[Federal Register Volume 87, Number 100 (Tuesday, May 24, 2022)]
[Proposed Rules]
[Pages 31495-31510]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-11153]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2022-0268; EPA-HQ-OAR-2021-0663; FRL-9805-01-R8]


Air Plan Disapproval; 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.

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SUMMARY: Pursuant to the Clean Air Act (CAA or the Act), the 
Environmental Protection Agency (EPA) is proposing to disapprove the 
State Implementation Plan (SIP) submittal from Wyoming regarding 
interstate transport for the 2015 8-hour 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 the EPA to promulgate a Federal Implementation Plan (FIP) 
to address the relevant interstate transport requirements, unless the 
EPA approves a subsequent SIP submittal that meets these requirements. 
Disapproval does not start a mandatory CAA sanctions clock.

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

ADDRESSES: You may send comments, identified as Docket No. EPA-R08-OAR-
2022-0268, to the Federal eRulemaking Portal at https://www.regulations.gov following the online instructions for submitting 
comments.
    Instructions: All submissions received must include Docket No. EPA-
R08-OAR-2022-0268. 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. The 
EPA Docket Office can be contacted at (202) 566-1744, and is located at 
EPA Docket Center Reading Room, WJC West Building, Room 3334, 1301 
Constitution Avenue NW, Washington, DC 20004. For further information 
on EPA Docket Center services and the current hours of operation at the 
EPA Docket Center, please visit us online at https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Ellen Schmitt, Air and Radiation 
Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver, 
Colorado, 80202-1129, telephone number: (303) 312-6728, email address: 
[email protected].

SUPPLEMENTARY INFORMATION:
    Public participation: Submit your comments, identified by Docket 
No. EPA-R08-OAR-2022-0268, at https://www.regulations.gov. Once 
submitted, comments cannot be edited or removed from the docket. The 
EPA may publish any comment received to its public docket. Do not 
submit to the 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. The 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-R08-OAR-2022-0268 
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R08-OAR-2022-0268 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-2022-
0268. For additional submission methods, please contact Ellen Schmitt, 
telephone number: (303) 312-6728, email address: [email protected]. 
For the EPA's full 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.
    The index for Docket No. EPA-HQ-OAR-2021-0663, 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).
    The 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.

[[Page 31496]]

    Throughout this document, ``we,'' ``us,'' and ``our'' means the 
EPA.

Table of Contents

I. Background
    A. Description of Statutory Background
    B. Description of the EPA's 4-Step Interstate Transport 
Regulatory Process
    C. Background on the EPA's Ozone Transport Modeling Information
    D. The EPA's Approach to Evaluating Interstate Transport SIPs 
for the 2015 8-Hour Ozone NAAQS
II. Wyoming SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone NAAQS
III. The EPA's Evaluation
    A. Evaluation of Information Provided by Wyoming Regarding Step 
1 and Step 2
    B. Evaluation of Information Provided Regarding Step 3
    C. Evaluation of Information Provided Regarding Step 4
    D. Conclusion
IV. Proposed Action
V. Statutory and Executive Order Reviews

I. Background

A. Description of Statutory Background

    On October 1, 2015, the 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).\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). The 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 the EPA's 4-Step Interstate Transport Regulatory 
Process

    The EPA is using the 4-Step Interstate Transport Framework (or 4-
Step Framework) to evaluate Wyoming's SIP submittal addressing the 
interstate transport provision for the 2015 8-hour ozone NAAQS. The 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\ Through the development and implementation of the 
CSAPR rulemakings and prior regional rulemakings pursuant to the 
interstate transport provision,\7\ the EPA, working in partnership with 
states, developed the following 4-Step 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.
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    \4\ See Federal Implementation Plans: Interstate Transport of 
Fine Particulate Matter and Ozone and Correction of SIP Approvals, 
76 FR 48208 (August 8, 2011).
    \5\ Cross-State Air Pollution Rule Update for the 2008 Ozone 
NAAQS, 81 FR 74504 (October 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).
    \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).
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C. Background on the EPA's Ozone Transport Modeling Information

    In general, the 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, the 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.
    The EPA has released several documents containing projected ozone 
design values, contributions, and information relevant to evaluating 
interstate transport with respect to the 2015 8-hour ozone NAAQS. 
First, on January 6, 2017, the 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, the 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 8-hour ozone NAAQS.\9\ On October 27, 2017, we released a 
memorandum (October 2017 memorandum) containing updated 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

[[Page 31497]]

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 8-hour 
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 8-
hour ozone NAAQS under Step 2 of the 4-Step Framework.\12\ The EPA 
subsequently issued two more memoranda in August and October 2018, 
providing additional information to states developing interstate 
transport SIP submissions for the 2015 8-hour 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 NAAQS at Step 1 of the 4-Step Framework.\13\
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    \8\ 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).
    \9\ 82 FR 1733 at 1735 (January 6, 2017).
    \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 (``October 2017 memorandum''), 
available in Docket No. EPA-HQ-OAR-2021-0663.
    \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 (``March 2018 memorandum''), 
available in Docket No. EPA-HQ-OAR-2021-0663.
    \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 No. 
EPA-HQ-OAR-2021-0663.
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    Since the release of the modeling data shared in the March 2018 
memorandum, the 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.\14\ This collaborative project was a multi-year 
joint effort by the EPA, MJOs, and states to develop a new, more recent 
emissions platform for use by the EPA and states in regulatory modeling 
as an improvement over the dated 2011-based platform that the EPA had 
used to project ozone design values and contribution data provided in 
the 2017 and 2018 memoranda. The 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, the EPA released and accepted public comment on 2023 modeling 
that used the 2016v1 emissions platform.\15\ Although the Revised CSPAR 
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\
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    \14\ The results of this modeling, as well as the underlying 
modeling files, are included in Docket 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 Docket No. EPA-HQ-OAR-2021-0663.
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    Following the final Revised CSAPR Update, the EPA made further 
updates to the 2016 emissions platform to include mobile emissions from 
the 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 this updated emissions platform, 2016v2, is described in the 
emissions modeling technical support document (TSD) supporting this 
proposed rule.\18\ The 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.\19\ The EPA now proposes to primarily rely on 
modeling 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 Framework. This modeling will generally be referenced 
within this action as 2016v2 modeling for 2023. By using the updated 
modeling results, the EPA is using the most current and technically 
appropriate information for this proposed rulemaking. Section III of 
this document and the Air Quality Modeling TSD for 2015 Ozone NAAQS 
Transport SIP Proposed Actions, included in Docket No. EPA-HQ-OAR-2021-
0663 for this proposal, contain additional detail on the EPA's 2016v2 
modeling. In this document, the EPA is accepting public comment on this 
updated 2023 modeling, which uses a 2016v2 emissions platform. Comments 
on the EPA's air quality modeling should be submitted in the Regional 
docket for this action, Docket No. EPA-R08-OAR-2022-0268. Comments are 
not being accepted in Docket No. EPA-HQ-OAR-2021-0663.
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    \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 Docket No. EPA-HQ-OAR-2021-0663.
    \19\ Ramboll Environment and Health, January 2021, www.camx.com.
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    States may have chosen to rely on the results of the EPA modeling 
and/or alternative modeling performed by states or MJOs to evaluate 
downwind air quality problems and contributions as part of their 
submissions. In Section III we evaluate how the Wyoming Department of 
Environmental Quality (WDEQ) used air quality modeling information in 
their submission.

D. The EPA's Approach To Evaluating Interstate Transport SIPs for the 
2015 8-Hour Ozone NAAQS

    The 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 8-hour ozone NAAQS. These policy judgments 
reflect consistency with relevant case law and past Agency practice as 
reflected in 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 in order to ensure an ``efficient and equitable'' approach. 
See EME Homer City Generation, LP v. EPA, 572 U.S. 489, 519 (2014).
    In the March, August, and October 2018 memoranda, the EPA 
recognized that states may be able to establish alternative approaches 
to addressing their interstate transport obligations for the 2015 8-
hour ozone NAAQS that vary from a nationally uniform framework.

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The 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, the 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 such 
potential ``flexibilities'' as may have been identified or suggested in 
the past, the EPA will evaluate whether the state adequately justified 
the technical and legal basis for doing so.
    The 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,\20\ however, the 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 
the EPA sought ``feedback from interested stakeholders.'' \21\ 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.'' \22\ 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 
submissions, the EPA will thoroughly review the technical and legal 
justifications for doing so.
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    \20\ March 2018 memorandum, Attachment A.
    \21\ Id. at A-1.
    \22\ Id.
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    The remainder of this section describes the 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 the 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).\23\ 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 303 at 313.
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    \23\ 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 August 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 the 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 the 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, the ``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). The 
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,\24\ which is now the Moderate area 
attainment date under CAA section 181 for ozone nonattainment. The 
Moderate area attainment date for the 2015 8-hour ozone NAAQS is August 
3, 2024.\25\ The EPA believes that 2023 is now the appropriate year for 
analysis of interstate transport obligations for the 2015 8-hour 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 8-hour ozone NAAQS.
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    \24\ We note that the court in Maryland did not have occasion to 
evaluate circumstances in which the EPA may determine that an upwind 
linkage to a downwind air quality problem exists at Steps 1 and 2 of 
the 4-Step 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.
    \25\ 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 August 3, 2018).
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    The EPA recognizes that the attainment date for nonattainment areas 
classified as Marginal for the 2015 8-hour 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 the 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, the EPA must act on SIP submittals using the 
information available at the time it takes such action. In this 
circumstance, the 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 23054 at 23074; see also Wisconsin, 938 F.3d at 322. 
Consequently, in this proposal the 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 8-hour ozone NAAQS.
2. Step 1 of the 4-Step Interstate Transport Framework
    In Step 1, the EPA identifies monitoring sites that are projected 
to have problems attaining and/or maintaining the NAAQS in the 2023 
analytic year. Where the 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

[[Page 31499]]

the EPA's 4-Step Framework. For sites that are identified as a 
nonattainment or maintenance receptor in 2023, we proceed to the next 
step of our 4-Step Framework by identifying the upwind state's 
contribution to those receptors.
    The EPA's approach to identifying ozone nonattainment and 
maintenance receptors in this action is consistent with the approach 
used in previous transport rulemakings. The 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.\26\
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    \26\ See North Carolina v. EPA, 531 F.3d 896, 910-11 (D.C. Cir. 
2008) (holding that the EPA must give ``independent significance'' 
to each prong of CAA section 110(a)(2)(D)(i)(I)).
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    For the purpose of this proposal, the 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 the EPA defined nonattainment receptors as those 
areas that both currently measure nonattainment and that the EPA 
projects will be in nonattainment in the future analytic year (i.e., 
2023).\27\
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    \27\ 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 25162 at 
25241, 25249 (January 14, 2005); see also North Carolina, 531 F.3d 
at 913-14 (affirming as reasonable the EPA's approach to defining 
nonattainment in CAIR).
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    In addition, in this proposal, the 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).\28\ Specifically, the 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 base period. The 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). The EPA also recognizes 
that previously experienced meteorological conditions (e.g., dominant 
wind direction, temperatures, vertical mixing, insolation, 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.
---------------------------------------------------------------------------

    \28\ See 76 FR 48208 (August 8, 2011). The CSAPR Update and the 
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, the 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, the 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, the 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 8-hour ozone NAAQS), the upwind state is not 
linked to a downwind air quality problem, and the EPA, therefore, 
concludes that the state does not significantly contribute 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 under CAA section 
110(a)(2)(D)(i)(I). The 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 8-hour ozone 
NAAQS (i.e., 0.70 ppb) at downwind receptors. This is consistent with 
the Step 2 approach that the 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. 
The EPA continues to find 1 percent to be an appropriate threshold. For 
ozone, as the 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. results 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. The 
EPA's analysis shows that much of the ozone transport problem being 
analyzed in this proposed rule is the result of the collective impacts 
of contributions from multiple 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 the 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 the 1 percent 
threshold).
    The 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,

[[Page 31500]]

the 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 that 
particular SIP submission.
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with the 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. The 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 the 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. Generally, 
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 to still be linked to 
one or more downwind receptor(s), states 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 the EPA has not prescribed a particular method for this 
assessment, the 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.\29\
---------------------------------------------------------------------------

    \29\ 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 the 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.
---------------------------------------------------------------------------

5. Step 4 of the 4-Step Interstate Transport Framework
    At Step 4, states (or the 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. Wyoming SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 8-Hour Ozone NAAQS

    On January 3, 2019, the WDEQ submitted a SIP revision addressing 
the CAA section 110(a)(2)(D)(i)(I) interstate transport requirements 
for the 2015 8-hour ozone NAAQS.\30\ The SIP submission provided WDEQ'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.\31\ The WDEQ SIP submission cited the EPA's 4-
Step Framework approach, but also included a ``weight-of-evidence'' 
analysis.\32\ Throughout the submission, the WDEQ also incorporated 
certain outside parties' ideas for ``flexibilities'' in assessing good 
neighbor obligations that had been listed in Attachment A to the March 
2018 memorandum.\33\ In their analysis, the WDEQ used the modeling 
released with the March 2018 memorandum to identify nonattainment and 
maintenance receptors in the Denver Metro/North Front Range 
nonattainment area in 2023 (Step 1).\34\ The WDEQ also relied on the 
EPA's modeling from the March 2018 memorandum to identify contributions 
to projected nonattainment and/or maintenance receptors and emissions 
from sources in the State in 2023 (Step 2).\35\ The WDEQ identified 
five nonattainment and maintenance receptors to which the State was 
projected to contribute equal to and greater than 0.70 ppb (1 percent 
of the 2015 ozone NAAQS).\36\ Table 1 provides information on the five 
nonattainment and maintenance receptors identified by the WDEQ in the 
State's SIP submittal.
---------------------------------------------------------------------------

    \30\ In its SIP submission, the WDEQ references its Air Quality 
Division (AQD). In this action, we simply reference the WDEQ. 
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-2022-0268.
    \31\ Wyoming State Implementation Plan, Attachment B at 10.
    \32\ See generally id. at 3-10.
    \33\ Id. at 3, 8.
    \34\ Id. at 3. The EPA notes that the modeling released with the 
October 2017 and March 2018 memoranda both used 2011 base year 
inventory data.
    \35\ Id. at 6.
    \36\ Id.

  Table 1--2023 Average and Maximum Design Values at Downwind Receptors With Wyoming Contributions Equal to and
                                             Greater Than 0.70 ppb a
----------------------------------------------------------------------------------------------------------------
                                                                                                      Wyoming
                                                                  Average design  Maximum design      modeled
            Site ID                    County           State       value (ppb)     value (ppb)    contribution
                                                                                                       (ppb)
----------------------------------------------------------------------------------------------------------------
80050002.......................  Arapahoe..........  CO                     69.3            71.3            1.04
80350004.......................  Douglas...........  CO                     71.1            73.2            1.00
80590006.......................  Jefferson.........  CO                     71.3            73.7            0.81

[[Page 31501]]

 
80590011.......................  Jefferson.........  CO                     70.9            73.9            1.03
80690011.......................  Larimer...........  CO                     71.2            73.0            0.88
----------------------------------------------------------------------------------------------------------------
\a\ Data according to March 2018 memorandum modeling.

    While the WDEQ presented all of the monitors that the modeling 
projected Wyoming would contribute equal to and greater than the 1 
percent threshold, the WDEQ indicated that they supported and applied 
the use of different thresholds, such as the 1 ppb limit that was 
established as part of the Significant Impact Level (SIL) for ozone, 
used in the Prevention of Significant Deterioration (PSD) permitting 
program. The WDEQ referenced the EPA's August 31, 2018 memorandum, 
which the State interpreted as the EPA approving 1 ppb as an 
alternative to the 1 percent of the NAAQS screening threshold at Step 
2.\37\ The WDEQ noted that by using a 1 ppb threshold, the State is 
only linked to three \38\ of the five receptors listed in Table 1.
---------------------------------------------------------------------------

    \37\ Id. at 6.
    \38\ Site ID 80050002 (Arapahoe), Site ID 80350004 (Douglas), 
and Site ID 80590011 (Jefferson). Id.
---------------------------------------------------------------------------

    Although the WDEQ's use of a 1 ppb threshold eliminated only two of 
the five receptor linkages, they relied on a weight-of-evidence 
approach at Step 2 of the 4-Step Framework to assert that Wyoming does 
not contribute to nonattainment or interfere with maintenance in 
another state (i.e., at none of the five receptors to which Wyoming's 
sources contribute greater than 1 percent of the NAAQS in the EPA's 
2011-based modeling).\39\ The WDEQ stated that the weight-of-evidence 
approach to evaluating transport in western states is appropriate, 
since the EPA recognized in the CSAPR Update that it was not 
appropriate to extend CSAPR to western states without first considering 
important regional differences such as topography, prevalence of 
wildfires, altitude, and other factors.\40\ The WDEQ referenced the 
EPA's past actions on California's and Arizona's 2008 ozone interstate 
transport SIPs as examples of the EPA relying on a weight-of-evidence 
approach to support approval of the SIP for western states with 
contributions greater than 1 percent of the NAAQS to a downwind 
receptor.\41\
---------------------------------------------------------------------------

    \39\ Id. at 3, 8-9.
    \40\ Id. at 2.
    \41\ Id. at 2-3, 6.
---------------------------------------------------------------------------

    In their weight-of-evidence argument, the WDEQ considered the EPA's 
approval of Arizona's interstate transport SIP for the 2008 ozone 
NAAQS, in which the total contributions from all states that 
contributed to the same receptor(s) were factored into the EPA's 
analysis.\42\ The WDEQ stated that for Arizona's 2008 ozone transport 
approval action, the EPA ``concluded that upwind state contribution to 
the receptors Arizona was linked to were negligible, `particularly when 
compared to the relatively large contributions from upwind states in 
the East.' '' \43\
---------------------------------------------------------------------------

    \42\ See ``Partial Approval and Partial Disapproval of Air 
Quality State Implementation Plans; Arizona; Infrastructure 
Requirements to Address Interstate Transport for the 2008 Ozone 
NAAQS,'' 81 FR 31513 (May 19, 2016).
    \43\ Wyoming State Implementation Plan, Attachment B at 6 
(citing 81 FR 15203).
---------------------------------------------------------------------------

    Additionally, the WDEQ asserted that the EPA's modeling results in 
the March 2018 memorandum illustrates a disparity between upwind 
contributions from states in the East versus the West.\44\ The WDEQ 
stated that the modeling showed that upwind contributions for one site 
in Connecticut (Site ID 90019003) was 44.24 ppb, 12 times as much as 
the in-state contributions of 3.71 ppb.\45\ The WDEQ compared this to 
the relative contribution levels at the Colorado receptors previously 
noted in Table 1. The WDEQ indicated that the highest collective 
contributions from upwind states to these receptors was 7.06 ppb to 
site 80590006 (one of the Jefferson County receptors) and that the in-
state (Colorado) contribution to the same receptor is 25.52 ppb. Table 
2 of this document provides the WDEQ's summary of in-state and upwind 
state contributions using the EPA's 2023 (2011 platform) modeling. The 
WDEQ stated in their SIP submission that the total contributions from 
upwind states to downwind receptors is much higher for eastern states 
than for western states and therefore the 1 percent threshold needs to 
be reevaluated for application in western states.\46\
---------------------------------------------------------------------------

    \44\ Id. at 6.
    \45\ Id.
    \46\ Id. at 7.
---------------------------------------------------------------------------

    The WDEQ concluded that the total collective contribution from 
upwind states to the Colorado receptors (including the Arapahoe, 
Douglas, and one Jefferson County receptor (Site ID 80590011)) is 
``negligible.'' \47\ For the other Jefferson County receptor (Site ID 
80580006) and the Larimer County receptor (the two receptors to which 
the WDEQ identified that Wyoming contributes above 1 percent of the 
NAAQs but below 1 ppb), the WDEQ did not include this argument 
regarding negligible collective contribution, but reiterated that their 
sources' contributions to this receptor are below 1 ppb, and therefore 
do not contribute significantly.\48\ Citing a potential flexibility 
from Attachment A to the March 2018 memorandum, the WDEQ also pointed 
to international and non-anthropogenic emissions contributions as 
additional support for concluding that it is unnecessary to reach a 
Step 3 analysis for Wyoming, since contributions from these categories 
make up over 50 percent of the total maximum design values at each of 
the five receptors under evaluation.\49\
---------------------------------------------------------------------------

    \47\ Id. at 7-8.
    \48\ Id. at 8.
    \49\ Id. at 8-9.

[[Page 31502]]



                                              Table 2--In-State vs. Collective Upwind State Contributions a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                               Total
                                                                                          Average design  Maximum design     In-state      contribution
                  Site                             County                   State           value (ppb)     value (ppb)    contribution     from upwind
                                                                                                                               (ppb)       states (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
80050002...............................  Arapahoe..................  CO                             69.3            71.3           22.94            5.98
80350004...............................  Douglas...................  CO                             71.1            73.2           24.71            5.94
80590006...............................  Jefferson.................  CO                             71.3            73.7           25.52            7.06
80590011...............................  Jefferson.................  CO                             70.9            73.9           24.72            6.98
80690011...............................  Larimer...................  CO                             71.2            73.0           21.74            6.33
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Data according to March 2018 memorandum modeling.

    The WDEQ's SIP submission also pointed to data that indicates that 
the ``counties currently classified as nonattainment for the 2015 
standards are projected to be in attainment by the year 2025.'' \50\ 
The WDEQ acknowledged that 2025 is not an applicable attainment year 
for the 2015 ozone NAAQS, but wishes to include this projection as part 
of its weight-of-evidence analysis and to help demonstrate that a 
downward trend in ozone exists.\51\ Also included in Wyoming's SIP 
submission is the State's projection for VOC and NOX 
emissions reductions, including an expected reduction of over 32,000 
tons per year (tpy) of NOX between 2011 and 2023.\52\ The 
WDEQ notes that at the time of its SIP submission, 21,252 tpy of those 
NOX reductions had yet to occur, but pointed to the Regional 
Haze Rule and other agreements between the EPA and Wyoming 
operators.\53\ The WDEQ also noted that additional emissions reductions 
would be achieved through the Tier 3 Vehicle Emissions and Fuel 
Standards national rulemaking.\54\ The State concluded that based on 
the anticipated reductions, requiring additional reductions would not 
be necessary.\55\
---------------------------------------------------------------------------

    \50\ Id. at 9.
    \51\ Id.
    \52\ Id.
    \53\ Id.
    \54\ Id.
    \55\ Id.
---------------------------------------------------------------------------

    Based on the results of its weight-of-evidence analysis at Step 2, 
the WDEQ'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.\56\
---------------------------------------------------------------------------

    \56\ Id at 9-10.
---------------------------------------------------------------------------

III. The EPA's Evaluation

    The EPA is proposing to find that Wyoming's January 3, 2019, SIP 
submission does not meet the State's obligations with respect to 
prohibiting emissions that contribute significantly to nonattainment or 
interfere with maintenance of the 2015 8-hour ozone NAAQS in any other 
state. The Agency's decision to propose disapproval of Wyoming's SIP 
submission is based on our evaluation of the SIP using the 4-Step 
Framework.

A. Evaluation of Information Provided by Wyoming Regarding Step 1 and 
Step 2

    At Step 1 and Step 2 of the 4-Step Framework, Wyoming relied on the 
EPA modeling released in the March 2018 memorandum to identify 
nonattainment and maintenance receptors and upwind state linkages to 
those nonattainment and maintenance receptors in 2023. In this 
proposal, the EPA relies on the Agency's most recently available 
modeling (2016v2) to identify upwind contributions and linkages to 
downwind air quality problems in 2023. The earlier modeling relied on 
by the WDEQ identified a number of nonattainment and maintenance 
receptor sites in 2023 as did the more recent 2016v2 2023 modeling. 
Thus, the EPA agrees with the WDEQ that for Step 1 under the 4-Step 
Interstate Transport Framework, a number of nonattainment and 
maintenance receptors for the 2015 ozone NAAQS were projected for 2023.
    As noted in Section II, at Step 2, the WDEQ completed a weight-of-
evidence analysis to conclude that it was not linked to any projected 
downwind receptors. The WDEQ stated that a weight-of-evidence approach 
at Step 2 was the most appropriate method for evaluating interstate 
transport obligations for western states, and that this approach was 
consistent with the EPA's past practice of relying on a weight-of-
evidence approach in evaluating interstate transport in the West under 
the 2008 ozone NAAQS. The EPA has not prescribed to states any specific 
methodology for developing SIP submissions, although the EPA has 
historically relied on the 4-Step Framework to complete its evaluation 
of state SIP submissions for ozone transport. Under the previous 2008 
ozone NAAQS, the EPA's action on western states' interstate transport 
SIP submissions has been informed using EPA modeling results and has 
considered additional factors as appropriate. In the CSAPR Update, the 
EPA stated, ``The EPA and western states, working together, are 
continuing to evaluate interstate transport obligations on a case-by-
case basis. The EPA will fulfill its backstop role with respect to 
issuing FIPs for western states if and when that becomes necessary.'' 
\57\ The EPA did note that there ``may be'' geographic factors to 
consider when acting on western states but did not attempt to elucidate 
what these were or how they may be relevant to interstate transport 
policy.\58\
---------------------------------------------------------------------------

    \57\ See 81 FR 74504, at 74523.
    \58\ See id. The EPA also noted that the western states on which 
it was not acting in the CSAPR Update were not thereby relieved of 
their statutory obligations to address interstate transport and that 
the analyses developed for the CSAPR Update, including air quality 
modeling and emissions control potential ``can be useful for western 
states in developing SIPs.'' Id.
---------------------------------------------------------------------------

    The EPA did not provide, as the WDEQ SIP submission suggests, 
specific regional differences or a set criteria that must be considered 
prior to acting on western state SIPs. Further, as discussed in more 
detail later in this section, the EPA's proposed action on this SIP 
submission is entirely consistent with the reasoning it previously 
applied in acting on SIP submissions for western states including 
Arizona, Utah, and Wyoming under the 2008 ozone NAAQS. Nonetheless, we 
will evaluate the evidence and arguments supplied by the WDEQ to 
determine whether the State's conclusion, that no further controls are 
necessary for Wyoming to meet its obligations under CAA 
110(a)(2)(D)(i)(I), is adequately supported.
    The first argument the WDEQ relied on to support its conclusion was 
an alternative threshold at Step 2 to determine a linkage. The WDEQ 
noted

[[Page 31503]]

their support of an alternative threshold to 1 percent of the 
NAAQS.\59\ As noted in Section II of the preamble, the WDEQ referred to 
the 1 ppb limit of the ozone SIL used in the PSD permitting program and 
relied on the August 2018 memorandum to conclude using a 1 ppb 
alternative contribution threshold at Step 2 is ``appropriate'' for 
Wyoming.\60\ The WDEQ further argued that there is a ``need to 
reevaluate the application of CSAPR and the associated 1 percent 
threshold in the West.'' \61\ As an initial matter, the EPA does not 
agree with the WDEQ's assessment that 1 percent is not an appropriate 
threshold for western states. 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, the EPA re-analyzed the threshold for purposes of the 2008 
ozone NAAQS and determined it was appropriate to continue to apply this 
threshold. See 86 FR 23054, 23085 (summarizing CSAPR and the CSAPR 
Update basis for use of 1 percent of the NAAQS threshold).
---------------------------------------------------------------------------

    \59\ Wyoming State Implementation Plan, Attachment B at 6.
    \60\ Id. at 6.
    \61\ Id. at 7.
---------------------------------------------------------------------------

    Further, the EPA has explained in prior actions on western states' 
ozone interstate transport SIPs that a 1 percent of the NAAQS threshold 
may be appropriate in the West just as much as in the East. In acting 
on Wyoming's interstate transport SIP submissions for the 2008 ozone 
NAAQS, the EPA consistently applied the 1 percent threshold, and 
rejected use of a higher threshold. The EPA explained that a 1 percent 
threshold was appropriate to apply for a Colorado receptor ``because 
the air quality problem in that area resulted in part from the 
relatively small individual contribution of upwind states that 
collectively contribute a larger portion of the ozone contributions 
(9.7%), comparable to some eastern receptors . . . .'' See 84 FR 3389, 
3391 (February 12, 2019).\62\
---------------------------------------------------------------------------

    \62\ While the EPA ultimately approved Wyoming's transport SIP 
submission as proposed in the 2019 action, the approval was on the 
basis of a unique air quality demonstration developed by Colorado 
itself to establish that there would be no air quality problem in 
Colorado with respect to the 2008 ozone NAAQS once air quality 
monitoring data influenced by ``atypical events'' were removed 
(assuming 2023 was the correct analytical year). See 84 FR 3392-94; 
84 FR 14270 (April 10, 2019) (final action; no comments received). 
No such basis for approval of Wyoming's transport SIP has been 
developed or submitted with respect to Colorado's ongoing air 
quality problems under the 2015 ozone NAAQS. Further, as presented 
in Table 5 in this document, at least four Colorado monitoring sites 
continue to have design values as of 2020 that are in excess of the 
2008 ozone NAAQS, let alone the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    In the EPA's action on Utah's SIP submission as to prong 2 for the 
2008 ozone NAAQS, the EPA further addressed the basis for applying a 1 
percent threshold at least as to Colorado receptors, and rejected 
comments advocating for a higher threshold. 81 FR 71991, 71994-95 
(October 19, 2016). As in its Wyoming actions, the EPA explained the 
basis for the 1 percent threshold as derived in CSAPR and the CSAPR 
Update rulemakings, and then explained that the same reasoning would 
hold true with respect to the Colorado receptors to which Utah was 
linked. Id. The EPA noted that Utah's state agency's advocacy for a 
higher contribution threshold of 2 percent of the NAAQS was not 
technically supported and ``appears to only be justified by the 
conclusion that Utah would not have been linked to Denver receptors at 
this level.'' Id. at 71995.
    When the EPA took action on Arizona's 2008 ozone NAAQS transport 
SIP submittal, it again found the 1 percent threshold appropriate to 
apply as to that western state. 81 FR 15200, 15202-03 (March 22, 2016). 
We stated that we disagreed with Arizona's contention that it is 
unclear what screening threshold is significant for southwestern states 
when addressing interstate transport contributions. We explained that 
we believe contribution from an individual state equal to or above 1 
percent of the NAAQS could be considered significant where the 
collective contribution of emissions from one or more upwind states is 
responsible for a considerable portion of the downwind air quality 
problem regardless of where the receptor is geographically located. See 
id. 15202.
    As discussed in further detail later in the section, the EPA found, 
based on an analysis of the California monitoring sites at issue in 
that action, that Arizona was not contributing to downwind 
nonattainment or maintenance problems. But this conclusion was not 
reached on the basis of an alternative threshold at Step 2, which, as 
explained previously, the EPA did not find justified to assume for an 
entire region such as the southwest.\63\
---------------------------------------------------------------------------

    \63\ The EPA received no comment on the Arizona 2008 ozone NAAQS 
interstate transport proposal and therefore finalized its approval 
without further analysis. 81 FR 31513 (May 19, 2016).
---------------------------------------------------------------------------

    The WDEQ also seeks to rely on the EPA's August 2018 memorandum as 
a basis for using a 1 ppb threshold. However, that 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 WDEQ's submission. The August 2018 memorandum did 
not establish a rule that the application of a 1 ppb threshold to 
determine a linkage would always be approvable, as the WDEQ appears to 
assume in its SIP submission. Rather, the EPA suggested that where the 
percentage of upwind state emissions is comparable to the amount 
captured at 1 percent, 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 Framework, for the purposes of identifying 
linkages to downwind receptors. This indicates that a more 
determinative conclusion of appropriateness would require further 
state-and-receptor-specific analysis.\64\ However, the WDEQ's SIP 
submission does not evaluate whether the level of upwind state 
contribution captured at the 1 ppb threshold is sufficiently comparable 
to the amount captured at 1 percent at each linked receptor. The WDEQ 
does not include any further technical analysis to sufficiently justify 
use of an alternative 1 ppb threshold at the linked receptors.
---------------------------------------------------------------------------

    \64\ The EPA provided comments on November 1, 2018, regarding 
the use of a 1 ppb threshold on the WDEQ's draft SIP submittal 
during the State's comment period. In these comments, the EPA 
indicated that the August 2018 memorandum suggested that, depending 
on the particular facts and circumstances, it may be reasonable and 
appropriate to use a 1 ppb threshold, and if the WDEQ wished to use 
a 1 ppb threshold in its SIP development, the EPA recommended 
Wyoming review the August 2018 memorandum and revise their arguments 
accordingly. The EPA's comments were included in the WDEQ's SIP 
submission and are also included in Docket No. EPA-R08-OAR-2022-
0268.
---------------------------------------------------------------------------

    The WDEQ also referred to the EPA's use of the ozone SIL in the PSD 
permitting program as additional justification for use of a 1 ppb 
threshold. The EPA's SIL guidance relates to a different provision of 
the CAA regarding implementation of the PSD permitting program, i.e., a 
program that applies in areas that have been designated attainment or 
unclassifiable for the NAAQS, and it is not applicable to the good 
neighbor provision, which requires states to eliminate significant 
contribution or interference with maintenance of the NAAQS at known and 
ongoing air quality problem areas in other states.
    The analytical gaps identified previously, as well as the EPA's 
consistent policy of applying a 1 percent of the NAAQS threshold even 
in the case of western states like Wyoming (particularly with respect 
to the Colorado receptors), indicate that the use of a 1 ppb threshold 
for the State is not approvable.

[[Page 31504]]

    The 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.\65\ (The memorandum also indicated that any higher alternative 
threshold, such as 2 ppb, would likely not be appropriate.) However, 
the 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 8-hour ozone NAAQS, the 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. For 
instance, in nearly all submittals, the states did not provide the 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, the 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.\66\ It was at the 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. Furthermore, the 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.\67\ 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 SIP submittal at 
Step 2 of the 4-Step 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. Further, it is not clear that 
national ozone transport policy is best served by allowing for less 
stringent thresholds at Step 2. The 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, the 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 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; \68\ 
in the 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 NAAQS threshold.
---------------------------------------------------------------------------

    \65\ August 2018 memorandum at 4.
    \66\ See ``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 
subsequently formally withdrawn the proposed approval. 87 FR 9477 
(February 22, 2022).
    \67\ We note that Congress has placed on the 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.
    \68\ 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. Accord 
76 FR 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, the EPA's experience since the issuance of that memorandum 
has revealed substantial programmatic and policy difficulties in 
attempting to implement this approach. Nonetheless, the EPA is not at 
this time rescinding the August 2018 memorandum. The basis for 
disapproval of Wyoming's SIP submission with respect to the Step 2 
analysis is, in the Agency's view, warranted even under the terms of 
the August 2018 memorandum. The 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, the EPA may 
determine to rescind the 2018 memorandum in the future.
    As described in Section I of this preamble, the 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 Wyoming contributes at or above the threshold of 1 percent 
of the 2015 8-hour ozone NAAQS (0.70 ppb) to any downwind nonattainment 
or maintenance receptor.

[[Page 31505]]

As shown in Table 3, the data \69\ indicate that in 2023, emissions 
from Wyoming contribute greater than 1 percent of the NAAQS to a 
nonattainment receptor in Douglas County, Colorado (Site ID 
80350004).\70\
---------------------------------------------------------------------------

    \69\ Design values and contributions at individual monitoring 
sites nationwide are provided in the file: 
2016v2_DVs_state_contributions.xlsx which is included in Docket No. 
EPA-HQ-OAR-2021-0663.
    \70\ 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 of the document. That 
modeling showed that Wyoming had a maximum contribution equal to or 
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 No. EPA-HQ-OAR-2021-0663.

                                       Table 3--Wyoming Linkage Results Based on the EPA's Updated 2023 Modeling a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                         2023 Average    2023  Maximum       Wyoming
               Receptor ID                           Location              Nonattainment/maintenance     design value     design value     contribution
                                                                                                            (ppb)            (ppb)            (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
80350004.................................  Douglas County, Colorado....  Nonattainment...............            71.7             72.3             0.81
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ According to data from 2016v2 platform modeling.

    Another argument the WDEQ made as part of its Step 2 weight-of-
evidence evaluation was a determination that emissions from sources in 
Wyoming are ``negligible'' when compared to in-state, non-U.S., and 
nonanthropogenic contributions to three receptors to which it 
contributed greater than 1 percent of the NAAQS (using the EPA's March 
2018 memorandum modeling results). Regarding the WDEQ's argument that 
contributions from Wyoming are negligible when considering total 
collective contributions from all upwind states to the same receptors, 
the EPA disagrees.
    The WDEQ makes reference to the EPA's approval of Arizona's 2008 
ozone NAAQS transport SIP as a basis for the claim that its emissions 
are negligible.\71\ In that action the EPA made an assessment of the 
nature of certain monitoring sites in California. The EPA noted that a 
``factor [. . .] relevant to determining the nature of a projected 
receptor's interstate transport problem is the magnitude of ozone 
attributable to transport from all upwind states collectively 
contributing to the air quality problem.'' 81 FR at 15203. The EPA 
observed that only one upwind state (Arizona) was linked above 1 
percent of the 2008 ozone NAAQS to the two relevant monitoring sites in 
California, and the cumulative ozone contribution from all upwind 
states (including those linked and unlinked) to those sites was 2.5 
percent and 4.4 percent of the total ozone concentration, respectively. 
The EPA determined the size of those cumulative upwind contributions 
was ``negligible, particularly when compared to the relatively large 
contributions from upwind states in the East or in certain other areas 
of the West.'' Id. (emphasis added). In the Arizona action, the EPA 
concluded the two California sites to which Arizona was linked should 
not be treated as receptors for the purposes of determining good 
neighbor obligations for the 2008 ozone NAAQS. Id.
---------------------------------------------------------------------------

    \71\ See 81 FR 15200 (March 22, 2016) (proposal); 81 FR 31513 
(May 19, 2016) (final rule; no comments received).
---------------------------------------------------------------------------

    As an initial matter, we note that this analysis is properly 
considered at Step 1 of the 4-Step Framework rather than at Step 2, as 
it is a determination of whether an interstate-pollution transport 
problem should be considered to exist at all, before reaching a 
determination as to which states contribute to that problem. As the EPA 
explained in its Arizona action, it considered the 1 percent of the 
NAAQS threshold appropriate to apply at Step 2. Id. at 15202. See also 
id. at 15203 (``EPA believes the emissions that result in transported 
ozone from upwind states have limited impacts on the projected air 
quality problems in El Centro, California and Los Angeles, California, 
and therefore should not be treated as receptors for purposes of 
determining the interstate transport obligations of upwind states.''). 
However, because Wyoming has presented this argument as a part of its 
weight-of-evidence analysis at Step 2, we present this analysis in turn 
here, as related to the WDEQ's Step 2 arguments.
    Turning to the substance of the WDEQ's argument that the EPA's 
Arizona action supports an approval here: The conclusions the EPA 
reached regarding El Centro and Los Angeles California cannot be 
reached with respect to the three receptors in Colorado examined by the 
WDEQ,\72\ and the EPA has consistently taken this same position across 
several prior actions addressing Wyoming's and Utah's interstate 
transport obligations, where we have concluded that the receptors in 
Colorado are ``substantially'' influenced by upwind-state emissions. 
See 82 FR 9155, 9157 (February 3, 2017). When acting on Wyoming's and 
Utah's 2008 ozone NAAQS interstate transport SIP submissions, the EPA's 
view was that ``the air quality problem in [the Denver nonattainment 
area of Colorado] resulted in part from the relatively small individual 
contribution of upwind states that collectively contribute a larger 
portion of the ozone contributions (9.7%), comparable to some eastern 
receptors . . . .'' See 84 FR 3389, 3391 (February 12, 2019). See also 
81 FR 71991, 71994-95 (October 19, 2016); 81 FR 28807, 28810 (May 10, 
2016) (Colorado receptors are impacted by interstate transport where 
total upwind state contribution is 11 percent of the total ozone 
concentration, and five states were projected to be linked).
---------------------------------------------------------------------------

    \72\ Site ID 80050002 (Arapahoe), Site ID 80350004 (Douglas), 
and Site ID 80590011 (Jefferson).
---------------------------------------------------------------------------

    Indeed, the EPA has specifically addressed this precise comparison 
between the circumstances of Arizona's approval and the nature of the 
receptors in Colorado. In approving Utah's interstate transport SIP as 
to prong 1 for the 2008 ozone NAAQS, the EPA found its analysis as to 
Arizona's impact on California sites did not apply to Utah's impact on 
Colorado's sites (which the EPA found remained to be at least 
maintenance receptors as to the 2008 ozone NAAQS). See 82 FR 9155, 9157 
(February 3, 2017) (``The EPA's assessment concluded that emissions 
reductions from Arizona are not necessary to address interstate 
transport because the total collective upwind state ozone contribution 
to these receptors is relatively low compared to the air quality 
problems typically addressed by the good neighbor provision. As 
discussed previously, the EPA similarly evaluated collective 
contribution to the Douglas County, Colorado monitor and finds the 
collective contribution of

[[Page 31506]]

transported pollution to be substantial.'') (emphasis added).\73\
---------------------------------------------------------------------------

    \73\ As noted in that action, because Utah was found to still be 
linked to Colorado's maintenance receptors under the 2008 ozone 
NAAQS, the EPA's disapproval of the SIP as to prong 2 remained in 
place, and accordingly, there is an outstanding obligation to 
resolve Utah's transport obligations with respect to the 2008 ozone 
NAAQS. See id. at 9156.
---------------------------------------------------------------------------

    The modeling data on which the WDEQ relied in its SIP submission 
continue to bear out these conclusions (see Appendix B, pages 6-8). 
That modeling showed contributions from more than one upwind state 
above 1 percent of the NAAQS at all Colorado receptors and showed total 
upwind contribution to be between 8 and 10 percent of the total ozone 
concentrations at those receptors.
    The EPA acknowledges that in its most recent modeling of 2023 
(using the 2016v2 platform), the degree of the interstate transport 
problem to Colorado is now projected to lessen somewhat compared to 
previous projections of 2023. However, these projected improvements are 
still not sufficient to draw a conclusion that Colorado is not impacted 
to a considerable degree by out of state emissions. The EPA's recent 
air quality modeling continues to show that multiple upwind states 
collectively contribute to projected downwind nonattainment or 
maintenance receptors in Colorado--specifically, California, Utah, and 
Wyoming all contribute above 1 percent of the NAAQS to at least one of 
Colorado's receptors in 2023. (In contrast, at the time EPA approved 
Arizona's 2008 ozone NAAQS good neighbor SIP, Arizona was the only 
state linked above 1 percent at the relevant California monitoring 
sites.) Further, our most recent modeling shows that the total upwind 
state contribution to ozone concentrations (from linked and unlinked 
states) at identified downwind air quality problems in Colorado is 
approximately 6 to 7 percent, as shown in Table 4. That remains higher 
than the 2 to 4 percent range of total upwind contribution the EPA 
found to be negligible with respect to the California sites analyzed in 
the Arizona action. Therefore, the EPA continues to find that the 
collective contribution of emissions from upwind states represents a 
significant portion of the ozone concentrations at projected 
nonattainment and maintenance receptors in Colorado.

                                    Table 4--All Upwind State Contributions to Nonattainment Receptors in Colorado a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                                                              Percent
                                                                                                                           Contribution    contribution
               Site ID                           State                    County          2023 Avg (ppb)  2023 Max (ppb)   of all upwind   of all upwind
                                                                                                                              states          states
                                                                                                                          combined (ppb)   combined \b\
--------------------------------------------------------------------------------------------------------------------------------------------------------
80350004.............................  Colorado................  Douglas................            71.7            72.3            5.17               7
80590006.............................  Colorado................  Jefferson..............            72.6            73.3            4.23               6
80590011.............................  Colorado................  Jefferson..............            73.8            74.4            4.34               6
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Based on data from 2016v2 platform modeling.
\b\ Calculated using the projected 2023 average design values for the applicable receptors.

    As noted, the Agency has consistently found that the 1 percent of 
the NAAQS threshold is appropriate for identifying interstate transport 
linkages for states collectively contributing to downwind ozone 
nonattainment or maintenance problems because that threshold captures a 
high percentage of the total pollution transport affecting downwind 
receptors. The EPA believes contribution from an individual state equal 
to or above 1 percent of the NAAQS could be considered significant 
where the collective contribution of emissions from one or more upwind 
state is responsible for a considerable portion of the downwind air 
quality problem regardless of where the receptor is geographically 
located. In this case, three states contributing to those identified 
receptors, including Wyoming, contribute emissions greater than or 
equal to 1 percent of the 2015 ozone NAAQS. In addition, the total 
upwind state contribution to ozone levels at the Colorado receptors is 
on the order of 4 to 5 ppb, or 6 to 7 percent of total ozone 
concentration, as shown in Table 4. Given these results, and the EPA's 
consistent use of the 1 percent threshold, in ozone transport actions 
across all areas of the country (including actions related to Wyoming 
and Utah's interstate transport obligations with respect to these same 
receptors), the EPA is proposing to determine that Wyoming contributes 
to nonattainment and interferences with maintenance of the 2015 ozone 
NAAQS for the Denver, Colorado area.
    The WDEQ, relying on potential ``flexibilities'' in Attachment A to 
the March 2018 memorandum, also claims that receptors in the West are 
predominantly impacted by local emissions and ``uncontrollable'' 
emissions such as those from non-U.S. sources or non-anthropogenic 
sources, and so the State ``contends that it is unnecessary to consider 
Step 3 in this analysis.'' \74\ As explained previously in the preamble 
of this document, the concepts presented in Attachment A to the March 
2018 memorandum were neither guidance nor determined by the EPA to be 
consistent with the CAA. While in-state, non-U.S., and non-
anthropogenic sources emissions may be contributing to an area's 
nonattainment or maintenance status, there is nothing in the CAA to 
suggest that these emissions serve to absolve upwind states of their 
obligations to control their own emissions.
---------------------------------------------------------------------------

    \74\ Wyoming SIP submission, Attachment B at 3, 8.
---------------------------------------------------------------------------

    With respect to local or in-state emissions, there is no statutory 
basis to conclude that such emissions must be controlled first before a 
contributing state's share can be controlled under CAA section 
110(a)(2)(D)(i)(I). 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 the 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

[[Page 31507]]

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 the EPA must address interstate transport 
obligations in line with the attainment schedule provided in the CAA 
(i.e., not after attainment-planning measures have been taken by the 
downwind state) in order to timely assist downwind states in attaining 
and maintain the NAAQS, and this attainment 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)).
    With respect to international and non-anthropogenic emissions 
contributions, the WDEQ's reasoning is inapplicable to the requirements 
of CAA section 110(a)(2)(D)(i)(I). The good neighbor provision requires 
states and the EPA to address interstate transport of air pollution 
that contributes to a 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. 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 also contribute some amount of 
pollution to the same receptors to which the state is linked.
    Further, the data supplied in Wyoming's SIP submission tends to be 
self-refuting on this point. Table 3 in Appendix B to the State's SIP 
submission indicates, according to the WDEQ, that ``more than 50 
percent'' of the total ozone concentrations at the Colorado receptors 
are from non-anthropogenic or non-U.S. emissions sources. Assuming 
those numbers are correct, this means that nearly 50 percent of the 
ozone levels at the Colorado receptors are the result of anthropogenic 
emissions originating in the U.S. Those emissions are clearly within 
the authority of states and the EPA to redress and reducing some 
portion of those emissions can be assumed to improve air quality at the 
Colorado receptors. While not all of those U.S. anthropogenic emissions 
can be attributed to Wyoming, Wyoming's emissions are shown by the 
modeling to contribute to Colorado's air quality problem at levels 
sufficient to warrant evaluation of emissions control opportunities at 
Step 3 of the EPA's longstanding analytical framework.
    The next analysis the WDEQ included in its SIP submission is 
NOX and VOC emissions trends. The WDEQ points to a projected 
downward trend of ozone levels at monitors within the Colorado 
nonattainment area through 2025, as well as an observed reduction since 
2011 in emissions of VOCs and NOX emissions in Wyoming 
through a combination of regulatory and permitting actions.\75\ The 
WDEQ also pointed to an estimate provided in the State's 2008 ozone 
NAAQS infrastructure SIP, which projected a decrease in NOX 
emissions between 2011 and 2023 of 32,985.5 tpy and a decrease of VOC 
emissions between 2011 and 2023 of 905.6 tpy as a result of the Wyoming 
Existing Source Rule.\76\ The EPA considers the measures the WDEQ 
described to be beneficial in reducing VOC and NOX 
emissions, and the EPA's most recent modeling has projected that there 
will be a downward trend of ozone at the Denver nonattainment monitors. 
However, the WDEQ has not provided any analysis to demonstrate that the 
reductions in their State will be sufficient to eliminate its 
contribution above 1 percent of the NAAQS to Colorado receptors, or 
that those receptors will cease to exist by 2023. The WDEQ did not 
quantify the total anticipated reductions in NOX and VOC 
emissions from its permitting actions and existing regulatory 
requirements nor did it evaluate the impact of those reductions in 
downwind air quality at the Denver area receptors. In general, the air 
quality modeling that the EPA has conducted already accounts for ``on-
the-books'' emissions control measures, including the expected 
reductions those measures achieve through 2023. Both the 2016v1 and the 
more current 2016v2 modeling clearly establish continued linkage from 
Wyoming to downwind receptors in 2023 at Steps 1 and 2, despite those 
emissions control efforts.
---------------------------------------------------------------------------

    \75\ Wyoming SIP submission, Attachment B at 9.
    \76\ Id.
---------------------------------------------------------------------------

    As explained previously in this document, the WDEQ's SIP submission 
does not provide an adequate technical analysis demonstrating that the 
SIP contains adequate provisions prohibiting emissions that will 
significantly contribute to nonattainment or interfere with the 2015 
ozone NAAQS in any other state. Moreover, Denver monitors continue to 
violate the 2015 ozone NAAQS and in fact many Denver monitors showed an 
increase in 2020 ozone design values when compared to the 2019 design 
values. See Table 5 which includes the last five years of the 3-year 
design values for the Denver nonattainment area monitors.

[[Page 31508]]



                                          Table 5. Ozone Design Values for Denver Nonattainment Area Monitors a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                             2014-2016       2015-2017       2016-2018       2017-2019       2018-2020
           AQS Site ID                   State              County         Design value    Design value    Design value    Design value    Design value
                                                                               (ppb)           (ppb)           (ppb)           (ppb)           (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
80013001........................  Colorado..........  Adams.............              67              67              67              65              69
80050002........................  Colorado..........  Arapahoe..........  ..............  ..............              73              74              77
80050006........................  Colorado..........  Arapahoe..........              67              67              69              69              71
80310002........................  Colorado..........  Denver............              66              68              69              68              70
80350004........................  Colorado..........  Douglas...........              77              77              78              78              81
80590005........................  Colorado..........  Jefferson.........              72              75              72              71              71
80590006........................  Colorado..........  Jefferson.........              77              77              78              76              79
80590011........................  Colorado..........  Jefferson.........              80              79              79              76              80
80690007........................  Colorado..........  Larimer...........              69              68              70              68              70
80690011........................  Colorado..........  Larimer...........              75              75              77              75              75
80691004........................  Colorado..........  Larimer...........              70              68              69              67              67
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ According to data from 2016v2 platform modeling.

    As shown in Table 5, the 3-year design values for majority of the 
Denver monitors increased between 2019 and 2020, indicating the end of 
any downward trend of ground-level ozone which the WDEQ may have seen 
previously. Additionally, the EPA's most recent modeling continues to 
indicate that emissions from Wyoming are projected to contribute to one 
downwind nonattainment or maintenance receptors in the Denver, Colorado 
area through 2023.
    In its January 2019 SIP submittal, the WDEQ acknowledges that 
receptors in the Denver, Colorado nonattainment area could be impacted 
by emissions from Wyoming, but despite the modeling results that 
indicate that, the WDEQ concludes that Wyoming is not ``linked'' at 
Step 2 and that emissions from the State do not significantly 
contribute to nonattainment in the Denver area.\77\ Overall, the EPA 
believes that Wyoming has not adequately addressed the modeled 
contributions to projected downwind receptors identified by the EPA's 
modeling. Therefore, based on the EPA's evaluation of the information 
submitted by the WDEQ, and based on the EPA's most recent modeling 
results for 2023, the EPA proposes to find that Wyoming 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.
---------------------------------------------------------------------------

    \77\ Id. at 10.
---------------------------------------------------------------------------

B. Evaluation of Information Provided Regarding Step 3

    At Step 3 of the 4-Step 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. The EPA has consistently applied this general approach 
(i.e., Step 3 of the 4-Step 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 the EPA has not directed states that they must conduct a 
Step 3 analysis in precisely the manner the 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 
the 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.
    Wyoming did not conduct such an analysis in its SIP submission, as 
a result of their conclusions pursuant to Step 1 and Step 2. As 
explained in connection with the evaluation of the WDEQ's Step 1 and 
Step 2 analyses, the EPA disagrees with those conclusions and 
accordingly the WDEQ should have proceeded to evaluate which emissions 
in the State should be deemed ``significant'' and therefore prohibited. 
We therefore propose that Wyoming 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 SIP submission because Wyoming failed to do so.

C. Evaluation of Information Provided Regarding Step 4

    Step 4 of the 4-Step 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, Wyoming's SIP 
submission did not contain an evaluation of additional emission control 
opportunities (or establish that no additional controls are required), 
thus, no information was provided at Step 4. As a result, the EPA 
proposes to disapprove Wyoming's January 3, 2019 SIP submission 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).

D. Conclusion

    Based on the EPA's evaluation of the WDEQ's SIP submission, the 
Agency is proposing to find that the portion of the State's January 3, 
2019 SIP submission addressing CAA section 110(a)(2)(D)(i)(I) does not 
meet Wyoming's interstate transport obligations, because it fails to 
contain the necessary provisions to eliminate emissions that will 
contribute significantly to nonattainment or

[[Page 31509]]

interfere with maintenance of the 2015 8-hour ozone NAAQS in any other 
state.

IV. Proposed Action

    We are proposing to disapprove the WDEQ's SIP submission pertaining 
to interstate transport of air pollution which will significantly 
contribute to nonattainment or interfere with maintenance of the 2015 
8-hour ozone NAAQS in other states. Under CAA section 110(c)(1), 
disapproval would establish a 2-year deadline for the EPA to promulgate 
a FIP for Wyoming 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 8-hour ozone NAAQS in other states, unless the EPA approves a SIP 
that meets these requirements. Disapproval does not start a mandatory 
CAA sanctions clock for Wyoming. The remaining elements of the State's 
January 3, 2019 submission are not addressed in this action and have 
been 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 the 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

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

    The 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 the 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 the EPA complete discretion whether to 
invoke the exception in (ii).\78\
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    \78\ 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 the 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), the 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, the 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. The 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 4-Step 
Framework. Further, the EPA proposes to determine and apply a set of 
nationally consistent policy judgments to apply the 4-Step Framework. 
The 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.\79\ For these reasons, the

[[Page 31510]]

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).\80\
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    \79\ 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.
    \80\ The 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 the EPA take a single final action on all such disapprovals, 
this action would be nationally applicable, and the 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.
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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: May 16, 2022.
KC Becker,
Regional Administrator, Region 8.
[FR Doc. 2022-11153 Filed 5-23-22; 8:45 am]
BILLING CODE 6560-50-P