[Federal Register Volume 87, Number 35 (Tuesday, February 22, 2022)]
[Proposed Rules]
[Pages 9798-9835]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2022-02961]



[[Page 9797]]

Vol. 87

Tuesday,

No. 35

February 22, 2022

Part II





Environmental Protection Agency





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40 CFR Part 52





Air Plan Disapproval; Arkansas, Louisiana, Oklahoma, and Texas; 
Interstate Transport of Air Pollution for the 2015 8-Hour Ozone 
National Ambient Air Quality Standards; Proposed Rule

  Federal Register / Vol. 87, No. 35 / Tuesday, February 22, 2022 / 
Proposed Rules  

[[Page 9798]]


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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R06-OAR-2021-0801, EPA-HQ-OAR-2021-0663; FRL-9338-01-R6]


Air Plan Disapproval; Arkansas, Louisiana, Oklahoma, and Texas; 
Interstate Transport of Air Pollution for the 2015 8-Hour Ozone 
National Ambient Air Quality Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Pursuant to the Federal Clean Air Act (CAA or the Act), the 
Environmental Protection Agency (EPA or Agency) is proposing to 
disapprove State Implementation Plan (SIP) submittals from Arkansas, 
Louisiana, Oklahoma and Texas regarding interstate transport for the 
2015 8-hour ozone national ambient air quality standard (NAAQS). This 
provision requires that each state's SIP contain adequate provisions to 
prohibit emissions from within the state from significantly 
contributing to nonattainment or interfering with maintenance of the 
NAAQS in other states. The ``good neighbor'' or ``interstate 
transport'' 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: Written comments must be received on or before April 25, 2022.

ADDRESSES: You may send comments, identified as Docket No. EPA-R06-OAR-
2021-0801, 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 [email protected]. Include 
Docket ID No. EPA-R06-OAR-2021-0801 in the subject line of the message.
    Instructions: All comments submitted 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. Out 
of an abundance of caution for members of the public and our staff, the 
EPA Docket Center and Reading Room are open to the public by 
appointment only to reduce the risk of transmitting COVID-19. Our 
Docket Center staff also continues to provide remote customer service 
via email, phone, and webform. For further information on the EPA 
Docket Center services and the current status, please visit us online 
at https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Sherry Fuerst, EPA Region 6 Office, 
AR-SI, 214-665-6454, [email protected]. We encourage the public to 
submit comments via https://www.regulations.gov, as there will be a 
delay in processing mail and no courier or hand deliveries will be 
accepted. Please call or email the contact above if you need 
alternative access to material indexed but not provided in the docket.

SUPPLEMENTARY INFORMATION: Public Participation: Submit your comments, 
identified by Docket ID No. EPA-R06-OAR-2021-0801, 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 the EPA's docket at 
https://www.regulations.gov any information you consider to be 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Multimedia submissions (audio, 
video, etc.) must be accompanied by a written comment. The written 
comment is considered the official comment and should include 
discussion of all points you wish to make. The EPA will generally not 
consider comments or comment contents located outside of the primary 
submission (i.e., on the web, cloud, or other file sharing system).
    There are two dockets supporting this action, EPA-R06-OAR-2021-0801 
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R06-OAR-2021-0801 contains 
information specific to Arkansas, Louisiana, Oklahoma, and Texas, 
including the notice of proposed rulemaking, submittals from the 
states, and the EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal 
Technical Support Document (EPA Region 6 TSD). Docket No. EPA-HQ-OAR-
2021-0663 contains additional modeling files, emissions inventory 
files, technical support documents, and other relevant supporting 
documentation regarding interstate transport of emissions for the 2015 
8-hour ozone NAAQS which are being used to support this action, 
including Preparation of Emissions Inventories for the 2016v2 North 
American Emissions Modeling Platform, and Air Quality Modeling TSD for 
2015 ozone NAAQS Transport SIP Proposed Actions. All comments regarding 
information in either of these dockets are to be made in Docket No. 
EPA-R06-OAR-2021-0801. For additional submission methods, please 
contact Sherry Fuerst, 214-665-6454, [email protected]. For the 
full EPA public comment policy, information about CBI or multimedia 
submissions, and general guidance on making effective comments, please 
visit https://www.epa.gov/dockets/commenting-epa-dockets. Due to public 
health concerns related to COVID-19, the EPA Docket Center and Reading 
Room are open to the public by appointment only. Our Docket Center 
staff also continues to provide remote customer service via email, 
phone, and webform. For further information and updates on EPA Docket 
Center services, please visit us online at https://www.epa.gov/dockets.
    The EPA continues to carefully and continuously monitor information 
from the Centers for Disease Control and Prevention (CDC), local area 
health departments, and our Federal partners so that we can respond 
rapidly as conditions change regarding COVID-19.
    The index to the dockets for this action, Docket No. EPA-R06-OAR-
2021-0801 and EPA-HQ-OAR-2021-0663, are available electronically at 
https://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 4-Step Interstate Transport 
Regulatory Process
    C. Background on the EPA's Ozone Transport Modeling Information
    D. The EPA's Approach to Evaluating Interstate Transport SIPs 
for the 2015 Ozone NAAQS
    1. Selection of Analytic Year
    2. Step 1 of the 4-Step Interstate Transport Framework
    3. Step 2 of the 4-Step Interstate Transport Framework

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    4. Step 3 of the 4-Step Interstate Transport Framework
    5. Step 4 of the 4-Step Interstate Transport Framework
II. Arkansas SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission
    A. Summary of ADEQ SIP Submission Addressing Interstate 
Transport of Air Pollution for the 2015 Ozone NAAQS
    B. EPA Evaluation of the ADEQ SIP Submission
    1. Evaluation of Information Provided by ADEQ Regarding Step 1
    2. Evaluation of Information Provided by ADEQ Regarding Step 2
    3. Results of the EPA's Step 1 and Step 2 Modeling and Findings 
for Arkansas
    4. Evaluation of Information Provided by ADEQ Regarding Step 3
    5. Evaluation of Information Provided by ADEQ Regarding Step 4
    6. Conclusion
III. Louisiana SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission
    A. Summary of LDEQ SIP Submission Addressing Interstate 
Transport of Air Pollution for the 2015 Ozone NAAQS
    B. EPA Evaluation of the LDEQ SIP Submission
    1. Evaluation of Information Provided by LDEQ Regarding Steps 1 
and 2
    2. Results of the EPA's Step 1 and Step 2 Modeling and Findings 
for Louisiana
    3. Evaluation of Information Provided by LDEQ Regarding Step 3
    4. Evaluation of Information Provided by LDEQ Regarding Step 4
    5. Conclusion
IV. Oklahoma SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission
    A. Summary of ODEQ SIP Submission Addressing Interstate 
Transport of Air Pollution for the 2015 Ozone NAAQS
    B. EPA Evaluation of the ODEQ SIP Submission
    1. Evaluation of Information Provided by ODEQ Regarding Steps 1 
and 2
    2. Results of the EPA's Step 1 and Step 2 Modeling and Findings 
for Oklahoma
    3. Evaluation of Information Provided by ODEQ Regarding Step 3
    4. Evaluation of Information Provided by ODEQ Regarding Step 4
    5. Conclusion
    C. Impact on Areas of Indian Country
V. Texas SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission
    A. Summary of TCEQ SIP Submission Addressing Interstate 
Transport of Air Pollution for the 2015 Ozone NAAQS
    B. EPA Evaluation of the TCEQ SIP Submission
    1. Evaluation of Information Provided by TCEQ Regarding Step 1
    i. Evaluation of TCEQ's Methodology for Identifying Maintenance 
Receptors
    ii. Evaluation of the TCEQ Modeling
    2. Evaluation of Information Provided by TCEQ Regarding Step 2
    3. Results of the EPA's Step 1 and Step 2 Modeling and Findings 
for Texas
    4. Evaluation of Information Provided by TCEQ Regarding Step 3
    5. Evaluation of Information Provided by TCEQ Regarding Step 4
    6. Conclusion
VI. Proposed Action
VII. Statutory and Executive Order Reviews

I. Background

A. Description of Statutory Background

    On October 1, 2015, the EPA promulgated a revision to the 2015 8-
hour ozone NAAQS (2015 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 requirements, often 
referred to as ``prongs'' within CAA section 110(a)(2)(D)(i)(I). A SIP 
for a new or revised NAAQS must contain adequate provisions prohibiting 
any source or other type of emissions activity within the state from 
emitting air pollutants in amounts that will significantly contribute 
to nonattainment of the NAAQS in another state (prong 1) or interfere 
with maintenance of the NAAQS in another state (prong 2). The EPA and 
states must give independent significance to prong 1 and prong 2 when 
evaluating downwind air quality problems under CAA section 
110(a)(2)(D)(i)(I).\3\
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    \1\ ``National Ambient Air Quality Standards for Ozone'', Final 
Rule, 80 FR 65292 (October 26, 2015). Although the level of the 
standard is specified in the units of ppm, ozone concentrations are 
also described in parts per billion (ppb). For example, 0.070 ppm is 
equivalent to 70 ppb.
    \2\ SIP revisions that are intended to meet the applicable 
requirements of section 110(a)(1) and (2) of the CAA are often 
referred to as infrastructure SIPs and the applicable elements under 
section 110(a)(2) are referred to as infrastructure requirements.
    \3\ See North Carolina v. EPA, 531 F.3d 896, 909-11 (D.C. Cir. 
2008).
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B. Description of the EPA's 4-Step Interstate Transport Regulatory 
Process

    The EPA is using the 4-Step interstate transport framework (or 4-
Step framework) described in detail below to evaluate states' SIP 
submittals addressing the interstate transport provision for the 2015 
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\
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    \4\ See ``Federal Implementation Plans: Interstate Transport of 
Fine Particulate Matter and Ozone and Correction of SIP Approvals'', 
76 FR 48208 (Aug. 8, 2011).
    \5\ See ``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 (D.C. Cir. 2019). The Revised CSAPR Update 
for the 2008 Ozone NAAQS, 86 FR 23054 (April 30, 2021), responded to 
the remand of the CSAPR Update in Wisconsin and the vacatur of a 
separate rule, the ``CSAPR Close-Out,'' 83 FR 65878 (December 21, 
2018), in New York v. EPA, 781 F. App'x. 4 (D.C. Cir. 2019).
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    Through the development and implementation of the CSAPR rulemakings 
and prior regional rulemakings pursuant to the interstate transport 
provision,\7\ the EPA, working in partnership with states, developed 
the following 4-Step framework to evaluate a state's obligations to 
eliminate interstate transport emissions under the interstate transport 
provision for the ozone NAAQS: (1) Identify monitoring sites that are 
projected to have problems attaining and/or maintaining the NAAQS 
(i.e., nonattainment and/or maintenance receptors); (2) identify states 
that impact those air quality problems in other (i.e., downwind) states 
sufficiently such that the states are considered ``linked'' and 
therefore warrant further review and analysis; (3) identify the 
emissions reductions necessary (if any), applying a multifactor 
analysis, to eliminate each linked upwind state's significant 
contribution to nonattainment or interference with maintenance of the 
NAAQS at the locations identified in Step 1; and (4) adopt permanent 
and enforceable measures needed to achieve those emissions reductions.
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    \7\ In addition to the CSAPR rulemakings, other regional 
rulemakings addressing ozone transport include the ``NOX 
SIP Call,'' 63 FR 57356 (October 27, 1998), and the ``Clean Air 
Interstate Rule'' (CAIR), 70 FR 25162 (May 12, 2005).

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[[Page 9800]]

C. Background on the EPA's Ozone Transport Modeling Information

    In general, the EPA has performed nationwide air quality modeling 
to project ozone design values (DVs) \8\ which are used in combination 
with measured data to identify nonattainment and maintenance receptors. 
To quantify the contribution of emissions from specific upwind states 
on 2023 ozone DVs for the identified downwind nonattainment and 
maintenance receptors, the EPA performed nationwide, state-level ozone 
source apportionment modeling for 2023. The source apportionment 
modeling provided contributions to ozone at receptors from precursor 
emissions of anthropogenic nitrogen oxides (NOX) and 
volatile organic compounds (VOCs) in individual upwind states.
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    \8\ A design value is a statistic that describes the air quality 
status of a given location relative to the level of the NAAQS. 
Design values are typically used to designate and classify 
nonattainment areas, as well as to assess progress towards meeting 
the NAAQS. See https://www.epa.gov/air-trends/air-quality-design-values#report.
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    The EPA has released several documents containing projected ozone 
design values, contributions, and information relevant to evaluating 
interstate transport with respect to the 2015 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 DVs 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 NAAQS.\10\ On October 27, 2017, we 
released a memorandum (October 2017 memorandum) containing updated 
modeling data for 2023, which incorporated changes made in response to 
comments on the NODA, and noted that the modeling may be useful for 
states developing SIPs to address interstate transport obligations for 
the 2008 ozone NAAQS.\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 ozone NAAQS at Step 1 of the 4-Step framework.\12\ The March 2018 
memorandum also included the then newly available contribution modeling 
data to assist states in evaluating their impact on potential downwind 
air quality problems for the 2015 ozone NAAQS under Step 2 of the 4-
Step 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 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\
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    \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 at 1735.
    \11\ See EPA memorandum, ``Information on the Interstate 
Transport State Implementation Plan Submissions for the 2008 Ozone 
National Ambient Air Quality Standards under Clean Air Act section 
110(a)(2)(D)(i)(I)'', October 27, 2017, (``October 2017 
memorandum'') available in Docket ID No. EPA-HQ-OAR-2021-0663 or at 
https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \12\ See EPA memorandum, ``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 or at https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \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 interstate transport provision. Any such 
determination would be made through notice-and-comment rulemaking.''
    \14\ See EPA memorandums, ``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 or at https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.
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    Since the release of the modeling data shared in the March 2018 
memorandum, the EPA performed updated modeling using a 2016-based 
emissions modeling platform (i.e., 2016v1). This emissions platform was 
developed under the EPA/Multi-Jurisdictional Organization (MJO)/state 
collaborative project.\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 DVs and contribution data provided in the 2017 
and 2018 memoranda. The EPA used the 2016v1 emissions to project ozone 
DVs 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\ See 85 FR 68964, 68981. Although the Revised CSAPR Update 
addressed transport for the 2008 ozone NAAQS, the projected DVs and 
contributions from the 2016v1 platform are also useful for identifying 
downwind ozone problems and linkages with respect to the 2015 ozone 
NAAQS.\17\
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    \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 (Oct. 30, 2020).
    \17\ See the Air Quality Modeling Technical Support Document for 
the Final Revised Cross-State Air Pollution Rule Update, available 
in Docket ID No. EPA-HQ-OAR-2021-0063 for this action.
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    Following the Revised CSAPR Update final rule, 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 
Technical Support Document (TSD) Preparation of Emissions Inventories 
for the 2016v2 North American Emissions Modeling Platform, which is 
included in Docket ID No. EPA-HQ-OAR-2021-0663. The EPA performed air 
quality modeling of the 2016v2 emissions using the most recent publicly 
released version of the Comprehensive Air-quality Model with extensions 
(CAMx) photochemical modeling, version 7.10.\19\ The EPA now proposes 
to rely on the air quality modeling performed using CAMx, version 7.10, 
and the newly available 2016v2 emissions platform in evaluating states' 
submissions with respect to Steps

[[Page 9801]]

1 and 2 of the 4-Step 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. Sections II-V of this action 
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 action, the EPA is inviting public comment on this updated 2023 
modeling, which uses a 2016v2 emissions platform. Per the instructions 
in the Supplementary Information section above, all public comments, 
including comments on the EPA's air quality modeling should be 
submitted in the Regional docket for this action, Docket ID No. EPA-
R06-OAR-2021-0801. Comments are not being accepted in Docket No. EPA-
HQ-OAR-2021-0663.
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    \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\ Ramboll Environment and Health, January 2021, www.camx.com.
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    States may have chosen to rely on the results of EPA modeling and/
or alternative modeling performed by states or Multi-Jurisdictional 
Organizations (MJOs) to evaluate downwind air quality problems and 
contributions as part of their submissions. In Sections II-V of this 
action, we evaluate how the states used air quality modeling 
information in their submissions.

D. The EPA's Approach to Evaluating Interstate Transport SIPs for the 
2015 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 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 1998 NOX SIP 
Call \20\ 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).
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    \20\ See 63 FR 57356. The NOX SIP Call required 22 
eastern states and the District of Columbia to submit state 
implementation plans (SIPs) that set statewide ozone season NOx 
budgets which would reduce emissions of NOX.
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    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 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 
Attachment A 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 review the technical and legal justifications 
for doing so.
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    \21\ March 2018 memorandum, Attachment A.
    \22\ Id. at A-1.
    \23\ Id.
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    The remainder of this section describes the EPA's proposed 
framework with respect to analytic year, definition of nonattainment 
and maintenance receptors, selection of contribution threshold, and 
multifactor control strategy analysis.
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.
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    \24\ For attainment dates for the 2015 8-hour ozone NAAQS, refer 
to CAA section 181(a), 40 CFR 51.1303, and ``Additional Air Quality 
Designations for the 2015 Ozone National Ambient Air Quality 
Standards'', 83 FR 25776 (June 4, 2018, effective Aug. 3, 2018).
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    On May 19, 2020, the D.C. Circuit issued a decision in Maryland v. 
EPA that cited the Wisconsin decision in holding that 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 interstate transport provision, to assess 
downwind air quality as expeditiously as practicable and no later than 
the next applicable

[[Page 9802]]

attainment date,\25\ which is now the Moderate area attainment date 
under CAA section 181 for ozone nonattainment. The Moderate area 
attainment date for the 2015 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 ozone NAAQS, because the 
2023 ozone season is the last relevant ozone season during which 
achieved emissions reductions in linked upwind states could assist 
downwind states with meeting the August 3, 2024, Moderate area 
attainment date for the 2015 ozone NAAQS.
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    \25\ We note that the court in Maryland did not have occasion to 
evaluate circumstances in which the EPA may determine that an upwind 
linkage to a downwind air quality problem exists at Steps 1 and 2 of 
the 4-Step 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 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 23074; see also Wisconsin, 938 F.3d at 322. Consequently, in 
this proposal the EPA proposes to 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 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 
framework. For sites that are identified as a nonattainment or 
maintenance receptor in 2023, we proceed to the next step of our 4-Step 
framework by identifying the upwind state's contribution to those 
receptors.
    The EPA's approach to identifying ozone nonattainment and 
maintenance receptors in this action is consistent with the approach 
used in previous transport rulemakings. The EPA's approach gives 
independent consideration to both the ``contribute significantly to 
nonattainment'' and the ``interfere with maintenance'' prongs of CAA 
section 110(a)(2)(D)(i)(I), consistent with the D.C. Circuit's 
direction in North Carolina v. EPA.\27\
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    \27\ See North Carolina v. EPA, 531 F.3d 896, 910-11 (D.C. Cir. 
2008) (holding that the EPA must give ``independent significance'' 
to each prong of CAA section 110(a)(2)(D)(i)(I)).
---------------------------------------------------------------------------

    For the purpose of this proposal, the EPA identifies 
``nonattainment'' receptors as those monitoring sites that are 
projected to have average DVs in 2023 that exceed the NAAQS and that 
are also measuring nonattainment based on the most recent monitored 
DVs. 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 receptor, was also applied in CAIR. See 70 FR at 
25241, 25249 (January 14, 2005); see also North Carolina, 531 F.3d 
at 913-14 (affirming as reasonable EPA's approach to defining 
nonattainment in CAIR).
---------------------------------------------------------------------------

    In addition, in this proposal, the EPA identifies a receptor to be 
a ``maintenance'' receptor for purposes of defining interference with 
maintenance, consistent with the method used in the CSAPR and upheld by 
the D.C. Circuit in EME Homer City Generation, L.P. v. EPA, 795 F.3d 
118, 136 (D.C. Cir. 2015).\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 DV 
at each receptor based on a projection of the maximum measured DV over 
the relevant period. The EPA interprets the projected maximum future DV 
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, 
air mass patterns) promoting ozone formation that led to maximum 
concentrations in the measured data may reoccur in the future. The 
maximum DV 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 DV 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 DVs above the level of the 
applicable NAAQS, but that are not currently measuring nonattainment 
based on the most recent official DVs. In addition, those monitoring 
sites with projected average DVs below the NAAQS, but with projected 
maximum DVs above the NAAQS are also identified as ``maintenance only'' 
receptors, even if they are currently measuring nonattainment based on 
the most recent official DVs.
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 ozone NAAQS), the upwind state is not ``linked'' 
to a downwind air quality problem, and the EPA, therefore, concludes 
that the state does not significantly contribute to

[[Page 9803]]

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 of controls as part of a 
multifactor 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 continue 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 
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. For ozone, as the EPA found in the Clean Air Interstate Rule 
(CAIR), CSAPR, and CSAPR Update, a portion of the nonattainment problem 
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 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 at 74518. See also 86 FR at 23085 (reviewing and explaining 
rationale from CSAPR); 76 FR at 48237-38 (for selection of 1 percent 
threshold).
    The EPA's August 2018 memorandum recognized that in certain 
circumstances, a state may be able to establish that an alternative 
contribution threshold of 1 ppb is justifiable. Where a state relies on 
this alternative threshold, and where that state determined that it was 
not linked at Step 2 using the alternative threshold, the EPA will 
evaluate whether the state provided a technically sound assessment of 
the appropriateness of using this alternative threshold based on the 
facts and circumstances underlying its application in the particular 
SIP submission.
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with the EPA's longstanding approach to eliminating 
significant contribution or interference with maintenance, at Step 3, 
states linked at Steps 1 and 2 are generally expected to prepare a 
multifactor analysis 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 preparing a 
multifactor assessment that evaluates additional available control 
opportunities. 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\
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    \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 NOX SIP Call, 63 FR 57356, 
57399-405. See also Revised CSAPR Update, 86 FR 23054, 23086-23116. 
Consistently across these rulemakings, the EPA has developed 
emissions inventories, analyzed different levels of control 
stringency at different cost thresholds, and assessed resulting 
downwind air quality improvements.
---------------------------------------------------------------------------

5. Step 4 of the 4-Step Interstate Transport Framework
    In Step 4, states (or the EPA) develop permanent and federally 
enforceable control strategies to achieve the emissions reductions 
determined to be necessary in Step 3 to eliminate significant 
contribution to nonattainment or interference with maintenance of the 
NAAQS. For a state linked in Steps 1 and 2 to rely on an emissions 
control measure in Step 3 to address its interstate transport 
obligations, that measure must be included in the state's SIP so that 
it is permanent and federally enforceable. See CAA section 110(a)(2)(D) 
(``Each such [SIP] shall . . . contain adequate provisions. . . .''). 
See also CAA section 110(a)(2)(A); Committee for a Better Arvin v. 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. Arkansas SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission

A. Summary of ADEQ SIP Submission Addressing Interstate Transport of 
Air Pollution for the 2015 Ozone NAAQS

    On October 10, 2019, the Arkansas Division of Environmental Quality 
(ADEQ) of the Arkansas Department of Energy and Environment made a SIP 
submission addressing interstate transport of air pollution for the 
2015 ozone NAAQS. The ADEQ SIP submission provided an analysis of 
Arkansas's air emissions impact to downwind states using the EPA's 4-
Step framework and an analytic year of 2023 and concluded that the 
State's air emissions will not contribute significantly to 
nonattainment or interfere with maintenance of the 2015 ozone NAAQS in 
other states.
    To identify downwind monitors projected to be in nonattainment and/
or have maintenance issues in 2023 (Step 1), ADEQ relied on the EPA's 
interstate transport modeling results that are included as an 
attachment to the March 2018 memorandum. The EPA modeling results 
included with the March 2018 memorandum provide: (1) Projected

[[Page 9804]]

average DV and maximum DV for the future year 2023 (fy 2023) for ozone 
monitors projected to be potential nonattainment or maintenance 
receptors in the 48 contiguous States and (2) the expected contribution 
of State emissions to the projected ozone concentrations at each ozone 
monitor.
    At Step 2, ADEQ identified those states to which Arkansas 
contributes emissions and then applied a 1 ppb contribution threshold 
to determine projected nonattainment and/or maintenance receptors in 
other states that might be significantly impacted by emissions from 
Arkansas. ADEQ provided three rationales as a basis to support their 
decision to rely on a 1 ppb contribution threshold. First, ADEQ cited 
to the August 2018 memorandum \31\ that compares the collective 
contribution captured by three different contribution thresholds: 1 
Percent of the NAAQS, 1 ppb, and 2 ppb. ADEQ summarized the August 2018 
memorandum and concluded that the 1 percent and 1 ppb contribution 
thresholds are generally comparable. Second, ADEQ referenced an April 
2018 memorandum \32\ in which the EPA examined the use of a significant 
impact level (SIL) value of 1 ppb for determining whether a proposed 
prevention of significant deterioration (PSD) source causes or 
contributes to a violation of the corresponding 2015 ozone NAAQS. 
Despite recognizing that a contribution threshold is not the same as a 
significance level, ADEQ claimed that a contribution threshold and 
significance level are sufficiently analogous to support the use of a 1 
ppb contribution threshold. The final rationale ADEQ provided was based 
on the consistency with the reported precision of Federal reference 
monitors for ozone and the rounding requirements found in 40 CFR part 
50, Appendix U, Interpretation of the Primary and Secondary National 
Ambient Air Quality Standards for Ozone. ADEQ noted that the 1 percent 
contribution threshold of 0.7 ppb is lower than the manufacturer's 
reported precision of Federal reference monitors for ozone and that the 
requirements found in Appendix U truncates monitor values of 0.7 ppb to 
0 ppb.
---------------------------------------------------------------------------

    \31\ ``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, available in Docket ID No. 
EPA-HQ-OAR-2021-0663 or at https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.
    \32\ See EPA memorandum from Peter Tsirigotis, Director of the 
Office of Air Quality planning and Standards, April 17, 2018, 
``Guidance on Significant Impact Levels for Ozone and Fine Particles 
in the Prevention of Significant Deterioration Permitting Program'' 
(``SILs Guidance'' or ``April 2018 memorandum''), available at: 
https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf.
---------------------------------------------------------------------------

    As stated previously, ADEQ identified all potential nonattainment 
and maintenance receptors for fy 2023 showing a contribution of 
emissions from Arkansas.\33\ These receptors are included in Table AR-
1.
---------------------------------------------------------------------------

    \33\ Table AR-1 lists all sites that the EPA projected to have a 
fy 2023 average DV or fy 2023 maximum DV greater than 70.9 ppb in 
our March 2018 memorandum. As Arkansas stated in the SIP submission, 
the EPA considers sites matching these criteria to be projected 
nonattainment areas and projected maintenance areas, respectively. 
ADEQ ranked these sites by Arkansas's potential contribution, which 
the EPA determined based on the daily eight-hour average 
contributions on the top ten concentration days in 2023.

  Table AR-1--Projected Nonattainment and Maintenance Receptors Identified by Arkansas Based on the EPA's March
                                                 2018 Memorandum
----------------------------------------------------------------------------------------------------------------
                                                                                                     Arkansas
                Receptor (site ID, county, state)                  2023 average    2023 maximum    contribution
                                                                     DV (ppb)        DV (ppb)          (ppb)
----------------------------------------------------------------------------------------------------------------
260050003, Allegan, MI..........................................              69            71.7            1.64
482011039, Harris, TX...........................................            71.8            73.5            0.99
480391004, Brazoria, TX.........................................              74            74.9            0.90
484392003, Tarrant, TX..........................................            72.5            74.8            0.78
481210034, Denton, TX...........................................            69.7              72            0.58
482011034, Harris, TX...........................................            70.8            71.6            0.54
551170006, Sheboygan, WI........................................            72.8            75.1            0.51
550790085, Milwaukee, WI........................................            71.2              73            0.40
482010024, Harris, TX...........................................            70.4            72.8            0.29
261630019, Wayne, MI............................................              69              71            0.27
240251001, Harford, MD..........................................            70.9            73.3            0.17
90019003, Fairfield, CT.........................................              73            75.9            0.13
90013007, Fairfield, CT.........................................              71              75            0.13
361030002, Suffolk, NY..........................................              74            75.5            0.12
360810124, Queens, NY...........................................            70.2              72            0.09
90099002, New Haven, CT.........................................            69.9            72.6            0.08
90010017, Fairfield, CT.........................................            68.9            71.2            0.07
80590006, Jefferson, CO.........................................            71.3            73.7            0.03
80590011, Jefferson, CO.........................................            70.9            73.9            0.02
81230009, Weld, CO..............................................            70.2            71.4            0.02
80350004, Douglas, CO...........................................            71.1            73.2            0.01
----------------------------------------------------------------------------------------------------------------

    Based on a 1 ppb contribution threshold, ADEQ identified only one 
fy 2023 projected maintenance receptor, Allegan County, MI, and no fy 
2023 projected nonattainment receptors linked to Arkansas. ADEQ also 
cited other modeling performed by TCEQ and Midwest Ozone Group, which 
showed that when different modeling protocols were employed, future 
year DV projections and contributions could differ considerably. ADEQ 
therefore elected to consider other evidence regarding its linkage to 
air quality in Allegan County, MI. Specifically, ADEQ analyzed back 
trajectory information to infer that there is no consistent or 
persistent relationship between elevated ozone days in Allegan County, 
MI and air traveling through Arkansas. ADEQ assessed wind patterns on 
elevated ozone days--days with a maximum daily average 8-hour ozone 
(MDA8) greater than 70.9 ppb in Allegan County,

[[Page 9805]]

MI. ADEQ used the National Oceanic and Atmospheric Administration 
(NOAA) HYbrid Single Particle Lagrangian Integrated Trajectory 
(HYSPLIT) \34\ model to evaluate wind back trajectories from over a 10-
year period (2008-2017).\35\ Over the course of the 10-year period, 
ADEQ identified 95 elevated ozone days (MDA8 > 70.9 ppb) for the 
Allegan County, MI monitor.\36\ Next, ADEQ identified the maximum ozone 
value within these elevated ozone days.\37\ Using HYSPLIT, ADEQ ran 72-
hour back trajectories using the hour of the maximum ozone value for 
each elevated day as the back trajectory start time. To consider the 
effects of vertical variations in wind flows on transport patterns, 
ADEQ used the following starting heights above ground level: 100m, 
500m, 1000m, and 1500m. ADEQ obtained 40 km grid meteorological data 
for the back trajectory analysis using Eta Data Assimilation System 
(EDAS) data.\38\ In total, ADEQ ran 152 back trajectories for each 
mixing height.\39\ ADEQ filtered the back trajectories to determine 
whether further analysis is warranted using two criteria. First, ADEQ 
filtered out back trajectories that had a starting hour mixing height 
below the back trajectory start height because ADEQ asserted these air 
parcels would not have reached ambient air \40\ at the Allegan County, 
MI monitor site. Second, ADEQ filtered out any back trajectory that did 
not have a path through any portion of Arkansas. After ADEQ applied 
their filter criteria, 41 out of 608 back trajectories (6.74%) remained 
from 22 out of the 95 elevated ozone days (23%) examined. Of the 10 
years examined, ADEQ also found that air passing through Arkansas only 
reached Allegan County, MI on four or more days in one year: 2012.\41\ 
For 2012, HYSPLIT analyses indicated 14 Arkansas-Allegan County, MI 
linked back trajectories for 7 days in total in 2012, whereas for 2011, 
2013, 2014, and 2016 the HYSPLIT analyses indicated three, two, zero 
and one days with Arkansas-Allegan County, MI linked back trajectories, 
respectively. For the 10 years ADEQ's performed HYSPLITs, ADEQ's 
HYSPLIT analysis indicated on average 2.2 days per year had 
trajectories with Arkansas-Allegan County, MI linked back trajectories. 
ADEQ also noted that these trajectories passed through other states and 
through Metropolitan Statistical Areas (MSAs) \42\ both before and 
after traversing through Arkansas. Specifically, ADEQ stated that 37 
trajectories passed through the Chicago-Naperville-Elgin, IL-IN-WI MSA 
prior to reaching Allegan County, MI. Based on these results, ADEQ 
concluded that other states and MSAs were more likely to have 
influenced ozone concentrations at the Allegan County, MI monitor on 
the days with back trajectories linked to Arkansas.
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    \34\ HYbrid Single-Particle Lagrangian Integrated Trajectory 
(HYSPLIT) model is a complete system for computing both simple air 
parcel trajectories and complex dispersion and deposition 
simulations. The model is designed to support a wide range of 
simulations related to the atmospheric transport and dispersion of 
pollutants and hazardous materials to the Earth's surface.
    \35\ ADEQ analyzed ten years of HYSPLIT back trajectories to 
examine potential relationships between elevated ozone days at the 
Allegan County, MI monitor and emissions from Arkansas. In the SIP 
submission ADEQ stated their rationale for looking at an extended 
period of time is to gain a more complete picture of how Arkansas's 
emissions might contribute to elevated ozone in Allegan County, MI, 
rather than relying entirely on the EPA's modeling simulation, which 
is based on a single base year.
    \36\ See the AirNow-Tech website at https://www.airnowtech.org/. 
AirNow-Tech is a website for air quality data management analysis, 
and decision support used by the Federal, State, Tribal, and local 
air quality organizations.
    \37\ If the same maximum eight-hour value occurred multiple 
times a day, ADEQ evaluated all incidences of the value for that 
day.
    \38\ EDAS is an intermittent data assimilation system that uses 
successive three-hour model forecasts to generate gridded 
meteorological fields that reflect observations covering the 
continental United States. EDAS is accessible at https://ready.arl.noaa.gov/edas40.php.
    \39\ Mixing heights (m), defined as the height above ground 
level of the layer adjacent to the ground over which an emitted or 
entrained inert non-buoyant tracer will be mixed by turbulence.
    \40\ Ambient air is the ``portion of the atmosphere, external to 
buildings, to which the general public has access.'' 40 CFR 50.1(e).
    \41\ The number of days in a given year and the number of 
consecutive years is of particular relevance for the ozone NAAQS, 
which is calculated based the annual fourth-highest daily maximum 
eight-hour concentration averaged over three consecutive years.
    \42\ MSA is defined as a geographic region with a high 
population density at its core and close economic ties throughout 
the area.
---------------------------------------------------------------------------

    In Step 3, ADEQ also considered air quality trends in Allegan 
County, MI, emission trends in other upwind states, relative 
contribution from other upwind states, and cost factors. ADEQ presented 
that ozone DVs in Allegan County, MI fluctuated over the 2008-2017 
period with higher concentration occurring from 2012 through 2014 but 
declining since 2014. ADEQ also mentioned that despite the most recent 
2017 DV for the Allegan County monitor continuing to show an exceedance 
of the 2015 ozone NAAQS, the EPA-projected 2023 ozone average DV at the 
Allegan County, MI monitor, based on data provided in the March 2018 
memorandum, is 69.0 ppb, which would be in attainment of the 2015 ozone 
NAAQS in 2023.
    Next, ADEQ included an evaluation of the relative contribution and 
the emission trends from the eight states \43\ with contributions 
greater than 1 ppb to the Allegan County, MI receptor. The emission 
trends evaluation examined ozone precursors, nitrogen oxides 
(NOX) and volatile organic compounds (VOC), from 2011 to 
2017 and the model projected fy 2023 emissions level. ADEQ noted that 
the two states with the highest contributions to Allegan County, MI--
Illinois and Indiana--have both experienced year-over-year decreases in 
NOX emissions in excess of 20,000 tons of NOX 
reduced per year. Arkansas had also experienced decreases in 
NOX emissions each evaluated year and emitted less 
NOX than any other of the potentially linked states. In 
addition, ADEQ referenced the EPA projections showing that most 
potentially linked states will continue to realize reductions in 
NOX, as well as VOCs, through 2023. ADEQ confirmed that 
based on this analysis, the overall general trends of NOX 
and VOC emissions are declining from Arkansas and the other linked 
states. The continuation of trends in the emissions reductions 
observed, particularly from Illinois and Indiana, are anticipated by 
ADEQ to result in air quality improvements in Allegan County, MI.
---------------------------------------------------------------------------

    \43\ The eight linked states include Illinois, 42%; Indiana, 
15%; Michigan, 7%; Missouri, 6%; Texas, 5%; Wisconsin, 4%; Oklahoma, 
3% and Arkansas, 4%. The remaining contribution is labeled at 
``Other''. The linkages are based on the EPA's modeling results that 
are attached to the March 2018 memorandum.
---------------------------------------------------------------------------

    In terms of cost analysis, ADEQ focused only on the cost of 
NOX controls at electric generating units (EGUs) in the 
State because EGUs are the largest source of NOX emissions 
that ADEQ regulates. In its analysis, ADEQ found that the costs to 
install additional NOX controls (selective catalytic 
reduction, SCR and selective noncatalytic reduction, SNCR) at EGUs 
exceed the EPA's cost thresholds used for the CSAPR and CSAPR Update 
rules.\44\ Based on ADEQ's evaluation of the evidence, ADEQ concluded 
that no additional controls beyond pre-existing

[[Page 9806]]

state and Federal regulations were warranted for Arkansas sources to 
satisfy interstate transport obligations for the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \44\ The EPA's Revised CSAPR Update, 86 FR 23054 (April 20, 
2021), states ``. . . EPA adjusted its representative cost for 
optimizing existing SNCR control to $1,800 per ton in response to 
comments received on the proposed rule . . . EPA views $1,600 per 
ton for optimization of existing SCR control and installation of 
state-of-the are NOX combustion controls and $1,800 per 
ton for optimization of existing SNCRs as comparable for policy 
purposes.'' ADEQ's screening analysis using the EPA tools 
(referencing the EPA's Air Pollution Control Cost Estimation 
Spreadsheet for SCR) shows that cost-effectiveness values for ozone-
season operation of SCR and SNCR are: $12,605-$31,580/ton for SCR 
and $4,221-$45,581 for SNCR. ADEQ notes that any costs imposed to 
install controls at the examined EGUs would be passed on to Arkansas 
ratepayers.
---------------------------------------------------------------------------

    Based on the determinations made by ADEQ at Steps 1 through 3, ADEQ 
did not include any new control measures in the SIP submission to 
reduce ozone precursor emissions as part of a Step 4 analysis.

B. EPA Evaluation of the ADEQ SIP Submission

    The EPA is proposing to find that ADEQ's October 10, 2019, SIP 
submission does not meet the State's obligations with respect to 
prohibiting emissions that contribute significantly to nonattainment or 
interfere with maintenance of the 2015 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 therefore proposing to 
disapprove ADEQ's SIP submission.
1. Evaluation of Information Provided by ADEQ Regarding Step 1
    At Step 1 of the 4-Step framework, ADEQ relied on the EPA modeling 
released in the March 2018 memorandum to identify nonattainment and 
maintenance receptors in 2023. As described in Section I of this 
action, the EPA has recently performed updated modeling using the 
2016v2 platform to evaluate interstate transport of ozone for a fy 
2023.\45\ The EPA proposes to primarily rely on the EPA's modeling 
using the 2016v2 platform (EPA 2016v2 modeling), to identify projected 
nonattainment and maintenance receptors in fy 2023. Updating the base 
period from 2011 (base period used in data included in the March 2018 
memorandum) to a more recent year (2016) allows for better projections 
of which monitors will have problems attaining and/or maintaining the 
2015 ozone NAAQS and factors in more recent base year DVs. The EPA 
notes that with a switch from 2011 base period meteorology to 2016 base 
period meteorology, it is normal and expected that the potential 
downwind nonattainment or maintenance receptors would change due to the 
different weather patterns that occurred in the different base periods, 
which impacts both the transport of pollutants from upwind states and 
what receptors have higher monitored values within nonattainment/
maintenance regions.\46\ Modeling using both the 2011 and 2016 based 
years consistently project that certain areas will have problems 
attaining and/or maintaining the 2015 ozone NAAQS including receptors 
in Texas.
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    \45\ Per the instructions in the Supplementary Information 
section above, all public comments, including comments on the EPA's 
air quality modeling should be submitted in the Regional docket for 
this action, Docket ID No. EPA-R06-OAR-2021-0801. Comments are not 
being accepted in Docket No. EPA-HQ-OAR-2021-0663.
    \46\ We note that ADEQ identified additional modeling performed 
by TCEQ and Midwest Ozone Group, but simply concluded that different 
modeling can lead to differences in DV projections and ozone 
contributions of these two alternative modeling analyses, only 
TCEQ's modeling using a 2012 base year identified receptors in Texas 
that projected different DVs for the Texas receptors identified in 
the EPA's 2011 base year. We discuss the EPA's review of the TCEQ's 
modeling elsewhere in this action and the Technical Support Document 
for this action ``EPA Region 6 2015 8-Hour Ozone Transport SIP 
Proposal Technical Support Document'' (EPA Region 6 2015 Ozone 
Transport SIP TSD.pdf) included in the Regional docket for this 
action (Docket ID No. EPA-R06-OAR-2021-0801), but we do conclude 
that TCEQ and recent monitoring data indicate that there are 
problematic receptors that are expected to be either nonattainment 
or maintenance receptors in 2023 including the Texas receptors that 
the EPA identified in our March 2018 memorandum with Arkansas 
linkages.
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2. Evaluation of Information Provided by ADEQ Regarding Step 2
    As noted earlier, ADEQ utilized a 1 ppb threshold at Step 2 to 
identify whether the State was ``linked'' to a projected downwind 
nonattainment or maintenance receptor. ADEQ identified linkages for 
Arkansas to one 2023 projected maintenance receptor, Allegan County, 
MI, and no 2023 projected nonattainment receptors.
    As discussed in the EPA's August 2018 memorandum, with appropriate 
additional analysis it may be reasonable for states to use a 1 ppb 
contribution threshold as an alternative to a 1 percent threshold, at 
Step 2 of the 4-Step interstate transport framework, for the purposes 
of identifying linkages to downwind receptors. However, the EPA's 
August 2018 memorandum provided that whether or not a 1 ppb threshold 
is appropriate must be based on an evaluation of state-specific 
circumstances, and no such evaluation was included in the state's 
submittal. Instead, ADEQ cited to the EPA's SILs Guidance as a basis to 
support the use of a 1 ppb threshold; however, ADEQ did not explain the 
relevance of the SILs Guidance to ADEQ's statutory obligation under the 
interstate transport provision. The SILs Guidance relates to a 
different provision of the Clean Air Act regarding implementation of 
the prevention of significant deterioration (PSD) permitting program, 
i.e., a program that applies in areas that have been designated 
attainment of the NAAQS. The SILs Guidance is not applicable to the 
interstate transport provision, which requires states to eliminate 
significant contribution or interference with maintenance of the NAAQS 
at known and ongoing air quality problem areas in other states. The EPA 
does not, in this action, agree that the State has justified its 
application of the 1 ppb threshold. In any case, both the EPA's most 
recent modeling, EPA 2016v2 modeling, and the modeling relied on by 
ADEQ in its SIP submittal, indicate that the State is projected to 
contribute greater than both the 1 percent and alternative 1 ppb 
thresholds. While the EPA does not, in this action, propose to approve 
of the State's application of the 1 ppb threshold, because the State 
has linkages greater than 1 ppb to projected downwind nonattainment or 
maintenance receptors, (as shown in Table AR-2) the State's use of this 
alternative threshold at Step 2 of the 4-Step interstate framework 
would not alter our review and proposed disapproval of this SIP 
submittal.
    Additionally, the EPA here shares further evaluation of its 
experience since the issuance of the August 2018 memorandum regarding 
use of alternative thresholds at Step 2. This experience leads the 
Agency to now believe it may not be appropriate to continue to attempt 
to recognize alternative contribution thresholds at Step 2. The August 
2018 memorandum stated that ``it may be reasonable and appropriate'' 
for states to rely on an alternative threshold of 1 ppb threshold at 
Step 2. (The memorandum also indicated that any higher alternative 
threshold, such as 2 ppb, would likely not be appropriate.) However, 
the EPA also provided that ``air agencies should consider whether the 
recommendations in this guidance are appropriate for each situation.'' 
Following receipt and review of 49 interstate transport SIP submittals 
for the 2015 ozone NAAQS, the EPA's experience has been that nearly 
every state that attempted to rely on a 1 ppb threshold did not provide 
sufficient information and analysis to support a determination that an 
alternative threshold was reasonable or appropriate for that state.
    For instance, in nearly all submittals, the states did not provide 
the EPA with analysis specific to their state or the receptors to which 
its emissions are potentially linked. In one case, the proposed 
approval of Iowa's SIP submittal, the EPA expended its own resources to 
attempt to supplement the information submitted by the state, in order 
to more thoroughly evaluate the state-specific circumstances that could

[[Page 9807]]

support approval.\47\ It was at the EPA's sole discretion to perform 
this analysis in support of the state's submittal, and the Agency is 
not obligated to conduct supplemental analysis to fill the gaps 
whenever it believes a state's analysis is insufficient. The Agency no 
longer intends to undertake supplemental analysis of SIP submittals 
with respect to alternative thresholds at Step 2 for purposes of the 
2015 ozone NAAQS.
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    \47\ ``Air Plan Approval; Iowa; Infrastructure State 
Implementation Plan Requirements for the 2015 Ozone National Ambient 
Air Quality Standard'', 85 FR 12232 (March 2, 2020). The agency 
received adverse comments on this proposed approval and has not 
taken final action with respect to this proposal.
---------------------------------------------------------------------------

    Furthermore, the EPA's experience since 2018 is that allowing for 
alternative Step 2 thresholds may be impractical or otherwise 
inadvisable for a number of additional policy reasons. For a regional 
air pollutant such as ozone, consistency in requirements and 
expectations across all states is essential. Based on its review of 
submittals to-date and after further consideration of the policy 
implications of attempting to recognize an alternative Step 2 threshold 
for certain states, the Agency now believes the attempted use of 
different thresholds at Step 2 with respect to the 2015 ozone NAAQS 
raises substantial policy consistency and practical implementation 
concerns.\48\ The availability of different thresholds at Step 2 has 
the potential to result in inconsistent application of interstate 
transport obligations based solely on the strength of a state's SIP 
submittal at Step 2 of the 4-Step interstate transport framework. From 
the perspective of ensuring effective regional implementation of 
interstate transport obligations, the more important analysis is the 
evaluation of the emissions reductions needed, if any, to address a 
state's significant contribution after consideration of a multifactor 
analysis at Step 3, including a detailed evaluation that considers air 
quality factors and cost. Where alternative thresholds for purposes of 
Step 2 may be ``similar'' in terms of capturing the relative amount of 
upwind contribution (as described in the August 2018 memorandum), 
nonetheless, use of an alternative threshold would allow certain states 
to avoid further evaluation of potential emission controls while other 
states must proceed to a Step 3 analysis. This can create significant 
equity and consistency problems among states.
---------------------------------------------------------------------------

    \48\ We note that Congress has placed on the EPA a general 
obligation to ensure the requirements of the CAA are implemented 
consistently across states and regions. See CAA section 301(a)(2). 
Where the management and regulation of interstate pollution levels 
spanning many states is at stake, consistency in application of CAA 
requirements is paramount.
---------------------------------------------------------------------------

    Further, it is not clear that national ozone transport policy is 
best served by allowing for less stringent thresholds at Step 2. The 
EPA recognized in the August 2018 memorandum that there was some 
similarity in the amount of total upwind contribution captured (on a 
nationwide basis) between 1 percent and 1 ppb. However, the EPA notes 
that while this may be true in some sense, that is hardly a compelling 
basis to move to a 1 ppb threshold. Indeed, the 1 ppb threshold has the 
disadvantage of losing a certain amount of total upwind contribution 
for further evaluation at Step 3 (e.g., roughly seven percent of total 
upwind state contribution was lost according to the modeling underlying 
the August 2018 memorandum; \49\ in EPA 2016v2 modeling, the amount 
lost is five percent). Considering the core statutory objective of 
ensuring elimination of all significant contribution to nonattainment 
or interference of the NAAQS in other states and the broad, regional 
nature of the collective contribution problem with respect to ozone, 
there does not appear to be a compelling policy imperative in allowing 
some states to use a 1 ppb threshold while others rely on a 1 percent 
of NAAQS threshold.
---------------------------------------------------------------------------

    \49\ See August 2018 memorandum, at page 4.
---------------------------------------------------------------------------

    Consistency with past interstate transport actions such as CSAPR, 
and the CSAPR Update and Revised CSAPR Update rulemakings (which used a 
Step 2 threshold of 1 percent of the NAAQS for two less stringent ozone 
NAAQS), is also important. Continuing to use a 1 percent of NAAQS 
approach ensures that as the NAAQS are revised and made more stringent, 
an appropriate increase in stringency at Step 2 occurs, so as to ensure 
an appropriately larger amount of total upwind-state contribution is 
captured for purposes of fully addressing interstate transport. Accord 
76 FR 48237-38.
    Therefore, notwithstanding the August 2018 memorandum's recognition 
of the potential viability of alternative Step 2 thresholds, and in 
particular, a potentially applicable 1 ppb threshold, the EPA's 
experience since the issuance of that memorandum has revealed 
substantial programmatic and policy difficulties in attempting to 
implement this approach. Nonetheless, the EPA is not, at this time, 
rescinding the August 2018 memorandum. The basis for the EPA's proposed 
disapproval of ADEQ's SIP submission with respect to the Step 2 
analysis is, in the Agency's view, warranted even under the terms of 
the August 2018 memorandum. The EPA invites comment on this broader 
discussion of issues associated with alternative thresholds at Step 2. 
(See Supplementary Information section above for details and docket to 
submit comments). Depending on public comments received in relation to 
this action and further evaluation of this issue, the EPA may determine 
to rescind the 2018 memorandum in the future.
    ADEQ included information in its SIP submission regarding back 
trajectories, emissions trends, and EGU cost controls to conclude that 
emissions from Arkansas should not be considered to contribute 
significantly to nonattainment or interfere with maintenance of the 
NAAQS in other states because there is not a persistent and consistent 
pattern of contribution from the State. While it is not entirely clear 
whether ADEQ was analyzing these factors under Step 2 or Step 3, the 
EPA is evaluating such arguments under Step 3, as we view these 
statements in the SIP submission to speak to whether or not a 
contribution is ``significant'' once a linkage is established.
3. Results of the EPA's Step 1 and Step 2 Modeling and Findings for 
Arkansas
    As described in Section I of this action, the EPA performed air 
quality modeling using the 2016v2 emissions platform to project DVs and 
contributions for 2023 (EPA 2016v2 modeling). This data was examined to 
determine if Arkansas contributes at or above the threshold of 1 
percent of the 2015 ozone NAAQS (0.70 ppb) to any downwind 
nonattainment or maintenance receptor. As shown in Table AR-2, the data 
\50\ indicate that in 2023, emissions from Arkansas contribute greater 
than 1 percent of the standards to nonattainment or maintenance-only 
receptors in Texas: Denton County (Monitor ID. 481210034), Brazoria 
County (Monitor ID. 480391004), Harris County (Monitor ID. 482010055, 
Monitor ID. 482011034,

[[Page 9808]]

and Monitor ID. 482011035).\51\ \52\ Therefore, based on the EPA's 
evaluation of the information submitted by ADEQ, and based on the EPA 
model 2016v2 results for 2023, the EPA proposes to find that Arkansas 
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.
---------------------------------------------------------------------------

    \50\ Design values and contributions at individual monitoring 
sites nationwide are provided in the file: 
2016v2_DVs_state_contributions.xlsx which is included in docket ID 
No. EPA-HQ-OAR-2021-0663.
    \51\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I of this action. That 
modeling showed that Arkansas 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.
    \52\ Allegan County Monitor ID. 260050003 is not a receptor in 
2023 in the EPA 2016v2 modeling. 2023 avg DV is 67.3 ppb and 2023 
Max. DV is 68.4 ppb, so the Allegan County monitor is not a receptor 
in 2023 for nonattainment or maintenance.

Table AR-2--Projected Nonattainment and Maintenance Receptors With Arkansas Linkages in 2023 Based on EPA 2016v2
                                                    Modeling
----------------------------------------------------------------------------------------------------------------
                                                                                                     Arkansas
   Receptor (site ID, county, state)         Nonattainment/        2023 average    2023 maximum    contribution
                                               maintenance           DV (ppb)        DV (ppb)          (ppb)
----------------------------------------------------------------------------------------------------------------
481210034, Denton, TX.................  Maintenance.............            70.4            72.2            0.76
480391004, Brazoria, TX...............  Maintenance.............            70.1            72.3            1.39
482010055, Harris, TX.................  Nonattainment...........            71.0            72.0            1.00
482011034, Harris, TX.................  Maintenance.............            70.3            71.6            1.38
482011035, Harris, TX.................  Maintenance.............            68.0            71.6            1.34
----------------------------------------------------------------------------------------------------------------

    We recognize that the results of the EPA modeling released in the 
March 2018 memorandum (2011 base year) and the EPA 2016v2 modeling 
(2016 base year) identified different receptors and linkages at Steps 1 
and 2 of the 4-Step framework. These differing results about receptors 
and linkages can be affected by the varying meteorology from year to 
year, but we do not think the differing results mean that the modeling 
or the EPA methodology for identifying receptors or linkages is 
inherently unreliable. Rather, these separate modeling runs indicated 
(1) that there were receptors that would struggle with nonattainment or 
maintenance in the future, and (2) that Arkansas was linked to some set 
of these receptors, even if the receptors and linkages differed from 
one another in their specifics (e.g., a different set of receptors were 
identified to have nonattainment or maintenance problems, or Arkansas 
was linked to different receptors in one modeling run versus another). 
We think this common result indicates that Arkansas's emissions were 
substantial enough to generate linkages at Steps 1 and 2 to some set of 
downwind receptors, under varying assumptions and meteorological 
conditions, even if the precise set of linkages changed between 
modeling runs. Under these circumstances, we think it is appropriate to 
proceed to a Step 3 analysis to determine what portion of Arkansas's 
emissions should be deemed ``significant.'' In doing so, we are not 
considering our own earlier modeling results included in EPA's March 
2018 memorandum to be of equal reliability relative to more recent EPA 
2016v2 modeling. However, where alternative or older modeling generated 
linkages, even if those linkages differ from linkages in EPA 2016v2 
modeling, that information provides further evidence, not less, in 
support of a conclusion that the state is required to proceed to Step 3 
to further evaluate its emissions.
4. Evaluation of Information Provided by ADEQ Regarding Step 3
    At Step 3 of the 4-Step framework, a state's emissions are further 
evaluated, in light of multiple factors, including air quality and cost 
considerations, to determine what, if any, emissions contribute 
significantly to nonattainment or interfere with maintenance and, thus, 
must be eliminated under CAA section 110(a)(2)(D)(i)(I).
    ADEQ included in their SIP submission a further analysis of its 
modeled linkage to Allegan, MI (the only linked receptor it analyzed, 
based on its application of a 1 ppb threshold). Arkansas stated that 
the purpose and its conclusion of this analysis was that it would not 
contribute significantly to the Allegan, MI monitor because the state's 
emissions did not result in a consistent and persistent pattern of 
ozone contribution. As stated earlier, EPA 2016v2 modeling projects 
that the Allegan County, MI receptor will be attaining and is not 
expected to have difficulty maintaining the standard in 2023. As such, 
the EPA is not relying on the comparative analysis of emissions trends 
that ADEQ provided in order to conclude that Arkansas's emissions do 
not contribute significantly to a nonattainment or maintenance problem 
in Allegan, MI. We note however, that ADEQ's SIP submission and 
response to comments do not clearly define what ADEQ considers to be 
persistent and consistent pattern of contribution. Rather, the SIP 
submission simply states that contribution should be deemed 
``significant'' only if there is a persistent and consistent pattern of 
several days with elevated ozone.
    To be clear, the modeling establishing linkages of Arkansas to 
downwind nonattainment and maintenance receptors already establishes 
that there is a consistent and persistent pattern of contribution on 
elevated ozone days from Arkansas to other states. That is because 
EPA's methodology for projecting future year ozone concentrations 
accounts for precisely these concerns--the relative response factor 
\53\ that is applied to historic monitored data to generate projections 
is calculated by looking only at days with elevated ozone levels (ten 
days is preferred with a minimum of five days). The EPA notes that 
monitored attainment with the ozone standard is determined by averaging 
the fourth high value recorded each year for three years. So, the EPA 
believes it is important to

[[Page 9809]]

estimate impacts on the days with highest projected ozone levels. The 
EPA's approach, as detailed in the Air Quality Modeling Technical 
Support Document for 2015 Ozone NAAQS Transport SIP Proposed Actions 
included in Docket ID No. EPA-HQ-OAR-2021-0663, does this by estimating 
the average fy 2023 impact from an upwind state on the days with the 
highest projected ozone levels at the downwind nonattainment or 
maintenance receptor. The days chosen to analyze the future impacts are 
chosen initially by the selecting the ten highest days in the base 
period modeling that are projected to be above 65 ppb in the base 
period. If there are not ten days above 65 ppb at a potential receptor, 
the number of days above 65 ppb are used as long as there is at least 
five days above 65 ppb in the base period. If the air quality modeling 
shows fewer than five days above 65 ppb in the base period, then the 
data for impacts at that receptor in fy 2023 are not calculated. The 
base and future year modeling for these five to ten days is then used 
to project fy 2023 ozone DVs to determine whether it is projected to be 
a nonattainment or maintenance receptor in 2023. For the same five to 
ten days identified, the future year modeling provides the estimated 
daily contribution at a potential receptor's future year daily MDA8 and 
these daily contributions are averaged for the five to ten days to 
result in the average contribution from the upwind area.
---------------------------------------------------------------------------

    \53\ The relative response factor (RRF) is a ratio developed 
using the modeled changes between the base case and future case for 
high ozone modeled days. Typically, the 10 highest MDA8 modeled days 
in the base case are found and the maximum value from the 3x3 grid 
centered on the monitor for each day is used to calculate a 10-day 
average base case modeled value. Then a similar concentration 
average is developed for same 10 base case days and the same grid 
cell that provided the base case concentration to calculate a future 
year 10-day average modeled value using the future year modeling 
results. The RRF is then calculated by using this future year 10-day 
average model value divided by the base case year 10-day average 
model value to develop a ratio representing the change in modeled 
ozone. The RRF is then multiplied times the base DV value to result 
in a projected future year DV.
---------------------------------------------------------------------------

    As mentioned previously, ADEQ used HYSPLIT back trajectories to 
assess wind patterns on elevated ozone days in an attempt to 
demonstrate that there is not persistent and consistent pattern of 
contribution from Arkansas to the Allegan County, MI receptor. 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 concentration 
at the end point monitor. The horizontal and vertical areas that 
potentially contribute to the end point concentration 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 
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.'' Since 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. 
Chemical transport models, such as the one relied upon by Arkansas to 
establish the linkage between Arkansas and those downwind receptors in 
the first instance, do take these factors into account and therefore 
provide a more robust assessment of ozone contribution.
    During ADEQ's public comment period, the EPA submitted comments 
noting concerns regarding the methodology ADEQ used in their HYSPLIT 
back trajectories analysis.\54\ While we are not providing a detailed 
evaluation of ADEQ's HYSPLIT analysis in this rulemaking, we do note 
that our review identified a number of concerns with how ADEQ screened 
out a number of back trajectories, which invalidates ADEQ's 
conclusions.\55\ While we disagree with ADEQ's methodologies and 
conclusions, we note that ADEQ's HYSPLIT back trajectory information 
did not show that the base years used in the EPA modeling (2011 and 
2016) demonstrated an unusual amount of transport of air parcels from 
Arkansas to nonattainment or maintenance receptors in downwind states 
(i.e., the modeling years used by the EPA do not skew the results 
toward finding linkages).\56\ Therefore, although Arkansas asserted 
that its additional air quality factor analysis using back trajectory 
analysis is a permissible way to interpret which contributions are 
``significant'' because that analysis examines whether there was a 
``persistent and consistent pattern of contribution on several days 
with elevated ozone,'' the modeled linkage at Step 2 is a superior 
approach for assessing the persistence of a state's contribution. It is 
superior because it is based on the average of the contributions on the 
five to ten highest ozone days. Considering the form of the standard, 
this is a sufficient number of days to determine if an impact is 
persistent enough to impact an area's ability to attain or maintain the 
standard. The modeling is also a better method because it accounts for 
dispersion while back trajectory analysis as performed by Arkansas only 
shows the centerline of air parcel travel and otherwise will leave out 
days when Arkansas would have contributed to downwind problems. 
Finally, because the modeling accounts for dispersion and chemical 
reactions, it can provide a quantitative estimate of contribution.
---------------------------------------------------------------------------

    \54\ The EPA reviewed the ADEQ SIP submission and provided 
comments during the State's public comment period for the proposed 
SIP action. The EPA's comment letter and ADEQ's response to comments 
are included in ADEQ's October 19, 2019, SIP submission, which is 
available in the Regional docket for this action (Docket ID No. EPA-
R06-OAR-2021-0801).
    \55\ Concerns included removing of HYSPLIT back trajectories 
based on start height, the start time that Arkansas used for the 
back trajectories and removing of back trajectories when the 
centerline passed near but not through Arkansas because Arkansas has 
some very large point sources near the Arkansas state line that 
could be contributing. Texas also screened their HYPSLIT back 
trajectories similarly to Arkansas and we have further discussed our 
concerns and why such screening invalidates conclusions from the 
HYSPLIT back trajectory analyses. See EPA's review and conclusions 
in discussion of TCEQ's HYSPLIT analyses in the ``EPA Region 6 2015 
8-Hour Ozone Transport SIP Proposal Technical Support Document'' 
(EPA Region 6 2015 Ozone Transport SIP TSD.pdf) included in the 
Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-
0801).
    \56\ ADEQ's summary of trajectories indicated that 2011 had 
three linked back trajectories and 2016 had one linked back 
trajectories and the EPA calculated the average for 2008-2017 in 
ADEQ's table was 2.2 linked back trajectories per year.
---------------------------------------------------------------------------

    ADEQ also contested the significance of its modeled contribution 
above 1 ppb based on the relatively larger contributions of other 
upwind states to the receptor to which it was linked. The EPA disagrees 
that a state's small contribution relative to other upwind states is a 
permissible basis for finding no obligation under the interstate 
transport provision. CAA 110(a)(2)(D)(i)(I) 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 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

[[Page 9810]]

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 arguments suggesting that upwind states should be 
excused from interstate transport 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 these 
arguments as essentially an argument ``that an upwind State 
`contributes significantly' to downwind nonattainment only when its 
emissions are the sole cause of downwind nonattainment.'' 938 F.3d 303 
at 324. The court explained that ``an upwind State can `contribute' to 
downwind nonattainment even if its emissions are not the but-for 
cause.'' Id. At 324-325. See also Catawba County v. EPA, 571 F.3d 20, 
39 (D.C. Cir. 2009) (rejecting the argument ``that `significantly 
contribute' unambiguously means `strictly cause''' because there is 
``no reason why the statute precludes EPA from determining that [an] 
addition of [pollutant] into the atmosphere is significant even though 
a nearby county's nonattainment problem would still persist in its 
absence''); Miss. Comm'n on Envtl. Quality v. EPA, 790 F.3d 138, 163 
n.12 (D.C. Cir. 2015) (observing that the argument that ``there likely 
would have been no violation at all . . . if it were not for the 
emissions resulting from [another source]'' is ``merely a rephrasing of 
the but-for causation rule that we rejected in Catawba County.''). 
Therefore, a state is not excused from eliminating its significant 
contribution on the basis that emissions from other states also 
contribute some amount of pollution to the same receptors to which the 
state is linked.
    ADEQ did not provide additional analysis for other receptors to 
which it was linked above 1 percent in the air quality modeling upon 
which it relied, and to which it continues to be linked in EPA 2016v2 
modeling. To effectively evaluate which emissions in the state should 
be deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. The EPA has consistently applied this general approach 
(i.e., Step 3 of the 4-Step interstate transport framework) when 
identifying emissions contributions that the Agency has determined to 
be ``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While the EPA has not directed states 
that they must conduct a Step 3 analysis in precisely the manner the 
EPA has done in its prior regional transport rulemakings, state 
implementation plans addressing the obligations in CAA section 
110(a)(2)(D)(i)(I) must prohibit ``any source or other type of 
emissions activity within the State'' from emitting air pollutants 
which will contribute significantly to downwind air quality problems. 
Thus, states must complete something similar to the EPA's analysis (or 
an alternative approach to defining ``significance'' that comports with 
the statute's objectives) to determine whether and to what degree 
emissions from a state should be ``prohibited'' to eliminate emissions 
that will ``contribute significantly to nonattainment in, or interfere 
with maintenance of'' the NAAQS in any other state. As discussed below, 
ADEQ did not conduct an adequate analysis in their SIP submission. We 
therefore propose that ADEQ was required to analyze emissions from the 
sources and other emissions activity from within the State to determine 
whether its contributions were significant, and we propose to 
disapprove its submission because Arkansas failed to adequately do so.
    In analyzing potential additional NOX controls, ADEQ 
found that additional controls on its EGUs would exceed the cost-
effectiveness thresholds identified in the CSAPR and CSAPR Update 
rules. For the cost analysis, Arkansas only focused on the potential 
costs of NOX controls for EGUs. As stated above, Arkansas 
found that the costs to install additional NOX controls 
(selective catalytic reduction, SCR, and selective noncatalytic 
reduction, SNCR) at electric generating units (EGUs) exceed EPA's cost 
thresholds used for the CSAPR and CSAPR Update rules. Based on the 
projected cost of these controls relative to the thresholds used in 
those two prior EPA rules, Arkansas concluded that no new controls 
beyond those Federal and State regulations already in existence were 
cost-effective, especially considering that Allegan County, MI is 
projected to be in attainment with the 2015 ozone NAAQS and Arkansas's 
small contribution relative to other states potentially linked to 
Allegan County, MI based on EPA's modeling.
    Arkansas's analysis is inadequate because its focus is only on 
EGUs.\57\ See Wisconsin, 938 F.3d at 318-20. We also find Arkansas's 
conclusions as to the availability of cost-effective controls for EGUs 
to be inadequate. Relying on the CSAPR Update's (or any other CAA 
program's) determination of cost-effectiveness without further Step 3 
analysis is not approvable. Cost-effectiveness must be assessed in the 
context of the specific CAA program; assessing cost-effectiveness in 
the context of 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 
potential air quality impacts of those reductions at downwind 
receptors. While the EPA has not established a benchmark cost-
effectiveness value for 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 under this NAAQS 
to reflect higher marginal control costs. ADEQ's submission failed to 
provide a justification for why the $1400/ton threshold used in the 
CSAPR Update is appropriate to rely on for the 2015 ozone NAAQS. ADEQ's 
analysis does not consider any air quality impacts of assessed controls 
at downwind receptors. As stated above, assessing cost-effectiveness in 
the context of ozone transport requires more than just assessing the 
cost of controls per ton of NOX removed. As such, ADEQ's 
assessment of the cost of controls and reliance on the marginal cost 
threshold of $1,400/ton used for the CSAPR Update is inadequate. 
Furthermore, EPA 2016v2 modeling captures all existing CSAPR trading 
programs in the baseline and confirms that these control programs were 
not sufficient to eliminate Arkansas's linkage at Steps 1 and 2 under 
the 2015 ozone NAAQS. The State was therefore obligated at Step 3 to 
assess additional control measures using a multifactor analysis.
---------------------------------------------------------------------------

    \57\ In 2017, National Emission Inventory (NEI) NOX 
emissions from EGU sources represent 56% percent of the total NOx 
emissions categories in Arkansas that report emissions to the NEI. 
See AR NOx.xlsx datasheet included in the Regional docket for this 
action (Docket ID No. EPA-R06-OAR-2021-0801).

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

[[Page 9811]]

5. Evaluation of Information Provided by ADEQ Regarding Step 4
    Step 4 of the 4-Step interstate transport framework calls for the 
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. ADEQ's SIP submission, 
which looked only at additional NOX controls at EGUs and 
dismissed such controls as not cost-effective relative to the 
thresholds established in earlier EPA transport rules, did not 
constitute an adequate emission reduction analysis at Step 3. Based on 
its conclusions, ADEQ did not revise its SIP to include any emission 
reductions. As a result, the EPA proposes to disapprove ADEQ's 
submittal on the separate, additional basis that Arkansas has not 
developed or included permanent and enforceable emissions reductions in 
its SIP necessary to meet the obligations of CAA section 
110(a)(2)(D)(i)(I).
6. Conclusion
    Based on the EPA's evaluation of ADEQ's SIP submission, the EPA is 
proposing to find that ADEQ's October 19, 2019, SIP submission 
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 ozone NAAQS in any other state.

III. Louisiana SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission

A. Summary of LDEQ SIP Submission Addressing Interstate Transport of 
Air Pollution for the 2015 Ozone NAAQS

    On November 13, 2019, the Louisiana Department of Environmental 
Quality (LDEQ) made a SIP submission addressing the State of 
Louisiana's interstate transport of air pollution for the 2015 ozone 
NAAQS. The SIP submission provided LDEQ's analysis of Louisiana's 
impact to downwind states and concluded that emissions from Louisiana 
will not contribute significantly to nonattainment or interfere with 
maintenance of the 2015 ozone NAAQS in other states.
    The LDEQ's SIP submission provided an analysis of Louisiana's air 
emissions impact to downwind states using a 3-Step alternative 
framework similar to the EPA's 4-Step framework. LDEQ's 3-Step 
alternative framework includes: Step 1: Identify monitors projected to 
be in nonattainment or have maintenance issues in a future year; Step 
2: Identify projected nonattainment and/or maintenance monitors in 
other states that might be impacted by emissions from Louisiana, 
tagging them for further review; and, Step 3: Determine if emissions 
from Louisiana contribute significantly to nonattainment or interfere 
with maintenance at the monitors tagged for review in Step 2. LDEQ 
noted that its Step 1 is identical to the EPA's Step 1, and its Steps 2 
and 3 are equivalent to the EPA's Step 2. Louisiana further noted that 
Steps 3 and 4 of the EPA's 4-Step framework are relevant only if 
emissions from Louisiana contribute significantly to nonattainment or 
interfere with maintenance at downwind monitors in another state.
    LDEQ's Step 1 was to identify downwind monitors projected to be in 
nonattainment and/or have maintenance issues in future year 2023 (fy 
2023). At this step, LDEQ relied on the EPA's interstate transport 
modeling results that are included as an attachment to the March 2018 
memorandum. The EPA March 2018 modeling results provided: (1) Projected 
average DV and maximum DV for 2023 for the ozone monitors (or 
``receptors'') in the 48 contiguous states and (2) the expected 
contribution of state emissions to the projected ozone concentrations 
at each ozone monitor.
    LDEQ used a contribution threshold of 1 ppb in LDEQ's Step 2 to 
identify projected nonattainment and/or maintenance receptors in other 
states that might be impacted by emissions from Louisiana and tagged 
them for further review. To support a 1 ppb contribution threshold, 
LDEQ's submission stated that a 1 percent threshold is inappropriate 
because that value is not detectable by a monitor and the value of 1 
percent of the 2015 ozone NAAQS would be truncated to zero if 
calculated in accordance with the method for determining DVs for the 
ozone NAAQS. LDEQ also stated that the more stringent threshold of 1 
percent of the NAAQS (0.7 ppb) is an order of magnitude smaller than 
the biases and errors typically documented for regional photochemical 
modeling.\58\ Based on LDEQ's approach of evaluating linkages at the 1 
ppb threshold, five Texas receptors were identified by Louisiana for 
analysis. The Texas receptors and corresponding receptor data presented 
in Louisiana's SIP are summarized further in this notice in Table LA-
1.\59\ The March 2018 memorandum identified monitors in Allegan, 
Michigan and Milwaukee and Sheboygan, Wisconsin as potential 
nonattainment and maintenance-only receptors linked to emissions from 
Louisiana based on 1 percent of the NAAQS threshold. However, Louisiana 
did not include the Allegan, Michigan and Milwaukee and Sheboygan, 
Wisconsin receptors in the State's analysis because the March 2018 
memorandum shows that Louisiana's projected modeled contribution values 
to each receptor is less than 1 ppb.
---------------------------------------------------------------------------

    \58\ The Louisiana SIP submittal did not provide a specific 
citation to the Simon et al., 2012 reference to support this 
assertion. However, we believe the reference is associated with the 
following article: Simon, H., Baker, K.R., Phillips, S., 2012. 
``Compilation and interpretation of photochemical model performance 
statistics published between 2006 and 2012''. Atmospheric 
Environment 61, 124-139.
    \59\ The five potential nonattainment and maintenance receptor 
monitors identified by LDEQ are from the Dallas-Fort Worth and 
Houston-Galveston-Brazoria, TX nonattainment areas for the 2015 
ozone NAAQS. The Louisiana SIP submittal appears to have 
inadvertently omitted Harris County, TX Monitor ID No. 482011034 for 
analysis. EPA's March 2018 memorandum identified this monitor as a 
maintenance receptor with a contribution of 3.38 ppb from Louisiana 
emissions.

 Table LA-1--Projected Nonattainment and Maintenance Receptors Identified by Louisiana Based on the EPA's March
                                                 2018 Memorandum
----------------------------------------------------------------------------------------------------------------
                                                                                                     Louisiana
                Receptor (site ID, county, state)                  2023  Average   2023  Maximum   Contribution
                                                                   DV (ppb) \60\   DV (ppb) \61\       (ppb)
----------------------------------------------------------------------------------------------------------------
480391004, Brazoria, TX.........................................            74.0            74.9            3.80

[[Page 9812]]

 
482011039, Harris, TX...........................................            71.8            73.5            4.72
484392003, Tarrant, TX..........................................            72.5            74.8            1.71
481210034, Denton, TX...........................................            69.7            72.0            1.92
482010024, Harris, TX...........................................            70.4            72.8            4.72
----------------------------------------------------------------------------------------------------------------

    For LDEQ's Step 3, Louisiana stated that an air emission 
contribution from the State should only be considered significant if 
there is a persistent and consistent pattern of contribution on several 
days with elevated ozone. In trying to determine whether there is a 
persistent and consistent pattern of contribution, LDEQ analyzed 
seasonal weather patterns, surface wind directions, and periodic back 
trajectories. LDEQ used the National Oceanic and Atmospheric 
Administration (NOAA) Hybrid Single Particle Lagrangian Integrated 
Trajectory (HYSPLIT) \62\ model to perform 99 back trajectories for 
exceedances from the receptor monitors identified in Table LA-1 for 
2016, 2017, and 2018. Based on an analysis of the HYSPLIT results, LDEQ 
stated that approximately 28% of the trajectories travel in or through 
Louisiana, and only 8% of those back trajectories originate in the 
State. The SIP submission also stated that a comparison of the EPA's 
modeled contribution between Texas and Louisiana monitors indicates 
that a far greater proportion of the total ozone detected in Louisiana 
originates in Texas rather than vice versa. Therefore, Louisiana 
concluded that the impact from the State's air emissions was 
insignificant to the overall attainment at the receptor monitors 
identified in Table LA-1 and does not significantly contribute to 
nonattainment or interfere with maintenance of the 2015 ozone NAAQS in 
other states.
---------------------------------------------------------------------------

    \60\ Information added from the EPA's March 2018 memorandum.
    \61\ Id.
    \62\ See FN 34.
---------------------------------------------------------------------------

B. EPA Evaluation of the LDEQ SIP Submission

    The EPA is proposing to find that LDEQ's November 13, 2019, SIP 
submission does not meet the State's obligations with respect to 
prohibiting emissions that contribute significantly to nonattainment or 
interfere with maintenance of the 2015 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 therefore proposing to 
disapprove Louisiana's SIP submission.
1. Evaluation of Information Provided by LDEQ Regarding Steps 1 and 2
    At Step 1 of the 4-Step interstate transport framework, LDEQ relied 
on EPA modeling released in the March 2018 memorandum to identify 
nonattainment and maintenance receptors in 2023. At Step 2 of the 4-
Step interstate transport framework, LDEQ relied on the EPA modeling 
released in the March 2018 memorandum to identify upwind state linkages 
to nonattainment and maintenance receptors in 2023. LDEQ additionally 
utilized a 1 ppb threshold at Step 2 to identify whether the state was 
``linked'' to a projected downwind nonattainment or maintenance 
receptor. As discussed in the EPA's August 2018 memorandum, with 
appropriate additional analysis it may be reasonable for states to use 
a 1 ppb contribution threshold, as an alternative to a 1 percent 
threshold, at Step 2 of the 4-Step interstate transport framework, for 
the purposes of identifying linkages to downwind receptors. In any 
case, the State is projected to contribute greater than both the 1 
percent and the alternative 1 ppb thresholds to receptors in Texas, 
regardless of whether we look at LDEQ's analysis (which relied on the 
EPA's older modeling) or updated modeling the EPA has performed in 
advance of this proposal. As seen in the tables LA-1 and LA-2, 
Louisiana contributes nearly five times the 1 ppb threshold to 
nonattainment or maintenance receptors in Texas. Therefore, while the 
EPA does not, in this action, approve of the State's application of the 
1 ppb threshold, because the State has linkages greater than 1 ppb to 
projected downwind nonattainment or maintenance receptors, the State's 
use of this alternative threshold at Step 2 of the 4-Step interstate 
framework would not alter our review and proposed disapproval of this 
SIP submittal.
    The EPA here shares further evaluation of its experience since the 
issuance of the August 2018 memorandum regarding use of alternative 
thresholds at Step 2. This experience leads the Agency to now believe 
it may not be appropriate to continue to attempt to recognize 
alternative contribution thresholds at Step 2. The August 2018 
memorandum stated that ``it may be reasonable and appropriate'' for 
states to rely on an alternative threshold of 1 ppb threshold at Step 
2.\63\ (The memorandum also indicated that any higher alternative 
threshold, such as 2 ppb, would likely not be appropriate.) However, 
the EPA also provided that ``air agencies should consider whether the 
recommendations in this guidance are appropriate for each situation.'' 
Following receipt and review of 49 interstate transport SIP submittals 
for the 2015 ozone NAAQS, the EPA's experience has been that nearly 
every state that attempted to rely on a 1 ppb threshold did not provide 
sufficient information and analysis to support a determination that an 
alternative threshold was reasonable or appropriate for that state.
---------------------------------------------------------------------------

    \63\ See August 2018 memorandum, at page 4.
---------------------------------------------------------------------------

    For instance, in nearly all submittals, the states did not provide 
the EPA with analysis specific to their state or the receptors to which 
its emissions are potentially linked. In one case, the proposed 
approval of Iowa's SIP submittal, the EPA expended its own resources to 
attempt to supplement the information submitted by the state, in order 
to more thoroughly evaluate the state-specific circumstances that could 
support approval.\64\ The Agency no longer intends to undertake 
supplemental analysis of SIP submittals with respect to alternative 
thresholds at Step 2 for purposes of the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \64\ ``Air Plan Approval; Iowa; Infrastructure State 
Implementation Plan Requirements for the 2015 Ozone National Ambient 
Air Quality Standard'', 85 FR 12232 (March 2, 2020). The Agency 
received adverse comments on this proposed approval and has not 
taken final action with respect to this proposal.
---------------------------------------------------------------------------

    Furthermore, the EPA's experience since 2018 is that allowing for 
alternative Step 2 thresholds may be

[[Page 9813]]

impractical or otherwise inadvisable for a number of additional policy 
reasons. For a regional air pollutant such as ozone, consistency in 
requirements and expectations across all states is essential. Based on 
its review of submittals to-date and after further consideration of the 
policy implications of attempting to recognize an alternative Step 2 
threshold for certain states, the Agency now believes the attempted use 
of different thresholds at Step 2 with respect to the 2015 ozone NAAQS 
raises substantial policy consistency and practical implementation 
concerns.\65\ The availability of different thresholds at Step 2 has 
the potential to result in inconsistent application of interstate 
transport obligations based solely on the strength of a state's SIP 
submittal at Step 2 of the 4-Step interstate transport framework. From 
the perspective of ensuring effective regional implementation of 
interstate transport obligations, the more important analysis is the 
evaluation of the emissions reductions needed, if any, to address a 
state's significant contribution after consideration of a multifactor 
analysis at Step 3, including a detailed evaluation that considers air 
quality factors and cost. Where alternative thresholds for purposes of 
Step 2 may be ``similar'' in terms of capturing the relative amount of 
upwind contribution (as described in the August 2018 memorandum), 
nonetheless, use of an alternative threshold would allow certain states 
to avoid further evaluation of potential emission controls while other 
states must proceed to a Step 3 analysis. This can create significant 
equity and consistency problems among states.
---------------------------------------------------------------------------

    \65\ We note that Congress has placed on the EPA a general 
obligation to ensure the requirements of the CAA are implemented 
consistently across states and regions. See CAA section 301(a)(2). 
Where the management and regulation of interstate pollution levels 
spanning many states is at stake, consistency in application of CAA 
requirements is paramount.
---------------------------------------------------------------------------

    Further, it is not clear that national ozone transport policy is 
best served by allowing for less stringent thresholds at Step 2. The 
EPA recognized in the August 2018 memorandum that there was some 
similarity in the amount of total upwind contribution captured (on a 
nationwide basis) between 1 percent and 1 ppb. However, the EPA notes 
that while this may be true in some sense, that is not a compelling 
basis to move to a 1 ppb threshold. Indeed, the 1 ppb threshold has the 
disadvantage of losing a certain amount of total upwind contribution 
for further evaluation at Step 3 (e.g., roughly seven percent of total 
upwind state contribution was lost according to the modeling underlying 
the August 2018 memorandum; \66\ in the EPA's updated modeling, the 
amount lost is five percent). Considering the core statutory objective 
of ensuring elimination of all significant contribution to 
nonattainment or interference of the NAAQS in other states and the 
broad, regional nature of the collective contribution problem with 
respect to ozone, there does not appear to be a compelling policy 
imperative in allowing some states to use a 1 ppb threshold while 
others rely on a 1 percent of NAAQS threshold.
---------------------------------------------------------------------------

    \66\ See August 2018 memorandum, at page 4.
---------------------------------------------------------------------------

    Consistency with past interstate transport actions such as CSAPR, 
and the CSAPR Update and Revised CSAPR Update rulemakings (which used a 
Step 2 threshold of 1 percent of the NAAQS for two less stringent ozone 
NAAQS), is also important. Continuing to use a 1 percent of NAAQS 
approach ensures that as the NAAQS are revised and made more stringent, 
an appropriate increase in stringency at Step 2 occurs, so as to ensure 
an appropriately larger amount of total upwind-state contribution is 
captured for purposes of fully addressing interstate transport. Accord 
76 FR 48237-38.
    Therefore, notwithstanding the August 2018 memorandum's recognition 
of the potential viability of alternative Step 2 thresholds, and in 
particular, a potentially applicable 1 ppb threshold, the EPA's 
experience since the issuance of that memorandum has revealed 
substantial programmatic and policy difficulties in attempting to 
implement this approach. Nonetheless, the EPA is not at this time 
rescinding the August 2018 memorandum. The basis for a proposed 
disapproval of LDEQ's SIP submission with respect to the Step 2 
analysis we believe is warranted under the terms of the August 2018 
memorandum. The EPA invites comment on this broader discussion of 
issues associated with alternative thresholds at Step 2. Depending on 
public comments received and further evaluation of this issue, the EPA 
may determine to rescind the 2018 memorandum in the future.
2. Results of the EPA's Step 1 and Step 2 Modeling and Findings for 
Louisiana
    As described in Section I of this action, the EPA performed air 
quality modeling using the 2016v2 emissions platform to project DVs and 
contributions for 2023.\67\ This data was examined to determine if 
Louisiana contributes at or above the threshold of 1 percent of the 
2015 ozone NAAQS (0.70 ppb) to any downwind nonattainment or 
maintenance receptor. As shown in Table LA-2, the data \68\ indicate 
that in 2023, emissions from Louisiana contributed greater than 1 
percent of the standards to nonattainment or maintenance-only receptors 
in Texas.\69\ Therefore, based on the EPA's evaluation of the 
information submitted by LDEQ, and based on the EPA's most recent 
modeling results for 2023, the EPA proposes to find that Louisiana 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.
---------------------------------------------------------------------------

    \67\ Per the instructions in the Supplementary Information 
section above, all public comments, including comments on the EPA's 
air quality modeling should be submitted in the Regional docket for 
this action, Docket ID No. EPA-R06-OAR-2021-0801. Comments are not 
being accepted in Docket No. EPA-HQ-OAR-2021-0663.
    \68\ DVs and contributions at individual monitoring sites 
nationwide are provided in the file: 
``2016v2_DVs_state_contributions.xlsx'', which is included in Docket 
ID No. EPA-HQ-OAR-2021-0663.
    \69\ These modeling results are consistent with the results of a 
prior round of 2023 modeling using the 2016v1 emissions platform, 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I of this action. That 
modeling showed that Louisiana 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 DVs And Contributions Revised CSAPR Update.xlsx'' in Docket 
No. EPA-HQ-OAR-2021-0663.

    Table LA-2--Projected Nonattainment and Maintenance Receptors With Louisiana Linkages Based on EPA 2016v2
                                                    Modeling
----------------------------------------------------------------------------------------------------------------
                                                                                                     Louisiana
   Receptor (site ID, county, state)         Nonattainment/        2023  Average   2023  Maximum   Contribution
                                               maintenance           DV (ppb)        DV (ppb)          (ppb)
----------------------------------------------------------------------------------------------------------------
482010024, Harris, TX.................  Nonattainment...........            75.2            76.8            4.31
482010055, Harris, TX.................  Nonattainment...........            71.0            72.0            5.39
480391004, Brazoria, TX...............  Maintenance.............            70.1            72.3            7.03

[[Page 9814]]

 
481210034, Denton, TX.................  Maintenance.............            70.4            72.2            3.22
482011034, Harris, TX.................  Maintenance.............            70.3            71.6            4.93
482011035, Harris, TX.................  Maintenance.............            68.0            71.6            4.77
----------------------------------------------------------------------------------------------------------------

3. Evaluation of Information Provided by LDEQ 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 contribute significantly 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 approach (i.e., 
Step 3 of the 4-Step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. 489, 519 (2014). While the EPA has not directed states 
that they must conduct a Step 3 analysis in precisely the manner the 
EPA has done in its prior regional transport rulemakings, state 
implementation plans addressing the obligations in CAA section 
110(a)(2)(D)(i)(I) must prohibit ``any source or other type of 
emissions activity within the State'' from emitting air pollutants 
which will contribute significantly to downwind air quality problems. 
Thus, states must complete an analysis similar to the EPA's (or an 
alternative approach to defining ``significance'' that comports with 
CAA requirements) to determine whether, and to what degree, emissions 
from a state should be ``prohibited'' to eliminate emissions that will 
``contribute significantly to nonattainment, or interfere with 
maintenance of'' the NAAQS in any other state. LDEQ did not conduct 
such an analysis in their SIP submission. Instead LDEQ interpreted the 
Act's requirements as only requiring an analysis of emission reductions 
where there was a ``consistent and persistent'' pattern of contribution 
and conducted an air-quality-only analysis in order to refute such a 
pattern. We propose to find that LDEQ was required to analyze emissions 
from the sources and other emissions activity from within Louisiana to 
determine whether its contributions were significant, and we propose to 
disapprove its submission because LDEQ did not do so.
    As noted, LDEQ stated in its SIP submission that emissions from 
Louisiana should not be considered to contribute significantly to 
nonattainment or interfere with maintenance of the NAAQS in other 
states because there is not a ``persistent and consistent'' pattern of 
contribution from the State. The SIP submission does not explain what 
LDEQ considers to be a persistent and consistent pattern of 
contribution, even after the LDEQ received a comment during its state 
comment period that requested that the LDEQ define ``persistent and 
consistent'' in terms of impacts on downwind states. The LDEQ 
responded, ``Louisiana has defined the pattern and has provided back 
trajectories on those monitored exceedances for the 2016-2018 ozone 
seasons, which will show that the definition is applicable to the 
conclusion.'' \70\ We do not agree that this suffices as an explanation 
as to why LDEQ does not need to further analyze its potential emission 
reductions under Step 3 before determining it has no statutory 
obligation under the interstate transport provision. In the case of 
Louisiana, modeling in the March 2018 memorandum and the EPA's more 
recent 2016v2 modeling both project that receptors in the Houston-
Galveston-Brazoria (HGB) and Dallas-Fort Worth (DFW) ozone 
nonattainment areas in Texas will have difficulty attaining or 
maintaining the 2015 ozone NAAQS, and Louisiana's contribution to these 
areas exceed both a 1 percent or a 1 ppb threshold. While linkages to 
specific receptors may change with updated modeling, both modeling 
analyses consistently show emissions from Louisiana impact both 
downwind nonattainment receptors and downwind maintenance receptors in 
Texas.
---------------------------------------------------------------------------

    \70\ See LDEQ SIP Submission, Appendix A, available in the 
Regional docket for this action (Docket ID No. EPA-R06-OAR-2021-
0801).
---------------------------------------------------------------------------

    The LDEQ SIP submission stated that Louisiana's contribution should 
be deemed ``significant'' per CAA section 110(a)(2)(D)(i)(I) only if 
there is a persistent and consistent pattern of contribution on several 
days with elevated ozone. LDEQ asserted that its linkages to Texas do 
not warrant further analysis because, according to LDEQ, emissions from 
Louisiana do not persistently and consistently contribute on several 
days of elevated ozone. However, the EPA modeling that LDEQ relied upon 
to demonstrate linkages in the first instance already establishes that 
there is a consistent and persistent pattern of contribution from 
Louisiana to Texas receptors on elevated ozone days. The EPA's 
methodology for projecting future year ozone concentrations accounts 
for precisely these concerns--the relative response factor \71\ that is 
applied to historic monitored data to generate projections is 
calculated by looking only at days with elevated ozone levels. The EPA 
notes that monitored attainment with the ozone standard is determined 
by averaging the fourth high value recorded each year for three years. 
So, the EPA believes it is important to estimate impacts on the days 
with highest projected ozone levels. The days chosen to analyze the 
future impacts are chosen initially by the selecting the 10 highest 
days in the base period modeling that are projected to be above 65 ppb 
in the base period. If there are not 10 days above 65 ppb at a 
potential receptor, the number of days above 65 ppb are used so long as 
there is at least five days above 65 ppb in the base period. If the air 
quality modeling shows fewer than five days above 65 ppb in the base 
period, then the data for impacts at that receptor in 2023 are not 
calculated. The base and future year modeling for these

[[Page 9815]]

5-10 days are then used to project 2023 ozone DVs to determine whether 
it is projected to be a nonattainment or maintenance receptor in 2023. 
For these same 5-10 days identified, the future year modeling provides 
the estimated daily contribution at a potential receptor's future year 
daily MDA8 and these daily contributions are averaged for the 5-10 days 
to result in the average contribution from the upwind area.
---------------------------------------------------------------------------

    \71\ See FN 53.
---------------------------------------------------------------------------

    LDEQ's air quality analysis used to dismiss its linkages to Texas 
receptors as not ``significant'' consists of an evaluation of seasonal 
weather patterns, surface wind directions, and periodic back 
trajectories. The State's weather pattern analysis relied on large-
scale weather patterns as they relate to commonly observed wind 
directions rather than weather patterns and conditions that are 
specifically conducive to ozone formation or tied to specific days when 
high ozone was monitored in the downwind areas. General weather pattern 
discussions that are not associated with specific ozone episodes are 
not generally informative of interstate transport decisions. It is 
necessary to investigate specific instances of high ozone, because as 
discussed previously, violations of the ozone standard can be driven by 
as few as 4 days per year because the compliance with the standard is 
evaluated based on the average of the fourth high value measured each 
of three consecutive years.
    LDEQ's wind rose analysis is based on surface sites in the Dallas-
Fort Worth areas, Houston-Galveston-Brazoria areas, and other areas in 
Texas and Louisiana, but the analysis does not address transport winds 
between Louisiana and the Texas areas with receptors on high ozone days 
at the identified receptors. There are several limitations associated 
with LDEQ's wind rose analysis: (1) Wind directions measured at the 
surface are not necessarily good indicators of the wind direction 
occurring at higher elevations, which tend to have a stronger influence 
on interstate ozone transport; (2) wind directions change spatially 
over the range of distance involved in transport from Louisiana to 
Texas; (3) wind directions change temporally over the range of time 
involved in ozone transport from Louisiana to Texas; and (4) the wind 
roses are based on wind data measured throughout the year, not just 
during either ozone season or monitored ozone episode days. In 
addition, as discussed previously, LDEQ's wind rose analysis is not 
limited to the wind conditions that are conducive to high ozone, so it 
does not provide information directly pertinent to when ozone is high 
at areas in Texas and whether Louisiana is a contributing area during 
those specific times.
    LDEQ also included 99 back trajectory analyses during the 2016, 
2017, and 2018 years for the dates of ozone exceedances at the monitors 
referenced in Table LA-1 of this action. 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.'' Since 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. 
LDEQ's HYSPLIT back trajectory analysis for 2016, 2017, and 2018 showed 
that on high ozone days in Texas at the receptors identified by the EPA 
in the 2018 memorandum that 28% of the trajectories passed through 
Louisiana. LDEQ proffered that some of these back trajectories did not 
pass directly over areas with emissions but did not consider that the 
back trajectories only represent a centerline and there are areas on 
either side of the centerline that would be contributing areas. LDEQ's 
trajectory analysis confirmed that Louisiana is an upwind area for the 
receptors in Texas 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).
    Photochemical modeling simulations for ozone interstate transport 
assessment is 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. For the 2015 ozone NAAQS 
interstate transport analysis, the EPA performed nationwide, state-
level ozone source apportionment modeling using CAMx to quantify the 
contribution of NOX and VOC emissions from all sources in 
each state to project 2023 ozone concentrations at ozone monitoring 
sites. Detailed information for the EPA's modeling may be found in the 
Air Quality Modeling TSD in Docket No. EPA-HQ-OAR-2021-0663.
    LDEQ concluded in the SIP submittal, citing an article \72\ 
published in 2012, that the use of 1 percent of the standard for 
modeled contribution as the sole definition of significant contribution 
is inappropriate for the 2015 ozone NAAQS. LDEQ's reasoning for this 
conclusion is that the more stringent 0.7 ppb threshold ``is an order 
of magnitude smaller than the biases and errors typically documented 
for regional photochemical modeling.'' First, the EPA does not use the 
1 percent threshold as the sole definition of significant contribution; 
at Step 2 of the analysis, the 1 percent threshold is used to identify 
contributions between states and downwind problem areas for further 
analysis at Step 3. Second, photochemical transport models such as CAMx 
have been extensively peer reviewed and used to support SIPs and 
explore relationships between inputs and air quality impacts in the 
U.S. and beyond. The EPA works to continually develop and update both 
the guidelines

[[Page 9816]]

on using modeling results and the latest versions of photochemical 
model platforms to support scientific assessments and regulatory 
determinations. Prior to using photochemical modeling to support a 
regulatory assessment, a model performance evaluation is completed to 
establish a benchmark to assess how accurately the model predicts 
observed concentrations and to identify model limitations. The model 
performance evaluation provides a better understanding of the model's 
limitations and biases and serves as a diagnostic evaluation for 
further model development and improvement. As discussed in Section I of 
this document and the Air Quality Modeling TSD in Docket No. EPA-HQ-
OAR-2021-0663, the EPA follows the most recent established modeling 
guidance and provides with this action the updated modeling analysis 
based on the recent CAMx model update. By using the most recent 2016v2 
photochemical modeling enhancements (EPA 2016v2 modeling) results are 
more representative of the projected local and regional air quality as 
it is based on more recent emission estimates with fewer years between 
the base case year (2016) and the future year (2023). In addition, to 
reduce the impact of any potential biases or errors, the EPA uses the 
modeling results in a relative sense rather than rely on absolute model 
predictions.\73\
---------------------------------------------------------------------------

    \72\ Simon et al., supra FN 58.
    \73\ See ``Modeling Guidance for Demonstrating Air Quality Goals 
for Ozone, PM2.5 and Regional Haze'', Nov. 29, 2018, at 
101, available at https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf (``2018 Air Quality 
Modeling Guidance''). See also ``Draft Modeling Guidance for 
Demonstrating Attainment of Air Quality Goals for Ozone, 
PM2.5, and Regional Haze'', Dec. 3, 2014, at 97-98, 
available at https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf (``2014 Draft 
Air Quality Modeling Guidance'').
---------------------------------------------------------------------------

    Furthermore, it is not appropriate to compare the bias/error 
involved in the estimation of total ozone to the potential error in the 
estimation of the subset of ozone that is contributed by a single 
state. For example, on a specific day the modeled vs. monitored ozone 
value may differ by 2 ppb but that is relatively small percentage of 
the total modeled ozone, which for a receptor of interest would be on 
the order of 70 ppb. It would be unrealistic to assign all the 2 ppb, 
in the above example, to the estimated impact from a single state as 
the 2 ppb error would be the combination of the error from all sources 
of ozone that contribute to the total, including estimated impacts from 
other states, the home state of the receptor and natural background 
emissions.
    In sum, the EPA disagrees that the estimates of potential error in 
the models estimates of total ozone, call into question the use of 1 
percent as a threshold for linkage. As noted earlier, in the case of 
Louisiana, the difference between a 1 percent threshold and a 1 ppb 
threshold is irrelevant to the decision here because linkages are 
present at both threshold levels. As to Louisiana's conclusion that the 
impacts from Louisiana's emissions are not persistent, the contribution 
analysis is the average impact for at least 5 days and up to 10 days 
for the 2016 base period which is sufficiently persistent considering 
the first through fourth high monitored values set the monitored DV.
    We recognize that the results of the EPA (2011 and 2016 base year) 
modeling indicated different receptors and linkages at Steps 1 and 2 of 
the 4-Step interstate transport framework. These differing results 
regarding receptors and linkages can be affected by the varying 
meteorology from year to year, but we do not think the differing 
results means that the modeling or the EPA or the state's methodology 
for identifying receptors or linkages is inherently unreliable. Rather, 
these separate modeling runs all indicated: (1) That there are 
receptors that would struggle with nonattainment or maintenance in the 
future; and (2) that Louisiana is linked to some set of these 
receptors, even if the receptors and linkages differed from one another 
in their specifics (e.g., Louisiana was linked to a different set of 
receptors in one modeling run versus another). These results indicates 
that Louisiana's emissions were substantial enough to generate linkages 
at Steps 1 and 2 to at least some set of downwind receptors, under 
varying assumptions and meteorological conditions, even if the precise 
set of linkages changed between modeling runs.
4. Evaluation of Information Provided by LDEQ 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, 
LDEQ's SIP submission did not contain an evaluation of additional 
emission control opportunities (or establish that no additional 
controls are required), thus, no information was provided at Step 4. To 
the extent that LDEQ discussed emissions reductions, the State only 
provided a summary of existing already implemented enforceable control 
regulations. The EPA's 2016v2 modeling analyses have already accounted 
for the implementation of the regulations cited by LDEQ's submission--
including the CSAPR rulemakings and prior regional rulemakings--and 
even with those reductions in place, the modeling results consistently 
show receptors that are projected to be in nonattainment or to struggle 
with maintenance, and Louisiana contributing to those receptors. 
Relying only on the existing enforceable control regulations is 
insufficient to address the Louisiana air emission contributions to 
linked downwind air quality problems. As a result, the EPA proposes to 
disapprove LDEQ'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).
5. Conclusion
    Based on the EPA's evaluation of LDEQ's SIP submission, the EPA is 
proposing to find that LDEQ's November 13, 2019, SIP submission 
pertaining to interstate transport of air pollution 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 ozone NAAQS in any other state.

IV. Oklahoma SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission

A. Summary of ODEQ SIP Submission Addressing Interstate Transport of 
Air Pollution for the 2015 Ozone NAAQS

    On October 25, 2018, the Oklahoma Department of Environmental 
Quality (ODEQ) made a SIP submission addressing interstate transport of 
air pollution for the 2015 ozone NAAQS. The SIP submission provided 
ODEQ's analysis of their impact to downwind states using the EPA's 4-
Step framework and an analytic year of 2023 and concluded that 
emissions from Oklahoma will not contribute significantly to 
nonattainment or interfere with maintenance of the 2015 ozone NAAQS in 
other states.
    To identify downwind air quality problems that are linked to 
emissions

[[Page 9817]]

from Oklahoma and therefore warrant further review and analysis (Steps 
1 and 2), ODEQ used EPA interstate transport modeling results found in 
the March 2018 memorandum. The EPA modeling results projected: (1) An 
average DV and a maximum DV for the year 2023 for ozone monitors in the 
48 contiguous States and (2) the expected contribution from emissions 
in each state to the ozone concentrations at each ozone monitor.
    ODEQ used the information from the March 2018 EPA memorandum to 
identify six downwind nonattainment and maintenance receptors \74\ with 
a contribution from Oklahoma of 1 percent of the 2015 ozone NAAQS (0.70 
parts ppb) or greater. ODEQ then applied a 1 ppb threshold to remove 
from further analysis three receptors with a contribution from Oklahoma 
of less than 1 ppb. ODEQ noted that the possibility of using an 
alternative contribution threshold was one of the areas of flexibility 
identified in the March 2018 EPA memorandum and discussed further in 
the August 2018 EPA memorandum. To support its alternative contribution 
threshold, ODEQ referenced an EPA memorandum from April 17, 2018, which 
recommended a Significant Impact Level (SIL) for ozone of 1.0 ppb for 
proposed sources subject to the Prevention of Significant Deterioration 
(PSD) permitting program.\75\ Table OK-1 provides information on the 
six nonattainment and maintenance receptors identified by ODEQ, 
including the three receptors ODEQ identified for further analysis.
---------------------------------------------------------------------------

    \74\ Nonattainment receptors are monitoring sites that are 
anticipated to have problems attaining and maintaining the 2015 
ozone NAAQS (i.e., average projected 2023 DV greater than 70.9 ppb). 
Maintenance receptors are monitoring sites that are anticipated to 
have problems maintaining the 2015 ozone NAAQS (i.e., maximum 
projected 2023 DV greater than 70.9 ppb).
    \75\ See FN 32.

 Table OK-1--Nonattainment and Maintenance Receptors Identified by ODEQ Based on the EPA's March 2018 Memorandum
----------------------------------------------------------------------------------------------------------------
                                                                           Oklahoma
   Receptor (site ID, county, state)     2023  average   2023  maximum   contribution      ODEQ's step 1 and 2
                                           DV (ppb)        DV (ppb)          (ppb)            determination
----------------------------------------------------------------------------------------------------------------
260050003, Allegan, MI................            69.0            71.7            1.31  Maintenance receptor
                                                                                         identified for further
                                                                                         analysis.
481210034, Denton, TX.................            69.7            72.0            1.23  Maintenance receptor
                                                                                         identified for further
                                                                                         analysis.
484392003, Tarrant, TX................            72.5            74.8            1.71  Nonattainment receptor
                                                                                         identified for further
                                                                                         analysis.
480391004, Brazoria, TX...............            74.0            74.9            0.90  Nonattainment receptor
                                                                                         with contribution less
                                                                                         than 1 ppb; no further
                                                                                         analysis.
550790085, Milwaukee, WI..............            71.2            73.0            0.76  Nonattainment receptor
                                                                                         with contribution less
                                                                                         than 1 ppb; no further
                                                                                         analysis.
551170006, Sheboygan, WI..............            72.8            75.1            0.95  Nonattainment receptor
                                                                                         with contribution less
                                                                                         than 1 ppb; no further
                                                                                         analysis.
----------------------------------------------------------------------------------------------------------------

    ODEQ further evaluated the two Texas receptors (Tarrant County and 
Denton County) and the receptor in Allegan County, MI. ODEQ did not 
further evaluate the contribution from Oklahoma to the receptors in 
Brazoria County, TX, Milwaukee County, WI, and Sheboygan County, WI 
because the contributions from Oklahoma to these receptors were less 
than 1 ppb.
    For the two remaining Texas receptors, ODEQ returned to Steps 1 and 
2 of the 4-Step interstate transport framework using modeling performed 
by the Texas Commission on Environmental Quality (TCEQ). The TCEQ 
modeling results are included in the Regional docket for this action 
(Docket ID No. EPA-R06-OAR-2021-0801). ODEQ stated that the primary 
difference between the EPA modeling and the TCEQ modeling is that the 
TCEQ modeling used 2012 as the ``base year'' for assessing interstate 
transport of ozone pollution in 2023 whereas the EPA modeling used 2011 
as the base year for that assessment. In addition, the ODEQ stated that 
TCEQ used a method different from the EPA's method to identify whether 
a monitor would have trouble maintaining the 2015 ozone NAAQS (i.e., a 
maintenance receptor). To identify maintenance receptors, TCEQ 
calculated a ``maintenance future year (fy) DV'' by projecting to 2023 
the most recent regulatory DV that contains the base year (i.e., the 
2012-2014 DV for a base year of 2012), whereas the EPA's methodology 
for identifying maintenance receptors uses the maximum DV, which is the 
highest monitored DV from among the three DVs that contain the base 
year (i.e., the 2009-2011, 2010-2012 and 2011-2013 DVs for a base year 
of 2011).
    To assess whether Oklahoma is linked to nonattainment of the 2015 
ozone standard at the Denton and Tarrant County sites, ODEQ switched to 
using the 2023 average DV projected by TCEQ rather than the EPA's 
projected average DVs. The ODEQ noted that the projected 2023 average 
DV was 68 ppb for the Denton County site and 66 ppb for the Tarrant 
County site based on the TCEQ modeling. ODEQ then claimed that these 
results demonstrate that both of these sites are in attainment in 2023.
    To assess whether Oklahoma interferes with maintenance of the 2015 
ozone standard at these two sites, ODEQ used (1) the Texas method to 
calculate a ``maintenance future year DV'' for 2023 and (2) a maximum 
DV calculated using the highest of the three base year DVs multiplied 
by a relative response factor derived from TCEQ's modeling (i.e., EPA's 
method for identifying maintenance receptors but using TCEQ's modeling 
rather than EPA's modeling). This assessment is summarized in Table OK-
2.

[[Page 9818]]



      Table OK-2--Summary of TCEQ Modeling (2012 Base Period) Used by ODEQ To Assess Maintenance Receptors
----------------------------------------------------------------------------------------------------------------
                                                         2023  maximum  Maintenance DV
   Receptor (site ID, county, state)     2023  average   DV (ppb) (EPA    (ppb)(TCEQ    ODEQ's step 1 and step 2
                                           DV (ppb)        method)*         method)           determination
----------------------------------------------------------------------------------------------------------------
481210034 Denton, TX..................              68            70.7            65.9  Future DVs project no
                                                                                         attainment or
                                                                                         maintenance problems.
484392003 Tarrant, TX.................              66            69.9            62.4  Future DVs project no
                                                                                         attainment or
                                                                                         maintenance problems.
----------------------------------------------------------------------------------------------------------------
* These values are not based on calculations made by the EPA. ODEQ calculated these values by using the maximum
  DV for the 2010-2014 5-year period (i.e., the highest of the DVs in 2012, 2013, and 2014) multiplied by
  relative response factor for the receptor obtained from TCEQ's modeling.

    ODEQ noted in their assessment that based on the TCEQ modeling and 
TCEQ definition of maintenance receptor, it is expected that the Denton 
and Tarrant sites will not experience nonattainment or maintenance 
problems in 2023. Because ODEQ claimed that the Denton and Tarrant 
County sites will not be nonattainment or maintenance receptors in 
2023, ODEQ did not analyze potential emissions reductions at Step 3 to 
address its contribution to these two sites.
    With respect to the remaining receptor at Allegan County, MI, ODEQ 
provided an analysis of projected 2023 DVs for this site and 
information on emissions trends in Oklahoma to assert that emissions 
from Oklahoma do not significantly contribute to nonattainment or 
interfere with maintenance of the 2015 ozone NAAQS at the Allegan 
County, MI site.
    ODEQ noted that (1) the DV for the Allegan County, MI site has had 
a substantial reduction in the last 6 years from 84 ppb in 2012 to 73 
ppb in 2017, a 1.8 ppb per year decrease, on average and (2) the 
Allegan County, MI site is substantially influenced by mobile sources 
from the Chicago area and these emissions are expected to be greatly 
reduced in the near future, by roughly a 1 ppb per year decrease, 
leading to attainment of the 2015 ozone standard. The ODEQ then 
calculated a projected 2023 maintenance DV for the Allegan County, MI 
site using the EPA's method, but assuming that the base year was 2016 
rather than 2011, as in the EPA's modeling or 2012 as in the TCEQ 
modeling. The ODEQ noted that the maximum DV in the 2016-centered base 
period (i.e., 2014-2016, 2015-2017, and 2016-2018) was 75 ppb at the 
Allegan County, Michigan site. The ODEQ then calculated the difference 
between the 2011-centered base period maximum DV of 86 ppb and the 2023 
projected maximum DV of 71.7 ppb, using data from the EPA's modeling. 
The ODEQ calculated a ``ppb per year'' reduction of 1.1917 ppb per 
year, based on the 14.3 ppb difference between the 2011-centered and 
2023 maximum DVs over the 12 years from 2011 to 2023. Finally, ODEQ 
applied the 1.1917 ppb per year value to the 2016-centered maximum DV 
of 75 ppb to estimate a 2023 maximum DV of 66.66 ppb.
    ODEQ also asserted that the relatively small contribution from 
Oklahoma (3% of total upwind state contributions) combined with the 
distance between Oklahoma sources and the Allegan County, Michigan 
site, warrants a focus on nearby states with greater proportional 
contributions as the most prudent approach to addressing interstate 
transport of ozone precursors for this receptor.
    The ODEQ also provided the anthropogenic NOX and VOC 
data of Oklahoma's emissions from EPA's emission trends and modeling to 
demonstrate an anticipated substantial reduction of NOX and 
VOC from 2011 to 2023: (1) Reductions of NOX from 405,000 to 
235,000 tons per year and (2) reductions of VOC from 414,000 to 295,000 
tons per year.\76\ ODEQ noted these reductions should result in 
considerable reductions in ozone concentrations. The ODEQ stated that 
due to the emissions reductions required by rules like CSAPR, the 2016 
CSAPR Update, and the regional haze requirements, the NOX 
emissions from electric generation in Oklahoma have dropped 
significantly during the ozone season from 38,285 tons per year in 2011 
to 10,435 tons per year in 2017. ODEQ also stated that changes in the 
Southwest Power Pool \77\, building of additional windfarms, and 
electric utilities installing solar generation facilities have led to 
Oklahoma NOX emissions reductions; and that any additional 
NOX reductions from the electric generation section would 
require more costly emissions controls. ODEQ concluded that the 
existing controls in Oklahoma have resulted in significant decreases in 
ozone DVs in Oklahoma and that additional controls would not be cost-
effective. Given their conclusions, ODEQ did not adopt additional 
controls to reduce ozone precursor emissions (Step 4).
---------------------------------------------------------------------------

    \76\ ODEQ used the EPA's emissions data shared alongside the 
October 2018 memorandum, ``state-
sector_annual_emissions_data_1.xlsx'' available at https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.
    \77\ The Southwest Power Pool is a regional electric 
transmission organization regulated by the Federal Energy Regulatory 
Commission whose purpose is promoting efficiency and reliability in 
the operation and planning of the electric transmission grid and 
ensuring non-discrimination in the provision of electric 
transmission services. It manages electric transmission in portions 
of fourteen states: Arkansas, Iowa, Kansas, Louisiana, Minnesota, 
Missouri, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, 
South Dakota, Texas and Wyoming. See 18 CFR 35.34 and https://www.ferc.gov/electric-power-markets.
---------------------------------------------------------------------------

B. EPA Evaluation of the ODEQ SIP Submission

    The EPA is proposing to find that ODEQ's October 25, 2018, SIP 
submission does not demonstrate that the State's obligations with 
respect to prohibiting emissions that contribute significantly to 
nonattainment or interfere with maintenance of the 2015 ozone NAAQS in 
any other state based on the EPA's evaluation of the SIP submission 
using the 4-Step interstate transport framework have been met. The EPA 
is therefore proposing to disapprove ODEQ's submission.
1. Evaluation of Information Provided by ODEQ Regarding Steps 1 and 2
    As noted earlier, ODEQ first used the information from the EPA's 
March 2018 memorandum to identify nonattainment and maintenance 
receptors with a contribution from Oklahoma of 0.70 ppb or greater 
(i.e., ODEQ identified receptors that would be deemed nonattainment and 
maintenance receptors under the EPA's methodology for Steps 1 and 2). 
ODEQ then utilized a 1 ppb threshold and elected not to further analyze 
any receptors to which it did not contribute greater than 1 ppb.

[[Page 9819]]

ODEQ provided further evaluation of the State's emissions to those 
receptors to which Oklahoma contributes greater than 1 ppb (i.e., 
Allegan County, MI, Denton County, TX and Tarrant County, TX).
    As discussed in the EPA's August 2018 memorandum, with appropriate 
additional analysis it may be reasonable for states to use a 1 ppb 
contribution threshold, as an alternative to a 1 percent threshold, at 
Step 2 of the 4-Step interstate transport framework, for the purposes 
of identifying linkages to downwind receptors. However, the EPA's 
August 2018 memorandum provided that whether or not a 1 ppb threshold 
is appropriate must be based on an evaluation of state-specific 
circumstances, and no such evaluation was included in the ODEQ's 
submittal. Instead, ODEQ's SIP submission justified the State's use of 
a 1 ppb threshold based on the threshold's use in the SILs 
Guidance.\78\ ODEQ did not explain the relevance of the SILs Guidance 
to Oklahoma's statutory obligation under the interstate transport 
provision. The SILs Guidance relates to a different provision of the 
CAA regarding implementation of the prevention of significant 
deterioration (PSD) permitting program, i.e., a program that applies in 
areas that have been designated attainment of the NAAQS, and it is not 
applicable to the interstate transport provision, which requires states 
to eliminate emissions that contribute significantly or interfere with 
maintenance of the NAAQS at known, ongoing, or projected air quality 
problem areas in other states. The EPA does not, in this action, agree 
that the State has justified its application of the 1 ppb threshold.
---------------------------------------------------------------------------

    \78\ See FN 32.
---------------------------------------------------------------------------

    Additionally, the EPA here shares further evaluation of its 
experience since the issuance of the August 2018 memorandum regarding 
use of alternative thresholds at Step 2. This experience leads the 
Agency to now believe it may not be appropriate to continue to attempt 
to recognize alternative contribution thresholds at Step 2. The August 
2018 memorandum stated that ``it may be reasonable and appropriate'' 
for states to rely on an alternative threshold of 1 ppb threshold at 
Step 2. (The memorandum also indicated that any higher alternative 
threshold, such as 2 ppb, would likely not be appropriate.) However, 
the EPA also provided that ``air agencies should consider whether the 
recommendations in this guidance are appropriate for each situation.'' 
Following receipt and review of 49 interstate transport SIP submittals 
for the 2015 ozone NAAQS, the EPA's experience has been that nearly 
every state that attempted to rely on a 1 ppb threshold did not provide 
sufficient information and analysis to support a determination that an 
alternative threshold was reasonable or appropriate for that state.
    For instance, in nearly all submittals, the states did not provide 
the EPA with analysis specific to their state or the receptors to which 
its emissions are potentially linked. In one case, the proposed 
approval of Iowa's SIP submittal, the EPA expended its own resources to 
attempt to supplement the information submitted by the state, in order 
to more thoroughly evaluate the state-specific circumstances that could 
support approval. \79\ It was at the EPA's sole discretion to perform 
this analysis in support of the state's submittal, and the Agency is 
not obligated to conduct supplemental analysis to fill the gaps 
whenever it believes a state's analysis is insufficient. The Agency no 
longer intends to undertake supplemental analysis of SIP submittals 
with respect to alternative thresholds at Step 2 for purposes of the 
2015 ozone NAAQS.
---------------------------------------------------------------------------

    \79\ ``Air Plan Approval; Iowa; Infrastructure State 
Implementation Plan Requirements for the 2015 Ozone National Ambient 
Air Quality Standard'', 85 FR 12232 (March 2, 2020). The agency 
received adverse comments on this proposed approval and has not 
taken final action with respect to this proposal.
---------------------------------------------------------------------------

    Furthermore, the EPA's experience since 2018 is that allowing for 
alternative Step 2 thresholds may be impractical or otherwise 
inadvisable for a number of additional policy reasons. For a regional 
air pollutant such as ozone, consistency in requirements and 
expectations across all states is essential. Based on its review of 
submittals to-date and after further consideration of the policy 
implications of attempting to recognize an alternative Step 2 threshold 
for certain states, the Agency now believes the attempted use of 
different thresholds at Step 2 with respect to the 2015 ozone NAAQS 
raises substantial policy consistency and practical implementation 
concerns.\80\ The availability of different thresholds at Step 2 has 
the potential to result in inconsistent application of interstate 
transport obligations based solely on the strength of a state's SIP 
submittal at Step 2 of the 4-Step interstate transport framework. From 
the perspective of ensuring effective regional implementation of 
interstate transport obligations, the more important analysis is the 
evaluation of the emissions reductions needed, if any, to address a 
state's significant contribution after consideration of a multifactor 
analysis at Step 3, including a detailed evaluation that considers air 
quality factors and cost. Where alternative thresholds for purposes of 
Step 2 may be ``similar'' in terms of capturing the relative amount of 
upwind contribution (as described in the August 2018 memorandum), 
nonetheless, use of an alternative threshold would allow certain states 
to avoid further evaluation of potential emission controls while other 
states must proceed to a Step 3 analysis. This can create significant 
equity and consistency problems among states.
---------------------------------------------------------------------------

    \80\ We note that Congress has placed on the EPA a general 
obligation to ensure the requirements of the CAA are implemented 
consistently across states and regions. See CAA section 301(a)(2). 
Where the management and regulation of interstate pollution levels 
spanning many states is at stake, consistency in application of CAA 
requirements is paramount.
---------------------------------------------------------------------------

    Further, it is not clear that national ozone transport policy is 
best served by allowing for less stringent thresholds at Step 2. The 
EPA recognized in the August 2018 memorandum that there was some 
similarity in the amount of total upwind contribution captured (on a 
nationwide basis) between 1 percent and 1 ppb. However, the EPA notes 
that while this may be true in some sense, that is hardly a compelling 
basis to move to a 1 ppb threshold. Indeed, the 1 ppb threshold has the 
disadvantage of losing a certain amount of total upwind contribution 
for further evaluation at Step 3 (e.g., roughly seven percent of total 
upwind state contribution was lost according to the modeling underlying 
the August 2018 memorandum; \81\ in EPA 2016v2 modeling, the amount 
lost is five percent). Considering the core statutory objective of 
ensuring elimination of all significant contribution to nonattainment 
or interference of the NAAQS in other states and the broad, regional 
nature of the collective contribution problem with respect to ozone, 
there does not appear to be a compelling policy imperative in allowing 
some states to use a 1 ppb threshold while others rely on a 1 percent 
of NAAQS threshold.
---------------------------------------------------------------------------

    \81\ See August 2018 memorandum, at page 4.
---------------------------------------------------------------------------

    Consistency with past interstate transport actions such as CSAPR, 
and the CSAPR Update and Revised CSAPR Update rulemakings (which used a 
Step 2 threshold of 1 percent of the NAAQS for two less stringent ozone 
NAAQS), is also important. Continuing to use a 1 percent of NAAQS 
approach ensures that as the NAAQS are revised and made more stringent, 
an appropriate increase in stringency at Step 2 occurs, so as to ensure 
an appropriately larger amount of total upwind-state contribution is 
captured for purposes of

[[Page 9820]]

fully addressing interstate transport. Accord 76 FR 48237-38.
    Therefore, notwithstanding the August 2018 memorandum's recognition 
of the potential viability of alternative Step 2 thresholds, and in 
particular, a potentially applicable 1 ppb threshold, the EPA's 
experience since the issuance of that memorandum has revealed 
substantial programmatic and policy difficulties in attempting to 
implement this approach. Nonetheless, the EPA is not, at this time, 
rescinding the August 2018 memorandum. The basis for the EPA's proposed 
disapproval of ADEQ's SIP submission with respect to the Step 2 
analysis is, in the Agency's view, warranted even under the terms of 
the August 2018 memorandum. The EPA invites comment on this broader 
discussion of issues associated with alternative thresholds at Step 2. 
(See Supplementary Information section above for details and docket to 
submit comments). Depending on public comments received in relation to 
this action and further evaluation of this issue, the EPA may determine 
to rescind the 2018 memorandum in the future.
    In any case, as discussed in the following subsection, based on the 
EPA's most recent modeling, the State is projected to contribute 
greater than both the one percent and alternative 1 ppb thresholds at 
the Denton County, TX receptor, (Monitor ID. 481210034). Based on the 
EPA's modeling results included in the March 2018 memorandum, Oklahoma 
was also projected to contribute 1.23 ppb to the Denton County, TX 
receptor. (In the EPA 2016v2 modeling the Allegan County, MI and 
Tarrant County, TX receptors are not projected to have problems 
attaining or maintaining the 2015 ozone NAAQS). Even under ODEQ's own 
analysis, the State was linked to receptors with contributions 
exceeding 1 ppb. Therefore, based on Oklahoma's linkages greater than 1 
ppb to projected downwind nonattainment or maintenance receptors, the 
State's use of this alternative threshold at Step 2 of the 4-Step 
interstate framework is inconsequential to our proposed action on the 
state's SIP.
    In the remainder of this section, EPA evaluates ODEQ's conclusions 
that emissions from Oklahoma do not contribute to nonattainment or 
interfere with maintenance at receptors in Tarrant County, TX (Monitor 
ID. 484392003) and Denton County, TX (Monitor ID. 481210034). We 
evaluate ODEQ's conclusions as to the Allegan, MI (Monitor ID. 
260050003) in Section IV.B.3 of this action.
    With regard to the Denton County and Tarrant County, TX receptors 
cited in ODEQ's submission, ODEQ chose to rely on the TCEQ's modeling 
and methodology, instead of the EPA modeling, and trends in ozone DVs 
and emissions to conclude that these monitoring sites will be in 
attainment by 2023 and will not have a problem maintaining the 2015 
ozone NAAQS. As noted in Section IV.A of this action, ODEQ used 
modeling results from the TCEQ along with the TCEQ alternative method 
for identifying maintenance receptors to claim that using the TCEQ 
modeling and methods, the Denton County and Tarrant County monitors 
would not have a problem maintaining the NAAQS in 2023. The ODEQ 
supplemented that analysis by citing the downward trend in 
NOX and VOC emissions in Oklahoma. ODEQ also provided TCEQ 
modeling and emissions data for the Dallas-Fort Worth nonattainment 
area to show that mobile sources represent the largest emissions 
category in this area and that emissions from this sector have declined 
since 2005 and are expected to continue to decline in the future. As 
described in Table OK-2, ODEQ (1) provided the average 2023 DV for the 
Denton County, TX receptor from the TCEQ modeling and (2) used TCEQ 
modeling data with a 2012 base year to calculate a 2023 maintenance DV 
of 65.9 ppb (using the TCEQ methodology for identifying maintenance 
receptors) and a 2023 maximum DV of 70.7 ppb (using the EPA methodology 
for identifying maintenance receptors, combined with TCEQ's modeling 
results). ODEQ relied on this information, which is based on TCEQ 
modeling with a 2012 base year, to conclude that the Denton County, TX 
and Tarrant County, TX monitors would not have problems attaining and 
maintaining the 2015 ozone NAAQS.
    ODEQ's SIP submission (or TCEQ, to the extent that Oklahoma is 
merely incorporating and relying on Texas' submission) does not 
adequately explain or justify how relying on TCEQ's method for 
identifying maintenance receptors reasonably identifies areas that will 
have difficulty maintaining the NAAQS. EPA proposes to find that ODEQ 
has provided no sound technical basis (either on its own or through 
reliance on Texas) for how its chosen methodology gives meaning to the 
CAA's instruction that states submit interstate transport SIPs that 
prohibit their states' emissions from interfering with the maintenance 
of the NAAQS in another state.
    In North Carolina v. EPA, 531 F.3d 896, 909-11 (D.C. Cir. 2008), 
the D.C. Circuit rejected the EPA's CAIR on the basis that the EPA had 
not adequately given meaning to the phrase ``interfere with 
maintenance'' in the interstate transport provision. Specifically, 
North Carolina argued that it had counties that were projected to 
attain the NAAQS in the future analytic year, but were at risk of 
falling back into nonattainment due to interference from upwind 
sources, particularly given year-to-year variability in ozone levels. 
The court agreed, holding that the EPA's rule did not adequately 
protect ``[a]reas that find themselves barely meeting attainment.'' Id. 
at 910. Consequently, the EPA has developed a methodology, used in its 
2011 CSAPR and its 2016 CSAPR Update and Revised CSAPR Update, for 
identifying areas that may struggle to maintain the NAAQS. See 76 FR at 
48227-28. EPA's approach to addressing maintenance receptors was upheld 
in the EME Homer City litigation. See 795 F.3d 118, 136-37. It was also 
upheld in Wisconsin. 938 F.3d at 325-26. In Wisconsin, the court noted 
that four upwind states were linked only to maintenance receptors and 
rejected the argument that application of the same control level as EPA 
imposes for those states linked to nonattainment receptors was 
unreasonable or unlawful absent a particularized showing of 
overcontrol. Id. at 327.
    In order to explain the differences between TCEQ's and the EPA's 
methodology for identifying maintenance receptors, it is helpful to 
provide some additional context of how the EPA projects future air 
quality.
    The EPA's air quality modeling guidance has long recommended 
developing a base DV (i.e., the DV that will be used as a starting 
point to model and analyze for purposes of projecting future air 
quality concentrations) that is the average of three DVs spanning a 
five-year period, centered around one year for which an emissions 
inventory will be submitted (e.g., if 2011 was the base emissions 
inventory year, a state would use monitored values from 2009-2011, 
2010-2012, 2011-2013 as the starting point for projecting air quality 
concentrations in future years).\82\ The average of these three DVs is 
then multiplied by a relative response factor \83\ to generate an 
average DV for the future year.\84\ If a receptor's average

[[Page 9821]]

future year DV is greater than or equal to the level of the NAAQS, and 
the receptor has recent monitored data that violates the NAAQS, that 
receptor is considered a ``nonattainment'' receptor at Step 1. To 
identify maintenance receptors, the EPA's methodology looks to the 
highest DV of the three DVs used to calculate the 5-year weighted 
average DV (e.g., in the 2011 example, if 2009-2011 had the highest DV 
of 2009-2011, 2010-2012, and 2011-2013). The EPA then applies the same 
relative response factor to that highest DV to generate a projected 
future maximum DV. Where a receptor's maximum DV exceeds the level of 
the NAAQS, the EPA has deemed those receptors to be ``maintenance'' 
receptors. This methodology was designed to address the D.C. Circuit's 
holding that the CAA's ``interference with maintenance'' prong requires 
states and the EPA to protect areas that may struggle with maintaining 
the standard in the face of variable conditions.
---------------------------------------------------------------------------

    \82\ See FN 73.
    \83\ See FN 53.
    \84\ While it is not critical to this discussion, for purposes 
of explanation, the relative response factor is a fractional change 
that represents how ozone at a given receptor responds to changes in 
emissions when all other variables are constant. For more 
explanation of the RRF, please see 2018 Air Quality Modeling 
Guidance or 2014 Draft Air Quality Modeling Guidance.
---------------------------------------------------------------------------

    In its modeling, TCEQ adopted an identical approach to the EPA's 
for identifying nonattainment receptors--it looked at three sets of DVs 
over a five-year period and averaged those DVs to generate a base year 
DV. TCEQ then applied a relative response factor to that base year DV 
to project a receptor's average DV in the future year. For maintenance 
receptors, however, TCEQ elected not to examine variability in DVs over 
a five-year period by using the highest DV of the three DVs making up 
the base year DV. Instead, TCEQ (and by extension, ODEQ), used only the 
most recent DV of the three DVs, regardless of whether the most recent 
DV was highest or lowest. TCEQ's proffered explanation for using the 
most recent DV to identify maintenance receptors was that the latest DV 
``takes into consideration . . . any emissions reductions that might 
have occurred.'' \85\ TCEQ in its submission does not explain why or 
how this methodology identifies those areas that may be meeting the 
NAAQS or that may be projected to meet the NAAQS but may nevertheless 
struggle to maintain the NAAQS, given meteorological variability. In 
fact, because TCEQ's stated purpose in using the most recent DV was to 
capture more recent emissions reductions, Texas' methodology appears to 
be aimed at limiting receptors which could be identified as maintenance 
receptors, compared to the EPA's methodology, which was designed to 
identify those areas that might struggle to maintain the NAAQS in 
particularly ozone conducive conditions.
---------------------------------------------------------------------------

    \85\ TCEQ submission at 3-39 to 3-40, available in the Regional 
docket for this action (Docket ID No. EPA-R06-OAR-2021-0801).
---------------------------------------------------------------------------

    As discussed further in the EPA Region 6 TSD \86\ for this action, 
the EPA has reviewed the set of 21 receptors for which Texas had 
contributions of 0.7 ppb or more in the EPA's 2016 base year modeling 
analyses, or TCEQ's modeling (2012 base year), and evaluated the 
results of using TCEQ's alternate maintenance methodology. For these 21 
receptors, TCEQ's method resulted in 15 of the 21 2023 maintenance DVs 
predicted to be lower than the 2023 nonattainment DVs from the 
nonattainment methodology that uses the 5-year center weighted average. 
Of these 15 receptors, three receptors have 2023 maintenance DVs that 
are 3 ppb lower, five receptors have 2023 maintenance DVs that are 2 
ppb lower, and seven receptors have 2023 maintenance DVs that are 1 ppb 
lower. In comparison, using the EPA's maintenance methodology results 
in all 21 2023 maintenance DVs being equal or up to 4 ppb higher than 
the 2023 nonattainment DVs. Again, the EPA uses the average of the 
three DVs that contain the base year modeled for the nonattainment 
methodology and the maximum of these three DVs for the maintenance 
methodology. Because TCEQ's maintenance methodology of just using the 
most recent DV (2012-2014 DV) often results in maintenance DVs lower 
than the 2023 nonattainment DVs methodology results, the EPA finds that 
the TCEQ methodology is not adequately identifying conditions when a 
receptor would have more difficulty maintaining the standard. In fact, 
the TCEQ's method also identified one receptor in their SIP submission 
as a nonattainment receptor in 2023 that would not have been identified 
as a maintenance receptor, which further highlights the concern that 
TCEQ's method did not adequately identify areas that may struggle to 
maintain the standard. TCEQ did not address whether the three years 
that comprise the most recent design value (i.e., 2012, 2013, and 2014) 
had meteorological conditions highly conducive for formation of high 
ozone concentrations and thus would be an appropriate time period to 
assess whether area could have difficulty maintaining the standard and 
the EPA's analysis confirms that this time period is not highly 
conducive to ozone formation, at least for many receptors. The 
consequence of TCEQ's maintenance method is that it often results in 
lower DVs than the nonattainment method as demonstrated by our 
analysis, which indicates that it is often not considering conditions 
when an area would have difficulty maintaining the standard. Further, 
it is unreasonable to have a method that would not identify 
nonattainment receptors also as maintenance receptors.
---------------------------------------------------------------------------

    \86\ ``EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal 
Technical Support Document'' (EPA Region 6 2015 Ozone Transport SIP 
TSD.pdf) included in Docket ID No. EPA-R06-OAR-2021-0801.
---------------------------------------------------------------------------

    Again, EPA also assessed a number of monitored DV trends that were 
provided in TCEQ's SIP and previous TCEQ attainment demonstration SIPs 
indicating that there are at times large annual fluctuations upward 
from year to year in monitored DVs (sometimes 2-3 ppb increase in one 
year) that are due to variations in meteorology. Neither TCEQ nor ODEQ 
addressed in their SIP submissions whether the three years that 
comprise the most recent DV (i.e., 2012, 2013, and 2014) had 
meteorological conditions conducive for formation of high ozone 
concentrations. On the other hand, the EPA methodology can identify 
variations in ozone levels that might result in difficulty in 
maintaining the standard over a longer period of time. The TCEQ method 
will only identify areas that have difficulty maintaining the standard 
for a single design value period and, as a result, does not address the 
meteorological variability issue sufficiently.
    In its SIP submittal, ODEQ contended that, based on TCEQ's use of a 
2012 base year, and using TCEQ's air quality modeling, even if Texas 
had used the EPA's method of identifying maintenance receptors, the 
projected maximum DV for the Denton County and Tarrant County receptors 
would be 70.7 ppb and 69.9 ppb, respectively, which are considered to 
be in attainment of the 2015 ozone NAAQS in 2023. However, this 
conclusion relied upon a relative response factor derived from the TCEQ 
modeling and TCEQ's modeling results, which are discussed in more 
detail in Section V of this action and in the EPA Region 6 TSD.\87\ 
TCEQ's modeled projections for 2023 including nonattainment and 
maintenance values (using either TCEQ' or EPA's methodology) are much 
lower than recent monitored values (2018-2020 DV and preliminary 2019-
2021 DVs) \88\ for

[[Page 9822]]

many monitors and the amount of further DV reductions needed to match 
TCEQ's modeling is more than is reasonably expected to occur for many 
monitors/receptors. This underestimation of future DVs results in mis-
identifying these two receptors and other receptors as not being 
nonattainment or maintenance receptors. Specifically, these two 
receptors would need to have at least a 3-4 ppb decrease in the next 2-
3 years just to attain the 2015 Ozone NAAQS in 2023. As discussed in 
the EPA Region 6 TSD, TCEQ's previous DFW Attainment Demonstration SIP 
includes long-term DV trends analysis that indicates that DFW DVs 
decrease approximately 1 ppb per year.\89\ Moreover, as discussed in 
Section IV.B.2 of this action, the EPA's updated modeling, which relies 
upon more recent data and the latest information on emissions 
reductions, indicates that the maximum design value in 2023 for the 
Denton County receptor is 72.2 ppb. Recent monitored air quality data 
at the Denton receptor are consistent with the EPA's projections that 
this is an area that will struggle to maintain the 2015 ozone NAAQS in 
2023; the 2020 DV for Denton was 72 ppb.\90\
---------------------------------------------------------------------------

    \87\ Id.
    \88\ Monitoring data from the EPA's Air Quality System (AQS) 
(https://www.epa.gov/aqs). 2021 monitoring data is preliminary and 
still has to undergo Quality Assurance/Quality Control analysis and 
be certified by the State of Texas, submitted to EPA, and reviewed 
and concurred on by EPA. 2018-2020 DVs are 72 ppb and 73 ppb at the 
Denton County and Tarrant County monitors/receptors respectively. 
Preliminary 2019-2021 DVs are 74 ppb and 72 ppb at the Denton County 
and Tarrant County monitors/receptors respectively.
    \89\ EPA also analyzed trends using AQS data, See EPA Region 6 
TSD.
    \90\ DVs 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.
---------------------------------------------------------------------------

    Finally, in its submittal, ODEQ pointed to the significant 
reductions in emissions that have occurred in the State, but the EPA 
believes these reductions have already been accounted for in the most 
recent modeling; therefore, even with these reductions, the Denton 
County, TX receptor is projected to struggle with maintenance of the 
2015 ozone NAAQS in 2023.
2. Results of the EPA's Step 1 and Step 2 Modeling and Findings for 
Oklahoma
    As described in Section I of this action, the EPA performed air 
quality modeling using the 2016v2 platform to project DVs and 
contributions for 2023. This data was examined to determine if Oklahoma 
contributes at or above the threshold of 1 percent of the 2015 ozone 
NAAQS (0.70 ppb) to any downwind nonattainment or maintenance receptor. 
As shown in Table OK-3, the most recent modeling data \91\ indicate 
that in 2023, emissions from Oklahoma contribute greater than one 
percent of the standard to maintenance-only receptors in Denton County, 
TX and in Cook County, IL. Oklahoma is not linked to any nonattainment 
receptors in EPA's most recent modeling (EPA 2016v2 modeling). 
Therefore, based on the EPA's evaluation of the information submitted 
by ODEQ and based on the EPA's most recent modeling results for 2023, 
the EPA proposes to find that Oklahoma 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.
---------------------------------------------------------------------------

    \91\ 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 above. That modeling showed that 
Oklahoma 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 ``Ozone DVs And Contributions 
Revised CSAPR Update.xlsx'' in Docket ID No. EPA-HQ-OAR-2021-0663.

Table OK-3--Projected Nonattainment and Maintenance Receptors With Oklahoma Linkages in 2023 Based on EPA 2016v2
                                                    Modeling
----------------------------------------------------------------------------------------------------------------
                                                                                                     Oklahoma
  Receptor (site ID, county,     Nonattainment/       2020 DV      2023  average   2023  maximum   contribution
            state)                 maintenance                       DV (ppb)        DV (ppb)          (ppb)
----------------------------------------------------------------------------------------------------------------
481210034, Denton, TX.........  Maintenance.....              72            70.4            72.2            1.19
170310032, Cook, IL...........  Maintenance.....              74            69.8            72.4            0.75
----------------------------------------------------------------------------------------------------------------

3. Evaluation of Information Provided by ODEQ 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 contribute significantly to nonattainment or interfere 
with maintenance and, thus, must be eliminated under CAA section 
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be 
deemed ``significant'' and therefore prohibited, states generally 
should prepare an accounting of sources and other emissions activity 
for relevant pollutants and assess potential, additional emissions 
reduction opportunities and resulting downwind air quality 
improvements. The EPA has consistently applied this general approach 
(i.e., Step 3 of the 4-Step interstate transport framework) when 
identifying emissions contributions that the Agency has determined to 
be ``significant'' (or interfere with maintenance) in each of its prior 
Federal, regional ozone transport rulemakings, and this interpretation 
of the statute has been upheld by the Supreme Court. See EME Homer 
City, 572 U.S. at 519. 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. ODEQ did not conduct 
such an analysis in their SIP submission.
    As noted earlier, ODEQ provided some data on emissions and already 
implemented emissions reductions for sources in Oklahoma and stated 
that the 2016 CSAPR Update is the only reasonable control warranted 
based on Oklahoma's limited contributions to the Michigan and Texas 
receptors. Thus, Oklahoma relied on its EGUs being subject to the CSAPR 
Update (which reflected a stringency at the nominal marginal cost 
threshold of $1400/ton (2011$) for the 2008 ozone NAAQS) to argue that 
it had already implemented all cost-effective emissions reductions, and 
had no additional statutory

[[Page 9823]]

obligation to prohibit emissions under CAA section 110(a)(2)(D)(i)(I) 
with respect to the 2015 ozone NAAQS.
    The EPA disagrees with ODEQ's conclusions for the following 
reasons: First, the CSAPR Update did not regulate non-electric 
generating units, and thus this analysis is incomplete. See Wisconsin, 
938 F.3d at 318-20. Second, relying on the CSAPR Update's (or any other 
CAA program's) determination of cost-effectiveness without further Step 
3 analysis is not approvable. Cost-effectiveness must be assessed in 
the context of the specific CAA program; assessing cost-effectiveness 
in the context of 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 established a benchmark cost-effectiveness value for 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 under this NAAQS to reflect higher marginal 
control costs. As such, the marginal cost threshold of $1,400/ton for 
the CSAPR Update (which addresses the 2008 ozone NAAQS and is in 2011$) 
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.
    In addition, the most recent EPA modeling captures all existing 
CSAPR trading programs in the baseline, and that modeling confirms that 
these control programs were not sufficient to eliminate Oklahoma's 
linkage at Steps 1 and 2 under the 2015 ozone NAAQS. The State was 
therefore obligated at Step 3 to assess additional control measures 
using a multifactor analysis.
    Finally, relying on a FIP at Step 3 is per se not approvable if the 
state has not adopted that program into its SIP and instead continues 
to rely on the FIP. States may not rely on FIP measures to meet SIP 
requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] shall . . 
. contain adequate provisions . . . .''). See also CAA section 
110(a)(2)(A); Committee for a Better Arvin v. 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).
    In addition, ODEQ's submission included a weight of evidence 
evaluation of its contribution to the Allegan County, MI receptor to 
conclude that it does not contribute significantly to nonattainment or 
maintenance at the receptor.
    The EPA disagrees with respect to ODEQ's assertion regarding the 
relatively small contribution of emissions from Oklahoma to the Allegan 
County, MI receptor compared to emissions from other upwind states such 
as Illinois. Whether emissions from other states or 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 contributing significantly 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.
    Further, the court in Wisconsin explained 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. Indeed, the D.C. Circuit in Wisconsin 
specifically rejected petitioner arguments suggesting that upwind 
states should be excused from interstate transport obligations on the 
basis that some other sources of emissions (whether international or 
another upwind state) could be considered the ``but-for'' cause of 
downwind air quality problem. 938 F.3dat 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 
at 324. The court explained that ``an upwind state can `contribute' to 
downwind nonattainment even if its emissions are not the but-for 
cause.'' Id.at 324-325. See also Catawba County v. EPA, 571 F.3d 20, 39 
(D.C. Cir. 2009) (rejecting the argument ``that `significantly 
contribute' unambiguously means `strictly cause''' because there is 
``no reason why the statute precludes EPA from determining that [an] 
addition of [pollutant] into the atmosphere is significant even though 
a nearby county's nonattainment problem would still persist in its 
absence''); Miss. Comm'n on Envtl. Quality v. EPA,790 F.3d 138, 163 n. 
12 (D.C. Cir. 2015) (observing that the argument the ``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 other upwind states also contribute some 
amount of pollution to the same receptors to which the state is linked.
    As explained in Section IV.A of this action, ODEQ's weight of 
evidence also concluded that the Allegan receptor would be attaining 
the NAAQS in 2023 based on an analysis that assumed a projection of a 
linear reduction in DVs across a 12-year period (2011 to projected 2023 
values), and then applied that annual reduction (1.1917 ppb/year) to 
the receptor's 2016-centered base period maximum DV (75 ppb). The EPA 
does not necessarily agree that the assumptions made in Oklahoma's 
weight-of-evidence analysis are reasonable; however, because the 
updated modeling also shows that Allegan County, MI is no longer a 
receptor in 2023, we propose to find such assumptions are 
inconsequential to our action on Oklahoma's SIP.
    We recognize that the results of the EPA (2011 and 2016 base year) 
modeling indicated different receptors and linkages at Steps 1 and 2 of 
the 4-Step interstate transport framework. These differing results 
regarding receptors and linkages can be affected by the varying 
meteorology from year to year, but we do not think the differing 
results mean that the modeling or the EPA methodology for identifying 
receptors or linkages is inherently unreliable. Rather, these separate 
modeling runs all indicated: (1) That there are receptors that would 
struggle with nonattainment or maintenance in the future; and (2) that 
Oklahoma was linked to some set of these receptors, even if the 
receptors and linkages differed from one another in their specifics 
(e.g., Oklahoma was linked to a different set of receptors in one 
modeling run versus another). These results indicate that emissions 
from Oklahoma are substantial enough to generate linkages at Steps 1 
and 2 to at least some downwind receptors, under varying assumptions 
and meteorological conditions, even if the precise set of linkages 
changed between modeling runs.
    We therefore propose that ODEQ was required to analyze emissions 
from the sources and other emissions activity from within the State to 
determine

[[Page 9824]]

whether its contributions were significant. Because ODEQ failed to 
perform this analysis, we propose to disapprove its submission.
4. Evaluation of Information Provided by ODEQ 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, 
ODEQ's SIP submission did not contain an evaluation of additional 
emission control opportunities (or establish that no additional 
controls are required), thus, no information was provided at Step 4. As 
a result, EPA proposes to disapprove ODEQ'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).
5. Conclusion
    Based on the EPA's evaluation of ODEQ's SIP submission, the EPA is 
proposing to find that the portion of ODEQ's SIP submission 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 which will interfere with maintenance 
of the 2015 ozone NAAQS in any other state.

C. Impact on Areas of Indian Country

    Following the U.S. Supreme Court decision in McGirt v Oklahoma, 140 
S Ct. 2452 (2020), the Governor of the State of Oklahoma requested 
approval under Section 10211(a) of the Safe, Accountable, Flexible, 
Efficient Transportation Equity Act of 2005: A Legacy for Users, Public 
Law 109-59, 119 Stat. 1144, 1937 (August 10, 2005) (``SAFETEA''), to 
administer in certain areas of Indian country (as defined at 18 U.S.C. 
1151) the State's environmental regulatory programs that were 
previously approved by the EPA for areas outside of Indian country. The 
State's request excluded certain areas of Indian country further 
described below. In addition, the State only sought approval to the 
extent that such approval is necessary for the State to administer a 
program in light of Oklahoma Dept. of Environmental Quality v. EPA, 740 
F.3d 185 (D.C. Cir. 2014).\92\
---------------------------------------------------------------------------

    \92\ In ODEQ v. EPA, the D.C. Circuit held that under the CAA, a 
state has the authority to implement a SIP in non-reservation areas 
of Indian country in the state, where there has been no 
demonstration of tribal jurisdiction. Under the D.C. Circuit's 
decision, the CAA does not provide authority to states to implement 
SIPs in Indian reservations. ODEQ did not, however, substantively 
address any request under the separate authority in Indian country 
provided specifically to Oklahoma under SAFETEA. That separate 
authority was not invoked until the State submitted its request 
under SAFETEA, and was not approved until the EPA's decision, 
described in this section, on October 1, 2020.
---------------------------------------------------------------------------

    On October 1, 2020, the EPA approved Oklahoma's SAFETEA request to 
administer all of the State's EPA-approved environmental regulatory 
programs, including the Oklahoma SIP, in the requested areas of Indian 
country. As requested by Oklahoma, the EPA's approval under SAFETEA 
does not include Indian country lands, including rights-of-way running 
through the same, that: (1) Qualify as Indian allotments, the Indian 
titles to which have not been extinguished, under 18 U.S.C. 1151(c); 
(2) are held in trust by the United States on behalf of an individual 
Indian or Tribe; or (3) are owned in fee by a Tribe, if the Tribe (a) 
acquired that fee title to such land, or an area that included such 
land, in accordance with a treaty with the United States to which such 
Tribe was a party, and (b) never allotted the land to a member or 
citizen of the Tribe.
    The EPA's approval under SAFETEA expressly provided that to the 
extent the EPA's prior approvals of Oklahoma's environmental programs 
excluded Indian country, any such exclusions are superseded for the 
geographic areas of Indian country covered by the EPA's approval of 
Oklahoma's SAFETEA request.\93\ The approval also provided that future 
revisions or amendments to Oklahoma's approved environmental regulatory 
programs would extend to the covered areas of Indian country (without 
any further need for additional requests under SAFETEA).\94\
---------------------------------------------------------------------------

    \93\ The EPA's prior approvals relating to Oklahoma's SIP 
frequently noted that the SIP was not approved to apply in areas of 
Indian country (consistent with the D.C. Circuit's decision in ODEQ 
v. EPA) located in the state. See, e.g., 85 FR 20178, 20180 (April 
10, 2020). Such prior expressed limitations are superseded by the 
EPA's approval of Oklahoma's SAFETEA request.
    \94\ On December 22, 2021, the EPA proposed to withdraw and 
reconsider the October 1, 2020 SAFETEA approval. See https://www.epa.gov/ok/proposed-withdrawal-and-reconsideration-and-supporting-information. The EPA is engaging in further consultation 
with tribal governments and expects to have discussions with the 
State of Oklahoma as part of this reconsideration. The EPA also 
notes that the October 1, 2020 approval is the subject of a pending 
challenge in Federal court. Pawnee Nation of Oklahoma v Regan, No. 
20-9635 (10th Cir.). The EPA may make further changes to the 
approval of Oklahoma's program to reflect the outcome of the 
proposed withdrawal and reconsideration of the October 1, 2020 
SAFETEA approval. To the extent any change occurs in the scope of 
Oklahoma's SIP authority in Indian country before the finalization 
of this proposed rule, such a change may affect the scope of the 
EPA's final action on the proposed rule.
---------------------------------------------------------------------------

    As explained earlier, the EPA is proposing to find that the portion 
of Oklahoma's SIP submission 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 which 
will contribute significantly to nonattainment or interfere with 
maintenance of the 2015 ozone NAAQS in any other state. Consistent with 
the D.C. Circuit's decision in ODEQ v. EPA and the EPA's October 1, 
2020, SAFETEA approval, this disapproval if finalized as proposed will 
extend to areas of Indian country in Oklahoma where the State has SIP 
planning authority.

V. Texas SIP Submission Addressing Interstate Transport of Air 
Pollution for the 2015 Ozone NAAQS and the EPA Evaluation of the SIP 
Submission

A. Summary of TCEQ SIP Submission Addressing Interstate Transport of 
Air Pollution for the 2015 Ozone NAAQS

    On August 17, 2018, the Texas Commission on Environmental Quality 
(TCEQ) made a SIP submission addressing interstate transport of air 
pollution for the 2015 ozone NAAQS. The SIP submission provided TCEQ's 
analysis of their impact to downwind states using a framework similar 
to EPA's 4-Step framework and concluded that emissions from Texas will 
not contribute significantly to nonattainment or interfere with 
maintenance of the 2015 ozone NAAQS in other states.
    In the submittal, TCEQ provided the steps they used to assess 
whether emissions from Texas contribute significantly to nonattainment 
or interfere with maintenance of the 2015 ozone NAAQS in other States: 
(1) Identify monitors projected to be in nonattainment or have 
maintenance issues in future year 2023; (2) identify for further review 
projected nonattainment and/or maintenance monitors in other states 
that are impacted by emissions from Texas; and (3) determine if 
emissions from Texas contribute significantly to nonattainment or 
interfere with maintenance at the monitors identified in TCEQ Step 2. 
TCEQ stated that their Step 1 is the same as EPA's Step 1 and that 
their Steps 2 and 3 are equivalent to EPA's Step 2. TCEQ used a

[[Page 9825]]

contribution threshold of one percent of the NAAQS (0.7 ppb) in their 
Step 2 analysis to identify nonattainmentand/or maintenance monitors in 
other states that are impacted by emissions from Texas. TCEQ further 
stated that EPA's Steps 3 and 4 are relevant only if emissions from 
Texas contribute significantly to nonattainment or interfere with 
maintenance at downwind monitors in another state. Because Texas TCEQ 
concluded that it has no such emissions, EPA's Steps 3 and 4 are not 
addressed in the SIP submission.
    To identify monitors projected to be in nonattainment or have 
maintenance issues in 2023, (EPA Step 1 and TCEQ Step 1), TCEQ 
conducted its own regional photochemical modeling using a 2012 base 
year. TCEQ's modeling and EPA's modeling differ in significant 
respects, which are discussed in detail in the EPA Region 6 2015 8-Hour 
Ozone Transport SIP Proposal Technical Support Document (EPA Region 6 
TSD).\95\ In particular, TCEQ used a 2012 base year, stating that (1) 
the year 2012 had above average temperatures across most of the U.S., 
except in some states in the southeast and (2) the year 2011, (which 
was used by the EPA in the NODA published on January 6, 2017 and the 
October 2017 updated modeling data for 2023),\96\ was a 
meteorologically anomalous year for Texas and surrounding states as it 
was the hottest year on record and the single-worst drought year 
recorded in Texas since 1895. TCEQ's modeling also used some different 
emissions estimates for the base year and future year 2023 emissions, 
including different future year emissions for EGUs. There were also 
some differences in methods used in the model results analysis and the 
model performance evaluation. TCEQ also used a different methodology 
than the EPA to identify monitors projected to be maintenance receptors 
in 2023. TCEQ used only the most recent DV containing the base year 
2012, (i.e., the monitored DV for 2012-2014), to project a 2023 
``maintenance DV'' for assessing whether a monitor would have 
maintenance issues. The EPA's methodology uses the maximum of the three 
consecutive regulatory DVs containing the base year, which is the 
highest monitored DV from among the three DVs that contain the 2011 
base year (i.e., the 2009-2011 DV, 2010-2012 DV or and 2011-2013 DV 
that all contain modeled base year of 2011), to project a 2023 maximum 
DV for assessing whether a monitor would have maintenance issues. Texas 
explained that it chose to define maintenance receptors in this way to 
capture more recent emission reductions. The SIP submittal also 
included a discussion of why TCEQ believes their approach for 
identifying maintenance receptors is appropriate. The TCEQ modeling and 
differences with the EPA modeling is discussed in detail in the EPA 
Region 6 TSD for this action.
---------------------------------------------------------------------------

    \95\ ``EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal 
Technical Support Document'' (EPA Region 6 2015 Ozone Transport SIP 
TSD.pdf) included in Docket ID No. EPA-R06-OAR-2021-0801.
    \96\ The NODA and the October 2017 modeling are discussed in 
Section I.C of this action.
---------------------------------------------------------------------------

    Based on their modeling, TCEQ provided: (1) A table of downwind 
receptors projected to be in nonattainment of the 2015 ozone NAAQS in 
2023 and have a contribution from Texas emissions at a threshold of 0.7 
ppb or greater and (2) a table of downwind maintenance receptors 
projected to have problems attaining and maintaining the 2015 ozone 
NAAQS in 2023 and have a contribution from Texas emissions at a 
threshold of 0.7 ppb or greater. TCEQ identified these receptors for 
further analysis. The nonattainment and maintenance receptors provided 
by TCEQ are listed in Table TX-1. TCEQ noted that except for Arapahoe 
County, CO (Monitor ID. 80050002) all the maintenance receptors are 
also nonattainment receptors.

 Table TX-1--Projected 2023 Nonattainment and Maintenance Receptors Identified by TCEQ Modeling Using 2012 Base
                                                      Year
----------------------------------------------------------------------------------------------------------------
                                                                                       2023
                                                                   2023  average  maintenance DV       Texas
                Receptor (site ID, county, state)                    DV (ppb)       (ppb) (TCEQ    contribution
                                                                                      method)          (ppb)
----------------------------------------------------------------------------------------------------------------
80350004, Douglas, CO...........................................              73              72            1.42
80590006, Jefferson, CO.........................................              72              73            1.26
80590011, Jefferson, CO.........................................              71              71            1.26
80690011, Larimer, CO...........................................              72              71            1.22
80050002, Arapahoe, CO..........................................             *70              71            1.15
40038001, Cochise, AZ...........................................              71            **69            1.06
60371201, Los Angeles, CA.......................................              80              78            0.76
60371701, Los Angeles, CA.......................................              80              82            0.72
60376012, Los Angeles, CA.......................................              87              86             0.9
60658001, Riverside, CA.........................................              88              85            0.73
60658005, Riverside, CA.........................................              84              83            0.71
60710001, San Bernardino, CA....................................              71              72            0.84
60710306, San Bernardino, CA....................................              76              77            0.81
60711004, San Bernardino, CA....................................              91              90            0.88
60714001, San Bernardino, CA....................................              82              79            0.86
60714003, San Bernardino, CA....................................              94              91            0.74
----------------------------------------------------------------------------------------------------------------
* TCEQ did not include this value in their SIP narrative (this cell was blank). The EPA obtained this value from
  data that was in TCEQ's spreadsheet of future 2023 DVs with state contributions.
** TCEQ did not provide this calculation. The EPA used TCEQ's modeling information to calculate this value using
  the Relative Response Factor in TCEQ spreadsheet of future 2023 DVs with state contributions and the monitor's
  2012-2014 DV (0.983 X 71 ppb, truncation applied).

    TCEQ also noted that in the EPA's 2017 Transport NODA, the EPA's 
modeling linked Texas to six receptors based on the receptors being 
identified as nonattainment or maintenance receptors and based on a 0.7 
ppb contribution threshold. TCEQ provided a table of those monitors 
along with the EPA and TCEQ modeling results for

[[Page 9826]]

those receptors (Table TX-2).\97\ TCEQ stated that the differences are 
due to changes the TCEQ made to modeling inputs (primarily the 
different base year of 2012 versus the EPA's 2011), analysis, and 
methodologies (primarily TCEQ's alternate maintenance receptor 
methodology), see the EPA Region 6 TSD included in the Regional docket 
for this action (Docket ID No. EPA-R06-OAR-2021-0801) for more details. 
With exception of the Jefferson County, CO receptor (Monitor ID. 
80590011) TCEQ did not further review its linkages to any of the 
receptors in Table TX-2.
---------------------------------------------------------------------------

    \97\ TCEQ SIP Submission, at page 3-49 (Table 3-12).

  Table TX-2--TCEQ Information on Receptors Linked to Texas by EPA Modeling in the Transport NODA Published on
                                                 January 6, 2017
----------------------------------------------------------------------------------------------------------------
                                                     EPA 2023        EPA Texas       TCEQ 2023      TCEQ Texas
        Receptor (site ID, county, state)           average DV     contribution     average DV     contribution
                                                       (ppb)           (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
260050003, Allegan, MI..........................            68.8            2.49              71            0.59
551170006, Sheboygan, WI........................            71.0            1.92              70            0.73
240251001, Harford, MD..........................            71.3            0.91              65            0.69
360850067, Richmond, NY.........................            71.2            0.77              62            0.67
361030002, Suffolk, NY..........................            71.3            0.71              67            0.63
80590011, Jefferson, CO.........................            69.7            1.03              71            1.26
----------------------------------------------------------------------------------------------------------------

    TCEQ then used a weight of evidence approach to assess whether 
emissions from Texas contribute significantly to nonattainment or 
interfere with maintenance at the receptors listed in Table TX-1. TCEQ 
stated that the Texas contribution to a receptor should be deemed 
``significant'' only if there is a persistent and consistent pattern of 
contribution on several days with elevated ozone. Consideration was 
given to factors such as DV trends, number of elevated ozone days, back 
trajectory analysis on elevated ozone days, modeled concentrations on 
future expected elevated ozone days, total interstate contributions at 
tagged monitors, and responsiveness of ozone to emissions from Texas. 
Based on their assessment, TCEQ concluded that emissions from Texas do 
not contribute significantly to nonattainment or interfere with 
maintenance of the 2015 ozone NAAQS at any downwind monitors. Our 
evaluation of the TCEQ submission is further discussed in Section V.B 
and in the EPA Region 6 TSD for this action.

B. EPA Evaluation of the TCEQ SIP Submission

    Based on the EPA's evaluation of the SIP submission, the EPA is 
proposing to find that TCEQ's August 17, 2018, SIP submission does not 
meet the State's obligations with respect to prohibiting emissions that 
contribute significantly to nonattainment or interfere with maintenance 
of the 2015 ozone NAAQS in any other state.
1. Evaluation of Information Provided by TCEQ Regarding Step 1
    As explained in Section I of this action, at Step 1 of the 4-Step 
interstate transport framework, the EPA identifies monitoring sites 
that are projected to have problems attaining and/or maintaining the 
NAAQS (i.e., nonattainment and maintenance receptors). In executing 
this step, TCEQ elected to rely on their own modeling and methodology 
for identifying receptors. The EPA is evaluating the TCEQ's modeling 
and methodology here at Step 1.
i. Evaluation of TCEQ's Methodology for Identifying Maintenance 
Receptors
    As discussed in Section V.A of this action, in addition to the use 
of an alternative modeling platform, TCEQ also created its own method 
for identifying maintenance receptors. TCEQ has not adequately 
explained or justified how its method for identifying maintenance 
receptors reasonably identifies areas that will have difficulty 
maintaining the NAAQS. The EPA proposes to find that TCEQ has not 
provided a sufficient technical basis for how its chosen methodology 
gives meaning to the CAA's instruction that states submit good neighbor 
SIPs that prohibit their states' emissions from interfering with the 
maintenance of the NAAQS in another state.
    In North Carolina v. EPA, 531 F.3d 896, 909-11 (D.C. Cir. 2008), 
the D.C. Circuit rejected the EPA's CAIR on the basis that the EPA had 
not adequately given meaning to the phrase ``interfere with 
maintenance'' in the good neighbor provision. Specifically, North 
Carolina argued that it had counties that were projected to attain the 
NAAQS in the future analytic year but were at risk of falling back into 
nonattainment due to interference from upwind sources, particularly 
given year-to-year variability in ozone levels. The court agreed, 
holding that the EPA's rule did not adequately protect ``[a]reas that 
find themselves barely meeting attainment.'' Id. at 910. Consequently, 
the EPA has developed a methodology, as described elsewhere in this 
action and used in its 2011 CSAPR and its 2016 CSAPR Update and Revised 
CSAPR Update, for identifying areas that may struggle to maintain the 
NAAQS. See 76 FR at 48227-28. The EPA's approach to addressing 
maintenance receptors was upheld in the EME Homer City litigation. See 
795 F.3d 118, 136-37. It was also upheld in Wisconsin. 938 F.3d at 325-
26. In Wisconsin, the court noted that four upwind states were linked 
only to maintenance receptors and rejected the argument that 
application of the same control level as the EPA imposes for those 
states linked to nonattainment receptors was unreasonable or unlawful 
absent a particularized showing of overcontrol. Id. at 327.
    To explain the differences between TCEQ's and the EPA's methodology 
for identifying maintenance receptors, it is helpful to provide some 
additional context of how the EPA projects future air quality. The 
EPA's air quality modeling guidance has long recommended developing a 
base design value (DV) \98\ (i.e., the design value that will be used 
as a starting point to model and analyze for purposes of projecting 
future air quality concentrations) that is the average of three DVs 
spanning a five-year period, centered around one year for which an 
emissions inventory will be submitted (e.g., if 2011 was the base 
emissions inventory year, a state would use monitored values from 2009-
2011, 2010-2012, 2011-2013 as the starting point for projecting air 
quality concentrations in future years).\99\ The

[[Page 9827]]

average of these three DVs is then multiplied by a relative response 
factor (RRF) \100\ to generate an average DV for the future year. If a 
receptor's average future year DV is greater than or equal to the level 
of the NAAQS, and the receptor has recent monitored data that violates 
the NAAQS, that receptor is considered a ``nonattainment'' receptor at 
Step 1. To identify maintenance receptors, the EPA's methodology looks 
to the highest DV of the three DVs used to calculate the 5-year 
weighted average design value (e.g., in the 2011 example, if 2009-2011 
had the highest design value of 2009-2011, 2010-2012, and 2011-2013). 
The EPA then applies the same relative response factor to that highest 
design value to generate a projected future maximum design value. Where 
a receptor's maximum design value exceeds the level of the NAAQS, the 
EPA has deemed those receptors to be ``maintenance'' receptors. This 
methodology was designed to address the D.C. Circuit's holding that the 
CAA's ``interference with maintenance'' prong requires states and the 
EPA to protect areas that may struggle with maintaining the standard in 
the face of inter-annual variability in ozone-conducive conditions.
---------------------------------------------------------------------------

    \98\ See FN 8.
    \99\ See FN 73.
    \100\ See FN 53.
---------------------------------------------------------------------------

    In its modeling, TCEQ adopted an identical approach to the EPA's 
for identifying nonattainment receptors--it looked at three sets of DVs 
over a five-year period and averaged those DVs to generate a base year 
DV. TCEQ then applied a relative response factor to that base year 
design value to project a receptor's average design value in the future 
year. For its maintenance receptors, however, TCEQ used only the most 
recent design value of the set of three DVs, regardless of whether the 
most recent design value was highest or lowest, instead of considering 
variability in conditions over a five-year period, or using the highest 
DV of the three DVs making up the base year design value. TCEQ's 
proffered explanation for using the most recent DV to identify 
maintenance receptors was that the latest DV ``takes into consideration 
. . . any emissions reductions that might have occurred.'' \101\ 
However, TCEQ in its submission does not explain how this methodology 
takes into account meteorological variability in identifying those 
areas that may be meeting the NAAQS or that may be projected to meet 
the NAAQS but may nevertheless struggle to maintain the NAAQS.
---------------------------------------------------------------------------

    \101\ TCEQ SIP submission at 3-39 to 3-40.
---------------------------------------------------------------------------

    TCEQ argued that the 3-year DV used includes some meteorological 
variability. Unfortunately, the three years of variation that TCEQ 
accounted for is already built into the structure of the standard. 
Thus, the TCEQ method gave no consideration to the variability between 
calculated DVs which provides a direct indication of the difficulty a 
receptor will have in maintaining the standard. In other words, to 
determine whether a receptor will have difficulty maintaining the 
standard, one must consider the variation in the metric that will be 
used to determine compliance with the standard. An indication of the 
variability of a metric cannot be determined by only considering a 
single estimate of that metric.
    TCEQ's stated purpose in using the most recent DV was to capture 
more recent emissions reductions. TCEQ's methodology, however, limits 
receptors which could be identified as maintenance receptors, compared 
to the EPA's methodology largely because it only looks at one design 
value period rather than selecting the maximum of the three DV periods 
EPA's methodology considers. Thus, TCEQ's methodology greatly reduces 
the probability that meteorological conditions which make it difficult 
to maintain the standard will be considered. As discussed further 
below, the effects of emissions trends are already captured through 
other aspects of the methodology to identify receptors. So, in trying 
to give more weight to emission reductions, by selecting only one 
design value (2012-2014) for its base year, TCEQ's methodology did not 
give any consideration to interannual variability in ozone-conducive 
meteorology as does the EPA's method.
    The EPA's methodology, using the maximum DV which accounts for the 
variability in ozone concentrations and DVs due to changes in 
meteorology over the five years of the base year DV period, was 
designed to identify those areas that might struggle to maintain the 
NAAQS in particularly ozone conducive conditions. TCEQ claimed that the 
EPA's method undervalues changes in air quality due to emission 
reductions and overvalues changes due to variation in meteorology. TCEQ 
pointed out that emissions nationwide are generally trending downward 
as a result of Federal motor vehicle standards and other technological 
improvements. The EPA agrees that ozone levels generally trend 
downward, but there is not a steady decline from year to year in ozone 
concentrations. Rather, ozone levels tend to vary from year to year 
with some years showing an increase instead of a decrease mainly due to 
inter-annual variability in ozone-conducive meteorology.\102\ The 
variation of DVs at individual monitors from year to year can be 
significant, even where emissions trend downwards. The EPA also 
assessed a number of monitored DV trends that were provided in TCEQ's 
SIP submission and previous TCEQ attainment demonstration SIPs 
indicating that there are at times large annual fluctuations upward 
from year to year in monitored DVs (sometimes 2-3 ppb increase in one 
year) that are due to variations in meteorology.\103\ This is precisely 
why it is important to consider highly variable meteorology and its 
influence on DVs--the issue at the heart of the D.C. Circuit's finding 
on ``interference with maintenance'' in North Carolina. Areas that are 
required under the Act to attain by an attainment date may fail to 
attain because of a combination of both local emissions, upwind 
emissions, and ozone conducive meteorology, among other factors. The 
North Carolina decision made clear that in interpreting the good 
neighbor provision, upwind state and the EPA obligations to reduce 
emissions must account for variable conditions that could cause an area 
that is sometimes attaining the NAAQS to fall out of attainment. See 
also Wisconsin, 938 F.3d at 327 (``Variations in atmospheric conditions 
and weather patterns can bring maintenance receptors into nonattainment 
even without elevated emissions.'').
---------------------------------------------------------------------------

    \102\ See EPA Region 6 TSD, included in Docket ID No. EPA-R06-
OAR-2021-0801.
    \103\ Id.
---------------------------------------------------------------------------

    In addition, TCEQ claimed that its use of the 2012-2014 DV (i.e., 
the most recent in the 5-year base period it examined) is more reliable 
than the EPA's method, because that more recent DV accounts for both 
emission reductions and because there is a shorter interval between the 
monitored DV and the projected DV. As we note elsewhere, the TCEQ's 
base year modeled inventory is 2012 emissions and the TCEQ's model 
projections for 2023 include the expected emission reductions from 2012 
thru 2014 and to 2023. By just using the 2012-2014 DV data, TCEQ 
claimed they are giving weight to emission reductions during the final 
base years where EPA's method does not. The effect of emission 
reductions, however, is already factored in the method since the 
modeling projection to 2023 is explicitly designed to project the 
changes in ozone due to emission reductions from the 2012 base year 
emission levels. So, in fact, the EPA method does give weight to 
emission reductions. Furthermore, since

[[Page 9828]]

TCEQ agrees that the average of the DVs based on 2010-2014 ozone levels 
are reliable enough to use in the identification of nonattainment 
receptors, it is unclear how the 2012-2014 period is deemed more 
reliable for the maintenance test since the modeled emissions are still 
for 2012. We also note, as discussed throughout this action, the EPA 
has updated its modeling to use a 2016 base year--that is, a five year 
period spanning 2014-2018, and applied its methodology for defining 
maintenance receptors using that five year base period. Using a more 
recent base period (EPA's 2016v2) provides the most recent design 
values, shorter period of projection (2016 to 2023 versus a 2011 or 
2012 base year) and a more accurate basis for projections of future air 
quality. We note that the EPA undertook a large collaborative multi-
year effort with states (including TCEQ) and other stakeholders input 
and review in developing the 2016v2 emission inventories. By virtue of 
this update, any monitored DV used by the EPA to identify maintenance 
receptors in this action accounts for more recent emission reductions 
and provides a shorter interval between base year monitored DV and the 
projected future analytic year.
    As discussed further in the EPA Region 6 TSD \104\ for this action, 
the EPA has reviewed the set of 21 receptors for which Texas had 
contributions of 0.7 ppb or more in the EPA's 2016 base year modeling 
analyses, or TCEQ's modeling (2012 base year), and evaluated the 
results of using TCEQ's alternate maintenance methodology. For these 21 
receptors, TCEQ's method resulted in 15 of the 21 2023 maintenance DVs 
predicted to be lower than the 2023 nonattainment DVs from the 
nonattainment methodology that uses the 5-year center weighted average. 
Of these 15 receptors, three receptors have 2023 maintenance DVs that 
are 3 ppb lower, five receptors have 2023 maintenance DVs that are 2 
ppb lower, and seven receptors have 2023 maintenance DVs that are 1 ppb 
lower. In comparison, using the EPA's maintenance methodology results 
in all 21 2023 maintenance DVs being equal or up to 4 ppb higher than 
the 2023 nonattainment DVs. Again, the EPA uses the average of the 
three DVs that contain the base year modeled for the nonattainment 
methodology and the maximum of these three DVs for the maintenance 
methodology. Because TCEQ's maintenance methodology of just using the 
most recent DV (2012-2014 DV) often results in maintenance DVs lower 
than the 2023 nonattainment DVs methodology results, the EPA finds that 
the TCEQ methodology is not adequately identifying conditions when a 
receptor would have more difficulty maintaining the standard. In fact, 
the TCEQ's method also identified one receptor in their SIP submission 
as a nonattainment receptor in 2023 that would not have been identified 
as a maintenance receptor, which further highlights the concern that 
TCEQ's method did not adequately identify areas that may struggle to 
maintain the standard. TCEQ did not address whether the three years 
that comprise the most recent design value (i.e., 2012, 2013, and 2014) 
had meteorological conditions highly conducive for formation of high 
ozone concentrations and thus would be an appropriate time period to 
assess whether area could have difficulty maintaining the standard and 
the EPA's analysis confirms that this time period is not highly 
conducive to ozone formation, at least for many receptors. The 
consequence of TCEQ's maintenance method is that it often results in 
lower DVs than the nonattainment test as demonstrated by our analysis, 
which indicates that it is often not considering conditions when an 
area would have difficulty maintaining the standard. It is also 
unreasonable to have a test that would not identify nonattainment 
receptors also as maintenance receptors.
---------------------------------------------------------------------------

    \104\ ``EPA Region 6 2015 8-Hour Ozone Transport SIP Proposal 
Technical Support Document'' (EPA Region 6 2015 Ozone Transport SIP 
TSD.pdf) included in Docket ID No. EPA-R06-OAR-2021-0801.
---------------------------------------------------------------------------

    TCEQ also made several additional assertions in support of their 
conclusion that their method for identifying maintenance receptors was 
the better reading of the CAA, compared to the EPA's. TCEQ claimed that 
its approach was more consistent with the CAA's concept of maintenance 
as areas that were formerly nonattainment and that have since attained 
and will continue to maintain by accounting for: (1) Emissions 
reductions occurring in the later design values of the base DV period; 
(2) ``commitments regarding contingency measures to address future 
emission reductions;'' and (3) the impact of any maintenance plans that 
are in place. TCEQ also asserted that the EPA's approach conflates the 
likelihood of attaining the standard in a future year and the ability 
of an attainment monitor to maintain that attainment status. 
Specifically, TCEQ argued that because any remedies devised to address 
nonattainment monitors would have to apply to maintenance monitors, a 
practical consequence of the EPA's approach is that it could lead to 
over-control and that it might require upwind states to consider or 
implement controls when the downwind state in which the monitor is 
located does not have any obligations to control local emissions. TCEQ 
argued that this ``conflation'' of nonattainment and maintenance 
results in there being no independent meaning to ``maintenance.''
    With respect to the first of these assertions from TCEQ, we note 
that TCEQ's methodology for identifying receptors (like the EPA's) is 
entirely distinct from ozone designations under the Clean Air Act; 
neither TCEQ nor the EPA take current or presumed future designations 
of areas into account, and any implementation requirements like a 
maintenance plan under CAA section 175A, in identifying receptors. 
TCEQ's' discussion, therefore, of maintenance plan contingency measures 
or maintenance plans generally is irrelevant and misplaced. None of the 
areas to which Texas is linked in the EPA 2016v2 modeling has been 
redesignated to attainment for the 2015 ozone NAAQS, and none of the 
areas to which Texas is linked in its own modeling has been 
redesignated to attainment for that NAAQS. We also fail to see how 
TCEQ's approach to identifying maintenance receptors differs in any 
relevant respect from the EPA's approach with regard to the alleged 
``conflation'' of projecting attainment in a future year rather than 
the ability of an attainment receptor to maintain attainment. Both TCEQ 
and the EPA identify maintenance receptors based on projections of air 
quality in a future year to determine whether the receptor will have 
difficulty attaining or maintaining the standard. TCEQ's arguments 
about overcontrol based on the application of a uniform remedy to 
states linked to both nonattainment and maintenance receptors were also 
not germane; in this case, TCEQ had identified no remedy to apply 
whatsoever because it had failed to identify that the emissions from 
Texas cause a problem in the first instance. The D.C. Circuit has 
already rejected the idea that the application of a uniform control to 
both nonattainment and maintenance receptors is on its face overcontrol 
or impermissible under the interstate transport provision. See 
Wisconsin, 938 F.3d at 327. Based on our evaluation of TCEQ's approach 
to identify maintenance receptors for 2023, we propose to find the 
State's approach is inadequate as it does not sufficiently identify 
maintenance receptors. Further, TCEQ had not explained how its

[[Page 9829]]

approach meets the statutory requirement to address areas that, even if 
meeting the NAAQS, may struggle to maintain the standard in years where 
conditions are conducive to ozone formation. Rather, the TCEQ had 
created its own approach to identify these areas that they describe as 
designed to account for the most emission reductions possible--i.e., 
the most recent DV of the three under analysis; an approach that likely 
under-identifies areas that will struggle to maintain the NAAQS and 
that certainly is not designed to capture potential air quality 
problems.
ii. Evaluation of the TCEQ Modeling
    As discussed in Section V.A of this action, TCEQ conducted regional 
photochemical modeling to identify nonattainment and maintenance 
receptors in 2023 using a 2012 base year. As discussed further in the 
EPA Region 6 TSD, we have several concerns with the reliability of 
TCEQ's modeling results. States are free to develop their own modeling, 
but that modeling must be technically supportable, and the EPA is 
obligated to assess and evaluate the reliability of that technical 
demonstration when determining whether the Act's requirements are met.
    The TCEQ's modeling underestimates future ozone levels. When the 
TCEQ 2023 projected concentrations are compared to 2020 and preliminary 
2021 monitor values, it is clear that the TCEQ modeling is projecting 
an unusual decline in ozone levels without there being an unusual level 
of emission reductions to support the decline. The EPA compared recent 
monitoring values and reasonably anticipated decreases in DVs by 2023 
both within Texas and in other parts of the country. These 
underestimations likely result in TCEQ's modeling not adequately 
identifying nonattainment and/or maintenance receptors in 2023. These 
underestimations also result in smaller projected contributions from 
Texas emissions to downwind states. See EPA Region 6 TSD for full 
analysis details.
    One analysis included in the EPA Region 6 TSD examined the average 
amount of improvement that would have to occur for the 9 monitors with 
the highest measured design values in the Dallas-Ft. Worth and Houston-
Galveston-Brazoria nonattainment areas (those with an observed 2018-
2020 DV of 74 ppb or greater) to reach the level of ozone projected by 
the TCEQ modeling. The average decrease needed by 2023 to meet TCEQ's 
2023 projected DVs is 7.56 ppb. Improvements of this magnitude do not 
occur in three years unless there is an unusually large change in 
emissions or a large change in meteorological conduciveness for ozone 
generation. TCEQ did not identify any large emission reductions not 
already accounted for in the modeling to be implemented in the 2021-
2023 timeframe nor is the EPA aware of such a change. This information 
supports our finding that that TCEQ's modeling is underestimating 
future ozone levels in the two nonattainment areas in Texas that make 
up a large proportion of the total ozone and a large portion of 
emissions of ozone pre-cursors that transport to downwind areas. This 
underestimation of future year ozone levels from Texas emissions can 
cause both an underestimation of ozone in downwind areas and also an 
underestimation of Texas's impact on downwind State's ozone 
nonattainment and maintenance receptors.
    TCEQ's modeling also underestimates 2023 ozone levels outside of 
the State of Texas including areas of interest in California, Colorado 
and the Midwest Region (Illinois, Wisconsin, and Michigan). The EPA 
discusses this underprediction for all of these areas in the EPA Region 
6 TSD. In Table TX-3, we present only the results for the Midwest 
Region along with the EPA's modeling prediction. We note that TCEQ's 
2023 modeled DVs are significantly lower than the EPA's 2023 modeled 
DVs. The table also provides recent monitored 2020 DVs and preliminary 
2021 DVs, which shows that recent monitored ozone concentrations are 
significantly higher than TCEQ's modeling projected for 2023. TCEQ's 
ozone DVs for these receptors would need to drop on the order of 7-15 
ppb in two to three years for TCEQ's projections to bear out. As noted 
previously, this would require an unusual amount of emission reductions 
without any control measures identified of sufficient magnitude. We 
note that the EPA's projected 2023 ozone DVs based on EPA 2016v2 
modeling show ozone DVs that are also lower than recent monitoring 
data. However, EPA 2016v2 modeling projections are much closer to 
anticipated 2023 ozone levels as compared to TCEQ's modeling. This 
indicates that the EPA's modeling is more accurate in identifying 
nonattainment and/or maintenance receptors in the Midwest Region. While 
the TCEQ modeling projects much lower overall ozone levels for the 
Midwest Region in 2023, the modeling does tend to corroborate the 
projected amount emissions that Texas may be contributing to projected 
ozone levels at 5 of the 7 nonattainment and maintenance receptors 
identified in the EPA's modeling.\105\ Thus, despite the differences in 
identification of nonattainment and maintenance receptors, both sets of 
modeling indicate that Texas's contribution to receptors in the Midwest 
Region are greater than 0.7 ppb (i.e., 1 percent of the 2015 ozone 
NAAQS). Table TX-3 provides information on those receptors, including 
the amount of contribution attributed to emissions from Texas based on 
EPA's 2016v2 modeling and TCEQ's modeling. Despite the differences in 
identification of nonattainment and maintenance receptors, both sets of 
modeling indicate that Texas's contribution to receptors in the Midwest 
are greater than 0.7 ppb (i.e., 1 percent of the 2015 ozone NAAQS).
---------------------------------------------------------------------------

    \105\ We note that for two of the Wisconsin receptors, TCEQ's 
modeling does not provide information to generate 2023 DVs, so only 
5 of the 7 monitors can be compared.

                           Table TX-3--EPA and TCEQ Modeling Results for Downwind Receptors Identified by EPA 2016v2 Modeling
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                                   Monitored 2018-
                                      2023 nonattainment/      EPA: 2023                              2020 DV/       EPA: Texas
 Receptor (site ID, county, state)      maintenance (EPA      average DV/   TCEQ: 2023 average DV/   preliminary    contribution        TCEQ: Texas
                                            2016v2)           maximum DV    maintenance DV (ppb)*  2019-2021 DV**       (ppb)        contribution (ppb)
                                                                 (ppb)                                  (ppb)
--------------------------------------------------------------------------------------------------------------------------------------------------------
170310001, Cook, IL................  Maintenance..........       69.6/73.4  60/58................           75/71            0.86  1.6.
170310032, Cook, IL................  Maintenance..........       69.8/72.4  68/66................           74/75            1.46  1.31.
170314201, Cook, IL................  Maintenance..........       69.9/73.4  64/62................           77/74            1.15  1.25.
170317002, Cook, IL................  Maintenance..........       70.1/73.0  66/65................           75/73            1.58  1.22.

[[Page 9830]]

 
550590019, Kenosha, WI.............  Nonattainment........       72.8/73.7  67/66................           74/74            1.72  1.44.
550590025, Kenosha, WI.............  Maintenance..........       69.2/72.3  No data***...........           74/72            1.81  No data.***
551010020, Racine, WI..............  Nonattainment........       71.3/73.2  No data***...........           73/73            1.34  No data.***
--------------------------------------------------------------------------------------------------------------------------------------------------------
* TCEQ did not provide sufficient data and analysis of the meteorology for the 2010-2014 period to support their claim that 2012-2014 period was a worst-
  case combination of meteorology compared to the 2010-2012 and 2011-2013 periods. If the future DV projected from this highest value is below the
  standard, one can be reasonably certain the receptor will not have difficulty maintaining the standard and, as such, upwind states will not interfere
  with maintenance in downwind states. Because the TCEQ method only looks at one DV and does not account for the variability in DVs due to
  meteorological conditions, it is less likely to identify maintenance receptors than the EPA method. See https://www.epa.gov/air-trends/air-quality-design-values
** Preliminary 2019-2021 DVs. Monitoring data from the EPA's Air Quality System (AQS) (https://www.epa.gov/aqs). 2021 monitoring data is preliminary and
  still has to undergo Quality Assurance/Quality Control analysis and be certified by the State of Texas, submitted to the EPA, and reviewed and
  concurred on by EPA. 2018-2020 DVs are 72 ppb and 73 ppb at the Denton County and Tarrant County monitors/receptors respectively. Preliminary 2019-
  2021 DVs are 74 ppb and 72 ppb at the Denton County and Tarrant County monitors/receptors respectively.
*** Kenosha, WI Monitor ID. 550590025 was installed and began operating May 13, 2013, so the first three year DV available is 2013-2015. Racine, WI
  Monitor ID. 551010020 was installed in April 14, 2014 so the first three year DV available is 2015-2017. TCEQ's modeling used monitored DV data for
  2010-2012, 2011-2013, and 2012-2014 to project to the future year. Since these monitors do not have valid DVs for these periods, TCEQ's modeling can't
  be used to project 2023 values and identify if they would be nonattainment or maintenance receptors.

    The EPA investigated TCEQs modeling and the underestimation for the 
future year. See the EPA Region 6 TSD for further information on our 
review. Our review indicated some underestimation bias in the base case 
and general model performance concerns but nothing that was a clear 
cause of the much lower 2023 DVs that TCEQ's modeling is projecting. 
For the EPA's 2016 base year modeling, the EPA undertook a large 
collaborative multi-year effort with states (including Texas) and other 
stakeholder input in developing the 2016 emission inventories including 
2016v2, so that the EPA's modeling would be based on the best data 
available. Using a 2016 base year also provides a more recent platform 
that shortens the number of years to project emission changes, reducing 
uncertainties in the 2023 projection compared to TCEQ's projection from 
a 2012 base to 2023 or the EPA's earlier 2011 base year modeling. Use 
of a more recent 2016 base year also allows for the use of monitored 
DVs from a more recent period. The combination of these and other 
issues discussed in the EPA Region 6 TSD result in less model 
uncertainty compared to TCEQ's 2012 base year modeling and has provided 
a better estimate of 2023 ozone levels and therefore, we believe a more 
reliable tool for predicting which areas of the country will be 
nonattainment or have difficulty maintaining the standard as well as 
assessing contributions from upwind states.
    The EPA's modeling using both 2011 and 2016 base year periods 
identified that Texas was linked to nonattainment and/or maintenance 
receptors in 2023 in the Midwest Region (Illinois, Wisconsin, and 
Michigan), while TCEQ's modeling using a 2012 base year indicated only 
linkages to western receptors. As discussed above and in the EPA Region 
6 TSD, the TCEQ's modeling is underestimating projected ozone levels in 
the Midwest Region for 2023. If TCEQ's 2023 modeled DVs were closer to 
recent observed monitoring data and anticipated 2023 monitored DVs, 
TCEQ would likely have also identified nonattainment and/or maintenance 
receptors in the Midwest Region.
    To summarize, TCEQ did its own modeling at Step 1. Our analysis 
shows that TCEQ's modeling likely underestimates ozone levels at 
potential receptors and that TCEQ's methodology for identifying 
maintenance receptors used to identify maintenance receptors fails to 
reasonably identify areas that will have difficulty maintaining the 
NAAQS.
2. Evaluation of Information Provided by TCEQ Regarding Step 2
    TCEQ, like the EPA, used a 1 percent of the ozone NAAQS (or 0.7 
ppb) as the ``linkage'' threshold to identify states as ``linked'' for 
contributions it made to areas with projected air quality problems. 
Although TCEQ asserted that the EPA treats the 1 percent threshold as 
the threshold by which the EPA determines ``significant contribution'' 
this is in fact incorrect. The EPA, like TCEQ, uses the 1 percent 
contribution threshold to identify those linkages between a 
contributing upwind state and a receptor projected to have air quality 
problems that warrant further review and additional analysis. We 
therefore endorse TCEQ' use of the 1 percent contribution threshold to 
identify linkages requiring further analysis. However, because we 
propose to disapprove TCEQ's identification of nonattainment and/or 
maintenance receptors (at Step 1) due to underestimations in TCEQ's 
modeling and their unsupported methodology of identifying maintenance 
receptors, their submission as to Step 2 is also flawed. We note, 
however, that even in its own modeling, TCEQ has identified 
nonattainment and/or maintenance receptors to which it contributed more 
than 1 percent of the NAAQS (i.e., identified linkages warranting 
additional analysis at Step 3).
3. Results of the EPA's Step 1 and Step 2 Modeling and Findings for 
Texas
    As described in Section I and elsewhere in this action, the EPA 
performed air quality modeling using the 2016v2 emissions platform to 
project design values and contributions for 2023. This data was 
examined to determine if Texas contributes at or above the threshold of 
1 percent of the 2015 ozone NAAQS (0.70 ppb) to any downwind 
nonattainment or maintenance receptor. As shown in Table TX-4, the data 
\106\ indicate that in 2023, emissions from Texas are projected to 
contribute greater than 1 percent of the standard to both

[[Page 9831]]

nonattainment and maintenance-only receptors in the Chicago, IL-IN-WI 
nonattainment area (4 Cook County, IL receptors and 2 Kenosha County, 
WI receptors) and the Milwaukee, WI nonattainment area (one Racine 
County receptor).\107\
---------------------------------------------------------------------------

    \106\ Design values and contributions at individual monitoring 
sites nationwide are provided in the file: 
``2016v2_DVs_state_contributions.xlsx'', which is included in docket 
ID No. EPA-HQ-OAR-2021-0663.
    \107\ These modeling results are consistent with the results of 
a prior round of 2023 modeling using the 2016v1 emissions platform 
which became available to the public in the fall of 2020 in the 
Revised CSAPR Update, as noted in Section I of this action. That 
modeling showed that Texas 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 No. EPA-HQ-OAR-2021-0663.

      Table TX-4--Projected Nonattainment and Maintenance Receptors With Texas Linkages Based on EPA 2016v2
----------------------------------------------------------------------------------------------------------------
                                                                                                       Texas
   Receptor (site ID, county, state)         Nonattainment/        2023  average   2023  maximum   contribution
                                               maintenance           DV (ppb)        DV (ppb)          (ppb)
----------------------------------------------------------------------------------------------------------------
170310001, Cook, IL...................  Maintenance.............            69.6            73.4            0.86
170310032, Cook, IL...................  Maintenance.............            69.8            72.4            1.46
170314201, Cook, IL...................  Maintenance.............            69.9            73.4            1.15
170317002, Cook, IL...................  Maintenance.............            70.1            73.0            1.58
550590019, Kenosha, WI................  Nonattainment...........            72.8            73.7            1.72
550590025, Kenosha, WI................  Maintenance.............            69.2            72.3            1.81
551010020, Racine, WI.................  Nonattainment...........            71.3            73.2            1.34
----------------------------------------------------------------------------------------------------------------

    We recognize that the results of the EPA (2011 and 2016 base year) 
and TCEQ (2012 base year) modeling indicated different receptors and 
linkages at Steps 1 and 2 of the 4-Step interstate transport framework. 
These differing results regarding receptors and linkages can be 
affected by the varying meteorology from year to year, but we do not 
think the differing results mean that the modeling or the EPA or the 
State's methodology for identifying receptors or linkages is inherently 
unreliable. Rather, the three separate modeling runs all indicated: (1) 
There were receptors that would struggle with nonattainment or 
maintenance in the future; and (2) Texas was linked to some set of 
these receptors, even if the receptors and linkages differed from one 
another in their specifics (e.g., a different set of receptors were 
identified to have nonattainment or maintenance problems, or Texas was 
linked to different receptors in one modeling run versus another). 
These results indicate that emissions from Texas were substantial 
enough to generate linkages at Steps 1 and 2 to some downwind 
receptors, under varying assumptions and meteorological conditions, 
even if the precise set of linkages changed between modeling runs. 
Under these circumstances, we think it is appropriate to proceed to a 
Step 3 analysis to determine what portion of emissions from Texas 
should be deemed ``significant.'' In doing so, we are not agreeing with 
the methods and assumptions contained in TCEQ's modeling (see previous 
discussion and the EPA Region 6 TSD included in the docket for this 
proposal for further discussion on evaluation of that modeling), or 
that we consider our own earlier modeling to be of equal reliability 
relative to more recent modeling. However, where alternative or older 
modeling generated linkages, even if those linkages differ from 
linkages in the EPA's most recent set of modeling (EPA 2016v2), that 
information provides further evidence, not less, in support of a 
conclusion that the State is required to proceed to Step 3 to further 
evaluate its emissions.
    Therefore, based on the EPA's evaluation of the information 
submitted by TCEQ and based on the EPA 2016v2 modeling results for 
2023, the EPA proposes to find that Texas 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.
4. Evaluation of Information Provided by TCEQ Regarding Step 3
    At Step 3 of the 4-Step interstate transport framework, a state's 
emissions are further evaluated, considering 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 approach (i.e., 
Step 3 of the 4-Step interstate transport framework) when identifying 
emissions contributions that the Agency has determined to be 
``significant'' (contribution to nonattainment or interfere with 
maintenance) in each of its prior Federal, regional ozone transport 
rulemakings, and this interpretation of the statute has been upheld by 
the Supreme Court. See EME Homer City, 572 U.S. 489, 519 (2014). While 
the EPA has not directed states that they must conduct a Step 3 
analysis in precisely the manner the EPA has done in its prior regional 
transport rulemakings, state implementation plans addressing the 
obligations in CAA section 110(a)(2)(D)(i)(I) must prohibit ``any 
source or other type of emissions activity within the State'' from 
emitting air pollutants which will contribute significantly to downwind 
air quality problems. Thus, states must complete something similar to 
the EPA's analysis (or an alternative approach to defining 
``significance'' that comports with the statute's objectives) to 
determine whether and to what degree emissions from a state should be 
``prohibited'' to eliminate emissions that will ``contribute 
significantly to nonattainment in, or interfere with maintenance of'' 
the NAAQS in any other state. TCEQ did not demonstrate such an analysis 
in their SIP submission. We therefore propose that TCEQ was required to 
analyze emissions from the sources and other emissions activity from 
within the State to determine whether its contributions were 
significant, and we propose to disapprove its submission because Texas 
failed to do so.
    Instead, as noted in Section V.A of this action, TCEQ interpreted 
the Act's requirements as only requiring an

[[Page 9832]]

analysis of emission reductions where ``there is a persistent and 
consistent pattern of contribution on several days with elevated 
ozone.'' TCEQ asserted that it would make the determination of whether 
such pattern existed based on a weight-of-evidence approach that takes 
into consideration air quality factors such as: Current attainment 
status of the monitors, design value trends, the meteorological 
conditions that lead to high ozone formation at the monitor, the number 
of days with elevated observed ozone, back trajectories, Texas' 
relative contribution on modeled high ozone days, Texas' contribution 
as part of the collective interstate contribution to future modeled 
DVs, alternate contribution method analysis, and model sensitivity runs 
to reductions of Texas' emissions on receptors. However, TCEQ stated 
that it did not consider or analyze all factors for every monitor. 
Thus, different factors were analyzed for the receptors in different 
regions (Colorado, Arizona, and Southern California). The EPA has 
reviewed the different factors that TCEQ provided for each of the 
regions in the EPA Region 6 TSD, but we will provide a brief summary of 
the evaluation below. TCEQ also asserted that use of the 1 percent 
threshold as the ``sole'' definition of significant contribution for 
the 2015 ozone NAAQS is inappropriate. Based on the application of 
selected factors for each of the monitors to which TCEQ's modeling 
found that it was linked, TCEQ concluded that none of its contributions 
to any other states were significant.
    As explained above, TCEQ has mischaracterized the EPA's 
interpretation of the CAA in stating that the EPA defines significant 
contribution ``solely'' using a 1 percent threshold. The EPA, like 
TCEQ, uses the 1 percent threshold to identify areas for further 
analysis. The difference is that the EPA in past analyses has examined 
potential emission reductions in linked upwind states and the air 
quality impacts at downwind receptors that would result from the 
implementation of those reductions to assess which contributions are 
``significant.'' This interpretation of significant contribution, as 
discussed above, has been upheld by the Supreme Court and the D.C. 
Circuit.
    As an initial matter, the EPA believes source apportionment 
modeling, as performed by the EPA and also by TCEQ, to determine which 
states are linked is an appropriate tool to identify impacts that are 
persistent enough to impact a downwind receptors ability to attain or 
maintain the standard. This approach is described in more detail above 
in Section II.B.4 of this action, but, in summary, averages the 
contributions from an upwind state for up to 10 days, which is 
preferred, (but a minimum 5 days) at a given receptor. Given the ozone 
standard is an average of the fourth high value from each of three 
years, the EPA technique, also used by Texas, is appropriate to 
identify impacts of sufficient persistence to impact a downwind 
receptor's ability to attain or maintain the standard.
    The EPA reviewed TCEQ's evaluation of the current attainment status 
of the monitors and design value trends, and concludes, as described in 
more detail in the EPA Region 6 TSD, that the provided information does 
not support the large decreases in ozone levels that TCEQ's modeling 
projects will occur by 2023. The analysis for California and Colorado 
receptors provides evidence that TCEQ's photochemical modeling is 
overestimating the ozone reductions expected at these receptors between 
2012 and 2023 and actually presents evidence that more nonattainment 
and/or maintenance receptors should have been identified.
    The EPA also reviewed the trends in the number of high ozone days 
per year provided by TCEQ for Colorado and California. While this data 
supports that the number of ozone exceedance days is improving, neither 
the analysis of the number of high ozone days in Colorado or California 
provide any evidence to refute the TCEQ's photochemical modeling 
results that show these areas should be considered nonattainment and/or 
maintenance receptors. TCEQs modeling overestimates ozone reductions 
yet still shows Texas linked to receptors at both nonattainment and 
maintenance levels in 2023.
    The TCEQ cited a conceptual model of ozone formation for areas in 
Southern California. TCEQ indicated that Southern California is 
isolated and transport into the basin is unlikely on a frequent basis, 
but this information does not refute the TCEQ's modeling. As discussed 
in Section III.B.3 of this action, 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. TCEQ's modeling showed transport at 10 monitors having 
contributions greater than 0.7 ppb on average for the 5-10 days used in 
the modeling analyses. Considering the form of the standard, this is a 
sufficient number of days to determine if an impact is persistent 
enough to impact an area's ability to attain or maintain the standard.
    TCEQ used the National Oceanic and Atmospheric Administration 
(NOAA) HYSPLIT \108\ model to produce back trajectories for all the 
monitored ozone exceedance days (2007-2016) for the five receptors in 
Colorado and 10 receptors in Southern California to evaluate how many 
of the back trajectories went through Texas. TCEQ also used data from 
these back trajectories to do an endpoint count analysis. We note that 
we have several concerns with how TCEQ performed the back trajectories 
including start time and heights, length (number of hours) of the back 
trajectory, inappropriate removal of some back trajectories based on 
start height, center-line height touch down, and trajectory center-line 
height when over Texas, and inappropriate counting of trajectories by 
not considering that the center-line represents the centerline of a 
much wider area of air parcels that could have reached the monitor/
receptor. Due to these concerns, as discussed in more detail in the EPA 
Region 6 TSD, the EPA finds the results of TCEQ's back trajectory and 
endpoint analysis flawed (underestimates back trajectories that reach 
Texas) and do not provide evidence that refutes the TCEQ photochemical 
modeling analysis results.
---------------------------------------------------------------------------

    \108\ See FN 34.
---------------------------------------------------------------------------

    We note that even valid back trajectories are of limited use as 
HYSPLIT simply estimates the path 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 (monitor) 
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

[[Page 9833]]

``linkages.'' Since 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. It is interesting to note that TCEQ's 
analysis of the back trajectories indicates that the 2012 meteorology 
used by TCEQ seemed to yield more back trajectories that reach Texas 
than most years for many of the Colorado monitors. This seems to be 
consistent with TCEQ identifying linkages to Colorado when the EPA's 
modeling of 2016 does not.
    TCEQ performed an alternate contribution analysis for the ten 
California receptors and the five Colorado receptors using all days 
modeled in 2023 that had values over 70 ppb rather than focus on just 
the 5-10 highest values under the EPA's technique. Particularly for 
California, this meant many more days could be included in the average 
which had the effect of showing a smaller estimated contribution. We 
believe it is appropriate to focus on the highest values as these are 
the ones that ultimately will have to be reduced for the standard to be 
attained. As discussed in the EPA Region 6 TSD, the EPA's review of 
TCEQ's alternate contribution method analysis for California and 
Colorado receptors is that it does not provide substantial evidence 
that refutes the TCEQ's photochemical modeling analysis results, 
including the contribution analysis using the EPA's contribution 
methodology.
    TCEQ provided an analysis of collective interstate contribution to 
the 2023 DV for the five Colorado and ten California receptors. The 
collective interstate contribution at tagged Colorado receptors ranges 
from 9.32% to 10.27%. The collective interstate contribution at tagged 
California receptors ranges from 3.2% to 4.58%. TCEQ argues that these 
are small percentages (Colorado and California) and not as high as the 
collective interstate contribution percentages the EPA calculated for 
monitors in Eastern States, which ranged from 17% to 67%. TCEQ also 
notes that a significant portion of the tagged Colorado monitors' 2023 
modeled DVs is due to background emissions (sum of contributions from 
to biogenic, fires, and boundary conditions). For the California 
receptors TCEQ argues that these percentages are small compared to 
Intra-State contribution.
    As an initial matter, the EPA is not solely relying on TCEQ's 
findings of linkages to Colorado and California but is also relying on 
its own findings of linkages to areas in the Midwest Region. As such, 
TCEQ's analysis of relative contributions to Colorado and California 
does not provide justification for not addressing downwind impacts. 
Nonetheless, EPA has found in the past that certain California 
receptors are so heavily impacted by local emissions, and total upwind 
contribution is so low, that those receptors may not be considered to 
be affected by interstate ozone transport. See 81 FR 15200 (Mar. 22, 
2016). However, this is a narrow circumstance that does not apply in 
the vast majority of cases and has never been applied outside of 
California. EPA has previously found, for instance, that receptors in 
Colorado are heavily impacted by upwind-state contribution. See 82 FR 
9155 (Feb. 3, 2017); 81 FR 71991 (Oct. 19, 2016). EPA need not draw any 
conclusions here regarding whether the California sites TCEQ identified 
should or should not be considered receptors for ozone-transport 
purposes. EPA affirms, contrary to TCEQ's suggestion, that the Colorado 
receptors TCEQ analyzed are impacted by upwind state contributions. 
However, the EPA's finding that Texas is linked to receptors in other 
states is based on still other linkages found in EPA's modeling to 
receptors in other states, which are clearly impacted by the collective 
contribution of multiple upwind states, including Texas. Under CAA 
section 110(a)(2)(D)(i)(I) downwind states are not obligated to reduce 
emissions on their own to resolve 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.
    TCEQ also performed photochemical modeling analysis using the 
Direct Decoupled Method (DDM) tool for receptors in Colorado. DDM 
provides a first derivative of the changes in ozone (linear 
relationship where the DDM value is the slope of the line for changes 
in ozone) resulting from changes in NOX emissions from all 
Texas' NOX emissions. The DDM modeling does show some 
response to Texas NOX emissions but from the scale it is 
hard to discern the level of response but it appears to be in the 0-2 
ppb range in general with some values in the 0.2 -2 ppb range for 
modeled values over 60 ppb. Since the modeling has underprediction and 
underestimation issues, these values could be higher. Not surprisingly, 
the DDM tool shows that monitors in Colorado are much more responsive 
to intra-state reductions than reductions in Texas. That said, the 
results of the DDM tool showing only a relatively small response to 
reductions is not inconsistent with the finding that Texas emissions 
contribute significantly to elevated readings in Colorado. As has been 
discussed elsewhere, the EPA believes a contribution of 1 percent of 
the standard is an appropriate threshold such that further analysis is 
warranted.
    Overall, these additional analyses performed by TCEQ do not provide 
sufficient evidence to refute the modeling results that TCEQ's modeling 
indicates downwind nonattainment and/or maintenance receptors in 
Colorado and Southern California are impacted by Texas emissions and 
Texas' contribution is 0.7 ppb or greater.\109\ In fact, the monitored 
ozone design value trends provide evidence that future year modeled 
ozone levels are underestimated by TCEQ's modeling and there are likely 
more receptors that should have been identified with additional 
potential linkages. Although Texas asserted that its additional air 
quality factor analysis is a permissible way to interpret which 
contributions are ``significant'' because that analysis examines 
whether there was a ``persistent and consistent pattern of contribution 
on several days with elevated ozone'' we find that such pattern is 
already established by a modeled linkage at Step 2.
---------------------------------------------------------------------------

    \109\ TCEQ also identified a monitor in Cochise County, Arizona 
(ID 40038001), but the monitor's recent DVs are below the NAAQS. 
From AQS, the 2014-2016 and 2015-2017 DVs are each 65 ppb; 2016-
2018, 2017-2019, and 2018-2020 DVs are 66 ppb; and preliminary 2019-
2021 DV is 66 ppb.
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    In addition, EPA 2016v2 modeling using 2016 base year meteorology 
indicates linkages from Texas to receptors in the Midwest Region but 
does not indicate impacts from Texas emissions on the Colorado and 
other western receptors identified by TCEQ. With a different base 
period such as TCEQ's 2012 base period meteorology and the EPA's 2016 
base period meteorology, it is not uncommon that the potential downwind 
nonattainment or maintenance receptors could change. These differing 
results about receptors and linkages can be affected by the varying 
meteorology from year to year and the selection of different base 
years, but we do not think the differing results mean that the modeling 
or the EPA methodology for identifying receptors or linkages is 
inherently unreliable. Rather, these separate modeling runs indicated 
(1) that there were receptors that would

[[Page 9834]]

struggle with nonattainment or maintenance in the future, and (2) that 
Texas was linked to some set of these receptors, even if the receptors 
and linkages differed from one another in their specifics (e.g., a 
different set of receptors were identified to have nonattainment or 
maintenance problems, or Texas was linked to different receptors in one 
modeling run versus another). We think this common result indicates 
that Texas's emissions were substantial enough to generate linkages at 
Steps 1 and 2 to some set of downwind receptors, under varying 
assumptions and meteorological conditions, even if the precise set of 
linkages changed between modeling runs.
    In sum, the EPA's more recent and robust 2016 base year modeling 
platform indicates that Texas is linked to several receptors in the 
Midwest Region as does the EPA's earlier 2011 base year modeling. 
TCEQ's 2012 base case modeling showed linkages to states in the west. 
As discussed, the EPA does not find the additional weight of evidence 
evaluations conducted by TCEQ provide compelling reasons to discount 
the impacts indicated in Colorado and California by the TCEQ modeling. 
In fact, we think TCEQ's modeling likely underestimates these issues. 
We therefore propose that Texas was required to analyze emissions from 
the sources and other emissions activity from within the State to 
determine whether its contributions were significant, and we propose to 
disapprove its submission because Texas failed to do so.
5. Evaluation of Information Provided by TCEQ 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. Texas indicated that 
because a number of counties in its state had been designated 
nonattainment for the 2015 ozone NAAQS, there could be attainment 
demonstration and potential controls contemplated in association with 
those nonattainment designations.\110\ However, the State's interstate 
transport submission did not revise its SIP to identify any specific 
emission reductions, nor did it include a revision to its SIP to ensure 
any such reductions were permanent and enforceable. The other control 
measures identified in TCEQ's submission are, as noted by TCEQ, already 
adopted and implemented measures and do not contain an evaluation of 
additional emission control opportunities (or establish that no 
additional controls are required). As a result, the EPA proposes to 
disapprove TCEQ's submittal on the separate, additional basis that the 
Texas has not included permanent and enforceable emissions reductions 
in its SIP as necessary to meet the obligations of CAA section 
110(a)(2)(d)(i)(I).
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    \110\ Pointing to anticipated upcoming emission reductions, even 
if they were not included in the analysis at Steps 1 and 2, is not 
sufficient as a Step 3 analysis, for the reasons discussed in 
Section V.B.4 of this action. In this section, we explain that to 
the extent such anticipated reductions are not included in the SIP 
and rendered permanent and enforceable, reliance on such anticipated 
reductions is also insufficient at Step 4.
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6. Conclusion
    Based on the EPA's evaluation of TCEQ's SIP submission, the EPA is 
proposing to find that the Texas August 17, 2018, SIP submission 
pertaining to interstate transport of air pollution 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 ozone NAAQS in any other state.

VI. Proposed Action

    We are proposing to disapprove the SIP submissions from Arkansas, 
Louisiana, Oklahoma, and Texas pertaining to interstate transport of 
air pollution which will significantly contribute to nonattainment or 
interfere with maintenance of the 2015 ozone NAAQS in other states. 
Under CAA section 110(c)(1), the disapprovals would establish a 2-year 
deadline for the EPA to promulgate FIPs for these states 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 ozone NAAQS in other states, 
unless the EPA approves SIPs that meet these requirements. Disapproval 
does not start a mandatory sanctions clock for Arkansas, Louisiana, 
Oklahoma, or Texas.

VII. Statutory and Executive Order Reviews

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

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

B. Paperwork Reduction Act (PRA)

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

C. Regulatory Flexibility Act (RFA)

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

D. Unfunded Mandates Reform Act (UMRA)

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

E. Executive Order 13132: Federalism

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

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

    This proposed action disapproving the portion of Oklahoma's SIP 
submission addressing the State's interstate transport obligations 
under CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone NAAQS will 
apply to certain areas of Indian country as discussed in Section IV.C 
of this action, and therefore, has tribal implications as specified in 
E.O. 13175 (65 FR 67249, November 9, 2000). However, this proposed 
action will neither impose substantial direct compliance costs on 
federally recognized tribal governments, nor preempt tribal law. This 
proposed action will not impose substantial direct compliance costs on 
federally recognized tribal governments because no actions will be 
required of tribal governments. This proposed action will

[[Page 9835]]

also not preempt tribal law as no Oklahoma tribe implements a 
regulatory program under the CAA, and thus does not have applicable or 
related tribal laws. Consistent with the EPA Policy on Consultation and 
Coordination with Indian Tribes (May 4, 2011), the EPA will offer 
consultation to tribal governments whose lands are located within the 
exterior boundaries of the State of Oklahoma that may be affected by 
this action.

G. Executive Order 13045: Protection of Children From Environmental 
Health Risks and Safety Risks

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

H. Executive Order 13211, Actions That Significantly Affect Energy 
Supply, Distribution or Use

    This action is not subject to Executive Order 13211, because it is 
not a significant regulatory action under Executive Order 12866.

I. National Technology Transfer and Advancement Act

    This rulemaking does not involve technical standards.

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

    The EPA believes the human health or environmental risk addressed 
by this action will not have potential disproportionately high and 
adverse human health or environmental effects on minority, low-income 
or indigenous populations. This action merely proposes to disapprove a 
SIP submission as not meeting the CAA.

K. CAA Section 307(b)(1)

    Section 307(b)(1) of the CAA governs judicial review of final 
actions by the EPA. This section provides, in part, that petitions for 
review must be filed in the D.C. Circuit: (i) When the agency action 
consists of ``nationally applicable regulations promulgated, or final 
actions taken, by the Administrator,'' or (ii) when such action is 
locally or regionally applicable, if ``such action is based on a 
determination of nationwide scope or effect and if in taking such 
action the Administrator finds and publishes that such action is based 
on such a determination.'' For locally or regionally applicable final 
actions, the CAA reserves to the EPA complete discretion whether to 
invoke the exception in (ii).\111\
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    \111\ In deciding whether to invoke the exception by making and 
publishing a finding that an action is based on a determination of 
nationwide scope or effect, the Administrator takes into account a 
number of policy considerations, including his judgment balancing 
the benefit of obtaining the D.C. Circuit's authoritative 
centralized review versus allowing development of the issue in other 
contexts and the best use of agency resources.
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    The EPA anticipates that this proposed rulemaking, if finalized, 
would be ``nationally applicable'' within the meaning of CAA section 
307(b)(1) because it would take final action on SIP submittals for the 
2015 ozone NAAQS for four states, which are located in three different 
Federal judicial circuits. It would apply uniform, nationwide 
analytical methods, policy judgments, and interpretation with respect 
to the same CAA obligations, i.e., implementation of interstate 
transport requirements under CAA section 110(a)(2)(D)(i)(I) for the 
2015 ozone NAAQS for states across the country, and final action would 
be based on this common core of determinations, described in further 
detail below.
    If the EPA takes final action on this proposed rulemaking[, in the 
alternative,] 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 interstate transport 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 the 4-Step framework. Further, the EPA proposes to 
determine and apply a set of nationally consistent policy judgments to 
apply the 4-Step framework. The EPA has selected a nationally uniform 
analytic year (2023) for this analysis and is applying a nationally 
uniform approach to nonattainment and maintenance receptors and a 
nationally uniform approach to contribution threshold analysis.\112\ 
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).\113\
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    \112\ 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.
    \113\ The EPA may take a consolidated, single final action on 
all of the proposed SIP disapproval actions with respect to 
obligations under CAA section 110(a)(2)(D)(i)(I) for the 2015 ozone 
NAAQS. Should the EPA take a single final action on all such 
disapprovals, this action would be nationally applicable, and the 
EPA would also anticipate, in the alternative, making and publishing 
a finding that such final action is based on a determination of 
nationwide scope or effect.
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List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Ozone.
    Authority: 42 U.S.C. 7401 et seq.

    Dated: February 1, 2022.
Earthea Nance,
Regional Administrator, Region 6.
[FR Doc. 2022-02961 Filed 2-18-22; 8:45 am]
BILLING CODE 6560-50-P