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Proposed Rule2022-02961

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

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Published

February 22, 2022

Issuing agencies

Environmental Protection Agency

Abstract

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.

Full Text

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[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 [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> following the online instructions for
submitting comments or via email to <a href="/cdn-cgi/l/email-protection#ee889b8b9c9d9ac09d868b9c9c97ae8b9e8fc0898198">[email&#160;protected]</a>. 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
<a href="https://www.regulations.gov/">https://www.regulations.gov/</a>, 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 <a href="https://www.epa.gov/dockets">https://www.epa.gov/dockets</a>.

FOR FURTHER INFORMATION CONTACT: Sherry Fuerst, EPA Region 6 Office,
AR-SI, 214-665-6454, <a href="/cdn-cgi/l/email-protection#335546564140471d405b5641414a735643521d545c45">[email&#160;protected]</a>. We encourage the public to
submit comments via <a href="https://www.regulations.gov">https://www.regulations.gov</a>, 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 <a href="https://www.regulations.gov">https://www.regulations.gov</a> (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
<a href="https://www.regulations.gov">https://www.regulations.gov</a> 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, <a href="/cdn-cgi/l/email-protection#98feedfdeaebecb6ebf0fdeaeae1d8fde8f9b6fff7ee">[email&#160;protected]</a>. For the
full EPA public comment policy, information about CBI or multimedia
submissions, and general guidance on making effective comments, please
visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>. 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 <a href="https://www.epa.gov/dockets">https://www.epa.gov/dockets</a>.
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
<a href="https://www.regulations.gov">https://www.regulations.gov</a>. 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

[[Page 9799]]

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 ``NO<INF>X</INF>
SIP Call,'' 63 FR 57356 (October 27, 1998), and the ``Clean Air
Interstate Rule'' (CAIR), 70 FR 25162 (May 12, 2005).

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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 (NO<INF>X</INF>) 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 <a href="https://www.epa.gov/air-trends/air-quality-design-values">https://www.epa.gov/air-trends/air-quality-design-values</a>#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
<a href="https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices">https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices</a>.
\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 <a href="https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices">https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices</a>.
\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 <a href="https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs">https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs</a>.
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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 <a href="https://www.epa.gov/moves/latest-version-motor-vehicle-emission-simulator-moves">https://www.epa.gov/moves/latest-version-motor-vehicle-emission-simulator-moves</a>.
\19\ Ramboll Environment and Health, January 2021, <a href="http://www.camx.com">www.camx.com</a>.
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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 NO<INF>X</INF> 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 NO<INF>X</INF> 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 NO<INF>X</INF>.
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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.
---------------------------------------------------------------------------

\21\ March 2018 memorandum, Attachment A.
\22\ Id. at A-1.
\23\ Id.
---------------------------------------------------------------------------

The remainder of this section describes the EPA's proposed
framework with respect to analytic year, definition of nonattainment
and maintenance receptors, selection of contribution threshold, and
multifactor control strategy 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).
---------------------------------------------------------------------------

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

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

\30\ As examples of general approaches for how such an analysis
could be conducted for their sources, states could look to the CSAPR
Update, 81 FR 74504, 74539-51; CSAPR, 76 FR 48208, 48246-63; CAIR,
70 FR 25162, 25195-229; or the NO<INF>X</INF> SIP Call, 63 FR 57356,
57399-405. See also Revised CSAPR Update, 86 FR 23054, 23086-23116.
Consistently across these rulemakings, the EPA has developed
emissions inventories, analyzed different levels of control
stringency at different cost thresholds, and assessed resulting
downwind air quality improvements.
---------------------------------------------------------------------------

5. Step 4 of the 4-Step Interstate Transport Framework
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 <a href="https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs">https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs</a>.
\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:
<a href="https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf">https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf</a>.
---------------------------------------------------------------------------

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

\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 <a href="https://www.airnowtech.org/">https://www.airnowtech.org/</a>.
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 <a href="https://ready.arl.noaa.gov/edas40.php">https://ready.arl.noaa.gov/edas40.php</a>.
\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.
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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
(NO<INF>X</INF>) 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
NO<INF>X</INF> emissions in excess of 20,000 tons of NO<INF>X</INF>
reduced per year. Arkansas had also experienced decreases in
NO<INF>X</INF> emissions each evaluated year and emitted less
NO<INF>X</INF> 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
NO<INF>X</INF>, as well as VOCs, through 2023. ADEQ confirmed that
based on this analysis, the overall general trends of NO<INF>X</INF>
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.
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\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
NO<INF>X</INF> controls at electric generating units (EGUs) in the
State because EGUs are the largest source of NO<INF>X</INF> emissions
that ADEQ regulates. In its analysis, ADEQ found that the costs to
install additional NO<INF>X</INF> 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 NO<INF>X</INF> 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.
---------------------------------------------------------------------------

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

\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 NO<INF>X</INF> 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 NO<INF>X</INF> controls for EGUs. As stated above, Arkansas
found that the costs to install additional NO<INF>X</INF> 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 NO<INF>X</INF> 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) NO<INF>X</INF>
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 NO<INF>X</INF> 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 NO<INF>X</INF> 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, PM<INF>2.5</INF> and Regional Haze'', Nov. 29, 2018, at
101, available at <a href="https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf">https://www.epa.gov/sites/default/files/2020-10/documents/o3-pm-rh-modeling_guidance-2018.pdf</a> (``2018 Air Quality
Modeling Guidance''). See also ``Draft Modeling Guidance for
Demonstrating Attainment of Air Quality Goals for Ozone,
PM<INF>2.5,</INF> and Regional Haze'', Dec. 3, 2014, at 97-98,
available at <a href="https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf">https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf</a> (``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 NO<INF>X</INF> and VOC
data of Oklahoma's emissions from EPA's emission trends and modeling to
demonstrate an anticipated substantial reduction of NO<INF>X</INF> and
VOC from 2011 to 2023: (1) Reductions of NO<INF>X</INF> 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 NO<INF>X</INF>
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 NO<INF>X</INF> emissions reductions; and that any additional
NO<INF>X</INF> 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 <a href="https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs">https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs</a>.
\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 <a href="https://www.ferc.gov/electric-power-markets">https://www.ferc.gov/electric-power-markets</a>.
---------------------------------------------------------------------------

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.
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[[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
NO<INF>X</INF> 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)
(<a href="https://www.epa.gov/aqs">https://www.epa.gov/aqs</a>). 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
a

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