[Federal Register Volume 87, Number 35 (Tuesday, February 22, 2022)]
[Proposed Rules]
[Pages 9838-9878]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-02953]



[[Page 9837]]

Vol. 87

Tuesday,

No. 35

February 22, 2022

Part III





Environmental Protection Agency





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





40 CFR Part 52





Air Plan Disapproval; Illinois, Indiana, Michigan, Minnesota, Ohio, 
Wisconsin; Air Plan Disapproval; Region 5 Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone National Ambient Air Quality 
Standards; Proposed Rule

  Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / 
Proposed Rules  

[[Page 9838]]


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

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2022-0006; EPA-HQ-OAR-2021-0663; FRL-9431-01-R5]


Air Plan Disapproval; Illinois, Indiana, Michigan, Minnesota, 
Ohio, Wisconsin; Air Plan Disapproval; Region 5 Interstate Transport of 
Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality 
Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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

SUMMARY: Pursuant to the Federal Clean Air Act (CAA or the Act), the 
Environmental Protection Agency (EPA) is proposing to disapprove State 
Implementation Plan (SIP) submittals from Illinois, Indiana, Michigan, 
Minnesota, Ohio, and Wisconsin regarding interstate transport for the 
2015 ozone national ambient air quality standards (NAAQS). The ``good 
neighbor'' or ``interstate transport'' provision requires that each 
state's SIP contain adequate provisions to prohibit emissions from 
within the state from significantly contributing to nonattainment or 
interfering with maintenance of the NAAQS in other states. This 
requirement is part of the broader set of ``infrastructure'' 
requirements, which are designed to ensure that the structural 
components of each state's air quality management program are adequate 
to meet the state's responsibilities under the CAA. This disapproval, 
if finalized, will establish a 2-year deadline for EPA to promulgate a 
Federal Implementation Plan (FIP) to address the relevant interstate 
transport requirements, unless EPA approves a subsequent SIP submittal 
that meets these requirements. Disapproval does not start a mandatory 
sanctions clock.

DATES: Comments: Written comments must be received on or before April 
25, 2022.

ADDRESSES: You may send comments, identified as Docket No. EPA-R05-OAR-
2022-0006, by any of the following methods: Federal Rulemaking Portal 
at https://www.regulations.gov following the online instructions for 
submitting comments or via email to [email protected]. Include Docket 
ID No. EPA-R05-OAR-2022-0006 in the subject line of the message.
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov/, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the ``Public Participation'' 
heading of the SUPPLEMENTARY INFORMATION section of this document. Out 
of an abundance of caution for members of the public and our staff, the 
EPA Docket Center and Reading Room are open to the public by 
appointment only to reduce the risk of transmitting COVID-19. Our 
Docket Center staff also continues to provide remote customer service 
via email, phone, and webform. For further information on EPA Docket 
Center services and the current status, please visit us online at 
https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Olivia Davidson, Environmental 
Scientist, Attainment Planning and Maintenance Section, Air Programs 
Branch (AR-18J), Environmental Protection Agency, Region 5, 77 West 
Jackson Boulevard, Chicago, Illinois 60604, (312) 886-0266, 
[email protected]. The EPA Region 5 office is open from 8:30 a.m. 
to 4:30 p.m., Monday through Friday, excluding Federal holidays and 
facility closures due to COVID-19.

SUPPLEMENTARY INFORMATION: 
    Public Participation: Submit your comments, identified by Docket ID 
No. EPA-R05-OAR-2022-0006, at https://www.regulations.gov (our 
preferred method), or the other methods identified in the ADDRESSES 
section. Once submitted, comments cannot be edited or removed from the 
docket. EPA may publish any comment received to its public docket. Do 
not submit to EPA's docket at https://www.regulations.gov any 
information you consider to be Confidential Business Information (CBI) 
or other information whose disclosure is restricted by statute. 
Multimedia submissions (audio, video, etc.) must be accompanied by a 
written comment. The written comment is considered the official comment 
and should include discussion of all points you wish to make. EPA will 
generally not consider comments or comment contents located outside of 
the primary submission (i.e., on the web, cloud, or other file sharing 
system).
    There are two dockets supporting this action, EPA-R05-OAR-2022-0006 
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R05-OAR-2022-0006 contains 
information specific to Illinois, Indiana, Michigan, Minnesota, Ohio, 
and Wisconsin, including the notice of proposed rulemaking. Docket No. 
EPA-HQ-OAR-2021-0663 contains additional modeling files, emissions 
inventory files, technical support documents, and other relevant 
supporting documentation regarding interstate transport of emissions 
for the 2015 ozone NAAQS which are being used to support this action. 
All comments regarding information in either of these dockets are to be 
made in Docket No. EPA-R05-OAR-2022-0006. For additional submission 
methods, please contact Olivia Davidson, (312) 886-0266, 
[email protected]. For the full EPA public comment policy, 
information about CBI or multimedia submissions, and general guidance 
on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets. Due to public health concerns related to COVID-
19, the EPA Docket Center and Reading Room are open to the public by 
appointment only. Our Docket Center staff also continues to provide 
remote customer service via email, phone, and webform. For further 
information and updates on EPA Docket Center services, please visit us 
online at https://www.epa.gov/dockets.
    EPA continues to carefully and continuously monitor information 
from the Centers for Disease Control and Prevention (CDC), local area 
health departments, and our Federal partners so that we can respond 
rapidly as conditions change regarding COVID-19. The index to the 
docket for this action, Docket No. EPA-R05-OAR-2022-0006, is available 
electronically at www.regulations.gov. While all documents in the 
docket are listed in the index, some information may not be publicly 
available due to docket file size restrictions or content (e.g., CBI).
    Throughout this document, ``we,'' ``us,'' and ``our'' means EPA.

I. Background

A. Description of Statutory Background

    On October 1, 2015, EPA promulgated a revision to the ozone NAAQS 
(2015 ozone NAAQS), lowering the level of both the primary and 
secondary standards to 0.070 parts per million (ppm).\1\ Section 
110(a)(1) of the CAA requires states to submit, within 3 years after 
promulgation of a new or revised standard, SIP submissions meeting the 
applicable requirements of section 110(a)(2).\2\ One of these 
applicable

[[Page 9839]]

requirements is found in CAA section 110(a)(2)(D)(i)(I), otherwise 
known as the ``interstate transport'' or ``good neighbor'' provision, 
which generally requires SIPs to contain adequate provisions to 
prohibit in-state emissions activities from having certain adverse air 
quality effects on other states due to interstate transport of 
pollution. There are two so-called ``prongs'' within CAA section 
110(a)(2)(D)(i)(I). A SIP for a new or revised NAAQS must contain 
adequate provisions prohibiting any source or other type of emissions 
activity within the state from emitting air pollutants in amounts that 
will significantly contribute to nonattainment of the NAAQS in another 
state (prong 1) or interfere with maintenance of the NAAQS in another 
state (prong 2). EPA and states must give independent significance to 
prong 1 and prong 2 when evaluating downwind air quality problems under 
CAA section 110(a)(2)(D)(i)(I).\3\
---------------------------------------------------------------------------

    \1\ National Ambient Air Quality Standards for Ozone, Final 
Rule, 80 FR 65292 (October 26, 2015). Although the level of the 
standard is specified in the units of ppm, ozone concentrations are 
also described in parts per billion (ppb). For example, 0.070 ppm is 
equivalent to 70 ppb.
    \2\ SIP revisions that are intended to meet the applicable 
requirements of section 110(a)(1) and (2) of the CAA are often 
referred to as infrastructure SIPs and the applicable elements under 
section 110(a)(2) are referred to as infrastructure requirements.
    \3\ See North Carolina v. EPA, 531 F.3d 896, 909-11 (D.C. Cir. 
2008).
---------------------------------------------------------------------------

B. Description of EPA's Four Step Interstate Transport Regulatory 
Process

    EPA is using the 4-step interstate transport framework (or 4-step 
framework) to evaluate the states' SIP submittals addressing the 
interstate transport provision for the 2015 ozone NAAQS. EPA has 
addressed the interstate transport requirements of CAA section 
110(a)(2)(D)(i)(I) with respect to prior ozone NAAQS in several 
regional regulatory actions, including the Cross-State Air Pollution 
Rule (CSAPR), which addressed interstate transport with respect to the 
1997 ozone NAAQS as well as the 1997 and 2006 fine particulate matter 
standards,\4\ and the Cross-State Air Pollution Rule Update (CSAPR 
Update) \5\ and the Revised CSAPR Update, both of which addressed the 
2008 ozone NAAQS.\6\
---------------------------------------------------------------------------

    \4\ See Federal Implementation Plans: Interstate Transport of 
Fine Particulate Matter and Ozone and Correction of SIP Approvals, 
76 FR 48208 (Aug. 8, 2011).
    \5\ Cross-State Air Pollution Rule Update for the 2008 Ozone 
NAAQS, 81 FR 74504 (Oct. 26, 2016).
    \6\ In 2019, the D.C. Circuit Court of Appeals remanded the 
CSAPR Update to the extent it failed to require upwind states to 
eliminate their significant contribution by the next applicable 
attainment date by which downwind states must come into compliance 
with the NAAQS, as established under CAA section 181(a). Wisconsin 
v. EPA, 938 F.3d 303, 313 (D.C. Cir. 2019). The Revised CSAPR Update 
for the 2008 Ozone NAAQS, 86 FR 23054 (April 30, 2021), responded to 
the remand of the CSAPR Update in Wisconsin and the vacatur of a 
separate rule, the ``CSAPR Close-Out,'' 83 FR 65878 (December 21, 
2018), in New York v. EPA, 781 F. App'x. 4 (D.C. Cir. 2019).
---------------------------------------------------------------------------

    Through the development and implementation of the CSAPR rulemakings 
and prior regional rulemakings pursuant to the interstate transport 
provision,\7\ EPA, working in partnership with states, developed the 
following 4-step interstate transport framework to evaluate a state's 
obligations to eliminate interstate transport emissions under the 
interstate transport provision for the ozone NAAQS: (1) Identify 
monitoring sites that are projected to have problems attaining and/or 
maintaining the NAAQS (i.e., nonattainment and/or maintenance 
receptors); (2) identify states that impact those air quality problems 
in other (i.e., downwind) states sufficiently such that the states are 
considered ``linked'' and therefore warrant further review and 
analysis; (3) identify the emissions reductions necessary (if any), 
applying a multifactor analysis, to eliminate each linked upwind 
state's significant contribution to nonattainment or interference with 
maintenance of the NAAQS at the locations identified in Step 1; and (4) 
adopt permanent and enforceable measures needed to achieve those 
emissions reductions.
---------------------------------------------------------------------------

    \7\ In addition to the CSAPR rulemakings, other regional 
rulemakings addressing ozone transport include the ``NOX 
SIP Call,'' 63 FR 57356 (October 27, 1998) and the ``Clean Air 
Interstate Rule'' (CAIR), 70 FR 25162 (May 12, 2005).
---------------------------------------------------------------------------

C. Background on EPA's Ozone Transport Modeling Information

    In general, EPA has performed nationwide air quality modeling to 
project ozone design values which are used in combination with measured 
data to identify nonattainment and maintenance receptors. To quantify 
the contribution of emissions from specific upwind states on 2023 ozone 
design values for the identified downwind nonattainment and maintenance 
receptors, EPA performed nationwide, state-level ozone source 
apportionment modeling for 2023. The source apportionment modeling 
provided contributions to ozone at receptors from precursor emissions 
of anthropogenic nitrogen oxides (NOX) and volatile organic 
compounds (VOCs) in individual upwind states.
    EPA has released several documents containing projected ozone 
design values, contributions, and information relevant to evaluating 
interstate transport with respect to the 2015 ozone NAAQS. First, on 
January 6, 2017, EPA published a notice of data availability (NODA) in 
which we requested comment on preliminary interstate ozone transport 
data including projected ozone design values and interstate 
contributions for 2023 using a 2011 base year platform.\8\ In the NODA, 
EPA used the year 2023 as the analytic year for this preliminary 
modeling because that year aligns with the expected attainment year for 
Moderate ozone nonattainment areas for the 2015 ozone NAAQS.\9\ On 
October 27, 2017, we released a memorandum (October 2017 memorandum) 
containing updated 2011 platform-based modeling data for 2023, which 
incorporated changes made in response to comments on the NODA, and 
noted that the modeling may be useful for states developing SIPs to 
address interstate transport obligations for the 2008 ozone NAAQS.\10\ 
On March 27, 2018, we issued a memorandum (March 2018 memorandum) 
noting that the same 2023 modeling data released in the October 2017 
memorandum could also be useful for identifying potential downwind air 
quality problems with respect to the 2015 ozone NAAQS at Step 1 of the 
4-step interstate transport framework.\11\ The March 2018 memorandum 
also included the then newly available contribution modeling data for 
2023 to assist states in evaluating their impact on potential downwind 
air quality problems for the 2015 ozone NAAQS under Step 2 of the 4-
step interstate transport framework.\12\ EPA subsequently issued two 
more memoranda in August and October 2018, providing additional 
information to states developing interstate transport SIP submissions 
for the 2015 ozone NAAQS concerning, respectively,

[[Page 9840]]

potential contribution thresholds that may be appropriate to apply in 
Step 2 of the 4-step interstate transport framework, and considerations 
for identifying downwind areas that may have problems maintaining the 
standard at Step 1 of the 4-step interstate transport framework.\13\
---------------------------------------------------------------------------

    \8\ See Notice of Availability of the Environmental Protection 
Agency's Preliminary Interstate Ozone Transport Modeling Data for 
the 2015 ozone National Ambient Air Quality Standard (NAAQS), 82 FR 
1733 (January 6, 2017).
    \9\ 82 FR at 1735.
    \10\ See Information on the Interstate Transport State 
Implementation Plan Submissions for the 2008 Ozone National Ambient 
Air Quality Standards under Clean Air Act Section 
110(a)(2)(D)(i)(I), October 27, 2017, available in docket EPA-HQ-
OAR-2021-0663 or at https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \11\ See Information on the Interstate Transport State 
Implementation Plan Submissions for the 2015 Ozone National Ambient 
Air Quality Standards under Clean Air Act Section 
110(a)(2)(D)(i)(I), March 27, 2018, available in docket EPA-HQ-OAR-
2021-0663 or at https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \12\ The March 2018 memorandum, however, provided, ``While the 
information in this memorandum and the associated air quality 
analysis data could be used to inform the development of these SIPs, 
the information is not a final determination regarding states' 
obligations under the good neighbor provision. Any such 
determination would be made through notice-and-comment rulemaking.''
    \13\ See Analysis of Contribution Thresholds for Use in Clean 
Air Act Section 110(a)(2)(D)(i)(I) Interstate Transport State 
Implementation Plan Submissions for the 2015 Ozone National Ambient 
Air Quality Standards, August 31, 2018 (``August 2018 memorandum''), 
and Considerations for Identifying Maintenance Receptors for Use in 
Clean Air Act Section 110(a)(2)(D)(i)(I) Interstate Transport State 
Implementation Plan Submissions for the 2015 Ozone National Ambient 
Air Quality Standards, October 19, 2018, available in docket EPA-HQ-
OAR-2021-0663 or at https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.
---------------------------------------------------------------------------

    Since the release of the modeling data shared in the March 2018 
memorandum, EPA has performed modeling using a 2016-based emissions 
modeling platform (i.e., 2016v1) This emissions platform was developed 
under the EPA/Multi-Jurisdictional Organization (MJO)/state 
collaborative project.\14\ This collaborative project was a multi-year 
joint effort by EPA, MJOs, and states to develop a new, more recent 
emissions platform for use by EPA and states in regulatory modeling as 
an improvement over the dated 2011-based platform that EPA had used to 
project ozone design values and contribution data provided in the 2017 
and 2018 memoranda. EPA used the 2016v1 emissions to project ozone 
Design values and contributions for 2023. On October 30, 2020, in the 
Notice of Proposed Rulemaking for the Revised CSAPR Update, EPA 
released and accepted public comment on 2023 modeling that used the 
2016v1 emissions platform.\15\ See 85 FR 68964, 68981. Although the 
Revised CSAPR Update addressed transport for the 2008 ozone NAAQS, the 
projected design values and contributions from the 2016v1 platform are 
also useful for identifying downwind ozone problems and linkages with 
respect to the 2015 ozone NAAQS.\16\
---------------------------------------------------------------------------

    \14\ The results of this modeling, as well as the underlying 
modeling files, are included in docket ID No. EPA-HQ-OAR-2021-0663.
    \15\ See 85 FR 68964, 68981.
    \16\ See the Air Quality Modeling Technical Support Document for 
the Final Revised Cross-State Air Pollution Rule Update, included in 
the Headquarters docket ID No. EPA-HQ-OAR-2021-0663.
---------------------------------------------------------------------------

    Following the final Revised CSAPR Update, EPA made further updates 
to the 2016 emissions platform to include mobile emissions from EPA's 
Motor Vehicle Emission Simulator MOVES3 model \17\ and updated 
emissions projections for electric generating units (EGUs) that reflect 
the emissions reductions from the Revised CSAPR Update, recent 
information on plant closures, and other sector trends. The construct 
of the updated emissions platform, 2016v2, is described in the 
emissions modeling technical support document (TSD) for this proposed 
rule.\18\
---------------------------------------------------------------------------

    \17\ Additional details and documentation related to the MOVES3 
model can be found at https://www.epa.gov/moves/latest-version-motor-vehicle-emission-simulator-moves.
    \18\ See Technical Support Document (TSD) Preparation of 
Emissions Inventories for the 2016v2 North American Emissions 
Modeling Platform included in the Headquarters docket ID No. EPA-HQ-
OAR-2021-0663.
---------------------------------------------------------------------------

    EPA's latest projections of the baseline EGU emissions uses the 
version 6--Summer 2021 Reference Case of the Integrated Planning Model 
(IPM).\19\ IPM is a multi-regional, dynamic, and deterministic linear 
programming model of the U.S. electric power sector. The model provides 
forecasts of least cost capacity expansion, electricity dispatch, and 
emission control strategies, while meeting energy demand, 
environmental, transmission, dispatch, and reliability constraints.
---------------------------------------------------------------------------

    \19\ Detailed information and documentation of EPA's Base Case, 
including all the underlying assumptions, data sources, and 
architecture parameters can be found on EPA's website at: https://www.epa.gov/airmarkets/epas-power-sector-modeling-platform-v6-using-ipm-summer-2021-reference-case.
---------------------------------------------------------------------------

    The IPM version 6--Summer 2021 Reference Case incorporated recent 
updates through the Summer of 2021 to account for updated Federal and 
State environmental regulations for EGUs. This projected base case 
accounts for the effects of the finalized Mercury and Air Toxics 
Standards rule (MATS), CSAPR, the CSAPR Update, the Revised CSAPR 
Update, New Source Review settlements, the final Effluent Limitation 
Guidelines (ELG) Rule, the Coal Combustion Residual (CCR) Rule, and 
other on-the-books Federal and State rules (including renewable energy 
tax credit extensions from the Consolidated Appropriations Act of 2021) 
through early 2021 impacting sulfur dioxide (SO2), 
NOX, directly emitted particulate matter, carbon dioxide, 
and power plant operations. It also includes final actions EPA has 
taken to implement the Regional Haze Rule and Best Available Retrofit 
Technology (BART) requirements. Further, the EPA Platform v6 uses 
demand projections from the Energy Information Agency's (EIA) Annual 
Energy Outlook (AEO) 2020.
    The IPM version 6--Summer 2021 Reference Case uses the National 
Electric Energy Data System (NEEDS) v6 database as its source for data 
on all existing and planned-committed units. Units are removed from the 
NEEDS inventory only if a high degree of certainty could be assigned to 
future implementation of the announced future closure or retirement. 
The available retirement-related information was reviewed for each 
unit, and the following rules are applied to remove:

    (i) Units that are listed as retired in the December 2020 EIA 
Form 860M
    (ii) Units that have a planned retirement year prior to June 30, 
2023 in the December 2020 EIA Form 860M
    (iii) Units that have been cleared by a regional transmission 
operator (RTO) or independent system operator (ISO) to retire before 
2023, or whose RTO/ISO clearance to retire is contingent on actions 
that can be completed before 2023
    (iv) Units that have committed specifically to retire before 
2023 under Federal or state enforcement actions or regulatory 
requirements
    (v) And finally, units for which a retirement announcement can 
be corroborated by other available information. Units required to 
retire pursuant to enforcement actions or state rules on July 1, 
2023 or later are retained in NEEDS v6.

    Retirements or closures taking place on or after July 1, 2023 are 
captured as constraints on those units in the IPM modeling, and the 
units are retired in future year projections per the terms of the 
related requirements. Any retirements excluded from the NEEDS v6 
inventory can be viewed in the NEEDS spreadsheet.\20\
---------------------------------------------------------------------------

    \20\ The ``Capacity Dropped'' and the ``Retired Through 2023'' 
worksheets in NEEDS lists all units that are removed from the NEEDS 
v6 inventory--NEEDS v6 Summer 2021 Reference Case. This data can be 
found on EPA's website at: https://www.epa.gov/airmarkets/national-electric-energy-data-system-needs-v6.
---------------------------------------------------------------------------

    As highlighted in previous rulemakings, the IPM documentation, and 
EPA's Power Sector Modeling website, EPA's goal is to explain and 
document the use of IPM in a transparent and publicly accessible 
manner, while also providing for concurrent channels for improving the 
model's assumptions and representation by soliciting constructive 
feedback to improve the model. This includes making all inputs and 
assumptions to the model, output files from the model, and IPM feedback 
form publicly available on EPA's website.
    EPA performed air quality modeling of the 2016v2 emissions using 
the most recent public release version of the Comprehensive Air-quality 
Model with extensions (CAMx) photochemical modeling, version 7.10.\21\ 
EPA now proposes to primarily rely on modeling

[[Page 9841]]

based on the updated and newly available 2016v2 emissions platform in 
evaluating these submissions with respect to Steps 1 and 2 of the 4-
step interstate transport framework and generally referenced within 
this action as 2016v2 modeling for 2023. By using the updated modeling 
results, EPA is using the most current and technically appropriate 
information for this proposed rulemaking. Section III of this action 
and the Air Quality Modeling TSD for 2015 Ozone NAAQS Transport SIP 
Proposed Actions, included in Docket ID No. EPA-HQ-OAR-2021-0663 for 
this proposal, contain additional detail on EPA's 2016v2 modeling. In 
this action, EPA is accepting public comment on this updated 2023 
modeling, which uses a 2016v2 emissions platform. Comments on EPA's air 
quality modeling should be submitted in the Regional docket for this 
action, docket ID No. EPA-R05-OAR-2022-0006. Comments are not being 
accepted in docket ID No. EPA-HQ-OAR-2021-0663.
---------------------------------------------------------------------------

    \21\ Ramboll Environment and Health, January 2021, www.camx.com.
---------------------------------------------------------------------------

    States may have chosen to rely on the results of EPA modeling and/
or alternative modeling performed by states or MJOs to evaluate 
downwind air quality problems and contributions as part of their 
submissions. As most Region 5 states have done so, in Sections III.A, 
III.B, III.C, III.D, and III.E, we evaluate how Region 5 states used 
air quality modeling information in their submissions.

D. EPA's Approach to Evaluating Interstate Transport SIPs for the 2015 
Ozone NAAQS

    EPA proposes to apply a consistent set of policy judgments across 
all states for purposes of evaluating interstate transport obligations 
and the approvability of interstate transport SIP submittals for the 
2015 ozone NAAQS. These policy judgments reflect consistency with 
relevant case law and past agency practice as reflected in the CSAPR 
and related rulemakings. Nationwide consistency in approach is 
particularly important in the context of interstate ozone transport, 
which is a regional-scale pollution problem involving many smaller 
contributors. Effective policy solutions to the problem of interstate 
ozone transport going back to the NOx SIP Call have necessitated the 
application of a uniform framework of policy judgments to ensure an 
``efficient and equitable'' approach. See EME Homer City, 572 U.S. 489, 
519 (2014).
    In the March, August, and October 2018 memoranda, EPA recognized 
that states may be able to establish alternative approaches to 
addressing their interstate transport obligations for the 2015 ozone 
NAAQS that vary from a nationally uniform framework. EPA emphasized in 
these memoranda, however, that such alternative approaches must be 
technically justified and appropriate in light of the facts and 
circumstances of each particular state's submittal. In general, EPA 
continues to believe that deviation from a nationally consistent 
approach to ozone transport must be substantially justified and have a 
well-documented technical basis that is consistent with relevant case 
law. Where states submitted SIPs that rely on any potential 
``flexibilities'' as may have been identified or suggested in the past, 
EPA will evaluate whether the state adequately justified the technical 
and legal basis for doing so.
    EPA notes that certain concepts included in an attachment to the 
March 2018 memorandum require unique consideration, and these ideas do 
not constitute agency guidance with respect to transport obligations 
for the 2015 ozone NAAQS. Attachment A to the March 2018 memorandum 
identified a ``Preliminary List of Potential Flexibilities'' that could 
potentially inform SIP development.\22\ However, EPA made clear in that 
Attachment that the list of ideas were not suggestions endorsed by the 
Agency but rather ``comments provided in various forums'' on which EPA 
sought ``feedback from interested stakeholders.'' \23\ Further, 
Attachment A stated, ``EPA is not at this time making any determination 
that the ideas discussed below are consistent with the requirements of 
the CAA, nor are we specifically recommending that states use these 
approaches.'' \24\ Attachment A to the March 2018 memorandum, 
therefore, does not constitute agency guidance, but was intended to 
generate further discussion around potential approaches to addressing 
ozone transport among interested stakeholders. To the extent states 
sought to develop or rely on these ideas in support of their SIP 
submittals, EPA will thoroughly review the technical and legal 
justifications for doing so.
---------------------------------------------------------------------------

    \22\ March 2018 memorandum, Attachment A.
    \23\ Id. at A-1.
    \24\ Id.
---------------------------------------------------------------------------

    The remainder of this section describes EPA's proposed framework 
with respect to analytic year, definition of nonattainment and 
maintenance receptors, selection of contribution threshold, and 
multifactor control strategy assessment.
1. Selection of Analytic Year
    In general, the states and EPA must implement the interstate 
transport provision in a manner ``consistent with the provisions of 
[title I of the CAA.]'' CAA section 110(a)(2)(D)(i). This requires, 
among other things, that these obligations are addressed consistently 
with the timeframes for downwind areas to meet their CAA obligations. 
With respect to ozone NAAQS, under CAA section 181(a), this means 
obligations must be addressed ``as expeditiously as practicable'' and 
no later than the schedule of attainment dates provided in CAA section 
181(a)(1).\25\ Several D.C. Circuit court decisions address the issue 
of the relevant analytic year for the purposes of evaluating ozone 
transport air-quality problems. On September 13, 2019, the D.C. Circuit 
issued a decision in Wisconsin v. EPA, remanding the CSAPR Update to 
the extent that it failed to require upwind states to eliminate their 
significant contribution by the next applicable attainment date by 
which downwind states must come into compliance with the NAAQS, as 
established under CAA section 181(a). 938 F.3d at 313.
---------------------------------------------------------------------------

    \25\ For attainment dates for the 2015 ozone NAAQS, refer to CAA 
section 181(a), 40 CFR 51.1303, and Additional Air Quality 
Designations for the 2015 Ozone National Ambient Air Quality 
Standards, 83 FR 25776 (June 4, 2018, effective Aug. 3, 2018).
---------------------------------------------------------------------------

    On May 19, 2020, the D.C. Circuit issued a decision in Maryland v. 
EPA that cited the Wisconsin decision in holding that EPA must assess 
the impact of interstate transport on air quality at the next downwind 
attainment date, including Marginal area attainment dates, in 
evaluating the basis for EPA's denial of a petition under CAA section 
126(b). Maryland v. EPA, 958 F.3d 1185, 1203-04 (D.C. Cir. 2020). The 
court noted that ``section 126(b) incorporates the Good Neighbor 
Provision,'' and, therefore, ``EPA must find a violation [of section 
126] if an upwind source will significantly contribute to downwind 
nonattainment at the next downwind attainment deadline. Therefore, the 
agency must evaluate downwind air quality at that deadline, not at some 
later date.'' Id. at 1204 (emphasis added). EPA interprets the court's 
holding in Maryland as requiring the states and the Agency, under the 
good neighbor provision, to assess downwind air quality as 
expeditiously as practicable and no later than the next applicable 
attainment date,\26\ which is

[[Page 9842]]

now the Moderate area attainment date under CAA section 181 for ozone 
nonattainment. The Moderate area attainment date for the 2015 ozone 
NAAQS is August 3, 2024.\27\ EPA believes that 2023 is now the 
appropriate year for analysis of interstate transport obligations for 
the 2015 ozone NAAQS, because the 2023 ozone season is the last 
relevant ozone season during which achieved emissions reductions in 
linked upwind states could assist downwind states with meeting the 
August 3, 2024 Moderate area attainment date for the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \26\ We note that the court in Maryland did not have occasion to 
evaluate circumstances in which EPA may determine that an upwind 
linkage to a downwind air quality problem exists at steps 1 and 2 of 
the interstate transport framework by a particular attainment date, 
but for reasons of impossibility or profound uncertainty the Agency 
is unable to mandate upwind pollution controls by that date. See 
Wisconsin, 938 F.3d at 320. The D.C. Circuit noted in Wisconsin that 
upon a sufficient showing, these circumstances may warrant 
flexibility in effectuating the purpose of the interstate transport 
provision.
    \27\ See CAA section 181(a); 40 CFR 51.1303; Additional Air 
Quality Designations for the 2015 Ozone National Ambient Air Quality 
Standards, 83 FR 25776 (June 4, 2018, effective Aug. 3, 2018).
---------------------------------------------------------------------------

    EPA recognizes that the attainment date for nonattainment areas 
classified as Marginal for the 2015 ozone NAAQS was August 3, 2021. 
Under the Maryland holding, any necessary emissions reductions to 
satisfy interstate transport obligations should have been implemented 
by no later than this date. At the time of the statutory deadline to 
submit interstate transport SIPs (October 1, 2018), many states relied 
upon EPA modeling of the year 2023, and no state provided an 
alternative analysis using a 2021 analytic year (or the prior 2020 
ozone season). However, EPA must act on SIP submittals using the 
information available at the time it takes such action. In this 
circumstance, EPA does not believe it would be appropriate to evaluate 
states' obligations under CAA section 110(a)(2)(D)(i)(I) as of an 
attainment date that is wholly in the past, because the Agency 
interprets the interstate transport provision as forward looking. See 
86 FR at 23074; see also Wisconsin, 938 F.3d at 322. Consequently, in 
this proposal EPA will use the analytical year of 2023 to evaluate each 
state's CAA section 110(a)(2)(D)(i)(I) SIP submission with respect to 
the 2015 ozone NAAQS.
2. Step 1 of the 4-Step Interstate Transport Framework
    In Step 1, EPA identifies monitoring sites that are projected to 
have problems attaining and/or maintaining the NAAQS in the 2023 
analytic year. Where EPA's analysis shows that a site does not fall 
under the definition of a nonattainment or maintenance receptor, that 
site is excluded from further analysis under EPA's 4-step interstate 
transport framework. For sites that are identified as a nonattainment 
or maintenance receptor in 2023, we proceed to the next step of our 4-
step interstate transport framework by identifying the upwind state's 
contribution to those receptors.
    EPA's approach to identifying ozone nonattainment and maintenance 
receptors in this action is consistent with the approach used in 
previous transport rulemakings. EPA's approach gives independent 
consideration to both the ``contribute significantly to nonattainment'' 
and the ``interfere with maintenance'' prongs of CAA section 
110(a)(2)(D)(i)(I), consistent with the D.C. Circuit's direction in 
North Carolina v. EPA.\28\
---------------------------------------------------------------------------

    \28\ See North Carolina v. EPA, 531 F.3d at 910-11 (D.C. Cir. 
2008) (holding that EPA must give ``independent significance'' to 
each prong of CAA section 110(a)(2)(D)(i)(I)).
---------------------------------------------------------------------------

    For the purpose of this proposal, EPA identifies nonattainment 
receptors as those monitoring sites that are projected to have average 
design values that exceed the NAAQS and that are also measuring 
nonattainment based on the most recent monitored design values. This 
approach is consistent with prior transport rulemakings, such as the 
CSAPR Update, where EPA defined nonattainment receptors as those areas 
that both currently measure nonattainment and that EPA projects will be 
in nonattainment in the future analytic year (i.e., 2023).\29\
---------------------------------------------------------------------------

    \29\ See 81 FR 74504 (October 26, 2016). This same concept, 
relying on both current monitoring data and modeling to define 
nonattainment receptor, was also applied in CAIR. See 70 FR 25241, 
25249 (January 14, 2005); see also North Carolina, 531 F.3d at 913-
14 (affirming as reasonable EPA's approach to defining nonattainment 
in CAIR).
---------------------------------------------------------------------------

    In addition, in this proposal, EPA identifies a receptor to be a 
``maintenance'' receptor for purposes of defining interference with 
maintenance, consistent with the method used in the CSAPR and upheld by 
the D.C. Circuit in EME Homer City Generation, L.P. v. EPA, 795 F.3d 
118, 136 (D.C. Cir. 2015).\30\ Specifically, EPA identified maintenance 
receptors as those receptors that would have difficulty maintaining the 
relevant NAAQS in a scenario that takes into account historical 
variability in air quality at that receptor. The variability in air 
quality was determined by evaluating the ``maximum'' future design 
value at each receptor based on a projection of the maximum measured 
design value over the relevant period. EPA interprets the projected 
maximum future design value to be a potential future air quality 
outcome consistent with the meteorology that yielded maximum measured 
concentrations in the ambient data set analyzed for that receptor 
(i.e., ozone conducive meteorology). EPA also recognizes that 
previously experienced meteorological conditions (e.g., dominant wind 
direction, temperatures, air mass patterns) promoting ozone formation 
that led to maximum concentrations in the measured data may reoccur in 
the future. The maximum design value gives a reasonable projection of 
future air quality at the receptor under a scenario in which such 
conditions do, in fact, reoccur. The projected maximum design value is 
used to identify upwind emissions that, under those circumstances, 
could interfere with the downwind area's ability to maintain the NAAQS.
---------------------------------------------------------------------------

    \30\ See 76 FR 48208 (August 8, 2011). CSAPR Update and Revised 
CSAPR Update also used this approach. See 81 FR 74504 (October 26, 
2016) and 86 FR 23054 (April 30, 2021).
---------------------------------------------------------------------------

    Recognizing that nonattainment receptors are also, by definition, 
maintenance receptors, EPA often uses the term ``maintenance-only'' to 
refer to those receptors that are not nonattainment receptors. 
Consistent with the concepts for maintenance receptors, as described 
above, EPA identifies ``maintenance-only'' receptors as those 
monitoring sites that have projected average design values above the 
level of the applicable NAAQS, but that are not currently measuring 
nonattainment based on the most recent official design values. In 
addition, those monitoring sites with projected average design values 
below the NAAQS, but with projected maximum design values above the 
NAAQS are also identified as ``maintenance only'' receptors, even if 
they are currently measuring nonattainment based on the most recent 
official design values.
3. Step 2 of the 4-Step Interstate Transport Framework
    In Step 2, EPA quantifies the contribution of each upwind state to 
each receptor in the 2023 analytic year. The contribution metric used 
in Step 2 is defined as the average impact from each state to each 
receptor on the days with the highest ozone concentrations at the 
receptor based on the 2023 modeling. If a state's contribution value 
does not equal or exceed the threshold of 1 percent of the NAAQS (i.e., 
0.70 ppb for the 2015 ozone NAAQS), the upwind state is not ``linked'' 
to a downwind air quality problem, and EPA, therefore, concludes that 
the state does not significantly contribute to nonattainment or 
interfere with maintenance of the NAAQS in the

[[Page 9843]]

downwind states. However, if a state's contribution equals or exceeds 
the 1 percent threshold, the state's emissions are further evaluated in 
Step 3, considering both air quality and cost as part of a multi-factor 
analysis, to determine what, if any, emissions might be deemed 
``significant'' and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I). EPA is proposing to rely in the first instance on 
the 1 percent threshold for the purpose of evaluating a state's 
contribution to nonattainment or maintenance of the 2015 ozone NAAQS 
(i.e., 0.70 ppb) at downwind receptors. This is consistent with the 
Step 2 approach that EPA applied in CSAPR for the 1997 ozone NAAQS, 
which has subsequently been applied in the CSAPR Update when evaluating 
interstate transport obligations for the 2008 ozone NAAQS. EPA 
continues to find 1 percent to be an appropriate threshold. For ozone, 
as EPA found in the Clean Air Interstate Rule (CAIR), CSAPR, and the 
CSAPR Update, a portion of the nonattainment problems from 
anthropogenic sources in the U.S. result from the combined impact of 
relatively small contributions from many upwind states, along with 
contributions from in-state sources and, in some cases, substantially 
larger contributions from a subset of particular upwind states. EPA's 
analysis shows that much of the ozone transport problem being analyzed 
in this proposed rule is still the result of the collective impacts of 
contributions from many upwind states. Therefore, application of a 
consistent contribution threshold is necessary to identify those upwind 
states that should have responsibility for addressing their 
contribution to the downwind nonattainment and maintenance problems to 
which they collectively contribute. Continuing to use 1 percent of the 
NAAQS as the screening metric to evaluate collective contribution from 
many upwind states also allows EPA and states to apply a consistent 
framework to evaluate interstate emissions transport under the 
interstate transport provision from one NAAQS to the next. See 81 FR at 
74518. See also 86 FR at 23085 (reviewing and explaining rationale from 
CSAPR, 76 FR at 48237-38, for selection of 1 percent threshold).
i. EPA's Experience With Alternative Step 2 Thresholds
    EPA's August 2018 memorandum recognized that in certain 
circumstances, a state may be able to establish that an alternative 
contribution threshold of 1 ppb is justifiable. Where a state relies on 
this alternative threshold, and where that state determined that it was 
not linked at Step 2 using the alternative threshold, EPA will evaluate 
whether the state provided a technically sound assessment of the 
appropriateness of using this alternative threshold based on the facts 
and circumstances underlying its application in the particular SIP 
submission.
    EPA here shares further evaluation of its experience since the 
issuance of the August 2018 memorandum regarding use of alternative 
thresholds at Step 2. This experience leads the Agency to now believe 
it may not be appropriate to continue to attempt to recognize 
alternative contribution thresholds at Step 2. The August 2018 
memorandum stated that ``it may be reasonable and appropriate'' for 
states to rely on an alternative threshold of 1 ppb threshold at Step 
2.\31\ (The memorandum also indicated that any higher alternative 
threshold, such as 2 ppb, would likely not be appropriate.) However, 
EPA also provided that ``air agencies should consider whether the 
recommendations in this guidance are appropriate for each situation.'' 
Following receipt and review of 49 good neighbor SIP submittals for the 
2015 ozone NAAQS, EPA's experience has been that nearly every state 
that attempted to rely on a 1 ppb threshold did not provide sufficient 
information and analysis to support a determination that an alternative 
threshold was reasonable or appropriate for that state.
---------------------------------------------------------------------------

    \31\ August 2018 memorandum at 4.
---------------------------------------------------------------------------

    For instance, in nearly all submittals, the states did not provide 
EPA with analysis specific to their state or the receptors to which its 
emissions are potentially linked. In one case, the proposed approval of 
Iowa's SIP submittal, EPA expended its own resources to attempt to 
supplement the information submitted by the state, in order to more 
thoroughly evaluate the state-specific circumstances that could support 
approval.\32\ It was at EPA's sole discretion to perform this analysis 
in support of the state's submittal, and the Agency is not obligated to 
conduct supplemental analysis to fill the gaps whenever it believes a 
state's analysis is insufficient. The Agency no longer intends to 
undertake supplemental analysis of SIP submittals with respect to 
alternative thresholds at Step 2 for purposes of the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \32\ Air Plan Approval; Iowa; Infrastructure State 
Implementation Plan Requirements for the 2015 Ozone National Ambient 
Air Quality Standard, 85 FR 12232 (March 2, 2020). The Agency 
received adverse comment on this proposed approval and has not taken 
final action with respect to this proposal.
---------------------------------------------------------------------------

    Furthermore, EPA's experience since 2018 is that allowing for 
alternative Step 2 thresholds may be impractical or otherwise 
inadvisable for a number of additional policy reasons. For a regional 
air pollutant such as ozone, consistency in requirements and 
expectations across all states is essential. Based on its review of 
submittals to-date and after further consideration of the policy 
implications of attempting to recognize an alternative Step 2 threshold 
for certain states, the Agency now believes the attempted use of 
different thresholds at Step 2 with respect to the 2015 ozone NAAQS 
raises substantial policy consistency and practical implementation 
concerns.\33\ The availability of different thresholds at Step 2 has 
the potential to result in inconsistent application of good neighbor 
obligations based solely on the strength of a state's implementation 
plan submittal at Step 2 of the 4-Step interstate transport framework. 
From the perspective of ensuring effective regional implementation of 
good neighbor obligations, the more important analysis is the 
evaluation of the emissions reductions needed, if any, to address a 
state's significant contribution after consideration of a multifactor 
analysis at Step 3, including a detailed evaluation that considers air 
quality factors and cost. Where alternative thresholds for purposes of 
Step 2 may be ``similar'' in terms of capturing the relative amount of 
upwind contribution (as described in the August 2018 memorandum), 
nonetheless, use of an alternative threshold would allow certain states 
to avoid further evaluation of potential emission controls while other 
states must proceed to a Step 3 analysis. This can create significant 
equity and consistency problems among states.
---------------------------------------------------------------------------

    \33\ EPA notes that Congress has placed on EPA a general 
obligation to ensure the requirements of the CAA are implemented 
consistently across states and regions. See CAA section 301(a)(2). 
Where the management and regulation of interstate pollution levels 
spanning many states is at stake, consistency in application of CAA 
requirements is paramount.
---------------------------------------------------------------------------

    Further, it is not clear that national ozone transport policy is 
best served by allowing for less stringent thresholds at Step 2. EPA 
recognized in the August 2018 memorandum that there was some similarity 
in the amount of total upwind contribution captured (on a nationwide 
basis) between 1 percent and 1 ppb. However, EPA notes that while this 
may be true in some sense, that is hardly a compelling basis to move to 
a 1 ppb threshold. Indeed, the 1 ppb threshold has the disadvantage of 
losing a certain

[[Page 9844]]

amount of total upwind contribution for further evaluation at Step 3 
(e.g., roughly seven percent of total upwind state contribution was 
lost according to the modeling underlying the August 2018 memorandum; 
\34\ in EPA's updated modeling, the amount lost is five percent). 
Considering the core statutory objective of ensuring elimination of all 
significant contribution to nonattainment or interference of the NAAQS 
in other states and the broad, regional nature of the collective 
contribution problem with respect to ozone, there does not appear to be 
a compelling policy imperative in allowing some states to use a 1 ppb 
threshold while others rely on a 1 percent of the NAAQS threshold.
---------------------------------------------------------------------------

    \34\ See August 2018 memorandum at 4.
---------------------------------------------------------------------------

    Consistency with past interstate transport actions such as CSAPR, 
and the CSAPR Update and Revised CSAPR Update rulemakings (which used a 
Step 2 threshold of 1 percent of the NAAQS for two less stringent ozone 
NAAQS), is also important. Continuing to use a 1 percent of NAAQS 
approach ensures that as the NAAQS are revised and made more stringent, 
an appropriate increase in stringency at Step 2 occurs, so as to ensure 
an appropriately larger amount of total upwind-state contribution is 
captured for purposes of fully addressing interstate transport. See 76 
FR 48208, 48237-38.
    Therefore, notwithstanding the August 2018 memorandum's recognition 
of the potential viability of alternative step 2 thresholds, and in 
particular, a potentially applicable 1 ppb threshold, EPA's experience 
since the issuance of that memorandum has revealed substantial 
programmatic and policy difficulties in attempting to implement this 
approach. Nonetheless, EPA is not at this time rescinding the August 
2018 memorandum. EPA invites comment on this broader discussion of 
issues associated with alternative thresholds at Step 2. Depending on 
comment and further evaluation of this issue, EPA may determine to 
rescind the August 2018 memorandum in the future.
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with EPA's longstanding approach to eliminating 
significant contribution or interference with maintenance at Step 3, 
states linked at Steps 1 and 2 are generally expected to prepare a 
multifactor assessment of potential emissions controls. EPA's analysis 
at Step 3 in prior Federal actions addressing interstate transport 
requirements has primarily focused on an evaluation of the cost-
effectiveness of potential emissions controls (on a marginal cost-per-
ton basis), the total emissions reductions that may be achieved by 
requiring such controls (if applied across all linked upwind states), 
and an evaluation of the air quality impacts such emissions reductions 
would have on the downwind receptors to which a state is linked; other 
factors may potentially be relevant if adequately supported. In 
general, where EPA's or alternative air quality and contribution 
modeling establishes that a state is linked at Steps 1 and 2, it will 
be insufficient at Step 3 for a state merely to point to its existing 
rules requiring control measures as a basis for approval. In general, 
the emissions-reducing effects of all existing emissions control 
requirements are already reflected in the air quality results of the 
modeling for Steps 1 and 2. If the state is shown still to be linked to 
one or more downwind receptor(s), the state must provide a well-
documented evaluation determining whether their emissions constitute 
significant contribution or interference with maintenance by evaluating 
additional available control opportunities by preparing a multifactor 
assessment. While EPA has not prescribed a particular method for this 
assessment, EPA expects states at a minimum to present a sufficient 
technical evaluation. This would typically include information on 
emissions sources, applicable control technologies, emissions 
reductions, costs, cost effectiveness, and downwind air quality impacts 
of the estimated reductions, before concluding that no additional 
emissions controls should be required.\35\
---------------------------------------------------------------------------

    \35\ As examples of general approaches for how such an analysis 
could be conducted for their sources, states could look to the CSAPR 
Update, 81 FR 74504, 74539-51; CSAPR, 76 FR 48208, 48246-63; CAIR, 
70 FR 25162, 25195-229; or the NOX SIP Call, 63 FR 57356, 
57399-405. See also Revised CSAPR Update, 86 FR 23054, 23086-23116. 
Consistently across these rulemakings, EPA has developed emissions 
inventories, analyzed different levels of control stringency at 
different cost thresholds, and assessed resulting downwind air 
quality improvements.
---------------------------------------------------------------------------

5. Step 4 of the 4-Step Interstate Transport Framework
    At Step 4, states (or EPA) develop permanent and federally 
enforceable control strategies to achieve the emissions reductions 
determined to be necessary at Step 3 to eliminate significant 
contribution to nonattainment or interference with maintenance of the 
NAAQS. For a state linked at Steps 1 and 2 to rely on an emissions 
control measure at Step 3 to address its interstate transport 
obligations, that measure must be included in the state's SIP so that 
it is permanent and federally enforceable. See CAA section 110(a)(2)(D) 
(``Each such [SIP] shall . . . contain adequate provisions . . .''). 
See also CAA 110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 
786 F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on 
by state to meet CAA requirements must be included in the SIP).

II. SIP Submissions Addressing Interstate Transport of Air Pollution 
for the 2015 Ozone NAAQS

    Five of the six states within EPA Region 5 that are included in 
this multi-state proposed disapproval have chosen to use air quality 
modeling performed by the Lake Michigan Air Directors Consortium 
(LADCO) \36\ as an alternative to or in addition to EPA's modeling for 
the purpose of identifying downwind receptors and upwind state 
contributions to these receptors relevant to their submissions. The 
LADCO modeling consisted of ozone season (May 1-September 30, 2011) 
model simulations using the Comprehensive Air Quality Model with 
Extensions, CAMx version 6.4 for a 2011 base year and 2023 as the 
future analytic year. In their modeling, LADCO used EPA's 2011-based 
``EN'' emissions modeling platform, except for emissions from EGU's in 
2023. In their modeling, LADCO used the Eastern Regional Technical 
Advisory Committee (ERTAC) EGU Tool version 2.7 \37\ to provide EGU 
emissions for 2023, whereas EPA used projected EGU emissions based on 
engineering analytics.\38\
---------------------------------------------------------------------------

    \36\ LADCO works collaboratively with state governments, tribal 
governments, and various Federal agencies in Illinois, Indiana, 
Michigan, Minnesota, Ohio, and Wisconsin.
    \37\ https://www.marama.org/2013-ertac-egu-forecasting-tool-documentation.
    \38\ Technical Support Document (TSD) Additional Updates to 
Emissions Inventories for the Version 6.3, 2011 Emissions Modeling 
Platform for the Year 2023 https://www.epa.gov/air-emissions-modeling/additional-updates-2011-and-2023-emissions-version-63-platform-technical.
---------------------------------------------------------------------------

    LADCO provided projected 2023 future year average and maximum 
design values using the methodology in EPA's 2014 modeling 
guidance.\39\ Although projected design values were presented based on 
the 3x3 approach and the ``no water cell'' approach, described in the 
March 2018 memorandum, LADCO relied upon design values from the 3x3 
approach for

[[Page 9845]]

calculating contribution metric values at each receptor.
---------------------------------------------------------------------------

    \39\ See EPA's 2014 Draft Guidance Document, ``Draft Modeling 
Guidance for Demonstrating Attainment of Air Quality Goals for 
Ozone, PM2s, and Regional Haze'', https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf.
---------------------------------------------------------------------------

    Source apportionment modeling was performed by LADCO using the CAMx 
Anthropogenic Precursor Culpability Assessment (APCA) tool to calculate 
contributions from individual states to ozone at downwind monitoring 
sites. In their modeling, LADCO tracked ozone contributions from only 
those states that contributed at or above a 1 percent of the NAAQS 
threshold to nonattainment and maintenance monitors in the EPA 2023 
modeling provided in the March 2018 memorandum.

A. Illinois

    Illinois Environmental Protection Agency (IEPA) submitted a SIP 
revision to address CAA Section 110(a)(2)(D)(i)(I) on May 21, 2019. The 
submission utilized LADCO modeling results previously mentioned. IEPA 
followed the 4-step interstate transport framework using an analytic 
year of 2023 to identify receptors, Illinois' linkages to receptors, 
and assess some emission reduction considerations. The following 
sections will discuss IEPA's submission and the information provided 
for each step in the process.
1. Information Provided by Illinois Regarding Step 1
    For Step 1 in the 4-step framework, the IEPA relied on LADCO 
modeling to identify monitoring sites that are projected to have 
problems attaining or maintaining the 2015 ozone NAAQS in 2023. As 
previously mentioned, the LADCO modeling used the same technique as EPA 
to calculate future year design values which were used to identify 
maintenance and nonattainment receptors but used the ERTAC EGU Tool for 
EGU emissions. IEPA noted they believed that the ERTAC EGU tool 
provides better estimates of growth and forecasts than EPA's EGU 
emission projections. IEPA identified two maintenance receptors in the 
Great Lakes area (Sheboygan, Wisconsin and Allegan County, Michigan) as 
well as and three nonattainment receptors and five additional 
maintenance receptors in the Northeast. Across the continental U.S., 
IEPA identified a total of twelve nonattainment or maintenance 
receptors: seven nonattainment receptors and five maintenance 
receptors.\40\
---------------------------------------------------------------------------

    \40\ IEPA's SIP submission, Table CC, page 15.
---------------------------------------------------------------------------

2. Information Provided by Illinois Regarding Step 2
    IEPA's submittal at Step 2 presented Illinois' projected 2023 
contribution of ozone emissions to the downwind maintenance and 
nonattainment receptors and based on LADCO's ``with water'' modeling 
\41\ IEPA used a contribution threshold of 1 ppb to define linkage as 
opposed to one percent of the 2015 ozone NAAQS standard (0.70 ppb). 
Illinois, relying on the August 2018 memorandum, argued that the 
state's reliance on the 1 ppb threshold to identify linkages was 
justified. First, IEPA asserted that the one percent of the NAAQS 
contribution threshold is arbitrary because it is not in the CAA. 
Second, IEPA claimed that a one percent of the NAAQS contribution 
threshold is inappropriate for the 2015 ozone NAAQS because 0.70 ppb is 
an order of magnitude smaller than the biases and errors typically 
documented for regional photochemical modeling. IEPA noted that 1 ppb 
is very small compared to the allowable error in peak performance and 
bias and in IEPA's view is a conservative Step 2 contribution 
threshold.
---------------------------------------------------------------------------

    \41\ Id.
---------------------------------------------------------------------------

    IEPA identified that Illinois is projected to contribute 14.93 ppb 
and 19.25 ppb, respectively, in 2023 to two maintenance receptors: 
Sheboygan, Wisconsin (Site ID: 55-117-0006), and Allegan, Michigan 
(Site ID: 26-005-0003). IEPA concluded that Illinois is linked above a 
contribution threshold of 1 ppb to these receptors.
3. Information Provided by Illinois Regarding Step 3
    IEPA provided several arguments to justify their conclusion that no 
additional emission reductions are necessary to satisfy Illinois' ozone 
transport obligations. The submittal stated that Illinois is developing 
new NOX RACT standards for the Chicago area that, in 
conjunction with existing NOX reductions, are estimated to 
reduce NOX emissions by up to 20,000 tons/year relative to 
existing state and Federal regulations impacting non-EGUs since 2014. 
IEPA claims that these reductions were not included in any 2023 
modeling. Illinois claims these expected emissions reductions, 
alongside future Federal rules, will be enough to meet Illinois' good 
neighbor obligations.
    IEPA asserted that Illinois' contributions to the Sheboygan, 
Wisconsin and Allegan County maintenance monitors, which are both in 
the LADCO domain, can be addressed in a manner that is fair and 
equitable for all involved states through Illinois' participation in 
LADCO. Illinois has been a member of LADCO since 1991. IEPA says that 
since the inception of LADCO in 1991, ambient ozone concentrations have 
drastically decreased in the Lake Michigan region. IEPA stated that it 
is working through LADCO to refine ozone forecasting for air quality 
and ozone receptors in the Midwest through various means including 
updating emissions inventories and a base case for the modeling that 
LADCO is preparing. IEPA stated that it expects field data from the 
2017 Lake Michigan Ozone Study will inform the LADCO states to better 
simulate the meteorology and chemistry of ozone in the Lake Michigan 
area.
    IEPA also attempted to rely on a concept related to international 
emissions, which was developed by outside parties and listed in 
Attachment A to the March 2018 memorandum. IEPA noted that if 
international emissions and offshore contributions to receptors from 
LADCO's modeling, 1.40 ppb to the Sheboygan, Wisconsin receptor and 
0.98 ppb at the Allegan County receptor, were subtracted off the top of 
the receptors' maximum design values, Allegan, Michigan receptor's 
maximum design value would be below 71 ppb and the Sheboygan, Wisconsin 
receptor's maximum design value would drop down to 71.4 ppb. IEPA noted 
that subtracting international and offshore contributions would result 
in Allegan County no longer qualifying as a maintenance receptor.
4. Information Provided by Illinois Regarding Step 4
    IEPA did not consider any new permanent and enforceable measures to 
reduce emissions in the SIP submission. IEPA instead noted they would 
continue to assist LADCO with future modeling and analysis and would 
work with EPA to identify additional ``flexibilities'' to define 
maintenance, quantify transport, and demonstrate attainment.\42\
---------------------------------------------------------------------------

    \42\ Illinois' SIP submission at 16.
---------------------------------------------------------------------------

B. Indiana

    On November 2, 2018 the Indiana Department of Environmental 
Management (IDEM) submitted a revision to the Indiana SIP addressing 
interstate transport of air pollution for the 2015 ozone NAAQS. The 
submission contained what the state characterized as a weight of 
evidence analysis of Indiana's ozone transport receptors utilizing 
LADCO modeling results previously mentioned. Indiana did not explicitly 
follow the 4-Step interstate transport framework but did examine 
downwind air quality and Indiana's contributions using an analytic year 
of 2023 to describe

[[Page 9846]]

Indiana's linkages to receptors. The following sections will describe 
IDEM's submission, and the information provided for each step in the 
process.
1. Information Provided by Indiana Regarding Step 1
    For Step 1 of the 4-Step framework, IDEM identified monitoring 
sites that are projected to have problems attaining and/or maintaining 
the 2015 ozone NAAQS in 2023. As previously mentioned, the LADCO 
modeling used the same technique as EPA to calculate future year design 
values which were used to identify maintenance and nonattainment 
receptors but used the ERTAC EGU Tool for EGU emissions. IDEM noted 
they believed that the ERTAC EGU tool provides better estimates of 
growth and forecasts than EPA's EGU emission projections. IDEM 
presented the LADCO results, based on the ``3x3'' approach, which 
identified ten receptors: Seven monitors with 2023 maximum design 
values above the NAAQS, or maintenance receptors, and three monitors 
with 2023 average design values greater than the 2015 ozone standard, 
or nonattainment receptors.\43\
---------------------------------------------------------------------------

    \43\ Indiana's SIP submission Attachment 1, Table 7, page 30.
---------------------------------------------------------------------------

2. Information Provided by Indiana Regarding Step 2
    IDEM's submittal presented Indiana's projected 2023 ozone 
contributions to maintenance and nonattainment receptors projected by 
the LADCO modeling. IDEM relied primarily on the August 2018 memorandum 
to justify the State's reliance on a 1 ppb contribution threshold to 
identify linkages, as opposed to the 1 percent of the 2015 ozone NAAQS 
standard (0.70 ppb) contribution threshold. IDEM noted that (1) the 
tolerance level of ozone monitors is 1 ppb and (2) model run results 
may contain biases larger than 1 percent of the NAAQS (0.70 ppb). Using 
a 1 ppb threshold, IDEM identified that Indiana is linked to three 
maintenance receptors: Sheboygan, Wisconsin (Monitor ID: 551170006), 
Allegan, Michigan (Monitor ID: 260050003), and Richmond, New York 
(Monitor ID: 360850067), and one nonattainment receptor: Harford, 
Maryland (Monitor ID: 240251001).\44\ \45\ However, IDEM concluded on 
the basis of its weight of evidence analysis, summarized in the 
following subsection, that the monitors at Sheboygan, Wisconsin and 
Allegan, Michigan would be in attainment in 2023.\46\
---------------------------------------------------------------------------

    \44\ Indiana's SIP submission Attachment 1, Table 1, page 12.
    \45\ IDEM acknowledged that both the Harford, Maryland and 
Richmond, New York receptors are nonattainment receptors in EPA's 
modeling. Indiana's SIP submission Attachment 1, page 12.
    \46\ Indiana's SIP submission Attachment 1, page 38, 53.
---------------------------------------------------------------------------

3. Information Provided by Indiana Regarding Step 3
    IDEM cited Indiana's rule amendments under CSAPR to conclude the 
State was already satisfying its good neighbor obligations for the 
ozone NAAQS.\47\ In support, IDEM provided a weight-of-evidence 
analysis to justify their conclusion that no additional emission 
reductions as necessary to satisfy Indiana's ozone transport 
obligations. The evidence consisted of an ozone monitoring data 
analysis, emissions analysis, and photochemical modeling analyses, 
including a back trajectory analysis.
---------------------------------------------------------------------------

    \47\ Indiana's SIP submission, page 6.
---------------------------------------------------------------------------

    IDEM provided information ozone and emissions trends. They cited a 
general decline in monitored ozone concentrations across Indiana from 
2007 through 2017, a decrease in Indiana's overall statewide 
NOX emissions and VOC emissions from 2005 to 2014, a 
decrease in Indiana EGU NOX emissions from 2011 to 2016, and 
projected decreases in Region 5 EGU NOX and VOC emissions 
through 2023 relative to a 2011 base year (based on both the ERTAC EGU 
Tool and EPA's EGU projections using the Integrated Planning Model 
(IPM)). IDEM credited the downward emissions trends to permanent and 
enforceable control measures. IDEM made the argument that overall 
decreasing ozone concentration and emissions trends in the State, and 
in the LADCO states, correlate with reduced contributions to 
nonattainment and maintenance receptors outside of Indiana. IDEM also 
identified air quality trends at the four downwind receptors to which 
IDEM determined Indiana was linked. IDEM asserted that a declining 
trend in three-year design values at the receptors in Harford, Maryland 
and Richmond, New York in combination with national emission reduction 
regulations in place for EGUs, tighter mobile source emission controls 
and other transport related emission reduction measures, would result 
in those two receptors reaching attainment over time. For the 
Sheboygan, Wisconsin and Allegan, Michigan receptors, IDEM concluded 
that if ozone design value trends continued as expected then those two 
receptors would reach attainment before 2023. IDEM also asserted they 
believed that the receptors in the Northeast (Harford, Maryland and 
Richmond, New York) received a greater contribution from local sources. 
IDEM represented EPA had reached the same conclusion, citing a May 14, 
2018 presentation.
    Next, IDEM presented an analysis of NOx controls for EGUs and non-
EGUs in the state from 2008 to 2017. IDEM considered current NOx 
control measures, consent decree requirements, and future fuel switches 
and retirements for large EGUs and non-EGUs. IDEM reported that the 
State has seen a downward trend in annual NOX emissions from 
both EGUs and non-EGUs due a combination of state and Federal rules 
targeting fossil fueled EGUs and other large sources of NOX. 
IDEM argued that it would not be cost-effective for non-EGUs to 
implement further NOX controls because in 2017 there were 
more than 93% fewer NOX emissions from non-EGUs when 
compared to EGUs. IDEM stated they expect to see continued future 
NOX emission reductions through 2028 from implementation of 
Federal rules, the expected shutdown of nine EGUs, planned fuel 
switches to natural gas for three EGUs, and enforceable consent decree 
caps on NOX emissions at eleven EGUs. IDEM noted that future 
retirements or retrofits to coal fired EGUs in Indiana were expected to 
reduce NOX emissions by several thousand tons beyond those 
projected by either LADCO or EPA. IDEM argued that the non-modeled 
emission reductions would further assure future year attainment of the 
ozone NAAQS at downwind receptors.
    For their photochemical analyses, IDEM presented LADCO modeling 
results to show contributions from individual states to 12 
monitors,\48\ as well as contributions from individual sectors to the 
same 12 monitors.\49\ IDEM noted that Indiana contributed above 1 ppb 
to monitors that would be receptors based on EPA's definitions. IDEM 
used these data as the backdrop to several arguments related to 
potential flexibilities identified in Attachment A to the March 2018 
memorandum.\50\ IDEM stated that additional emissions reductions from 
EGU and non-EGU sources in Indiana are becoming more difficult to 
require because of reduced effectiveness of controls to make 
significant decreases in ozone values, operational concerns, and 
increased

[[Page 9847]]

costs for customers. IDEM asserted that emission reductions from local 
mobile and nonroad sources would be more beneficial to the receptors 
than additional reductions from EGUs and non-EGUs in Indiana because 
EGUs and non-EGUs contribute less to the receptors than either the 
mobile or nonroad sectors. IDEM also argued that EPA should address 
contributions from Canada and Mexico as well as contributions from 
offshore commercial marine vessels. In addition, IDEM compared 2012-
2017 monitoring data to LADCO's and EPA's modeling and concluded that 
all four linked receptors were already below the projected 2023 design 
values. IDEM also calculated Indiana's portion of contribution to the 
Harford, Maryland receptor as 0.077 ppb (based on a contribution 
threshold of 1 ppb) and determined that Indiana would need to reduce 
its contribution by 0.0077 ppb to bring the Harford, Maryland receptor 
into attainment. IDEM argued that 0.0077 ppb is well within the error 
of the model and it would be ``difficult'' to translate into an 
emission reduction requirement.\51\
---------------------------------------------------------------------------

    \48\ Indiana's SIP submission, Attachment 1, Table 9.
    \49\ Indiana's SIP submission, Attachment 1, Table 11.
    \50\ Based on the reference to the potential flexibilities in 
Attachment A to the March 2018 memorandum on page 2 of Attachment 1 
to Indiana's SIP submission, EPA assumes the reference to 
``flexibilities'' on page 38 of Attachment 1 likewise references 
Attachment A to the March 2018 memorandum.
    \51\ Indiana's SIP submission, Attachment 1 at 42.
---------------------------------------------------------------------------

    Finally, IDEM provided a back trajectory analysis to evaluate 
contributions from Indiana to the Harford, Maryland and Richmond, New 
York receptors on exceedance days from 2015 to 2017. These back 
trajectories were conducted at 10 meters and 750 meters and initialized 
at 18Z Greenwich Mean Time over a three-year period from 2015-2017. The 
trajectories were run backwards over a 72-hour period from the 
exceedance day measured at each of the monitors. Considering the 
Harford, Maryland receptor, Indiana measured one back trajectory at 10 
meters and six back trajectories at 750 meters that passed through 
Indiana. For the Richmond, New York receptor, out of 27 exceedance 
days, Indiana measured three back trajectories at 10 meters and eight 
trajectories at 750 meters that passed through Indiana. Indiana argues 
that only a fraction of the exceedance days at the Harford and Richmond 
receptors has back trajectories that pass-through Indiana. Based on 
this analysis, IDEM concluded that those receptors are more likely to 
be impacted by local emissions and suggested that emission reductions 
should come first from the surrounding areas in the Northeast before 
from Indiana.
4. Information Provided by Indiana Regarding Step 4
    IDEM did not provide a Step 4 analysis.

C. Michigan

    Environment, Great Lakes and Energy (EGLE) (formerly Michigan 
Department of Environmental Quality) submitted a SIP revision to 
address CAA Section 110(a)(2)(D)(i)(I) on March 5, 2019. EGLE utilized 
EPA modeling released with the March 2018 memorandum and LADCO modeling 
and followed the 4-step interstate transport framework using an 
analytic year of 2023 to describe Michigan's linkages to receptors in 
other states. The submission also contained a weight-of-evidence 
analysis to support EGLE's conclusions. The following sections will 
discuss EGLE's submission and the information provided for each step in 
the process.
1. Information Provided by Michigan Regarding Step 1
    For Step 1 in the 4-step framework, EGLE identified monitoring 
sites that are projected to have problems attaining and/or maintaining 
the 2015 ozone NAAQS in 2023. EGLE presented the results from both the 
EPA modeling from the March 2018 memorandum and LADCO (using both the 
with- and without-water approaches). EGLE noted that they believe the 
ERTAC EGU Tool uses a more transparent and state-driven data gathering 
mechanism for EGU emissions and control projects. EPA's modeling 
projected 16 receptors to which Michigan is projected to contribute in 
2023. LADCO modeling (with and without water) identified 15 receptors 
to which Michigan is projected to contribute in 2023.
2. Information Provided by Michigan Regarding Step 2
    The first part of EGLE's submittal's step 2 analysis presented 
Michigan's projected contributions to maintenance and nonattainment 
receptors in 2023 from both the LADCO modeling (with and without water) 
and the EPA modeling released with the March 2018 memorandum. The 
submittal noted similar contribution concentrations between the two, 
but found that the LADCO results often yielded slightly lower 
contribution from Michigan sources than the EPA modeling for some 
receptors. The state claimed this is attributed to LADCO's use of the 
ERTAC EGU tool which they stated includes information on EGU shutdowns 
and facility-specific information not included in the EPA modeling. 
EGLE stated they had more confidence in the LADCO modeling.
    Further, EGLE attempted to rely on the 1 ppb Significant Impact 
Level (SIL) threshold from Guidance on Significant Impact Levels for 
Ozone and Fine Particles in the Prevention of Significant Deterioration 
Permitting Program (April 17, 2018) \52\ for the Prevention of 
Significant Deterioration (PSD) permitting program as an appropriate 
contribution threshold to determine whether Michigan was linked to any 
receptors at step 2. Michigan argued that if a stationary source's 
contributions are insignificant below 1 ppb, then a state's interstate 
transport contributions below 1 ppb are likewise insignificant. EGLE 
performed an analysis on contribution thresholds to analyze whether a 1 
ppb threshold is appropriate for identifying Michigan's linkages. The 
analysis looked at all 15 receptors to which Michigan contributes, 
based on the LADCO with water modeling, and plotted potential 
contribution thresholds ranging from 0.5 to 1.4 ppb against collective 
upwind contributions from all source categories and states with 
contribution above 0.5 ppb. EGLE plotted the collective contribution as 
a function of contribution threshold and concluded the first inflection 
point occurred in a majority of the collective contribution at a 
contribution threshold between 0.9 and 1 ppb, correlating with the PSD 
permitting SIL of 1 ppb. Based on this analysis, EGLE concluded that a 
1 ppb contribution threshold was appropriate for use in the good 
neighbor context. EGLE also mentioned the August 2018 memorandum, 
described in Section I of this proposal, as additional support for the 
use of a 1 ppb contribution threshold.\53\
---------------------------------------------------------------------------

    \52\ https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf.
---------------------------------------------------------------------------

    EGLE's Step 2 conclusion was that, based on LADCO with water 
modeling, Michigan was projected to be linked above a 1 ppb 
contribution threshold in 2023 to three maintenance receptors; 1.85 ppb 
to Sheboygan, Wisconsin (Site ID: 36-081-0124), 1.22 ppb to Queens, New 
York (Site ID: 36-085-0067), and 1.03 ppb to Richmond, New York (Site 
ID: 55-117-0006).
3. Information Provided by Michigan Regarding Step 3
    EGLE provided what it characterized as a ``weight-of-evidence 
analysis'' in step 3 to justify their conclusion that no additional 
emissions reductions are necessary to satisfy Michigan's ozone 
transport obligations for the ozone NAAQS. The evidence presented in 
EGLE's submittal consisted primarily of an argument that upwind states 
should have a lower responsibility to other states when the upwind 
state is only linked to maintenance-only receptors.

[[Page 9848]]

EGLE's analysis focused in large part on the Sheboygan, Wisconsin 
maintenance receptor (Site ID: 36-081-0124), as EGLE concluded it was 
the receptor to which Michigan was projected to contribute the most in 
2023 at 1.85 ppb.
    On the issue of maintenance receptors, the state referenced a 
concept identified by outside parties and listed in Attachment A to the 
March 2018 memorandum, which was to consider whether the remedy for 
upwind states linked to maintenance receptors could be less stringent 
than those linked to nonattainment receptors. EGLE reasoned that 
because the CAA incudes different SIP development requirements for 
nonattainment and maintenance areas, that likewise nonattainment and 
maintenance areas should be treated differently in good neighbor SIPs. 
EGLE argued that because the CAA does not require emission reductions 
from maintenance areas, then upwind states can potentially make a 
sufficient showing they have no obligation to reduce emissions to 
monitors in other states projected to be maintaining the NAAQS. EGLE 
said they believe the reduction of projected contributions to projected 
maintenance receptors is not required in certain circumstances, such as 
when: (1) The projected maintenance exceedance is very small in 
magnitude, (2) the projected contribution is very small, especially 
compared to other states' contributions, (3) sector contributions 
demonstrate the majority of contribution is from either sources already 
federally regulated or sources without the possibility of additional 
regulation, (4) there are large impacts of international emissions, and 
(5) there are downward emission trends.
    Applying this logic to the Sheboygan, Wisconsin receptor, EGLE 
argued that because the projected maximum design value at that receptor 
is 72.8 ppb, the projected exceedance above the 2015 ozone NAAQS of 1.9 
ppb is very small (values are truncated to ppb, thus 70.9 ppb would be 
considered in attainment of the NAAQS). Based on this number, EGLE 
argued that further emissions reductions from Michigan would be overly 
burdensome. Secondly, citing a potential flexibility in Attachment A to 
the March 2018 memorandum related to sector contribution, EGLE claimed 
that 77% of contribution to the Sheboygan receptor is from federally 
regulated sources or sources that cannot be regulated by Michigan. EGLE 
noted that the other sectors of contribution it identified--oil and 
gas, EGUs, and non-EGUs--are already controlled by Michigan. EGLE 
argued Michigan sources should not be required to implement additional 
contribution reductions in light of the relative size of their 
contribution.
    Citing Attachment A to the March 2018 memorandum, again, EGLE 
argued that the three receptors to which Michigan is linked are heavily 
influenced by international emissions and other states. EGLE shared 
that LADCO modeling projects Michigan's contribution to the Sheboygan 
receptor (1.85 ppb) is less than projected contributions from 
international contributions and boundary conditions (16.61 ppb), 
Illinois (14.93 ppb), Wisconsin (9.1 ppb), biogenic sources (7.19 ppb), 
and Indiana (6.19 ppb). EGLE used these numbers and an apportionment of 
contributions from states and other sources to the amount the Sheboygan 
monitor exceeds the 2015 ozone NAAQS to conclude that additional 
emissions reductions from Michigan should not be required. 
Additionally, EGLE argued that international contributions to the 
Sheboygan receptor, which is geographically close to Canada, should be 
eliminated from the projected DV, in which case the Sheboygan monitor 
would be in attainment.
    EGLE also cited Attachment A to the March 2018 memorandum along 
with an interpretation of EME Homer City to argue that EPA cannot 
require reductions that would result in a reduction greater than an 
upwind state's portion of the difference between the NAAQS and a 
maintenance receptor's projected maximum design value. EGLE claimed 
that Michigan's apportioned contribution to three linked receptors, 
when distributed proportionally among other states that also contribute 
more than 1 ppb to those receptors, is less than 0.12 ppb, but that 
Michigan's responsibility to the exceedance is actually substantially 
less than that amount when the home state's responsibility is 
considered. EGLE also stated Michigan's apportioned contribution is at 
less than 0.05 ppb of the projected maintenance exceedance at the 
Sheboygan receptor, which is less than the variation among the modeled 
maximum design values by both LADCO and EPA. EGLE concluded that 
because of built-in modeling noise it would be ``difficult'' to either 
verify that Michigan contributed 0.05 ppb to the Sheboygan, Wisconsin 
receptor or for Michigan to require any additional reduction from 
sources in the state.\54\ EGLE speculated it was quite likely that the 
three linked receptors would maintain the NAAQS without any emissions 
reductions from Michigan at all because the projected exceedances were 
small.
---------------------------------------------------------------------------

    \54\ Michigan's SIP submission at 27.
---------------------------------------------------------------------------

    The state also stated that Michigan has downward emissions trends 
(44% and 18% reduction in industrial point source NOX and 
VOC emissions from 2008 through 2016, respectively) that are expected 
to continue to decline or stay consistent over time due to projected 
reductions in emissions from point sources of NOX and VOCs 
EGUs, mobile sources and through other Federal measures. For EGUs, EGLE 
pointed out that the shutdown of the Marquette Board of Light & Power 
Shiras Steam Plant shut down was not included in either EPA or LADCO 
modeling and that the U.S. Energy Information Agency's Annual Energy 
Outlook anticipates growth in renewable energy in Michigan in 2019 and 
a decline in coal beginning in 2022. EGLE also provided a list of 
additional coal-fired EGUs that they stated were expected to retire by 
2023. To support the conclusion that emissions will further be reduced 
from mobile sources and through other Federal action, EGLE listed 
several on the books and on the way Federal regulations. Finally, EGLE 
noted existing controls on the oil and gas sector (applicable Federal 
standards), non-EGUs (subject to the NOX SIP Call), and EGUs 
(subject to CSAPR Update).
4. Information Provided by Michigan Regarding Step 4
    EGLE concluded it would be unreasonable for Michigan to take 
further actions to address its obligations under the good neighbor 
provisions for the ozone NAAQS, and so at Step 4 EGLE determined that 
no permanent and enforceable measures to reduce emissions were 
necessary.

D. Minnesota

    Minnesota Pollution Control Agency (MPCA) submitted a SIP revision 
to address CAA Section 110(a)(2)(D)(i)(I) on October 1, 2018. The 
submission utilized both EPA modeling released with the March 2018 
memorandum and LADCO modeling results previously mentioned. Minnesota 
followed the 4-step interstate transport framework and used an analytic 
year of 2023 to describe Minnesota's lack of contributions to out of 
state receptors and assess emission reduction considerations. The 
following sections will summarize MPCA's submission and the information 
provided for each step in the process.

[[Page 9849]]

1. Information Provided by Minnesota Regarding Step 1
    For Step 1 in the 4-step framework, MPCA identified monitoring 
sites that are projected to have problems attaining and/or maintaining 
the 2015 ozone NAAQS in 2023 according to LADCO modeling and EPA 
modeling released in the March 2018 memorandum.\55\ As previously 
mentioned, the LADCO modeling efforts used the same technique as EPA to 
calculate future year design values which are used to identify 
maintenance and nonattainment receptors. The submittal expressed MPCA's 
opinion that the ERTAC EGU tool used in LADCO's modeling is superior to 
EPA's 2023en modeling platform because the ERTAC EGU tool addresses 
economic factors, preserves system reliability, and includes controls 
or emissions reductions measure justified through some legal framework.
---------------------------------------------------------------------------

    \55\ MPCA's SIP submittal at Tables 2 and 3, pages 8-9.
---------------------------------------------------------------------------

2. Information Provided by Minnesota Regarding Step 2
    MPCA's submittal at Step 2 presented Minnesota's projected 2023 
ozone contributions to maintenance and nonattainment receptors 
identified by both LADCO modeling and EPA modeling released in the 
March 2018 memorandum.\55\ The submittal noted there were differences 
in identified receptors between the two modeling results, and that the 
LADCO results overall yielded slightly lower projected contributions to 
downwind receptors from Minnesota sources than EPA modeling.
    Minnesota relied on a contribution threshold of 1 percent of the 
ozone NAAQS (0.70 ppb) to define linkages for a state's contribution to 
downwind air quality problems. Both the LADCO modeling and the EPA 
modeling released in the March 2018 memorandum projected that Minnesota 
contributes less than 1 percent of the NAAQS to all downwind receptors. 
MPCA showed in Table 2 of its submission that the highest projected 
contribution to a receptor in 2023 was 0.40 ppb, based on EPA modeling 
released in the March 2018 memorandum, or 0.45 ppb, based on LADCO ``no 
water'' modeling, to the Milwaukee, Wisconsin receptor (Site ID: 55-
079-0085). Based on this analysis, MPCA concluded that Minnesota was 
not linked above 1 percent of the NAAQS to any downwind receptor, and 
therefore would not contribute to nonattainment or interference with 
maintenance in other state with respect to the ozone NAAQS.
3. Information Provided by Minnesota Regarding Step 3
    Despite concluding Minnesota was not linked at Step 2, MPCA 
proceeded with a Step 3 analysis. MPCA provided air quality data in 
Step 3 to justify that no additional emissions reductions are necessary 
to satisfy their transport obligations. MPCA provided evidence of 
decreasing ambient ozone concentrations in Minnesota from the mid-1990s 
through 2017 as well as decreasing NOX and VOC emissions 
from the state from 2002 through 2015 to further support their 
conclusion.\56\
---------------------------------------------------------------------------

    \56\ See Minnesota's SIP submittal Figures 1-3, pages 10-11.
---------------------------------------------------------------------------

    The state concluded that decreasing ambient ozone concentrations in 
the state point to Minnesota contributing less to ozone in downwind 
states as time goes on. Minnesota provided an analysis of 
NOX and VOC emissions levels in the state from 2002 through 
2015 to further support this point. According to MPCA, NOX 
emissions have been steadily declining in the state from all sectors 
and especially from EGUs due to emission limits and reductions required 
in that category. MPCA also asserted that VOCs emissions have also seen 
a similar decline in Minnesota in the years reported. MPCA concluded 
that decreasing emissions in the state would make it unlikely for the 
state to contribute significantly to nonattainment or interference with 
maintenance in downwind states.
4. Information Provided by Minnesota Regarding Step 4
    Citing declining emissions and their conclusion that Minnesota was 
not projected to contribute above 1 percent of the NAAQS to any 
receptor, MPCA concluded that no additional permanent or enforceable 
measures would be needed to address ozone transport contribution from 
Minnesota sources. MPCA determined the existing emission controls would 
be sufficient to maintain Minnesota's continued contribution of less 
than 1 percent of the NAAQS to downwind receptors. In support of this 
argument, Minnesota provided a list of several Federal and State 
emissions regulations applicable to sources in Minnesota, including 
Part 70 permits, the CSAPR NOX trading programs, Mercury and 
Air Toxics Standards, and various state standards for SO2, 
particulate matter, NOX, NO2, and VOC. Hence, 
Minnesota declined to consider any new permanent and enforceable 
measures to reduce emissions as part of the Step 4 analysis.

E. Ohio

    On September 28, 2018 the Ohio Environmental Protection Agency 
(OEPA) submitted a revision to the Ohio SIP addressing interstate 
transport of air pollution for the 2015 ozone NAAQS. OEPA stated that 
its submittal, which relied on an analytic year of 2023, conforms with 
EPA's four-step framework. The following sections will describe what 
OEPA provided for each step.
1. Information Provided by Ohio Regarding Step 1
    For Step 1 in the 4-step framework, OEPA first identified 10 
monitoring sites in the Northeast and Midwest that are projected to be 
nonattainment, nonattainment/maintenance, or maintenance-only receptors 
for the 2015 ozone NAAQS in 2023 based on LADCO's modeling and EPA's 
method for defining nonattainment and maintenance receptors (See Table 
1 below, reproduced from OEPA's submission).

                                          Table 1--Ohio's Projected 2023 Nonattainment and Maintenance Monitors
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                2023
                                                      2015-2017       2023                       OH                         Maintenance    Status  (TX
      Site ID               County          State         DV       Average DV  2023 Max DV  contribution       Status          DV (TX       approach)
                                                                                                                             approach)
--------------------------------------------------------------------------------------------------------------------------------------------------------
36-103-0002........  Suffolk............  NY                  76         71.6         73.1          1.75  Nonattainment/           69.7  Nonattainment.
                                                                                                           Maintenance.
09-001-9003........  Fairfield..........  CT                  83         71.4         74.2          1.58  Nonattainment/           73.7  Nonattainment/
                                                                                                           Maintenance.                   Maintenance.

[[Page 9850]]

 
24-035-1001........  Harford............  MD                  75         71.0         73.3          2.83  Nonattainment/           67.0  Nonattainment.
                                                                                                           Maintenance.
36-085-0067........  Richmond...........  NY                  76         70.9         72.4          2.24  Maintenance.....         68.0  Attainment.
55-117-0006........  Sheyboygan.........  WI                  80         70.5         72.8          1.17  Maintenance.....         71.1  Maintenance.
09-009-9002........  New Haven..........  CT                  82         69.9         72.6          1.12  Maintenance.....         72.6  Maintenance.
09-001-3007........  Fairfield..........  CT                  83         69.8         73.7          1.84  Maintenance.....         73.7  Maintenance.
36-081-0124........  Queens.............  NY                  74         69.2         71.0          1.88  Maintenance.....         70.1  Attainment.
09-001-0017........  Fairfield..........  CT                  79         68.9         71.2          1.05  Maintenance.....         71.2  Maintenance.
26-005-0003........  Allegan............  MI                  73         68.8         71.5          0.19  Maintenance--Not         71.5  Maintenance--No
                                                                                                           Linked.                        t Linked.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    OEPA then claimed that EPA's methodology for determining 
maintenance-only receptors is inappropriate because it is more 
stringent than EPA's methodology for identifying nonattainment monitors 
and is inconsistent with the CAA. In OEPA's view, EPA's methodology 
results in greater emissions reduction requirements to address 
maintenance receptors than nonattainment receptors. Citing stakeholder-
identified potential flexibilities that were listed in an attachment to 
EPA's March 2018 memorandum, OEPA used an alternative method developed 
by the Texas Commission for Environmental Quality (TCEQ) to identify 
maintenance receptors. This method determines a future year design 
value (DV) for purposes of identifying maintenance-only receptors by 
applying the model-predicted relative response factor (RRF) to the most 
recent 3-year design value (i.e., 2011-2013 design value) within the 
five-year base period (i.e., 2009-2013), rather than the highest 3-year 
DV in the same 5-year base period, which is used in EPA's approach. 
OEPA stated that using the TCEQ approach accounts for emissions 
reductions over the five-year period, while also accounting for 
meteorological variability, since the design value is calculated based 
on monitoring data from a three-year period. By using the TCEQ 
approach, Ohio concluded that four monitors which would be either 
nonattainment/maintenance receptors under EPA's method would, under the 
TCEQ method, actually be nonattainment-only receptors (i.e., sites 
261030002 in Suffolk, New York, 240251001 in Harford, Maryland) or 
monitors in attainment (i.e., sites 360850067 in Richmond, New York, 
and 360810124 in Queens, New York) in 2023.\57\
---------------------------------------------------------------------------

    \57\ Ohio's SIP submission, Table 1.
---------------------------------------------------------------------------

    OEPA's submittal provided information on inter-annual 
meteorological variability, ozone design value trends at the four 
monitoring sites that the state eliminated as receptors, as well as 
recent and projected trends in NOX and VOC emissions to 
support the use of an alternative definition of maintenance receptors. 
The meteorological information provided in OEPA's submission included 
nationwide maps showing the maximum temperature anomaly (i.e., 
departure from the long-term average or ``normal'') for the period May 
through October in the years 2011, 2012, and 2013. OEPA concluded from 
these maps that temperatures in the Northeast and Midwest were above or 
much above average during May through October in each of the years 
2011, 2012, and 2013. OEPA examined trends in ozone design values at 
each of the four monitoring sites in question and concluded that design 
values at these sites have declined substantially from 2000 through 
2017 and that although there has been a slight leveling off or increase 
in recent years, this is no greater than the normal year to year 
variability. In addition, based on the emissions trends data, OEPA 
stated that NOX emissions have declined in concert with 
these trends in design values and are projected to continue to decline 
through 2028 for the continental U.S. as well as those states that were 
projected to be linked to the four monitors eliminated under the TCEQ 
approach. Based on their analysis of the meteorological and ozone and 
emissions trends data, OEPA concluded that the four monitoring sites 
identified previously are not reasonably expected to have difficulty 
maintaining the standards in 2023.
2. Information Provided by Ohio Regarding Step 2
    OEPA's submittal presented the projected 2023 ozone contributions 
from Ohio to ten maintenance and nonattainment receptors in the 
Northeast and Midwest using data from the LADCO source apportionment 
modeling. LADCO's contribution data identified a total of nine 
receptors in 2023 (3 nonattainment and 6 maintenance-only) with modeled 
contributions from emissions in Ohio that exceed both a one percent of 
the 2015 NAAQS threshold (i.e., 0.70 ppb) and a 1 ppb contribution 
threshold (Table 1). Despite acknowledging Ohio was linked to the same 
number of receptors under either a 1 percent of the NAAQS or 1 ppb, 
OEPA maintained they had concerns about both thresholds being too 
stringent, noting that Ohio would have two linkages if the threshold 
were 3 percent and zero linkages if the threshold were 4 percent.
    As noted above, OEPA applied the TCEQ method for identifying 
maintenance-only receptors, and concluded that four of the receptors to 
which Ohio was linked would not have difficulty maintaining the NAAQS 
in 2023. However, after eliminating these four monitoring sites as 
having maintenance issues, OEPA acknowledged that Ohio would still be 
linked to seven receptors in 2023.
3. Information Provided by Ohio Regarding Step 3
    OEPA provided what they characterize as a weight of evidence 
analysis in Step 3 to justify their conclusion that no additional 
emissions reductions are necessary to satisfy Ohio's interstate 
transport obligations under the 2015 ozone NAAQS. OEPA argued that 
their analysis demonstrated that any additional controls beyond those 
on the books or already planned would result in overcontrol of sources 
in Ohio, likely at cost-prohibitive levels.
    First, OEPA attempted to show that NOX and VOC 2023 
emissions from EGU, nonEGU, and onroad sectors had been overestimated 
by 21,761 tons of NOX and 3,240 tons of VOC annually, and 
7,040 tons of NOX and 878 tons of VOC per ozone season. The 
submittal performed an evaluation of the ERTAC EGU Tool, emphasizing 
that projected 2023 EGU emissions from eight facilities

[[Page 9851]]

were overestimated, analyzed through a comparison of actual emissions 
data obtained from EPA's Clean Air Markets Database (CAMD) and CSAPR/
CSAPR Update allocations obtained from EPA's CSAPR website with 
projected emissions in 2023 obtained from ERTAC EGU tool. OEPA also 
based its conclusions on an expected increase of natural gas sources 
projected by the U.S. Energy Information's Annual Energy Outlook 2018 
and recently permitted natural gas facilities not reflected in the 
ERTAC EGU tool. Further, OEPA evaluated emissions from nine non-EGU 
sources to claim EPA's 2023 projected emissions were overestimated. For 
this analysis, OEPA compared actual emissions data trends from Ohio's 
Emissions Inventory System18 with projected emissions from EPA's Air 
Emissions Modeling Platform 2011v6.319 to conclude EPA's projections 
overestimated non-EGU emissions. OEPA also asserted that EPA's 
projections of vehicle miles traveled (VMT) were higher than the local 
projections.
    OEPA's submittal also looked at NOX and VOC emissions 
trends, and asserted that from 2011 to 2016, NOX emissions 
declined while VOC emissions remained steady. Additionally, based on 
state-specific data, OEPA posited that Ohio's VOC emissions will 
decrease even more rapidly than predicted by EPA because the large 
growth in the State's oil and gas sector had begun to level off. OEPA 
attributed the trends it identified to several Federal and State 
programs, including SIP approved state programs, non-SIP approved 
programs such as NOX RACT, Architectural and Industrial 
Maintenance (AIM) Coatings rules, Ohio's Beneficiary Mitigation Plan 
for the Volkswagen settlement, and Federal programs such as CAIR and 
CSAPR, NOX SIP Call, the National Emission Standards for 
Hazardous Air Pollutants (NESHAP), the Regional Haze Rule, BART, 
SO2 Data Requirements Rule, and MATS.
    In addition to emissions trends data, OEPA noted LADCO modeling 
projected downwind trends in design values at the ten receptors from 
2000 through 2017 and included a reference to ``a May 14, 2018 
presentation, U.S. EPA Office of Air Quality Planning and Standards 
(OAQPS)''.\58\ OEPA also stated that LADCO sector-based source 
apportionment modeling indicates a significant contribution from onroad 
sources at nine receptors. OEPA argued that local onroad emissions 
should be addressed by EPA before EPA requires additional reductions 
from upwind states. OEPA also suggested EPA should take into account 
the impact on ozone of the proposed Safer Affordable Fuel-Efficient 
(SAFE) Vehicles Rule before taking final action on SAFE. Further, OEPA 
asserted that Ohio's contribution to nine monitors is in the 1 or 2 ppb 
range while the home state and initial and boundary contributions are 
each up to 19 ppb, and the contribution from Canada/Mexico is in the 
same range as Ohio's. OEPA argued that ignoring international emissions 
sources and placing all responsibility for addressing receptors on 
upwind states would result in overcontrol.
---------------------------------------------------------------------------

    \58\ Ohio's SIP submission at 43.
---------------------------------------------------------------------------

    OEPA concluded that there were no cost-effective measures to be 
taken for EGU or non-EGU sources in Ohio. To support this claim, OEPA 
pointed to the cost effectiveness threshold of $1400/ton from the CSAPR 
Update (81 FR 74508, October 26, 2016), and while OEPA recognized that 
it was developed for the 2008 ozone standard, OEPA stated they believed 
it is a reasonable cost-effectiveness level for the 2015 ozone NAAQS. 
As for non-EGUs, OEPA asserted that those sectors were adequately 
controlled by the Boiler MACT and numerous other MACT categories, BART, 
SO2 Data Requirements Rule and other Federal regulations.
4. Information Provided by Ohio Regarding Step 4
    OEPA concluded, based on its weight of evidence analysis, that no 
additional emissions reduction measures beyond existing and planned 
controls are necessary to address ozone transport contribution from 
Ohio sources for the 2015 ozone NAAQS.

F. Wisconsin

    Wisconsin Department of Natural Resources (WDNR) submitted a SIP 
revision to address CAA Section 110(a)(2)(D)(i)(I) on September 14, 
2018. The submittal notes state and Federal rules applicable to sources 
in Wisconsin that are relevant to interstate transport, as well as 
Wisconsin's participation in LADCO. WDNR identified CAIR, CSAPR, CSAPR 
Update, Wisconsin's regional haze SIP applicable for the 2008-2018 
planning period, and state PSD programs. Further, WDNR cited continued 
consultation with LADCO, three Wisconsin Administrative Code statutes 
that could be relied on ``[i]f needed'' to address disagreements for 
SIP development in other states' nonattainment areas, and an adequate 
PSD program.\59\ The statues mentioned include Wisconsin Administrative 
Code, Natural Resources (Wis. Admin. Code, NR), subsections 285.11, 
285.13 and 285.15. The first two address air pollution control 
department duties and powers. The third, Wisconsin Statute 285.15, 
entitled Interstate Agreement, gives the governor the authority to 
enter an agreement to solve interstate pollution transport with 
Illinois, Indiana and Michigan if the area includes portions of both 
Wisconsin and Illinois.\60\ WDNR does not explicitly reach the 
conclusion that Wisconsin has satisfied the good neighbor provision for 
the 2015 ozone NAAQS, but it is implied. WDNR did not reference the 4-
step framework. WDNR did not rely on any modeling, identify any 
receptors, or determine whether Wisconsin contributes any amount of 
ozone precursor emissions to downwind states. The submittal does not 
include an analysis of potential NOX controls. WDNR did not 
rely on any EPA memoranda. No supporting documentation was provided. 
Apart from the cited rules and LADCO membership, WDNR provided no 
discussion or analysis to determine whether they have any obligations 
under the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \59\ Wisconsin's SIP submission at 4.
    \60\ See Wis. Admin. Code NR 285.15 (2021), available at https://docs.legis.wisconsin.gov/statutes/statutes/285/ii/11.
---------------------------------------------------------------------------

III. EPA Evaluation

    EPA is proposing to find that the Illinois, Indiana, Michigan, 
Minnesota, Ohio, and Wisconsin's SIP submissions do not meet the 
states' obligations with respect to prohibiting emissions that 
contribute significantly to nonattainment or interfere with maintenance 
of the 2015 ozone NAAQS in any other state based on EPA's evaluation of 
the SIP submissions using the 4-step interstate transport framework, 
and EPA is therefore proposing to disapprove Illinois, Indiana, 
Michigan, Minnesota, Ohio, and Wisconsin's SIP submissions.

A. Illinois

1. Evaluation of Information Provided by Illinois Regarding Step 1
    For Step 1 in the 4-step framework, IEPA identified monitoring 
sites that are projected to have problems attaining or maintaining the 
2015 ozone NAAQS in 2023. As previously mentioned, the LADCO modeling 
efforts used the same technique as EPA to calculate future year design 
values used to identify maintenance and nonattainment receptors. IEPA 
presented the LADCO results with water cells, which identified five 
monitors with 2023 maximum design values greater than the

[[Page 9852]]

2015 ozone standard, or maintenance receptors, and seven monitors with 
2023 average design values greater than the 2015 ozone standard, or 
nonattainment receptors. Since new modeling has been performed by EPA 
with updated emission data, EPA proposes to rely on the most recent 
modeling to identify nonattainment and maintenance receptors with 
linkage to Wisconsin in 2023. Nonetheless, the alternative modeling 
relied on by IEPA also identified a number of nonattainment and 
maintenance receptor sites in 2023. See Table CC on page 15 of IEPA's 
submittal. Thus, even under the alternative modeling of 2023, IEPA 
acknowledges in its submittal the existence of several nonattainment 
and maintenance receptors.
2. Evaluation of Information Provided by the State Regarding Step 2
    Although Illinois relied on alternative modeling to EPA's modeling, 
Illinois acknowledged in their SIP submission that it is linked to one 
or more downwind receptors above either a 1 percent of the NAAQS or a 1 
ppb contribution threshold in 2023. Because the alternative modeling 
relied on by the state also demonstrates that a linkage exists between 
the state and downwind receptors at step 2, EPA need not conduct a 
comparative assessment of the alternative modeling; the state concedes 
that it is linked. IEPA's analysis corroborates the conclusion in EPA's 
most recent modeling in that the modeling demonstrates the State to be 
linked above 1 percent of the NAAQS to a downwind receptor, as 
described in the next section.
    IEPA, relying on a concept listed in Attachment A to the March 2018 
memorandum, attempted to justify the use of a 1 ppb threshold at step 2 
to identify whether the state was ``linked'' to a projected downwind 
nonattainment or maintenance receptor. As explained in Section I above, 
the concepts presented in Attachment A to the March 2018 memorandum 
were developed by outside parties; they are neither guidance nor 
determined by EPA to be consistent with the CAA. However, EPA's August 
2018 memorandum also addressed possible alternative thresholds and 
suggested that, with appropriate additional analysis, it may be 
reasonable for states to use a 1 ppb contribution threshold, as an 
alternative to a 1 percent of the NAAQS threshold, at Step 2 of the 4-
Step interstate transport framework for the purposes of identifying 
linkages to downwind receptors.
    As an initial matter, EPA does not accept Illinois' argument that a 
1 percent of the NAAQS contribution threshold at Step 2 is 
``inappropriate'' for the 2015 ozone NAAQS due to modeling biases and 
errors.\61\ The explanation for how the 1 percent contribution 
threshold was originally derived is available in the 2011 CSAPR 
rulemaking. See 76 FR 48208, 48237-38. Further, in the CSAPR Update, 
EPA re-analyzed the threshold for purposes of the 2008 ozone NAAQS and 
determined it was appropriate to continue to apply this threshold. EPA 
compared the 1 percent threshold to a 0.5 percent of NAAQS threshold 
and a 5 percent of NAAQS threshold. EPA found that the lower threshold 
did not capture appreciably more upwind state contribution compared to 
the 1 percent threshold, while the 5 percent threshold allowed too much 
upwind state contribution to drop out from further analysis. See Final 
CSAPR Update Air Quality Modeling TSD, at 27-30 (EPA-HQ-OAR-2015-0596-
0144). If EPA were to apply this analysis to the 2015 ozone NAAQS using 
the updated modeling based on the 2016v2 emissions platform, a 5 
percent of the NAAQS contribution threshold (i.e., 3.5 ppb) only 
captures approximately 50 percent of the total upwind contribution. 
Compared to a 1 percent threshold, a 5 percent threshold would, on 
average, forgo 27 percent of the total upwind contribution. As EPA 
noted in the August 2018 memorandum, the use of even a 2 ppb 
contribution threshold under the modeling released with the March 2018 
memorandum would only capture about 55 percent of all upwind 
contributions, and therefore ``emission reductions from states linked 
at that higher threshold may be insufficient to address collective 
upwind state contribution to downwind air quality problems.'' \31\
---------------------------------------------------------------------------

    \61\ Illinois' SIP submission at 8, 14.
---------------------------------------------------------------------------

    With these figures in mind, IEPA's claims that the contribution 
threshold should be substantially higher than 1 or even 2 ppb solely on 
the basis of modeling uncertainty cannot be accepted. First, both 
LADCO's and EPA's modeling techniques are sufficiently reliable and fit 
for the purpose to measure upwind contribution levels down to at least 
one percent of the NAAQS. EPA's recommended model attainment test is 
based on application of the model in a relative sense rather than 
relying upon absolute model predictions.\62\ All models have 
limitations resulting from uncertainties in inputs and scientific 
formulation. To minimize the effects of these uncertainties, the 
modeling is anchored to base period measured data in EPA's guidance 
approach for projecting design values. Notably, EPA also uses our 
source apportionment modeling in a relative sense when calculating the 
average contribution metric (used to identify linkages). In this method 
the magnitude of the contribution metric is tied to the magnitude of 
the projected average design value which is tied to the base period 
average measured design value. EPA's guidance has not established a 
bright line criteria for judging whether or not statistical measures of 
model performance constitute acceptable or unacceptable model 
performance. So, contrary to what Illinois appears to be claiming with 
regards to modeling biases, there are no EPA recommended measures of 
allowable error. Although EPA does not typically focus on using 
particular benchmarks as the sole criteria for model performance, EPA 
notes that the model performance for the updated modeling based on the 
2016v2 emissions platform is generally within the benchmarks 
recommended by Emery.\63\
---------------------------------------------------------------------------

    \62\ See Section 4.1' ``Overview of Modeled Attainment Test in 
EPA Modeling Guidance for Demonstrating Air Quality Goals for Ozone, 
PM2.5, and Regional Haze. November 2018. EPA 454-R-18-
009. https://www.epa.gov/scram/sip-modeling-guidance-documents.
    \63\ Christopher Emery, Zhen Liu, Armistead G. Russel, M. Talat 
Odman, Greg Yarwood and Naresh Kumar (2017). Recommendations on 
statistics and benchmarks to assess photochemical model performance, 
Journal of the Air & Waste Management Association, 67:5,582-598, 
DOI: 10.1080/10962247.2016.1265027.
---------------------------------------------------------------------------

    EPA has successfully applied a 1 percent of NAAQS threshold to 
identify linked upwind states in three prior rulemakings. And the D.C. 
Circuit has declined to establish bright line criteria for model 
performance. In upholding EPA's approach to evaluating interstate 
transport in CSAPR, the D.C. Circuit held that they would not 
``invalidate EPA's predictions solely because there might be 
discrepancies between those predictions and the real world. That 
possibility is inherent in the enterprise of prediction.'' EME Homer 
City Generation, L.P. v. EPA, 795 F.3d 118, 135 (2015). The court 
continued to note that ``the fact that a `model does not fit every 
application perfectly is no criticism; a model is meant to simplify 
reality in order to make it tractable.''' Id. at 135-36 (quoting 
Chemical Manufacturers Association v. EPA, 28 F.3d 1259, 1264 (D.C. 
Cir. 1994).
    Finally, EPA's August 2018 memorandum provided that whether use of 
a 1 ppb threshold is appropriate must be based on an evaluation of 
state-specific circumstances, and no such evaluation was included in 
the

[[Page 9853]]

submission. IEPA did not conduct such an analysis. EPA's experience 
with the alternative Step 2 thresholds is further discussed in Section 
I.D.3.i. As discussed there, EPA is considering withdrawing the August 
2018 memorandum.
    However, based on both the state's alternative modeling and EPA's 
updated modeling, the state is projected to contribute greater than 
both the 1 percent and alternative 1 ppb thresholds. While EPA does 
not, in this action, approve of the IEPA's application of the 1 ppb 
threshold, based on Illinois' linkages greater than 1 ppb to projected 
downwind nonattainment or maintenance receptors, the state's use of 
this alternative threshold at step 2 of the 4-step interstate framework 
would not alter our review and proposed disapproval this SIP submittal.
3. Results of EPA's Step 1 and Step 2 Modeling and Findings for 
Illinois
    As described in Section I, EPA performed air quality modeling using 
the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
Illinois contributes at or above the threshold of 1 percent of the 2015 
ozone NAAQS (0.70 ppb) to any downwind nonattainment or maintenance 
receptor. As shown in Table 2, the data \64\ indicate that in 2023, 
emissions from Illinois contribute greater than 1 percent of the 
standard to nonattainment or maintenance-only receptors in 
Wisconsin.\65\
---------------------------------------------------------------------------

    \64\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file:'' 
2016v2_DVs_state_contributions.xlsx'' which is included in docket ID 
No. EPA-HQ-OAR-2021-0663.
    \65\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I. That modeling showed 
that Illinois had a maximum contribution greater than 0.70 ppb to at 
least one nonattainment or maintenance-only receptor in 2023. These 
modeling results are included in the file ``Ozone Design Values And 
Contributions Revised CSAPR Update.xlsx'' in docket ID No. EPA-HQ-
OAR-2021-0663.

                      Table 2--Illinois Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023 Average    2023  Maximum     Illinois
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                                   maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
550590025....................  Kenosha, WI.....  Maintenance....            69.2            72.3           18.55
550590019....................  Kenosha, WI.....  Nonattainment..            72.8            73.7           18.13
551010020....................  Racine, WI......  Nonattainment..            71.3            73.2           13.86
----------------------------------------------------------------------------------------------------------------

    Therefore, based on EPA's evaluation of the information submitted 
by IEPA, and based on EPA's most recent modeling results for 2023, EPA 
proposes to find that Illinois is linked at Steps 1 and 2 and has an 
obligation to assess potential emissions reductions from sources or 
other emissions activity at Step 3 of the 4-step framework. EPA will 
proceed to Step 3 of the 4-step interstate transport framework to 
assess the arguments the state presented as to why, despite this 
linkage, the state should not be considered to significantly contribute 
to nonattainment or interfere with maintenance of the NAAQS in any 
other state.
4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the obligations in CAA section 110(a)(2)(D)(i)(I) must 
prohibit ``any source or other type of emissions activity within the 
state'' from emitting air pollutants which will contribute 
significantly to downwind air quality problems. Thus, states must 
complete something similar to EPA's analysis (or an alternative 
approach to defining ``significance'' that comports with the statute's 
objectives) to determine whether and to what degree emissions from a 
state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment in or interfere with 
maintenance of'' the NAAQS in any other state. IEPA did not conduct 
such an analysis in Illinois' SIP submission.
    IEPA argued that Illinois' contributions to the nonattainment 
monitors in the LADCO domain, namely the Allegan and Sheboygan 
receptors, EPA can be fairly and adequately addressed through Illinois' 
participation in LADCO. Though IEPA suggested that LADCO may be 
partially responsible for decreases in ambient ozone concentrations in 
the Lake Michigan area, LADCO is not a regulatory agency responsible 
for implementing emissions controls. Furthermore, Illinois did not 
provide any information on any planned emission reductions, or 
evaluation of control strategies that the LADCO states intend to 
implement within their domain, that would reduce either the ozone 
concentrations or Illinois' contributions at the nonattainment or 
maintenance monitors to which IEPA identified Illinois as linked. 
IEPA's basis for concluding that LADCO participation may relieve 
Illinois of any good neighbor obligations to downwind receptors is 
entirely unsubstantiated and does not present any basis on which EPA 
can approve IEPA's SIP submittal. As such, EPA proposes to find 
Illinois' LADCO participation as inadequate to resolve Illinois' good 
neighbor obligations for the 2015 ozone NAAQS.

[[Page 9854]]

    The submittal also stated that Illinois is developing new 
NOX RACT standards for the Chicago area that, in conjunction 
with existing regulations and future Federal reductions, are estimated 
to reduce NOX emissions by up to 20,000 tons/year which had 
not yet been reflected in modeling to 2023. However, Illinois failed to 
provide any information on the control measures or implementation 
schedule that would achieve the estimated 20,000 tons/year in 
reductions. IEPA did not quantify how the emissions reductions they 
estimated would impact air quality at downwind receptors or Illinois' 
contributions. In fact, Illinois has not yet finalized the 
NOX RACT rule for Chicago. In general, any changes in the 
emissions inventory and on-the-books controls relevant to emissions in 
2023 have now been incorporated into EPA's modeling using the 2016v2 
emissions platform, which projects a continuing contribution from 
Illinois to out of state receptors above a threshold of 1 percent of 
the NAAQS (at Steps 1 and 2) despite these measures. Therefore, IEPA's 
SIP submission should have evaluated the availability of additional air 
quality controls to improve downwind air quality at nonattainment and 
maintenance receptors at Step 3.
    Additionally, states may not rely on non-SIP measures to meet SIP 
requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] shall . . 
. contain adequate provisions . . . .''). See also CAA section 
110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 786 F.3d 
1169, 1175-76 (9th Cir. 2015) (holding that measures relied on by state 
to meet CAA requirements must be included in the SIP). IEPA did not 
attempt to revise Illinois' SIP to include these measures in order to 
implement its good neighbor obligations. Further, the listing of 
existing or on-the-way control measures, whether approved into the 
State's SIP or not, does not substitute for a complete Step 3 analysis 
under EPA's 4-step framework to define ``significant contribution.'' 
IEPA did not identify the control measures, provide an assessment of 
the overall effects of these measures, note when the reductions would 
be achieved, or explain what the overall resulting air quality effects 
would be at identified out of state receptors. IEPA did not evaluate 
additional, potential emissions control opportunities, or their costs 
or impacts, or attempt to analyze whether, if applied more broadly 
across linked states, the emissions reductions would constitute the 
elimination of significant contribution on a regional scale. IEPA did 
not offer an explanation as to whether any faster or more stringent 
emissions reductions that may be available were prohibitively costly or 
infeasible. Although EPA acknowledges states are not necessarily bound 
to follow its own analytical framework at Step 3, IEPA did not attempt 
to determine or justify an appropriate uniform cost-effectiveness 
threshold for the more stringent 2015 ozone NAAQS. This would have been 
similar to the approach to defining significant contribution that EPA 
has applied in prior rulemakings such as CSAPR and or the CSAPR Update, 
even if such an analysis is not technically mandatory.
    Finally, under the Wisconsin decision, states and EPA may not delay 
implementation of measures necessary to address good neighbor 
requirements beyond the next applicable attainment date without a 
showing of impossibility or necessity. See 938 F.3d at 320. The IEPA's 
submittal is insufficient to the extent the implementation timeframes 
for identified control measures were left unidentified, unexplained, or 
too uncertain to permit EPA to form a judgment as to whether the timing 
requirements for good neighbor obligations have been met.
    IEPA also attempted to rely on a concept related to international 
emissions identified in Attachment A to the March 2018 memorandum--a 
concept that apparently had its origins outside EPA and was not 
endorsed or recommend by EPA at the time or since. IEPA noted that 
Illinois would be linked to only one receptor if international and 
offshore emissions were simply subtracted from the receptor's maximum 
design values. As explained in Section I.D above, the concepts 
presented in Attachment A to the March 2018 memorandum were neither 
guidance nor determined by EPA to be consistent with the CAA. EPA made 
clear at the time that it would thoroughly review the technical and 
legal justifications states put forward in relying on any concepts from 
Attachment A to the March 2018 memorandum. In this case, what IEPA 
proposes is clearly unacceptable.
    The state's reasoning related to international and offshore 
emissions is inapplicable to the requirements of CAA section 
110(a)(2)(D)(i)(I). The good neighbor provision requires states and EPA 
to address interstate transport of air pollution that contributes to 
downwind states' ability to attain and maintain NAAQS. Whether 
emissions from other states or other countries also contribute to the 
same downwind air quality issue is irrelevant in assessing whether a 
downwind state has an air quality problem, or whether an upwind state 
is significantly contributing to that problem. States are not obligated 
under CAA section 110(a)(2)(D)(i)(I) to reduce emissions sufficient on 
their own to resolve downwind receptors' nonattainment or maintenance 
problems. Rather, states are obligated to eliminate their own 
``significant contribution'' or ``interference'' with the ability of 
other states to attain or maintain the NAAQS.
    Indeed, the D.C. Circuit in Wisconsin specifically rejected 
petitioner arguments suggesting that upwind states should be excused 
from good neighbor obligations on the basis that some other source of 
emissions (whether international or another upwind state) could be 
considered the ``but-for'' cause of downwind air quality problem. See 
938 F.3d at 323-324. The court viewed petitioners' arguments as 
essentially an argument ``that an upwind state `contributes 
significantly' to downwind nonattainment only when its emissions are 
the sole cause of downwind nonattainment.'' Id. at 324. The court 
explained that ``an upwind state can `contribute' to downwind 
nonattainment even if its emissions are not the but-for cause.'' Id. at 
324-325. See also Catawba County v. EPA, 571 F.3d 20, 39 (D.C. Cir. 
2009) (rejecting the argument ``that `significantly contribute' 
unambiguously means `strictly cause' '' because there is ``no reason 
why the statute precludes EPA from determining that [an] addition of 
[pollutant] into the atmosphere is significant even though a nearby 
county's nonattainment problem would still persist in its absence''); 
Miss. Comm'n on Envtl. Quality v. EPA, 790 F.3d 138, 163 n.12 (D.C. 
Cir. 2015) (observing that the argument that ``there likely would have 
been no violation at all . . . if it were not for the emissions 
resulting from [another source]'' is ``merely a rephrasing of the but-
for causation rule that we rejected in Catawba County''). Therefore, a 
state is not excused from eliminating its significant contribution on 
the basis that international emissions also contribute some amount of 
pollution to the same receptors to which the state is linked. Illinois' 
argument related to international and offshore emissions fails to 
change the status of any receptor at Step 1, to eliminate Illinois' 
linkages at Step 2, or to provide sufficient evidence that Illinois 
does not contribute significantly to receptors at Step 3.
    We therefore propose that Illinois was required to analyze 
emissions from the sources and other emissions activity from within the 
state to determine whether its contributions were

[[Page 9855]]

significant, and we propose to disapprove its submission because 
Illinois failed to do so.
5. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-step interstate transport framework calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at Step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. IEPA identified future 
NOX RACT standards for the Chicago area and unnamed Federal 
rules were sufficient to resolve Illinois' good neighbor obligations 
for the 2015 ozone NAAQS. However, Illinois did not revise its SIP to 
include these emission reductions in a revision to its SIP to ensure 
the reductions were permanent and enforceable. As a result, EPA 
proposes to disapprove Illinois' submittal on the separate,\66\ 
additional basis that the Illinois has not included permanent and 
enforceable emissions reductions in its SIP as necessary to meet the 
obligations of CAA section 110(a)(2)(d)(i)(I).
---------------------------------------------------------------------------

    \66\ Pointing to anticipated upcoming emission reductions is not 
sufficient as a step 3 analysis, for the reasons discussed in 
Section 4. In this section, we explain that to the extent such 
anticipated reductions are not included in the SIP and rendered 
permanent and enforceable, reliance on such anticipated reductions 
is also insufficient at step 4.
---------------------------------------------------------------------------

6. Conclusion
    Based on EPA's evaluation of Illinois SIP submission, EPA is 
proposing to find that the portion of Illinois' May 21, 2018 SIP 
submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet the 
state's interstate transport obligations, because it fails to contain 
the necessary provisions to eliminate emissions that will contribute 
significantly to nonattainment or interfere with maintenance of the 
2015 ozone NAAQS in any other state.

B. Indiana

1. Evaluation of Information Provided by Indiana Regarding Step 1
    IDEM relied on LADCO modeling released in 2018 to identify 
nonattainment and maintenance receptors in 2023. As described 
previously in this action, LADCO performed a modeling demonstration 
like that of EPA's 2018 transport modeling efforts, except with use of 
the ERTAC EGU Tool for EGU emissions. LADCO identified nonattainment 
and maintenance receptors using EPA methodology identified in Section 
I. IDEM elected to rely on LADCO's modeling results, which identified 
similar receptors to EPA's modeling included in the March 2018 memo. 
Since new modeling has been performed by EPA which includes updated 
emission data using the 2016v2 platform, EPA proposes to primarily rely 
on the most recent modeling to identify nonattainment and maintenance 
receptors in 2023 (see Table 3 further in this action).
    Nonetheless, the LADCO modeling relied on by IDEM also identified a 
number of nonattainment and maintenance receptor sites in 2023. See 
Table 7 on page 30 of Attachment 1 to Indiana's submittal. Thus, even 
under the LADCO modeling for 2023, IDEM acknowledges in its submittal 
the existence of several nonattainment and maintenance receptors.
    IDEM essentially argues that two of the receptors to which Indiana 
was linked would not actually be receptors in 2023. Based on updated 
modeling of EPA's 2016v2 emissions platform, EPA agrees with IDEM that 
that the Allegan, Michigan monitor is not expected to be a receptor in 
2023, but not the receptor in Sheboygan, Wisconsin. Regardless, EPA 
disagrees with the line of reasoning IDEM put forward to argue that 
those two monitors would not be receptors to the extent such reasoning 
could be applied to Indiana's linkages in EPA's modeling using the 
2016v2 emissions platform. First, IDEM concluded that if ozone design 
value trends continued as expected then those two receptors would reach 
attainment before 2023. In addition, IDEM compared 2012-2017 monitoring 
data with LADCO's and EPA's modeling and concluded that the Sheboygan, 
Wisconsin and Allegan, Michigan receptor monitors were already below 
the 2023 projections. Additionally, EPA's updated modeling, which 
considers more recent design values and emissions, continues to find 
that Indiana is linked to downwind nonattainment and maintenance 
receptors, despite downward trends in emissions and design values
2. Evaluation of Information Provided by the State Regarding Step 2
    Although Indiana relied on alternative modeling to EPA's modeling, 
Indiana acknowledged in its SIP submission that it is linked to one or 
more downwind receptors above either a 1 percent of the NAAQS or 1 ppb 
contribution threshold in 2023. Because the alternative modeling relied 
on by IDEM also demonstrates that a linkage exists between the state 
and one or more downwind receptors at Step 2, EPA need not conduct a 
comparative assessment of the alternative modeling; the State concedes 
that it is linked. IDEM's analysis corroborates the conclusion in EPA's 
most recent modeling, described in the next section.
    IDEM additionally utilized a 1 ppb threshold at Step 2 to identify 
whether it was linked to a projected downwind nonattainment or 
maintenance receptor. As discussed in EPA's August 2018 memorandum, 
with appropriate additional analysis it may be reasonable for states to 
use a 1 ppb contribution threshold, as an alternative to a 1 percent 
threshold, at Step 2 of the 4-Step interstate transport framework, for 
the purposes of identifying linkages to downwind receptors. However, 
IDEM's submission did not contain any additional analysis of 
contributions at the receptors to which they were linked to support 
their claim that a 1 ppb threshold was an appropriate Step 2 screening 
threshold. Rather, IDEM claimed that a threshold of 1 percent was too 
low because it is less than the ozone monitoring ``tolerance level'' of 
1 ppb (i.e., precision) used for reporting measured ozone 
concentrations. In its submittal IDEM failed to provide any basis for 
asserting that the precision of an ozone monitor is applicable to the 
precision of ozone contributions which are not a directly measured 
quantity. Regardless, total upwind contributions are well above 1 ppb 
at all receptors to which Indiana is linked based on modeling by LADCO 
and by EPA. In addition, Indiana alone contributes above 1 ppb to 
several downwind receptors. Because contributions are not directly 
measured, modeling is used to apportion projected ozone design values 
into contributions from individual states and other sources of ozone 
precursors (e.g., fires and biogenic sources). The projected ozone 
design values are calculated using the method recommended in EPA's 
modeling guidance.\67\ As part of this method, projected design values 
are reported with a precision of a tenth of a ppb. Consistent with our 
modeling guidance, ozone contributions are evaluated with a precision 
of a tenth of a ppb. For example, a contribution of 0.6999 . . . ppb is 
reported as 0.69 ppb and evaluated as 0.6 ppb which is below the 1 
percent threshold.
---------------------------------------------------------------------------

    \67\ Modeling Guidance for Demonstrating Air Quality Goals for 
Ozone, PM2.5, and Regional Haze. November 2018. EPA 454-
R-18-009. https://www.epa.gov/scram/sip-modeling-guidance-documents.
---------------------------------------------------------------------------

    Indiana seemingly conflates the contribution threshold at Step 2 
with a Step 3 determination of ``significance'' (which is reached only 
after the application of a multi-factor analysis), regardless EPA does 
not accept

[[Page 9856]]

Indiana's argument that a 1 percent of the NAAQS contribution threshold 
at Step 2 is ``not appropriate'' for the 2015 ozone NAAQS on the basis 
of unwarranted modeling reliability concerns.\68\ The explanation for 
how the 1 percent contribution threshold was originally derived is 
available in the 2011 CSAPR rulemaking. See 76 FR 48208, 48237-38. 
Further, in the CSAPR Update, EPA re-analyzed the threshold for 
purposes of the 2008 ozone NAAQS and determined it was appropriate to 
continue to apply this threshold. EPA compared the 1 percent threshold 
to a 0.5 percent of NAAQS threshold and a 5 percent of NAAQS threshold. 
EPA found that the lower threshold did not capture appreciably more 
upwind state contribution compared to the 1 percent threshold, while 
the 5 percent threshold allowed too much upwind state contribution to 
drop out from further analysis. See Final CSAPR Update Air Quality 
Modeling TSD, at 27-30 (EPA-HQ-OAR-2015-0596-0144). If EPA were to 
apply this analysis to the 2015 ozone NAAQS using the updated modeling 
based on the 2016v2 emissions platform, a 5 percent of the NAAQS 
contribution threshold would forgo nearly 30 percent of the total 
upwind contribution, on average, for those receptors to which Indiana 
is linked using a 1 percent threshold. As EPA noted in the August 2018 
memorandum, the use of even a 2 ppb contribution threshold under the 
modeling released with the March 2018 memorandum would only capture 
about 55 percent of all upwind contributions, and therefore ``emission 
reductions from states linked at that higher threshold may be 
insufficient to address collective upwind state contribution to 
downwind air quality problems.'' \69\
---------------------------------------------------------------------------

    \68\ Indiana's SIP submission, Attachment 1 at 4.
    \69\ August 2018 memorandum at 4.
---------------------------------------------------------------------------

    With these figures in mind, IDEM's claims that the contribution 
threshold should be substantially higher than 1 or even 2 ppb solely on 
the basis of modeling uncertainty cannot be accepted. First, both 
IDEM's and EPA's modeling techniques are sufficiently reliable and fit 
for the purpose to measure upwind contribution levels down to at least 
one percent of the NAAQS. EPA's recommended model attainment test is 
based on application of the model in a relative sense rather than 
relying upon absolute model predictions.\70\ All models have 
limitations resulting from uncertainties in inputs and scientific 
formulation. To minimize the effects of these uncertainties, the 
modeling is anchored to base period measured data in EPA's guidance 
approach for projecting design values. Notably, EPA also uses our 
source apportionment modeling in a relative sense when calculating the 
average contribution metric (used to identify linkages). In this method 
the magnitude of the contribution metric is tied to the magnitude of 
the projected average design value which is tied to the base period 
average measured design value. EPA's guidance has not established a 
bright-line criteria for judging whether or not statistical measures of 
model performance constitute acceptable or unacceptable model 
performance. So, contrary to what Indiana appears to be claiming with 
regards to modeling biases, there are no EPA recommended measures of 
allowable error. Although EPA does not typically focus on using 
particular benchmarks as the sole criteria for model performance, EPA 
notes that the model performance for the updated modeling based on the 
2016v2 emissions platform is generally within the benchmarks 
recommended by Emery, et al., (2017).\71\
---------------------------------------------------------------------------

    \70\ See Section 4.1' ``Overview of Modeled Attainment Test in 
EPA Modeling Guidance for Demonstrating Air Quality Goals for Ozone, 
PM2.5, and Regional Haze. November 2018. EPA 454-R-18-
009. https://www.epa.gov/scram/sip-modeling-guidance-documents.
    \71\ Christopher Emery, Zhen Liu, Armistead G. Russel, M. Talat 
Odman, Greg Yarwood and Naresh Kumar (2017). Recommendations on 
statistics and benchmarks to assess photochemical model performance, 
Journal of the Air & Waste Management Association, 67:5,582-598, 
DOI: 10.1080/10962247.2016.1265027.
---------------------------------------------------------------------------

    EPA has successfully applied a 1 percent of NAAQS threshold to 
identify linked upwind states in three prior rulemakings. And the D.C. 
Circuit has declined to establish bright line criteria for model 
performance. In upholding EPA's approach to evaluating interstate 
transport in CSAPR, the Supreme Court held that they would not 
``invalidate EPA's predictions solely because there might be 
discrepancies between those predictions and the real world. That 
possibility is inherent in the enterprise of prediction.'' EME Homer 
City Generation, L.P. v. EPA, 795 F.3d 118, 135 (2015). The court 
continued to note that ``the fact that a `model does not fit every 
application perfectly is no criticism; a model is meant to simplify 
reality in order to make it tractable.' '' Id. at 135-36 (quoting 
Chemical Manufacturers Association v. EPA, 28 F.3d 1259, 1264 (D.C. 
Cir. 1994).
    EPA's August 2018 memorandum provided that whether use of a 1 ppb 
threshold is appropriate must be based on an evaluation of state-
specific circumstances, and no such evaluation was included in the 
submission. EPA's experience with the alternative Step 2 thresholds is 
further discussed in Section I.D.3.i. As discussed there, EPA is 
considering withdrawing the August 2018 memorandum.
3. Results of EPA's Step 1 and Step 2 Modeling and Findings for Indiana
    As described in Section I, EPA performed air quality modeling using 
the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
Indiana contributes at or above the threshold of 1 percent of the 2015 
ozone NAAQS (0.70 ppb) to any downwind nonattainment or maintenance 
receptor. As shown in Table 3, the data \72\ indicate that in 2023, 
emissions from Indiana contribute greater than 1 percent of the 
standard to nonattainment or maintenance-only receptors in Wisconsin, 
Illinois, Connecticut, and Pennsylvania.\73\
---------------------------------------------------------------------------

    \72\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file: 
2016v2_DVs_state_contributions.xlsx which is included in docket ID 
No. EPA-HQ-OAR-2021-0663.
    \73\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I. That modeling showed 
that Indiana had a maximum contribution greater than 0.70 ppb to at 
least one nonattainment or maintenance-only receptor in 2023. These 
modeling results are included in the file ``Ozone Design Values And 
Contributions Revised CSAPR Update.xlsx'' in docket ID No. EPA-HQ-
OAR-2021-0663.

                       Table 3--Indiana Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023  Average   2023  Maximum      Indiana
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                                   maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
550590025....................  Kenosha, WI.....  Maintenance....            69.2            72.3            7.10
170310032....................  Cook, IL........  Maintenance....            69.8            72.4            7.03

[[Page 9857]]

 
550590019....................  Kenosha, WI.....  Nonattainment..            72.8            73.7            6.60
551010020....................  Racine, WI......  Nonattainment..            71.3            73.2            6.60
170317002....................  Cook, IL........  Maintenance....            70.1            73.0            6.33
170310076....................  Cook, IL........  Maintenance....            69.3            72.1            6.21
170310001....................  Cook, IL........  Maintenance....            69.6            73.4            5.44
170314201....................  Cook, IL........  Maintenance....            69.9            73.4            4.65
90099002.....................  New Haven, CT...  Nonattainment..            71.8            73.9            0.87
90019003.....................  Fairfield, CT...  Nonattainment..            76.1            76.4            0.76
90013007.....................  Fairfield, CT...  Nonattainment..            74.2            75.1            0.75
420170012....................  Bucks, PA.......  Maintenance....            70.7            72.2            0.73
----------------------------------------------------------------------------------------------------------------

    Therefore, based on EPA's evaluation of the information submitted 
by IDEM, and based on EPA's most recent modeling results for 2023, EPA 
proposes to find that Indiana is linked at Steps 1 and 2 and has an 
obligation to assess potential emissions reductions from sources or 
other emissions activity at Step 3 of the 4-Step framework. EPA 
therefore will proceed to Step 3 of the 4-Step interstate transport 
framework to assess the arguments the State presented as to why, 
despite this linkage, the state should not be considered to 
significantly contribute to nonattainment or interfere with maintenance 
of the NAAQS in any other state.
4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-Step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-Step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the obligations in CAA section 110(a)(2)(D)(i)(I) must 
prohibit ``any source or other type of emissions activity within the 
state'' from emitting air pollutants which will contribute 
significantly to downwind air quality problems. Thus, states must 
complete something similar to EPA's analysis (or an alternative 
approach to defining ``significance'' that comports with the statute's 
objectives) to determine whether and to what degree emissions from a 
state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment in, or interfere with 
maintenance of'' the NAAQS in any other state. IDEM did not conduct 
such an analysis in their SIP submission.
    IDEM first asserted that Indiana's rule amendments under CSAPR 
meant that Indiana was already meeting the good neighbor requirements 
for the 2015 ozone NAAQS. The submittal, however, did not contain a 
demonstration at Step 3 that the State was adequately controlling its 
emissions for purposes of the good neighbor provision, particularly 
because the State conceded in its submission that it was potentially 
significantly contributing to one or more receptors in 2023 at Steps 1 
and 2. The SIP submittal pointed to the state's existing NOX 
control measures, consent decree requirements, and future fuel switches 
and retirements for large EGUs and non-EGUs for the years 2008 through 
2017 to conclude Indiana is already meeting its good neighbor 
obligations for the 2015 ozone NAAQS.
    However, the state's submittal does not include a sufficient 
examination or a technical justification that could support the 
conclusion that the state has no further good neighbor obligations for 
the 2015 ozone NAAQS. In particular, the state did not conduct in its 
submittal an analysis of potential additional emissions reductions 
measures to further reduce its impact on the identified downwind 
receptors. For example, although Indiana did include in its submission 
a list of controls at individual emissions units at facilities in the 
state, IDEM did not analyze additional potential NOX 
emissions control technologies, their associated costs, estimated 
emissions reductions, and downwind air quality improvements. Nor does 
the submittal include an analysis of whether such potential, additional 
control technologies or measures could reduce the impact of Indiana's 
emissions on out of state receptors. Though there is not a prescribed 
method for a Step 3 analysis, EPA has consistently applied Step 3 of 
the good neighbor framework through a more rigorous evaluation of 
potential additional control technologies or measures than what Indiana 
provided in its submission. Identifying a range of various emissions 
control measures that have been or may be enacted at the state level, 
without analysis of the impact of those measures on the out of state 
receptors, is not analytically sufficient. In general, the air quality 
modeling that EPA has conducted (as well the modeling relied on by 
Indiana in its submittal) already accounts for ``on-the-books'' 
emissions control measures. Both sets of modeling clearly establish 
continued linkage from Indiana to downwind receptors in 2023 at Steps 1 
and 2, despite those emissions control efforts.
    IDEM provided what they characterized as a weight of evidence 
analysis consisting of monitoring data, emissions data, and 
photochemical modeling to justify their conclusion that no additional 
emission reductions would be necessary to satisfy Indiana's ozone 
transport obligations. First, IDEM

[[Page 9858]]

presented evidence of downward trends of statewide ozone concentrations 
and emissions, as well as a decrease in projected EGU emissions in 2023 
relative to 2011. Despite these trends, however, the LADCO modeling 
that Indiana depended on for its submittal still identified that 
Indiana would contribute over 1 ppb to one or more receptors in 2023.
    As for downwind design value trends, EPA disagrees that IDEM's 
reliance on trends data to conclude that the Harford, Maryland and 
Richmond, New York monitors would reach attainment ``over time'' is 
sufficient to support a conclusion that Indiana has no good neighbor 
obligations. The states and EPA are to address interstate transport 
obligations ``as expeditiously as practicable'' and no later than the 
attainment schedule set in accordance with CAA section 181(a). See 
North Carolina, 531 F.3d at 911-13; Wisconsin, 938 F.3d at 313-20; 
Maryland, 958 F.3d at 1204; New York v. EPA, 964 F.3d 1214, 1226 (D.C. 
Cir. 2020); New York v. EPA, 781 Fed. App'x 4, 6-7 (D.C. Cir. 2019). 
IDEM asserted that EGUs are well controlled in Indiana and cited 
several state and Federal regulations that EGUs may be subject to in 
Indiana. In general, however, the listing of existing or on-the-way 
control measures, whether approved into the state's SIP or not, does 
not substitute for a complete Step 3 analysis under EPA's 4-Step 
framework to define ``significant contribution.'' IDEM did not provide 
an assessment of the overall effects of the identified control measures 
or explain what the overall resulting air quality effects would be at 
identified out of State receptors. IDEM did not perform an analysis of 
all large NOX emitting EGU for factors that may affect the 
facilities' emissions, including but not limited to allowance prices, 
fuel prices, and enforceable limits. IDEM did not evaluate additional, 
potential emissions control opportunities, or their costs or impacts, 
or attempt to analyze whether, if applied more broadly across linked 
states, the emissions reductions would constitute the elimination of 
significant contribution on a regional scale. IDEM did not offer an 
explanation as to whether any faster or more stringent emissions 
reductions that may be available were prohibitively costly or 
infeasible. Although EPA acknowledges states are not necessarily bound 
to follow its own analytical framework at Step 3, IDEM did not attempt 
to determine or justify an appropriate uniform cost-effectiveness 
threshold. This would have been similar to the approach to defining 
significant contribution that EPA has applied in prior rulemakings such 
as CSAPR and or the CSAPR Update, even if such an analysis is not 
technically mandatory. As discussed previously, both the LADCO modeling 
relied on by the state and EPA's updated modeling indicates sources in 
Indiana are linked to downwind air quality problems for the 2015 ozone 
standard. However, Indiana's SIP submittal did not include an analysis 
of potential NOX emissions control technologies, associated 
costs, estimated emissions reductions, and downwind air quality in 
order to determine whether the State had eliminated the State's 
downwind contribution in amounts which will significantly contribute to 
nonattainment or interfere with maintenance. Thus, EPA proposes to 
disapprove Indiana's SIP submission on the separate, additional basis 
that the SIP submittal did not assess additional emission control 
opportunities.
    IDEM concluded it is not cost-effective to evaluate and implement 
controls on non-EGUs in the state on the sole basis that the majority 
of NOX emissions in the state come from EGUs. EPA cannot 
accept the assertion as it is insufficiently supported. Cost-
effectiveness must be assessed in the context of the specific CAA 
program; assessing cost-effectiveness in the context of ozone transport 
should reflect a more comprehensive evaluation of the nature of the 
interstate transport problem, the total emissions reductions available 
at several cost thresholds, and the air quality impacts of the 
reductions at downwind receptors. EPA notes that there are as many as 
two dozen non-EGU facilities in Indiana with more than 300 tons per 
year of NOX emissions each, but IDEM did not analyze control 
opportunities at these sources at all in the SIP submission.
    IDEM also argued that additional emissions reductions from EGU and 
non-EGU sources in Indiana ``are getting more difficult to mandate'' 
because of reduced effectiveness of controls to make significant 
decreases in ozone values, operational concerns, and increased costs 
for customers.\74\ Again, the SIP submission does not contain 
sufficient evidence to support that conclusion. IDEM did not identify 
controls that had reduced effectiveness or explain why they believed 
they had reduced effectiveness. IDEM did not describe what any 
operational concerns were for any controls, nor did IDEM provide any 
information to support their claim that controls would increase costs 
for consumers. While Indiana's existing control measures have 
undoubtedly reduced the amount of transported ozone pollution to other 
states and have contributed to the downward emissions trends and 
improving air quality in the State as shown in the state's SIP 
submittal, in the Revised CSAPR Update, EPA's analysis found that 
despite Indiana's existing control programs, additional emissions 
reductions were achievable from EGUs in the state, even under the level 
of control stringency EPA determined appropriate to eliminate 
significant contribution for the 2008 ozone NAAQS. In any case, EPA has 
not established a benchmark cost-effectiveness threshold for good 
neighbor obligations for the 2015 ozone NAAQS, and IDEM in its 
submittal has not conducted an analysis to establish one for EPA to 
evaluate.
---------------------------------------------------------------------------

    \74\ Indiana's SIP submission, Attachment 1 at 37.
---------------------------------------------------------------------------

    IDEM also identified several planned retirements or retrofits to 
coal fired EGUs in Indiana that were not included in any modeling 
available at the time of Indiana's submission and stated they would 
reduce emissions several thousand tons beyond the modeling. Further, 
EPA's assessment of future air quality conditions generally accounts 
for on-the-books emission reductions and the most up-to-date forecast 
of future emissions in the absence of the transport policy being 
evaluated (i.e., base case conditions).\75\ As described in more detail 
in Section I, EPA's latest projections of the baseline EGU emissions 
uses the version 6--Summer 2021 Reference Case of the IPM. The IPM 
version 6--Summer 2021 Reference Case uses the NEEDS v6 database as its 
source for data on all existing and planned-committed units. Units are 
removed from the NEEDS inventory only if a high degree of certainty 
could be assigned to future implementation of the announced future 
closure or retirement. Any retirements excluded from the NEEDS v6 
inventory can be viewed in the NEEDS spreadsheet.\76\ EPA looked into 
the upcoming retirements cited by IDEM and following the guidelines 
regarding retirements for the IPM version--6 Summer 2021 Reference Case 
certain units are not excluded from the NEEDS v6 inventory. There are 
other retirements that were not included in the SIP submission that 
were excluded

[[Page 9859]]

from the NEEDS v6 inventory for the 2023 projections. This includes 
retirements at AES Petersburg, Merom, and RM Schahfer. In other words, 
in general, any changes in the emissions inventory and on-the-books 
controls relevant to emissions in 2023 have now been incorporated into 
the EPA's modeling using the 2016v2 emissions platform, which projects 
a continuing contribution from Indiana to out of state receptors above 
a threshold of 1 percent of the NAAQS (at Steps 1 and 2) despite these 
measures. Therefore, in light of continuing contribution to out of 
state receptors from Indiana notwithstanding these identified 
retirements, IDEM's SIP submission should have evaluated the 
availability of additional air quality controls to improve downwind air 
quality at nonattainment and maintenance receptors at Step 3 
Furthermore, under the Wisconsin decision, states and EPA may not delay 
implementation of measures necessary to address good neighbor 
requirements beyond the next applicable attainment date without a 
showing of impossibility or necessity. See 938 F.3d at 320. The IDEM's 
submittal is insufficient to the extent the implementation timeframes 
for several claimed expected shutdowns were left unidentified, 
unexplained, or too uncertain to permit EPA to form a judgment as to 
whether the timing requirements for good neighbor obligations have been 
met.
---------------------------------------------------------------------------

    \75\ See 81 FR 74504 at 74517; 85 FR 68964 at 68979.
    \76\ The ``Capacity Dropped'' and the ``Retired Through 2023'' 
worksheets in NEEDS lists all units that are removed from the NEEDS 
v6 inventory--NEEDS v6 Summer 2021 Reference Case. This data can be 
found on EPA's website at: https://www.epa.gov/airmarkets/national-electric-energy-data-system-needs-v6.
---------------------------------------------------------------------------

    Additionally, IDEM explained in only the most general terms how the 
unaccounted emissions reductions would influence downwind air quality 
or Indiana's contributions to other state. IDEM also did not quantify 
how the emissions reductions they estimated would impact air quality at 
downwind receptors or Indiana's contributions. IDEM did not demonstrate 
that the downwind improvements from these regulations and programs 
would be sufficient to eliminate Indiana's linkages or prohibit the 
State's emissions in amounts that will contribute significantly to 
nonattainment or interfere with maintenance of the NAAQS in any other 
state.
    IDEM also made several arguments related to potential flexibilities 
identified in Attachment A to the March 2018 memorandum.\77\ As 
explained previously in Section I, the concepts presented in Attachment 
A to the March 2018 memorandum were neither guidance nor determined by 
EPA to be consistent with the CAA. EPA will thoroughly review the 
technical and legal justifications IDEM put forward in their attempt to 
use a potential flexibility from Attachment A to the March 2018 
memorandum.
---------------------------------------------------------------------------

    \77\ Based on the reference to the potential flexibilities in 
Attachment A to the March 2018 memorandum on page 2 of Attachment 1 
to Indiana's SIP submission, EPA assumes the reference to 
``flexibilities'' on page 38 of Attachment 1 likewise references 
Attachment A to the March 2018 memorandum.
---------------------------------------------------------------------------

    IDEM suggested that local emissions reductions from the 
jurisdiction where downwind receptors are located should first be 
implemented and accounted for before imposing obligations on upwind 
states under the interstate transport provision. IDEM represented that 
EPA had concluded that monitors in the Northeast ``are impacted from 
more local emissions'' by citing a May 14, 2018 presentation. The 
purpose of that presentation was to share a technical, exploratory 
analysis of ozone trends. IDEM misrepresented the contents of the 
presentation, which labeled the results as ``preliminary'' and 
indicated that ``[f]urther exploration of the relative contribution 
from various source sectors within the NE Corridor and in nearby upwind 
states might also be informative.'' \78\ These preliminary results of 
that analysis are generally consistent with EPA's updated modeling 
using the 2016v2 emissions platform. Although EPA's modeling shows that 
a large portion of the transport problem affecting the receptors in 
Coastal Connecticut is indeed from sources within the Ozone Transport 
Region (OTR), a substantial portion of the transport problem at these 
receptors, on the order of 25 percent, is the result of transport from 
states outside the OTR. However, the relevance of that presentation to 
the evaluation of Indiana's good neighbor obligations is not clear. As 
already discussed, the statute and the case law (particularly the 
holdings in Wisconsin and Maryland) make clear that good neighbor 
obligations are not merely supplementary to or deferable until after 
local emission reductions are achieved. Further, based on EPA's 
modeling released with the March 2018 memorandum, nearly all of the 
receptors to which Indiana is linked are also heavily impacted by 
distant upwind state emissions in addition to local sources and sources 
in neighboring states. The Wisconsin decision's holding in regard to 
international contribution (discussed in more detail later) is equally 
applicable to an upwind state's claims that some other state's 
emissions, or local emissions, are more to blame than its own 
emissions. See 938 F.3d 303 at 323-25 (``an upwind state can 
`contribute' to downwind nonattainment even if its emissions are not 
the but-for cause'').
---------------------------------------------------------------------------

    \78\ Indiana's SIP submission, Appendix E at 4, 17.
---------------------------------------------------------------------------

    There is nothing in the CAA that supports Indiana's position on 
local sources, and Indiana does not provide grounds on which to approve 
its SIP submission. The D.C. Circuit has held on five different 
occasions that the timing framework for addressing interstate transport 
obligations must be consistent with the downwind areas' attainment 
schedule. In particular, for the ozone NAAQS, the states and EPA are to 
address interstate transport obligations ``as expeditiously as 
practicable'' and no later than the attainment schedule set in 
accordance with CAA section 181(a). See North Carolina, 531 F.3d at 
911-13; Wisconsin, 938 F.3d at 313-20; Maryland, 958 F.3d at 1204; New 
York v. EPA, 964 F.3d 1214, 1226 (D.C. Cir. 2020); New York v. EPA, 781 
Fed. App'x 4, 6-7 (D.C. Cir. 2019). The court in Wisconsin explained 
its reasoning in part by noting that downwind jurisdictions often may 
need to heavily rely on emissions reductions from upwind states in 
order to achieve attainment of the NAAQS, 938 F.3d at 316-17; such 
states would face increased regulatory burdens including the risk of 
bumping up to a higher nonattainment classification if attainment is 
not reached by the relevant deadline, Maryland, 958 F.3d at 1204. The 
statutory framework of the CAA and these cases establish clearly that 
states and EPA must address interstate transport obligations in line 
with the attainment schedule provided in the CAA in order to timely 
assist downwind states in attaining and maintain the NAAQS, and this 
schedule is ``central to the regulatory scheme.'' Wisconsin, 938 F.3d 
at 316 (quoting Sierra Club v. EPA, 294 F.3d 155, 161 (D.C. Cir. 
2002)).
    IDEM similarly suggested that international and offshore emissions 
contributions should be part of the good neighbor calculus. IDEM's 
reasoning related to international and offshore emissions is 
inapplicable to the requirements of CAA section 110(a)(2)(D)(i)(I). The 
good neighbor provision requires states and EPA to address interstate 
transport of air pollution that contributes to downwind states' ability 
to attain and maintain NAAQS. Whether emissions from other states or 
other countries also contribute to the same downwind air quality issue 
is irrelevant in assessing whether a downwind state has an air quality 
problem, or whether an upwind state is significantly contributing to 
that problem. States are not obligated under CAA section 
110(a)(2)(D)(i)(I) to reduce

[[Page 9860]]

emissions sufficient on their own to resolve downwind receptors' 
nonattainment or maintenance problems. Rather, states are obligated to 
eliminate their own ``significant contribution'' or ``interference'' 
with the ability of other states to attain or maintain the NAAQS.
    Indeed, the D.C. Circuit in Wisconsin specifically rejected 
petitioner arguments suggesting that upwind states should be excused 
from good neighbor obligations on the basis that some other source of 
emissions (whether international or another upwind state) could be 
considered the ``but-for'' cause of downwind air quality problem. See 
938 F.3d at 323-324. The court viewed petitioners' arguments as 
essentially an argument ``that an upwind state `contributes 
significantly' to downwind nonattainment only when its emissions are 
the sole cause of downwind nonattainment.'' Id. at 324. The court 
explained that ``an upwind state can `contribute' to downwind 
nonattainment even if its emissions are not the but-for cause.'' Id. at 
324-325. See also Catawba County v. EPA, 571 F.3d 20, 39 (D.C. Cir. 
2009) (rejecting the argument ``that `significantly contribute' 
unambiguously means `strictly cause''' because there is ``no reason why 
the statute precludes EPA from determining that [an] addition of 
[pollutant] into the atmosphere is significant even though a nearby 
county's nonattainment problem would still persist in its absence''); 
Miss. Comm'n on Envtl. Quality v. EPA, 790 F.3d 138, 163 n.12 (D.C. 
Cir. 2015) (observing that the argument that ``there likely would have 
been no violation at all . . . if it were not for the emissions 
resulting from [another source]'' is ``merely a rephrasing of the but-
for causation rule that we rejected in Catawba County''). Therefore, a 
state is not excused from eliminating its significant contribution on 
the basis that international emissions also contribute some amount of 
pollution to the same receptors to which the state is linked.
    IDEM also calculated Indiana's portion of contribution to the 
Harford, Maryland receptor was 0.077 ppb, and determined that Indiana 
would need to reduce its contribution by 0.0077 ppb (based on a 
contribution threshold of 1 ppb) to bring the Maryland receptor into 
attainment. IDEM argued that 0.0077 ppb is well within the error of the 
model and would be ``difficult'' to translate into an emission 
reduction requirement.\79\ We first note that this approach is a 
deviation from EPA's traditional approach of apportioning upwind-state 
responsibility at Step 3 using a uniform cost of control metric set at 
a level that maximizes cost-effectiveness of emissions reductions in 
relation to downwind state impacts across all linked states. Thus, this 
is not how EPA has interpreted the statutory term ``significant'' in 
the past, and EPA does not reach a conclusion whether this approach 
would be approvable, had IDEM had imposed emissions reductions in line 
with this logic.
---------------------------------------------------------------------------

    \79\ Indiana's SIP submission, Attachment 1 at 42.
---------------------------------------------------------------------------

    We do not need to reach that point in the analysis, however, 
because, having selected that approach to defining its obligations, 
IDEM proceeded to ignore the result. IDEM's submission identified 
Indiana's proportional contribution as 0.077 ppb to the Harford, 
Maryland receptor. Having acknowledged Indiana was responsible for 
eliminating up to 0.0077 ppb of contribution, IDEM claimed that because 
that amount was within the ``error of the model'' that it would be 
``difficult'' to require that amount of reductions from Indiana 
sources.
    This argument does not rise to the level of acceptable proof. EPA 
has routinely been capable of successfully implementing good neighbor 
obligations through the CSAPR framework, and achieving significant 
downwind air quality improvements through upwind-state reductions, at 
levels of ``significant contribution'' comparable or even less than 
those found in Indiana's submission, irrespective of alleged modeling 
errors. See Wisconsin, 938 F.3d at 322-23 (rejecting Wisconsin's 
argument that it should not face good neighbor obligations on the basis 
that its emission reductions would only improve a downwind receptor by 
two ten-thousandths of a part per billion).
    After measuring Indiana's significant contribution, IDEM suggested 
that modeling uncertainty was too great to either require emissions 
reductions. But IDEM had measured the state's significant contribution 
and was therefore identifying the measurable amount of significant 
contribution the state was legally responsible for eliminating. See 
Michigan v. EPA, 213 F.3d 663, 683-84 (D.C. Cir. 2000) (significant 
contribution must be ``measurable''). Further, scientific uncertainty 
may only be invoked to avoid comporting with the requirements of the 
CAA when ``the scientific uncertainty is so profound that it precludes 
. . . reasoned judgment'' Massachusetts v. EPA, 127 S.Ct. 1438 (2007). 
See Wisconsin, 938 F.3d at 318-19 (``Scientific uncertainty, however, 
does not excuse EPA's failure to align the deadline for eliminating 
upwind States' significant contributions with the deadline for downwind 
attainment of the NAAQS.''). See also EME Homer City, 795 F.3d 118, 
135-36 (``We will not invalidate EPA's predictions solely because there 
might be discrepancies between those predictions and the real world. 
That possibility is inherent in the enterprise of prediction.''). 
IDEM's arguments related to modeling uncertainty do not establish a 
level of uncertainty so high as to preclude reasoned judgement.
    IDEM provided an analysis of back trajectories from the Harford and 
Richmond receptors to support its contention that Indiana does not 
contribute significantly to nonattainment or maintenance at those 
monitors, and that the receptors are more impacted by local emissions 
anyway. IDEM also relied on an EPA presentation from 2018 to support 
this conclusion.
    As already discussed, the statute and the case law (particularly 
the holdings in Wisconsin and Maryland) make clear that good neighbor 
obligations are not merely supplementary to or deferable until after 
local emission reductions are achieved. Further, all of the receptors 
to which Indiana is linked are heavily impacted by upwind state 
emissions in addition to local sources and conditions. The Wisconsin 
decision's holding in regard to international contribution (discussed 
previously) is equally applicable to an upwind state's claims that some 
other state's emissions, or local emissions, are more to blame than its 
own emissions. See 938 F.3d 303 at 323-25 (``an upwind state can 
`contribute' to downwind nonattainment even if its emissions are not 
the but-for cause'').
    Further, EPA finds Indiana's back trajectory analysis to be 
deficient in proving that Indiana does not contribute significantly to 
nonattainment or maintenance at the Harford and Richmond monitors that 
the State was linked to in the LADCO modeling. Indiana's back 
trajectory analysis shows a linkage between Indiana and the monitors 
when evaluating two altitudes, 10 meters and 750 meters, on several of 
the exceedance days at these monitoring sites. By only evaluating two 
altitudes, Indiana neglects to consider the wide range of heights that 
might show back trajectories leading back to Indiana, potentially 
further tying the state to more exceedance events. Furthermore, 10 
meters is too low of an altitude to measure long range transport and it 
would have been appropriate for Indiana to analyze several higher 
altitudes to bolster its back trajectory analysis.

[[Page 9861]]

    Back trajectories alone are not sufficient to disconnect upwind 
States from downwind receptors. Relying solely on back trajectories for 
establishing linkages neglects the myriad of factors, most importantly 
photochemical reactions, that are important for determining the 
magnitude of ozone and precursor transport from upwind states to 
downwind receptors. In this regard, EPA and LADCO modeling which 
accounts for 3 dimensional meteorological conditions, regional 
emissions, and photochemical reactions is the most complete, and 
technically sound method to establish linkages between upwind states 
and downwind nonattainment and maintenance receptors.
    The information and claims presented by IDEM did not provide 
sufficient evidence to support alternative conclusions that EPA is 
proposing to make in this action: Namely, that several receptors exist, 
Indiana contributes to those receptors above a 1 percent of the NAAQS 
contribution threshold, and that Indiana continues to have good 
neighbor obligations that need to be addressed for the 2015 ozone 
NAAQS. We therefore propose that Indiana was required to analyze 
emissions from the sources and other emissions activity from within the 
state to determine whether its contributions were significant, and we 
propose to disapprove its submission because Indiana failed to do so.
5. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-Step interstate transport framework calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at Step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. IDEM identified the State's 
existing NOX control measures, consent decree requirements, 
and future fuel switches and retirements for large EGUs and non-EGUs 
for the years 2008 through 2017 \80\ States may not rely on non-SIP 
measures to meet SIP requirements. See CAA section 110(a)(2)(D) (``Each 
such [SIP] shall . . . contain adequate provisions . . . .''). See also 
CAA section 110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 
786 F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on 
by state to meet CAA requirements must be included in the SIP). 
However, the state did not revise its SIP to include these emission 
reductions in a revision to its SIP to ensure the reductions were 
permanent and enforceable. As a result, EPA proposes to disapprove 
Indiana's submittal on the separate, additional basis that Indiana has 
not included permanent and enforceable emissions reductions in its SIP 
as necessary to meet the obligations of CAA section 
110(a)(2)(d)(i)(I).6.
---------------------------------------------------------------------------

    \80\ Pointing to anticipated upcoming emission reductions, even 
if they were not included in the analysis at Steps 1 and 2, is not 
sufficient as a Step 3 analysis, for the reasons discussed in 
Section II.B.4. In this section, we explain that to the extent such 
anticipated reductions are not included in the SIP and rendered 
permanent and enforceable, reliance on such anticipated reductions 
is also insufficient at Step 4.
---------------------------------------------------------------------------

6. Conclusion
    Based on EPA's evaluation of Indiana's SIP submission, EPA is 
proposing to find that the portion of Indiana's November 12, 2018 SIP 
submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet the 
state's interstate transport obligations, because it fails to contain 
the necessary provisions to eliminate emissions that will contribute 
significantly to nonattainment or interfere with maintenance of the 
2015 ozone NAAQS in any other state.

C. Michigan

1. Evaluation of Information Provided by Michigan Regarding Step 1
    At Step 1 of the 4-step interstate transport framework, Michigan 
relied primarily on the LADCO modeling released in 2018 to identify 
nonattainment and maintenance receptors in 2023. As described 
previously in this action, LADCO performed a modeling demonstration 
like that of EPA modeling released with the March 2018 memorandum, 
except with use of the ERTAC EGU Tool to replace specific EGU 
information. LADCO identified nonattainment and maintenance receptors 
using EPA methodology. EGLE elected to rely on LADCO's ``water only'' 
modeling results, but also presented results from EPA's modeling 
released with the March 2018 memorandum. EGLE noted that in general, 
design values in the LADCO modeling were lower. However, since new 
modeling has been performed by EPA which includes updated emission data 
using the 2016v2 platform, EPA proposes to primarily rely on the most 
recent modeling to identify nonattainment and maintenance receptors in 
2023. Nonetheless, the alternative modeling relied on by EGLE also 
identified a number of nonattainment and maintenance receptor sites in 
2023. See Table 2 on page 14 of EGLE's submittal. Thus, even under its 
alternative modeling of 2023, EGLE acknowledges in its submittal the 
existence of several nonattainment and maintenance receptors.
2. Evaluation of Information Provided by the State Regarding Step 2
    Although Michigan relied on alternative modeling to EPA's modeling, 
EGLE acknowledged in their SIP submission that Michigan is linked above 
either a 1 percent of the NAAQS or 1 ppb or threshold to one or more 
downwind receptors in 2023 (1.85 ppb to Sheboygan, Wisconsin (Site ID: 
36-081-0124), 1.22 ppb to Queens, New York (Site ID: 36-085-0067), and 
1.03 ppb to Richmond, New York (Site ID: 55-117-0006)). Because the 
alternative modeling relied on by the state also demonstrates that a 
linkage exists between the state and downwind receptors at Step 2, EPA 
need not conduct a comparative assessment of the alternative modeling; 
the state concedes that it is linked. EGLE's analysis corroborates the 
conclusion in EPA's most recent modeling, described in the next 
section.
    EGLE, relying on a concept from outside parties listed in 
Attachment A to the March 2018 memorandum, attempted to justify the use 
of a 1 ppb threshold at Step 2 to identify whether the state was 
``linked'' to a projected downwind nonattainment or maintenance 
receptor. In part, EGLE attempted to justify the use of a 1 ppb 
contribution threshold based on the 2018 PSD SIL guidance document. 
EGLE also referenced EPA's August 2018 memorandum, which said that with 
appropriate additional analysis it may be reasonable for states to use 
a 1 ppb contribution threshold, as an alternative to a one percent 
threshold, at Step 2 of the 4-Step interstate transport framework for 
the purposes of identifying linkages to downwind receptors. As 
explained in Section I above, the concepts presented in Attachment A to 
the March 2018 memorandum were neither guidance nor determined by EPA 
to be consistent with the CAA. Further, EGLE did not explain the 
relevance of the SILs Guidance to which it referred. This guidance 
relates to a different provision of the Clean Air Act regarding 
implementation of the prevention of significant deterioration (PSD) 
permitting program, i.e., a program that applies in areas that have 
been designated attainment of the NAAQS, and it is not applicable to 
the good neighbor provision, which requires

[[Page 9862]]

states to eliminate significant contribution or interference with 
maintenance of the NAAQS at known and ongoing air quality problem areas 
in other states. Further, it is not correct to conflate the use of the 
term ``significance'' as used in the SIL guidance, with the term 
``contribution,'' which is the appliable statutory term that EPA 
applies at Step 2 of the 4-step interstate transport framework. 
(``Significance'' within the 4-step framework is evaluated at Step 3 
through a multifactor analysis, for those states that are determined to 
``contribute'' to downwind receptors at Steps 1 and 2. See Section 
I.D.4 above.) Given the fundamentally different statutory objectives 
and context, EPA disagrees with EGLE's contention that the SIL guidance 
is applicable in the good neighbor context.
    EGLE's attempt to show ``inflection points'' through collectively 
presenting contribution data at each linked receptor and its claim that 
1 ppb reflects the most meaningful inflection point are likewise not 
compelling. The presented data show a range of upwind contribution 
levels captured by different contribution thresholds depending on which 
receptor is analyzed. Certain receptors show a substantial downward 
trend in captured total upwind contribution well before a threshold of 
1 ppb. Therefore, EPA does not find this evidence supportive of a 1 ppb 
threshold.
    EPA does not accept Michigan's position that a 1 percent of the 
NAAQS contribution threshold at Step 2 ``may not be appropriate'' for 
the 2015 ozone NAAQS due to modeling biases and errors.\81\ The 
explanation for how the 1 percent contribution threshold was originally 
derived is available in the 2011 CSAPR rulemaking. See 76 FR 48208, 
48237-38. Further, in the CSAPR Update, EPA re-analyzed the threshold 
for purposes of the 2008 ozone NAAQS and determined it was appropriate 
to continue to apply this threshold. EPA compared the 1 percent 
threshold to a 0.5 percent of NAAQS threshold and a 5 percent of NAAQS 
threshold. EPA found that the lower threshold did not capture 
appreciably more upwind state contribution compared to the 1 percent 
threshold, while the 5 percent threshold allowed too much upwind state 
contribution to drop out from further analysis. See Final CSAPR Update 
Air Quality Modeling TSD, at 27-30 (EPA-HQ-OAR-2015-0596-0144). If EPA 
were to apply this analysis to the 2015 ozone NAAQS using the updated 
modeling based on the 2016v2 emissions platform, a 5 percent of the 
NAAQS contribution threshold (i.e., 3.5 ppb) only captures 
approximately 50 percent of the total upwind contribution. Compared to 
a 1 percent threshold, a 5 percent threshold would, on average, forgo 
27 percent) of the total upwind contribution. As EPA noted in the 
August 2018 memorandum, the use of a 2 ppb contribution threshold under 
the modeling released with the March 2018 memorandum would only capture 
about 55 percent of all upwind contributions, and therefore ``emission 
reductions from states linked at that higher threshold may be 
insufficient to address collective upwind state contribution to 
downwind air quality problems.''\31\
---------------------------------------------------------------------------

    \81\ Michigan's SIP submission at 16.
---------------------------------------------------------------------------

    With these figures in mind, EGLE's claim based on unwarranted 
concerns over modeling uncertainty cannot be accepted. Both LADCO's and 
EPA's modeling techniques are sufficiently reliable and fit for the 
purpose to measure upwind contribution levels down to at least one 1 
percent of the NAAQS. EPA's recommended model attainment test is based 
on application of the model in a relative sense rather than relying 
upon absolute model predictions.\82\ All models have limitations 
resulting from uncertainties in inputs and scientific formulation. To 
minimize the effects of these uncertainties, the modeling is anchored 
to base period measured data in EPA's guidance approach for projecting 
design values. Notably, EPA also uses our source apportionment modeling 
in a relative sense when calculating the average contribution metric 
(used to identify linkages). In this method the magnitude of the 
contribution metric is tied to the magnitude of the projected average 
design value which is tied to the base period average measured design 
value. EPA's guidance has not established a bright-line criteria for 
judging whether or not statistical measures of model performance 
constitute acceptable or unacceptable model performance. So, contrary 
to what Michigan appears to be claiming with regards to modeling 
biases, there are no EPA recommended measures of allowable error. 
Although EPA does not typically focus on using particular benchmarks as 
the sole criteria for model performance, EPA notes that the model 
performance for the updated modeling based on the 2016v2 emissions 
platform is generally within the benchmarks recommended by Emery.\83\
---------------------------------------------------------------------------

    \82\ See Section 4.1' ``Overview of Modeled Attainment Test in 
EPA Modeling Guidance for Demonstrating Air Quality Goals for Ozone, 
PM2.5, and Regional Haze. November 2018. EPA 454-R-18-
009. https://www.epa.gov/scram/sip-modeling-guidance-documents.
    \83\ Christopher Emery, Zhen Liu, Armistead G. Russel, M. Talat 
Odman, Greg Yarwood and Naresh Kumar (2017). Recommendations on 
statistics and benchmarks to assess photochemical model performance, 
Journal of the Air & Waste Management Association, 67:5,582-598, 
DOI: 10.1080/10962247.2016.1265027.
---------------------------------------------------------------------------

    EPA has successfully applied a 1 percent of the NAAQS threshold to 
identify linked upwind states in three prior rulemakings. And the D.C. 
Circuit has also declined to establish bright line criteria for model 
performance. In upholding EPA's approach to evaluating interstate 
transport in CSAPR, the D.C. Circuit held that they would not 
``invalidate EPA's predictions solely because there might be 
discrepancies between those predictions and the real world. That 
possibility is inherent in the enterprise of prediction.'' EME Homer 
City Generation, L.P. v. EPA, 795 F.3d 118, 135 (2015). The court 
continued to note that ``the fact that a `model does not fit every 
application perfectly is no criticism; a model is meant to simplify 
reality in order to make it tractable.' '' Id. at 135-36 (quoting 
Chemical Manufacturers Association v. EPA, 28 F.3d 1259, 1264 (D.C. 
Cir. 1994).
    EPA's August 2018 memorandum provided that whether use of a 1 ppb 
threshold is appropriate must be based on an evaluation of state-
specific circumstances, and no such evaluation was included in the 
submission. EPA's experience with the alternative Step 2 thresholds is 
further discussed in Section I.D.3.i. As discussed there, EPA is 
considering withdrawing the August 2018 memorandum.
    Based on EPA's updated modeling (as well as the LADCO's 2018 
modeling (with water) the state elected to rely on in its SIP 
submission), the state is projected to contribute greater than both the 
1 percent and alternative 1 ppb thresholds. While EPA does not, in this 
action, approve of the state's application of the 1 ppb threshold, 
based on its linkages greater than 1 ppb to projected downwind 
nonattainment or maintenance receptors, the state's use of this 
alternative threshold at Step 2 of the 4-Step interstate framework is 
inconsequential to our action on this SIP submission.
3. Results of EPA's Step 1 and Step 2 Modeling and Findings for 
Michigan
    As described in Section I, EPA performed air quality modeling using 
the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
Michigan contributes at or above the threshold of 1 percent of the

[[Page 9863]]

2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or 
maintenance receptor. As shown in Table 4, the data \84\ indicate that 
in 2023, emissions from Michigan contribute greater than one percent of 
the standard to nonattainment or maintenance-only receptors in 
Illinois, Connecticut, Wisconsin, and Pennsylvania.\85\
---------------------------------------------------------------------------

    \84\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file 
``2016v2_DVs_state_contributions.xlsx'' which is included in docket 
ID No. EPA-HQ-OAR-2021-0663.
    \85\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I. That modeling showed 
that Illinois had a maximum contribution greater than 0.70 ppb to at 
least one nonattainment or maintenance-only receptor in 2023. These 
modeling results are included in the file ``Ozone Design Values & 
Contributions Revised CSAPR Update.xlsx'' in docket ID No. EPA-HQ-
OAR-2021-0663.

                      Table 4--Michigan Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023  Average   2023  Maximum     Michigan
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                (county, state)    maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
170314201....................  Cook, IL........  Maintenance....            69.9            73.4            1.67
170310076....................  Cook, IL........  Maintenance....            69.3            72.1            1.54
90099002.....................  New Haven, CT...  Nonattainment..            71.8            73.9            1.27
170317002....................  Cook, IL........  Maintenance....            70.1            73.0            1.26
170310032....................  Cook, IL........  Maintenance....            69.8            72.4            1.21
550590025....................  Kenosha, WI.....  Maintenance....            69.2            72.3            1.17
550590019....................  Kenosha, WI.....  Nonattainment..            72.8            73.7            1.07
90010017.....................  Fairfield, CT...  Nonattainment..            73.0            73.7            1.07
551010020....................  Racine, CT......  Nonattainment..            71.3            73.2            1.02
90013007.....................  Fairfield, CT...  Nonattainment..            74.2            75.1            0.94
170310001....................  Cook, IL........  Maintenance....            69.6            73.4            0.93
90019003.....................  Fairfield, CT...  Nonattainment..            76.1            76.4            0.92
420170012....................  Bucks, PA.......  Nonattainment..            70.7            72.2            0.75
----------------------------------------------------------------------------------------------------------------

    Therefore, based on EPA's evaluation of the information submitted 
by EGLE, and based on EPA's most recent modeling results for 2023, EPA 
proposes to find that Michigan is linked at Steps 1 and 2 and has an 
obligation to assess potential emissions reductions from sources or 
other emissions activity at Step 3 of the 4-step framework. EPA 
therefore will proceed to Step 3 of the 4-step interstate transport 
framework to assess the arguments the state presented as to why, 
despite this linkage, the state should not be considered to 
significantly contribute to nonattainment or interfere with maintenance 
of the NAAQS in any other state.
4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the obligations in CAA section 110(a)(2)(D)(i)(I) must 
prohibit ``any source or other type of emissions activity within the 
State'' from emitting air pollutants which will contribute 
significantly to downwind air quality problems. Thus, states must 
complete something similar to EPA's analysis (or an alternative 
approach to defining ``significance'' that comports with the statute's 
objectives) to determine whether and to what degree emissions from a 
state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment in, or interfere with 
maintenance of'' the NAAQS in any other state.
    EGLE did not conduct a sufficient step 3 analysis in Michigan's SIP 
submission. As explained previously, at Step 3 EGLE instead applied a 
weight of evidence analysis to argue that the state needed no 
additional emission reductions despite concluding Michigan was linked 
to three receptors at Step 2. The evidence presented in EGLE's 
submittal consisted primarily of support for the argument that upwind 
states should have a lower responsibility to other states when the 
upwind state is only linked to maintenance receptors. EGLE's analysis 
focused on the Sheboygan, Wisconsin maintenance receptor (Site ID: 36-
081-0124), as EGLE concluded it was the receptor to which Michigan was 
projected to contribute the most in 2023 at 1.85 ppb. EGLE also relied 
on several ideas in Attachment A to the March 2018 memorandum to 
further discount the importance of its own emissions. As noted in 
Section I, the ideas listed in Attachment A to the March 2018 
memorandum were not agency guidance nor had EPA determined them to be 
consistent with the requirements of the CAA. EPA will thoroughly review 
the technical and legal justifications ELGE made put forward in their 
attempt to use them as flexibilities.
    In its submittal, EGLE cited a concept in Attachment A to the March 
2018 memorandum to ``[c]onsider whether the remedy for upwind states 
linked to maintenance receptors could be less

[[Page 9864]]

stringent than those linked to nonattainment receptors'' and argued 
that because the CAA incudes different SIP development requirements for 
nonattainment and maintenance areas, that likewise nonattainment and 
maintenance areas should be treated differently in good neighbor SIPs. 
EGLE posited that because the CAA does not require emission reductions 
from maintenance areas, then upwind states can potentially make a 
sufficient showing they have no obligation to reduce emissions to 
monitors in other states projected to be maintaining the NAAQS. EGLE 
specifically noted that (1) the projected exceedance at the Sheboygan, 
Wisconsin receptor is very small, (2) the majority of the projected 
contribution to the Sheboygan, Wisconsin receptor is from federally 
regulated sources or sources Michigan cannot otherwise regulate, (3) 
Michigan's projected contribution to all three linked receptors is 
small compared to the projected contribution from other states and 
sources, (4) there are large projected contributions to the Sheboygan, 
Wisconsin receptor from international emissions, (5) Michigan's 
contributions to projected exceedance at the three maintenance 
receptors are small relative to other sources that also contribute more 
than 1 ppb to those receptors, (6) the modeling variability is greater 
than Michigan's contributions to the amount of the projected exceedance 
at each linked receptor and (7) there is a downward emissions trend in 
Michigan.
    As a general matter, EPA disagrees with EGLE's premise that if no 
emission reductions are needed for the receptor to which Michigan 
contributes the most, that automatically no emission reductions are 
needed for the other receptors to which Michigan is linked. EGLE 
unreasonably failed to analyze receptor-specific circumstances present 
at other receptors to which it was linked, and this is particularly the 
case because EGLE chose to rely so heavily on receptor-specific 
information to support their conclusions with respect to the Sheboygan 
receptor. Further, while the set of receptors to which Michigan is 
linked has changed in the most recent modeling (and now includes 
nonattainment receptors), EPA disagrees with Michigan's arguments to 
the extent such reasoning could be applied to Michigan's linkages 
identified in EPA's 2016v2 emissions platform modeling.
    EGLE argued that because the Sheboygan, Wisconsin receptor, had a 
small projected exceedance over the NAAQS, requiring additional 
emission reductions in Michigan would be ``premature'' and 
``burdensome.'' \86\ EGLE's premise goes beyond the concept in 
Attachment A to the 2018 memorandum that emission-reduction obligations 
as to maintenance receptors may be different; rather, EGLE argues that 
not only should Michigan have lower obligations with respect to 
maintenance receptors, but no obligations at all. Under the D.C. 
Circuit's decision in North Carolina, states and EPA are required to 
give independent significance to the ``interference with maintenance'' 
prong of section 110(a)(2)(D)(i)(I). 531 F.3d at 910. Since CSAPR, 
EPA's nationally consistent policy framework for addressing interstate 
ozone transport has given meaning to this prong through a separate 
definition of maintenance receptors at step 1 of the 4-step interstate 
transport framework. For states linked only to those receptors, EPA has 
found it appropriate to apply an emissions control solution that is 
uniform with the strategy applied for states that are linked to 
nonattainment receptors. See 76 FR at 48271. EPA's approach to 
addressing interference with maintenance under prong 2 for ozone NAAQS 
has been upheld twice, including on remand from the Supreme Court 
decision EGLE cited. See EME Homer City Generation, L.P., 795 F.3d at 
136; Wisconsin, 938 F.3d at 325-27. See also 86 FR at 23074. 
Particularly given this context, Michigan's SIP does not provide 
sufficient evidence to support less stringent or even no standards of 
emissions reductions relative to what would result from EPA's 
historical approach of addressing emissions activities from upwind 
states that are linked to maintenance-only receptors.
---------------------------------------------------------------------------

    \86\ See Michigan SIP submission p. 20.
---------------------------------------------------------------------------

    Further, EPA believes it would be inconsistent with the CAA for EPA 
to identify receptors that are at risk of NAAQS violations given 
certain conditions due to transported upwind emissions and then not 
prohibit the emissions that place the receptor at risk. The Supreme 
Court held that it was a permissible interpretation of the statute to 
apportion responsibility for states linked to nonattainment receptors 
considering ``both the magnitude of upwind states' contributions and 
the cost associated with eliminating them.'' EME Homer City, 572 U.S. 
at 518-19. It is equally reasonable and permissible to use these 
factors to apportion responsibility among upwind states linked to 
maintenance receptors because the goal in both instances is to prohibit 
the ``amounts'' of pollution that will either significantly contribute 
to nonattainment or interfere with maintenance of the NAAQS downwind. 
See Id. 515 n.18 (finding EPA's uniform-cost approach reasonable as to 
both prongs of the good neighbor provision). EPA's updated modeling 
indicates that Michigan will remain linked to downwind nonattainment 
and maintenance receptors for the 2015 ozone standard at least through 
2023. Consequently, EPA believes EGLE's assertion that upwind states 
linked to maintenance-only receptors should be held to less stringent 
standards of emissions reductions (as compared to states linked to a 
nonattainment receptor) is inappropriate, whether applied to its 
downwind linkages in either the modeling EGLE relied on or in EPA's 
more recent modeling.
    EGLE also claimed that Attachment A to the March 2018 memorandum 
suggested states linked only to maintenance receptors should consider 
whether emissions reduction factors should be influenced by high 
international contributions and high contributions from other states 
and sources. As a concept presented by outside parties, Attachment A to 
the March 2018 memorandum listed an idea that states may consider 
whether air quality, cost, or emission reduction factors should be 
weighted differently in areas where international contributions are 
relatively high. EPA did not at the time endorse this concept, nor does 
it do so now. However, EGLE did not present an approach or explain how 
international contributions to the linked receptors should influence 
the weighting of air quality, cost, or emission reductions at Step 3. 
Rather, EGLE suggested that if a receptor is near an international 
border, then international contribution could simply be removed from 
that monitor's projected design value. This is neither appropriate nor 
acceptable under the good neighbor provision or any other provision of 
the Clean Air Act. Michigan's approach effectively takes the position 
that no air quality problem should be deemed to exist at a downwind 
receptor location under the false assumption that the international 
portion of emissions affecting that area simply do not exist. EPA 
categorically rejects this approach as an entirely unacceptable form of 
air quality planning.
    EGLE further cited contributions from other states and sources to 
the linkages it identified to conclude it would be ``unreasonable'' for 
linked states with relatively low contributions to reduce their 
contributions.\87\ The Step 2 threshold (whether at 1 percent or 1

[[Page 9865]]

ppb) is intended to reflect the ``collective contribution'' nature of 
the interstate ozone transport problem and the complexity of the 
various linkages among states. Cf. EME Homer City, 572 U.S. at 515-16. 
The threshold functions as a screening step toward a more detailed 
analysis of emission-reduction opportunities across all of the states 
that contribute to some extent (i.e., above the threshold) to a 
downwind air quality problem. To simply conclude that nothing need be 
done regarding emissions that exceed the step 2 threshold because those 
emissions can be characterized as ``small'' compared to others' 
emissions (by the upwind state's lights at least) is an attempt to 
simply move the ``contribution'' threshold at Step 2 and is clearly 
insufficient at Step 3.
---------------------------------------------------------------------------

    \87\ See Michigan SIP submission p. 32.
---------------------------------------------------------------------------

    Whether emissions from other states or other countries also 
contribute to the same downwind air quality issue is irrelevant in 
assessing whether a downwind state has an air quality problem, or 
whether an upwind state is significantly contributing to that problem. 
States are not obligated under CAA section 110(a)(2)(D)(i)(I) to reduce 
emissions sufficient on their own to resolve downwind receptors' 
nonattainment or maintenance problems. Rather, states are obligated to 
eliminate their own ``significant contribution'' or ``interference'' 
with the ability of other states to attain or maintain the NAAQS.
    Further, the court in Wisconsin explained that downwind 
jurisdictions often may need to heavily rely on emissions reductions 
from upwind states in order to achieve attainment of the NAAQS, 938 
F.3d at 316-17; such states would face increased regulatory burdens 
including the risk of bumping up to a higher nonattainment 
classification if attainment is not reached by the relevant deadline, 
Maryland, 958 F.3d at 1204. Indeed, the D.C. Circuit in Wisconsin 
specifically rejected petitioner arguments suggesting that upwind 
states should be excused from good neighbor obligations on the basis 
that some other source of emissions (whether international or another 
upwind state) could be considered the ``but-for'' cause of downwind air 
quality problem. 938 F.3d at 323-324. The court viewed petitioners' 
arguments as essentially an argument ``that an upwind state 
`contributes significantly' to downwind nonattainment only when its 
emissions are the sole cause of downwind nonattainment.'' 938 F.3d at 
324. The court explained that ``an upwind state can `contribute' to 
downwind nonattainment even if its emissions are not the but-for 
cause.'' Id. at 324-325. See also Catawba County v. EPA, 571 F.3d 20, 
39 (D.C. Cir. 2009) (rejecting the argument ``that `significantly 
contribute' unambiguously means `strictly cause' '' because there is 
``no reason why the statute precludes EPA from determining that [an] 
addition of [pollutant] into the atmosphere is significant even though 
a nearby county's nonattainment problem would still persist in its 
absence''); Miss. Comm'n on Envtl. Quality v. EPA, 790 F.3d 138, 163 
n.12 (D.C. Cir. 2015) (observing that the argument that ``there likely 
would have been no violation at all . . . if it were not for the 
emissions resulting from [another source]'' is ``merely a rephrasing of 
the but-for causation rule that we rejected in Catawba County.''). 
Therefore, a state is not excused from eliminating its significant 
contribution on the basis that emissions from other sources also 
contribute some amount of pollution to the same receptors to which the 
state is linked. Thus, the state's arguments related to contributions 
from other sources, including removing international emissions from 
projected design values at the Sheboygan, Wisconsin monitor, are 
insufficient at Step 3 of the analysis.
    EGLE's submission included an apportionment analysis to quantify 
individual states' relative responsibility of the projected exceedances 
at the three linked receptors. EGLE cited Attachment A to the March 
2018 memorandum as well as EME Homer City Generation to suggest 
Michigan could be found to be only responsible for eliminating its 
share of the projected exceedances relative to other states that also 
contribute more than 1 ppb to the same receptors. We first note that 
this approach is a deviation from EPA's traditional approach of 
apportioning upwind-state responsibility at Step 3 using a uniform cost 
of control metric set at a level that maximizes cost-effectiveness of 
emissions reductions in relation to downwind state impacts across all 
linked states. Thus, this is not how EPA has interpreted the statutory 
term ``significant'' in the past, and EPA does not reach a conclusion 
whether this approach would be approvable, had EGLE had imposed 
emissions reductions in line with this logic. We do not need to reach 
that point in the analysis, however, because, having selected that 
approach to defining its obligations, EGLE proceeded to ignore the 
result.
    EGLE's submission identified Michigan's proportional contribution 
as less than 0.12 ppb to the three linked receptors and .05 ppb to the 
Sheboygan, Wisconsin receptor. Having acknowledged Michigan was 
responsible for eliminating up to 0.12 ppb of contribution to the 
downwind receptors, EGLE claimed that modeling ``noise'' made it 
``difficult'' to require that amount of reductions from Michigan 
sources. EGLE further opined that the downwind jurisdiction's share of 
responsibilities likely made Michigan's contributions even lower and 
the projected exceedances were so small that those three receptors were 
likely to not have difficulty attaining the NAAQS anyway. EPA has 
routinely been capable of successfully implementing good neighbor 
obligations through the CSAPR framework, and achieving significant 
downwind air quality improvements through upwind-state reductions, at 
levels of ``significant contribution'' comparable or even less than 
those found in Michigan's submittal, irrespective of alleged ``modeling 
noise.'' See Wisconsin, 938 F.3d at 322-23 (rejecting Wisconsin's 
argument that it should not face good neighbor obligations on the basis 
that its emission reductions would only improve a downwind receptor by 
two ten-thousandths of a part per billion).
    After measuring Michigan's significant contribution, EGLE suggested 
that modeling uncertainty was too great to either require emissions 
reductions or demonstrate that EGLE had any linkages to maintenance 
receptors at all. But EGLE had measured the state's significant 
contribution and was therefore identifying the measurable amount of 
significant contribution the state was legally responsible for 
eliminating. See Michigan v. EPA, 213 F.3d 663, 683-84 (D.C. Cir. 2000) 
(significant contribution must be ``measurable''). Further, scientific 
uncertainty may only be invoked to avoid comporting with the 
requirements of the CAA when ``the scientific uncertainty is so 
profound that it precludes . . . reasoned judgment'' Massachusetts v. 
EPA, 127 S.Ct. 1438 (2007). See Wisconsin, 938 F.3d at 318-19 
(``Scientific uncertainty, however, does not excuse EPA's failure to 
align the deadline for eliminating upwind States' significant 
contributions with the deadline for downwind attainment of the 
NAAQS.''). See also EME Homer City, 795 F.3d 118, 135-36 (``We will not 
invalidate EPA's predictions solely because there might be 
discrepancies between those predictions and the real world. That 
possibility is inherent in the enterprise of prediction.''). EGLE's 
arguments related to modeling uncertainty or ``noise'' do not establish 
a level of uncertainty so high as to

[[Page 9866]]

preclude reasoned judgement. EGLE argued that the three maintenance 
receptors at issue could maintain the NAAQS without further emissions 
reductions from any linked upwind state. In support, EGLE's submission 
provided a list of on-the-way and on-the-books emission reductions 
measures to argue that Michigan's good neighbor obligations were 
already satisfied. EGLE provided references to certain facility 
retirements in Michigan, Federal mobile source rules, Federal rules 
reducing NOX and VOCs such as MATS and the Oil and Natural 
Gas Industry Standards, the NOX SIP Call, and CSAPR Update.
    EPA's assessment of future air quality conditions generally already 
accounts for on-the-books emission reductions and the most up-to-date 
forecast of future emissions in the absence of the transport policy 
being evaluated (i.e., base case conditions).\88\ As described in more 
detail in Section I, EPA's latest projections of the baseline EGU 
emissions uses the version 6--Summer 2021 Reference Case of the 
IPM.\89\ The IPM version 6--Summer 2021 Reference Case uses the NEEDS 
v6 database as its source for data on all existing and planned-
committed units. Units are removed from the NEEDS inventory only if a 
high degree of certainty could be assigned to future implementation of 
the announced future closure or retirement. Any retirements excluded 
from the NEEDS v6 inventory can be viewed in the NEEDS spreadsheet.\90\ 
The inventory for these projections takes account of the retirement of 
the Marquette Board of Light & Power Shiras Steam Plant, Lansing Board 
of Water and Light, Eckert Station, Units 1 and 3-6; DTE, River Rouge, 
Unit 3; We Energies, Presque Isle Power Plant, Units 5-9; DTE St. 
Clair, Units 1-4 and 6-7; DTE Trenton Channel, Unit 9; Wyandotte, Unit 
5; Consumers Energy Karn, Units 1-2.
---------------------------------------------------------------------------

    \88\ See 81 FR 74504 at 74517; 85 FR 68964 at 68979.
    \89\ Detailed information and documentation of EPA's Base Case, 
including all the underlying assumptions, data sources, and 
architecture parameters can be found on EPA's website at: https://www.epa.gov/airmarkets/epas-power-sector-modeling-platform-v6-using-ipm-summer-2021-reference-case.
    \90\ We note that for one of the units EGLE listed as projected 
to retire, Wyandotte--Unit 5, this facility was still included in 
the NEEDS as operating. Additionally, the unit IDs listed by EGLE in 
the SIP submittal may be different from those listed in EPA's NEEDS 
v6 inventory--NEEDS v6 Summer 2021 Reference Case, however we have 
verified that these emissions decreases have been accounted for in 
our most recent modeling.
---------------------------------------------------------------------------

    Additionally, EPA's modeling using the 2016v2 emissions platform 
accounts for the onroad and nonroad rules that Michigan identified, 
such as the Tier 3 Motor Vehicle Emission and Fuel Standards, to the 
extent still on the books and projected to have ozone-precursor 
emissions consequences.\91\
---------------------------------------------------------------------------

    \91\ See Technical Support Document (TSD) Preparation of 
Emissions Inventories for the 2016v2 North American Emissions 
Modeling Platform included in the Headquarters docket ID No. EPA-HQ-
OAR-2021-0663.
---------------------------------------------------------------------------

    In other words, changes in the emissions inventory and on-the-books 
controls relevant to emissions in 2023 that EGLE claims EPA missed in 
its prior modeling have now been incorporated into EPA's most recent 
modeling of 2023 using the 2016v2 emissions platform. This modeling 
projects a continuing contribution from Michigan to thirteen out-of-
state receptors above a threshold of 1 percent of the NAAQS (at Steps 1 
and 2) despite these measures--nine of which have contribution from 
Michigan above 1 ppb and seven of which are nonattainment receptors 
(see Table 4).\92\ Therefore, in light of continuing contribution to 
out of state receptors from Michigan notwithstanding these identified 
on-the-books control measures, EGLE's SIP submission should have 
evaluated the availability of additional air quality controls to 
improve downwind air quality at nonattainment and maintenance receptors 
at Step 3.
---------------------------------------------------------------------------

    \92\ Notably, in focusing its Step 3 analysis only on a single 
receptor, EGLE gave no weight to the scope of its contribution to 
downwind air quality problems. Linkages to thirteen receptor sites 
in EPA's most recent modeling indicate that Michigan's emissions 
have widespread effects in other states--effects that the State's 
SIP submittal would do nothing to address.
---------------------------------------------------------------------------

    Nor does EGLE's listing of existing control measures or overall 
emission trends serve as an adequate substitute for a Step 3 analysis 
of additional potential emission reductions. In general, the listing of 
existing or on-the-way control measures, whether approved into the 
State's SIP or not, does not substitute for a complete step 3 analysis 
under EPA's 4-step framework to define ``significant contribution.'' 
ELGE did not provide an assessment of the overall effects of these 
measures, when the emissions reductions would be achieved, and what the 
overall resulting air quality effects would be at identified out of 
state receptors. EGLE did not identify which portion of ongoing 
emissions trends were not already accounted for in steps 1 and 2 of the 
analysis (EPA addresses specific identified changes in emissions 
inventory in the discussion above). EGLE did not evaluate additional, 
potential emissions control opportunities, or their costs or impacts, 
or attempt to analyze whether, if applied more broadly across linked 
states, the emissions reductions would constitute the elimination of 
significant contribution on a regional scale. The state did not offer 
an explanation as to whether any faster or more stringent emissions 
reductions that may be available were prohibitively costly or 
infeasible. Although EPA acknowledges states are not necessarily bound 
to follow its own analytical framework at step 3, we note that the 
state did not attempt to determine or justify an appropriate uniform 
cost-effectiveness threshold for the more stringent 2015 ozone NAAQS. 
This would have been similar to the approach to defining significant 
contribution that EPA has applied in prior rulemakings such as CSAPR 
and or the CSAPR Update, even if such an analysis is not technically 
mandatory.
    Further, the state's attempt to categorize certain sectors of 
emissions as beyond its regulatory control is unpersuasive. Clearly the 
state possesses regulatory authority over its EGU and non-EGU large 
stationary sources as well as authority over other types of ``emissions 
activity within the state,'' see CAA section 110(a)(2)(D)(i). And while 
mobile sources are generally regulated at the Federal level under title 
II of the Clean Air Act, the state also has the authority to undertake 
any number of measures to reduce emissions from mobile sources through 
means and techniques that are not preempted by title II. See, e.g., CAA 
sections 182(b)(3), 182(b)(4), 182(c)(3), 182(c)(4), 182(c)(5), 
182(d)(1), 182(e)(3), and 182(e)(4) (identifying programs to control 
mobile source emissions that states are required to implement depending 
on the degree of ozone nonattainment). Specifically with respect to 
EGUs, EPA notes that no EGU NOX control program has yet been 
established to implement good neighbor requirements for the 2015 ozone 
NAAQS. Thus reliance on prior programs, such as the CSAPR Update or 
Revised CSAPR Update, is misplaced, since those programs only addressed 
good neighbor obligations under the less stringent 2008 ozone NAAQS.
    Finally, under the Wisconsin decision, states and EPA may not delay 
implementation of measures necessary to address good neighbor 
requirements beyond the next applicable attainment date without a 
showing of impossibility or necessity. See 938 F.3d at 320. In those 
cases where the measures identified by Michigan had implementation 
timeframes beyond the next relevant attainment dates, the submission 
did not offer a demonstration of impossibility of earlier 
implementation of those control measures that would go into effect 
after

[[Page 9867]]

2024. Similarly, the State's submittal is insufficient to the extent 
the implementation timeframes for identified control measures were left 
unidentified, unexplained, or too uncertain to permit EPA to form a 
judgment as to whether the timing requirements for good neighbor 
obligations have been met.
    For the reasons listed above, EPA proposes to find that Michigan 
has not satisfied its obligations of the good neighbor SIP provisions 
at Step 3 of the 4-step transport framework. We propose that Michigan 
was required to analyze emissions more fully from the sources and other 
emissions activity from within the state to determine whether its 
contributions were significant, and we propose to disapprove its 
submission because Michigan failed to do so.
5. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-step interstate transport framework calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at Step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. EGLE provided references to 
on the books and on the way Federal mobile source rules, MATS and the 
Oil and Natural Gas Industry Standards, the NOX SIP Call, 
and CSAPR Update. As an initial matter, pointing to or listing existing 
state or Federal control measures is not what is called for at Step 4. 
Rather Step 4 requires the development of permanent and enforceable 
measures to implement those measures determined to be required at Step 
3. EGLE claimed that nothing was required of Michigan at Step 3 and 
thus EGLE stated that it did not believe anything was required at Step 
4. Therefore, we do not interpret the list of existing state or Federal 
measures to be EGLE's attempt at implementation at Step 4.
    Because Michigan's SIP submission did not contain an evaluation of 
additional emission control opportunities (or establish that no 
additional controls are required), no information was provided at Step 
4. As a result, EPA proposes to disapprove Michigan's submittal on the 
separate, additional basis that the state has not developed permanent 
and enforceable emissions reductions necessary to meet the obligations 
of CAA section 110(a)(2)(d)(i)(I).
6. Conclusion
    Based on EPA's evaluation of EGLE's SIP submission, EPA is 
proposing to find that the portion of Michigan's March 5, 2019 SIP 
submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet the 
state's interstate transport obligations, because it fails to contain 
the necessary provisions to eliminate emissions that will contribute 
significantly to nonattainment or interfere with maintenance of the 
2015 ozone NAAQS in any other state.

D. Minnesota

1. Evaluation of Information Provided by Minnesota Regarding Steps 1 
and 2
    At Step 1 of the 4-step interstate transport framework, Minnesota 
relied on both LADCO modeling and EPA modeling released in the March 
2018 memorandum and to identify nonattainment and maintenance receptors 
in 2023. As described previously, LADCO performed a modeling 
demonstration like that of EPA's 2018 transport modeling, except with 
use of the ERTAC EGU Tool to supplement state specific EGU information. 
LADCO identified nonattainment and maintenance receptors using EPA 
methodology. MPCA presented several nonattainment and maintenance 
receptors identified by both LADCO modeling, showing ``no water'' and 
``with water'' results and EPA modeling released with the March 2018 
memorandum. Since new modeling has been performed by EPA with updated 
emission data, EPA proposes to primarily rely on the most recent 
modeling to identify nonattainment and maintenance receptors in 2023. 
MPCA made several criticisms of EPA's method for projecting EGU 
emissions in EPA's modeling released with the March 2018 memorandum. 
Although EPA does not agree with those criticisms, we note that EPA is 
relying on a different method for projecting emissions from EGUs in the 
updated modeling using the 2016v2 emissions platform as explained in 
more detail in Section I.
    Nonetheless, the alternative modeling relied on by MPCA also 
identified a number of nonattainment and maintenance receptor sites in 
2023. See Tables 2 and 3 on pages 8 and 9 of MPCA's submittal. Thus, 
even under the alternative modeling of 2023, MPCA acknowledges in its 
submittal the existence of several nonattainment and maintenance 
receptors.
    At Step 2 of the 4-Step interstate transport framework, MPCA relied 
on both LADCO modeling and EPA modeling released in the March 2018 
memorandum to identify upwind state linkages to nonattainment and 
maintenance receptors in 2023. Based on both modeling results, MPCA 
concluded that Minnesota would contribute below 1 percent of the NAAQS 
to receptors in 2023. However, in this proposal, EPA relies on the 
Agency's most recently available modeling, which uses a more recent 
base year and more up-to-date emissions inventories, to identify upwind 
contributions and ``linkages'' to downwind air quality problems in 2023 
using a threshold of 1 percent of the NAAQS. As shown in Table 5 
(explained in the next section), the updated EPA modeling identifies 
Minnesota's maximum contribution to a downwind nonattainment or 
maintenance receptor is greater than 1 percent of the standard (i.e., 
0.70 ppb). Although the state did not rely on a 1 ppb contribution 
threshold in its SIP submittal, EPA recognizes that the modeling the 
MPCA used relied on the most recently available EPA modeling at the 
time the state submitted its SIP submittal (EPA modeling released in 
the March 2018 memorandum as well as the LADCO modeling). The 2018 
modeling indicated the state was not projected to contribute above one 
1 percent of the NAAQS to a projected downwind nonattainment or 
maintenance receptor. Therefore, the state may not have considered 
analyzing the reasonableness and appropriateness of a 1 ppb threshold 
at Step 2 of the 4-step Step interstate transport framework per the 
August 2018 memorandum. EPA's August 2018 memorandum provided that 
whether use of a 1 ppb threshold is appropriate must be based on an 
evaluation of state-specific circumstances, and no such evaluation was 
included in the submission. EPA's experience with the alternative Step 
2 thresholds is further discussed in Section I.D.3.i. As discussed 
there, EPA is considering withdrawing the August 2018 memorandum.
2. Results of EPA's Step 1 and Step 2 Modeling and Findings for 
Minnesota
    As described in Section I, EPA performed air quality modeling using 
the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
Minnesota contributes at or above the threshold of 1 percent of the 
2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or 
maintenance receptor. As shown in

[[Page 9868]]

Table 5, the data \93\ indicate that in 2023, emissions from Minnesota 
contribute greater than 1 percent of the standards to two maintenance-
only receptors in Illinois. These modeling results are consistent with 
the results of a prior round of 2023 modeling using the 2016v1 
emissions platform that became available to the public in the fall of 
2020 in the Revised CSAPR Update, as noted in Section I, which showed 
that Minnesota had a maximum contribution of 0.86 ppb to a 
nonattainment or maintenance receptor in 2023.\94\
---------------------------------------------------------------------------

    \93\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file: 
2016v2_DVs_state_contributions.xlsx which is included in docket ID 
No. EPA-HQ-OAR-2021-0663.
    \94\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I. That modeling showed 
that Minnesota had a maximum contribution greater than 0.70 ppb to 
at least one nonattainment or maintenance-only receptor in 2023. 
These modeling results are included in the file ``Ozone Design 
Values And Contributions Revised CSAPR Update.xlsx'' in docket EPA-
HQ-OAR-2021-0663.

                      Table 5--Minnesota Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023  Average   2023  Maximum     Minnesota
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                                   maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
170310001....................  Cook............  Maintenance....            69.6            73.4            0.97
170310076....................  Cook............  Maintenance....            69.3            72.1            0.79
----------------------------------------------------------------------------------------------------------------

    Based on EPA's evaluation of the information submitted by MPCA, and 
based on EPA's most recent modeling results for 2023 using the 2016v2 
emissions platform, EPA proposes to find that Minnesota is linked at 
Steps 1 and 2 and has an obligation to assess potential emissions 
reductions from sources or other emissions activity at Step 3 of the 4-
Step framework. Despite the linkage EPA determines exists at Step 2, 
the state concluded in its submission based on other factors that it 
should not be considered to significantly contribute to nonattainment 
or interfere with maintenance of the NAAQS in other states. Therefore, 
EPA will proceed to evaluate MPCA's additional analyses at Step 3 of 
the 4-Step interstate transport framework.
4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-Step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the obligations in CAA section 110(a)(2)(D)(i)(I) must 
prohibit ``any source or other type of emissions activity within the 
state'' from emitting air pollutants which will contribute 
significantly to downwind air quality problems. Thus, states must 
complete something similar to EPA's analysis (or an alternative 
approach to defining ``significance'' that comports with the statute's 
objectives) to determine whether and to what degree emissions from a 
state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment in or interfere with 
maintenance of'' the NAAQS in any other state. MPCA did not conduct 
such an analysis in their SIP submission.
    Neither the LADCO modeling nor EPA modeling released with the March 
2018 memorandum indicated that Minnesota would contribute over 1 
percent of the NAAQS to any nonattainment or maintenance receptor in 
2023. Therefore, MPCA stated they did not consider it necessary to 
consider further emission reductions because Minnesota was not 
projected to contribute to downwind air quality issues above the 
contribution threshold. Despite this, Minnesota provided supporting 
analysis to strengthen the conclusions of the modeling results. MPCA 
presented evidence that ambient ozone concentrations in Minnesota had 
been at or below the NAAQS from the late 1990s to 2017, and that 
NOX and VOCs emissions had been steadily decreasing from 
2002 through 2015. MPCA asserted that these trends would translate to 
continued reductions in ozone being transported from the state to 
nonattainment or maintenance receptors. Additionally, MPCA listed 
several state and Federal regulatory programs that control or 
incentivize NOX and VOC limits, including the CSAPR 
NOX trading program.
    EPA does not dispute the evidence about ambient ozone 
concentrations and NOX and VOC emissions trends or existence 
of the NOX and VOC controls presented by Minnesota.\95\ 
However, as explained in Section I.C, the most recent EPA modeling 
captures numerous updates to the 2016 emissions platform, including all 
existing CSAPR trading programs, in the baseline,\96\ and that modeling 
confirms that most these control programs were not sufficient to 
eliminate Minnesota's linkage at Steps 1 and 2 under the 2015 ozone 
NAAQS. The state therefore has good neighbor obligations under the 2015 
8-hour NAAQS and is obligated at Step 3 to assess additional control 
measures using a multifactor analysis.
---------------------------------------------------------------------------

    \95\ See Minnesota's SIP submittal Figures 1-3, pages 10-11.
    \96\ For a complete explanation of air quality modeling of the 
2016v2 emissions platform modeling, please see ``AQ Modeling 
TSD_2016v2 Platform.pdf'' included in docket ID No. EPA-HQ-OAR-2021-
0663.
---------------------------------------------------------------------------

    MPCA identified state permitting programs, rules, voluntary 
programs, and the CSAPR NOX trading program,

[[Page 9869]]

among others, as NOX and VOC control measures which satisfy 
Minnesota's good neighbor obligations under the 2015 ozone NAAQs. In 
general, however, the listing of existing or on-the-way control 
measures, whether approved into the state's SIP or not, does not 
substitute for a complete Step 3 analysis under EPA's 4-step framework 
to define ``significant contribution.'' Minnesota's submission does not 
include an assessment of the overall effects of these measures, when 
the reductions would be achieved, and what the overall resulting air 
quality effects would be observed at identified out-of-state receptors. 
Minnesota's submission does not include an evaluation of additional 
potential emissions control opportunities, or their costs or impacts, 
or attempt to analyze whether, if applied more broadly across linked 
states, the emissions reductions would constitute the elimination of 
significant contribution on a regional scale. The state's submission 
did not contain an explanation as to whether any faster or more 
stringent emissions reductions that may be available were prohibitively 
costly or infeasible. Furthermore, states may not rely on non-SIP 
measures to meet SIP requirements, and Minnesota has not revised its 
SIP to contain the CSAPR NOX trading program or the non-SIP 
approved rules MPCA identified. See CAA section 110(a)(2)(D) (``Each 
such [SIP] shall . . . contain adequate provisions . . . .''). See also 
CAA section 110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 
786 F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on 
by state to meet CAA requirements must be included in the SIP).
    As mentioned above, EPA has newly available information that 
indicates sources in Minnesota are linked to downwind air quality 
problems for the 2015 ozone standard. Therefore, EPA proposes to 
disapprove Minnesota's August 20, 2018 interstate transport SIP 
submission on the separate, additional basis that the SIP submittal did 
not assess additional emissions control opportunities.
5. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-Step interstate transport frameworks calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at Step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. MPCA identified state 
permitting programs, rules, voluntary programs, and the CSAPR 
NOX trading program, among others, as NOX and VOC 
control measures which are not all part of Minnesota's SIP. Although 
the state has since incorporated some of these control measures into 
their SIP, Minnesota did not revise its SIP to include all these 
emission reductions in a revision to its SIP to ensure the reductions 
were permanent and enforceable and eliminate their significant 
contribution to nonattainment or interference with maintenance of the 
NAAQS. As a result, EPA proposes to disapprove Minnesota's submittal on 
the separate, additional basis that the Minnesota has not developed 
permanent and enforceable emissions reductions necessary to meet the 
obligations of CAA section 110(a)(2)(d)(i)(I).
6. Conclusion
    Based on EPA's evaluation of Minnesota's SIP submission and after 
consideration of updated EPA modeling using the 2016-based emissions 
modeling platform, EPA is proposing to find that the portion of 
Minnesota's October 1, 2018 SIP submission addressing CAA section 
110(a)(2)(D)(i)(I) does not meet the state's interstate transport 
obligations for 2015 ozone NAAQS, because it fails to contain the 
necessary provisions to eliminate emissions that will contribute 
significantly to nonattainment or interfere with maintenance of the 
NAAQS in any other state.

E. Ohio

1. Evaluation of Information Provided by Ohio Regarding Steps 1
    At Step 1 of the 4-step interstate transport framework, OEPA relied 
on LADCO modeling released in 2018 to identify nonattainment and 
maintenance receptors in 2023. As described previously in this action, 
LADCO performed modeling similar to EPA's modeling released in the 
March 2018 memorandum, except with use of ERTAC for projecting future 
year EGU emissions. LADCO identified nonattainment and maintenance 
receptors using EPA methodology. OEPA elected to rely on LADCO's 
``3x3'' modeling results, which identified similar receptors to EPA's 
modeling included in the March 2018 memorandum.
    However, OEPA elected to use an alternative method developed by 
TCEQ for identifying maintenance receptors at Step 1 of the 4-step 
framework. Using the TCEQ method to identify maintenance receptors OEPA 
claimed that four maintenance receptors based on EPA's approach would 
not have difficulty maintaining the NAAQS in 2023. OEPA relied on the 
potential flexibilities in Attachment A to the March 2018 in support of 
its use of the TCEQ method. As explained in Section I.C above, the 
concepts presented in Attachment A to the March 2018 memorandum were 
neither guidance nor determined by EPA to be consistent with the CAA. 
OEPA submitted Ohio's SIP submission before EPA released its October 
2018 memorandum discussing maintenance receptors. Regardless, EPA will 
examine the legal and technical merits of OEPA's arguments related to 
the use of an alternative maintenance-only definition in light of the 
October 2018 memorandum. OEPA has not adequately explained or justified 
how TCEQ's method for identifying maintenance receptors reasonably 
identifies areas that will have difficulty maintaining the NAAQS. That 
is, EPA proposes to find that OEPA has provided no sound technical 
basis for how TCEQ's methodology gives meaning to the CAA's instruction 
that states submit good neighbor SIPs that prohibit their states' 
emissions from interfering with the maintenance of the NAAQS in another 
state.
    In North Carolina v. EPA, 531 F.3d 896, 909-11 (D.C. Cir. 2008), 
the D.C. Circuit rejected EPA's CAIR on the basis that EPA had not 
adequately given meaning to the phrase ``interfere with maintenance'' 
in the good neighbor provision. Specifically, North Carolina argued 
that it had counties that were projected to attain the NAAQS in the 
future analytic year, but were at risk of falling back into 
nonattainment due to interference from upwind sources, particularly 
given year-to-year variability in ozone levels. The court agreed, 
holding that EPA's rule did not adequately protect ``[a]reas that find 
themselves barely meeting attainment.'' Id. at 910. Consequently, EPA 
has developed a methodology, used in its 2011 CSAPR and its 2016 CSAPR 
Update and Revised CSAPR Update, for identifying areas that may 
struggle to maintain the NAAQS. See 76 FR at 48227-28. EPA's approach 
to addressing maintenance receptors was upheld in the EME Homer City 
litigation. See 795 F.3d 118, 136-37. It was also upheld in Wisconsin. 
938 F.3d at 325-26. In Wisconsin, the court noted that four upwind 
states were linked only to maintenance receptors and rejected the 
argument that application of the same control level as EPA imposes for 
those states linked to nonattainment receptors was unreasonable or 
unlawful absent a

[[Page 9870]]

particularized showing of overcontrol. Id. at 327.
    In order to explain the differences between TCEQ's and EPA's 
methodology for identifying maintenance receptors, it is helpful to 
provide some additional context for how EPA projects future air 
quality. EPA's air quality modeling guidance has long recommended 
developing a base design value (i.e., the design value that will be 
used as a starting point to model and analyze for purposes of 
projecting future air quality concentrations) that is the average of 
three design values spanning a five-year period, centered around one 
year for which an emissions inventory will be submitted (e.g., if 2011 
was the base emissions inventory year, a state would use monitored 
values from 2009-2011, 2010-2012, 2011-2013 as the starting point for 
projecting air quality concentrations in future years). The average of 
these three design values is then multiplied by a relative response 
factor to generate an average design value for the future year. If a 
receptor's average future year design value is greater than or equal to 
the level of the NAAQS, and the receptor has recent monitored data that 
violates the NAAQS, that receptor is considered a ``nonattainment'' 
receptor at step 1. To identify maintenance receptors, EPA's 
methodology looks to the highest design value of the three DVs used to 
calculate the 5-year weighted average design value (e.g., in the 2011 
example, if 2009-2011 had the highest design value of 2009-2011, 2010-
2012, and 2011-2013). EPA then applies the same relative response 
factor to that highest design value to generate a projected future 
maximum design value. Where a receptor's maximum design value exceeds 
the level of the NAAQS, EPA has deemed those receptors to be 
``maintenance'' receptors. This methodology was designed to address the 
D.C. Circuit's holding that the CAA's ``interference with maintenance'' 
prong requires states and EPA to protect areas that may struggle with 
maintaining the standard in the face of variable conditions.
    For its maintenance receptors, TCEQ elected not to use the highest 
design value of the three DVs making up the base period average design 
value. Instead, Texas (and by extension, Ohio), used the most recent 
design value of the three DVs, regardless of whether the most recent 
design value was highest or lowest. OEPA's proffered explanation for 
using the most recent design value to identify maintenance receptors 
was that the latest design value ``takes into consideration . . . any 
emissions reductions that might have occurred.'' \97\ OEPA in its 
submission did not explain why or how this methodology identifies those 
areas that may be meeting the NAAQS or that may be projected to meet 
the NAAQS but may nevertheless struggle to maintain the NAAQS, given 
interannual variability in ozone conducive meteorology. In fact, 
because the TCEQ's methodology adopted by OEPA uses the most recent 
design value to capture more recent emissions reductions rather than 
capture variable conditions, the methodology appears to be aimed at 
limiting receptors which could be identified as maintenance receptors, 
compared to EPA's methodology, which was designed to identify those 
areas that might struggle to maintain the NAAQS in ozone conducive 
conditions.
---------------------------------------------------------------------------

    \97\ TCEQ submission at 3-39 to 3-40.
---------------------------------------------------------------------------

    EPA disagrees that the use of latest three years for calculating a 
DV properly accounts for the effects of meteorological variability for 
the purpose of identifying projected maintenance receptors. Rather, the 
use of a three-year average is intended to average out, not account 
for, the effects of inter-annual variability in ozone conducive 
meteorology. EPA reviewed the information provided by OEPA and proposes 
to find that the information is insufficient to support the use of an 
alternative approach. OEPA analysis of meteorological information did 
not discuss or consider how other meteorological factors that are 
typically associated with high ozone episodes such as humidity, solar 
radiation, vertical mixing, and/or other meteorological indicators such 
as cooling-degree days to confirm whether conditions affecting these 
monitors may have been conducive to ozone formation during the 2009 
through 2013 base period. In addition, the ozone trends data provided 
in OEPA submittal indicate that several of the receptors in Coastal 
Connecticut to which Ohio is linked by more than 1 ppb continue to 
measure ozone design values close to or exceeding 80 ppb with no 
overall downward trend in the most recent data in the submittal.\98\ In 
any event, OEPA's use of an alternative approach to identifying 
maintenance receptors does not result in a dispositive change in 
receptor status for purposes of EPA's evaluation of OEPA's SIP 
submittal at Step 1 because OEPA did not reach the conclusion that 
there were no receptors in 2023 or claim at Step 2 that Ohio was not 
linked to any receptor on the basis of the use of an alternative 
definition of maintenance receptor.
---------------------------------------------------------------------------

    \98\ See ``2010 Thru 2020 Ozone Design Values.xlsx'' in docket 
ID No. EPA-HQ-OAR-2021-0663.
---------------------------------------------------------------------------

    In conclusion, the modeling relied on by OEPA identified a number 
of nonattainment and maintenance receptor sites in the Midwest and 
Northeast in 2023. See Table 1 on page 8 of OEPA's submittal. Under 
EPA's approach to defining nonattainment and maintenance receptors, 
Ohio was shown to be linked to three ``nonattainment/maintenance'' 
receptors and six ``maintenance'' receptors. Under an alternative 
approach to defining receptors (discussed below), OEPA concluded that 
Ohio was shown to be linked to two ``nonattainment'' receptors, one 
``nonattainment/maintenance'' receptor, and four ``maintenance'' 
receptors. Thus, based on using the LADCO's 2023 modeling and even 
under an alternative approach to defining ``maintenance'' receptors, 
OEPA acknowledges in its submittal the existence of several 
nonattainment and maintenance receptors in the Midwest and Northeast. 
EPA further evaluates Ohio's linkage to these receptors in the 
following section.
2. Evaluation of Information Provided by the State Regarding Step 2
    Although OEPA relied on alternative modeling to EPA's modeling, 
OEPA acknowledged in their SIP submission that Ohio is linked above 
either a 1 percent of the NAAQS or a 1 ppb contribution threshold to 
one or more downwind receptors in 2023. Because the LADCO modeling 
relied on by the state also demonstrates that a linkage exists between 
the state and downwind receptors at Step 2, EPA need not conduct a 
comparative assessment of the alternative modeling; the state concedes 
that it is linked above either 1 percent of the NAAQS or 1 ppb.
    The state additionally evaluated the use of an alternative 
threshold exceeding 1 ppb at Step 2 to identify whether the state was 
``linked'' to a projected downwind nonattainment or maintenance 
receptor. EPA's August 2018 memorandum provided that whether use of a 1 
ppb threshold is appropriate must be based on an evaluation of state-
specific circumstances, but that the use of a threshold greater than 1 
ppb at Step 2 would likely not be appropriate because higher thresholds 
would not capture a sufficient amount of total upwind state 
contribution to allow for the development of effective remedies at Step 
3.\31\ In particular, EPA found that a 2 ppb threshold would cause 45% 
of total upwind contribution to be removed from further analysis across 
all

[[Page 9871]]

receptors as compared to a 1 percent of NAAQS threshold.
    EPA does not accept Ohio's position that a 1 percent of the NAAQS 
contribution threshold at Step 2 is ``impractical and infeasible'' for 
the 2015 ozone NAAQS because ``it results in very small contributions 
having substantial consequences.'' \99\ This argument conflates the 
contribution threshold at Step 2 with a determination of 
``significance'' reached at Step 3 after a multi-factor analysis. In 
its submittal, OEPA justified a higher threshold than either 1 percent 
or 1 ppb by noting that, if applied, these alternative thresholds (3 or 
4 percent of the NAAQS) would progressively de-link the State from an 
increasing number of identified downwind receptors. EPA likewise 
disagrees with this reasoning; selecting progressively higher 
contribution thresholds simply on the basis that they would excuse an 
ever greater number of upwind states from having any good neighbor 
obligations lacks any persuasive technical justification and is 
inconsistent with the purposes of the Act.
---------------------------------------------------------------------------

    \99\ Michigan's SIP submission at 16.
---------------------------------------------------------------------------

    The explanation for how the 1 percent contribution threshold was 
originally derived is available in the 2011 CSAPR rulemaking. See 76 FR 
48208, 48237-38. Further, in the CSAPR Update, EPA re-analyzed the 
threshold for purposes of the 2008 ozone NAAQS and determined it was 
appropriate to continue to apply this threshold. EPA compared the 1 
percent threshold to a 0.5 percent of NAAQS threshold and a 5 percent 
of NAAQS threshold. EPA found that the lower threshold did not capture 
appreciably more upwind state contribution compared to the 1 percent 
threshold, while the 5 percent threshold allowed too much upwind state 
contribution to drop out from further analysis. See Final CSAPR Update 
Air Quality Modeling TSD, at 27-30 (EPA-HQ-OAR-2015-0596-0144). If EPA 
were to apply this analysis to the 2015 ozone NAAQS using the updated 
modeling based on the 2016v2 emissions platform, a 5 percent of the 
NAAQS contribution threshold (i.e., 3.5 ppb) only captures 
approximately 50 percent of the total upwind contribution. Compared to 
a 1 percent threshold, a 5 percent threshold would, on average, forgo 
27 nearly 30 percent) of the total upwind contribution. As EPA noted in 
the August 2018 memorandum, the use of a 2 ppb contribution threshold 
under the modeling released with the March 2018 memorandum would only 
capture about 55 percent of all upwind contributions, and therefore 
``emission reductions from states linked at that higher threshold may 
be insufficient to address collective upwind state contribution to 
downwind air quality problems.''\31\
    Based on EPA's updated modeling and the LADCO modeling, the state 
is projected to contribute greater than both the 1 percent and 
alternative 1 ppb thresholds. While EPA does not, in this action, 
approve of the state's application of the 1 ppb threshold, based on its 
linkages greater than 1 ppb to projected downwind nonattainment or 
maintenance receptors, the state's use of this alternative threshold at 
Step 2 of the 4-Step interstate framework would not alter our review 
and proposed disapproval of this SIP submittal.

                        Table 6--Ohio Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023  Average   2023  Maximum       Ohio
         Receptor ID               Location       Nonattainment/   design value    design value    Contribution
                                (county, state)    maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
90099002.....................  New Haven, CT...  Nonattainment..            71.8            73.9            1.94
90019003.....................  Fairfield, CT...  Nonattainment..            76.1            76.4            1.90
420170012....................  Bucks, PA.......  Maintenance....            70.7            72.2            1.88
90013007.....................  Fairfield, CT...  Nonattainment..            74.2            75.1            1.87
170317002....................  Cook, IL........  Maintenance....            70.1            73.0            1.69
550590019....................  Kenosha, WI.....  Nonattainment..            72.8            73.7            1.67
550590025....................  Kenosha, WI.....  Maintenance....            69.2            72.3            1.33
170310032....................  Cook, IL........  Maintenance....            69.8            72.4            1.26
170314201....................  Cook, IL........  Maintenance....            69.9            73.4            1.23
170310076....................  Cook, IL........  Maintenance....            69.3            72.1            1.23
90010017.....................  Fairfield, CT...  Nonattainment..            73.0            73.7            1.18
551010020....................  Racine, WI......  Nonattainment..            71.3            73.2            1.00
170310001....................  Cook, IL........  Maintenance....            69.6            73.4            0.82
----------------------------------------------------------------------------------------------------------------

4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I). As explained in Section II.E, Ohio relied on a 
combination of both cost and air quality factors to determine that 
there were no further reductions necessary for Ohio to meet its 
obligations under the interstate transport provision. In this 
subsection, we have evaluated the information provided by the state at 
Step 3 to support this conclusion.
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the

[[Page 9872]]

obligations in CAA section 110(a)(2)(D)(i)(I) must prohibit ``any 
source or other type of emissions activity within the State'' from 
emitting air pollutants which will contribute significantly to downwind 
air quality problems. Thus, states must complete something similar to 
EPA's analysis (or an alternative approach to defining ``significance'' 
that comports with the statute's objectives) to determine whether and 
to what degree emissions from a state should be ``prohibited'' to 
eliminate emissions that will ``contribute significantly to 
nonattainment in, or interfere with maintenance of'' the NAAQS in any 
other state. OEPA did not conduct such an analysis in their SIP 
submission.
    OEPA's submission concluded that projected emissions were 
overestimated for the EGU, non-EGU, and onroad sectors. OEPA claimed 
that the ERTAC EGU tool's emissions inventories were overestimated for 
eight specific sources for various reasons, including adoption of rules 
in late 2016 and early 2017, CSAPR and CSAPR Update allocations, and 
substantive changes in plant operation. The submission also asserted 
that ERTAC EGU tool version 2.7 does not consider that future energy 
generation sources will likely be a steady level of coal with 
increasing natural gas and renewable fuels, citing an un-enumerated 
number of natural gas source permits issued by Ohio and projected 
trends identified in the US Energy Information Administration's Annual 
Energy Outlook (AEO) 2018.\100\ Similarly, the submission claimed 
projected emissions from EPA's Air Emissions Modeling Platform 2011v6.3 
were overestimated for nine non-EGU point sources, primarily based on 
actual emissions trends from 2010 to 2017. OEPA also claimed that EPA 
over projected onroad emissions using 2023 vehicle miles traveled 
(VMT). However, OEPA did not explain how accounting for changed 
projected emissions from those 17 sources or the onroad sector would 
have resulted in different outcomes with regards to the identification 
of downwind receptors or Ohio's contributions or linkages in the 2023 
analytic year. Furthermore, nationwide trends and an unspecified number 
of state permits are insufficient by themselves to support a conclusion 
that EGUs in Ohio would not be affected by generation shifting. EPA 
notes the information presented from the AEO is related to nationwide 
trends and OEPA did not explain what the nationwide trends revealed 
about Ohio's level of contribution or good neighbor obligations to 
downwind receptors. Merely claiming that the modeling used to project 
receptors and contributions relies on overestimated emissions 
projections without an explanation of how the inputs would affect the 
outcome is not enough to draw a conclusion at Step 2 that Ohio is not 
linked to any downwind receptor or a conclusion at Step 3 that Ohio 
does not contribute significantly or interfere with maintenance in any 
other state. Considered individually or in the context of the other 
information and arguments put forward by OEPA, select EGU, non-EGU, and 
onroad emissions evaluations and nation-wide projections of fuel types 
fail to show that additional emissions reductions are either not cost-
effective or permanent and federally enforceable. OEPA did not 
demonstrate that the downwind improvements from these regulations and 
programs would be sufficient to eliminate the state's significant 
contribution or interference with maintenance.
---------------------------------------------------------------------------

    \100\ See https://www.eia.gov/outlooks/archive/aeo18/, last 
accessed 1/18/2022.
---------------------------------------------------------------------------

    Further, EPA's assessment of future air quality conditions 
generally accounts for on-the-books emission reductions and the most 
up-to-date forecast of future emissions in the absence of the transport 
policy being evaluated (i.e., base case conditions).\101\ As described 
in more detail in Section I, EPA's latest projections of the baseline 
EGU emissions uses the version 6--Summer 2021 Reference Case of the 
IPM.\102\ The IPM version 6--Summer 2021 Reference Case uses the NEEDS 
v6 database as its source for data on all existing and planned-
committed units. Units are removed from the NEEDS inventory only if a 
high degree of certainty could be assigned to future implementation of 
the announced future closure or retirement. Any retirements excluded 
from the NEEDS v6 inventory can be viewed in the NEEDS 
spreadsheet.\103\ The inventory for these projections contains various 
Ohio EGUs including the Avon Lake Power Plant in Lorain County 
(Facility ID 0247030013), Painesville Municipal Electric Plant in Lake 
County (Facility ID 0243110008), and the Department of Public 
Utilities, City of Orrville in Wayne County (Facility ID 0285010188). 
Mingo Junction Energy Center in Jefferson County (Facility ID 
0641090234) and the Conesville Power Plant (Facility ID 0616000000) 
retired in 2020.
---------------------------------------------------------------------------

    \101\ See 81 FR 74504 at 74517; 85 FR 68964 at 68979.
    \102\ Detailed information and documentation of EPA's Base Case, 
including all the underlying assumptions, data sources, and 
architecture parameters can be found on EPA's website at: https://www.epa.gov/airmarkets/epas-power-sector-modeling-platform-v6-using-ipm-summer-2021-reference-case.
    \103\ The ``Capacity Dropped'' and the ``Retired Through 2023'' 
worksheets in NEEDS lists all units that are removed from the NEEDS 
v6 inventory--NEEDS v6 Summer 2021 Reference Case. This data can be 
found on EPA's website at: https://www.epa.gov/airmarkets/national-electric-energy-data-system-needs-v6.
---------------------------------------------------------------------------

    Also, EPA's non-EGU emissions inventory in the updated modeling 
using the 2016v2 emissions platform does not include either Carmeuse 
Lime Inc Millersville Operations (Facility ID 0372000081) or RockTenn 
CP, LLC (Facility ID 0616010001). EPA's latest modeling also uses 
emissions inventories that incorporate Ohio's submitted 2023 VMT 
data.\104\ In other words, in general, any changes in the emissions 
inventory and on-the-books controls relevant to emissions in 2023 have 
now been incorporated into EPA's modeling using the 2016v2 emissions 
platform, which projects a continuing contribution from Ohio to out of 
state receptors above a threshold of 1 percent of the NAAQS (at Steps 1 
and 2) despite these measures. Therefore, in light of continuing 
contribution to out of state receptors from Indiana notwithstanding 
these identified retirements, OEPA's SIP submission should have 
evaluated the availability of additional air quality controls to 
improve downwind air quality at nonattainment and maintenance receptors 
at Step 3.
---------------------------------------------------------------------------

    \104\ Technical Support Document (TSD) Preparation of Emissions 
Inventories for the 2016v2 North American Emissions Modeling 
Platform, section 4.3.2. Available in the Headquarters docket ID No. 
EPA-HQ-OAR-2021-0663.
---------------------------------------------------------------------------

    Ohio's projected contribution to downwind receptors in EPA's 
updated modeling is lower relative to the LADCO modeling results 
presented in OEPA's submission; it could be assumed that these 
decreases are due to overestimation of sources that were corrected in 
the updated modeling. These results could also be attributed to Federal 
programs in place (NOX RACT, AIM Coatings Rules, CSAPR, NOx 
SIP Call, NESHAPs, RHR, BART, SO2 Data Requirements rule, 
and MATS) as OEPA suggests. Regardless, despite the lessened projected 
contributions, Ohio's contributions continue to be projected to be 
above 1 percent of the NAAQS to one or more receptors in 2023 as shown 
in Table 6.
    OEPA's assessment of actual and projected NOX and VOC 
emissions trends and listing of various regulations likewise do not 
support a conclusion that existing controls in Ohio adequately address 
the state's good neighbor obligations for the 2015 ozone NAAQS. For 
one, OEPA listed numerous non-SIP measures and states may not rely on 
non-SIP measures to

[[Page 9873]]

meet SIP requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] 
shall . . . contain adequate provisions . . . .''). See also CAA 
section 110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 786 
F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on by 
state to meet CAA requirements must be included in the SIP). OEPA did 
not attempt to revise Ohio's SIP to include all these measures.\105\ In 
general, the listing of existing or on-the-way control measures, 
whether approved into the state's SIP or not, does not substitute for a 
complete Step 3 analysis under EPA's 4-step framework to define 
``significant contribution.'' OEPA's submittal does not include an 
assessment of the overall effects of these measures, when the 
reductions would be achieved, and what the overall resulting air 
quality effects would be observed at identified out-of-state receptors. 
The state's submission does not include an evaluation of additional 
potential emissions control opportunities, or their costs or impacts, 
or attempt to analyze whether, if applied more broadly across linked 
states, the emissions reductions would constitute the elimination of 
significant contribution on a regional scale. The state's submission 
did not contain an explanation as to whether any faster or more 
stringent emissions reductions that may be available were prohibitively 
costly or infeasible. Second, the information and claims presented by 
OEPA did not provide sufficient evidence to support alternative 
conclusions that EPA is proposing to make in this action: Namely, that 
several receptors exist, Ohio contributes to those receptors above a 1 
percent of the NAAQS contribution threshold, and that Ohio continues to 
have good neighbor obligations that need to be addressed for the 2015 
ozone NAAQS.
---------------------------------------------------------------------------

    \105\ EPA notes that OEPA submitted a source specific 
NOX emission limit contained in the Ohio NOX 
RACT Rules for approval into the Ohio SIP, approved by EPA on 
September 8, 2017 (82 FR 42451).
---------------------------------------------------------------------------

    OEPA also pointed to declining design values at the ten receptors 
identified by LADCO to support their conclusion that no further 
emissions reductions were required from Ohio to meet their interstate 
transport obligations. They additionally reference a May 14, 2018 EPA 
presentation, stating that EPA indicated remaining ozone air quality 
problems were becoming more local and less regional in nature. While it 
is true that since 2011, design values have generally declined, air 
quality problems at some locations are projected to continue out to 
2023 and beyond, based on EPA's 2018 modeling provided in the March 
2018 memorandum, LADCO's modeling completed in 2018, EPA's modeling 
results used in the Revised CSAPR Update, and EPA's updated modeling 
results. In addition, each of these modeling analyses show that Ohio 
will contribute to the air quality problems in excess of 1 percent of 
the 2015 ozone standards in 2023. Regarding the May 14, 2018 
presentation, EPA assumes the state is referencing a presentation given 
by an EPA air quality modeler, which Indiana attached to their SIP 
submission. The purpose of that presentation was to share a technical, 
exploratory analysis of ozone trends. The results of that presentation, 
which were labeled as ``preliminary'' indicated that ``[f]urther 
exploration of the relative contribution from various source sectors 
within the NE Corridor and in nearby upwind states might also be 
informative.'' \106\ The preliminary results of that analysis are 
generally consistent with EPA's updated modeling using the 2016v2 
emissions platform. Although EPA's modeling shows that a large portion 
of the transport problem affecting the receptors in Coastal Connecticut 
is indeed from sources within the Ozone Transport Region (OTR), a 
substantial portion of the transport problem at these receptors, on the 
order of 25 percent, is the result of transport from states outside the 
OTR. However, the relevance of that presentation to the evaluation of 
Ohio's good neighbor obligations is not clear. As already discussed, 
the statute and the case law (particularly the holdings in Wisconsin 
and Maryland) make clear that good neighbor obligations are not merely 
supplementary to or deferable until after local emission reductions are 
achieved. Further, based on EPA's modeling released with the March 2018 
memorandum, nearly all of the receptors to which Ohio is linked are 
also heavily impacted by distant upwind state emissions in addition to 
local sources and sources in neighboring states. The Wisconsin 
decision's holding in regard to international contribution (discussed 
in more detail later) is equally applicable to an upwind state's claims 
that some other state's emissions, or local emissions, are more to 
blame than its own emissions. See 938 F.3d 303 at 323-25 (``an upwind 
state can `contribute' to downwind nonattainment even if its emissions 
are not the but-for cause'').
---------------------------------------------------------------------------

    \106\ Indiana's SIP submission, Appendix E at 4, 17.
---------------------------------------------------------------------------

    OEPA also put forward an argument that onroad mobile sources in 
downwind states should be more stringently controlled before any 
additional sources in upwind states. This is equivalent to the claim 
that local emissions reductions from the jurisdiction where the 
downwind receptor is located must first be implemented and accounted 
for before imposing obligations on upwind states under the interstate 
transport provision. However, there is nothing in the CAA that supports 
that position, and it does not provide grounds on which to approve 
OEPA's SIP submission. The D.C. Circuit has held on five different 
occasions that the timing framework for addressing interstate transport 
obligations must be consistent with the downwind areas' attainment 
schedule. In particular, for the ozone NAAQS, the states and EPA are to 
address interstate transport obligations ``as expeditiously as 
practicable'' and no later than the attainment schedule set in 
accordance with CAA section 181(a). See North Carolina, 531 F.3d at 
911-13; Wisconsin, 938 F.3d at 313-20; Maryland, 958 F.3d at 1204; New 
York v. EPA, 964 F.3d 1214, 1226 (DC Cir. 2020); New York v. EPA, 781 
Fed. App'x 4, 6-7 (DC Cir. 2019). The court in Wisconsin explained that 
downwind jurisdictions often may need to heavily rely on emissions 
reductions from upwind states in order to achieve attainment of the 
NAAQS, 938 F.3d at 316-17; such states would face increased regulatory 
burdens including the risk of bumping up to a higher nonattainment 
classification if attainment is not reached by the relevant deadline, 
Maryland, 958 F.3d at 1204. The statutory framework of the CAA and 
these cases establish clearly that states and EPA must address 
interstate transport obligations in line with the attainment schedule 
provided in the Act in order to timely assist downwind states in 
attaining and maintain the NAAQS, and this schedule is ``central to the 
regulatory scheme.'' Wisconsin, 938 F.3d at 316 (quoting Sierra Club v. 
EPA, 294 F.3d 155, 161 (D.C. Cir. 2002)).
    As for the suggestion that EPA should assess the SAFE Vehicles 
Rule's impact on ozone before finalizing, EPA and the National Highway 
Traffic Safety Administration finalized the revisions to the greenhouse 
gas (GHG) and CAFE standards for light duty vehicles in 2020.\107\ 
However, that final action is not expected to have a meaningful impact 
on ozone-precursor emissions. Because the vehicles affected by the

[[Page 9874]]

2017-2025 GHG standards would still need to meet applicable criteria 
pollutant emissions standards (e.g., the Tier 3 emissions standards; 
see 79 FR 23414), the SAFE Vehicles Rule anticipated that any impacts 
of the SAFE Vehicles Rule on ozone precursor emissions ``would most 
likely be far too small to observe.'' See 85 FR 25041. On December 30, 
2021, EPA revised the GHG light duty standards for model years 2023 and 
later to make them more stringent.\108\ The impacts of the SAFE 
Vehicles Rule are included in the 2016v2 onroad emissions as described 
in the emissions modeling TSD in Section 4.3.2.\109\
---------------------------------------------------------------------------

    \107\ The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule 
for Model Years 2021-2026 Passenger Cars and Light Trucks, 85 FR 
24174 (April 30, 2020) (SAFE Vehicles Rule).
    \108\ Revised 2023 and Later Model Year Light-Duty Vehicle 
Greenhouse Gas Emissions Standards, 86 FR 74434 (December 30, 2021).
    \109\ See Technical Support Document (TSD) Preparation of 
Emissions Inventories for the 2016v2 North American Emissions 
Modeling Platform included in the Headquarters docket ID No. EPA-HQ-
OAR-2021-0663.
---------------------------------------------------------------------------

    Further, OEPA makes the argument that assigning all responsibility 
to Ohio and other upwind states for downwind air quality problems 
despite home state and international contributions would result in 
overcontrol of Ohio sources. OEPA's reasoning related to emissions in 
downwind states and international emissions is inapplicable to the 
requirements of CAA section 110(a)(2)(D)(i)(I). As an initial matter, 
CAA section 110(a)(2)(D)(i)(I) only requires that upwind states 
prohibit those emissions that ``contribute significantly to 
nonattainment'' or ``interfere with maintenance of the NAAQS.'' It does 
not require that the upwind states bear the full burden of bringing 
downwind states into attainment or that a threshold ppb improvement 
from upwind states emission reductions be met in order for them to be 
required (once the 1 percent threshold has been satisfied). However, 
the good neighbor provision does require states and EPA to address 
interstate transport of air pollution that contributes to downwind 
states' ability to attain and maintain NAAQS. Whether emissions from 
other states or other countries also contribute to the same downwind 
air quality issue is irrelevant in assessing whether a downwind state 
has an air quality problem, or whether an upwind state is significantly 
contributing to that problem. States are not obligated under CAA 
section 110(a)(2)(D)(i)(I) to reduce emissions sufficient on their own 
to resolve downwind receptors' nonattainment or maintenance problems. 
Rather, states are obligated to eliminate their own ``significant 
contribution'' or ``interference'' with the ability of other states to 
attain or maintain the NAAQS.
    Indeed, after OEPA submitted Ohio's SIP submission, the D.C. 
Circuit in Wisconsin specifically rejected petitioner arguments 
suggesting that upwind states should be excused from good neighbor 
obligations on the basis that some other source of emissions (whether 
international or another upwind state) could be considered the ``but-
for'' cause of downwind air quality problem. 938 F.3d 303 at 323-324. 
The court viewed petitioners' arguments as essentially an argument 
``that an upwind state `contributes significantly' to downwind 
nonattainment only when its emissions are the sole cause of downwind 
nonattainment.'' 938 F.3d 303 at 324. The court explained that ``an 
upwind state can `contribute' to downwind nonattainment even if its 
emissions are not the but-for cause.'' Id. at 324-325. See also Catawba 
County v. EPA, 571 F.3d 20, 39 (D.C. Cir. 2009) (rejecting the argument 
``that `significantly contribute' unambiguously means `strictly 
cause''' because there is ``no reason why the statute precludes EPA 
from determining that [an] addition of [pollutant] into the atmosphere 
is significant even though a nearby county's nonattainment problem 
would still persist in its absence''); Miss. Comm'n on Envtl. Quality 
v. EPA, 790 F.3d 138, 163 n.12 (D.C. Cir. 2015) (observing that the 
argument that ``there likely would have been no violation at all . . . 
if it were not for the emissions resulting from [another source]'' is 
``merely a rephrasing of the but-for causation rule that we rejected in 
Catawba County.''). Therefore, a state is not excused from eliminating 
its significant contribution on the basis that international emissions, 
or emissions from other sources, also contribute some amount of 
pollution to the same receptors to which the state is linked.
    Finally, as part of its cost-effectiveness evaluation, OEPA relied 
on its EGUs being subject to the CSAPR Update (which reflected a 
stringency at the nominal marginal cost threshold of $1400/ton (2011$) 
for the 2008 8-hour ozone NAAQS) to argue that it has already 
implemented all cost-effective emissions reductions. For non-EGUs, OEPA 
did not identify a cost-effectiveness threshold, but rather listed a 
few regulations (the Boiler MACT and other MACT categories, BART, 
SO2 Data Requirements Rule and other unidentified Federal 
regulations) to draw the conclusion that emissions reductions had been 
achieved from non-EGUs in Ohio. First, the CSAPR Update did not 
regulate non-electric generating units, and thus this analysis is 
incomplete. See Wisconsin, 938 F.3d at 318-20. Second, relying on the 
CSAPR Update's (or any other CAA program's) determination of cost-
effectiveness without further Step 3 analysis is not approvable. Cost-
effectiveness must be assessed in the context of the specific CAA 
program; assessing cost-effectiveness in the context of ozone transport 
should reflect a more comprehensive evaluation of the nature of the 
interstate transport problem, the total emissions reductions available 
at several cost thresholds, and the air quality impacts of the 
reductions at downwind receptors. While EPA has not established a 
benchmark cost-effectiveness value for 2015 ozone NAAQS interstate 
transport obligations, because the 2015 ozone NAAQS is a more stringent 
and more protective air quality standard, it is reasonable to expect 
control measures or strategies to address interstate transport under 
this NAAQS to reflect higher marginal control costs. As such, the 
marginal cost threshold of $1,400/ton for the CSAPR Update (which 
addresses the 2008 ozone NAAQS and is in 2011$) is not an appropriate 
cost threshold and cannot be approved as a benchmark to use for 
interstate transport SIP submissions for the 2015 ozone NAAQS. The lack 
of a sufficient cost-effectiveness evaluation also means that Ohio's 
claims that requiring additional emissions reductions would result in 
overcontrol is premature. Ohio's submission does present sufficient 
evidence to support that conclusion.
    In addition, the updated EPA modeling captures all existing CSAPR 
trading programs in the baseline, and that modeling confirms that these 
control programs were not sufficient to eliminate Ohio's linkage at 
Steps 1 and 2 under the 2015 ozone NAAQS. The state was therefore 
obligated at Step 3 to assess additional control measures using a 
multifactor analysis.
    Finally, relying on a FIP at Step 3 is per se not approvable if the 
state has not adopted that program into its SIP and instead continues 
to rely on the FIP. States may not rely on non-SIP measures to meet SIP 
requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] shall . . 
. contain adequate provisions . . . .''). See also CAA section 
110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 786 F.3d 
1169, 1175-76 (9th Cir. 2015) (holding that measures relied on by state 
to meet CAA requirements must be included in the SIP). We therefore 
propose that Ohio was required to analyze emissions from the sources 
and other emissions activity from within the state to determine whether 
its contributions were

[[Page 9875]]

significant, and we propose to disapprove its submission because Ohio 
failed to do so.
5. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-step interstate transport framework calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. OEPA identified 
NOX RACT rules limiting NOX emissions from new 
and existing sources, VOC reduction measures through control of 
architectural and industrial maintenance coatings, and reallocation of 
funds received through a settlement with Volkswagen to be applied to 
on-road and off-road mobile emissions reductions through replacements 
and infrastructure updates.\110\ However, OEPA did not revise Ohio's 
SIP to include these emission reductions in a revision to its SIP to 
ensure the reductions were permanent and enforceable.\105\ As a result, 
EPA proposes to disapprove OEPA submittal on the separate, additional 
basis that the Ohio has not included permanent and enforceable 
emissions reductions in its SIP as necessary to meet the obligations of 
CAA section 110(a)(2)(d)(i)(I).
---------------------------------------------------------------------------

    \110\ Pointing to anticipated upcoming emission reductions, even 
if they were not included in the analysis at Steps 1 and 2, is not 
sufficient as a Step 3 analysis, for the reasons discussed in 
Section [Ohio step 3 analysis section]. In this section, we explain 
that to the extent such anticipated reductions are not included in 
the SIP and rendered permanent and enforceable, reliance on such 
anticipated reductions is also insufficient at Step 4.
---------------------------------------------------------------------------

6. Conclusion
    Based on EPA's evaluation of Ohio's SIP submission, EPA is 
proposing to find that the portion of Ohio's September 28, 2018 SIP 
submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet the 
state's interstate transport obligations for the 2015 ozone NAAQS, 
because it fails to contain the necessary provisions to eliminate 
emissions that will contribute significantly to nonattainment or 
interfere with maintenance of the 2015 ozone NAAQS in any other state.

F. Wisconsin

1. Evaluation of Information Provided by Wisconsin Regarding Steps 1 
and 2
    WDNR did not perform an analysis under the 4-step framework to 
assess Wisconsin's good neighbor obligations. The submission did not 
identify areas in other states that may have trouble attaining or 
maintaining the 2015 ozone NAAQS. Nor did WDNR perform a Step 2 
analysis to identify Wisconsin's contribution to areas that are 
projected to have difficulty attaining or maintaining the NAAQS or 
reach a conclusion about whether Wisconsin is linked to any receptors.
2. Results of EPA's Step 1 and Step 2 Modeling and Findings for 
Wisconsin
    As described in Section I, EPA performed air quality modeling using 
the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
Wisconsin contributes at or above the threshold of one percent of the 
2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or 
maintenance receptor. As shown in Table 7, the data \111\ indicate that 
in 2023, emissions from Wisconsin contribute greater than one percent 
of the standard to nonattainment or maintenance-only receptors in 
Illinois.\112\ Therefore, based on EPA's evaluation of the information 
submitted by WDNR, and based on EPA's most recent modeling results for 
2023, EPA proposes to find that Wisconsin is linked at Steps 1 and 2 
and has an obligation to assess potential emissions reductions from 
sources or other emissions activity at Step 3 of the 4-step framework.
---------------------------------------------------------------------------

    \111\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file 
``2016v2_DVs_state_contributions.xlsx'' which is included in docket 
ID No. EPA-HQ-OAR-2021-0663.
    \112\ These modeling results are consistent with the results of 
a prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I. That modeling showed 
that Wisconsin had a maximum contribution greater than 0.70 ppb to 
at least one nonattainment or maintenance-only receptor in 2023. 
These modeling results are included in the file ``Ozone Design 
Values And Contributions Revised CSAPR Update.xlsx'' in docket ID 
No. EPA-HQ-OAR-2021-0663.

                      Table 7--Wisconsin Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023  Average   2023  Maximum     Wisconsin
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                (county, state)    maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
170310032....................  Cook, IL........  Maintenance....            69.8            72.4            2.61
170314201....................  Cook, IL........  Maintenance....            69.9            73.4            2.55
170310076....................  Cook, IL........  Maintenance....            69.3            72.1            2.47
170310001....................  Cook, IL........  Maintenance....            69.6            73.4            2.41
170317002....................  Cook, IL........  Maintenance....            70.1            73.0            1.47
----------------------------------------------------------------------------------------------------------------

    As shown in Table 7, the updated EPA modeling identifies 
Wisconsin's maximum contribution Because the entire technical basis for 
the state's submittal is that the state has satisfied good neighbor 
obligations through implementation of various rules, including CSAPR 
Update, EPA proposes to disapprove the SIP submission based on EPA's 
finding that WDNR has not provided adequate information to allow EPA to 
assess whether Wisconsin has adequate provisions to prohibit emissions 
in amounts which will contribute significantly to nonattainment or 
interfere with maintenance in any other state. Though this deficiency 
would be sufficient on its own to disapprove Wisconsin's good neighbor 
submission, EPA will proceed to evaluate the additional points raised 
by WDNR at Step 3 of the 4-step interstate transport framework.
3. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-step interstate transport framework, a state's 
emissions are further evaluated, in light of multiple factors, 
including air quality and cost considerations, to determine what, if 
any, emissions significantly contribute to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).

[[Page 9876]]

    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. EPA has consistently applied this general approach (i.e., 
Step 3 of the 4-step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While EPA has not directed states that 
they must conduct a Step 3 analysis in precisely the manner EPA has 
done in its prior regional transport rulemakings, state implementation 
plans addressing the obligations in CAA section 110(a)(2)(D)(i)(I) must 
prohibit ``any source or other type of emissions activity within the 
state'' from emitting air pollutants which will contribute 
significantly to downwind air quality problems. Thus, states must 
complete something similar to EPA's analysis (or an alternative 
approach to defining ``significance'' that comports with the statute's 
objectives) to determine whether and to what degree emissions from a 
state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment in, or interfere with 
maintenance of'' the NAAQS in any other state. The state did not 
conduct such an analysis in their SIP submission.
    WDNR listed several rules relevant to interstate transport and 
seemingly relied on its participation in LADCO to suggest sources in 
Wisconsin are adequately controlled for purposes of the good neighbor 
provision for the 2015 ozone NAAQS. WDNR mentioned Wisconsin's FIPs 
under CSAPR and CSAPR Update. EPA disagrees that this is a sufficient 
approach for assessing good neighbor obligations.
    First, the CSAPR Update did not regulate non-electric generating 
units, and thus this analysis is incomplete. See Wisconsin, 938 F.3d at 
318-20. Second, relying on the CSAPR Update (or any other CAA program) 
without further Step 3 analysis is not approvable. While EPA has not 
established a benchmark cost-effectiveness value for 2015 ozone NAAQS 
interstate transport obligations, because the 2015 ozone NAAQS is a 
more stringent and more protective air quality standard, it is 
reasonable to expect control measures or strategies to address 
interstate transport under this NAAQS to reflect higher marginal 
control costs. As such, the CSAPR Update Rule is not an appropriate 
analysis and cannot be approved to satisfy interstate transport 
obligations for the 2015 ozone NAAQS.
    In addition, the updated EPA modeling captures all existing CSAPR 
trading programs in the baseline, and that modeling confirms that these 
control programs were not sufficient to eliminate the Wisconsin's 
linkage at Steps 1 and 2 under the 2015 ozone NAAQS. The state was 
therefore obligated at Step 3 to assess additional control measures 
using a multifactor analysis.
    Finally, relying on a FIP at Step 3 is per se not approvable if the 
state has not adopted that program into its SIP and instead continues 
to rely on the FIP. States may not rely on non-SIP measures to meet SIP 
requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] shall . . 
. contain adequate provisions . . . .''). See also CAA section 
110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 786 F.3d 
1169, 1175-76 (9th Cir. 2015) (holding that measures relied on by state 
to meet CAA requirements must be included in the SIP).
    WDNR cited continued consultation with LADCO, three Wis. Admin. 
Code subsections that could be relied on ``if needed'' to address 
disagreements for SIP development in other states' nonattainment areas, 
and an adequate PSD program. WDNR did not attempt to revise Wisconsin's 
SIP to include to include all these measures. In general, the listing 
of existing or on-the-way control measures, including potential future 
emissions reductions obtained through participation in LADCO, whether 
approved into the state's SIP or not, does not substitute for a 
complete Step 3 analysis under EPA's 4-step framework to define 
``significant contribution.'' WDNR did not identify control measures, 
provide an assessment of the overall effects of these measures, note 
when the reductions would be achieved, or explain what the overall 
resulting air quality effects would be at identified out of state 
receptors. WDNR did not evaluate additional, potential emissions 
control opportunities, or their costs or impacts, or attempt to analyze 
whether, if applied more broadly across linked states, the emissions 
reductions would constitute the elimination of significant contribution 
on a regional scale. WDNR did not offer an explanation as to whether 
any faster or more stringent emissions reductions that may be available 
were prohibitively costly or infeasible. Although EPA acknowledges 
states are not necessarily bound to follow its own analytical framework 
at Step 3, WDNR did not attempt to determine or justify an appropriate 
uniform cost-effectiveness threshold. This would have been similar to 
the approach to defining significant contribution that EPA has applied 
in prior rulemakings such as CSAPR and or the CSAPR Update, even if 
such an analysis is not technically mandatory.
    As mentioned previously, Wis. Admin. Code NR 285.15, entitled 
Interstate Agreement, gives the governor the authority to enter an 
agreement to solve interstate pollution transport with Illinois, 
Indiana, and Michigan if the area includes portions of both Wisconsin 
and Illinois. Furthermore, Wis. Admin. Code, NR 285.1560 does not 
provide for emission reductions toward resolving good neighbor 
obligations, as while the statute allows for consultation, there is no 
indication this rule has been exercised to resolve good neighbor 
obligations or explain how the rule would impact areas in Illinois to 
which Wisconsin is linked. Under the Wisconsin decision, states and EPA 
may not delay implementation of measures necessary to address good 
neighbor requirements beyond the next applicable attainment date 
without a showing of impossibility or necessity. See 938 F.3d at 320. 
Wisconsin's submittal is insufficient to the extent the implementation 
timeframes for the cited control measures were left unidentified, 
unexplained, or too uncertain to permit EPA to form a judgment as to 
whether the timing requirements for good neighbor obligations have been 
met.
    We therefore propose that Wisconsin was required to analyze 
emissions from the sources and other emissions activity from within the 
state to determine whether its contributions were significant, and we 
propose to disapprove its submission because Wisconsin failed to do so.
4. Evaluation of Information Provided Regarding Step 4
    Step 4 of the 4-step interstate transport framework calls for 
development of permanent and federally enforceable control strategies 
to achieve the emissions reductions determined to be necessary at Step 
3 to eliminate significant contribution to nonattainment or 
interference with maintenance of the NAAQS. As mentioned previously, 
Wisconsin's SIP submission did not contain an evaluation of additional 
emission

[[Page 9877]]

control opportunities (or establish that no additional controls are 
required), thus, no information was provided at Step 4. As a result, 
EPA proposes to disapprove Wisconsin' submittal on the separate, 
additional basis that the state has not developed permanent and 
enforceable emissions reductions necessary to meet the obligations of 
CAA section 110(a)(2)(d)(i)(I).
5. Conclusion
    Based on EPA's evaluation of Wisconsin's SIP submission, EPA is 
proposing to find that the portion of Wisconsin's September 14, 2018 
SIP submission addressing CAA section 110(a)(2)(D)(i)(I) does not meet 
Wisconsin's interstate transport obligations, because it fails to 
contain the necessary provisions to eliminate emissions that will 
contribute significantly to nonattainment or interfere with maintenance 
of the 2015 ozone NAAQS in any other state.

IV. Proposed Action

    We are proposing to disapprove the portions of Illinois, Indiana, 
Michigan, Minnesota, Ohio, and Wisconsin's SIP submissions pertaining 
to interstate transport of air pollution which will significantly 
contribute to nonattainment or interfere with maintenance of the 2015 
ozone NAAQS in other states. Under CAA section 110(c)(1), disapproval 
would establish a 2-year deadline for EPA to promulgate a FIP for 
states to address the CAA section 110(a)(2)(D)(i)(I) interstate 
transport requirements pertaining to significant contribution to 
nonattainment and interference with maintenance of the 2015 ozone NAAQS 
in other states, unless EPA approves a SIP that meets these 
requirements. Disapproval does not start a mandatory sanctions clock 
for Illinois, Indiana, Michigan, Minnesota, Ohio, or Wisconsin. The 
remaining elements of the states' submissions are not addressed in this 
action and either have been or will be acted on in a separate 
rulemaking.

V. Statutory and Executive Order Reviews

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

    This action is not a significant regulatory action and was 
therefore not submitted to the Office of Management and Budget for 
review.

B. Paperwork Reduction Act (PRA)

    This proposed action does not impose an information collection 
burden under the PRA because it does not contain any information 
collection activities.

C. Regulatory Flexibility Act (RFA)

    I certify that this action will not have a significant economic 
impact on a substantial number of small entities under the RFA. This 
action merely proposes to disapprove a SIP submission as not meeting 
the CAA.

D. Unfunded Mandates Reform Act (UMRA)

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

E. Executive Order 13132: Federalism

    This action does not have federalism implications. 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.

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

    This action does not have tribal implications as specified in 
Executive Order 13175. This action does not apply on any Indian 
reservation land, any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction, or non-reservation areas of 
Indian country. Thus, Executive Order 13175 does not apply to this 
action.

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

    EPA interprets Executive Order 13045 as applying only to those 
regulatory actions that concern environmental health or safety risks 
that EPA has reason to believe may disproportionately affect children, 
per the definition of ``covered regulatory action'' in section 2-202 of 
the Executive Order. This action is not subject to Executive Order 
13045 because it merely proposes to disapprove a SIP submission as not 
meeting the CAA.

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

    This action is not subject to Executive Order 13211, because it is 
not a significant regulatory action under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

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

    EPA believes the human health or environmental risk addressed by 
this action will not have potential disproportionately high and adverse 
human health or environmental effects on minority, low-income or 
indigenous populations. This action merely proposes to disapprove a SIP 
submission as not meeting the CAA.

K. CAA Section 307(b)(1)

    Section 307(b)(1) of the CAA governs judicial review of final 
actions by EPA. This section provides, in part, that petitions for 
review must be filed in the D.C. Circuit: (i) When the agency action 
consists of ``nationally applicable regulations promulgated, or final 
actions taken, by the Administrator,'' or (ii) when such action is 
locally or regionally applicable, if ``such action is based on a 
determination of nationwide scope or effect and if in taking such 
action the Administrator finds and publishes that such action is based 
on such a determination.'' For locally or regionally applicable final 
actions, the CAA reserves to EPA complete discretion whether to invoke 
the exception in (ii).\113\
---------------------------------------------------------------------------

    \113\ In deciding whether to invoke the exception by making and 
publishing a finding that an action is based on a determination of 
nationwide scope or effect, the Administrator takes into account a 
number of policy considerations, including his judgment balancing 
the benefit of obtaining the D.C. Circuit's authoritative 
centralized review versus allowing development of the issue in other 
contexts and the best use of agency resources.
---------------------------------------------------------------------------

    EPA anticipates that this proposed rulemaking, if finalized, would 
be ``nationally applicable'' within the meaning of CAA section 
307(b)(1) because it would take final action on SIP submittals for the 
2015 ozone NAAQS for six states, which are located in three different 
Federal judicial circuits. It would apply uniform, nationwide 
analytical methods, policy judgments, and interpretation with respect 
to the same CAA obligations, i.e., implementation of good neighbor 
requirements under CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone 
NAAQS for states across the country, and final action would be based on 
this common core of determinations, described in further detail below.
    If EPA takes final action on this proposed rulemaking, in the 
alternative,

[[Page 9878]]

the Administrator intends to exercise the complete discretion afforded 
to him under the CAA to make and publish a finding that the final 
action (to the extent a court finds the action to be locally or 
regionally applicable) is based on a determination of ``nationwide 
scope or effect'' within the meaning of CAA section 307(b)(1). Through 
this rulemaking action (in conjunction with a series of related actions 
on other SIP submissions for the same CAA obligations), EPA interprets 
and applies section 110(a)(2)(d)(i)(I) of the CAA for the 2015 ozone 
NAAQS based on a common core of nationwide policy judgments and 
technical analysis concerning the interstate transport of pollutants 
throughout the continental U.S. In particular, EPA is applying here 
(and in other proposed actions related to the same obligations) the 
same, nationally consistent 4-step framework for assessing good 
neighbor obligations for the 2015 ozone NAAQS. EPA relies on a single 
set of updated, 2016-base year photochemical grid modeling results of 
the year 2023 as the primary basis for its assessment of air quality 
conditions and contributions at steps 1 and 2 of that framework. 
Further, EPA proposes to determine and apply a set of nationally 
consistent policy judgments to apply the 4-step framework. EPA has 
selected a nationally uniform analytic year (2023) for this analysis 
and is applying a nationally uniform approach to nonattainment and 
maintenance receptors and a nationally uniform approach to contribution 
threshold analysis.\114\ For these reasons, the Administrator intends, 
if this proposed action is finalized, to exercise the complete 
discretion afforded to him under the CAA to make and publish a finding 
that this action is based on one or more determinations of nationwide 
scope or effect for purposes of CAA section 307(b)(1).\115\
---------------------------------------------------------------------------

    \114\ A finding of nationwide scope or effect is also 
appropriate for actions that cover states in multiple judicial 
circuits. In the report on the 1977 Amendments that revised section 
307(b)(1) of the CAA, Congress noted that the Administrator's 
determination that the ``nationwide scope or effect'' exception 
applies would be appropriate for any action that has a scope or 
effect beyond a single judicial circuit. See H.R. Rep. No. 95-294 at 
323, 324, reprinted in 1977 U.S.C.C.A.N. 1402-03.
    \115\ EPA may take a consolidated, single final action on all of 
the proposed SIP disapproval actions with respect to obligations 
under CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS. 
Should EPA take a single final action on all such disapprovals, this 
action would be nationally applicable, and EPA would also 
anticipate, in the alternative, making and publishing a finding that 
such final action is based on a determination of nationwide scope or 
effect.
---------------------------------------------------------------------------

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Ozone.

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

    Dated: January 31, 2022.
Debra Shore,
Regional Administrator, Region 5.
[FR Doc. 2022-02953 Filed 2-18-22; 8:45 am]
BILLING CODE 6560-50-P


