Document ID: EPA-R08-OAR-2022-0315-0001
Agency: epa
Document Type: Proposed Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: Utah; Interstate Transport of Air Pollution for the 2015 8-hour Ozone National Ambient Air Quality Standards; Disapproval
Posted Date: 2022-05-24T04:00Z

[Federal Register Volume 87, Number 100 (Tuesday, May 24, 2022)]
[Proposed Rules]
[Pages 31470-31484]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-11152]

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

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.

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

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 (202) 566-1744, and is located at 
EPA Docket Center Reading Room, WJC West Building, Room 3334, 1301 
Constitution Avenue NW, Washington, DC 20004. For further information 
on EPA Docket Center services and the current hours of operation at the 
EPA Docket Center, please visit us online at https://www.epa.gov/dockets.

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

SUPPLEMENTARY INFORMATION: 
    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: (303) 312-7104, 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

[[Page 31471]]

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\
---------------------------------------------------------------------------

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

B. Description of 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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

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

[[Page 31472]]

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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

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

    Following the final Revised CSAPR Update, 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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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

[[Page 31473]]

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.
---------------------------------------------------------------------------

    \20\ March 2018 memorandum, Attachment A.
    \21\ Id. at A-1.
    \22\ Id.
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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.
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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)).
---------------------------------------------------------------------------

    For the purpose of this proposal, the EPA identifies nonattainment 
receptors as those monitoring sites that are

[[Page 31474]]

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\
---------------------------------------------------------------------------

    \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).
---------------------------------------------------------------------------

    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

[[Page 31475]]

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.

[[Page 31476]]

   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.

[[Page 31477]]

                                              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

[[Page 31478]]

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

[[Page 31479]]

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

[[Page 31480]]

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

[[Page 31481]]

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

[[Page 31482]]

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

[[Page 31483]]

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.

[[Page 31484]]

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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    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\
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

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