 
instance, documentation from land owners/managers, satellite-derived 
pixels (portions of digital images) indicating the presence of fires; 
satellite images of the dispersing smoke and smoke plume transport or 
trajectory calculations (calculations to determine the direction of 
transport of pollutant emissions from their point of origin) connecting 
fires with the receptors.
    2. Identification of the spatial pattern of the affected area (the 
size, shape, and area of geographic coverage). This could include, for 
instance, the use of satellite or surface measurement data.
    3. Information about temporal patterns (e.g., the time and duration 
of an event in relation to measured downwind concentrations, air 
quality trends over time and space). This could include, for instance, 
observed sequential concentration spikes at multiple locations in a 
downwind direction.
    4. Identification of the chemical composition of measured 
concentrations. This could include, for instance, organic or crustal 
material in excess of typically observed quantities to differentiate 
from other high concentration events.
    5. Extremely high wind speeds, or unusual transport conditions 
relative to historically typical levels for the season of the year in 
which the claimed event occurred.
    This list is not exhaustive and not all of these kinds of 
information and/or documentation will need to be provided in every 
instance. A particular instance may require more or less documentation, 
depending on the particular facts or circumstances in that instance. 
The simplest demonstrations could consist of newspaper accounts or 
satellite images to demonstrate that an event occurred together with 
daily and seasonal average ambient concentrations to demonstrate an 
unusually high ambient concentration level which is clearly indicative 
of an exceptional impact. Such is the case with events such as volcanic 
eruptions and nearby forest fires. In one instance, we determined that 
wildfires upwind of the San Diego area caused high concentrations of 
particulate matter measured in October 2003 based on the actual 
physical damage caused by fire to the ambient monitor. Depending on the 
nature of the event, meteorological conditions, severity and spatial 
extent of measured ambient concentrations (including relevant chemical 
components when available) relative to what typically occurs in the 
area, and on emissions of pollutants from the exceptional event which 
have similar characteristics to those of other sources in the area, 
additional showings could be required on a case-by-case basis. In 
particular, we anticipate that significantly more effort will be needed 
to establish that an exceptional event caused a particular 
concentration in an urban area in which there are numerous and diverse 
sources and complex meteorology and topography, and where the emissions 
from the event in question may well be similar to those from other 
sources contributing to measured concentrations, as compared to an area 
that has relatively few sources, simple terrain and less complex 
meteorology, and where emissions associated with the event are both 
substantially greater than and different in composition from those of 
other nearby sources. Because of the variability in the nature of 
exceptional events and the resulting demonstration requirements, States 
should consult with the appropriate EPA Regional Office early in the 
process of preparing their demonstrations.
    We are not proposing to specify what will be required as a minimum 
level of documentation in all cases because facts and circumstances 
will vary significantly based on, among other things, geography, 
meteorology and the relative complexity of source contributions to 
measured concentrations in any particular location. However, we request 
comment on whether we should adopt a set of minimum demonstration 
requirements to ensure a reasonable degree of national consistency in 
approaches to demonstrating exceptional events, and if so, what 
elements should be included in the demonstration. We believe, however, 
that at a minimum, the elements of such a demonstration

[[Page 12602]]

should include a showing that an event occurred at a time when 
meteorological conditions were conducive to transporting emissions from 
the event downwind to the monitor recording a high concentration of one 
or more criteria pollutants.

G. Special Considerations Relevant to Proposed Standards for 
PM10-2.5

    As noted in EPA's notice of proposed rulemaking reviewing the NAAQS 
for particulate matter (71 FR 2620; January 17, 2006), fine particles 
(PM2.5) are produced chiefly by combustion processes and by 
atmospheric reactions of various gaseous pollutants, whereas thoracic 
coarse particles (PM10-2.5) are generally emitted directly 
as particles as a result of mechanical processes that crush or grind 
larger particles or the resuspension of dusts. Sources of fine 
particles include, for example, motor vehicles, power generation, 
combustion sources at industrial facilities, and residential fuel 
burning. Sources of thoracic coarse particles include, for example, 
resuspension of traffic-related emissions such as tire and brake lining 
materials, and direct emissions from industrial operations, 
construction and demolition activities. Fine particles can remain 
suspended in the atmosphere for days to weeks and can be transported 
thousands of kilometers, whereas thoracic coarse particles generally 
deposit rapidly on the ground or other surfaces and are not readily 
transported across urban or broader areas (71 FR 2620, 2625; January 
17, 2006).
    Based on preliminary analysis, we generally anticipate that 
demonstrations that ambient concentrations of PM10-2.5 have 
been affected by exceptional events will involve similar analytical 
steps to demonstrations for PM2.5 but will be simpler than 
demonstrations for PM2.5.\9\ This conclusion is based on 
preliminary evaluation of estimated PM10-2.5 concentrations 
derived from historical PM10 and PM2.5 data. We 
examined those days on which PM10 exceedances were flagged 
as due to exceptional events but where PM2.5 concentrations 
were not also flagged, indicating that the event in question was 
dominated by coarse particles. The results of this analysis suggest 
that exceptional events related to PM10-2.5 are relatively 
infrequent, occur predominantly in the western States and are 
overwhelmingly high wind events. Thus, with the exception of western 
areas, we do not anticipate that exceptional events will be a 
predominate factor in decisions made related to attainment or 
nonattainment determinations for the proposed PM10-2.5 
standards (See memo from Mark Schmidt, OAQPS, to docket entitled 
``Analysis of Flagged Particulate Matter Data,'' February 10, 2006). 
Moreover, in light of the above analysis and the evidence on which it 
is based, we believe that exceptional events demonstrations for 
PM10-2.5 will involve relatively straightforward showings 
that when high concentrations occurred at the affected monitors, 
concentrations at available rural monitors (e.g., IMPROVE network 
monitors) were also elevated and that meteorological conditions (i.e., 
wind speed and wind direction) were conducive to transport from upwind 
sources of re-entrained coarse particles. It may be beneficial to 
examine continuous PM10-2.5 monitoring data as well, as they 
may indicate extremely high short-term values (e.g., 1 hour or less) 
that heavily influence 24-hour concentrations and are consistent with 
extreme high wind events. For instance, when we examined air quality 
concentrations recorded in El Paso, Texas during a dust storm that 
occurred on April 26-27, 2002 we found two consecutive 24-hour average 
concentrations of PM10 (654 [mu]g/m\3\) and PM2.5 
(56 [mu]g/m\3\) which were dominated by a peak 1-hour concentration of 
2700 [mu]g/m\3\ which occurred in the late evening of April 26-27.
---------------------------------------------------------------------------

    \9\ The demonstrations related to PM10-2.5 are 
contingent upon the final outcome related to the rulemaking on the 
NAAQS for PM10-2.5.
---------------------------------------------------------------------------

H. Public Availability of Air Quality Data and Demonstrations Related 
to Exceptional Events

    Sections 40 CFR parts 58.35 and 58.28 of EPA's air quality 
monitoring rules state that all data, flagged or unflagged, should be 
available to the public for comparison to the NAAQS to determine if 
exceedances have occurred. The EPA is proposing to require that all 
relevant flagged data, along with the reasons for the data being 
flagged, and a demonstration that the flagged data are caused by 
exceptional events be made available by the State for public review and 
comment prior to the demonstration being submitted to EPA for a 
decision concerning whether to exclude the data from regulatory 
consideration. Notice and availability of such data and demonstrations 
must be adequate and consistent with States' administrative procedures 
governing similar submissions. EPA is not proposing to require that 
public hearings be held on exceptional events demonstrations, but 
leaves this matter to the States' discretion.

V. Additional Requirements

    Pursuant to section 319, EPA is proposing new regulations to 
address exceptional events. Also EPA is proposing one option, and is 
taking comments on three alternative options, to address the issue of 
whether, and to what extent, States might be required to adopt specific 
mitigation plans or measures. Section 319 states that EPA must 
promulgate regulations that are consistent with paragraph 3 which 
enumerates certain principles and minimum regulatory requirements. The 
first part of paragraph 3 states that in promulgating regulations under 
section 319, EPA shall follow five principles, including the principle 
that each State ``must take necessary measures to safeguard public 
health regardless of the source of air pollution.'' Section 
319(b)(3)(A). This section does not, however, specify what measures may 
be ``necessary'' in this context. In order to address this principle, 
EPA is proposing to exclude trivial and more routine background air 
quality impacts from qualifying as an exceptional event and is also 
proposing a ``but for'' test as a precondition to qualification as an 
exceptional event (See: section IV). In addition, EPA is also proposing 
one approach and is taking comments on three other alternative options 
concerning State actions in anticipation of or in response to 
exceptional events. These proposed options range from being very 
detailed and more prescriptive to very flexible and less prescriptive. 
While EPA does not believe section 319(b)(3)(A) explicitly requires, in 
and of itself, that States develop mitigating measures or plans under 
options (1), (2), and (3) as discussed below, EPA solicits comment on 
whether this subparagraph supports the exertion of other legal 
authority to require mitigating actions or plans and solicits comment 
on issues regarding its legal authority to require mitigation measures 
and plans, and the legal basis for not requiring mitigation measures or 
plans. We are also requesting comments on the proposed approach and the 
three alternatives, and on any modifications to or combinations of any 
of the four approaches.

A. Option 1: Proposed Option: Require Public Notification, Education 
and Appropriate and Reasonable Measures

    In cases where exceedances or violations of a NAAQS are caused by 
an exceptional event, EPA is proposing that once a State becomes aware 
that an exceptional event is occurring, is predicted to occur, or has 
occurred, the State must take appropriate action to:

[[Page 12603]]

    1. Provide notice to the public of the event. This may include, but 
is not limited to, using the media to alert the public of the event.
    2. Provide public education concerning the potential health risks 
associated with being exposed to high ambient concentrations of 
pollutant(s) related to the event. This may include, but is not limited 
to, providing information to sensitive populations related to the 
health risks associated with the event.
    3. Take appropriate and reasonable measures to abate or minimize 
the exposure of the public to high concentrations of air pollution 
associated with the exceptional event. This may include, but is not 
limited to, taking reasonable and appropriate actions to implement 
control measures on significant contributing anthropogenic sources to 
reduce potential exposure of the public to emissions associated with 
natural events. For example, in the case of volcanic or seismic 
activity, this may include, but is not limited to, providing for prompt 
clean up of the ash deposits related to the event to prevent re-
entrainment.
    Under this option, where a State is requesting that air quality 
data be excluded as an exceptional event, the State must submit, as 
part of its demonstration, the appropriate documentation to show that 
the State provided appropriate public notice and public education 
concerning the event in question, and that the State took reasonable 
measures to abate or minimize the exposure of the public, where 
appropriate.
    The concept of having States take steps to reduce emissions, where 
appropriate, and to develop mitigation plans to address impacts 
associated with exceptional events was first instituted under the 
PM10 Natural Events Policy. The mitigation plans required 
under the PM10 Natural Events Policy were called Natural 
Events Action Plans (NEAPS). In instances where a State requested that 
air quality data influenced by a natural event be excluded, the State 
was required to develop and implement a NEAP.
    In developing a NEAP, States were expected to: Establish a public 
notification and education program related to natural events; minimize 
public exposure to high concentrations of pollutants related to natural 
events; provide a process for abatement of controllable anthropogenic 
sources related to natural events; identify, study, and implement 
practical mitigation measures as necessary; and provide for a periodic 
re-evaluation of the NEAP every 3-5 years.
    Due to past success with the implementation of NEAPs, EPA is 
proposing to base the requirements to mitigate the impact of 
exceptional events on the general concepts and elements described above 
from the PM10 Natural Events Policy. The EPA is proposing 
this approach to provide flexibility to the States to implement those 
measures that it considers to be reasonable and appropriate under 
particular circumstances to protect public health in the event of an 
exceptional event. The EPA believes that this approach allows States to 
use their experience in addressing those exceptional events that occur 
most frequently in their respective jurisdictions, and in providing 
notice to sensitive populations concerning the harmful effects of 
prolonged exposure to high concentrations of pollution associated with 
various types of exceptional events, yet could be consistent with both 
the principles and requirements of section 319. The proposed approach 
also allows EPA to fulfill its oversight responsibility, while still 
providing flexibility to States to implement reasonable measures to 
address the effects of exceptional events on public health. A possible 
disadvantage of this option is that it has the potential to result in 
inconsistencies in the way that exceptional events are addressed by 
States and in the actions that are taken to mitigate public health 
impacts associated with exceptional events, although such 
inconsistencies exist in any program that allows flexibility of any 
kind. We believe that despite this, such flexibility makes for a better 
and more efficient program in terms of taking specific mitigation 
actions that fit the circumstances of each case.

B. Option 2: The Development of a Mitigation Plan by States Under 
Section 110 of the CAA

    Under this option, States would be required to adopt a general 
mitigation plan to address exceptional events before the occurrence of 
an event as a part of the State's SIP required under section 110(a)(1) 
of the CAA. Section 110(a)(1) requires States to adopt and submit to 
EPA, within 3 years following the promulgation of a new or revised 
NAAQS, a plan which provides for the implementation, maintenance, and 
enforcement of the standard in each air quality region within the 
State. The EPA believes that section 110(a)(1) of the CAA provides EPA 
with the statutory authority to require States to submit plans to 
address the mitigation of public health impacts due to exceptional 
events that cause exceedances or violations of the NAAQS, because such 
plans assist in the maintenance and enforcement of the NAAQS and could 
be consistent with both the principles and requirements of section 319. 
Under this alternative, States would be required to develop and adopt 
the general requirements and procedures necessary for the 
implementation of a mitigation plan as a part of its section 110(a)(1) 
SIP to address a new or revised NAAQS. As a part of this plan, EPA 
would require States to identify the actions the State intends to take 
to reduce the impact of exceptional events on public health. Since the 
precise nature and cause of exceptional events may not be foreseeable, 
in many cases, these requirements would be general, and similar to the 
types of actions that States have already identified and adopted in 
their section 110 plans intended to address emergency episodes as 
required under section 110(g) and 40 CFR part 51.152. Once the general 
requirements of the mitigation plan are in place under section 110, the 
State would only need to take action on an episodic basis to implement 
the requirements of the mitigation plan for the affected area following 
the occurrence of an exceptional event.
    The general plan requirements would include provisions for 
providing public notification of an event; providing a program to 
educate the public on the harmful effects of prolonged exposure to 
emissions associated with an exceptional event; and implementing 
reasonable measures to mitigate the public health impacts of an 
exceptional event (e.g., the implementation of control measures to 
abate or minimize the effect of high concentrations of emissions 
associated with an exceptional event). In cases where control measures 
are required to address the impacts associated with an exceptional 
event, the State would implement the required measures on an episodic 
basis, meaning in response to a specific event that affects the air 
quality of a particular area.
    In cases where anthropogenic sources contribute to emissions 
related to a recurring natural event, appropriate control measures 
would have to be implemented on all significant contributing 
anthropogenic sources related to the event in the affected area.\10\ 
Natural events, which are

[[Page 12604]]

defined as a class of exceptional events under this rule, may recur 
frequently in affected areas. Under this option, as well as under 
Option 3 below, after a natural event occurs, and it is determined that 
anthropogenic sources have significantly contributed to the emissions 
associated with that event, EPA is proposing that at a minimum, 
Reasonably Available Control Measures (RACM) must be implemented on the 
anthropogenic sources that contributed to the emissions associated with 
the event. Reasonable Available Control Measures are defined as those 
control measures that are considered to be reasonable, and economically 
feasible, to implement in an area for a given source type. States 
should consult the most recent EPA control guidance for the affected 
pollutant to determine what control measures might be considered as 
RACM for the affected source types associated with emissions due to a 
natural event. This requirement is also consistent with the policy 
currently being implemented under the ``PM10 Natural Events 
Policy.''
---------------------------------------------------------------------------

    \10\ In the case of the proposed NAAQS for PM10-2.5, 
these options would not apply to sources which are proposed to be 
excluded from consideration, e.g., agriculture and mining 
activities.
---------------------------------------------------------------------------

    Also, EPA requests comments on whether, instead of RACM, the 
appropriate level of controls that should be implemented on these 
source types is Best Available Control Measures (BACM). Best Available 
Control Measures is a term first identified in the CAA under part D, 
subpart 4, related to the implementation of the PM10 
standard. For PM10, BACM are defined as techniques that 
achieve the maximum degree of emissions reductions from a source as 
determined on a case-by-case basis, considering both the technological 
and economic feasibility of implementing the control measures for the 
affected source (59 FR 42010; August 16, 1994). Currently, EPA requires 
the implementation of BACM on contributing anthropogenic sources under 
the PM10 Natural Events Policy for high wind events. Under 
this option, as well as under Option 3 below, the State would also be 
required to submit the mitigation plan for the affected area to the 
appropriate EPA Regional Office for review and concurrence. Once the 
State has received concurrence from the Regional Office on the control 
measures identified for the anthropogenic sources contributing to 
exceedances associated with natural events, the State would be required 
to include the measures as a part of its section 110(a)(1) SIP related 
to the mitigation plan for the area. As is the case with the control 
plans required for emergency episode plans under section 110(g), the 
State will not be required to submit the specific control measures as a 
part of the mitigation plan to EPA to be made federally enforceable. 
Pursuant to section 107(d)(3)and section 319 (b)(3)(B) of the CAA, it 
is EPA's intention to adopt a flexible approach and not redesignate an 
area as nonattainment, or seek a SIP call for an area, so long as the 
State continues to implement the requirements related to the mitigation 
plan for the area, as well as the control measures for significant 
contributing anthropogenic sources related to a natural event.
    Where a State provides adequate documentation to show that RACM was 
being implemented for the affected sources at the time that the natural 
event in question occurred, a State need not implement further control 
measures in the area related to the natural event. In cases where RACM 
was not implemented for contributing anthropogenic sources at the time 
of the natural event, the State would be required to implement RACM as 
expeditiously as practicable, but in no case later than 18 months from 
the end of the calendar quarter in which the event occurred. The EPA 
requests comments on whether this proposed time period is appropriate 
for the implementation of RACM for significant contributing 
anthropogenic sources under this option or whether another time period 
is more appropriate.
    The advantage of this particular option is that all States would 
have a general plan in place for how to address exceptional events once 
they occur and could take immediate action to protect public health. It 
would also allow States to evaluate proactively what actions need to be 
taken to address anthropogenic sources related to exceptional events, 
and to consider the most efficient and effective ways to educate the 
sensitive populations most likely to be harmed should an event occur.
    It is important to note that if we selected Option 3 regarding the 
timeline for flagging of data and submission of demonstrations, a 
disadvantage would be that flagging and demonstrations could 
potentially be delayed significantly past the time when States would be 
required to implement RACM under this option for mitigation plans. We 
request comment on when RACM should be implemented by States in the 
event that we select Flagging and Demonstration Option 3.

C. Option 3: The Development of a Mitigation Plan for Episodic Events

    Under this option, where appropriate, EPA would require a State to 
develop and implement a mitigation plan for an area following the 
occurrence of an exceptional event. This is in contrast to Option 2 
above, which would require each State to adopt a plan under section 110 
of the CAA containing the general provisions of a mitigation plan in 
advance of the occurrence of any exceptional event. Under this third 
option, the mitigation plan would only be developed by the State 
following the occurrence of an exceptional event for which a State 
requested exclusion of air quality data. The mitigation plan would be 
required to address the actions that would be taken by the State 
related to future similar events, yet could be consistent with the 
principles and requirements of section 319. The mitigation plan under 
this option would have the same provisions to plans developed under 
Option 2 above, including the requirements to notify the public that an 
event is expected to occur, or is occurring, or has occurred, to 
provide for public education related to the health effects associated 
with the event, and to identify the actions that would be taken by the 
State to mitigate the impact of any recurrence of the event on public 
health. The mitigation plan must include a detailed description of 
planned actions that would be implemented if the event recurs. It would 
also provide for an implementation schedule which identifies the 
actions that would be taken related to the recurrence of an event, and 
it should identify the principal parties that would be responsible for 
carrying out the stated actions under the mitigation plan.
    In cases where a State intends to request that EPA exclude data 
from regulatory consideration that has been affected by an exceptional 
event under this option, the State must submit the plan to EPA for 
review and concurrence. However, EPA will not take action to make the 
mitigation plan federally enforceable. Under this option States would 
develop a mitigation plan for an area where an exceptional event has 
caused an exceedance or violation of a NAAQS no later than 18 months 
following the end of the calendar quarter in which the event occurred. 
The EPA requests comments on whether 18 months is an appropriate time 
period for the development and adoption of a mitigation plan under this 
option or whether another time period is more appropriate.
    As stated in Option 2 above, in cases where anthropogenic sources 
contribute to emissions related to a recurring natural event, RACM must 
be implemented for all significant contributing anthropogenic sources. 
Where a State provides adequate documentation to show that RACM was 
being implemented for the affected

[[Page 12605]]

sources in the area at the time that the event occurred, no action 
would be required by the State to implement further control measures 
related to the event for the affected area. In cases where a 
determination is made that RACM was not being implemented for 
significant contributing anthropogenic sources at the time of the 
event, the State would be required to adopt and implement RACM as 
expeditiously as practicable, but in no case later than 3 years 
following the end of the calendar quarter in which the event occurred. 
The EPA requests comment on the appropriateness of the time period 
being proposed for the implementation of control measures related to 
significant contributing anthropogenic sources associated with a 
recurring natural event under this option.
    An advantage of this alternative is that a State can more carefully 
tailor the actions that it will take to mitigate the effect of the 
exceptional event based on its prior experience, which will help ensure 
protection of public health. However, the disadvantage of this 
particular option is that it would apply more specifically to one type 
of event, so that if a new or different type of exceptional event 
occurred, there would be no provisions in place under the mitigation 
plan to address it. Each time a new type of event occurs, the State 
would need to submit or revise the plan to address the new event.

D. Option 4: Do Not Require States To Adopt and Implement Specific 
Mitigation Plans or Measures Under This Rule

    Under this option, EPA would not require a State to develop and 
implement a mitigation plan for exceptional events, or to take specific 
mitigation measures as described in options 1-3 in order for EPA to 
exclude data from regulatory consideration because it results from an 
exceptional event. This approach would allow States to have the maximum 
degree of flexibility in determining what actions should be taken to 
mitigate the impacts of exceptional events, e.g., public notification, 
public education, efforts to reduce exposures, or other necessary 
measures to safeguard public health. Thus, States would not be 
obligated to take any particular actions to mitigate exposures such as 
those in Option 1, to develop and implement a formal mitigation plan as 
part of the SIP such as that in proposed Option 2, or to develop a more 
formal plan with requirements not a part of the SIP such as that in 
proposed Option 3.
    This proposed approach would require a much less formal method for 
States to take necessary measures to safeguard public health, yet could 
be consistent with both the principles and requirements of section 319. 
The statute does not identify specific ways in which EPA must satisfy 
its principles and requirements. Moreover, as detailed above, EPA is 
proposing to exclude only certain types of exceptional events from 
regulatory determinations with respect to the NAAQS. In section IV, EPA 
is proposing options for percentile criteria, case-by-case evaluation, 
and establishment of a ``but for'' test in order for an event to 
qualify as an exceptional event for which data can be excluded with 
respect to exceedences or violations of the NAAQS. These requirements, 
in and of themselves, may offer appropriate protection of public 
health. Under this view, EPA should give States broad flexibility in 
determining how best to respond to individual exceptional events. Given 
the States' concern with the health of their citizens, and taking into 
consideration the other requirements of this rule, in this view States 
would have sufficient incentive to take appropriate actions to protect 
public health.
    One benefit of this option is that it would allow States to 
maintain the maximum degree of flexibility to respond to exceptional 
events and to take appropriate actions to protect public health without 
unnecessarily limiting their ability to seek exceptional events 
treatment for the data. One potential limitation of this proposed 
approach is that it might result in inconsistencies among States in 
addressing exceptional events and in mitigating the impacts of those 
events.
    The EPA requests comments on all options described above. 
Additionally, EPA requests comments on specific modifications that 
should be made to one or more of the options provided above, or on any 
combination of these options.

VI. Special Treatment of Certain Events Under This Rule

    As stated in section III.C., above, this proposed rule applies to 
data affected by natural events, which are a subset of exceptional 
events, at air quality monitoring sites where it has been determined 
that concentrations due to these events have caused or substantially 
contributed to exceedances or violations of the NAAQS in an affected 
area. This proposed rule applies to several types of natural events, 
including volcanic and seismic actives, natural disasters, high wind 
events, unwanted fires, and stratospheric ozone intrusions, and to 
transported pollution originating from national and international 
sources that otherwise meets the criteria and requirements for 
exceptional events. Some types of exceptional events have unusual 
characteristics which require special consideration in the context of 
this proposed rulemaking. We discuss each of these special issues, and 
the necessary accommodations, below.

A. Volcanic and Seismic Activities

    Volcanic and seismic activities may affect air quality for an 
extended period of time after the initial occurrence of the event in 
question. Therefore, EPA believes it is appropriate to consider an 
extended timeframe for flagging and exclusion of data associated with 
such events. Specifically, EPA is proposing that emissions attributed 
to anthropogenic activities that re-entrain volcanic ash and dust from 
seismic activity during the first year (12 months) following an event 
will be treated as due to the natural event. Based on prior 
experiences, and on consultation with States, we believe that 1 year is 
an adequate amount of time for cleaning ash deposits from areas where 
anthropogenic activities (e.g., vehicle traffic) may cause re-
entrainment and possible exceedances of the particulate matter NAAQS. 
After a year, however, exceedances or violations due to re-entrainment 
of ash deposits will not be provided special consideration under this 
rule. The EPA, however, requests comments on whether another time 
period is more appropriate and reasonable to allow for clean up of ash 
deposits following volcanic or seismic activity.

B. High Wind Events

    Where high wind events result in exceedances or violations of 
PM2.5 standards, we are proposing that they will be treated 
as natural events pursuant to this proposed rule if there is a clear 
causal relationship demonstrated between the exceedances measured and 
the high wind event in question, and if anthropogenic activities which 
contribute to PM2.5 emissions in conjunction with the high 
wind event are reasonably well controlled.
    For the proposed 24-hour PM10-2.5 standard, we propose 
to exclude measured exceedances from consideration if it is 
demonstrated that high winds resulted in the transport of airborne 
particulate matter in concentrations that caused an exceedance or 
violation of the NAAQS.\11\ States would be expected to

[[Page 12606]]

control emissions from contributing anthropogenic sources as 
appropriate under the definition of the proposed PM10-2.5 
indicator.
---------------------------------------------------------------------------

    \11\ As discussed in rules proposed at 71 FR 2665-2668, January 
17, 2006, and 71 FR 2710 and 2731, 2736-40, January 17, 2006, where 
properly sited monitors show exceedances or violations of proposed 
PM10-2.5 standards, it will generally be presumed that 
such concentrations are due to emissions of urban origin and 
therefore subject to regulations, unless shown to be due to an 
exceptional event.
---------------------------------------------------------------------------

C. Stratospheric Ozone Intrusion

    Consideration of stratospheric ozone intrusions applies only to the 
8-hour ozone standard. The occurrence of such inversions is extremely 
difficult to measure or document given currently measured 
meteorological parameters. The infrequence, short duration, and 
localized nature of such events makes it difficult to use currently 
available, general meteorological data, which are usually collected at 
isolated locations like airports, to determine whether a stratospheric 
ozone intrusion has occurred. The EPA believes it is important to 
differentiate between stratospheric ozone intrusion, which is an 
exceptional event for the purpose of flagging data, and other non-
exceptional meteorological events. Although data have been identified 
in the past showing the result of stratospheric ozone intrusion, no 
standard definition or criteria have been established for concrete 
identification. Therefore, EPA's determination of whether a 
stratospheric ozone intrusion has occurred is a case-by-case decision 
based on reasonable judgment considering the season of the year; time 
of day; persistence, duration, type and severity of accompanying 
meteorological conditions associated with the ozone measurement in 
question; and other data showing that conditions were not conducive to 
local high ozone production but for this intrusion.

VII. Treatment of Fireworks Displays

    While we are not including fireworks displays in our proposed rule 
governing exceptional events, we are proposing as a policy matter to 
address certain displays in a manner similar to exceptional events. 
Some national and/or cultural traditions, such as July 4th Independence 
Day and Chinese New Year, have long included fireworks displays as 
important--indeed, many might assert essential--elements of their 
observances. While this issue is not specifically covered in CAA 
section 319, EPA believes that Congress did not intend to require EPA 
to consider air quality violations associated with such cultural 
traditions in regulatory determinations to prohibit these activities.
    We are not aware of any information showing adverse air quality 
impacts caused by individual use of fireworks in relatively small 
quantities. However, analyses of monitoring data collected on July 4th 
and July 5th indicates that large fireworks displays, in combination 
with other sources, can in some circumstances be potentially 
significant sources of air pollutant emissions. For this reason, States 
are encouraged to take reasonable precautions to minimize exposures to 
emissions from fireworks displays, as well as to manage associated 
activities that may have significant impact in the areas where these 
events are held. Such actions may include alerting the public to the 
potential for short-term air quality impacts that may result from the 
discharge of fireworks at large displays, monitoring prevailing winds, 
and locating displays downwind of concentrations of people. States are 
encouraged, too, to explore the use of lower-emitting fireworks, such 
as those developed for frequent use at amusement parks.
    For these reasons, where States can show that the use of fireworks 
displays is integral to significant traditional national, ethnic, or 
other cultural events, we are proposing that air quality data 
associated with such events could be excluded. We request comments on 
alternative approaches to addressing emissions from fireworks at such 
events.

VIII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

    Under Executive Order 12866 (58 FR 51735, October 4, 1993), EPA 
must determine whether the regulatory action is ``significant'' and, 
therefore, subject to the Office of Management and Budget (OMB) review 
and the requirements of the Executive Order. The order defines 
``significant regulatory action'' as one that is likely to result in a 
rule that may:
    (1) Have an annual effect on the economy of $100 million or more or 
adversely affect in a material way the economy, a sector of the 
economy, productivity, competition, jobs, the environment, public 
health or safety, or State, local, or Tribal governments or 
communities;
    (2) Create a serious inconsistency or otherwise interfere with an 
action taken or planned by another agency;
    (3) Materially alter the budgetary impact of entitlements, grants, 
user fees, or loan programs or the rights and obligations of recipients 
thereof; or
    (4) Rraise novel legal or policy issues arising out of legal 
mandates, the President's priorities, or the principles set forth in 
the Executive Order.
    Pursuant to the terms of Executive Order 12866, it has been 
determined that the proposed rule is a ``significant regulatory 
action.'' As such, this proposed rule was submitted to OMB for review 
under Executive Order 12866.

B. Paperwork Reduction Act

    This action does not impose an information collection burden. The 
information being requested under this rule is consistent with current 
requirements related to information needed to verify the authenticity 
of monitoring data submitted to EPA's AQS data base, and to justify 
data that has been flagged as being affected by exceptional or natural 
events. The OMB has previously approved the information collection 
requirements contained in the existing regulations at 40 CFR part 
58.01, subparts A through E, under the provisions of the Paperwork 
Reduction Act, 44 U.S.C. 3501 et seq. and assigned OMB control number 
2060-0084, EPA ICR number 940.17. A copy of the OMB approved 
Information Collection Request (ICR) may be obtained from Susan Auby, 
Collection Strategies Division; U.S. Environmental Protection Agency 
(2822T); 1200 Pennsylvania Ave., NW., Washington, DC 20460 or by 
calling (202) 566-1672.
    Burden means that total time, effort, or financial resources 
expended by persons to generate, maintain, retain, or disclose or 
provide information to or for a Federal agency. This includes the time 
needed to review instructions; develop, acquire, install, and utilize 
technology and systems for the purposes of collecting, validating, and 
verifying information, processing and maintaining information, and 
disclosing and providing information; adjust the existing ways to 
comply with any previously applicable instructions and requirements; 
train personnel to be able to respond to a collection of information; 
search data sources; complete and review the collection of information; 
and transmit or otherwise disclose the information. An Agency may not 
conduct or sponsor, and a person is not required to respond to a 
collection of information unless it displays a currently valid OMB 
control number. The OMB control numbers for EPA's regulations in the 
CFR are listed in 40 CFR part 9.

[[Page 12607]]

C. Regulatory Flexibility Act

    The Regulatory Flexibility Act (RFA) generally requires an agency 
to prepare a regulatory flexibility analysis of any rule subject to 
notice and comment rulemaking requirements under the Administrative 
Procedures Act (APA) or any other statute unless the EPA certifies that 
the rule will not have a significant economic impact on a substantial 
number of small entities. Small entities include small businesses, 
small organizations, and small governmental jurisdictions. For the 
purpose of assessing the impacts of today's proposed rule on small 
entities, small entity is defined as: (1) A small business that is a 
small industry entity as defined in the U.S. Small Business 
Administration (SBA) size standards. (See 13 CFR 121); (2) a small 
governmental jurisdiction that is a government of a city, county, town, 
school district or special district with a population of less than 
50,000; and (3) a small organization that is any not-for-profit 
enterprise which is independently owned and operated and is not 
dominate in its field.
    Courts have interpreted the RFA to require a regulatory flexibility 
analysis only when small entities will be subject to the requirements 
of the rule. See, Michigan v. EPA, 213 F.3d 663, 668-69 (D.C. Cir., 
2000), cert. den., 532 U.S. 903 (2001). This rule would not establish 
requirements applicable to small entities. Instead, this rule provides 
the criteria necessary for State, local, or Tribal air quality agencies 
to meet in order to properly flag data as being influenced by an 
exceptional or natural event. The rule also provides information 
concerning what action should be taken by a State, local, or Tribal air 
quality agency to protect public health once EPA has provided a 
concurrence on data that has been flagged as being influenced by an 
exceptional or natural event. Because affected States would have 
discretion to choose the sources that may need to be regulated and the 
emissions reductions each selected source would have to achieve using 
RACM or BACM related to anthropogenic sources in the area determined to 
be influenced by an exceptional or natural event, EPA could not predict 
the effect of the rule on small entities.
    After considering the economic impacts of today's proposed rule on 
small entities, I certify that this rule will not have a significant 
economic impact on a substantial number of small entities.

D. Unfunded Mandates Reform Act

    Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), Public 
Law 104-4, establishes requirements for Federal Agencies to assess the 
effects of their regulatory actions on State, local and Tribal 
governments and the private sector. Under section 202 of the UMRA, EPA 
generally must prepare a written statement, including a cost-benefit 
analysis, for proposed and final rules with ``Federal mandates'' that 
may result in expenditures to State governments, in the aggregate, or 
to the private sector, of $100 million or more in any 1 year. Before 
promulgating an EPA rule for which a written statement is needed, 
section 205 of the UMRA generally requires EPA to identify and consider 
a reasonable number of regulatory alternatives and adopt the least 
costly, most cost-effective or least burdensome alternative that 
achieves the objectives of the rule. The provisions of section 205 do 
not apply when they are inconsistent with applicable law. Moreover, 
section 205 allows EPA to adopt an alternative other than the least 
costly, most cost-effective or least burdensome alternative if the 
Administrator publishes with the final rule an explanation of why that 
alternative was not adopted. Before EPA establishes any regulatory 
requirements that may significantly or uniquely affect small 
governments, including Tribal governments, it must have developed under 
section 203 of the UMRA a small government agency plan. The plan must 
provide for notifying potentially affected small governments to have 
meaningful and timely input in the development of EPA regulatory 
proposals with significant Federal intergovernmental mandates, and 
informing, educating, and advising small government on compliance with 
regulatory requirements.
    Today's action does not include a Federal mandate within the 
meaning of UMRA that may result in expenditures of $100 million or more 
in any 1 year by either State, local, or Tribal governments in the 
aggregate or to the private sector, and therefore, is not subject to 
the requirements of sections 202 and 205 of the UMRA.
    Inasmuch as this action simply provides the criteria for State, 
local, or Tribal air quality agencies to flag data to be discounted for 
regulatory purposes that is being influenced by exceptional or natural 
events, this proposed Federal action will not impose mandates that will 
require expenditures of $100 million or more in the aggregate in any 1 
year.

E. Executive Order 13132: Federalism

    Executive Order 13132, entitled ``Federalism'' (64 FR 43255, August 
10, 1999), requires EPA to develop an accountable process to ensure 
``meaningful and timely input by State and local officials in the 
development of regulatory policies that have federalism implications.'' 
``Policies that have federalism implications'' is defined in the 
Executive Order to include regulations that have ``substantial direct 
effects on the States, or the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government.''
    This proposed rule does not have federalism implications. It will 
not have substantial direct effects on the States, on the relationship 
between the national government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
as specified in Executive Order 13132. The CAA establishes the scheme 
whereby States take the lead in developing plans to meet the NAAQS. 
This rule will not modify the relationship of the States and EPA for 
purposes of developing programs to implement the NAAQS. Thus, Executive 
Order 13132 does not apply to this rule.

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

    Executive Order 13175, entitled ``Consultation and Coordination 
with Indian Tribal Governments'' (65 FR 67249, November 9, 2000), 
requires EPA to develop an accountable process to ensure ``meaningful 
and timely input by Tribal officials in the development of regulatory 
policies that have Tribal implications.'' This proposed rule does not 
have ``Tribal implications'' as specified in Executive Order 13175. The 
rule provides information concerning what action should be taken by a 
State, local, or Tribal air quality agency implementing relevant air 
quality programs to protect public health once EPA has provided a 
concurrence on data that has been flagged as being influenced by an 
exceptional or natural event. The CAA and the Tribal Authority Rule 
(TAR) give Tribes the opportunity to develop and implement CAA 
programs, but it leaves to the discretion of the Tribe whether to 
develop these programs and which programs, or appropriate elements of a 
program, the Tribe will adopt.
    This rule does not have Tribal implications as defined by Executive 
Order 13175. It does not have a

[[Page 12608]]

substantial direct effect on one or more Indian Tribes, because no 
Tribe has implemented an air quality management program related to the 
PM NAAQS at this time. Furthermore, this rule does 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 developing plans 
to attain the NAAQS, and this rule does nothing to modify that 
relationship. Because this rule does not have Tribal implications, 
Executive Order 13175 does not apply.

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

    Executive Order 13045: ``Protection of Children From Environmental 
Health and Safety Risks'' (62 FR 19885, April 23, 1997) applies to any 
rule that (1) is determined to be ``economically significant'' as 
defined under Executive Order 12866, and (2) concerns an environmental 
health and safety risk that EPA has reason to believe may have a 
disproportionate effect on children. If the regulatory action meets 
both criteria, EPA must evaluate the environmental health or safety 
effects of the planned rule on children, and explain why the planned 
regulation is preferable to other potentially effective and reasonably 
feasible alternatives considered by EPA.
    This action is not subject to Executive Order 13045 because it is 
not economically significant as defined in Executive Order 12866, and 
because EPA does not have reason to believe that the environmental 
health risks or safety risks addressed by this rule present a 
disproportionate risk or safety risk to children. The rule provides 
information concerning what action should be taken by a State, local, 
or Tribal air quality agency to protect public health once EPA has 
provided a concurrence on data that has been flagged as being 
influenced by an exceptional or natural event.

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

    This rule is not a ``significant energy action'' as defined in 
Executive Order 13211, ``Actions that Significantly Affect Energy 
Supply, Distribution, or Use,'' (66 FR 28355, May 22, 2001) because it 
is not likely to have a significant adverse effect on the supply, 
distribution, or use of energy. Further, we have concluded that this 
rule is not likely to have any adverse energy effects.

I. National Technology Transfer Advancement Act

    Section 12(d) of the National Technology Transfer Advance ment Act 
of 1995 (NTTAA), Public Law No. 104-113, section 12(d) (15 U.S.C. 272 
note) directs EPA to use voluntary consensus standards (VCS) in its 
regulatory activities unless to do so would be inconsistent with 
applicable law or otherwise impracticable. Voluntary consensus 
standards are technical standards (e.g., materials specifications, test 
methods, sampling procedures, and business practices) that are 
developed or adopted by VCS bodies. The NTTAA directs EPA to provide 
Congress, through OMB, explanations when EPA decides not to use 
available and applicable VCS.
    This action does not involve technical standards. Therefore, EPA 
did not consider the use of any VCS.

List of Subjects in 40 CFR Parts 50 and 51

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

    Dated: March 1, 2006.
Stephen L. Johnson,
Administrator.

    In consideration of the foregoing, the Environmental Protection 
Agency proposes to amend 40 CFR parts 50 and 51 as follows:

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

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

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

    2. Amend Sec.  50.1 to add paragraphs (j), (k), and (l) to read as 
follows:


Sec.  50.1  Definitions.

* * * * *
    (j) Exceptional event means an event that affects air quality; is 
not reasonably controllable or preventable; is a natural event or an 
event caused by human activity that is unlikely to recur at a 
particular location; and is determined by the Administrator in 
accordance with 40 CFR 50.13 to be an exceptional event; it does not 
include stagnation of air masses or meteorological inversions; a 
meteorological event involving high temperatures or lack of 
precipitation; or air pollution relating to source noncompliance.
    (k) Natural event means an event in which human activity plays 
little or no direct causal role.
    (l) 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.
    3. Add Sec.  50.14 to read as follows:


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

    (a) Requirements. (1) A State may request EPA to exclude data 
showing exceedances or violations of the national ambient air quality 
standards that are directly due to an exceptional event from use in 
determinations by demonstrating to EPA's satisfaction that such event 
caused a specific air pollution concentration at a particular air 
quality monitoring location.
    (2) Demonstrations may include any reliable and accurate data, but 
must demonstrate a clear causal relationship between the measured 
exceedance or violation of such standards and the event.
    (b) Determinations by EPA. (1) EPA shall exclude data due to such 
event from use in determinations where a State demonstrates:
    (i) That an exceptional event caused a specific air pollution 
concentration resulting in an exceedance or violation of the national 
ambient air quality standards at a particular air quality monitoring 
location; and
    (ii) That it has taken appropriate actions to protect public 
health.
    (2) [Reserved]
    (c) Schedules and procedures--(1) Public notification. (i) 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]
    OPTION 1 for paragraphs (c)(2) through (c)(4):
    (2) Flagging of data. (i) A State shall notify EPA of its intent to 
exclude one or more measured exceedances of an applicable ambient air 
quality standard as being due to an exceptional event by placing a flag 
in the appropriate field for the data record of concern in accordance 
with the schedules for submission of data to the AQS data base in 40 
CFR 58.35.
    (ii) Flags placed on data in accordance with this section shall be 
deemed informational only, and the data shall not be excluded from 
determinations with respect to exceedances or violations of the 
national ambient air quality standards unless and until EPA notifies 
the State of its concurrence by placing a concurrence flag in the 
appropriate field for the data record in the AQS data base.

[[Page 12609]]

    (3) Submission of demonstrations. (i) A State that has flagged data 
as being due to an exceptional event shall, after notice and 
opportunity for public comment, submit a complete demonstration to EPA 
in support of its request for exclusion not later than 180 days 
following the end of the calendar quarter in which the flagged 
concentration was recorded.
    (A) Extensions. Where a State demonstrates to the satisfaction of 
EPA that additional time is needed to obtain information or complete 
analyses to demonstrate that an exceptional event caused an exceedance 
or violation of an ambient air quality standard, and that such 
information is likely to have significant probative value, then EPA may 
grant an extension of the date for submission of demonstrations of not 
more than an additional 90 days.
    (B) [Reserved]
    (ii) [Reserved]
    (4) EPA review and concurrence or nonconcurrence. (i) EPA shall 
complete its review and concur or nonconcur with a State's request for 
exclusion not later than 30 days following receipt of a complete 
submission from the State. EPA shall notify the State of its 
concurrence or nonconcurrence by placing a flag in the appropriate 
field for the data record in the AQS data base.
    (A) Extensions. Where additional time is needed to complete its 
review of the State's demonstration, EPA may extend the time for review 
by not more than an additional 30 days.
    (B) [Reserved]
    (ii) [Reserved]
    OPTION 2 for paragraphs (c)(2) through (c)(4):
    (2) Flagging of data. (i) A State shall notify EPA of its intent to 
exclude one or more measured exceedances of an applicable ambient air 
quality standard as being due to an exceptional event by placing a flag 
in the appropriate field for the data record of concern in accordance 
with the schedules for submission of data to the AQS data base in 40 
CFR 58.35.
    (ii) Flags placed on data in accordance with this section shall be 
deemed informational only, and the data shall not be excluded from 
determinations with respect to exceedances or violations of the 
national ambient air quality standards unless and until EPA notifies 
the State of its concurrence by placing a concurrence flag in the 
appropriate field for the data record in the AQS data base.
    (3) Submission of demonstrations. (i) A State that has flagged data 
as being due to an exceptional event shall, after notice and 
opportunity for public comment, submit a complete demonstration to EPA 
in support of its request for exclusion not later than 3 years 
following the end of the calendar quarter in which the flagged 
concentration was recorded.
    (ii) [Reserved]
    (4) EPA review and concurrence or nonconcurrence. (i) EPA shall 
complete its review and concur or nonconcur with a State's request for 
exclusion not later than 30 days following receipt of a complete 
submission from the State. EPA shall notify the State of its 
concurrence or nonconcurrence by placing a flag in the appropriate 
field for the data record in the AQS data base.
    (A) Extensions. Where additional time is needed to complete its 
review of the State's demonstration, EPA may extend the time for review 
by not more than an additional 30 days.
    (B) [Reserved]
    (ii) [Reserved]
    OPTION 3 for paragraphs (c)(2) through (c)(4):
    (2) Flagging of data. (i) A State shall notify EPA of its intent to 
exclude one or more measured exceedances of an applicable ambient air 
quality standard as being due to an exceptional event by placing a flag 
in the appropriate field for the data record of concern not later than 
180 days prior to the date on which EPA intends to propose 
determinations with respect to violations of applicable national 
ambient air quality standards.
    (ii) Flags placed on data in accordance with this section shall be 
deemed informational only, and the data shall not be excluded from 
determinations with respect to exceedances or violations of the 
national ambient air quality standards unless and until EPA notifies 
the State of its concurrence by placing a concurrence flag in the 
appropriate field for the data record in the AQS data base.
    (3) Submission of demonstrations. (i) A State that has flagged data 
as being due to an exceptional event shall, after notice and 
opportunity for public comment, submit a complete demonstration to EPA 
in support of its request for exclusion not later than 180 days prior 
to the date on which EPA intends to propose determinations with respect 
to violations of applicable national ambient air quality standards.
    (ii) [Reserved]
    (4) EPA review and concurrence or nonconcurrence. (i) EPA shall 
complete its review and concur or nonconcur with a State's request for 
exclusion not later than 30 days following receipt of a complete 
submission from the State. EPA shall notify the State of its 
concurrence or nonconcurrence by placing a flag in the appropriate 
field for the data record in the AQS data base.
    (A) Extensions. Where additional time is needed to complete its 
review of the State's demonstration, EPA may extend the time for review 
by not more than an additional 30 days.
    (B) [Reserved]
    (ii) [Reserved]

PART 51--NATIONAL PRIMARY AND SECONDARY NATIONAL AMBIENT AIR 
QUALITY STANDARDS

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

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

    2. Add Subpart Y consisting of Sec.  51.920 to read as follows:

Subpart Y--Exceptional Events

    OPTION 1 for Sec.  51.920:


Sec.  51.920  Mitigation of exceptional events.

    (a) As a condition for EPA's approval of a request to exclude air 
quality data due to exceptional events from use, each State must take 
appropriate and reasonable actions to protect public health from 
exceedances or violations of the national ambient air quality standards 
due to exceptional events. 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.
    (3) Provide for the implementation of reasonable measures to 
protect public health from exceedances or violations of ambient air 
quality standards caused by exceptional events.
    (a) [Reserved]
    OPTION 2 for Sec.  51.920:


Sec.  51.920  Mitigation of exceptional events.

    (a) As a condition for EPA's approval of a request to exclude air 
quality data due to exceptional events from use, each plan must include 
a mitigation action plan which provides for appropriate actions to 
protect public health from exceedances or violations of the national 
ambient air quality standards due to exceptional events. Each 
mitigation action plan 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

[[Page 12610]]

levels of air quality during and following an exceptional event.
    (3) Describe the procedures by which appropriate actions will be 
identified and taken to prevent or mitigate public health threats 
associated with exceptional events.
    (4) Provide for the implementation of reasonably available control 
measures to reduce emissions from those anthropogenic sources which are 
not exempt under Sec.  50.13(a)(2)(ii) of this chapter and which 
interact with recurring natural events to contribute to exceedances or 
violations of applicable national ambient air quality standards.
    (b) States should periodically reevaluate mitigation action plans 
for adequacy and revise them as necessary and appropriate.
    OPTION 3 for Sec.  51.920:


Sec.  51.920  Mitigation of exceptional events.

    (a) As a condition for EPA's approval of a request to exclude air 
quality data due to exceptional events from use in determinations with 
respect to exceedances or violations of the national ambient air 
quality standards, each State must adopt and implement a mitigation 
action plan for an affected area which provides for appropriate actions 
to protect public health from exceedances or violations of national 
ambient air quality standards due to exceptional events which is to be 
implemented in an affected area on an episodic basis. Mitigation action 
plans need not be incorporated into the applicable implementation plan, 
but each mitigation action plan 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.
    (3) Describe the procedures by which appropriate actions will be 
identified and taken to prevent or mitigate public health threats 
associated with exceptional events.
    (4) Provide for the implementation of reasonably available control 
measures to reduce emissions from those anthropogenic sources which are 
not exempt under Sec.  50.13(a)(2)(ii) of this chapter and which 
interact with recurring natural events to contribute to exceedances or 
violations of applicable national ambient air quality standards.
    (b) States should periodically reevaluate mitigation action plans 
for adequacy and revise them as necessary and appropriate.

[FR Doc. 06-2179 Filed 3-9-06; 8:45 am]

BILLING CODE 6560-50-P
