[Federal Register Volume 87, Number 100 (Tuesday, May 24, 2022)]
[Proposed Rules]
[Pages 31443-31462]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-11150]


=======================================================================
-----------------------------------------------------------------------

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2022-0394; EPA-HQ-OAR-2021-0663; FRL-9772-01-R9]


Air Plan Disapproval; California; 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 Clean Air Act (CAA or the ``Act''), the 
Environmental Protection Agency (EPA) is proposing to disapprove a 
State Implementation Plan (SIP) submittal from California addressing 
interstate transport for the 2015 8-hour ozone national ambient air 
quality standards (NAAQS). The ``good neighbor'' or ``interstate 
transport'' provision of the Act requires that each state's SIP contain 
adequate provisions to prohibit emissions from within the state from 
significantly contributing to nonattainment or interfering with 
maintenance of the NAAQS in other states. This requirement is part of 
the broader set of ``infrastructure'' requirements, which are designed 
to ensure that the structural components of each state's air quality 
management program are adequate to meet the state's responsibilities 
under the CAA. This disapproval, if finalized, will establish a 2-year 
deadline for the EPA to promulgate a Federal Implementation Plan (FIP) 
to address the relevant interstate transport requirements, unless the 
EPA approves a subsequent SIP submittal that meets these requirements. 
Disapproval does not start a mandatory 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-R09-OAR-
2022-0394, by any of the following methods: Federal eRulemaking Portal 
at https://www.regulations.gov following the online instructions for 
submitting comments or via email to <a href="/cdn-cgi/l/email-protection#412a242d2d386f35292e2c203231012431206f262e37"><span class="__cf_email__" data-cfemail="99f2fcf5f5e0b7edf1f6f4f8eae9d9fce9f8b7fef6ef">[email protected]</span></a>. Include 
Docket ID No. EPA-R09-OAR-2022-0394 in the subject line of the message.
    Instructions: All submissions received must include the Docket ID 
No. for this rulemaking. Comments received may be posted without change 
to https://www.regulations.gov, including any personal information 
provided. For detailed instructions on sending comments and additional 
information on the rulemaking process, see the ``Public Participation'' 
heading of the SUPPLEMENTARY INFORMATION section of this document.

FOR FURTHER INFORMATION CONTACT: Tom Kelly, EPA Region IX, 75 Hawthorne 
St., San Francisco, CA 94105. By phone: 415-972-3856 or by email at 
<a href="/cdn-cgi/l/email-protection#365d535a5a4f18425e595b5745467653465718515940"><span class="__cf_email__" data-cfemail="066d636a6a7f28726e696b6775764663766728616970">[email protected]</span></a>.

SUPPLEMENTARY INFORMATION:
    Public Participation: Submit your comments, identified by Docket ID 
No. EPA-R09-OAR-2022-0394, at https://www.regulations.gov (our 
preferred method), or the other methods identified in the ADDRESSES 
section. Once submitted, comments cannot be edited or removed from the 
docket. 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

[[Page 31444]]

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-R09-OAR-2022-0394 
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R09-OAR-2022-0394 contains 
information specific to California, 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 that are being 
used to support this action. All comments regarding information in 
either of these dockets are to be made in Docket No. EPA-R09-OAR-2022-
0394. For additional submission methods, if you need assistance in a 
language other than English, or if you are a person with disabilities 
who needs a reasonable accommodation at no cost to you, please contact 
Tom Kelly, (415) 972-3856, <a href="/cdn-cgi/l/email-protection#abc0cec7c7d285dfc3c4c6cad8dbebcedbca85ccc4dd"><span class="__cf_email__" data-cfemail="4b202e272732653f2324262a383b0b2e3b2a652c243d">[email protected]</span></a>. 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 to the docket for this action, Docket No. EPA-R09-OAR-
2022-0394, is available electronically at www.regulations.gov. While 
all documents in the docket are listed in the index, some information 
may not be publicly available due to docket file size restrictions or 
content (e.g., CBI).
    Throughout this document, ``we,'' ``us,'' and ``our'' means the 
EPA.

Table of Contents

I. Background
    A. Description of Statutory Background
    B. Description of the EPA's Four 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. SIP Submission Addressing Interstate Transport of Air Pollution 
for the 2015 8-Hour Ozone NAAQS
    A. Information Provided at Steps 1 and 2
    B. Information Provided at Step 3
    C. Information Provided at Step 4
III. EPA Evaluation
    A. Evaluation of California Weight of Evidence Analysis
    B. Evaluation of Information Provided by California Regarding 
Step 1 and 2
    C. Results of the EPA's Step 1 and Step 2 Modeling and Findings 
for California
    D. Evaluation of Information Provided Regarding Step 3
    E. Evaluation of Information Provided Regarding Step 4
    F. Tribal Consultation
    G. Conclusion
IV. Proposed Action
V. Statutory and Executive Order Reviews

I. Background

A. Description of Statutory Background

    On October 1, 2015, the EPA promulgated a revision to the ozone 
NAAQS (``2015 8-hour ozone NAAQS''), lowering the level of both the 
primary and secondary standards to 0.070 parts per million (ppm).\1\ 
Section 110(a)(1) of the CAA requires states to submit, within 3 years 
after promulgation of a new or revised standard, SIP submissions 
meeting the applicable requirements of section 110(a)(2).\2\ One of 
these applicable requirements is found in CAA section 
110(a)(2)(D)(i)(I), otherwise known as the ``interstate transport'' or 
``good neighbor'' provision, which generally requires SIPs to contain 
adequate provisions to prohibit in-state emissions activities from 
having certain adverse air quality effects on other states due to 
interstate transport of pollution. There are two so-called ``prongs'' 
within CAA section 110(a)(2)(D)(i)(I). An interstate SIP submission 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 (DC Cir. 
2008).
---------------------------------------------------------------------------

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

    The EPA is using the 4-step interstate transport framework (or 4-
step framework) to evaluate the state's SIP submittal addressing the 
interstate transport provision for the 2015 8-hour ozone NAAQS. The EPA 
has addressed the interstate transport requirements of CAA section 
110(a)(2)(D)(i)(I) with respect to prior ozone NAAQS in several 
regional regulatory actions, including the Cross-State Air Pollution 
Rule (CSAPR), which addressed interstate transport with respect to the 
1997 ozone NAAQS as well as the 1997 and 2006 fine particulate matter 
standards,\4\ and the Cross-State Air Pollution Rule Update (CSAPR 
Update) \5\ and the Revised CSAPR Update, both of which addressed the 
2008 ozone NAAQS.\6\ Through the development and implementation of the 
CSAPR rulemakings and prior regional rulemakings pursuant to the 
interstate transport provision,\7\ the EPA, working in partnership with 
states, developed the following 4-step framework to evaluate a State's 
obligations to eliminate interstate transport emissions under the 
interstate transport provision for the ozone NAAQS: (1) Identify 
monitoring sites that are projected to have problems attaining and/or 
maintaining the NAAQS (i.e., nonattainment and/or maintenance 
receptors); (2) identify states that impact those air quality problems 
in other (i.e., downwind) states sufficiently such that the states are 
considered ``linked'' and therefore warrant further review and 
analysis; (3) identify the emissions reductions necessary (if any), 
applying a multifactor analysis, to eliminate each linked upwind 
state's significant contribution to nonattainment or interference with 
maintenance of the

[[Page 31445]]

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 (Aug. 8, 2011).
    \5\ Cross-State Air Pollution Rule Update for the 2008 Ozone 
NAAQS, 81 FR 74504 (Oct. 26, 2016).
    \6\ In 2019, the D.C. Circuit Court of Appeals remanded the 
CSAPR Update to the extent it failed to require upwind states to 
eliminate their significant contribution by the next applicable 
attainment date by which downwind states must come into compliance 
with the NAAQS, as established under CAA section 181(a). Wisconsin 
v. EPA, 938 F.3d 303, 313 (DC 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 (DC Cir. 2019).
    \7\ In addition to the CSAPR rulemakings, other regional 
rulemakings addressing ozone transport include the ``NO<INF>X</INF> 
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

    The EPA has performed nationwide air quality modeling to project 
ozone design values that are used in combination with measured data to 
identify nonattainment and maintenance receptors. To quantify the 
contribution of emissions from specific upwind states to 2023 ozone 
design values for the identified downwind nonattainment and maintenance 
receptors, the EPA performed nationwide, state-level ozone source 
apportionment modeling. The source apportionment modeling provided 
contributions to ozone at receptors from precursor emissions of 
anthropogenic nitrogen oxides (NO<INF>X</INF>) and volatile organic 
compounds (VOCs) in individual states and other sources.\8\
---------------------------------------------------------------------------

    \8\ More information on the source apportionment modeling can be 
found in the Air Quality Modeling Technical Support Document for the 
2015 Ozone NAAQS Transport SIP Proposed Actions.
---------------------------------------------------------------------------

    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.\9\ 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.\10\ On October 27, 2017, we released a 
memorandum using the ``en'' emissions inventory (``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.\11\ 
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.\12\ The March 2018 
memorandum also included the then newly available contribution modeling 
data for 2023 to assist states in evaluating their impact on potential 
downwind air quality problems for the 2015 8-hour ozone NAAQS under 
Step 2 of the 4-step interstate transport framework.\13\ 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.\14\
---------------------------------------------------------------------------

    \9\ 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).
    \10\ 82 FR 1733, 1735.
    \11\ See Information on the Interstate Transport State 
Implementation Plan Submissions for the 2008 Ozone National Ambient 
Air Quality Standards under Clean Air Act Section 
110(a)(2)(D)(i)(I), October 27, 2017, available in docket ID No. 
EPA-HQ-OAR-2021-0663.
    \12\ 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.
    \13\ 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.''
    \14\ 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 (``October 2018 
memorandum''), 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.\15\ 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.\16\ 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.\17\
---------------------------------------------------------------------------

    \15\ The results of this modeling, as well as the underlying 
modeling files, are included in docket ID No. EPA-HQ-OAR-2021-0663.
    \16\ See 85 FR 68964, 68981.
    \17\ 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 \18\ and 
updated emissions projections for electric generating units (EGUs) that 
reflect the emissions reductions from the Revised CSAPR Update, recent 
information on plant closures, and other sector trends. The construct 
of the updated emissions platform, 2016v2, is described in the 
emissions modeling technical support document (TSD) for this proposed 
rule.\19\ 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.\20\ The EPA now proposes to primarily rely on 
modeling based on the updated and newly

[[Page 31446]]

available 2016v2 emissions platform in evaluating these submissions 
with respect to Steps 1 and 2 of the 4-step interstate transport 
framework and generally referenced within this action as 2016v2 
modeling for 2023. By using the updated modeling results, the EPA is 
using the most current and technically appropriate information for this 
proposed rulemaking. Section III.C. of this notice 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 notice, 
the EPA is accepting public comment on this updated 2023 modeling, 
which uses the 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-R09-OAR-2022-0394. Comments are not being 
accepted in docket ID No. EPA-HQ-OAR-2021-0663.
---------------------------------------------------------------------------

    \18\ 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.
    \19\ 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.
    \20\ Ramboll Environment and Health, January 2021, www.camx.com.
---------------------------------------------------------------------------

    States may have chosen to rely on the results of EPA modeling and/
or alternative modeling performed by states or MJOs to evaluate 
downwind air quality problems and contributions as part of their 
submissions. In Section III.A. and III.B. we evaluate how California 
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 NO<INF>X</INF> SIP Call 
have necessitated the application of a uniform framework of policy 
judgments in order to ensure an ``efficient and equitable'' approach. 
See EME Homer City Generation, LP v. EPA, 572 U.S. 489, 519 (2014).
    In the March, August, and October 2018 memoranda, the EPA 
recognized that states may be able to establish alternative approaches 
to addressing their interstate transport obligations for the 2015 8-
hour ozone NAAQS that vary from a nationally uniform framework. The EPA 
emphasized in these memoranda, however, that such alternative 
approaches must be technically justified and appropriate in light of 
the facts and circumstances of each particular state's submittal. In 
general, the EPA continues to believe that deviation from a nationally 
consistent approach to ozone transport must be substantially justified 
and have a well-documented technical basis that is consistent with 
relevant case law. Where states submitted SIPs that rely on any such 
potential ``flexibilities'' as may have been identified or suggested in 
the past, the EPA will evaluate whether the state adequately justified 
the technical and legal basis for doing so.
    The EPA notes that certain concepts included in an attachment to 
the March 2018 memorandum require unique consideration, and these ideas 
do not constitute agency guidance with respect to transport obligations 
for the 2015 ozone NAAQS. Attachment A to the March 2018 memorandum 
identified a ``Preliminary List of Potential Flexibilities'' that could 
potentially inform SIP development.\21\ 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.'' \22\ 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.'' \23\ 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.
---------------------------------------------------------------------------

    \21\ March 2018 memorandum, Attachment A.
    \22\ Id. at A-1.
    \23\ 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).\24\ Several D.C. Circuit court decisions address the issue 
of the relevant analytic year for the purposes of evaluating ozone 
transport air quality problems. On September 13, 2019, the D.C. Circuit 
issued a decision in Wisconsin v. EPA, remanding the CSAPR Update to 
the extent that it failed to require upwind states to eliminate their 
significant contribution by the next applicable attainment date by 
which downwind states must come into compliance with the NAAQS, as 
established under CAA section 181(a). 938 F.3d at 313.
---------------------------------------------------------------------------

    \24\ For attainment dates for the 2015 8-hour ozone NAAQS, refer 
to CAA section 181(a), 40 CFR 51.1303, and Additional Air Quality 
Designations for the 2015 Ozone National Ambient Air Quality 
Standards, 83 FR 25776 (June 4, 2018, effective 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,\25\ which is now the

[[Page 31447]]

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.\26\ 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.
---------------------------------------------------------------------------

    \25\ 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.
    \26\ See CAA section 181(a); 40 CFR 51.1303; Additional Air 
Quality Designations for the 2015 Ozone National Ambient Air Quality 
Standards, 83 FR 25776 (June 4, 2018, effective Aug. 3, 2018).
---------------------------------------------------------------------------

    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 at 23054, 23074; see also Wisconsin, 938 F.3d at 322. 
Consequently, in this proposal the EPA will use the analytical year of 
2023 to evaluate each state's CAA section 110(a)(2)(D)(i)(I) SIP 
submission with respect to the 2015 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.\27\
---------------------------------------------------------------------------

    \27\ See North Carolina v. EPA, 531 F.3d at 910-11 (holding that 
the EPA must give ``independent significance'' to each prong of CAA 
section 110(a)(2)(D)(i)(I)).
---------------------------------------------------------------------------

    For the purpose of this proposal, the EPA identifies nonattainment 
receptors as those monitoring sites that are projected to have average 
design values that exceed the NAAQS and that are also measuring 
nonattainment based on the most recent monitored design values. This 
approach is consistent with prior transport rulemakings, such as the 
CSAPR Update, where the EPA defined nonattainment receptors as those 
areas that both currently measure nonattainment and that the EPA 
projects will be in nonattainment in the future analytic year (i.e., 
2023).\28\
---------------------------------------------------------------------------

    \28\ 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, 
25241 and 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).\29\ 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.
---------------------------------------------------------------------------

    \29\ 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),

[[Page 31448]]

the upwind state is not ``linked'' to a downwind air quality problem, 
and the EPA, therefore, concludes that the state does not significantly 
contribute to nonattainment or interfere with maintenance of the NAAQS 
in the downwind states. However, if a state's contribution equals or 
exceeds the 1 percent threshold, the state's emissions are further 
evaluated in Step 3, considering both air quality and cost as part of a 
multi-factor analysis, to determine what, if any, emissions might be 
deemed ``significant'' and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I). The EPA is proposing to rely in the first instance 
on the 1 percent threshold for the purpose of evaluating a state's 
contribution to nonattainment or maintenance of the 2015 8-hour ozone 
NAAQS (i.e., 0.70 ppb) at downwind receptors. This is consistent with 
the Step 2 approach that the EPA applied in CSAPR for the 1997 ozone 
NAAQS, which has subsequently been applied in the CSAPR Update when 
evaluating interstate transport obligations for the 2008 ozone NAAQS. 
The EPA continues to find 1 percent to be an appropriate threshold. For 
ozone, as the EPA found in the Clean Air Interstate Rule (CAIR), CSAPR, 
and 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 still the result of the collective 
impacts of contributions from many upwind states. Therefore, 
application of a consistent contribution threshold is necessary to 
identify those upwind states that should have responsibility for 
addressing their contribution to the downwind nonattainment and 
maintenance problems to which they collectively contribute. Continuing 
to use 1 percent of the NAAQS as the screening metric to evaluate 
collective contribution from many upwind states also allows 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 74504, 74518. See also 86 FR 23054, 23085 
(reviewing and explaining rationale from CSAPR, 76 FR 48,208, 48237-38, 
for selection of 1 percent threshold).
    The EPA's August 2018 memorandum recognized that in certain 
circumstances, a state may be able to establish that an alternative 
contribution threshold of 1 ppb is justifiable. Where a state relies on 
this alternative threshold, and where that state determined that it was 
not linked at Step 2 using the alternative threshold, the EPA will 
evaluate whether the state provided a technically sound assessment of 
the appropriateness of using this alternative threshold based on the 
facts and circumstances underlying its application in the particular 
SIP submission.
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with the EPA's longstanding approach to eliminating 
significant contribution or interference with maintenance, at Step 3, 
states linked at Steps 1 and 2 are generally expected to prepare a 
multifactor assessment of potential emissions controls. The EPA's 
analysis at Step 3 in prior federal actions addressing interstate 
transport requirements has primarily focused on an evaluation of cost-
effectiveness of potential emissions controls (on a marginal cost-per-
ton basis), the total emissions reductions that may be achieved by 
requiring such controls (if applied across all linked upwind states), 
and an evaluation of the air quality impacts such emissions reductions 
would have on the downwind receptors to which a state is linked; other 
factors may potentially be relevant if adequately supported. In 
general, where the EPA's or alternative air quality and contribution 
modeling establishes that a state is linked at Steps 1 and 2, it will 
be insufficient at Step 3 for a state merely to point to its existing 
rules requiring control measures as a basis for approval. In general, 
the emissions-reducing effects of all existing emissions control 
requirements are already reflected in the air quality results of the 
modeling for Steps 1 and 2. If the state is shown 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.\30\
---------------------------------------------------------------------------

    \30\ 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 NO<INF>X</INF> 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. SIP Submission Addressing Interstate Transport of Air Pollution for 
the 2015 8-Hour Ozone NAAQS

    In California, the California Air Resources Board (CARB or 
``State'') is the state agency responsible for the adoption and 
submission to the EPA of California state, county, and local SIPs and 
SIP revisions. CARB submitted its infrastructure SIP revision (``2018 
Infrastructure SIP,'' ``California's 2018 Submittal,'', or ``2018 
Submittal'') for the 2015 ozone NAAQS on October 1, 2018.\31\ In 2021, 
the EPA finalized action on most of the ``infrastructure'' requirements 
in that submittal but did not act on the interstate transport 
requirements of 110(a)(2)(D)(i)(I).\32\ We are proposing action on the 
interstate transport portions of California's 2018 Submittal in this 
action.
---------------------------------------------------------------------------

    \31\ Letter dated October 1, 2018, from Richard W. Corey, 
Executive Officer, CARB, to Michael Stoker, Regional Administrator, 
EPA Region IX.
    \32\ 86 FR 16533 (March 30, 2021).

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

[[Page 31449]]

A. Information Provided at Steps 1 and 2

    Enclosure 4 of California's 2018 Submittal contains the state's 
``Good Neighbor State Implementation Plan.'' For Steps 1 and 2 of its 
four-step analysis, California reviewed the results of the EPA's 
modeling runs released with the January 2017 NODA, the October 2017 
memorandum, and the March 2018 memorandum.\33\ CARB presented modeled 
design values for monitoring sites that the modeling released with the 
January 2017 NODA or the October 2017 memoranda projected to be 
nonattainment or maintenance receptors in 2023, using the EPA's 
definition of those terms.\34\ CARB explained it focused its evaluation 
on receptor sites in Colorado and Arizona because those were the 
western states, other than California, where the EPA's modeling 
identified nonattainment or maintenance sites in 2023 using the data in 
the March 2018 memorandum.\35\ Accordingly, CARB identified the 
following receptor sites and modeled design values, noting that the 
EPA's modeling released with the October 2017 memorandum and March 2018 
memorandum yielded the same design values for 2023.\36\
---------------------------------------------------------------------------

    \33\ California's 2018 Submittal, p. A4-10.
    \34\ Id. at A4-11, Table 1.
    \35\ Id. at A4-10.
    \36\ Id.

                                Table 1--Modeled Receptor Design Values in Western States in California's 2018 Submittal
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                           January 2017    January 2017    October 2017    October 2017
                                                                                             modeling-       modeling-       modeling-       modeling-
                   Site                                County                 AQS No.      average 2023    maximum 2023    average 2023    maximum 2023
                                                                                             DV (ppb)        DV (ppb)        DV (ppb)        DV (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Colorado
--------------------------------------------------------------------------------------------------------------------------------------------------------
Chatfield.................................  Douglas.....................     08-035-0004            69.6            71.6            71.1            73.2
Rocky Flats North.........................  Jefferson...................     08-059-0006            70.5            72.9            71.3            73.7
NREL......................................  Jefferson...................     08-059-0011            69.7            72.7            70.9            73.9
Fort Collins West.........................  Larimer.....................     08-069-0011            68.6            70.4            71.2            73.0
Highland Reservoir........................  Arapahoe....................     08-005-0002            68.0            70.0            69.3            71.3
Weld Co. Tower............................  Weld........................     08-123-0009            67.2            68.3            70.2            71.4
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                         Arizona
--------------------------------------------------------------------------------------------------------------------------------------------------------
West Phoenix..............................  Maricopa....................     04-013-0019            67.9            70.0            69.3            71.4
North Phoenix.............................  Maricopa....................     04-013-1004            68.7            69.8            69.8            71.0
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: California's 2018 Submittal, p. A4-11, Table 1.

    To ``assess the potential for transport impacts from California to 
Colorado receptors,'' CARB identified geographic and meteorologic 
features of the Denver Metro/North Front Range nonattainment area.\37\ 
Geographic features identified by CARB included the Front Range, 
extending up to 8,000 feet in elevation on the western side of the 
metropolitan area, as well as mountains on the southern and 
southeastern end of the area. CARB noted that both form barriers to air 
flow.\38\ CARB also notes that to the east and north of the Denver area 
are gradually rising hills that generally are open to airflow with the 
Denver area. Meteorological conditions identified by CARB include 
sunlight, temperature and winds conducive to formation of ozone, and 
diurnal recirculation that allows emissions and ozone concentrations to 
build up over multi-day periods.\39\ CARB additionally notes that this 
terrain, combined with unique atmospheric conditions and high 
temperatures during the summer months, are highly conducive to the 
accumulation of local emissions and the formation of ozone in the 
Denver-Aurora-Lakewood Core Based Statistical Area, and, additionally, 
allows for ozone concentrations to remain higher for more hours, 
leading to higher 8-hour averages at monitoring sites.
---------------------------------------------------------------------------

    \37\ Id. at A4-13.
    \38\ Id.
    \39\ Id. at A4-13-A4-14.
---------------------------------------------------------------------------

    CARB notes additional local features that contribute to high ozone 
concentrations in the Denver nonattainment area, including upslope and 
downslope flow in the foothill regions on broad high-pressure days near 
several violating monitoring sites. CARB also claims that wildfires had 
an impact on ozone concentrations in the Denver area, specifically 
noting that on September 4, 2017, large wildfire events across five 
western states brought plumes of smoke southward along the Front Range, 
inevitably mixing with the surface, and as a result, elevated ozone 
concentrations were observed at the Rocky Flats North site, reaching 
0.078 ppm 8-hour average ozone concentrations.
    CARB conducted a trajectory analysis from California to Colorado 
using the National Oceanic and Atmospheric Administration (NOAA) Hybrid 
Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model.\40\ 
CARB found that only two percent of nearly 500 backward trajectories 
from Colorado receptor sites on high ozone days in June and July 
(initiated from 10, 1000, and 2000 meters above ground level with a 
duration of 96 hours) indicated air parcels may have traveled from a 
mixed layer within California, where pollutants become well dispersed, 
to a mixed layer at the Colorado receptor sites.\41\ CARB also found 
only one forward trajectory (starting at 10 meters above the ground 
with a duration of 96 hours) from the mixed layer in California reached 
the mixed layer at a Colorado receptor site.\42\According to CARB, this 
suggests that the complexity of the physical environment between 
California and Colorado limits the reproducibility of modeled transport 
and that considerable multi-faceted analyses would be necessary to 
explore transport mechanisms through areas of complex terrain.\43\
---------------------------------------------------------------------------

    \40\ Id. at A4-17.
    \41\ Id. at A4-17-A4-18.
    \42\ Id. at A4-18.
    \43\ Id.
---------------------------------------------------------------------------

    CARB's conclusion based on the HYSPLIT trajectories was that upper-
level air was almost always above the mixed layer over California, 
Colorado, or both.\44\ Without vertical mixing of the air between the 
mixed layer near the ground and the upper level, CARB

[[Page 31450]]

asserted, little to no impact from transport of emissions or pollutants 
would be expected at the surface.\45\ CARB concluded that transport 
from California emissions sources to Colorado is possible but extremely 
unlikely on high ozone days at the Colorado receptor sites identified 
by the EPA modeling.\46\ CARB also noted that this conclusion appeared 
consistent with Colorado's weight of evidence (WOE) analysis for its 
Denver Metro/North Front Range attainment plan SIP submittal for the 
0.075 ppm 8-hour ozone standard.\47\
---------------------------------------------------------------------------

    \44\ Id.
    \45\ Id.
    \46\ Id. at A4-18-A4-19.
    \47\ Id. at A4-19.
---------------------------------------------------------------------------

    CARB also attempted to rely on one of the preliminary ``potential 
flexibilities'' in Attachment A to the EPA's March 2018 memorandum to 
evaluate California's impacts on receptors in Colorado.\48\ CARB cited 
the idea of ``consider[ing] removal of certain data from modeling 
analysis for the purposes of projecting design values and calculating 
the contribution metric where data removal is based on model 
performance and technical analyses support the exclusion.'' \49\ In 
making use of this potential flexibility, CARB used exceptional event 
data from Colorado's ``weight of evidence'' (WOE) analysis included in 
its Denver Metro/North Front Range attainment SIP submittal for the 
0.075 ppm 8-hour ozone standard.\50\ CARB asserted that, although 
Colorado did not submit formal demonstrations for these events under 
the Exceptional Event Rule because they did not affect design values in 
the area's attainment year, the EPA concurred with Colorado's 
assessment that the model Colorado used for its Denver Metro/North 
Front Range attainment SIP submittal was properly configured, met EPA 
performance requirements, and was appropriately used in its 
application.\51\
---------------------------------------------------------------------------

    \48\ Id. at A4-23.
    \49\ Id. at A4-23. See also March 2018 memorandum, Attachment A 
at A-2.
    \50\ California's 2018 Submittal at A4-23-A4-24 (citing 83 FR 
14807 (April 6, 2018) and 83 FR 31068 (July 3, 2018)).
    \51\ Id. at A4-23.
---------------------------------------------------------------------------

    To recalculate projected design values excluding exceptional event 
data flagged by Colorado, CARB first calculated design values from 
prior years for the four monitors analyzed in Colorado's Denver Metro/
North Front Range attainment SIP submittal for the 2008 8-hour ozone 
standard of 0.075 ppm (Chatfield, Rocky Flats North, NREL, and Fort 
Collins West) as well as for two additional monitors: Highland 
Reservoir and Weld Co. Tower.\52\ CARB found that the average design 
values for the years 2009-2011, 2010-2012, and 2011-2013 dropped by 1-2 
ppb at all six sites when data flagged by Colorado was excluded.\53\ 
CARB found that maximum base year design values dropped by 2-3 ppb.\54\
---------------------------------------------------------------------------

    \52\ Id. at A4-23-A4-24.
    \53\ Id. at A4-24.
    \54\ Id.
---------------------------------------------------------------------------

    CARB also attempted to replicate Colorado's future design value 
calculations from Colorado's WOE analysis to be consistent with 
Colorado's approach by using the ``el'' version of the emissions 
inventory.\55\ CARB excluded Colorado's flagged events to recalculate 
design values for future year modeling for 2023 based on EPA's Good 
Neighbor SIP modeling released in the January 2017 NODA (using the 
``el'' emissions inventory).\56\ CARB calculated that average design 
values at the six sites dropped by 1 to 2 ppb, and maximum design 
values dropped by 2 ppb.\57\ CARB found this resulted in no 
nonattainment or maintenance receptors being projected in Colorado in 
2023.\58\
---------------------------------------------------------------------------

    \55\ Id. at A4-25
    \56\ Id. at A4-26.
    \57\ Id. A4-26.
    \58\ Id.
---------------------------------------------------------------------------

    CARB repeated the same process with EPA's Good Neighbor SIP 
modeling released in the October 2017 memorandum using the ``en'' 
emissions inventory.\59\ CARB found that excluding data flagged by 
Colorado reduced the 2023 average design values by 0-2 ppb and the 
maximum design values by 1-2 ppb. CARB asserted that its approach was 
consistent with Attachment A to the March 2018 memorandum with respect 
to ``collaboration among states linked to a common receptor and among 
linked upwind and downwind states in developing and applying a 
regionally consistent approach.'' \60\
---------------------------------------------------------------------------

    \59\ Id. at A4-27.
    \60\ Id. at A4-23.
---------------------------------------------------------------------------

    CARB analyzed the projected design values in the October 2017 
memorandum and March 2018 memorandum in order to understand why the 
2023 design values in Colorado were higher in the latter modeling 
compared to the former.\61\ CARB noted that ``receptors'' in Colorado 
based on the January 2017 modeling were clean in 2023 after removing 
atypical events, but some of these sites became receptors in the March 
2018 modeling even after atypical events were removed in the projection 
of 2023 design values. CARB performed an analysis of contributions and 
emissions to determine why four monitors in Denver changed from being 
clean (after removing atypical events) in the older January 2017 
modeling to maintenance-only receptors (after removing atypical events) 
using the March 2018 modeling. CARB concluded that higher emissions, 
and therefore higher contributions, from Colorado sources were the 
primary reason why the four monitors changed from clean in the January 
2017 modeling to maintenance-only in the March 2018 modeling. CARB used 
this result to argue that emissions in Colorado, not California, are 
responsible for the projected maintenance problem at these four 
receptors.\62\ CARB also noted that differences in EPA's methodology 
for calculating average contributions at individual monitors between 
the January 2017 NODA and the March 2018 memorandum could have 
contributed to the receptor changes that CARB identified in its 
submittal. CARB further noted that the updated emissions inventory 
(``en'') would not have accounted for Colorado's planned controls on 
Colorado's nonpoint source emissions from oil and gas and therefore 
overstated those emissions.\63\
---------------------------------------------------------------------------

    \61\ Id. at A4-29.
    \62\ Id. At A4-29--A4-33
    \63\ Id. at A4-31-A4-32.
---------------------------------------------------------------------------

    Ultimately, CARB decided it was more appropriate to rely on the 
``en'' emissions inventory-based modeling released with the October 
2017 memorandum, stating that this would be the more conservative 
approach.\64\
---------------------------------------------------------------------------

    \64\ Id. at A4-32-A4-33.
---------------------------------------------------------------------------

    To analyze receptors in, and California's contributions to, 
Arizona, CARB first noted that the EPA's modeling released with the 
October 2017 memorandum identified the West Phoenix and North Phoenix 
monitoring sites in the Phoenix-Mesa nonattainment area as potential 
maintenance receptors, while the earlier version of the modeling 
released with the January 2017 NODA did not project any receptors in 
Arizona.\65\ CARB identified geographic features of the Phoenix-Mesa 
nonattainment area, including the Sierra Estrella Mountains to the 
southwest, the White Tank Mountains to the west, the Bradshaw Mountains 
to the north and northeast, the Superstition Mountains to the east, and 
the South Mountains to the south.\66\ CARB explained this ``topographic 
bowl'' significantly limits air flow during non-stormy periods.\67\ 
CARB also identified meteorological factors affecting the Phoenix area, 
such as upper-level high pressure systems over

[[Page 31451]]

the western U.S. that produce high temperatures, limit cloud formation, 
and generally lead to light winds.\68\ Additional meteorological 
factors identified by CARB included cooling in the evening that brings 
emissions and pollutants back to the metropolitan area at night, the 
summer monsoon, temperature inversions outside of monsoon season, 
atmospheric mixing heights of several thousand feet on hot afternoons, 
and ``dry'' thunderstorms that may ignite wildfires.\69\
---------------------------------------------------------------------------

    \65\ Id. at A4-35.
    \66\ Id.
    \67\ Id. at A4-35.
    \68\ Id. at A4-35-A4-36.
    \69\ Id. at A4-26.
---------------------------------------------------------------------------

    CARB also conducted a simplified, short-ranged trajectory 
analysis.\70\ CARB viewed backward HYSPLIT model trajectories for the 
two receptor sites in Arizona to evaluate the potential for transport 
of ozone or ozone precursors from California. CARB concluded that air 
is typically from within the Phoenix area for trajectories at 100 and 
500 meters above ground level and that trajectories at 1000 meters are 
most frequently from the north-northeast, southeast, or southwest. CARB 
interpreted its analysis to suggest air from California was unlikely to 
be a significant factor contributing to higher ozone values in 
Phoenix.\71\
---------------------------------------------------------------------------

    \70\ Id. at A4-39.
    \71\ Id.
---------------------------------------------------------------------------

    CARB then compared the two receptor sites' 2023 projections from 
the two versions of transport modeling that EPA released in the January 
2017 NODA (``el'' emissions inventory) and the October 2017 memorandum 
(``en'' emissions inventory). CARB noted that the design values at the 
two Arizona sites increased by 1-2 ppb from the earlier to the later 
version of the EPA's modeling, and that based on the contribution data 
included in the March 2018 memorandum, Arizona's own contribution 
increased by 1.8-2.2 ppb.\72\ CARB concluded that the difference in 
Arizona's design values appeared to be mainly driven from Arizona's own 
contributions, and that the balance of difference between Arizona's 
contributions and the changes to the design values came from emissions 
categorized as ``Other'', which included emissions from Canada and 
Mexico.\73\ Specifically, CARB noted that fire impacts increased at 
both sites and that international contributions increased at the West 
Phoenix site.\74\ At both sites, CARB explained that the home state's 
contribution grew by more than the amount necessary to make the site a 
maintenance receptor in modeling released with the October 2017 
memorandum (using the ``en'' emissions inventory).\75\ CARB also noted 
that, while Arizona's contribution increased from the modeling released 
with the January 2017 NODA (``el'' emissions inventory) to the modeling 
results released with the October 2017 memorandum (``en'' emissions 
inventory), California's contribution decreased at both monitoring 
sites between the same versions.\76\
---------------------------------------------------------------------------

    \72\ Id. at A4-40.
    \73\ Id. A4-40-A4-41.
    \74\ Id. at A4-42.
    \75\ Id. at A4-43.
    \76\ Id.
---------------------------------------------------------------------------

    CARB decided to give more weight to the modeling results released 
with the October 2017 memorandum (``en'' emissions inventory),\77\ 
which indicated that California contributes above 1 percent of the 
NAAQs to two maintenance receptors in Arizona. However, CARB concluded 
that the differences between the modeling results based on the ``el'' 
and ``en'' emissions inventories resulting in increased modeled design 
values for the two maintenance receptors in Arizona were not due to 
increased contributions from California.\78\ Based on this information, 
CARB found it ``reasonable to conclude that emissions from California 
do not significantly interfere with attainment/maintenance of the 0.070 
ppm 8-hour ozone NAAQS at the modeled ozone receptors in Arizona.'' 
\79\
---------------------------------------------------------------------------

    \77\ Id. at A4-44.
    \78\ Id.
    \79\ Id.
---------------------------------------------------------------------------

    Overall, California's conclusion for Step 2 was that it is linked 
to downwind sites in Colorado and Arizona, based on the EPA modeling 
results released with the October 2017 memorandum.\80\ However, based 
on the additional analyses CARB provided at Step 2 (and further 
analysis of emissions control measures provided at Step 3 of their 
submittal), CARB concludes that California does not contribute 
significantly to nonattainment or interfere with maintenance of the 
2015 ozone NAAQS in other states.
---------------------------------------------------------------------------

    \80\ Id.
---------------------------------------------------------------------------

B. Information Provided at Step 3

    For Step 3, CARB reviewed and evaluated California's emissions 
control measures.\81\ CARB noted that, based on the 2011 National 
Emissions Inventory (NEI) and based on 2023 projected emissions, a 
NO<INF>X</INF> control strategy would be most effective for reducing 
regional scale ozone transport.\82\ Table 2 below shows California 
emissions in 2011 and 2023 by sector and percentage.
---------------------------------------------------------------------------

    \81\ Id. at A4-45.
    \82\ Id. at A4-46.

                                         Table 2--California Emissions in 2021 and 2023 by Sector and Percentage
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                NOX                                            VOCs
               Modeled emissions by sector               -----------------------------------------------------------------------------------------------
                                                              Mobile        Stationary         >Area          Mobile        Stationary         Area
--------------------------------------------------------------------------------------------------------------------------------------------------------
Percent of 2011 NEI Emissions...........................            78.4            11.2            10.4            34.8             6.5            58.7
Percent of 2023 Projected Emissions.....................            67.1            26.9             6.0            28.6            29.3            42.1
--------------------------------------------------------------------------------------------------------------------------------------------------------
Source: California's 2018 Submittal, p. A4-46, Table 31.

    CARB noted that a NO<INF>X</INF>-focused approach is consistent 
with the EPA's historical focus for transport control measures, then 
summarized its controls for mobile sources, stationary sources, and 
consumer products.\83\
---------------------------------------------------------------------------

    \83\ Id. at A4-46-A4-56.
---------------------------------------------------------------------------

    CARB summarized its NO<INF>X</INF> controls for mobile sources, 
including the Smog Check program, low emission vehicle fleet standards 
and zero emission vehicle regulation, and California's reformulated 
gasoline standard. CARB also described programs to reduce 
NO<INF>X</INF> emissions from heavy-duty vehicles by nearly 70 percent 
by 2023 and from off-road equipment by 45 percent by 2031. In the South 
Coast Air Quality Management District, CARB stated that mobile source 
control programs are projected to reduce NO<INF>X</INF> emissions by 
153 tons per day (tpd) in 2023 and by 184 tpd by 2031. CARB also noted 
that the federal government has primary regulatory authority over 
mobile sources such as ocean-going vessels, aircraft, and 
locomotives.\84\
---------------------------------------------------------------------------

    \84\ Id. at A4-47-A4-48.
---------------------------------------------------------------------------

    CARB also described NO<INF>X</INF> controls for stationary sources, 
noting that California's 35 air districts have primary authority over 
those sources. CARB

[[Page 31452]]

provided examples of prohibitory rules for NO<INF>X</INF> and VOC 
already approved into the California SIP. These included rules 
controlling VOC emissions from Graphic Arts Operations in the Ventura 
County Air Pollution Control District (APCD), Placer County APCD, and 
San Diego County APCD. Other examples included rules controlling 
NO<INF>X</INF> emissions from Natural Gas-Fired Fan-Type Central 
Furnaces and Small Water Heaters in Santa Barbara APCD, from Gasoline 
Transfer and Dispensing in the South Coast Air Quality Management 
District, from Natural Gas-Fired Water Heaters, Small Boilers, and 
Process Heaters in Placer County APCD, and from Large Water Heaters and 
Small Boilers in Ventura County APCD. Separately, CARB described 
California's consumer product control program to regulate reactive 
organic gas emissions, a subset of VOCs.\85\
---------------------------------------------------------------------------

    \85\ Id. at A4-48-A4-53.
---------------------------------------------------------------------------

    After summarizing these controls, CARB provided information about 
its electric generating units (EGUs) and non-EGU stationary 
sources.\86\ Noting that the EPA has historically targeted EGUs for 
reductions in ozone transport pollution, CARB stated that the only two 
EGUs in the state emitting NO<INF>X</INF> at rates higher than 0.061 
lb/MMBtu are either ``unlikely'' to have further cost-effective 
emission control opportunities or planned to retire by the end of 
2019.\87\ CARB also explained that the only EGU emitting more than 250 
tpy NO<INF>X</INF> in 2011 ceased operation in 2014, and that two EGUs 
emitting over 100 tpy NO<INF>X</INF> in the San Joaquin Valley APCD 
ceased operation in 2011.\88\
---------------------------------------------------------------------------

    \86\ Id. at A4-54-A4-55.
    \87\ Id. at A4-54.
    \88\ Id. at A4-54-A4-55.
---------------------------------------------------------------------------

    CARB also noted that in 2016, the EPA assessed further 
NO<INF>X</INF> reductions from EGUs and that the CSAPR Update resulted 
in a cost threshold of $1400 per ton.\89\ CARB stated that the EPA's 
analysis showed ozone season EGU NO<INF>X</INF> reductions in 
California would not occur until the $5000 per ton emissions-control 
scenario.\90\ CARB concluded that due to ``strict and comprehensive 
emissions regulations on emissions, EGUs do not appreciably contribute 
to NO<INF>X</INF> such that the emissions could significantly 
contribute to ozone formation in another state.'' \91\
---------------------------------------------------------------------------

    \89\ Id. at A4-55.
    \90\ Id.
    \91\ Id.
---------------------------------------------------------------------------

    For non-EGUs, CARB noted that, although they emitted 6.7 times as 
much NO<INF>X</INF> as EGUs did in 2011 in California, they only 
represented 5.2 percent of the statewide NO<INF>X</INF> inventory.\92\ 
CARB concluded that, for the large non-EGU sources that are either 
subject to NO<INF>X</INF> control measures that have not been submitted 
for approval into the California SIP, or fall outside the geographic 
jurisdiction of the applicable district rules, further emission 
controls would be unlikely to reduce any potential impact on downwind 
states' air quality because such sources comprise no more than 0.8 
percent of the total NO<INF>X</INF> emitted in California in 2011.\93\ 
CARB also highlighted its consumer product control program, which 
regulates reactive organic gas.\94\
---------------------------------------------------------------------------

    \92\ Id.
    \93\ Id., p. A4-55
    \94\ Id. at A4-56.
---------------------------------------------------------------------------

    CARB's Step 3 conclusion was that ``the State's emission reduction 
control system leads the nation in stringency for most sectors of 
emission sources'' and that ``California's emission reduction programs 
adequately prohibit the emission of air pollutants in amounts that will 
significantly contribute to nonattainment, or interfere with 
maintenance, of the 0.070 ppm 8-hour ozone standard in any downwind 
state.'' \95\
---------------------------------------------------------------------------

    \95\ Id., p. A4-57
---------------------------------------------------------------------------

C. Information Provided at Step 4

    For its Step 4 analysis, CARB stated, ``Although linked to other 
western states with projected air quality problems in 2023, California 
is not significantly contributing to nonattainment or maintenance 
problems in any other states. This is in large part due to the 
stringency of California's air pollution control program. Therefore, no 
further reductions or measures are necessary for Good Neighbor SIP 
purposes.'' \96\
---------------------------------------------------------------------------

    \96\ Id.
---------------------------------------------------------------------------

    CARB then provided a weight of evidence (WOE) analysis. The WOE 
analysis purported to ``describe the U.S. EPA's contribution modeling 
when grouping upwind states' contributions,'' asserted that transport 
relationships among eastern and western states are different, and 
argued that the role of interstate transport in western states is a 
very small portion of projected design values and that the collective 
impact of all upwind states is also a small portion.\97\ CARB also 
asserted that previous rounds of EPA's photochemical modeling 
identified smaller collective contribution for western states than 
eastern states.\98\
---------------------------------------------------------------------------

    \97\ Id. at A4-58-A4-69.
    \98\ Id. at A4-59.
---------------------------------------------------------------------------

    CARB's WOE analysis further described differences it claims exist 
between transport in eastern and western states.\99\ Differences 
asserted by CARB included large populations in eastern states, the 
relatively small size of eastern states and consequent high population 
density, and numerous metropolitan areas in eastern states that cross 
state boundaries. CARB also noted the complex topography in western 
states, which presents a challenge to air quality modeling, as well as 
the relative distances between nonattainment areas and emissions 
sources in western states and the larger overall sizes of western 
states compared to eastern states.\100\
---------------------------------------------------------------------------

    \99\ Id. at A4-61-A4-67.
    \100\ Id. at A4-63.
---------------------------------------------------------------------------

    CARB continued its WOE analysis by reiterating that California has 
little impact on ozone levels outside its borders, specifically because 
of the distance between California's eastern border and its emissions 
sources, as well as because of the Sierra Nevada mountains, which limit 
airflow from California to the east and which are sparsely 
populated.\101\ CARB's WOE analysis concluded with a per-capita 
NO<INF>X</INF> emissions comparison across the states, in which 
California ranked nearly last (even though it ranked second highest in 
total NO<INF>X</INF> emissions (after Texas)), and stated, ``U.S. EPA's 
modeling of state contributions bears out the expectation that 
California's impacts on other states would be very small.'' \102\
---------------------------------------------------------------------------

    \101\ Id. at A4-67-A4-69.
    \102\ Id. at A4-68.
---------------------------------------------------------------------------

    In summary, California's 2018 submittal concluded that, while 
California is linked to receptors in Arizona and Colorado with 
projected air quality problems in 2023, California is not significantly 
contributing to nonattainment or maintenance problems in any other 
states.\103\ Further, CARB asserted that its emissions reduction 
programs adequately prohibit the emission of air pollutants for 
transport purposes, and that California has already adopted and 
implemented permanent and enforceable measures of sufficient stringency 
to ensure that the state does not contribute significantly to ozone 
nonattainment or maintenance problems in downwind states.\104\
---------------------------------------------------------------------------

    \103\ Id. at A4-72-A4-73.
    \104\ Id. at A4-73-A4-74.
---------------------------------------------------------------------------

III. EPA Evaluation

    The EPA is proposing to find that California's 2018 SIP Submittal 
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 
based on the EPA's evaluation of the SIP submission using the 4-step 
interstate transport framework, and the EPA is

[[Page 31453]]

therefore proposing to disapprove California's 2018 SIP Submittal.

A. Evaluation of California Weight of Evidence Analysis

    As an initial matter, the EPA will address CARB's ``WOE analysis'' 
that included the statement: ``[b]y not promulgating a version of the 
CSAPR in the West, U.S. EPA could be viewed as tacitly acknowledging a 
disparity in the significance of interstate transport of ozone between 
western and eastern states.'' \105\ That is an incorrect 
interpretation. The EPA took comment on including western states in the 
CSAPR Update, but did not finalize due to the possibility that ``there 
may be additional factors to consider in the EPA's and state's 
evaluations'' such as unspecified ``geographically specific 
factors[.]'' \106\ The EPA stated explicitly that even though no 
western state was included in the CSAPR Update, ``western states are 
not relieved of their statutory obligation to address interstate 
transport under the [CAA] section 110(a)(2)(d)(i)(I)'' and that the 
``EPA and western states, working together, are continuing to evaluate 
interstate transport obligations on a case-by-case basis.'' \107\
---------------------------------------------------------------------------

    \105\ Id. at A4-62.
    \106\ 81 FR 74503, 74523.
    \107\ Id.
---------------------------------------------------------------------------

    While the EPA has in limited circumstances found unique issues 
associated with addressing ozone transport in western states, the EPA 
has consistently applied the 4-step transport framework in western 
states and has identified ozone transport problems in the west that are 
similar to those in the east.\108\ For example, in a prior action 
addressing California's interstate transport obligations for the 2008 
ozone NAAQS, the EPA concluded that ``the collective contribution of 
emissions from upwind states represent a considerable portion of the 
ozone concentrations at the maintenance receptors in the Denver area.'' 
\109\ Similarly, 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 percent), comparable to some eastern receptors . . . .'' \110\
---------------------------------------------------------------------------

    \108\ See 81 FR 31513 (May 19, 2016) (Arizona); 83 FR 65093 
(December 19, 2018) (California); 85 FR 26361 (May 4, 2020) (New 
Mexico); 81 FR 71991 (Oct. 19, 2016) (Utah prong 2); 82 FR 9155 
(February 3, 2017) (Utah prong 1); 84 FR 14270 (April 10, 2019) 
(Wyoming).
    \109\ 83 FR 5381 (February 7, 2018). See also 82 FR 9155, 9157 
(February 3, 2017).
    \110\ See 84 FR 3389, 3391 (Feb. 12, 2019). 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 11 percent of the total ozone 
concentration and five states were projected to be linked).
---------------------------------------------------------------------------

    The remaining discussion in CARB's WOE analysis is of limited 
relevance to the question of assessing interstate ozone transport. 
CARB's description of western geography, settlement patterns, early 
American expansionist policy, and historically low population density 
do not overcome the fundamental conclusion from each successive round 
of EPA modeling, discussed below: California contributes more than 1 
percent of the 2015 ozone NAAQS to multiple nonattainment and/or 
maintenance receptors in other states. As explained in further detail 
below, the EPA has examined the reliability of its nationwide modeling 
for characterizing ozone transport in the west and finds that the 
modeling is reliable. The remainder of CARB's analysis at Steps 3 and 4 
is not approvable. CARB did not adequately evaluate additional 
emissions control opportunities to support its conclusion that 
emissions from sources in California do not significantly contribute to 
nonattainment or interfere with maintenance in other States. The EPA 
acknowledges that California may have one of, if not the, most 
stringent emissions control strategies in the country, but the state 
remains obligated to analyze additional control opportunities once a 
linkage has been established at Steps 1 and 2. Finally, while the EPA 
approved California's transport SIP submittal for the 2008 ozone NAAQS 
at Step 3 on the basis that the State's emissions were overall 
relatively well-controlled, the EPA cannot reach the same conclusion 
here for the more stringent 2015 ozone NAAQS. In particular, the EPA 
finds persistent linkages between California and several out of state 
receptors under the more stringent NAAQS. Further, the EPA finds based 
on new modeling, see Section III.B. of this document, that the State 
failed to adequately assess emissions control opportunities at certain 
non-EGU facilities.

B. Evaluation of Information Provided by California Regarding Step 1 
and 2

1. Different Versions of EPA Modeling and Regulatory Flexibility
    At Step 1 and 2 of the 4-step interstate transport framework, CARB 
assessed the EPA modeling released with the January 2017 NODA and the 
October 2017 memorandum, noting they yielded the same design values to 
identify nonattainment and maintenance receptors in Colorado and 
Arizona in 2023.\111\ CARB used the EPA's modeling released with the 
January 2017 NODA and the March 2018 memorandum to identify 
California's contributions to receptors in Colorado and Arizona, and 
decided to give more weight to the contribution modeling released with 
the March 2018 memorandum (which was based on the ``en'' emissions 
inventory).<SUP>112 113</SUP> With regard to the Arizona receptors, 
CARB compared different versions of the EPA's modeling and noted that 
California's contribution decreased from the earlier to later modeling 
versions, while Arizona's own emissions increased. Ultimately, CARB 
chose to rely on the version of the EPA modeling that identified 2 
receptors in Arizona, as well as contributions from California to those 
receptors above 1 percent of the NAAQS.\114\ CARB acknowledged that 
California is linked to downwind air quality problems in Arizona above 
the 1 percent of the NAAQS threshold at Step 2.\115\
---------------------------------------------------------------------------

    \111\ Id. at A4-11 and Table 1.
    \112\ Id. at A4-33. A4-34, A4-36.
    \113\ As explained in Section I, the October 2017 memorandum 
provided projected ozone design values for 2023. The data released 
in the March 2018 memorandum built off the information provided in 
the October 2017 memorandum by including contribution data to assist 
states in the development of their interstate transport SIPs for the 
2015 ozone NAAQS.
    \114\ Id. at A4-44.
    \115\ Id.
---------------------------------------------------------------------------

    With regard to receptors in Colorado, CARB likewise compared 
different versions of the EPA's modeling. Additionally, however, CARB 
attempted to rely on a potential ``flexibility'' identified in 
Attachment A to the March 2018 memorandum to exclude exceptional events 
flagged by Colorado in its Denver Metro/North Front Range attainment 
SIP submittal for the 2008 ozone NAAQS to revise base year design 
values. This analysis led CARB to conclude that there will be fewer 
receptors in Colorado in 2023 than under either the EPA's modeled 
design values released with the January 2017 NODA or the October 2017 
memorandum: Zero nonattainment or maintenance receptors using the 
January 2017 NODA version of EPA's modeling and the ``el'' emissions 
inventory, and zero nonattainment and four maintenance receptors using 
the October 2017 memorandum version of EPA's modeling and the ``en'' 
emissions inventory.
    Nonetheless, CARB's analysis did not conclude that California was 
not linked below 1 percent of the NAAQS to the

[[Page 31454]]

four maintenance sites it identified in Colorado. On the contrary, CARB 
acknowledged that it chose to rely on the EPA modeling released with 
the October 2017 memorandum (using the ``en'' emissions inventory) and 
that California was linked to four maintenance receptors in Colorado 
using that version of the modeling, even after CARB removed flagged 
data.\116\
---------------------------------------------------------------------------

    \116\ A4-33, A4-34.
---------------------------------------------------------------------------

    As explained in Section I.D. above, the concepts presented in 
Attachment A to the March 2018 memorandum were neither guidance nor 
determined by the EPA to be consistent with the CAA. The EPA made clear 
at the time that it would thoroughly review the technical and legal 
justifications states put forward in relying on any concepts from 
Attachment A to the March 2018 memorandum. In this case, what CARB 
proposes is potentially consistent with the EPA's modeling guidance, 
insofar as the EPA has recognized that it may be appropriate to exclude 
certain flagged data associated with atypical events (e.g., wildfires) 
when calculating base period design values to project to a future year. 
However, CARB's removal of atypical data did not change its conclusion 
that there are receptors in Colorado in 2023 and that California 
contributes above 1 percent of the NAAQS to one or more of them.\117\
---------------------------------------------------------------------------

    \117\ Id. at A4-44.
---------------------------------------------------------------------------

2. Wildfires
    In response to California's claim that recorded violations at 
projected receptors in both Colorado and Arizona are heavily influenced 
by wildfires experienced in western states, the EPA acknowledges that 
wildfires could influence downwind pollutant concentrations and that it 
is likely that wildfires would occur in 2023 and future years. However, 
there is no way to accurately forecast the timing, location, and extent 
of fires across a future three-year period that would be used to 
calculate ozone design values. In the EPA's CSAPR Update Modeling 
provided in the March 2018 memorandum and in the EPA's 2016v2 emissions 
platform based modeling, the EPA held the meteorological data and the 
fire and biogenic emissions constant at base year levels in the future 
year modeling, as those emissions are highly-correlated with the 
meteorological conditions in the base year.
    CARB's analysis focused on changes in air quality projections at 
receptors after removing data associated with atypical events (e.g., 
wildfires) and questioned whether the number of receptors would be 
diminished or be nonexistent by 2023 if those data were removed. 
However, we note that measured design values at the identified Colorado 
and Arizona receptors continue to have design values well in excess of 
the 2015 ozone NAAQS, as shown in Tables 3 and 4 below.\118\
---------------------------------------------------------------------------

    \118\ In addition, the EPA's most recent modeling identifies 
receptors in 2023 in Utah, Nevada, and on tribal lands. Yuma, 
Arizona is also identified as a receptor in EPA's most recent 
modeling, while the Phoenix area no longer has receptors and now has 
a longer timeframe for attainment due to proposed changes in 
nonattainment classification. Projections for receptors that the 
EPA's most recent modeling identifies are provided later in this 
notice in Table 5.
    \119\ Historic design values at individual monitoring sites 
nationwide are provided in the file: 2010-2020 Design Values.xlsx 
which is included in docket ID No. EPA-HQ-OAR-2021-0663. Design 
value reports can also be obtained on EPA's website at https://www.epa.gov/air-trends/air-quality-design-values.
    \120\ Design values obtained from https://www.epa.gov/air-trends/air-quality-design-values, April 21, 2022.
    \121\ CARB presented data for these two Maricopa County monitors 
in its submittal. Those monitors are no longer projected to be 
receptors in the EPA's most recent modeling. However, Yuma, Arizona, 
along with monitors in Utah, Nevada, and on tribal land, as 
described in Table 5 of this notice, are still projected to be 
receptors.

                                        Table 3--Ozone Design Values for Denver Nonattainment Area Monitors \119\
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                             2014-2016       2015-2017       2016-2018       2017-2019       2018-2020
           AQS site ID                   State              County         Design value    Design value    Design value    Design value    Design value
                                                                               (ppb)           (ppb)           (ppb)           (ppb)           (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
80013001........................  Colorado..........  Adams.............              67              67              67              65              69
80050002........................  Colorado..........  Arapahoe..........  ..............  ..............              73              74              77
80050006........................  Colorado..........  Arapahoe..........              67              67              69              69              71
80310002........................  Colorado..........  Denver............              66              68              69              68              70
80350004........................  Colorado..........  Douglas...........              77              77              78              78              81
80590005........................  Colorado..........  Jefferson.........              72              75              72              71              71
80590006........................  Colorado..........  Jefferson.........              77              77              78              76              79
80590011........................  Colorado..........  Jefferson.........              80              79              79              76              80
80690007........................  Colorado..........  Larimer...........              69              68              70              68              70
80690011........................  Colorado..........  Larimer...........              75              75              77              75              75
80691004........................  Colorado..........  Larimer...........              70              68              69              67              67
--------------------------------------------------------------------------------------------------------------------------------------------------------


                                           Table 4--Ozone Design Values for Selected Arizona Monitors 120 121
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                             2014-2016       2015-2017       2016-2018       2017-2019       2018-2020
           AQS site ID                   State              County         Design value    Design value    Design value    Design value    Design value
                                                                               (ppb)           (ppb)           (ppb)           (ppb)         (ppb) \b\
--------------------------------------------------------------------------------------------------------------------------------------------------------
04-013-0019.....................  Arizona...........  Maricopa..........              73              74              74              73              74
04-013-1004.....................  Arizona...........  Maricopa..........              75              75              76              75              78
40278011........................  Arizona...........  Yuma..............              74              72              71              71              68
--------------------------------------------------------------------------------------------------------------------------------------------------------

    While elevated ozone levels in some instances may be associated 
with wildfires or other atypical events, presently neither Arizona or 
Colorado have sought, nor has the EPA concurred on, exceptional events 
demonstrations that would indicate official design values at these 
monitors should be appreciably lower than presently reported.
3. Back Trajectory Analysis
    For both Colorado and Arizona, CARB analyzed HYSPLIT back 
trajectories, but these also did not affect CARB's conclusions 
regarding California's linkages to downwind monitors.

[[Page 31455]]

HYSPLIT back trajectory analyses use archived meteorological modeling 
that includes actual observed data (surface, upper air, airplane data, 
etc.) and modeled meteorological fields to estimate the most likely 
route of an air parcel transported to a receptor at a specified time. 
The method essentially follows a parcel of air backward in hourly steps 
for a specified length of time. HYSPLIT estimates the central path in 
both the vertical and horizontal planes. The HYSPLIT central path 
represents the centerline with the understanding that there are areas 
on each side horizontally and vertically that also contribute to the 
concentrations at the end point. The horizontal and vertical areas that 
potentially contribute to concentrations at the endpoint grow wider 
from the centerline the further back in time the trajectory goes. 
Therefore, a HYSPLIT centerline does not have to pass directly over 
emissions sources or emission source areas but merely relatively near 
emission source areas for those areas to contribute to concentrations 
at the trajectory endpoint. The EPA relies on back trajectory analysis 
as a corollary analysis along with observation-based meteorological 
wind fields at multiple heights to examine the general plausibility of 
the photochemical model ``linkages.'' Because the back trajectory 
calculations do not account for any air pollution formation, 
dispersion, transformation, or removal processes as influenced by 
emissions, chemistry, deposition, etc., the trajectories cannot be used 
to develop quantitative contributions. Therefore, back trajectories 
cannot be used to quantitatively evaluate the magnitude of the existing 
photochemical contributions from upwind states to downwind receptors. 
In this regard, photochemical modeling simulations for ozone interstate 
transport assessments are relied upon by the EPA to simulate the 
formation and fate of oxidant precursors, primary and secondary 
particulate matter concentrations, and deposition over regional and 
urban spatial scales. Photochemical modeling is the most sophisticated 
tool available to estimate future ozone levels and contributions to 
those modeled future ozone levels. Consideration of the different 
processes that affect primary and secondary pollutants at the regional 
scale in different locations is fundamental to understanding and 
assessing the effects of emissions on air quality concentrations.
    CARB's HYSPLIT back trajectory analysis showed that on high ozone 
days in Colorado at the receptors identified by the EPA in the March 
2018 memorandum ``only one backward and forward trajectory pairing 
indicated that emissions in the California mixed layer should have 
reached the mixed layer at a Colorado receptor site.'' CARB claims this 
suggests that ``the complexity of the physical environment between 
California and Colorado limits the reproducibility of modeled transport 
and that considerable multi-faceted analyses would be necessary to 
explore transport mechanisms through areas of complex terrain.'' \122\ 
For Arizona, CARB concluded that ``[o]nly a few trajectories extend 
from California'' to the Phoenix area.\123\ CARB's trajectory analysis 
confirmed that California is an upwind area for the receptors in 
Colorado and Arizona often enough to potentially contribute to 
nonattainment or interfere with maintenance. The analysis did not 
provide evidence that was contrary to the conclusions of the EPA's 
photochemical modeling analyses (i.e., the EPA's modeling results in 
the March 2018 memorandum and EPA 2016v2 model).
---------------------------------------------------------------------------

    \122\ Id. at A4-18, A4-34.
    \123\ Id. at A4-39, A4-40 Figure 5.
---------------------------------------------------------------------------

    Further, the EPA finds CARB's back trajectory analysis to be 
deficient in proving that California does not contribute significantly 
to nonattainment or maintenance at the monitors in Colorado that the 
State was linked to in the EPA's modeling results in the March 2018 
memorandum. CARB's back trajectory analysis for Colorado shows a 
linkage between California and the monitors when evaluating three 
altitudes: 10 meters, 1,000 meters, and 2,000 meters, during June and 
July, when most exceedances occurred at these sites. By only evaluating 
these altitudes, CARB neglects to consider the wide range of heights 
that might show back trajectories leading back to sources in 
California, which could potentially further tie the state to more ozone 
exceedance events. In addition, by excluding trajectories with a 
centerline above the mixed layer the analysis fails to consider 
transported pollutants at elevations below the centerline which may be 
in the mixed layer and therefore impact ground level ozone 
concentrations.
    Similarly for its analysis of Arizona linkages, CARB's back 
trajectory analysis shows a linkage between California and the monitors 
when evaluating three altitudes: 100 meters, 500 meters, and 1,000 
Meters on ozone exceedance days in 2015 and 2016. CARB's back 
trajectories for Arizona use a relatively short 24-hour time period, 
which limits their reliability for evaluating long-distance transport 
of emissions. As evident from Figure 5 in CARB's SIP submission, there 
were a number of exceedance days in Phoenix with 24-hour back 
trajectories that point westward toward California. These trajectories 
may have crossed portions of California if the trajectories were 
calculated for a longer time period, such as 48 hours. This would 
further strengthen the linkage to California that is already indicated 
by CARB's analysis.
    In California's 2018 submittal, CARB noted that projected 2023 DVs 
in Denver and Phoenix increased from the ``el'' modeling released in 
the January 2017 NODA and the ``en'' modeling released in the October 
2017 memorandum. For Denver, CARB noted that there were three 2023 
receptors, all maintenance-only, based on the ``el'' modeling, whereas 
with the ``en'' modeling projected three monitors to be nonattainment 
and three monitors to be maintenance-only. For Phoenix, CARB noted that 
there were no receptors projected for 2023 based on the ``el'' 
modeling, whereas with the ``en'' modeling, two monitors are projected 
to be maintenance-only. Based on an analysis of the change in ``home 
state'' emissions and contributions vs contributions and emissions from 
California in the ``el'' modeling vs the ``en'' modeling, CARB argues 
that the nonattainment and maintenance receptors found in the ``en'' 
modeling in Denver and Phoenix are due to increases in emissions in the 
``home state'' rather than contributions from California.
    With respect to the information California provided that is related 
to local emissions and the impact on air quality at the Denver 
nonattainment area receptors, this information is insufficient to 
approve California's 2018 SIP submittal. As an initial matter, we do 
not agree with CARB's conclusions that the remaining nonattainment or 
maintenance problems in Arizona or in Colorado (after accounting for 
flagged data) should be ascribed solely to an increase in local 
emissions in the home state. While CARB asserts that its relative 
contribution to the problems has declined, CARB does not establish with 
any quantitative evidence that this contribution drops below 1 percent 
of the NAAQS.
    More fundamentally, regardless of whether local emissions are the 
largest contributor to a specific nonattainment or maintenance 
receptor, the good neighbor provision requires that upwind states 
prohibit emissions that contribute significantly to nonattainment or 
interfere with maintenance of the NAAQS in downwind states. The EPA

[[Page 31456]]

evaluates a state's obligations to eliminate interstate transport 
emissions under the interstate transport provision according to the 
EPA's 4-step process, and the EPA's updated modeling at Steps 1 and 2 
has identified a linkage between emission from California sources and 
downwind nonattainment and maintenance receptors.
    Further, the EPA disagrees with the implication that local 
emissions reductions from the jurisdiction where the downwind receptor 
is located must first be implemented and accounted for before imposing 
obligations on upwind states under the interstate transport provision. 
There is nothing in the CAA that supports that position, and it does 
not provide grounds on which to approve California's 2018 SIP 
submittal. 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 Act in order to timely assist 
downwind states in attaining and maintain the NAAQS, and this schedule 
is ``central to the regulatory scheme.'' Wisconsin, 938 F.3d at 316 
(quoting Sierra Club v. EPA, 294 F.3d 155, 161 (D.C. Cir. 2002)).
    Additionally, the 2018 SIP submittal does not assess whether 
California's own emissions contributed to nonattainment or interfered 
with maintenance at the linked receptors, or substantiate that 
emissions from California's sources were not interacting with these 
monitors. Consequently, the application of local emission reduction 
measures does not absolve upwind states and sources from the 
responsibility of addressing their significant contribution. Moreover, 
California still has an obligation under the Act to address its 
downwind contribution to ozone nonattainment or interference with 
maintenance regardless of the emission reduction potential for local 
control measures. Furthermore, given that the EPA's updated modeling 
indicates that California is linked to nonattainment and maintenance 
receptors at Step 2, the EPA disagrees with CARB's claims regarding the 
application of local emission reduction measures with respect to its 
downwind linkages in the most recent modeling.
    CARB presents a number of arguments that the unique topography and/
or meteorology in the western region and, in particular, in and 
surrounding the Denver and Phoenix nonattainment areas support a 
conclusion that California does not significantly contribute or 
interfere with maintenance in those areas. For example, CARB argues 
that the mountainous topography in California traps ozone-precursors 
in-state, and that the Rocky Mountains in Colorado and the mountains 
around Phoenix, Arizona also form barriers to the transport of ozone 
pollution.\124\ First, we note that despite these potential 
considerations, CARB itself acknowledges in its 2018 submittal that 
California is linked to at least some receptors in Colorado and Arizona 
at Step 2 based on the modeling analysis on which it primarily relies. 
Second, even if CARB intended these arguments to support an alternative 
argument that it is not linked to those receptors, the EPA finds that 
these entirely qualitative discussions are insufficient to overcome the 
robust, quantitative basis to find linkages exist based on the 
modeling.
---------------------------------------------------------------------------

    \124\ See, e.g., A4-13-14.
---------------------------------------------------------------------------

    We agree with CARB that the terrain in the western U.S. is complex. 
A complex topography can have a number of impacts on the transport of 
air and air pollutants, such as enhance vertical mixing of air, serve 
as a barrier to transported air pollution, enhance accumulation of 
local emissions in basins and valleys, and influence air flows up, 
down, and across valleys. While topography can have a significant 
effect on pollutant (e.g., ozone) formation and transport, it does not 
prevent transport within the State and beyond. Mountain passes through 
surrounding ranges can serve as ``transport corridors'' for ozone. For 
example, in Southern California, areas where upwind pollution is 
funneled through valley topography experience some of the highest 
measured ozone concentrations, despite lower local emissions.
    In Southern California there are several examples of transport 
corridors that funnel ozone and ozone precursors. The Riverside County 
(Coachella) 2015 8-hour ozone NAAQS design value for 2020 was 88 ppb. 
The area is affected by transported emissions from the South Coast Air 
Basin through the San Gorgonio Pass.\125\ Similarly, the Kern County 
(Eastern Kern), CA 2015 8-hour ozone NAAQS design value for 2020 was 86 
ppb and is primarily influenced by emissions transported from the San 
Joaquin Valley through the Tehachapi Pass.<SUP>126 127</SUP> Ozone and 
its precursors can be transported into the southern Mojave Desert Air 
Basin from the greater Los Angeles Air Basin through the Cajon Pass. 
Ozone can also be transported eastward to the Salton Sea Air Basin 
through the San Gorgonio Pass and from the San Diego Air Basin through 
other mountain passes continuing into Arizona. In addition to transport 
within the mixed layer, orographic lifting of ozone from the surface to 
the free troposphere by the so called ``mountain chimney effect'' is a 
potential additional pathway for venting of pollutants into the free 
troposphere and making them available for long-range transport to 
downwind states (Langford et. al., 2010 and Li et. al., 
2015).<SUP>128 129</SUP> While Southern California offers evidence of 
funneling of pollution through mountain passes and upwelling of 
pollution into troposphere, we have no reason to conclude these effects 
could

[[Page 31457]]

not occur in the Sierra Nevada Mountains and the Denver Metro/North 
Front Range.
---------------------------------------------------------------------------

    \125\ Final 2016 Air Quality Management Plan, at 7-23, South 
Coast Air Quality Management District, March 2017.
    \126\ Historic design values at individual monitoring sites 
nationwide are provided in the file: 2010-2020 Design Values.xlsx 
that is included in docket ID No. EPA-HQ-OAR-2021-0663. Design value 
reports can also be obtained on EPA's website at https://www.epa.gov/air-trends/air-quality-design-values.
    \127\ See ``CALIFORNIA Final Area Designations for the 2015 
Ozone National Ambient Air Quality Standards Technical Support 
Document (TSD)'' at pg 67, 178; available in docket ID No. EPA-HQ-
OAR-2017-0548 (83 FR 25776, April 30, 2018). Also available on EPA's 
website at https://www.epa.gov/sites/default/files/2018-05/documents/ca_tsd_combined_final_0.pdf.
    \128\ Langford, A., Senff, C., Alvarez, R., Banta, R., Hardesty, 
R.: Long[hyphen]range transport of ozone from the Los Angeles Basin: 
A case study, J. Geophys. Res., 37, L06807, doi:10.1029/
2010GL042507.
    \129\ Li, J., Georgescu, M., Hyde, P., Mahalov, A., and 
Moustaoui, M.: Regional-scale transport of air pollutants: Impacts 
of Southern California emissions on Phoenix ground-level ozone 
concentrations, Atmos. Chem. Phys., 15, 9345-9360, https://doi.org/10.5194/acp-15-9345-2015, 2015.
---------------------------------------------------------------------------

    The EPA has previously explained that its nationwide photochemical 
grid modeling is reliable for applications in the western region of the 
U.S. In disapproving Utah's 2008 ozone transport SIP submittal for 
prong 2, the EPA rejected comments that its CAMx modeling (the same 
modeling software used here) did not account for unique western 
geographical considerations. See 81 FR 71991, 71992-93 (Oct. 19, 2016). 
In particular, the EPA noted that the modeling accounted for 
differences in emissions (including wildfires), meteorology, and 
topography'' across all regions of the U.S. Id. at 71993. The EPA found 
that neither the commenters, nor the state in its SIP submittal, had 
adduced any additional factors that would be relevant for projecting 
ozone concentrations in the west that were not already factored into 
and documented in both the modeling itself and in the EPA's technical 
support documents explaining that modeling. Id. The same holds true 
here. As explained in Appendix A of the Air Quality Modeling TSD 
included in docket ID No. EPA-HQ-OAR-2021-0663, the EPA has found that 
its updated 2016v2 emissions platform-based modeling performs equally 
as well in eastern and western regions in terms of replicating the 
relative magnitude of concentrations and day-to-day variability that 
are characteristic of observed 8-hour daily maximum ozone 
concentrations in each region. It is also important to note that the 
model accurately captures substantial geographical difference in the 
temporal nature of ozone concentrations at the receptors in the west, 
including in the Denver nonattainment area, compared to receptors in 
the East.\130\ The EPA continues to find its modeling reliable for 
characterizing ozone concentrations and contribution values in the 
western region of the United States. As such, CARB's qualitative 
discussions of western geography fail to present evidence that calls 
into question the results of the EPA's photochemical grid modeling.
---------------------------------------------------------------------------

    \130\ See Appendix A--Model Performance Evaluation for 2016v2 
Base Year CAMx Simulation, of Air Quality Modeling TSD for 2015 
Ozone NAAQS Transport SIP Proposed Actions, at A-10.
---------------------------------------------------------------------------

C. Results of the EPA's Step 1 and Step 2 Modeling and Findings for 
California

    As described in section I, the EPA performed air quality modeling 
using the 2016v2 emissions platform to project design values and 
contributions for 2023. These data were examined to determine if 
California 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 3, the data \131\ indicate that 
in 2023, emissions from California contribute greater than 1 percent of 
the standard (i.e., 0.70 ppb) to nonattainment or maintenance-only 
receptors in Arizona, Colorado, Nevada, and Utah.\132\ Emissions from 
California also contribute greater than 1 percent of the standard to 
nonattainment receptors on, or representative of, the Morongo and 
Pechanga reservations.\133\
---------------------------------------------------------------------------

    \131\ Design values and contributions at individual monitoring 
sites nationwide are provide in the file: 
2016v2_DVs_state_contributions.xlsx which is included in docket ID 
No. EPA-HQ-OAR-2021-0663.
    \132\ 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 California had a maximum contribution greater than 0.70 ppb to 
at least one nonattainment or maintenance-only receptor in 2023. 
These modeling results are included in the file ``Ozone Design 
Values and Contributions Revised CSAPR Update.xlsx'' in docket EPA-
HQ-OAR-2021-0663.
    \133\ We note that, consistent with the EPA's prior good 
neighbor actions in California, the regulatory ozone monitor located 
on the Morongo Band of Mission Indians (``Morongo'') reservation is 
a projected downwind receptor in 2023. See monitoring site 060651016 
in Table 3. We also note that the Temecula, California regulatory 
ozone monitor is a projected downwind receptor in 2023 and in past 
regulatory actions has been deemed representative of air quality on 
the Pechanga Band of Luise[ntilde]o Indians (``Pechanga'') 
reservation. See, e.g., Approval of Tribal Implementation Plan and 
Designation of Air Quality Planning Area; Pechanga Band of 
Luise[ntilde]o Mission Indians, 80 FR 18120, at 18121-18123 (April 
3, 2015); see also monitoring site 060650016 in Table 3. The 
presence of receptors on, or representative of, the Morongo and 
Pechanga reservations does not trigger obligations for the Morongo 
and Pechanga Tribes. Nevertheless, these receptors are relevant to 
the EPA's assessment of any linked upwind states' good neighbor 
obligations. See, e.g., Approval and Promulgation of Air Quality 
State Implementation Plans; California; Interstate Transport 
Requirements for Ozone, Fine Particulate Matter, and Sulfur Dioxide, 
83 FR 65093 (December 19, 2018). Under 40 CFR 49.4(a), tribes are 
not subject to the specific plan submittal and implementation 
deadlines for NAAQS-related requirements, including deadlines for 
submittal of plans addressing transport impacts.
---------------------------------------------------------------------------

    Therefore, based on the EPA's evaluation of the information 
submitted by California, and based on the EPA's most recent modeling 
results for 2023, the EPA proposes to find that California 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.

                     Table 5--California Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023 Average    2023  Maximum    California
     Receptor ID          Location           Nonattainment/        design value    design value    contribution
                                              maintenance              (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
40278011............  Yuma (AZ)......  Maintenance-only.........            70.5            72.2            5.09
80350004............  Denver/          Nonattainment............            71.7            72.3            0.91
                       Chatfield (CO).
80590006............  Rocky Flats      Nonattainment............            72.6            73.3            1.03
                       (CO).
80590011............  Denver/NREL      Nonattainment............            73.8            74.4            1.17
                       (CO).
320030075...........  Las Vegas/       Maintenance-only.........            70.0            71.0            7.44
                       Northwest (NV).
490110004...........  SLC/Bountiful    Nonattainment............            72.9            75.1            2.25
                       (UT).
490353006...........  SLC/Hawthorne    Nonattainment............            73.6            75.3            2.46
                       (UT).
490353013...........  SLC/Herriman     Nonattainment............            74.4            74.9            1.42
                       (UT).
490570002...........  SLC/Ogden (UT).  Maintenance-only.........            70.6            72.5            2.24
490571003...........  SLC/             Maintenance-only.........            70.5            71.5            2.16
                       Harrisonville
                       (UT).
060651016...........  Morongo Band of  Nonattainment............            89.8            90.9           34.24
                       Mission
                       Indians.
060650016...........  Pechanga Band    Nonattainment............            72.0            72.9           26.32
                       of Mission
                       Indians
                       (represented
                       by Temecula
                       (CA)).
----------------------------------------------------------------------------------------------------------------


[[Page 31458]]

    Based on the EPA's evaluation of the information provided in 
California's 2018 submittal and based on the results of the EPA's 
2016v2 emissions platform modeling, the EPA will proceed to evaluate 
these additional arguments at Step 3 of the 4-step interstate transport 
framework.

D. 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 interferes with maintenance) in each of its 
prior federal, regional ozone transport rulemakings, and this 
interpretation of the statute has been upheld by the Supreme Court. See 
EME Homer City, 572 U.S. 489, 519 (2014). While the EPA has not 
directed states that they must conduct a Step 3 analysis in precisely 
the manner the EPA has done in its prior regional transport 
rulemakings, state implementation plans addressing the obligations in 
CAA section 110(a)(2)(D)(i)(I) must prohibit ``any source or other type 
of emissions activity within the State'' from emitting air pollutants 
which will contribute significantly to downwind air quality problems. 
Thus, states must complete something similar to the EPA's analysis (or 
an alternative approach to defining ``significance'' that comports with 
the statute's objectives) to determine whether and to what degree 
emissions from a state should be ``prohibited'' to eliminate emissions 
that will ``contribute significantly to nonattainment in, or interfere 
with maintenance of'' the NAAQS in any other state. California did not 
conduct such an analysis in its 2018 SIP Submittal.
    As previously indicated in section II.B. California's 2018 SIP 
Submittal provided an overview of NO<INF>X</INF> emissions by sector 
for 2011 NEI emissions and 2023 projections. CARB also provided a 
summary of regulations controlling NO<INF>X</INF> and VOCs at the state 
and district level for various sectors, many of which had been approved 
into California's SIP. CARB asserted in the 2018 Submittal that, 
despite its contributions, California had met its good neighbor 
obligations through the implementation and enforcement of stringent 
NO<INF>X</INF> and VOC control measures that go beyond the EPA's 
presumptive cost threshold in the CSAPR Update for highly cost-
effective emissions reductions, and through the ongoing adoption and 
revision of additional control measures to further ensure the reduction 
of ozone in both California and downwind areas.
    CARB, however, did not provide an adequate demonstration at Step 3 
that California was adequately controlling its emissions for the 
purposes of the good neighbor provision for the 2015 ozone NAAQS, 
particularly because CARB acknowledged in its 2018 SIP Submittal that 
its emissions were linked to Arizona and Colorado receptors at Steps 1 
and 2. In general, the air quality modeling that the EPA has conducted 
as well as the modeling relied on by CARB in its submittal already 
account for ``on-the-books'' emissions control measures. Both sets of 
modeling analyzed by CARB (confirmed by the EPA's most recent modeling) 
clearly establish continued linkages from California to downwind 
receptors in 2023 at Steps 1 and 2. In general, the listing of existing 
or on-the-way control measures, whether approved into the state's SIP 
or not, does not substitute for a complete Step 3 analysis under the 
EPA's 4-Step framework to define ``significant contribution.'' \134\ 
CARB's submittal does not include an assessment of the overall effects 
of the identified control measures it identifies or explain what the 
overall resulting air quality effects would be at identified out-of-
state receptors.
---------------------------------------------------------------------------

    \134\ See discussion further in this Section discussing why EPA 
finds its analysis in the approval of California's 2008 ozone NAAQS 
transport SIP to be appropriate or sufficient for purposes of this 
action.
---------------------------------------------------------------------------

    Further, CARB did not conduct in its submittal any analysis of 
potential additional emissions-reduction measures to further reduce its 
impact on the identified downwind receptors. For example, CARB did not 
include in the 2018 SIP Submittal an accounting of facilities in the 
State along with an analysis of potential NO<INF>X</INF> emissions 
control technologies, their associated costs, estimated emissions 
reductions, and downwind air quality improvements. Nor does the 
submittal include an analysis of whether such potential additional 
control technologies or measures could reduce the impact of 
California's emissions on out of state receptors. Though there is not a 
prescribed method for a Step 3 analysis, the EPA has consistently 
applied Step 3 of the good neighbor framework through a more rigorous 
evaluation of potential additional control technologies or measures 
than what was provided in the SIP submission. Identifying a range of 
various emissions controls measures that have been or may be enacted at 
the state or local level, without analysis of the impact of those 
measures on the out of state receptors, is not analytically sufficient.
    CARB did not offer an explanation as to whether any more stringent 
emissions reductions that may be available were prohibitively costly or 
infeasible. CARB did note that the EPA's 2016 cost-effectiveness 
analysis of EGU emission reductions in the CSAPR Update for the 2008 
ozone NAAQS found that NO<INF>X</INF> emission reductions at California 
EGUs would be achieved at a significantly higher cost threshold than 
the cost threshold finalized for the states ultimately included in the 
CSAPR Update. CARB further stated that what the ``EPA found true with 
respect to the 0.075 ppm 8-hour ozone standard is equally valid 
concerning the 0.070 ppm 8-hour ozone standard. California's emission 
reduction programs adequately prohibit the emission of air pollutants 
in amounts that will significantly contribute to nonattainment, or 
interfere with maintenance, of the 0.070 ppm 8-hour ozone standard in 
any downwind state.'' \135\
---------------------------------------------------------------------------

    \135\ Id. at A4-57.
---------------------------------------------------------------------------

    However, this is incorrect. There is no reason to suppose that the 
EPA or states should conclude that the same degree of emissions-control 
stringency that was deemed approvable to address good neighbor 
obligations to meet a less stringent NAAQS should apply to a more 
stringent NAAQS. While the EPA has not finalized a benchmark cost-
effectiveness threshold for good neighbor obligations for the more 
stringent 2015 ozone NAAQS, it was not the EPA's obligation to do so 
prior to states developing their SIP submissions.\136\ CARB, in its 
2018 SIP

[[Page 31459]]

Submittal, has not conducted an analysis to establish one for the EPA 
to evaluate, and this is grounds for disapproval.
---------------------------------------------------------------------------

    \136\ The EPA notes that it has proposed a cost-effectiveness 
threshold of $11,000 per ton for EGUs in determining good neighbor 
obligations for the 2015 ozone NAAQS after assessing the full range 
of NO<INF>X</INF> mitigation strategies that could be applied to 
fossil-fuel fired EGUs. ``Federal Implementation Plan Addressing 
Regional Ozone Transport for the 2015 Ozone National Ambient Air 
Quality Standard'' 87 FR 20036, 20091-93 (April 6, 2022). While this 
does not represent a final promulgated cost-effectiveness benchmark 
for EGUs that California is expected to have applied, the EPA's Step 
3 analysis in the proposed FIP indicates the relative paucity of 
analysis in California's SIP submittal regarding emissions control 
opportunities at Step 3. Nonetheless, the EPA has not proposed to 
apply the EGU control strategy in its proposed FIP action to 
California. See id. at 20088. The EPA continues to find in this 
proposal that California's EGUs are sufficiently controlled for 
ozone-precursor emissions for purposes of good neighbor obligations 
under the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    More fundamentally, relying on the CSAPR Update's (or any other CAA 
program's) determination of cost-effectiveness without further Step 3 
analysis is insufficient. Cost-effectiveness must be assessed in the 
context of the specific CAA program; assessing cost-effectiveness in 
the context of interstate ozone transport should reflect a more 
comprehensive evaluation of the nature of the interstate transport 
problem, the total emissions reductions available at several cost 
thresholds, and the air quality impacts of the reductions at downwind 
receptors. While the EPA has not finalized a benchmark cost-
effectiveness value for the 2015 ozone NAAQS interstate transport 
obligations, because the 2015 ozone NAAQS is a more stringent and more 
protective air quality standard, it is reasonable to expect control 
measures or strategies to address interstate transport of ozone to 
reflect higher marginal control costs. As such, the marginal cost 
threshold of $1,400 per ton for the CSAPR Update (which addresses the 
2008 ozone NAAQS and is in 2011$) is not an appropriate cost threshold 
and cannot be approved as a benchmark to use for interstate transport 
SIP submissions for the 2015 ozone NAAQS.
    Although the EPA acknowledges states are not necessarily bound to 
follow the EPA's own analytical framework at Step 3, CARB did not 
attempt to determine or justify an appropriate uniform cost-
effectiveness threshold. This would have been similar to the approach 
to defining significant contribution that the EPA has applied in prior 
rulemakings such as CSAPR and the CSAPR Update, even if conducting 
precisely this type of analysis is not technically mandatory. For 
example, CARB did not conduct its own updated EGU analysis of all large 
NO<INF>X</INF> emitting EGUs. Nonetheless, the EPA finds based on its 
own analysis that additional emissions reductions are not required from 
EGUs to address California's good neighbor obligations for the 2015 
ozone NAAQS.\137\
---------------------------------------------------------------------------

    \137\ The EPA reached this proposed conclusion for EGUs in 
California in the context of a recent proposed federal 
implementation plan and proposes the same conclusions for these 
sources in this action. See ``Federal Implementation Plan Addressing 
Regional Ozone Transport for the 2015 Ozone National Ambient Air 
Quality Standard,'' 87 FR 20036, 20088 (April 6, 2022).
---------------------------------------------------------------------------

    As stated in the SIP submittal, the Greenleaf One unit emits at 
higher rates with a low utilization, resulting in only 2 tons of 
NO<INF>X</INF> in the 2021 ozone season. Therefore, the EPA agrees it 
is unlikely that any significant cost-effective emission reduction 
opportunities exist at this facility. In addition, California has 
highlighted the retirements of the Redondo Beach units and the ACE 
Cogeneration facility. The EPA has confirmed the retirements of these 
and other units in California in the IPM version 6--Summer 2021 
Reference Case database.\138\ The EPA IPM version 6--Summer 2021 
Reference Case uses the National Electric Energy Data System (NEEDS) v6 
database as its source for data on all existing and planned-committed 
units. Units are removed from the NEEDS inventory only if a high degree 
of certainty could be assigned to future implementation of the 
announced future closure or retirement. The available retirement-
related information was reviewed for each unit, and the following rules 
are applied to remove:
---------------------------------------------------------------------------

    \138\ The ``Capacity Dropped'' and the ``Retired Through 2023'' 
worksheets in NEEDS list all units that are removed from the NEEDS 
v6 inventory--NEEDS v6 Summer 2021 Reference Case. This data can be 
found on the EPA's website at: https://www.epa.gov/airmarkets/national-electric-energy-data-system-needs-v6.
---------------------------------------------------------------------------

    (i) Units that are listed as retired in the December 2020 EIA Form 
860M;
    (ii) Units that have a planned retirement year prior to June 30, 
2023 in the December 2020 EIA Form 860M;
    (iii) Units that have been cleared by a regional transmission 
operator (RTO) or independent system operator (ISO) to retire before 
2023, or whose RTO/ISO clearance to retire is contingent on actions 
that can be completed before 2023;
    (iv) Units that have committed specifically to retire before 2023 
under federal or state enforcement actions or regulatory requirements;
    (v) And finally, units for which a retirement announcement can be 
corroborated by other available information. Units required to retire 
pursuant to enforcement actions or state rules on July 1, 2023 or later 
are retained in NEEDS v6.
    The majority of the EGUs in California have emissions controls and 
are sufficiently regulated, resulting in the lowest fossil fuel 
emission rate and highest share of renewable generation among the 26 
states examined at the EPA's Step 3 analysis for the proposed Federal 
Implementation Plan Addressing Regional Ozone Transport for the 2015 
Ozone National Ambient Air Quality Standard. 87 FR 20036, 20088. The 
EPA evaluated the EGU sources within the state of California and found 
there were no covered coal steam sources greater than 100 MW that would 
have emissions reduction potential according to the EPA's assumed EGU 
SCR retrofit mitigation technologies. The NO<INF>X</INF> emission level 
for California was unchanged at 1,216 tons of NO<INF>X</INF> across the 
various emission control scenarios. The EPA's Step 3 analysis, 
including analysis of the emissions reduction factors from EGU sources 
in the state, therefore resulted in no additional emission reductions 
required to eliminate significant contribution from any EGU sources in 
California.
    The EPA proposes that California's Step 3 analysis was likewise 
insufficient for non-EGU stationary sources. But whereas EPA is able to 
conclude, based on the foregoing analysis, that additional emissions 
reductions are not required from EGU sources in California, we can 
reach no such conclusion with respect to other industrial sources of 
emissions in the State. For non-EGUs, CARB did not complete an 
evaluation of cost effective control opportunities, and instead simply 
provided a cursory analysis that provided a few examples of regulations 
to conclude that ``further emission controls would be unlikely to 
reduce any potential impact on downwind states' air quality[.]'' \139\ 
CARB did not investigate additional potential emissions control 
opportunities, or their costs or impacts, or attempt to analyze 
whether, if applied more broadly across linked states, the emissions 
reductions would constitute the elimination of significant contribution 
on a regional scale.
---------------------------------------------------------------------------

    \139\ Id. at A4-55.
---------------------------------------------------------------------------

    The EPA acknowledges that it has previously approved California's 
2008 ozone NAAQS transport SIP at Step 3 based on a relatively cursory 
review of California's existing emissions control programs. See 83 FR 
65093, 65094-95 (Dec. 19, 2018). That approval pre-dates the D.C. 
Circuit's decision in Wisconsin v. EPA, 938 F.3d 903 (D.C. Cir. 2019), 
in which the court found the EPA had not properly justified failing to 
analyze emissions reduction opportunities from industrial sources 
outside the power

[[Page 31460]]

sector. Id. at 918-20. At that time, the CSAPR Update had only 
addressed reductions from the power sector and applied a cost threshold 
of $1400 per ton. The EPA's analysis of California focused on the fact 
that California's EGU fleet was very well controlled and that all 
receptors for the 2008 ozone NAAQS were projected to be clean by 2023. 
83 FR 65093, 65095. The EPA engaged in an extremely limited review of 
other emissions control opportunities in California at non-EGU 
industrial sources, despite acknowledging that these sources emitted 
6.7 times as much NO<INF>X</INF> as EGUs, and 19 large stationary 
sources each individually emitted over 500 tons per year. Id.
    The EPA finds that good reasons exist for no longer considering 
such a cursory analysis of emissions reduction opportunities beyond the 
power sector to be adequate for purposes of CAA section 
110(a)(2)(D)(i)(I). First, the EPA and the states are implementing the 
more stringent 2015 ozone NAAQS of 70 ppb. Under that more stringent 
NAAQS, our analysis at Steps 1 and 2 indicates a continuing linkage 
between California's emissions and persistent air quality problems (at 
least through 2026) in other states in the EPA's modeling. Further, 
while California may be relatively ``well controlled'' as a state 
overall on a per capita basis, the same could be said of other states 
throughout the country that continue to contribute above 1 percent of 
the NAAQS to at least one out of state receptor despite relatively 
stringent ozone-precursor emissions control programs. In the CSAPR 
Update and the Revised CSAPR Update, the EPA has found that states such 
as New York and New Jersey may nonetheless be found to have additional 
emissions control obligations in order to address their significant 
contribution under Section 110(a)(2)(D)(i)(I).\140\ Further, the 
relevance of a per capita emissions rate, which CARB cites as 
relatively low for California, is not readily apparent. California is a 
large and very populous state, and by CARB's own admission, total 
NO<INF>X</INF> emissions from the State are second highest in the 
country, behind only Texas. Finally, the EPA recognizes the critical 
importance of consistency in application of good neighbor requirements 
across all states, especially with respect to regional-scale pollutants 
such as ozone. The EPA's regional analysis in the proposed FIP 
(discussed below) indicates emissions control opportunities at non-EGUs 
in California at the same stringency as EPA's Step 3 assessment of 22 
other states. Therefore, for all of these reasons, the EPA does not 
view the degree of analysis at Step 3 that supported approval in the 
prior California transport action to be sufficient to justify approval 
in this case.
---------------------------------------------------------------------------

    \140\ See, e.g., ``Disapproval of Interstate Transport 
Requirements for the 2008 Ozone National Ambient Air Quality 
Standards; New York and New Jersey'', 86 FR 60602 (November 3, 
2021).
---------------------------------------------------------------------------

    The EPA notes that in the proposed FIP for California for the 2015 
ozone NAAQS, we identified several potential cost-effective 
NO<INF>X</INF> controls for non-EGUs in California.\141\ The EPA's non-
EGU analysis in the proposed FIP focused on several industrial sectors 
and found impactful emissions reduction opportunities up to $7,500 per 
ton, which the EPA proposed are needed to address 23 upwind state's 
(including California's) good neighbor obligations for the 2015 ozone 
NAAQS. See 87 FR 20036, 20089-90. In particular for California, the EPA 
found 1,666 tons of ozone season NO<INF>X</INF> emissions reduction 
available from a 2019 baseline of 14,579 tons of ozone season emissions 
from the non-EGU sectors analyzed. Id. at 20090. The EPA proposed to 
require these reductions in part because, in conjunction with the other 
emission control strategies proposed in the FIP across the entire 
region of linked upwind states, the EPA found ozone levels would 
improve on average by 0.64 ppb across all impacted receptors, including 
those receptors affected by California's emissions. Id. at 20096. The 
EPA proposed to determine that these controls would eliminate 
significant contribution and interference with maintenance for the 2015 
ozone NAAQS.
---------------------------------------------------------------------------

    \141\ 87 FR 20036 (April 6, 2022).
---------------------------------------------------------------------------

    The EPA acknowledges that California need not have conducted a Step 
3 analysis in precisely the manner as the proposed FIP, and we further 
acknowledge that our FIP for California and other states is only a 
proposal at this stage and is currently undergoing public comment. 
Nonetheless, the proposed FIP presents an example of how a potentially 
approvable Step 3 analysis could have been conducted by CARB and 
highlights that cost-effective emissions reduction opportunities likely 
exist in California that could address interstate transport 
obligations, which CARB failed to analyze in the 2018 SIP Submittal.
    CARB also attempted to support its conclusion that California does 
not significantly contribute to nonattainment or maintenance in other 
states in part because it suggested that emissions originating from 
outside California, such as local emissions in Arizona and Colorado, as 
well as international emissions, and wildfires, were the primary driver 
of higher modeled design values at monitoring sites in those states 
using the EPA modeling released with the January 2017 NODA and the 
October 2017 memorandum.\142\
---------------------------------------------------------------------------

    \142\ See California's 2018 Submittal at A4-33-A4-34, A4-44.
---------------------------------------------------------------------------

    With respect to local, international, and non-anthropogenic 
emissions contributions, CARB's reasoning is inapplicable to the 
requirements of CAA section 110(a)(2)(D)(i)(I). The good neighbor 
provision requires states and the EPA to address interstate transport 
of air pollution that contributes to downwind states' ability to attain 
and maintain the NAAQS. Whether emissions from other states or other 
countries also contribute to the same downwind air quality issue is 
irrelevant in assessing whether a downwind state has an air quality 
problem, or whether an upwind state is significantly contributing to 
that problem. States are not obligated under CAA section 
110(a)(2)(D)(i)(I) to reduce emissions sufficient on their own to 
resolve downwind receptors' nonattainment or maintenance problems. 
Rather, states are obligated to eliminate their own ``significant 
contribution'' or ``interference'' with the ability of other states to 
attain or maintain the NAAQS.
    Indeed, the D.C. Circuit in Wisconsin specifically rejected 
petitioner arguments suggesting that upwind states should be excused 
from good neighbor obligations on the basis that some other source of 
emissions (whether international or another upwind state) could be 
considered the ``but-for'' cause of downwind air quality problem. 938 
F.3d 303 at 323-324. The court viewed petitioners' arguments as 
essentially an argument ``that an upwind State `contributes 
significantly' to downwind nonattainment only when its emissions are 
the sole cause of downwind nonattainment.'' 938 F.3d 303 at 324. The 
court explained that ``an upwind State can `contribute' to downwind 
nonattainment even if its emissions are not the but-for cause.'' Id. at 
324-325. See also Catawba County v. EPA, 571 F.3d 20, 39 (D.C. Cir. 
2009) (rejecting the argument ``that `significantly contribute' 
unambiguously means `strictly cause' '' because there is ``no reason 
why the statute precludes EPA from determining that [an] addition of 
[pollutant] into the atmosphere is significant even though a nearby 
county's nonattainment problem would still persist in its absence''); 
Miss. Comm'n on Envtl. Quality v. EPA, 790 F.3d 138, 163 n.12 (D.C. 
Cir. 2015)

[[Page 31461]]

(observing that the argument that ``there likely would have been no 
violation at all . . . if it were not for the emissions resulting from 
[another source]'' is ``merely a rephrasing of the but-for causation 
rule that we rejected in Catawba County.''). Therefore, a state is not 
excused from eliminating its significant contribution on the basis that 
international emissions also contribute some amount of pollution to the 
same receptors to which the state is linked.
    In conclusion, at Step 3, we propose that California was required 
to analyze emissions from the sources and other emissions activity from 
within the state to determine whether its contributions to 
nonattainment were significant or interfered with maintenance of the 
NAAQS in downwind states, and we propose to disapprove the 2018 SIP 
Submittal on the separate, additional basis that it did not assess 
additional emission control opportunities.

E. 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, 
California's 2018 SIP Submittal 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. Instead, CARB concluded that the state already has ``measures 
of sufficient stringency to ensure that this State does not contribute 
significantly to downwind ozone problems, whether they be nonattainment 
or maintenance, in other states.'' \143\ As a result, the EPA proposes 
to disapprove California'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) for the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \143\ Id. at A4-58
---------------------------------------------------------------------------

F. Tribal Consultation

    On February 15, 2022, the EPA sent letters to the Morongo and 
Pechanga tribes inviting consultation on this proposed action.\144\ On 
March 2, 2022, the EPA held an informational meeting with the Morongo 
Tribe. The Morongo and Pechanga tribes did not request consultation on 
this Regional action. On April 7, 2022, the EPA opened a 30-day window 
for federally recognized tribes to request consultation on the national 
FIP proposal.
---------------------------------------------------------------------------

    \144\ Letter dated February 14, 2022, from Elizabeth J. Adams, 
Director, Air and Radiation Division, EPA Region IX to Mark Macarro, 
Chairperson, Pechanga Band of Luise[ntilde]o Indians of the Pechanga 
Reservation, Re: Invitation to Consult on California's Interstate 
Transport State Implementation Plan for the 2015 Ozone National 
Ambient Air Quality Standards; and letter dated February 14, 2022, 
from Elizabeth J. Adams, Director, Air and Radiation Division, EPA 
Region IX to Charles Martin, Chairperson, Morongo Band of Mission 
Indians, Re: Invitation to Consult on California's Interstate 
Transport State Implementation Plan for the 2015 Ozone National 
Ambient Air Quality Standards.
---------------------------------------------------------------------------

G. Conclusion

    Based on the EPA's evaluation of California's SIP submission, the 
EPA is proposing to find that the portion of California's October 1, 
2018 SIP Submittal addressing CAA section 110(a)(2)(D)(i)(I) does not 
meet the State's interstate transport obligations, because it fails to 
contain the necessary provisions to eliminate emissions that will 
contribute significantly to nonattainment or interfere with maintenance 
of the 2015 8-hour ozone NAAQS in any other state.

IV. Proposed Action

    We are proposing to disapprove Enclosure 4 of California's 2018 SIP 
Submittal 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 California 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 submittal that meets these requirements. Disapproval 
does not start a mandatory sanctions clock for California. The 
remaining elements of the State's October 1, 2018 SIP Submittal are not 
addressed in this action and have been acted on in a separate 
rulemaking.\145\
---------------------------------------------------------------------------

    \145\ 86 FR 16533 (March 30, 2021).
---------------------------------------------------------------------------

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 (OMB) 
for review.

B. Paperwork Reduction Act (PRA)

    This action does not impose an information collection burden under 
the PRA, because this proposed SIP disapproval, if finalized, will not 
in-and-of itself create any new information collection burdens, but 
will simply disapprove certain State requirements for inclusion in the 
SIP.

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 will not impose any requirements on small entities. This 
proposed SIP disapproval, if finalized, will not in-and-of itself 
create any new requirements but will simply disapprove certain State 
requirements for inclusion in the SIP.

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. This action proposes to disapprove pre-existing 
requirements under State or local law, and imposes no new requirements. 
Accordingly, no additional costs to State, local, or tribal 
governments, or to the private sector, result from this action.

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: Coordination With Indian Tribal Governments

    This action does not have tribal implications, as specified in 
Executive Order 13175, because the SIP revision that the EPA is 
proposing to disapprove would not apply on any Indian reservation land 
or in any other area where the EPA or an Indian tribe has demonstrated 
that a tribe has jurisdiction and will not impose substantial direct 
costs on tribal governments or preempt tribal law. Thus, Executive 
Order 13175 does not apply to this action.

[[Page 31462]]

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 this proposed SIP disapproval, if 
finalized, will not in-and-of itself create any new regulations, but 
will simply disapprove certain State requirements for inclusion in the 
SIP.

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 (NTTAA)

    Section 12(d) of the NTTAA directs the EPA to use voluntary 
consensus standards in its regulatory activities unless to do so would 
be inconsistent with applicable law or otherwise impractical. The EPA 
believes that this action is not subject to the requirements of section 
12(d) of the NTTAA because application of those requirements would be 
inconsistent with the CAA.

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

    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).\146\
---------------------------------------------------------------------------

    \146\ 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.\147\ 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).\148\
---------------------------------------------------------------------------

    \147\ 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.
    \148\ 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 15, 2022.
Martha Guzman Aceves,
Regional Administrator, Region IX.
[FR Doc. 2022-11150 Filed 5-23-22; 8:45 am]
BILLING CODE 6560-50-P


</pre><script data-cfasync="false" src="/cdn-cgi/scripts/5c5dd728/cloudflare-static/email-decode.min.js"></script></body>
</html>