Document ID: EPA-R08-OAR-2023-0375-0001
Agency: epa
Document Type: Proposed Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: Wyoming; Interstate Transport of Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality Standards
Posted Date: 2023-08-14T04:00Z

[Federal Register Volume 88, Number 155 (Monday, August 14, 2023)]
[Proposed Rules]
[Pages 54998-55006]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2023-16441]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2023-0375; EPA-HQ-OAR-2021-0663; FRL-11233-01-R8]

Air Plan Approval; Wyoming; Interstate Transport of Air Pollution 
for the 2015 8-Hour Ozone National Ambient Air Quality Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule and withdrawal of proposed rule.

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SUMMARY: Pursuant to the Federal Clean Air Act (CAA or the Act), the 
Environmental Protection Agency (EPA) is proposing to approve the 
portion of a Wyoming State Implementation Plan (SIP) submission 
addressing interstate transport for the 2015 8-hour ozone national 
ambient air quality standards (NAAQS). EPA is also withdrawing our 
prior May 24, 2022 proposed disapproval of the interstate transport 
portion of the Wyoming SIP submission. 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.

DATES: Written comments must be received on or before September 13, 
2023. As of August 14, 2023, the proposed rule published on May 24, 
2022, at 87 FR 31495, is withdrawn.

ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R08-
OAR-2023-0375, to the Federal Rulemaking Portal: https://www.regulations.gov. Follow the online instructions for submitting 
comments. Once submitted, comments cannot be edited or removed from 
www.regulations.gov. EPA may publish any comment received to its public 
docket. Do not submit electronically any information you consider to be 
Confidential Business Information (CBI) or other information whose 
disclosure is

[[Page 54999]]

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). For additional submission 
methods, the full EPA public comment policy, information about CBI or 
multimedia submissions, and general guidance on making effective 
comments, please visit https://www2.epa.gov/dockets/commenting-epa-dockets.
    Docket: There are two dockets supporting this action, EPA-R08-OAR-
2023-0375 and EPA-HQ-OAR-2021-0663. Docket No. EPA-R08-OAR-2023-0375 
contains information specific to Wyoming, 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 8-hour 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-R08-OAR-2023-0375. All documents in the docket are listed in the 
www.regulations.gov index. Although listed in the index, some 
information is not publicly available, e.g., CBI or other information 
whose disclosure is restricted by statute. Certain other material, such 
as copyrighted material, will be publicly available only in hard copy. 
Publicly available docket materials are available electronically in 
www.regulations.gov.

FOR FURTHER INFORMATION CONTACT: Adam Clark, Air and Radiation 
Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, 
Colorado 80202-1129, telephone number: (303) 312-7104, email address: 
[email protected].

SUPPLEMENTARY INFORMATION: Throughout this document whenever ``we,'' 
``us,'' or ``our'' is used, we mean EPA.

Table of Contents

I. Background
    A. Description of Statutory Background
    B. Description of EPA's 4-Step Interstate Transport Regulatory 
Process
    C. Background on EPA's Ozone Transport Modeling Information
    D. EPA's Approach to Evaluating Interstate Transport SIPs for 
the 2015 Ozone NAAQS
    1. Selection of Analytic Year
    2. Step 1 of the 4-Step Interstate Transport Framework
    3. Step 2 of the 4-Step Interstate Transport Framework
    4. Step 3 of the 4-Step Interstate Transport Framework
    5. Step 4 of the 4-Step Interstate Transport Framework
II. Wyoming SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone NAAQS
    A. Summary of Wyoming's 2015 Ozone Interstate Transport SIP 
Submission
    B. Prior Notices Related to Wyoming's SIP Submission
III. EPA's Evaluation
IV. Proposed Action
V. Statutory and Executive Order Reviews

I. Background

A. Description of Statutory Background

    On October 1, 2015, EPA promulgated a revision to the ozone NAAQS 
(2015 8-hour ozone NAAQS), lowering the level of both the primary and 
secondary standards to 0.070 parts per million (ppm) for the 8-hour 
standard.\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 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\
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    \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).
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B. Description of EPA's 4-Step Interstate Transport Regulatory Process

    EPA is using the 4-step interstate transport framework (or 4-step 
framework) to evaluate Wyoming's January 3, 2019 SIP submission 
addressing interstate transport 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 NAAQS in several 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\ the 
Cross-State Air Pollution Rule Update (CSAPR Update) \5\ and the 
Revised Cross-State Air Pollution Rule Update (Revised CSAPR 
Update),\6\ both of which addressed the 2008 ozone NAAQS.\7\
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    \4\ 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\ Revised Cross-State Air Pollution Rule Update for the 2008 
Ozone NAAQS, 86 FR 23054 (April 30, 2021).
    \7\ 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). The 
Revised CSAPR Update was upheld in Midwest Ozone Group v. EPA, 61 
F.4th 187 (D.C. Cir. 2023).
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    Shaped through the years by input from state air agencies \8\ and 
other stakeholders on EPA's prior interstate transport rulemakings and 
SIP actions,\9\ as well as a number of court decisions, EPA has 
developed and used 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

[[Page 55000]]

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.
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    \8\ See 63 FR 57356, 57361 (October 27, 1998).
    \9\ In addition to 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).
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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 at Step 1. To 
quantify the contribution of emissions from individual upwind states on 
2023 ozone design values for the identified downwind nonattainment and 
maintenance receptors at Step 2, EPA has performed multiple iterations 
of nationwide, state-level ozone source apportionment modeling for 
2023. The source apportionment modeling projected 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 air agencies 
for evaluation of interstate transport with respect to the 2015 ozone 
NAAQS. First, on January 6, 2017, EPA published a notice of data 
availability (NODA) in which the Agency requested comment on 
preliminary interstate ozone transport data including projected ozone 
design values and interstate contributions for 2023 using a 2011 base 
year platform.\10\ In the NODA, EPA used the year 2023 as the analytic 
year for this preliminary modeling because this year aligns with the 
expected attainment year for Moderate ozone nonattainment areas for the 
2015 8-hour ozone NAAQS.\11\ On October 27, 2017, EPA released a 
memorandum (October 2017 memorandum) containing updated modeling data 
for 2023, which incorporated changes made in response to comments on 
the NODA, and was intended to provide information to assist states' 
efforts to develop SIP submissions to address interstate transport 
obligations for the 2008 ozone NAAQS.\12\ On March 27, 2018, EPA 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.\13\ 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 8-hour ozone NAAQS under Step 2 of the 4-step interstate 
transport framework.\14\ EPA notes that the State of Wyoming relied 
upon 2023 modeling contribution data released with the March 2018 
memorandum in developing its 2019 SIP submission. 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, 
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.\15\
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    \10\ See Notice of Availability of the Environmental Protection 
Agency's Preliminary Interstate Ozone Transport Modeling Data for 
the 2015 8-hour Ozone National Ambient Air Quality Standard (NAAQS), 
82 FR 1733 (January 6, 2017).
    \11\ 82 FR 1735.
    \12\ 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 ID No. 
EPA-HQ-OAR-2021-0663.
    \13\ 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 (``March 2018 memorandum''), 
available in docket ID No. EPA-HQ-OAR-2021-0663.
    \14\ 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.''
    \15\ 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 ID No. 
EPA-HQ-OAR-2021-0663.
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    Following the release of the modeling data shared in the March 2018 
memorandum, EPA performed updated 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.\16\ 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.\17\ Although the Revised CSAPR Update 
addressed transport for the 2008 ozone NAAQS, the projected design 
values and contributions from the 2016v1 platform were also useful for 
identifying downwind ozone problems and linkages with respect to the 
2015 ozone NAAQS.\18\
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    \16\ The results of this modeling, as well as the underlying 
modeling files, are included in docket ID No. EPA-HQ-OAR-2021-0663. 
The 2016v1 emissions modeling technical support document is 
available in Docket ID No. EPA-HQ-OAR-2020-0272-0187. Both dockets 
are available at https://www.regulations.gov.
    \17\ See 85 FR 68964, 68981.
    \18\ 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.
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    Following the final Revised CSAPR Update, EPA made further updates 
to the 2016-based emissions platform to include updated onroad mobile 
emissions from Version 3 of EPA's Motor Vehicle Emission Simulator 
(MOVES) model (MOVES3) \19\ and updated emissions projections for 
electric generating units (EGUs) that reflected the emissions 
reductions from the Revised CSAPR Update, recent information on plant 
closures, and other inventory improvements. EPA published these 
emissions inventories on its website in September of 2021 and invited 
initial feedback from states and other interested stakeholders.\20\ The 
construct of the updated emissions platform, 2016v2, is described in 
the

[[Page 55001]]

``Technical Support Document (TSD): Preparation of Emissions 
Inventories for the 2016v2 North American Emissions Modeling 
Platform,'' hereafter known as the 2016v2 Emissions Modeling TSD, and 
is included in Docket No. EPA-HQ-OAR-2021-0663. The EPA performed air 
quality modeling using the 2016v2 emissions to provide projections of 
ozone design values and contributions in 2023 and 2026 that reflect the 
effects on air quality of the 2016v2 emissions platform. EPA used the 
results of the 2016v2 modeling as part of our previous proposed 
evaluation of the Wyoming 2019 SIP submission with respect to Steps 1 
and 2 of the 4-step interstate transport framework. See 87 FR 31495 
(May 24, 2022).
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    \19\ 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.
    \20\ https://www.epa.gov/air-emissions-modeling/2016v2-platform.
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    EPA invited and received comments on the 2016v2 emissions 
inventories and modeling used to support proposals, including the 
proposal on Wyoming, related to interstate transport under the 2015 
ozone NAAQS. In response to these comments, EPA made a number of 
updates to the 2016v2 inventories and model design to construct a 
2016v3 emissions platform which was used to update the air quality 
modeling. EPA used this updated modeling to inform a final rulemaking 
taking final action on 21 interstate transport SIP submissions for the 
2015 ozone NAAQS, which did not include Wyoming.\21\ Details on the 
2016v3 air quality modeling and the methods for projecting design 
values and determining contributions in 2023 and 2026 are described in 
the TSD titled ``Air Quality Modeling Final Rule TSD--2015 Ozone NAAQS 
Good Neighbor Plan,'' hereafter known as the Final Good Neighbor Plan 
AQM TSD.\22\ Additional details related to the updated 2016v3 emissions 
platform are located in the TSD titled ``Preparation of Emissions 
Inventories for the 2016v3 North American Emissions Modeling 
Platform,'' hereafter known as the 2016v3 Emissions Modeling TSD, 
included in Docket ID No. EPA-HQ-OAR-2021-0663.\23\
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    \21\ ``Air Plan Disapprovals; Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone National Ambient Air Quality 
Standards,'' 88 FR 9336 (February 13, 2023), and ``Federal ``Good 
Neighbor Plan'' for the 2015 Ozone National Ambient Air Quality 
Standards,'' 88 FR 36654 (June 5, 2023).
    \22\ Air Quality Modeling Final Rule Technical Support 
Document--2015 Ozone NAAQS Good Neighbor Plan in Docket ID No. EPA-
R08-OAR-2023-0375.
    \23\ 2016v3 Emissions Modeling TSD in Docket ID No. EPA-HQ-OAR-
2021-0663.
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    In this proposed action, EPA primarily relies on modeling based on 
the updated 2016v3 emissions platform in evaluating Wyoming's 2019 
submission with respect to Steps 1 and 2 of the 4-step interstate 
transport framework, which will generally be referenced within this 
action as the ``2016v3 modeling'' for 2023 and 2026. By using the 
updated modeling results, EPA is using the most current and technically 
appropriate information for this proposed rulemaking. In this proposed 
action, EPA is accepting public comment on the 2016v3 modeling solely 
as it relates to Wyoming's interstate transport obligations for the 
2015 ozone NAAQS. EPA is not reopening the modeling in relation to any 
other state or regulatory action. Any comments received on the modeling 
that are not relevant to the evaluation of Wyoming's interstate-
transport obligations will be treated as beyond the scope of this 
action.

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 submissions for the 
2015 ozone NAAQS under CAA section 110(a)(2)(D)(i)(I). These policy 
judgments conform with relevant case law and past agency practice as 
reflected in CSAPR and related rulemakings. Employing a nationally 
consistent 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 in order to ensure an ``efficient and equitable'' 
approach. See EME Homer City Generation, LP v. EPA, 572 U.S. 489, 519 
(2014).
    The remainder of this section describes EPA's analytic 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.]'' See 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).\24\ 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, 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). See 938 F.3d 303, 313.
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    \24\ For attainment dates for the 2015 8-hour 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).
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    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) 
(Maryland). 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,\25\ which is currently the 2015 ozone NAAQS 
Moderate area attainment date of August 3, 2024 under CAA section 181 
for ozone nonattainment.\26\ Thus, 2023 remains

[[Page 55002]]

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.
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    \25\ 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.
    \26\ 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).
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    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 
on EPA's 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 submissions 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 23074; see also Wisconsin, 938 F.3d at 322 (rejecting Delaware's 
argument that EPA should have used an analytic year of 2011 instead of 
2017). Consequently, in this proposal EPA will use the analytical year 
of 2023 to evaluate Wyoming's CAA section 110(a)(2)(D)(i)(I) SIP 
submission with respect to the 2015 ozone NAAQS.\27\
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    \27\ EPA recognizes that by the time final action is taken with 
respect to this SIP submission, the 2023 ozone season will likely be 
wholly in the past. However, as discussed in section III., the 
available modeling information indicates that our analysis would not 
change as to Wyoming for any later year.
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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, EPA proceeds to the next step of the 
4-step interstate transport framework by identifying which upwind 
states contribute to those receptors above the contribution threshold.
    EPA's approach to identifying ozone nonattainment and maintenance 
receptors in this action 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.\28\
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    \28\ See North Carolina v. EPA, 531 F.3d at 910-11 (holding that 
the EPA must give ``independent significance'' to each prong of CAA 
section 110(a)(2)(D)(i)(I)).
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    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 
analytic year (i.e., 2023).\29\
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    \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).
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    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 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) (EME Homer City II).\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, and 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.
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    \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).
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    Nonattainment receptors are also, by definition, maintenance 
receptors, and so 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 earlier, 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.\31\ 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.
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    \31\ The Agency often uses the terms maintenance receptor and 
maintenance-only receptor interchangeably when discussing 
maintenance receptors that are not also nonattainment receptors.

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[[Page 55003]]

    The Agency has also taken a closer look at measured ozone levels at 
monitoring sites in 2021 and 2022 for the purposes of informing the 
identification of additional receptors in 2023. As explained in more 
detail in the February 13, 2022 final action disapproving 19 states' 
good neighbor SIP submissions, and partially approving and partially 
disapproving 2 states' good neighbor SIP submissions, see 88 FR 9349-
50, we find there is a basis to consider certain sites with elevated 
ozone levels that are not otherwise identified as receptors to be an 
additional type of maintenance-only receptor given the likelihood that 
ozone levels above the NAAQS could persist at those locations through 
at least 2023. We refer to these as violating-monitor maintenance-only 
receptors (``violating monitors''). In this action, EPA proposes to use 
certified monitoring data as an additional method to identify 
maintenance-only receptors. In the case of Wyoming, this analysis 
confirms that the state is not projected to be linked to any violating-
monitor receptors. EPA is not reopening this methodology, except to the 
extent of its application to Wyoming, nor in relation to the evaluation 
of any other state's good neighbor obligations for the 2015 ozone 
NAAQS. Any such comments on those topics will be treated as beyond the 
scope of this action.
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 contribute significantly to nonattainment or interfere 
with maintenance of the NAAQS in the 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 pursuant to the requirements of CAA section 
110(a)(2)(D)(i)(I).
    In this proposed action, EPA relies in the first instance on the 1 
percent of the NAAQS threshold for the purpose of evaluating a state's 
contribution to nonattainment or maintenance of the 2015 ozone NAAQS 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 and Revised CSAPR Update when 
evaluating interstate transport obligations for the 2008 ozone NAAQS. 
EPA continues to find 1 percent of the NAAQS to be an appropriate 
threshold. For ozone, as EPA found in the CAIR, CSAPR, and CSAPR 
Update, a portion of the nonattainment problems from anthropogenic 
sources in the U.S. results from the combined impact of relatively 
small contributions, typically from multiple upwind states and, in some 
cases, substantially larger contributions from a subset of particular 
upwind states, along with contributions from in-state sources. EPA's 
analysis shows that much of the ozone transport problem in the United 
States is still the result of the collective impacts of contributions 
from 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 74518; see also 86 FR 23085 
(reviewing and explaining rationale from CSAPR, 76 FR 48237-38, for 
selection of 1 percent threshold).
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with EPA's longstanding approach to eliminating 
significant contribution and interference with maintenance, at Step 3, 
a multifactor assessment of potential emissions controls is conducted 
for states linked at Steps 1 and 2. EPA's analysis at Step 3 in prior 
Federal actions addressing interstate transport requirements has 
primarily focused on an evaluation of 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 state-provided 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 SIP approval. In 
general, the emissions-reducing effects of all existing emissions 
control requirements are already reflected in the future year projected 
air quality results of the modeling for Steps 1 and 2. If the state is 
shown to still be linked to one or more downwind receptor(s) despite 
these existing controls, but that state believes it has no outstanding 
good neighbor obligations, EPA expects the state to provide sufficient 
justification to support a conclusion by EPA that the state has 
adequate provisions prohibiting ``any source or other type of emissions 
activity within the State from emitting any air pollutant in amounts 
which will'' ``contribute significantly to nonattainment in, or 
interfere with maintenance by,'' any other state with respect to the 
NAAQS. See CAA section 110(a)(2)(D)(i)(I). 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.\32\
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    \32\ 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, the EPA has developed 
emissions inventories, analyzed different levels of control 
stringency at different cost thresholds, and assessed resulting 
downwind air quality improvements.
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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

[[Page 55004]]

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 section 110(a)(2)(A); Committee for a Better Arvin v. EPA, 
786 F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on 
by a state to meet CAA requirements must be included in the SIP).

II. Wyoming SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone NAAQS

A. Summary of Wyoming's 2015 Ozone Interstate Transport SIP Submission

    On January 3, 2019, Wyoming submitted a SIP submission to EPA 
addressing the infrastructure requirements of CAA section 110(a)(1) and 
(2), including the CAA section 110(a)(2)(D)(i)(I) interstate transport 
requirements, for the 2015 8-hour ozone NAAQS.\33\ The SIP submission 
provided Wyoming's analysis of the State's impact to downwind states 
and concluded that emissions from Wyoming will not significantly 
contribute to nonattainment or interfere with maintenance of the 2015 
ozone NAAQS in other states in 2023.\34\ The SIP submission cited EPA's 
4-step framework, but also included a ``weight-of-evidence'' 
analysis.\35\ Based on the results of its ``weight-of-evidence'' 
analysis at Step 2, Wyoming's 2019 SIP submission concluded that 
emissions from the State are not linked to a downwind projected 
nonattainment or maintenance receptor and therefore do not contribute 
to nonattainment or interfere with the maintenance of the 2015 ozone 
NAAQS in any downwind state.\36\
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    \33\ See Wyoming State Implementation Plan, Interstate 
Transport, To Satisfy the Requirements of Clean Air Act 
110(a)(2)(i)(I) for the 8-Hour Ozone NAAQS Promulgated in October 
2015, December 2018, located in the docket for this rulemaking at 
regulations.gov, Docket No. EPA-R08-OAR-2023-0375.
    \34\ Wyoming State Implementation Plan, Attachment B at 10.
    \35\ See generally id. at 3-10.
    \36\ Id. at 9-10.
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B. Prior Notices Related to Wyoming's SIP Submission

    On May 24, 2022, the EPA proposed disapproval of the portion of 
Wyoming's January 3, 2019 SIP submission addressing CAA section 
110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS. 87 FR 31495. In EPA's 
proposed disapproval, as part of the evaluation of Wyoming's 
submission, we considered the most recently updated modeling platform 
available at the time, 2016v2, which established one linkage from 
Wyoming to the Douglas County nonattainment receptor in Colorado (Site 
ID 80350004), with a projected 2023 contribution from Wyoming of 0.81 
ppb.\37\ When EPA completed updated modeling for 2023 and 2026 using 
the 2016v3 platform, Wyoming was not projected to be linked to any 
downwind nonattainment or maintenance-only receptors in 2023, with a 
maximum projected contribution of 0.68 ppb at the Douglas County 
nonattainment receptor in 2023.\38\ On January 31, 2023, EPA signed a 
final rulemaking, finalizing disapproval of 19 SIP submissions, and 
partially approved and partially disapproved two SIP submissions, for 
inadequately addressing the good neighbor provision for the 2015 ozone 
NAAQS and noted that EPA was not taking final action at that time on 
two SIP submissions for which EPA had proposed disapproval, including 
Wyoming's.\39\ Based on the updated modeling using the 2016v3 platform, 
discussed in section I.C. above, as well as EPA's evaluation in section 
III. below, EPA is now withdrawing our May 24, 2022 proposed 
disapproval of the 110(a)(2)(D)(i)(I) portion of Wyoming's January 3, 
2019 SIP submission, at 87 FR 31495.
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    \37\ 87 FR 31505.
    \38\ See Final Good Neighbor Plan AQM TSD in Docket ID No. EPA-
R08-OAR-2023-0375.
    \39\ See Air Plan Disapprovals; Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone National Ambient Air Quality 
Standards, 88 FR 9336 (February 13, 2023).
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III. EPA's Evaluation

    Wyoming's 2019 SIP submission addressing CAA section 
110(a)(2)(D)(i)(I) for the 2015 Ozone NAAQS relies on the 4-step 
framework and the analytic year 2023 contribution modeling results 
released with the March 2018 memorandum to conclude that Wyoming does 
not significantly contribute to nonattainment or interfere with 
maintenance of the 2015 ozone NAAQS in any other state at Step 2 of the 
4-step framework.
    As described in section I.C. of this proposal, EPA performed air 
quality modeling to project ozone design values and contributions for 
2023 and 2026 using the 2016v3 emissions platform. EPA proposes to rely 
primarily on this updated modeling in evaluating Wyoming's transport 
SIP submission. The design values and contributions from the updated 
modeling were examined to determine if Wyoming contributes at or above 
the threshold of 1 percent of the 2015 ozone NAAQS (0.70 ppb) to any 
downwind nonattainment or maintenance receptor.\40\ The data \41\ 
indicate that the highest contributions from Wyoming to downwind 
nonattainment and maintenance-only receptors are 0.68 ppb and 0.67 ppb 
in 2023, respectively, and 0.40 ppb and 0.59 ppb in 2026, 
respectively.\42\ EPA's evaluation of Wyoming's contributions to 
violating-monitor maintenance-only receptors indicate the State's 
maximum contribution is 0.42 ppb in 2023.\43\
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    \40\ EPA need not assess the data and analysis in Wyoming's 
submission, as EPA's updated modeling corroborates Wyoming's 
conclusion that the State will not significantly contribute to 
nonattainment or interfere with maintenance of the 2015 ozone NAAQS 
in any other state.
    \41\ Design values and contributions at individual monitoring 
sites nationwide are provided in the file Final GNP O3 DVs 
Contributions, which is included in docket ID No. EPA-R08-OAR-2023-
0375.
    \42\ EPA's analysis indicates that in 2023 Wyoming will have a 
0.68 ppb impact at the projected nonattainment receptor in Douglas 
County, Colorado (site ID 80350004), and a 0.67 ppb impact at the 
projected maintenance-only receptor in Larimer County, Colorado 
(site ID 80690011). EPA's analysis indicates maximum 2026 Wyoming 
emission impacts of 0.40 ppb at projected nonattainment receptors in 
Jefferson County, Colorado (sites 80590006 and 80590011), and 0.59 
at a projected maintenance receptor in Larimer County, Colorado 
(site 80690011).
    \43\ EPA's analysis indicates that in 2023 Wyoming will have a 
0.42 ppb impact at the violating-monitor maintenance-only receptor 
in Arapahoe County, Colorado (site ID 80050002).
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    EPA's evaluation of measured and monitored data and contribution 
values in 2023 and 2026 indicates that the contribution to ozone 
concentrations in other states from emissions in Wyoming will not equal 
or exceed the contribution threshold of 0.70 ppb. Thus, EPA proposes to 
find that the State does not impact downwind air quality problems such 
that it should be considered ``linked'' at Step 2 of the 4-step 
framework, and therefore does not warrant further review and analysis 
at Steps 3 and 4. The results of EPA's evaluation are consistent with 
the conclusion drawn by Wyoming in the 2019 SIP submission that 
emissions from sources in Wyoming will not contribute to nonattainment 
or interfere with maintenance of the 2015 ozone NAAQS in any other 
state. For these reasons, EPA is proposing to approve Wyoming's 2019 
SIP submission with regard to the interstate transport requirements of 
CAA section 110(a)(2)(D)(i)(I).

IV. Proposed Action

    Based on EPA's evaluation of the impact of air emissions from 
Wyoming

[[Page 55005]]

to downwind states using 2023 analytic year modeling as described in 
this document, EPA is proposing to approve Wyoming's January 3, 2019 
SIP submission as meeting the interstate transport requirements of CAA 
section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS. EPA is seeking 
public comment on the issues discussed in this proposed rule. We will 
accept comments from the public on this proposal for the next 30 days.

V. Statutory and Executive Order Reviews

    Under the CAA, the Administrator is required to approve a SIP 
submission that complies with the provisions of the Act and applicable 
Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in 
reviewing SIP submissions, the EPA's role is to approve state choices, 
provided that they meet the criteria of the CAA. Accordingly, this 
action merely proposes to approve state law as meeting Federal 
requirements and does not impose additional requirements beyond those 
imposed by state law. For that reason, this action:
     Is not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the CAA; and
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where EPA or an Indian tribe has 
demonstrated that a tribe has jurisdiction. In those areas of Indian 
country, the proposed rule does not have tribal implications and will 
not impose substantial direct costs on tribal governments or preempt 
tribal law as specified by Executive Order 13175 (65 FR 67249, November 
9, 2000).
    Executive Order 12898 (Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations, 59 FR 7629, 
Feb. 16, 1994) directs Federal agencies to identify and address 
``disproportionately high and adverse human health or environmental 
effects'' of their actions on minority populations and low-income 
populations to the greatest extent practicable and permitted by law. 
EPA defines environmental justice (EJ) as ``the fair treatment and 
meaningful involvement of all people regardless of race, color, 
national origin, or income with respect to the development, 
implementation, and enforcement of environmental laws, regulations, and 
policies.'' EPA further defines the term fair treatment to mean that 
``no group of people should bear a disproportionate burden of 
environmental harms and risks, including those resulting from the 
negative environmental consequences of industrial, governmental, and 
commercial operations or programs and policies.'' Wyoming did not 
evaluate environmental justice considerations as part of its SIP 
submission; the CAA and applicable implementing regulations neither 
prohibit nor require such an evaluation. EPA did not perform an EJ 
analysis and did not consider EJ in this action. Consideration of EJ is 
not required as part of this action, and there is no information in the 
record inconsistent with the stated goal of E.O. 12898 of achieving 
environmental justice for people of color, low-income populations, and 
Indigenous peoples.
    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 to decide whether 
to invoke the exception in (ii).\44\
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    \44\ 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.
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    If EPA takes final action on this proposed rulemaking, 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 and finalized 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 nationally uniform analytic years for this analysis and is 
applying a nationally uniform approach to nonattainment and maintenance 
receptors and a nationally uniform approach to contribution threshold 
analysis.\45\ 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 a determination of nationwide scope or

[[Page 55006]]

effect for purposes of CAA section 307(b)(1).\46\
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    \45\ 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.
    \46\ If EPA takes a consolidated, single final action on this 
and any other proposed SIP actions with respect to obligations under 
CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS, that action 
may be nationally applicable, and EPA would also anticipate that in 
that instance, in the alternative, the Administrator would make and 
publish a finding that such final action is based on a determination 
of nationwide scope or effect.
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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: July 27, 2023.
K.C. Becker,
Regional Administrator, Region 8.
[FR Doc. 2023-16441 Filed 8-11-23; 8:45 am]
BILLING CODE 6560-50-P