[Federal Register Volume 87, Number 100 (Tuesday, May 24, 2022)]
[Proposed Rules]
[Pages 31470-31484]
[FR Doc No: 2022-11152]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R08-OAR-2022-0315; EPA-HQ-OAR-2021-0663; FRL-9806-01-R8]

Air Plan Disapproval; Utah; 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 federal Clean Air Act (CAA or the Act), the
Environmental Protection Agency (EPA) is proposing to disapprove the
State Implementation Plan (SIP) submittal from Utah regarding
interstate transport for the 2015 8-hour ozone national ambient air
quality standard (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. If the EPA finalizes this disapproval, the EPA will
continue to be subject to an obligation to promulgate a Federal
Implementation Plan (FIP) to address the relevant interstate transport
requirements, which was triggered by a finding of failure to submit
issued in December of 2019. 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-
2022-0315, to the Federal eRulemaking Portal at https://www.regulations.gov following the online instructions for submitting
comments.
    Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public participation''
heading of the SUPPLEMENTARY INFORMATION section of this document. The
EPA Docket Office can be contacted at<PHONE_NUMBER>, 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: Adam Clark, Air and Radiation
Division, EPA, Region 8, Mailcode 8ARD-IO, 1595 Wynkoop Street, Denver,
Colorado, 80202-1129, telephone number:<PHONE_NUMBER>, email address:
[email protected].

SUPPLEMENTARY INFORMATION:
    Public participation: Submit your comments, identified by Docket ID
No. EPA-R08-OAR-2022-0315, 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 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-2022-0315
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R08-OAR-2022-0315 contains
information specific to Utah, 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-
0315. For additional submission methods, please contact Adam Clark,
telephone number:<PHONE_NUMBER>, email address: [email protected].
For the full EPA public comment policy, information about CBI or
multimedia submissions, and general guidance on making effective
comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets.
    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.
    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. Utah 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 Utah 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 Utah'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 interstate transport framework
to evaluate a state's obligations to eliminate interstate transport
emissions under the interstate transport provision for the ozone NAAQS:
(1) Identify monitoring sites that are projected to have problems
attaining and/or maintaining the NAAQS (i.e., nonattainment and/or
maintenance receptors); (2) identify states that impact those air
quality problems in other (i.e., downwind) states sufficiently such
that the states are considered ``linked'' and therefore warrant further
review and analysis; (3) identify the emissions reductions necessary
(if any), applying a multifactor analysis, to eliminate each linked
upwind state's significant contribution to nonattainment or
interference with maintenance of the NAAQS at the locations identified
in Step 1; and (4) adopt permanent and enforceable measures needed to
achieve those emissions reductions.
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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
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 interstate transport

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 standard at Step 1 of the 4-step
interstate transport 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 ID 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 ID 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 ID 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 ID No. EPA-HQ-OAR-2021-0663.
    \15\ See 85 FR 68964, 68981.
    \16\ See the Air Quality Modeling Technical Support Document for
the Final Revised Cross-State Air Pollution Rule Update, included in
the Headquarters docket ID No. EPA-HQ-OAR-2021-0663.
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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 an
emissions modeling technical support document (TSD) included in the
docket for 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 interstate transport 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 ID 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 ID No. EPA-R08-OAR-2022-0315. Comments are not
being accepted in docket ID 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 the Headquarters docket ID 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 Utah 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
submittals for the 2015 8-hour ozone NAAQS. These policy judgments
reflect consistency with relevant case law and past agency practice as
reflected in the CSAPR and related rulemakings. Nationwide consistency
in approach is particularly important in the context of interstate
ozone transport, which is a regional-scale pollution problem involving
many smaller contributors. Effective policy solutions to the problem of
interstate ozone transport going back to the NOX SIP Call
have necessitated the application of a uniform framework of policy
judgments 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. 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 submittals, 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, ``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 interstate transport framework by a particular attainment date,
but for reasons of impossibility or profound uncertainty the Agency
is unable to mandate upwind pollution controls by that date. See
Wisconsin, 938 F.3d at 320. The D.C. Circuit noted in Wisconsin that
upon a sufficient showing, these circumstances may warrant
flexibility in effectuating the purpose of the interstate transport
provision.
    \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 Utah'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 the EPA's 4-step
interstate transport framework. For sites that are identified as a
nonattainment or maintenance receptor in 2023, we proceed to the next
step of our 4-step interstate transport framework by identifying the
upwind state's contribution to those receptors.
    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 receptors, 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 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). CSAPR Update and Revised
CSAPR Update also used this approach. See 81 FR 74504 (October 26,
2016) and 86 FR 23054 (April 30, 2021).
---------------------------------------------------------------------------

    Recognizing that nonattainment receptors are also, by definition,
maintenance receptors, 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 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 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 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, 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 the 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 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. Utah SIP Submission Addressing Interstate Transport of Air
Pollution for the 2015 8-Hour Ozone NAAQS

    On October 24, 2019, the State of Utah submitted a SIP revision to
the EPA addressing the 110(a)(1) and (2) infrastructure requirements
for the 2015 ozone NAAQS, including CAA section 110(a)(2)(D)(i)(I). The
EPA evaluated this submission for completeness pursuant to the criteria
in 40 CFR part 51, appendix V, and concluded that it was incomplete
because Utah had not provided the necessary certification under section
2.1(g) of appendix V that a public hearing was held or provided the
opportunity for the public to request a public hearing in accordance
with 40 CFR 51.102(a). On November 21, 2019, the EPA sent a letter to
Utah explaining our incompleteness determination.\30\ On December 5,
2019, the EPA issued a finding that several states, including Utah, had
failed to submit SIPs to meet the interstate transport requirements of
CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS. See 84 FR
66612. On January 29, 2020, the State submitted a new SIP revision
addressing the infrastructure requirements for the 2015 ozone NAAQS,
including CAA section 110(a)(2)(D)(i)(I), as well as CAA section
110(a)(2)(D)(i)(I) prong 2 for the 2008 ozone NAAQS.\31\
---------------------------------------------------------------------------

    \30\ The EPA's November 21, 2019 letter to the State of Utah is
included in docket ID EPA-R08-OAR-2022-0315 for this action.
    \31\ The EPA is not proposing any action on the 2008 ozone
portion of Utah's January 29, 2020 submittal, or any of the other
infrastructure elements apart from those portions submitted to meet
the requirements of CAA section 110(a)(2)(D)(i)(I) for the 2015
ozone NAAQS.
---------------------------------------------------------------------------

    The SIP submission provided an analysis by the Utah Division of Air
Quality (UDAQ) of the State's impact on air quality in downwind states
and concluded that emissions from Utah will not significantly
contribute to nonattainment or interfere with maintenance of the 2015
ozone NAAQS in other states in 2023.\32\ In the SIP submittal, UDAQ
conducted a weight-of-evidence analysis, which sought to rely in part
on certain outside parties' ideas for ``flexibilities'' in assessing
good neighbor obligations that had been listed in Attachment A to the
March 2018 memorandum. See section I.D. above. UDAQ's weight-of-
evidence analysis utilized the EPA's 4-step interstate transport
framework approach. At Step 1 of the framework, UDAQ used EPA modeling
released with the March 2018 memorandum to conclude that the Denver
nonattainment area was the only area with identified nonattainment and
maintenance receptors in 2023 to which sources in Utah could possibly
contribute (Step 1).\33\ In identifying this area at Step 1, UDAQ
considered the ``flexibility'' listed in Attachment A of the March 2018
memo, consideration of ``the current and projected local emission
reductions and whether downwind areas have considered and/or used
available mechanisms for regulatory relief.'' UDAQ considered current
and projected emissions reductions in the Denver nonattainment
area.\34\ Specifically, UDAQ considered recent oil and gas control
requirements Colorado adopted for oil and gas sources within the Denver
nonattainment area.\35\
---------------------------------------------------------------------------

    \32\ Utah's SIP submission at C-005, C-013.
    \33\ Id. at C-007. The EPA notes that the modeling released with
the March 2018 memorandum used 2011 base year inventory data.
    \34\ Id.
    \35\ Id.
---------------------------------------------------------------------------

    At Step 2 of the 4-step interstate transport framework, UDAQ
utilized a weight of evidence approach.\36\ As part of its weight of
evidence, UDAQ considered EPA's modeling from the March 2018 memorandum
to identify which nonattainment and/or maintenance receptors were
linked to emissions from Utah. UDAQ identified five nonattainment and
maintenance receptors to which the State was projected to contribute
greater than 0.70 ppb (1 percent) to the 2023 design values. Table 1
provides information on the five nonattainment and maintenance
receptors identified by UDAQ in their SIP submittal.
---------------------------------------------------------------------------

    \36\ Id. at C-007-C008.

   Table 1--2023 Average and Maximum Design Values at Downwind Receptors With Utah Contributions Equal to and
                                             Greater Than 0.70 ppb a
----------------------------------------------------------------------------------------------------------------
                                                                      Average         Maximum      Utah modeled
          Receptor ID               State           County         design value    design value    contribution
                                                                       (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
Nonattainment Receptors:
    80350004...................  CO           Douglas...........            71.1            73.2            1.08
    80590006...................  CO           Jefferson.........            71.3            73.7            0.83
    80690011...................  CO           Larimer...........            71.2            73.0            1.05
Maintenance Receptors:
    80050002...................  CO           Arapahoe..........            69.3            71.3            1.23
    80590011...................  CO           Jefferson.........            70.9            73.9            1.04
----------------------------------------------------------------------------------------------------------------
\a\ Data according to March 2018 memorandum modeling.

    UDAQ presented all of the monitors to which the State was modeled
to contribute at or above the 1 percent of the NAAQS threshold.
However, UDAQ indicated in their SIP submittal that they support the
use of a 1 ppb threshold and referenced the EPA's August 2018
memorandum, which they characterized as the EPA finding alternative
thresholds as ``appropriate.'' \37\ UDAQ conducted a comparison of the
1 percent and 1 ppb thresholds at the five nonattainment or maintenance
receptor sites shown in Table 1, analyzing the differences in capture
of upwind contribution under the two thresholds (60% for 1 percent and
47% for 1 ppb) to assert that the 1 ppb threshold is appropriate
because the capture rates were comparable.\38\ UDAQ noted that by using
a 1 ppb threshold, the State would only be linked to four \39\ of the
five receptors listed in Table 1. UDAQ still elected to evaluate
contributions from the fifth receptor (Receptor ID 806590011) ``to make
a more complete assessment of the modeled results.'' \40\ Table 2
provides UDAQ's analysis of the two contribution thresholds as
presented in its January 29, 2020 submission.
---------------------------------------------------------------------------

    \37\ Utah's SIP submission at C-008.
    \38\ Id.
    \39\ Each of the five receptors apart from Receptor ID 80590006
(Jefferson, Colorado).
    \40\ Utah's SIP submission at C-008.

                                   Table 2--Comparison of 2023 Contribution Thresholds at Receptor Sites in Colorado a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Sum of upwind   Sum of upwind    Percent of      Percent of
                                                                           Total upwind       contr.          contr.       upwind contr.   upwind contr.
                Receptor ID                            County              state contr.    captured with   captured with  captured using  captured using
                                                                               (ppb)       0.70 ppb (1%)       1 ppb        a 0.70 ppb        a 1 ppb
                                                                                threshold       threshold    (1%) threshold     threshold
--------------------------------------------------------------------------------------------------------------------------------------------------------
80050002..................................  Arapahoe....................            5.98            3.47            3.47            58.0            58.0
80350004..................................  Douglas.....................            5.94            3.35            3.35            56.4            56.4
80590006..................................  Jefferson...................            7.06            4.68            2.34            66.3            33.1
80590011..................................  Jefferson...................            6.98            4.51            3.57            64.6            51.1
80690011..................................  Larimer.....................            6.33            3.48            2.60            55.0            41.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Data according to March 2018 memorandum modeling.

    In its weight-of-evidence analysis, UDAQ also referenced the EPA's
proposed approval of Arizona's interstate transport SIP for the 2008
ozone NAAQS as providing an administrative precedent for its
conclusions regarding Utah.\41\ UDAQ stated that in that proposal, the
EPA considered ``the magnitude of ozone attributable to transport from
all upwind states collectively contributing to the air quality
problem'' and, after considering the total contributions from all
states that contributed to the same receptors linked to Arizona,
determined the collective contribution of emissions to those downwind
receptors was negligible ``particularly when compared to the relatively
large contributions from upwind states in the East.'' To support the
applicability of the Arizona action, UDAQ again pointed to the March
2018 memorandum modeling to illustrate ``the disparity between upwind
contributions from states in the East versus the West.'' \42\
Specifically, UDAQ cited modeled collective upwind state contributions
to receptors in Connecticut (44.24 ppb to Receptor ID 900190003) and
New York (30.68 ppb to Receptor ID 360810124) in comparison to the
lesser in-state contributions (3.71 ppb to Receptor ID 900190003 and
13.55 ppb to Receptor ID 360810124) to these receptors. UDAQ then
compared these ratios against the highest collective contributions from
upwind states to any of the Colorado nonattainment or maintenance
receptors (7.06 ppb to Receptor ID 80590006) and the in-state
(Colorado) contribution to this receptor (25.52 ppb). Table 3 provides
UDAQ's summary of in-state and upwind state contributions using the
March 2018 memorandum modeling. UDAQ asserted that the difference in
magnitude between Colorado's modeled in-state contributions to its
nonattainment and maintenance receptors and Utah's modeled
contributions, especially when compared to receptors in the eastern
U.S., led the State to conclude that their interstate contributions to
these receptors are negligible.\43\
---------------------------------------------------------------------------

    \41\ Id. (quoting 81 FR 15200 (March 22, 2016)).
    \42\ Id.
    \43\ Id. at C-009.

                                              Table 3--In-State vs. Collective Upwind State Contributions a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total
                                                                                Average         Maximum        In-state      contribution
              Receptor ID                          County                   State          design value    design value    contribution     from upwind
                                                                                (ppb)           (ppb)           (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.

    As part of its weight of evidence analysis, UDAQ also considered
the impacts of non-anthropogenic and international contributions on the
Denver area receptors to which it was linked by the March 2018
memorandum modeling, claiming that this was identified as a flexibility
under Step 3 in the March 2018 memorandum.\44\ UDAQ included the
information provided in Table 4 to support this point and asserted that
the high level of ``[u]ncontrollable'' emissions made it unnecessary
for the State to consider Step 3 of the 4-step interstate transport
framework in its analysis.\45\
---------------------------------------------------------------------------

    \44\ Id.
    \45\ Id.

   Table 4--Contributions From Canada/Mexico, Offshore, Fire, and Biogenic Emissions and the Initial/Boundary Conditions to Colorado Receptor Sites a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Total
                                                                        2023  Maximum   Non-U.S./non     Initial and     uncontrollable   Percent of max
               Receptor ID                           County             design value     anthro \b\       Boundary        contribution          DV
                                                                            (ppb)           (ppb)        conditions          (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
80050002................................  Arapahoe...................            71.3            5.39           34.84              40.23              56
80350004................................  Douglas....................            73.2            5.53           34.74              40.27              55
80590006................................  Jefferson..................            73.7            7.13           31.41              38.54              52
80590011................................  Jefferson..................            73.9            6.05           32.96              39.01              53
80690011................................  Larimer....................            73.0            8.42           34.54              42.96              59
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ Data according to March 2018 memorandum modeling.
\b\ Includes contributions from Canada/Mexico, Offshore, Fire, and Biogenic sources.

    Lastly, UDAQ's weight-of-evidence argument points to reductions in
ozone precursor pollutants nitrogen oxides (NOX) and
volatile organic compounds (VOC) that have taken place in the State
since 2011, the base year for the March 2018 memorandum modeling.\46\
UDAQ asserted that their statewide emissions inventory had decreased by
37% (NOX) and 30% (VOC), respectively, between 2011 and
2017.\47\ UDAQ also pointed to then-forthcoming Best Available Control
Technology (BACT) requirements for the Salt Lake City, UT
PM2.5 Nonattainment Area, estimating these would result in
projected further reductions of 1,440 tons/year of NOX and
5,624 tons/year of VOC within the nonattainment area by 2020.\48\ UDAQ
also discussed the anticipated reduction in mobile source emissions due
to the national Tier 3 Vehicle Emissions and Fuel Standards, as well as
increased inspection and compliance requirements for the oil and gas
sector, though they did not quantify either of these reductions.\49\
UDAQ concluded that it would not be necessary to require additional
reductions at Steps 3 and 4 given the amount of reductions already
achieved.\50\
---------------------------------------------------------------------------

    \46\ Id. at C-011.
    \47\ Id.
    \48\ Id.
    \49\ Id.
    \50\ Id. at C-013.
---------------------------------------------------------------------------

    Overall, Utah's SIP submittal asserts that: (1) A 1 ppb threshold
is appropriate for states contributing to the Denver area receptors,
including Utah; (2) contributions from Utah to linked nonattainment and
maintenance receptors are not significant when considering in-state
contributions from Colorado and total collective contributions from all
upwind states; (3) contributions from Utah should not be controlled at
Step 3 due to the amount of uncontrollable international and non-
anthropogenic emissions contributing to the downwind nonattainment and
maintenance receptors, and; (4) emissions of VOCs and NOX in
Utah are declining or have declined such that it is unnecessary to
require further reductions at Steps 3 and 4. UDAQ asserted that the
combined information in its weight of evidence analysis demonstrates
that emissions from the State do not significantly contribute to
nonattainment or interfere with the maintenance of the 2015 ozone NAAQS
in any downwind state.

III. The EPA's Evaluation

    The EPA is proposing to find that Utah's January 29, 2020 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 Utah's SIP
submission is based on our evaluation of the SIP using the 4-step
interstate transport framework.

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

    At Step 1 and Step 2 of the 4-step interstate transport framework,
UDAQ relied on 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 UDAQ identified a
number of nonattainment and maintenance receptor sites in 2023 as did
the more recent 2023 modeling. Thus, EPA agrees with UDAQ 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 in the Denver area.
    In their January 2020 SIP submittal, UDAQ stated that a 1 ppb
threshold is appropriate for the Denver area receptors to which it is
linked. As noted in Section II of this proposed action, UDAQ cited the
EPA's August 2018 memorandum to justify using a 1 ppb alternative
contribution threshold at Step 2 as a basis to assert that Utah would
not be linked to some projected downwind nonattainment or maintenance
receptors. UDAQ did not appear to argue in its submittal that 1 percent
of the NAAQS would not be an appropriate threshold for upwind
contribution to the Denver area receptors, and purported to evaluate
contribution even at a fifth receptor to which it contributed less than
1 ppb (See Submittal at C-009). The EPA views the 1 percent of NAAQS
threshold as the more appropriate threshold, as explained elsewhere in
this document.\51\
---------------------------------------------------------------------------

    \51\ We note 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 81 FR 74504, 74518-19.
---------------------------------------------------------------------------

    As discussed in the August 2018 memorandum, the EPA suggested that,
with appropriate additional analysis, it may be reasonable for states
to use a 1 ppb contribution threshold, as an alternative to a 1 percent
threshold, at Step 2 of the 4-step interstate transport framework, for
the purposes of identifying linkages to downwind receptors. Utah
conducted an analysis comparing the 1 ppb and 1 percent thresholds, as
shown in Table 2 of this document and asserted that the 1 ppb threshold
is appropriate because the capture rates are generally comparable in
the March 2018 memorandum modeling. However, UDAQ did not adequately
explain how a 1 ppb threshold would be justified with respect to all
the receptors to which Utah is linked. While the EPA agrees that the
capture rate is comparable with regard to some of the listed Denver
area receptors, the use of the alternative 1 ppb threshold would have
the result of reducing the amount of cumulative upwind state
contributions that would be captured for other receptors. Specifically,
the two Jefferson Country receptors (sites 80590006 and 80590011)
captured 33.2% and 13.5% less upwind contribution, respectively, at 1
ppb than at 1 percent using the March 2018 memorandum modeling UDAQ
relied on (see Table 2). This far exceeds the roughly 7 percent loss in
total upwind state contributions the EPA found would occur at 1 ppb on
a nationwide basis in its August 2018 memorandum, but UDAQ offered no
further explanation why that level of loss in cumulative upwind state
contribution would be approvable with respect to the receptors to which
it was linked. Indeed, this degree of loss in cumulative upwind state
contribution appears more comparable to what would occur at a threshold
of 2 ppb, which the EPA indicated in its August 2018 memorandum would
generally not be approvable.\52\ While the EPA does not, in this
action, approve of UDAQ's application of the 1 ppb threshold, because
all of Utah's linkages based on the EPA's updated 2016v2 modeling (See
Table 5 below) are greater than 1 ppb to projected downwind
nonattainment or maintenance receptors, UDAQ's use of this alternative
threshold at Step 2 of the 4-step interstate framework would not alter
our review and proposed disapproval of this SIP submittal.
---------------------------------------------------------------------------

    \52\ See August 2018 memorandum at 4.
---------------------------------------------------------------------------

    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.\53\ (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 that state, in order to more
thoroughly evaluate the state-specific circumstances that could support
approval.\54\ It was at the EPA's sole discretion to perform this
analysis in support of Iowa'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.\55\ 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 interstate transport framework. From the
perspective of ensuring effective regional implementation of good
neighbor obligations, the more important analysis is the evaluation of
the emissions

reductions needed, if any, to address a state's significant
contribution after consideration of a multifactor analysis at Step 3,
including a detailed evaluation that considers air quality factors and
cost. Where alternative thresholds for purposes of Step 2 may be
``similar'' in terms of capturing the relative amount of upwind
contribution (as described in the August 2018 memorandum), nonetheless,
use of an alternative threshold would allow certain states to avoid
further evaluation of potential emission controls while other states
must proceed to a Step 3 analysis. This can create significant equity
and consistency problems among states. 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; \56\
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.
---------------------------------------------------------------------------

    \53\ Id.
    \54\ 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
(Feb. 22, 2022).
    \55\ 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.
    \56\ 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 Utah'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 August 2018 memorandum in the future.
    As described in Section I of this preamble, the EPA recently
performed air quality modeling using the 2016v2 emissions platform to
project design values and contributions for 2023. These data were
examined to determine if Utah 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. As shown in Table 5, the EPA's
2016v2 modeling projects that in 2023, emissions from Utah will
contribute greater than 1 percent of the standard to nonattainment
receptors in both Douglas and Jefferson Counties, Colorado.\57\
---------------------------------------------------------------------------

    \57\ These modeling results are consistent with the results of a
prior round of 2023 modeling using the 2016v1 emissions platform
which became available to the public in the fall of 2020 in the
Revised CSAPR Update, as noted in Section I. That modeling showed
that Utah had a maximum contribution equal to or greater than 0.70
ppb to multiple nonattainment or maintenance-only receptor in 2023.
These modeling results are included in the file ``Ozone Design
Values and Contributions Revised CSAPR Update.xlsx'' in docket EPA-
HQ-OAR-2021-0663.

                       Table 5--Utah Linkage Results Based on EPA Updated 2023 Modeling a
----------------------------------------------------------------------------------------------------------------
                                                                   2023 Average    2023  Maximum       Utah
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                                   maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
80350004.....................  Douglas County,   Nonattainment..            71.7            72.3            1.37
                                CO.
80590006.....................  Jefferson         Nonattainment..            72.6            73.3            1.10
                                County, CO.
80590011.....................  Jefferson         Nonattainment..            73.8            74.4            1.06
                                County, CO.
----------------------------------------------------------------------------------------------------------------
\a\ According to data from 2016v2 platform modeling.

    In regard to UDAQ's argument that contributions from Utah are not
significant when considering total collective contributions from all
upwind states to the same receptors, as well as UDAQ's argument that
ozone transport is somehow fundamentally different in the west than the
east, the EPA disagrees. The EPA's recent air quality modeling shows
that multiple upwind states collectively contributed to projected
downwind nonattainment or maintenance receptors in Colorado. In
particular, the EPA found that the total upwind states' contribution to
ozone concentrations (from linked and unlinked states) to identified
downwind air quality problems in Colorado is between 6 and 7 percent,
as shown in Table 6. The EPA has found 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.
    In its SIP submittal, UDAQ pointed to the EPA's approval of an
Arizona interstate transport SIP for the 2008 ozone NAAQS based on
collective transport contributions.\58\ However, for that SIP, Arizona
was the only state linked to the downwind monitoring sites at issue and
the range of total upwind-state contributions to those sites identified
in the Arizona case were

very low as well, in the range of 2.5 to 4.4 percent of the design
value for all upwind states, including both linked (above 1 percent)
and unlinked (below 1 percent) state contributions.
---------------------------------------------------------------------------

    \58\ 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).

                                    Table 6--All Upwind State Contributions to Nonattainment Receptors in Colorado a
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                Contribution       Percent
                                                                                of all upwind   contribution
               Site ID                           State                    County          2023 Avg (ppb)  2023 Max (ppb)      states      of all  upwind
                                                                                combined         states
                                                                                (ppb) \b\     combined \c\
--------------------------------------------------------------------------------------------------------------------------------------------------------
80350004.............................  Colorado................  Douglas................            71.7            72.3            5.17            7.21
80590006.............................  Colorado................  Jefferson..............            72.6            73.3            4.23            5.83
80590011.............................  Colorado................  Jefferson..............            73.8            74.4            4.34            5.88
--------------------------------------------------------------------------------------------------------------------------------------------------------
\a\ According to data from 2016v2 platform modeling.
\b\ The contribution from all upwind states and percent contribution are based on individual upwind contributions that are truncated to two digits to
  the right of the decimal, as provided in regulations.gov at document EPA-HQ-OAR-2021-0668-0069.
\c\ Calculated using the projected 2023 average design values for the applicable receptors.

    As noted, the EPA has consistently found that the 1 percent
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 states is
responsible for a considerable portion of the downwind air quality
problem regardless of where the receptor is geographically located. In
the case of the two Jefferson County, Colorado nonattainment receptors
listed in Table 6, two states, including Utah, contribute emissions
greater than or equal to 1 percent of the 2015 ozone NAAQS. Three
states, also including Utah, contribute above 1 percent to the
nonattainment receptor located in Douglas County, CO. Given the 2016v2
modeling results and the EPA's consistent application of the 1 percent
threshold to establish linkages, the EPA is proposing to determine that
Utah contributes to nonattainment and interferes with maintenance of
the 2015 ozone NAAQS in the Denver, Colorado area.
    Further, the EPA has explained in prior actions on western states'
ozone transport SIPs that a 1 percent threshold may be appropriate in
the west just as much as in the east. When the EPA took action on
Utah's SIP submittal as to prong 2 for the 2008 ozone NAAQS, the EPA
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 (Oct. 19, 2016). The EPA explained the
basis for the 1 percent threshold as derived in the CSAPR and 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 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.
    Similarly, in acting on Wyoming's interstate transport submittals
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 (Feb. 12, 2019).
    When the EPA approved Arizona's 2008 ozone NAAQS transport SIP
submittal, it 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 below, 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.
    UDAQ relies on the EPA's approval of Arizona's 2008 ozone NAAQS
transport SIP as a basis for the claim that its contributions to
Colorado are ``negligible.'' \59\ 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 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 that 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.
---------------------------------------------------------------------------

    \59\ 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 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 UDAQ 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 UDAQ's Step 2 arguments.
    Turning to the substance of UDAQ'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 receptors in Colorado, 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 (Feb. 3,
2017). The EPA's view in acting on Wyoming and Utah's 2008 ozone NAAQS
SIP submittals 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
(Feb. 12, 2019).\60\ See also 81 FR 71991, 71994-95 (Oct. 19, 2016); 81
FR 28807, 28810 (May 10, 2016) (Colorado receptors are impacted by
interstate transport where total upwind state contribution is about 11
percent of the total ozone concentration, and five states were
projected to be linked).
---------------------------------------------------------------------------

    \60\ While EPA ultimately approved Wyoming's transport SIP
submittal as proposed in this 2019 action, this 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).
---------------------------------------------------------------------------

    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 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 at least maintenance receptors as
to the 2008 ozone NAAQS). See 82 FR 9155, 9157 (Feb. 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 transported
pollution to be substantial'') (emphasis added).\61\
---------------------------------------------------------------------------

    \61\ As noted in that action, because Utah was found to still be
linked to Colorado's maintenance receptors under the 2008 ozone
NAAQS, EPA's disapproval of the SIP as to prong 2 remained in place.
See id. at 9156.
---------------------------------------------------------------------------

    The modeling data on which UDAQ relied in its SIP submittal (from
the EPA's March 2018 memorandum) continue to bear out these conclusions
(see Table 3 of UDAQ's submittal). That modeling showed contributions
from more than one upwind state above 1 percent of the NAAQS at all
Colorado receptors, and it showed total upwind-state contribution to be
between 8 and 10 percent of the total ozone concentrations at those
receptors. The EPA disagrees that that degree of upwind state
contribution can be characterized as ``negligible.''
    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 at identified downwind air
quality problems in Colorado is approximately 6 to 7 percent, as shown
in Table 6. That remains higher than the 2 to 4% 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.
    Based on the EPA's evaluation of Utah's January 2020 submission and
consideration of the EPA's most recent (2016v2) modeling results for
2023, the EPA proposes to find that Utah 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.

B. Evaluation of Information Provided Regarding Step 3

    At Step 3 of the 4-step interstate transport framework, a state's
emissions are further evaluated, in light of multiple factors,
including air quality and cost considerations, to determine what, if
any, emissions significantly contribute to nonattainment or interfere
with maintenance and, thus, must be eliminated under CAA section
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be
deemed ``significant'' and therefore prohibited, states generally
should prepare an accounting of sources and other emissions activity
for relevant pollutants and assess potential, additional emissions
reduction opportunities and resulting downwind air quality
improvements. The EPA has consistently applied this general approach
(i.e., Step 3 of the 4-step interstate transport framework) when
identifying emissions contributions that the Agency has determined to
be ``significant'' (or interfere with maintenance) in each of its prior
federal, regional ozone transport rulemakings, and this interpretation
of the statute has been upheld by the Supreme Court. See EME Homer
City, 572 U.S. 489, 519 (2014). While 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.
    UDAQ did not conduct such an analysis in its SIP submission,
determining instead that the relatively large impact of so-called
``uncontrollable'' emissions (i.e., international and non-anthropogenic
emissions) and home state emissions at the Colorado receptors, as well
as emissions reductions already achieved as a result of other
regulatory programs, meant the State had no further obligation to
assess or implement additional emissions control measures at Steps 3 or
4. The EPA disagrees with these conclusions for the reasons below.
    UDAQ asserted that receptors in the western U.S. are much more
impacted by emissions from non-U.S. sources or non-anthropogenic
sources (see Table 4) than by upwind State contributions, especially
when compared to such impacts in the eastern U.S., making Utah's
contributions to Denver area receptors comparably negligible. The EPA
disagrees that contributions from other sources, including
international or non-anthropogenic emissions, in any way excuse Utah
from addressing its own significant contribution to nonattainment or
interference with maintenance at downwind areas under CAA section
110(a)(2)(D)(i)(I). The EPA acknowledges that the consideration of
international contributions was among the ``Preliminary List of
Potential Flexibilities'' provided in the March 2018 memorandum, as
UDAQ noted. However, as described in section I.D. of this proposed
action, the EPA does not consider the potential flexibilities described
in the March 2018 memorandum as constituting agency guidance; rather,
the EPA must thoroughly review the technical and legal merits of
invoking the concepts in that Appendix.
    UDAQ's reasoning related to international and non-anthropogenic
emissions 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 downwind states' ability to attain and maintain NAAQS. Whether
emissions from other countries or non-anthropogenic sources 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 some amount of ``uncontrollable'' emissions (whether
international or non-anthropogenic) also contribute some amount of
pollution to the same receptors to which the state is linked.
    Further, the data supplied in UDAQ's SIP submission tends to be
self-refuting on this point. Table 4 of the submission indicates that
52 percent-59 percent (depending on receptor) of the total ozone
concentrations at the Colorado receptors are from non-anthropogenic or
non-U.S. emissions sources. This means that between 41 percent-48
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 Utah, Utah'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 EPA also disagrees that greater in-state emissions, in this
case anthropogenic emissions generated in Colorado, preclude upwind
states' good neighbor obligations 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 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 in order to timely assist downwind states in
attaining and

maintaining the NAAQS, and this schedule is ``central to the regulatory
scheme.'' Wisconsin, 938 F.3d at 316 (quoting Sierra Club v. EPA, 294
F.3d 155, 161 (D.C. Cir. 2002)). Therefore, the EPA does not find that
it should be the sole responsibility of the downwind state to resolve
its nonattainment, especially after having established that collective
contribution of emissions from multiple upwind states is responsible
for a considerable portion of the downwind air quality problem. To that
end, the EPA does not find UDAQ's arguments regarding the impacts of
emissions from sources other than upwind states to be relevant to the
analysis of interstate transport to Denver area nonattainment
receptors. Therefore, the EPA finds that Utah has not adequately
addressed its modeled contributions to projected downwind nonattainment
receptors identified by the EPA.
    UDAQ also pointed to reductions in emissions of VOCs and
NOX in the State through a combination of regulatory
actions. Though the EPA considers the measures UDAQ described to be
beneficial in reducing VOCs and NOX in the State, UDAQ's
analysis primarily quantifies anticipated reductions from area source
rules in the Salt Lake City 2006 PM2.5 nonattainment area.
These rules all were finalized between 2008 and 2018 (see UDAQ
submittal Table 5). UDAQ also cites but does not quantify emissions
reductions from certain oil and gas sector rules which have effective
dates in March 2019 (Table 6 in UDAQ's submittal). However, the EPA's
modeling captures the air quality effects of existing on-the-books
control measures in the emissions inventory baseline, and that modeling
confirms that these control programs were not sufficient to eliminate
Utah's linkage at Steps 1 and 2 under the 2015 8-hour ozone NAAQS. The
State was therefore obligated at Step 3 to assess additional control
measures using a multifactor analysis.
    Further, the emissions reductions cited in Table 5 of UDAQ's
submittal are predominantly from reductions in VOC emissions. The EPA
has long recognized that the more important ozone-precursors for
purposes of addressing regional and long-range interstate ozone
transport are nitrogen oxides (NOX).\62\ According to Table
5 of the submittal, the existing rules UDAQ cited may achieve on the
order of roughly 600 tons of NOX reductions per ozone season
(roughly 4 tons per day multiplied by the number of days in an ozone
season). The import of this figure is unclear; regardless, UDAQ did not
explain the baseline from which that amount of emissions reductions was
derived, nor did UDAQ explain how or why that amount of emissions
reduction is sufficient to eliminate significant contribution or
interference with maintenance. For example, UDAQ could have but did not
conduct a comparative assessment of additional emissions control
opportunities and associated costs, develop a regional emissions-
reduction assessment, or analyze the air quality benefits of those
strategies at the downwind receptors. All of these are factors in the
analysis the EPA has consistently performed at Step 3 over several
ozone transport rulemakings such as CSAPR and the CSAPR Update.
---------------------------------------------------------------------------

    \62\ See, e.g., 86 FR 23054, 23087.
---------------------------------------------------------------------------

    In particular, UDAQ's analysis failed to evaluate emissions and
emissions-reduction opportunities from most of the highest emitting NOx
sources in the State, including multiple electric generating units
located further east of the Salt Lake City, Utah area and thus closer
to the Denver area receptors to which Utah contributes greater than 1
percent of the NAAQS. A state conducting a Step 3 analysis should
undertake an evaluation of these kinds of substantial and potentially
cost-effective emissions reduction opportunities, and the failure to do
so is grounds for disapproval.
    For these reasons, the EPA finds that the historically-achieved
emissions reductions listed in Utah's January 2020 submission are not a
satisfactory Step 3 analysis and do not demonstrate that the Utah SIP
contains adequate provisions prohibiting emissions that will
significantly contribute to nonattainment or interfere with maintenance
of the 2015 ozone NAAQS in any other state.
    We therefore propose to find that Utah was required to analyze
emissions from the sources and other emissions activity from within the
State to determine whether its contributions were significant, and we
propose to disapprove its submission because the State failed to do so.

C. Evaluation of Information Provided Regarding Step 4

    Step 4 of the 4-step interstate transport framework calls for
development of permanent and federally enforceable control strategies
to achieve the emissions reductions determined to be necessary at Step
3 to eliminate significant contribution to nonattainment or
interference with maintenance of the NAAQS. As mentioned previously,
Utah'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 Utah's submittal on the
separate, additional basis that the State has not developed permanent
and enforceable emissions reductions necessary to meet the obligations
of CAA section 110(a)(2)(D)(i)(I).

D. Conclusion

    Based on the EPA's evaluation of Utah's SIP submission, the Agency
is proposing to find that the portion of the State's January 29, 2020
SIP submission addressing CAA section 110(a)(2)(D)(i)(I) for the 2015
8-hour ozone NAAQS does not meet Utah's interstate transport
obligations, because it fails to contain the necessary provisions to
eliminate emissions that will contribute significantly to nonattainment
or interfere with maintenance of this NAAQS in any other state.

IV. Proposed Action

    We are proposing to disapprove Utah'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 Utah 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 Utah. The remaining elements of the State's January
29, 2020 submission are not addressed in this action and either have
been or will be acted on in a separate rulemaking.

V. Statutory and Executive Order Reviews

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

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

B. Paperwork Reduction Act (PRA)

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

C. Regulatory Flexibility Act (RFA)

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

D. Unfunded Mandates Reform Act (UMRA)

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

E. Executive Order 13132: Federalism

    This action does not have federalism implications. It will not have
substantial direct effects on the states, on the relationship between
the national government and the states, or on the distribution of power
and responsibilities among the various levels of government.

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

    This action does not have tribal implications as specified in
Executive Order 13175. This action does not apply on any Indian
reservation land, any other area where 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).\63\
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    \63\ 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
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.\64\ For these reasons, the
Administrator intends, if this proposed action is finalized, to
exercise the complete discretion afforded to him under the CAA to make
and publish a finding that this action is based on one or more
determinations of nationwide scope or effect for purposes of CAA
section 307(b)(1).\65\
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    \64\ 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.
    \65\ 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. 2022-11152 Filed 5-23-22; 8:45 am]
BILLING CODE 6560-50-P