[Federal Register Volume 87, Number 35 (Tuesday, February 22, 2022)]
[Proposed Rules]
[Pages 9838-9878]
[FR Doc No: 2022-02953]

Vol. 87

Tuesday,

No. 35

February 22, 2022

Part III

Environmental Protection Agency

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40 CFR Part 52

Air Plan Disapproval; Illinois, Indiana, Michigan, Minnesota, Ohio,
Wisconsin; Air Plan Disapproval; Region 5 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

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R05-OAR-2022-0006; EPA-HQ-OAR-2021-0663; FRL-9431-01-R5]

Air Plan Disapproval; Illinois, Indiana, Michigan, Minnesota,
Ohio, Wisconsin; Air Plan Disapproval; Region 5 Interstate Transport of
Air Pollution for the 2015 8-Hour Ozone National Ambient Air Quality
Standards

AGENCY: Environmental Protection Agency (EPA).

ACTION: Proposed rule.

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SUMMARY: Pursuant to the Federal Clean Air Act (CAA or the Act), the
Environmental Protection Agency (EPA) is proposing to disapprove State
Implementation Plan (SIP) submittals from Illinois, Indiana, Michigan,
Minnesota, Ohio, and Wisconsin regarding interstate transport for the
2015 ozone national ambient air quality standards (NAAQS). The ``good
neighbor'' or ``interstate transport'' provision requires that each
state's SIP contain adequate provisions to prohibit emissions from
within the state from significantly contributing to nonattainment or
interfering with maintenance of the NAAQS in other states. This
requirement is part of the broader set of ``infrastructure''
requirements, which are designed to ensure that the structural
components of each state's air quality management program are adequate
to meet the state's responsibilities under the CAA. This disapproval,
if finalized, will establish a 2-year deadline for EPA to promulgate a
Federal Implementation Plan (FIP) to address the relevant interstate
transport requirements, unless EPA approves a subsequent SIP submittal
that meets these requirements. Disapproval does not start a mandatory
sanctions clock.

DATES: Comments: Written comments must be received on or before April
25, 2022.

ADDRESSES: You may send comments, identified as Docket No. EPA-R05-OAR-
2022-0006, by any of the following methods: Federal Rulemaking Portal
at https://www.regulations.gov following the online instructions for
submitting comments or via email to [email protected]. Include Docket
ID No. EPA-R05-OAR-2022-0006 in the subject line of the message.
    Instructions: All submissions received must include the Docket ID
No. for this rulemaking. Comments received may be posted without change
to https://www.regulations.gov/, including any personal information
provided. For detailed instructions on sending comments and additional
information on the rulemaking process, see the ``Public Participation''
heading of the SUPPLEMENTARY INFORMATION section of this document. 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 EPA Docket
Center services and the current status, please visit us online at
https://www.epa.gov/dockets.

FOR FURTHER INFORMATION CONTACT: Olivia Davidson, Environmental
Scientist, Attainment Planning and Maintenance Section, Air Programs
Branch (AR-18J), Environmental Protection Agency, Region 5, 77 West
Jackson Boulevard, Chicago, Illinois 60604,<PHONE_NUMBER>,
[email protected]. The EPA Region 5 office is open from 8:30 a.m.
to 4:30 p.m., Monday through Friday, excluding Federal holidays and
facility closures due to COVID-19.

SUPPLEMENTARY INFORMATION:
    Public Participation: Submit your comments, identified by Docket ID
No. EPA-R05-OAR-2022-0006, at https://www.regulations.gov (our
preferred method), or the other methods identified in the ADDRESSES
section. Once submitted, comments cannot be edited or removed from the
docket. EPA may publish any comment received to its public docket. Do
not submit to EPA's docket at https://www.regulations.gov any
information you consider to be Confidential Business Information (CBI)
or other information whose disclosure is restricted by statute.
Multimedia submissions (audio, video, etc.) must be accompanied by a
written comment. The written comment is considered the official comment
and should include discussion of all points you wish to make. 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-R05-OAR-2022-0006
and EPA-HQ-OAR-2021-0663. Docket No. EPA-R05-OAR-2022-0006 contains
information specific to Illinois, Indiana, Michigan, Minnesota, Ohio,
and Wisconsin, including the notice of proposed rulemaking. Docket No.
EPA-HQ-OAR-2021-0663 contains additional modeling files, emissions
inventory files, technical support documents, and other relevant
supporting documentation regarding interstate transport of emissions
for the 2015 ozone NAAQS which are being used to support this action.
All comments regarding information in either of these dockets are to be
made in Docket No. EPA-R05-OAR-2022-0006. For additional submission
methods, please contact Olivia Davidson,<PHONE_NUMBER>,
[email protected]. For the full EPA public comment policy,
information about CBI or multimedia submissions, and general guidance
on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets. Due to public health concerns related to COVID-
19, the EPA Docket Center and Reading Room are open to the public by
appointment only. Our Docket Center staff also continues to provide
remote customer service via email, phone, and webform. For further
information and updates on EPA Docket Center services, please visit us
online at https://www.epa.gov/dockets.
    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
docket for this action, Docket No. EPA-R05-OAR-2022-0006, is available
electronically at www.regulations.gov. While all documents in the
docket are listed in the index, some information may not be publicly
available due to docket file size restrictions or content (e.g., CBI).
    Throughout this document, ``we,'' ``us,'' and ``our'' means EPA.

I. Background

A. Description of Statutory Background

    On October 1, 2015, EPA promulgated a revision to the 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 so-called ``prongs'' within CAA section
110(a)(2)(D)(i)(I). A SIP for a new or revised NAAQS must contain
adequate provisions prohibiting any source or other type of emissions
activity within the state from emitting air pollutants in amounts that
will significantly contribute to nonattainment of the NAAQS in another
state (prong 1) or interfere with maintenance of the NAAQS in another
state (prong 2). 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 EPA's Four Step Interstate Transport Regulatory
Process

    EPA is using the 4-step interstate transport framework (or 4-step
framework) to evaluate the states' SIP submittals addressing the
interstate transport provision for the 2015 ozone NAAQS. 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\ 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\ EPA, working in partnership with states, developed the
following 4-step interstate transport framework to evaluate a state's
obligations to eliminate interstate transport emissions under the
interstate transport provision for the ozone NAAQS: (1) Identify
monitoring sites that are projected to have problems attaining and/or
maintaining the NAAQS (i.e., nonattainment and/or maintenance
receptors); (2) identify states that impact those air quality problems
in other (i.e., downwind) states sufficiently such that the states are
considered ``linked'' and therefore warrant further review and
analysis; (3) identify the emissions reductions necessary (if any),
applying a multifactor analysis, to eliminate each linked upwind
state's significant contribution to nonattainment or interference with
maintenance of the NAAQS at the locations identified in Step 1; and (4)
adopt permanent and enforceable measures needed to achieve those
emissions reductions.
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    \7\ In addition to the CSAPR rulemakings, other regional
rulemakings addressing ozone transport include the ``NOX
SIP Call,'' 63 FR 57356 (October 27, 1998) and the ``Clean Air
Interstate Rule'' (CAIR), 70 FR 25162 (May 12, 2005).
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C. Background on EPA's Ozone Transport Modeling Information

    In general, EPA has performed nationwide air quality modeling to
project ozone design values which are used in combination with measured
data to identify nonattainment and maintenance receptors. To quantify
the contribution of emissions from specific upwind states on 2023 ozone
design values for the identified downwind nonattainment and maintenance
receptors, EPA performed nationwide, state-level ozone source
apportionment modeling for 2023. The source apportionment modeling
provided contributions to ozone at receptors from precursor emissions
of anthropogenic nitrogen oxides (NOX) and volatile organic
compounds (VOCs) in individual upwind states.
    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, EPA published a notice of data availability (NODA) in
which we requested comment on preliminary interstate ozone transport
data including projected ozone design values and interstate
contributions for 2023 using a 2011 base year platform.\8\ In the NODA,
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 ozone NAAQS.\9\ On
October 27, 2017, we released a memorandum (October 2017 memorandum)
containing updated 2011 platform-based modeling data for 2023, which
incorporated changes made in response to comments on the NODA, and
noted that the modeling may be useful for states developing SIPs to
address interstate transport obligations for the 2008 ozone NAAQS.\10\
On March 27, 2018, we issued a memorandum (March 2018 memorandum)
noting that the same 2023 modeling data released in the October 2017
memorandum could also be useful for identifying potential downwind air
quality problems with respect to the 2015 ozone NAAQS at Step 1 of the
4-step interstate transport framework.\11\ The March 2018 memorandum
also included the then newly available contribution modeling data for
2023 to assist states in evaluating their impact on potential downwind
air quality problems for the 2015 ozone NAAQS under Step 2 of the 4-
step interstate transport framework.\12\ 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.\13\
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    \8\ See Notice of Availability of the Environmental Protection
Agency's Preliminary Interstate Ozone Transport Modeling Data for
the 2015 ozone National Ambient Air Quality Standard (NAAQS), 82 FR
1733 (January 6, 2017).
    \9\ 82 FR at 1735.
    \10\ See Information on the Interstate Transport State
Implementation Plan Submissions for the 2008 Ozone National Ambient
Air Quality Standards under Clean Air Act Section
110(a)(2)(D)(i)(I), October 27, 2017, available in docket EPA-HQ-
OAR-2021-0663 or at https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \11\ See Information on the Interstate Transport State
Implementation Plan Submissions for the 2015 Ozone National Ambient
Air Quality Standards under Clean Air Act Section
110(a)(2)(D)(i)(I), March 27, 2018, available in docket EPA-HQ-OAR-
2021-0663 or at https://www.epa.gov/interstate-air-pollution-transport/interstate-air-pollution-transport-memos-and-notices.
    \12\ The March 2018 memorandum, however, provided, ``While the
information in this memorandum and the associated air quality
analysis data could be used to inform the development of these SIPs,
the information is not a final determination regarding states'
obligations under the good neighbor provision. Any such
determination would be made through notice-and-comment rulemaking.''
    \13\ See Analysis of Contribution Thresholds for Use in Clean
Air Act Section 110(a)(2)(D)(i)(I) Interstate Transport State
Implementation Plan Submissions for the 2015 Ozone National Ambient
Air Quality Standards, August 31, 2018 (``August 2018 memorandum''),
and Considerations for Identifying Maintenance Receptors for Use in
Clean Air Act Section 110(a)(2)(D)(i)(I) Interstate Transport State
Implementation Plan Submissions for the 2015 Ozone National Ambient
Air Quality Standards, October 19, 2018, available in docket EPA-HQ-
OAR-2021-0663 or at https://www.epa.gov/airmarkets/memo-and-supplemental-information-regarding-interstate-transport-sips-2015-ozone-naaqs.
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    Since the release of the modeling data shared in the March 2018
memorandum, EPA has performed modeling using a 2016-based emissions
modeling platform (i.e., 2016v1) This emissions platform was developed
under the EPA/Multi-Jurisdictional Organization (MJO)/state
collaborative project.\14\ This collaborative project was a multi-year
joint effort by EPA, MJOs, and states to develop a new, more recent
emissions platform for use by EPA and states in regulatory modeling as
an improvement over the dated 2011-based platform that EPA had used to
project ozone design values and contribution data provided in the 2017
and 2018 memoranda. EPA used the 2016v1 emissions to project ozone
Design values and contributions for 2023. On October 30, 2020, in the
Notice of Proposed Rulemaking for the Revised CSAPR Update, EPA
released and accepted public comment on 2023 modeling that used the
2016v1 emissions platform.\15\ See 85 FR 68964, 68981. Although the
Revised CSAPR Update addressed transport for the 2008 ozone NAAQS, the
projected design values and contributions from the 2016v1 platform are
also useful for identifying downwind ozone problems and linkages with
respect to the 2015 ozone NAAQS.\16\
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    \14\ The results of this modeling, as well as the underlying
modeling files, are included in docket ID No. EPA-HQ-OAR-2021-0663.
    \15\ See 85 FR 68964, 68981.
    \16\ See the Air Quality Modeling Technical Support Document for
the Final Revised Cross-State Air Pollution Rule Update, included in
the Headquarters docket ID No. EPA-HQ-OAR-2021-0663.
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    Following the final Revised CSAPR Update, EPA made further updates
to the 2016 emissions platform to include mobile emissions from EPA's
Motor Vehicle Emission Simulator MOVES3 model \17\ and updated
emissions projections for electric generating units (EGUs) that reflect
the emissions reductions from the Revised CSAPR Update, recent
information on plant closures, and other sector trends. The construct
of the updated emissions platform, 2016v2, is described in the
emissions modeling technical support document (TSD) for this proposed
rule.\18\
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    \17\ Additional details and documentation related to the MOVES3
model can be found at https://www.epa.gov/moves/latest-version-motor-vehicle-emission-simulator-moves.
    \18\ See Technical Support Document (TSD) Preparation of
Emissions Inventories for the 2016v2 North American Emissions
Modeling Platform included in the Headquarters docket ID No. EPA-HQ-
OAR-2021-0663.
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    EPA's latest projections of the baseline EGU emissions uses the
version 6--Summer 2021 Reference Case of the Integrated Planning Model
(IPM).\19\ IPM is a multi-regional, dynamic, and deterministic linear
programming model of the U.S. electric power sector. The model provides
forecasts of least cost capacity expansion, electricity dispatch, and
emission control strategies, while meeting energy demand,
environmental, transmission, dispatch, and reliability constraints.
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    \19\ Detailed information and documentation of EPA's Base Case,
including all the underlying assumptions, data sources, and
architecture parameters can be found on EPA's website at: https://www.epa.gov/airmarkets/epas-power-sector-modeling-platform-v6-using-ipm-summer-2021-reference-case.
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    The IPM version 6--Summer 2021 Reference Case incorporated recent
updates through the Summer of 2021 to account for updated Federal and
State environmental regulations for EGUs. This projected base case
accounts for the effects of the finalized Mercury and Air Toxics
Standards rule (MATS), CSAPR, the CSAPR Update, the Revised CSAPR
Update, New Source Review settlements, the final Effluent Limitation
Guidelines (ELG) Rule, the Coal Combustion Residual (CCR) Rule, and
other on-the-books Federal and State rules (including renewable energy
tax credit extensions from the Consolidated Appropriations Act of 2021)
through early 2021 impacting sulfur dioxide (SO2),
NOX, directly emitted particulate matter, carbon dioxide,
and power plant operations. It also includes final actions EPA has
taken to implement the Regional Haze Rule and Best Available Retrofit
Technology (BART) requirements. Further, the EPA Platform v6 uses
demand projections from the Energy Information Agency's (EIA) Annual
Energy Outlook (AEO) 2020.
    The IPM version 6--Summer 2021 Reference Case uses the National
Electric Energy Data System (NEEDS) v6 database as its source for data
on all existing and planned-committed units. Units are removed from the
NEEDS inventory only if a high degree of certainty could be assigned to
future implementation of the announced future closure or retirement.
The available retirement-related information was reviewed for each
unit, and the following rules are applied to remove:

    (i) Units that are listed as retired in the December 2020 EIA
Form 860M
    (ii) Units that have a planned retirement year prior to June 30,
2023 in the December 2020 EIA Form 860M
    (iii) Units that have been cleared by a regional transmission
operator (RTO) or independent system operator (ISO) to retire before
2023, or whose RTO/ISO clearance to retire is contingent on actions
that can be completed before 2023
    (iv) Units that have committed specifically to retire before
2023 under Federal or state enforcement actions or regulatory
requirements
    (v) And finally, units for which a retirement announcement can
be corroborated by other available information. Units required to
retire pursuant to enforcement actions or state rules on July 1,
2023 or later are retained in NEEDS v6.

    Retirements or closures taking place on or after July 1, 2023 are
captured as constraints on those units in the IPM modeling, and the
units are retired in future year projections per the terms of the
related requirements. Any retirements excluded from the NEEDS v6
inventory can be viewed in the NEEDS spreadsheet.\20\
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    \20\ The ``Capacity Dropped'' and the ``Retired Through 2023''
worksheets in NEEDS lists all units that are removed from the NEEDS
v6 inventory--NEEDS v6 Summer 2021 Reference Case. This data can be
found on EPA's website at: https://www.epa.gov/airmarkets/national-electric-energy-data-system-needs-v6.
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    As highlighted in previous rulemakings, the IPM documentation, and
EPA's Power Sector Modeling website, EPA's goal is to explain and
document the use of IPM in a transparent and publicly accessible
manner, while also providing for concurrent channels for improving the
model's assumptions and representation by soliciting constructive
feedback to improve the model. This includes making all inputs and
assumptions to the model, output files from the model, and IPM feedback
form publicly available on EPA's website.
    EPA performed air quality modeling of the 2016v2 emissions using
the most recent public release version of the Comprehensive Air-quality
Model with extensions (CAMx) photochemical modeling, version 7.10.\21\
EPA now proposes to primarily rely on modeling

based on the updated and newly available 2016v2 emissions platform in
evaluating these submissions with respect to Steps 1 and 2 of the 4-
step interstate transport framework and generally referenced within
this action as 2016v2 modeling for 2023. By using the updated modeling
results, EPA is using the most current and technically appropriate
information for this proposed rulemaking. Section III 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 EPA's 2016v2 modeling. In
this action, EPA is accepting public comment on this updated 2023
modeling, which uses a 2016v2 emissions platform. Comments on EPA's air
quality modeling should be submitted in the Regional docket for this
action, docket ID No. EPA-R05-OAR-2022-0006. Comments are not being
accepted in docket ID No. EPA-HQ-OAR-2021-0663.
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    \21\ Ramboll Environment and Health, January 2021, www.camx.com.
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    States may have chosen to rely on the results of EPA modeling and/
or alternative modeling performed by states or MJOs to evaluate
downwind air quality problems and contributions as part of their
submissions. As most Region 5 states have done so, in Sections III.A,
III.B, III.C, III.D, and III.E, we evaluate how Region 5 states used
air quality modeling information in their submissions.

D. EPA's Approach to Evaluating Interstate Transport SIPs for the 2015
Ozone NAAQS

    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 NOx SIP Call have necessitated the
application of a uniform framework of policy judgments to ensure an
``efficient and equitable'' approach. See EME Homer City, 572 U.S. 489,
519 (2014).
    In the March, August, and October 2018 memoranda, 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. 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, 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 potential
``flexibilities'' as may have been identified or suggested in the past,
EPA will evaluate whether the state adequately justified the technical
and legal basis for doing so.
    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.\22\ However, EPA made clear in that
Attachment that the list of ideas were not suggestions endorsed by the
Agency but rather ``comments provided in various forums'' on which EPA
sought ``feedback from interested stakeholders.'' \23\ 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.'' \24\ 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, EPA will thoroughly review the technical and legal
justifications for doing so.
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    \22\ March 2018 memorandum, Attachment A.
    \23\ Id. at A-1.
    \24\ Id.
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    The remainder of this section describes EPA's proposed framework
with respect to analytic year, definition of nonattainment and
maintenance receptors, selection of contribution threshold, and
multifactor control strategy assessment.
1. Selection of Analytic Year
    In general, the states and 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).\25\ 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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    \25\ For attainment dates for the 2015 ozone NAAQS, refer to CAA
section 181(a), 40 CFR 51.1303, and Additional Air Quality
Designations for the 2015 Ozone National Ambient Air Quality
Standards, 83 FR 25776 (June 4, 2018, effective Aug. 3, 2018).
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    On May 19, 2020, the D.C. Circuit issued a decision in Maryland v.
EPA that cited the Wisconsin decision in holding that 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 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). EPA interprets the court's
holding in Maryland as requiring the states and the Agency, under the
good neighbor provision, to assess downwind air quality as
expeditiously as practicable and no later than the next applicable
attainment date,\26\ 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.\27\ EPA believes that 2023 is now the
appropriate year for analysis of interstate transport obligations for
the 2015 ozone NAAQS, because the 2023 ozone season is the last
relevant ozone season during which achieved emissions reductions in
linked upwind states could assist downwind states with meeting the
August 3, 2024 Moderate area attainment date for the 2015 ozone NAAQS.
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    \26\ We note that the court in Maryland did not have occasion to
evaluate circumstances in which EPA may determine that an upwind
linkage to a downwind air quality problem exists at steps 1 and 2 of
the interstate transport framework by a particular attainment date,
but for reasons of impossibility or profound uncertainty the Agency
is unable to mandate upwind pollution controls by that date. See
Wisconsin, 938 F.3d at 320. The D.C. Circuit noted in Wisconsin that
upon a sufficient showing, these circumstances may warrant
flexibility in effectuating the purpose of the interstate transport
provision.
    \27\ 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).
---------------------------------------------------------------------------

    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 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, EPA must act on SIP submittals using the
information available at the time it takes such action. In this
circumstance, 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 EPA will use the analytical year of 2023 to evaluate each
state's CAA section 110(a)(2)(D)(i)(I) SIP submission with respect to
the 2015 ozone NAAQS.
2. Step 1 of the 4-Step Interstate Transport Framework
    In Step 1, EPA identifies monitoring sites that are projected to
have problems attaining and/or maintaining the NAAQS in the 2023
analytic year. Where 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 EPA's 4-step interstate
transport framework. For sites that are identified as a nonattainment
or maintenance receptor in 2023, we proceed to the next step of our 4-
step interstate transport framework by identifying the upwind state's
contribution to those receptors.
    EPA's approach to identifying ozone nonattainment and maintenance
receptors in this action is consistent with the approach used in
previous transport rulemakings. 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.\28\
---------------------------------------------------------------------------

    \28\ See North Carolina v. EPA, 531 F.3d at 910-11 (D.C. Cir.
2008) (holding that EPA must give ``independent significance'' to
each prong of CAA section 110(a)(2)(D)(i)(I)).
---------------------------------------------------------------------------

    For the purpose of this proposal, EPA identifies nonattainment
receptors as those monitoring sites that are projected to have average
design values that exceed the NAAQS and that are also measuring
nonattainment based on the most recent monitored design values. This
approach is consistent with prior transport rulemakings, such as the
CSAPR Update, where EPA defined nonattainment receptors as those areas
that both currently measure nonattainment and that EPA projects will be
in nonattainment in the future analytic year (i.e., 2023).\29\
---------------------------------------------------------------------------

    \29\ 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 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, 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).\30\ Specifically, EPA identified maintenance
receptors as those receptors that would have difficulty maintaining the
relevant NAAQS in a scenario that takes into account historical
variability in air quality at that receptor. The variability in air
quality was determined by evaluating the ``maximum'' future design
value at each receptor based on a projection of the maximum measured
design value over the relevant period. EPA interprets the projected
maximum future design value to be a potential future air quality
outcome consistent with the meteorology that yielded maximum measured
concentrations in the ambient data set analyzed for that receptor
(i.e., ozone conducive meteorology). 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 design value gives a reasonable projection of
future air quality at the receptor under a scenario in which such
conditions do, in fact, reoccur. The projected maximum design value is
used to identify upwind emissions that, under those circumstances,
could interfere with the downwind area's ability to maintain the NAAQS.
---------------------------------------------------------------------------

    \30\ 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, 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, EPA identifies ``maintenance-only'' receptors as those
monitoring sites that have projected average design values above the
level of the applicable NAAQS, but that are not currently measuring
nonattainment based on the most recent official design values. In
addition, those monitoring sites with projected average design values
below the NAAQS, but with projected maximum design values above the
NAAQS are also identified as ``maintenance only'' receptors, even if
they are currently measuring nonattainment based on the most recent
official design values.
3. Step 2 of the 4-Step Interstate Transport Framework
    In Step 2, 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 EPA, therefore, concludes that
the state does not significantly contribute to nonattainment or
interfere with maintenance of the NAAQS in the

downwind states. However, if a state's contribution equals or exceeds
the 1 percent threshold, the state's emissions are further evaluated in
Step 3, considering both air quality and cost as part of a multi-factor
analysis, to determine what, if any, emissions might be deemed
``significant'' and, thus, must be eliminated under CAA section
110(a)(2)(D)(i)(I). EPA is proposing to rely in the first instance on
the 1 percent threshold for the purpose of evaluating a state's
contribution to nonattainment or maintenance of the 2015 ozone NAAQS
(i.e., 0.70 ppb) at downwind receptors. This is consistent with the
Step 2 approach that 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. EPA
continues to find 1 percent to be an appropriate threshold. For ozone,
as EPA found in the Clean Air Interstate Rule (CAIR), CSAPR, and the
CSAPR Update, a portion of the nonattainment problems from
anthropogenic sources in the U.S. result from the combined impact of
relatively small contributions from many upwind states, along with
contributions from in-state sources and, in some cases, substantially
larger contributions from a subset of particular upwind states. 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 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).
i. EPA's Experience With Alternative Step 2 Thresholds
    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, 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.
    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.\31\ (The memorandum also indicated that any higher alternative
threshold, such as 2 ppb, would likely not be appropriate.) However,
EPA also provided that ``air agencies should consider whether the
recommendations in this guidance are appropriate for each situation.''
Following receipt and review of 49 good neighbor SIP submittals for the
2015 ozone NAAQS, 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.
---------------------------------------------------------------------------

    \31\ August 2018 memorandum at 4.
---------------------------------------------------------------------------

    For instance, in nearly all submittals, the states did not provide
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, 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.\32\ It was at 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.
---------------------------------------------------------------------------

    \32\ Air Plan Approval; Iowa; Infrastructure State
Implementation Plan Requirements for the 2015 Ozone National Ambient
Air Quality Standard, 85 FR 12232 (March 2, 2020). The Agency
received adverse comment on this proposed approval and has not taken
final action with respect to this proposal.
---------------------------------------------------------------------------

    Furthermore, 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.\33\ The availability of different thresholds at Step 2 has
the potential to result in inconsistent application of good neighbor
obligations based solely on the strength of a state's implementation
plan submittal at Step 2 of the 4-Step interstate transport framework.
From the perspective of ensuring effective regional implementation of
good neighbor obligations, the more important analysis is the
evaluation of the emissions reductions needed, if any, to address a
state's significant contribution after consideration of a multifactor
analysis at Step 3, including a detailed evaluation that considers air
quality factors and cost. Where alternative thresholds for purposes of
Step 2 may be ``similar'' in terms of capturing the relative amount of
upwind contribution (as described in the August 2018 memorandum),
nonetheless, use of an alternative threshold would allow certain states
to avoid further evaluation of potential emission controls while other
states must proceed to a Step 3 analysis. This can create significant
equity and consistency problems among states.
---------------------------------------------------------------------------

    \33\ EPA notes that Congress has placed on 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. 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, 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;
\34\ in 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 the NAAQS threshold.
---------------------------------------------------------------------------

    \34\ See August 2018 memorandum at 4.
---------------------------------------------------------------------------

    Consistency with past interstate transport actions such as CSAPR,
and the CSAPR Update and Revised CSAPR Update rulemakings (which used a
Step 2 threshold of 1 percent of the NAAQS for two less stringent ozone
NAAQS), is also important. Continuing to use a 1 percent of NAAQS
approach ensures that as the NAAQS are revised and made more stringent,
an appropriate increase in stringency at Step 2 occurs, so as to ensure
an appropriately larger amount of total upwind-state contribution is
captured for purposes of fully addressing interstate transport. See 76
FR 48208, 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, EPA's experience
since the issuance of that memorandum has revealed substantial
programmatic and policy difficulties in attempting to implement this
approach. Nonetheless, EPA is not at this time rescinding the August
2018 memorandum. EPA invites comment on this broader discussion of
issues associated with alternative thresholds at Step 2. Depending on
comment and further evaluation of this issue, EPA may determine to
rescind the August 2018 memorandum in the future.
4. Step 3 of the 4-Step Interstate Transport Framework
    Consistent with EPA's longstanding approach to eliminating
significant contribution or interference with maintenance at Step 3,
states linked at Steps 1 and 2 are generally expected to prepare a
multifactor assessment of potential emissions controls. EPA's analysis
at Step 3 in prior Federal actions addressing interstate transport
requirements has primarily focused on an evaluation of the 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 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 still to be linked to
one or more downwind receptor(s), the state must provide a well-
documented evaluation determining whether their emissions constitute
significant contribution or interference with maintenance by evaluating
additional available control opportunities by preparing a multifactor
assessment. While EPA has not prescribed a particular method for this
assessment, 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.\35\
---------------------------------------------------------------------------

    \35\ As examples of general approaches for how such an analysis
could be conducted for their sources, states could look to the CSAPR
Update, 81 FR 74504, 74539-51; CSAPR, 76 FR 48208, 48246-63; CAIR,
70 FR 25162, 25195-229; or the NOX SIP Call, 63 FR 57356,
57399-405. See also Revised CSAPR Update, 86 FR 23054, 23086-23116.
Consistently across these rulemakings, EPA has developed emissions
inventories, analyzed different levels of control stringency at
different cost thresholds, and assessed resulting downwind air
quality improvements.
---------------------------------------------------------------------------

5. Step 4 of the 4-Step Interstate Transport Framework
    At Step 4, states (or EPA) develop permanent and federally
enforceable control strategies to achieve the emissions reductions
determined to be necessary at Step 3 to eliminate significant
contribution to nonattainment or interference with maintenance of the
NAAQS. For a state linked at Steps 1 and 2 to rely on an emissions
control measure at Step 3 to address its interstate transport
obligations, that measure must be included in the state's SIP so that
it is permanent and federally enforceable. See CAA section 110(a)(2)(D)
(``Each such [SIP] shall . . . contain adequate provisions . . .'').
See also CAA 110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A.,
786 F.3d 1169, 1175-76 (9th Cir. 2015) (holding that measures relied on
by state to meet CAA requirements must be included in the SIP).

II. SIP Submissions Addressing Interstate Transport of Air Pollution
for the 2015 Ozone NAAQS

    Five of the six states within EPA Region 5 that are included in
this multi-state proposed disapproval have chosen to use air quality
modeling performed by the Lake Michigan Air Directors Consortium
(LADCO) \36\ as an alternative to or in addition to EPA's modeling for
the purpose of identifying downwind receptors and upwind state
contributions to these receptors relevant to their submissions. The
LADCO modeling consisted of ozone season (May 1-September 30, 2011)
model simulations using the Comprehensive Air Quality Model with
Extensions, CAMx version 6.4 for a 2011 base year and 2023 as the
future analytic year. In their modeling, LADCO used EPA's 2011-based
``EN'' emissions modeling platform, except for emissions from EGU's in
2023. In their modeling, LADCO used the Eastern Regional Technical
Advisory Committee (ERTAC) EGU Tool version 2.7 \37\ to provide EGU
emissions for 2023, whereas EPA used projected EGU emissions based on
engineering analytics.\38\
---------------------------------------------------------------------------

    \36\ LADCO works collaboratively with state governments, tribal
governments, and various Federal agencies in Illinois, Indiana,
Michigan, Minnesota, Ohio, and Wisconsin.
    \37\ https://www.marama.org/2013-ertac-egu-forecasting-tool-documentation.
    \38\ Technical Support Document (TSD) Additional Updates to
Emissions Inventories for the Version 6.3, 2011 Emissions Modeling
Platform for the Year 2023 https://www.epa.gov/air-emissions-modeling/additional-updates-2011-and-2023-emissions-version-63-platform-technical.
---------------------------------------------------------------------------

    LADCO provided projected 2023 future year average and maximum
design values using the methodology in EPA's 2014 modeling
guidance.\39\ Although projected design values were presented based on
the 3x3 approach and the ``no water cell'' approach, described in the
March 2018 memorandum, LADCO relied upon design values from the 3x3
approach for

calculating contribution metric values at each receptor.
---------------------------------------------------------------------------

    \39\ See EPA's 2014 Draft Guidance Document, ``Draft Modeling
Guidance for Demonstrating Attainment of Air Quality Goals for
Ozone, PM2s, and Regional Haze'', https://www.epa.gov/sites/default/files/2020-10/documents/draft-o3-pm-rh-modeling_guidance-2014.pdf.
---------------------------------------------------------------------------

    Source apportionment modeling was performed by LADCO using the CAMx
Anthropogenic Precursor Culpability Assessment (APCA) tool to calculate
contributions from individual states to ozone at downwind monitoring
sites. In their modeling, LADCO tracked ozone contributions from only
those states that contributed at or above a 1 percent of the NAAQS
threshold to nonattainment and maintenance monitors in the EPA 2023
modeling provided in the March 2018 memorandum.

A. Illinois

    Illinois Environmental Protection Agency (IEPA) submitted a SIP
revision to address CAA Section 110(a)(2)(D)(i)(I) on May 21, 2019. The
submission utilized LADCO modeling results previously mentioned. IEPA
followed the 4-step interstate transport framework using an analytic
year of 2023 to identify receptors, Illinois' linkages to receptors,
and assess some emission reduction considerations. The following
sections will discuss IEPA's submission and the information provided
for each step in the process.
1. Information Provided by Illinois Regarding Step 1
    For Step 1 in the 4-step framework, the IEPA relied on LADCO
modeling to identify monitoring sites that are projected to have
problems attaining or maintaining the 2015 ozone NAAQS in 2023. As
previously mentioned, the LADCO modeling used the same technique as EPA
to calculate future year design values which were used to identify
maintenance and nonattainment receptors but used the ERTAC EGU Tool for
EGU emissions. IEPA noted they believed that the ERTAC EGU tool
provides better estimates of growth and forecasts than EPA's EGU
emission projections. IEPA identified two maintenance receptors in the
Great Lakes area (Sheboygan, Wisconsin and Allegan County, Michigan) as
well as and three nonattainment receptors and five additional
maintenance receptors in the Northeast. Across the continental U.S.,
IEPA identified a total of twelve nonattainment or maintenance
receptors: seven nonattainment receptors and five maintenance
receptors.\40\
---------------------------------------------------------------------------

    \40\ IEPA's SIP submission, Table CC, page 15.
---------------------------------------------------------------------------

2. Information Provided by Illinois Regarding Step 2
    IEPA's submittal at Step 2 presented Illinois' projected 2023
contribution of ozone emissions to the downwind maintenance and
nonattainment receptors and based on LADCO's ``with water'' modeling
\41\ IEPA used a contribution threshold of 1 ppb to define linkage as
opposed to one percent of the 2015 ozone NAAQS standard (0.70 ppb).
Illinois, relying on the August 2018 memorandum, argued that the
state's reliance on the 1 ppb threshold to identify linkages was
justified. First, IEPA asserted that the one percent of the NAAQS
contribution threshold is arbitrary because it is not in the CAA.
Second, IEPA claimed that a one percent of the NAAQS contribution
threshold is inappropriate for the 2015 ozone NAAQS because 0.70 ppb is
an order of magnitude smaller than the biases and errors typically
documented for regional photochemical modeling. IEPA noted that 1 ppb
is very small compared to the allowable error in peak performance and
bias and in IEPA's view is a conservative Step 2 contribution
threshold.
---------------------------------------------------------------------------

    \41\ Id.
---------------------------------------------------------------------------

    IEPA identified that Illinois is projected to contribute 14.93 ppb
and 19.25 ppb, respectively, in 2023 to two maintenance receptors:
Sheboygan, Wisconsin (Site ID: 55-117-0006), and Allegan, Michigan
(Site ID: 26-005-0003). IEPA concluded that Illinois is linked above a
contribution threshold of 1 ppb to these receptors.
3. Information Provided by Illinois Regarding Step 3
    IEPA provided several arguments to justify their conclusion that no
additional emission reductions are necessary to satisfy Illinois' ozone
transport obligations. The submittal stated that Illinois is developing
new NOX RACT standards for the Chicago area that, in
conjunction with existing NOX reductions, are estimated to
reduce NOX emissions by up to 20,000 tons/year relative to
existing state and Federal regulations impacting non-EGUs since 2014.
IEPA claims that these reductions were not included in any 2023
modeling. Illinois claims these expected emissions reductions,
alongside future Federal rules, will be enough to meet Illinois' good
neighbor obligations.
    IEPA asserted that Illinois' contributions to the Sheboygan,
Wisconsin and Allegan County maintenance monitors, which are both in
the LADCO domain, can be addressed in a manner that is fair and
equitable for all involved states through Illinois' participation in
LADCO. Illinois has been a member of LADCO since 1991. IEPA says that
since the inception of LADCO in 1991, ambient ozone concentrations have
drastically decreased in the Lake Michigan region. IEPA stated that it
is working through LADCO to refine ozone forecasting for air quality
and ozone receptors in the Midwest through various means including
updating emissions inventories and a base case for the modeling that
LADCO is preparing. IEPA stated that it expects field data from the
2017 Lake Michigan Ozone Study will inform the LADCO states to better
simulate the meteorology and chemistry of ozone in the Lake Michigan
area.
    IEPA also attempted to rely on a concept related to international
emissions, which was developed by outside parties and listed in
Attachment A to the March 2018 memorandum. IEPA noted that if
international emissions and offshore contributions to receptors from
LADCO's modeling, 1.40 ppb to the Sheboygan, Wisconsin receptor and
0.98 ppb at the Allegan County receptor, were subtracted off the top of
the receptors' maximum design values, Allegan, Michigan receptor's
maximum design value would be below 71 ppb and the Sheboygan, Wisconsin
receptor's maximum design value would drop down to 71.4 ppb. IEPA noted
that subtracting international and offshore contributions would result
in Allegan County no longer qualifying as a maintenance receptor.
4. Information Provided by Illinois Regarding Step 4
    IEPA did not consider any new permanent and enforceable measures to
reduce emissions in the SIP submission. IEPA instead noted they would
continue to assist LADCO with future modeling and analysis and would
work with EPA to identify additional ``flexibilities'' to define
maintenance, quantify transport, and demonstrate attainment.\42\
---------------------------------------------------------------------------

    \42\ Illinois' SIP submission at 16.
---------------------------------------------------------------------------

B. Indiana

    On November 2, 2018 the Indiana Department of Environmental
Management (IDEM) submitted a revision to the Indiana SIP addressing
interstate transport of air pollution for the 2015 ozone NAAQS. The
submission contained what the state characterized as a weight of
evidence analysis of Indiana's ozone transport receptors utilizing
LADCO modeling results previously mentioned. Indiana did not explicitly
follow the 4-Step interstate transport framework but did examine
downwind air quality and Indiana's contributions using an analytic year
of 2023 to describe

Indiana's linkages to receptors. The following sections will describe
IDEM's submission, and the information provided for each step in the
process.
1. Information Provided by Indiana Regarding Step 1
    For Step 1 of the 4-Step framework, IDEM identified monitoring
sites that are projected to have problems attaining and/or maintaining
the 2015 ozone NAAQS in 2023. As previously mentioned, the LADCO
modeling used the same technique as EPA to calculate future year design
values which were used to identify maintenance and nonattainment
receptors but used the ERTAC EGU Tool for EGU emissions. IDEM noted
they believed that the ERTAC EGU tool provides better estimates of
growth and forecasts than EPA's EGU emission projections. IDEM
presented the LADCO results, based on the ``3x3'' approach, which
identified ten receptors: Seven monitors with 2023 maximum design
values above the NAAQS, or maintenance receptors, and three monitors
with 2023 average design values greater than the 2015 ozone standard,
or nonattainment receptors.\43\
---------------------------------------------------------------------------

    \43\ Indiana's SIP submission Attachment 1, Table 7, page 30.
---------------------------------------------------------------------------

2. Information Provided by Indiana Regarding Step 2
    IDEM's submittal presented Indiana's projected 2023 ozone
contributions to maintenance and nonattainment receptors projected by
the LADCO modeling. IDEM relied primarily on the August 2018 memorandum
to justify the State's reliance on a 1 ppb contribution threshold to
identify linkages, as opposed to the 1 percent of the 2015 ozone NAAQS
standard (0.70 ppb) contribution threshold. IDEM noted that (1) the
tolerance level of ozone monitors is 1 ppb and (2) model run results
may contain biases larger than 1 percent of the NAAQS (0.70 ppb). Using
a 1 ppb threshold, IDEM identified that Indiana is linked to three
maintenance receptors: Sheboygan, Wisconsin (Monitor ID: 551170006),
Allegan, Michigan (Monitor ID: 260050003), and Richmond, New York
(Monitor ID: 360850067), and one nonattainment receptor: Harford,
Maryland (Monitor ID: 240251001).\44\ \45\ However, IDEM concluded on
the basis of its weight of evidence analysis, summarized in the
following subsection, that the monitors at Sheboygan, Wisconsin and
Allegan, Michigan would be in attainment in 2023.\46\
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    \44\ Indiana's SIP submission Attachment 1, Table 1, page 12.
    \45\ IDEM acknowledged that both the Harford, Maryland and
Richmond, New York receptors are nonattainment receptors in EPA's
modeling. Indiana's SIP submission Attachment 1, page 12.
    \46\ Indiana's SIP submission Attachment 1, page 38, 53.
---------------------------------------------------------------------------

3. Information Provided by Indiana Regarding Step 3
    IDEM cited Indiana's rule amendments under CSAPR to conclude the
State was already satisfying its good neighbor obligations for the
ozone NAAQS.\47\ In support, IDEM provided a weight-of-evidence
analysis to justify their conclusion that no additional emission
reductions as necessary to satisfy Indiana's ozone transport
obligations. The evidence consisted of an ozone monitoring data
analysis, emissions analysis, and photochemical modeling analyses,
including a back trajectory analysis.
---------------------------------------------------------------------------

    \47\ Indiana's SIP submission, page 6.
---------------------------------------------------------------------------

    IDEM provided information ozone and emissions trends. They cited a
general decline in monitored ozone concentrations across Indiana from
2007 through 2017, a decrease in Indiana's overall statewide
NOX emissions and VOC emissions from 2005 to 2014, a
decrease in Indiana EGU NOX emissions from 2011 to 2016, and
projected decreases in Region 5 EGU NOX and VOC emissions
through 2023 relative to a 2011 base year (based on both the ERTAC EGU
Tool and EPA's EGU projections using the Integrated Planning Model
(IPM)). IDEM credited the downward emissions trends to permanent and
enforceable control measures. IDEM made the argument that overall
decreasing ozone concentration and emissions trends in the State, and
in the LADCO states, correlate with reduced contributions to
nonattainment and maintenance receptors outside of Indiana. IDEM also
identified air quality trends at the four downwind receptors to which
IDEM determined Indiana was linked. IDEM asserted that a declining
trend in three-year design values at the receptors in Harford, Maryland
and Richmond, New York in combination with national emission reduction
regulations in place for EGUs, tighter mobile source emission controls
and other transport related emission reduction measures, would result
in those two receptors reaching attainment over time. For the
Sheboygan, Wisconsin and Allegan, Michigan receptors, IDEM concluded
that if ozone design value trends continued as expected then those two
receptors would reach attainment before 2023. IDEM also asserted they
believed that the receptors in the Northeast (Harford, Maryland and
Richmond, New York) received a greater contribution from local sources.
IDEM represented EPA had reached the same conclusion, citing a May 14,
2018 presentation.
    Next, IDEM presented an analysis of NOx controls for EGUs and non-
EGUs in the state from 2008 to 2017. IDEM considered current NOx
control measures, consent decree requirements, and future fuel switches
and retirements for large EGUs and non-EGUs. IDEM reported that the
State has seen a downward trend in annual NOX emissions from
both EGUs and non-EGUs due a combination of state and Federal rules
targeting fossil fueled EGUs and other large sources of NOX.
IDEM argued that it would not be cost-effective for non-EGUs to
implement further NOX controls because in 2017 there were
more than 93% fewer NOX emissions from non-EGUs when
compared to EGUs. IDEM stated they expect to see continued future
NOX emission reductions through 2028 from implementation of
Federal rules, the expected shutdown of nine EGUs, planned fuel
switches to natural gas for three EGUs, and enforceable consent decree
caps on NOX emissions at eleven EGUs. IDEM noted that future
retirements or retrofits to coal fired EGUs in Indiana were expected to
reduce NOX emissions by several thousand tons beyond those
projected by either LADCO or EPA. IDEM argued that the non-modeled
emission reductions would further assure future year attainment of the
ozone NAAQS at downwind receptors.
    For their photochemical analyses, IDEM presented LADCO modeling
results to show contributions from individual states to 12
monitors,\48\ as well as contributions from individual sectors to the
same 12 monitors.\49\ IDEM noted that Indiana contributed above 1 ppb
to monitors that would be receptors based on EPA's definitions. IDEM
used these data as the backdrop to several arguments related to
potential flexibilities identified in Attachment A to the March 2018
memorandum.\50\ IDEM stated that additional emissions reductions from
EGU and non-EGU sources in Indiana are becoming more difficult to
require because of reduced effectiveness of controls to make
significant decreases in ozone values, operational concerns, and
increased

costs for customers. IDEM asserted that emission reductions from local
mobile and nonroad sources would be more beneficial to the receptors
than additional reductions from EGUs and non-EGUs in Indiana because
EGUs and non-EGUs contribute less to the receptors than either the
mobile or nonroad sectors. IDEM also argued that EPA should address
contributions from Canada and Mexico as well as contributions from
offshore commercial marine vessels. In addition, IDEM compared 2012-
2017 monitoring data to LADCO's and EPA's modeling and concluded that
all four linked receptors were already below the projected 2023 design
values. IDEM also calculated Indiana's portion of contribution to the
Harford, Maryland receptor as 0.077 ppb (based on a contribution
threshold of 1 ppb) and determined that Indiana would need to reduce
its contribution by 0.0077 ppb to bring the Harford, Maryland receptor
into attainment. IDEM argued that 0.0077 ppb is well within the error
of the model and it would be ``difficult'' to translate into an
emission reduction requirement.\51\
---------------------------------------------------------------------------

    \48\ Indiana's SIP submission, Attachment 1, Table 9.
    \49\ Indiana's SIP submission, Attachment 1, Table 11.
    \50\ Based on the reference to the potential flexibilities in
Attachment A to the March 2018 memorandum on page 2 of Attachment 1
to Indiana's SIP submission, EPA assumes the reference to
``flexibilities'' on page 38 of Attachment 1 likewise references
Attachment A to the March 2018 memorandum.
    \51\ Indiana's SIP submission, Attachment 1 at 42.
---------------------------------------------------------------------------

    Finally, IDEM provided a back trajectory analysis to evaluate
contributions from Indiana to the Harford, Maryland and Richmond, New
York receptors on exceedance days from 2015 to 2017. These back
trajectories were conducted at 10 meters and 750 meters and initialized
at 18Z Greenwich Mean Time over a three-year period from 2015-2017. The
trajectories were run backwards over a 72-hour period from the
exceedance day measured at each of the monitors. Considering the
Harford, Maryland receptor, Indiana measured one back trajectory at 10
meters and six back trajectories at 750 meters that passed through
Indiana. For the Richmond, New York receptor, out of 27 exceedance
days, Indiana measured three back trajectories at 10 meters and eight
trajectories at 750 meters that passed through Indiana. Indiana argues
that only a fraction of the exceedance days at the Harford and Richmond
receptors has back trajectories that pass-through Indiana. Based on
this analysis, IDEM concluded that those receptors are more likely to
be impacted by local emissions and suggested that emission reductions
should come first from the surrounding areas in the Northeast before
from Indiana.
4. Information Provided by Indiana Regarding Step 4
    IDEM did not provide a Step 4 analysis.

C. Michigan

    Environment, Great Lakes and Energy (EGLE) (formerly Michigan
Department of Environmental Quality) submitted a SIP revision to
address CAA Section 110(a)(2)(D)(i)(I) on March 5, 2019. EGLE utilized
EPA modeling released with the March 2018 memorandum and LADCO modeling
and followed the 4-step interstate transport framework using an
analytic year of 2023 to describe Michigan's linkages to receptors in
other states. The submission also contained a weight-of-evidence
analysis to support EGLE's conclusions. The following sections will
discuss EGLE's submission and the information provided for each step in
the process.
1. Information Provided by Michigan Regarding Step 1
    For Step 1 in the 4-step framework, EGLE identified monitoring
sites that are projected to have problems attaining and/or maintaining
the 2015 ozone NAAQS in 2023. EGLE presented the results from both the
EPA modeling from the March 2018 memorandum and LADCO (using both the
with- and without-water approaches). EGLE noted that they believe the
ERTAC EGU Tool uses a more transparent and state-driven data gathering
mechanism for EGU emissions and control projects. EPA's modeling
projected 16 receptors to which Michigan is projected to contribute in
2023. LADCO modeling (with and without water) identified 15 receptors
to which Michigan is projected to contribute in 2023.
2. Information Provided by Michigan Regarding Step 2
    The first part of EGLE's submittal's step 2 analysis presented
Michigan's projected contributions to maintenance and nonattainment
receptors in 2023 from both the LADCO modeling (with and without water)
and the EPA modeling released with the March 2018 memorandum. The
submittal noted similar contribution concentrations between the two,
but found that the LADCO results often yielded slightly lower
contribution from Michigan sources than the EPA modeling for some
receptors. The state claimed this is attributed to LADCO's use of the
ERTAC EGU tool which they stated includes information on EGU shutdowns
and facility-specific information not included in the EPA modeling.
EGLE stated they had more confidence in the LADCO modeling.
    Further, EGLE attempted to rely on the 1 ppb Significant Impact
Level (SIL) threshold from Guidance on Significant Impact Levels for
Ozone and Fine Particles in the Prevention of Significant Deterioration
Permitting Program (April 17, 2018) \52\ for the Prevention of
Significant Deterioration (PSD) permitting program as an appropriate
contribution threshold to determine whether Michigan was linked to any
receptors at step 2. Michigan argued that if a stationary source's
contributions are insignificant below 1 ppb, then a state's interstate
transport contributions below 1 ppb are likewise insignificant. EGLE
performed an analysis on contribution thresholds to analyze whether a 1
ppb threshold is appropriate for identifying Michigan's linkages. The
analysis looked at all 15 receptors to which Michigan contributes,
based on the LADCO with water modeling, and plotted potential
contribution thresholds ranging from 0.5 to 1.4 ppb against collective
upwind contributions from all source categories and states with
contribution above 0.5 ppb. EGLE plotted the collective contribution as
a function of contribution threshold and concluded the first inflection
point occurred in a majority of the collective contribution at a
contribution threshold between 0.9 and 1 ppb, correlating with the PSD
permitting SIL of 1 ppb. Based on this analysis, EGLE concluded that a
1 ppb contribution threshold was appropriate for use in the good
neighbor context. EGLE also mentioned the August 2018 memorandum,
described in Section I of this proposal, as additional support for the
use of a 1 ppb contribution threshold.\53\
---------------------------------------------------------------------------

    \52\ https://www.epa.gov/sites/default/files/2018-04/documents/sils_policy_guidance_document_final_signed_4-17-18.pdf.
---------------------------------------------------------------------------

    EGLE's Step 2 conclusion was that, based on LADCO with water
modeling, Michigan was projected to be linked above a 1 ppb
contribution threshold in 2023 to three maintenance receptors; 1.85 ppb
to Sheboygan, Wisconsin (Site ID: 36-081-0124), 1.22 ppb to Queens, New
York (Site ID: 36-085-0067), and 1.03 ppb to Richmond, New York (Site
ID: 55-117-0006).
3. Information Provided by Michigan Regarding Step 3
    EGLE provided what it characterized as a ``weight-of-evidence
analysis'' in step 3 to justify their conclusion that no additional
emissions reductions are necessary to satisfy Michigan's ozone
transport obligations for the ozone NAAQS. The evidence presented in
EGLE's submittal consisted primarily of an argument that upwind states
should have a lower responsibility to other states when the upwind
state is only linked to maintenance-only receptors.

EGLE's analysis focused in large part on the Sheboygan, Wisconsin
maintenance receptor (Site ID: 36-081-0124), as EGLE concluded it was
the receptor to which Michigan was projected to contribute the most in
2023 at 1.85 ppb.
    On the issue of maintenance receptors, the state referenced a
concept identified by outside parties and listed in Attachment A to the
March 2018 memorandum, which was to consider whether the remedy for
upwind states linked to maintenance receptors could be less stringent
than those linked to nonattainment receptors. EGLE reasoned that
because the CAA incudes different SIP development requirements for
nonattainment and maintenance areas, that likewise nonattainment and
maintenance areas should be treated differently in good neighbor SIPs.
EGLE argued that because the CAA does not require emission reductions
from maintenance areas, then upwind states can potentially make a
sufficient showing they have no obligation to reduce emissions to
monitors in other states projected to be maintaining the NAAQS. EGLE
said they believe the reduction of projected contributions to projected
maintenance receptors is not required in certain circumstances, such as
when: (1) The projected maintenance exceedance is very small in
magnitude, (2) the projected contribution is very small, especially
compared to other states' contributions, (3) sector contributions
demonstrate the majority of contribution is from either sources already
federally regulated or sources without the possibility of additional
regulation, (4) there are large impacts of international emissions, and
(5) there are downward emission trends.
    Applying this logic to the Sheboygan, Wisconsin receptor, EGLE
argued that because the projected maximum design value at that receptor
is 72.8 ppb, the projected exceedance above the 2015 ozone NAAQS of 1.9
ppb is very small (values are truncated to ppb, thus 70.9 ppb would be
considered in attainment of the NAAQS). Based on this number, EGLE
argued that further emissions reductions from Michigan would be overly
burdensome. Secondly, citing a potential flexibility in Attachment A to
the March 2018 memorandum related to sector contribution, EGLE claimed
that 77% of contribution to the Sheboygan receptor is from federally
regulated sources or sources that cannot be regulated by Michigan. EGLE
noted that the other sectors of contribution it identified--oil and
gas, EGUs, and non-EGUs--are already controlled by Michigan. EGLE
argued Michigan sources should not be required to implement additional
contribution reductions in light of the relative size of their
contribution.
    Citing Attachment A to the March 2018 memorandum, again, EGLE
argued that the three receptors to which Michigan is linked are heavily
influenced by international emissions and other states. EGLE shared
that LADCO modeling projects Michigan's contribution to the Sheboygan
receptor (1.85 ppb) is less than projected contributions from
international contributions and boundary conditions (16.61 ppb),
Illinois (14.93 ppb), Wisconsin (9.1 ppb), biogenic sources (7.19 ppb),
and Indiana (6.19 ppb). EGLE used these numbers and an apportionment of
contributions from states and other sources to the amount the Sheboygan
monitor exceeds the 2015 ozone NAAQS to conclude that additional
emissions reductions from Michigan should not be required.
Additionally, EGLE argued that international contributions to the
Sheboygan receptor, which is geographically close to Canada, should be
eliminated from the projected DV, in which case the Sheboygan monitor
would be in attainment.
    EGLE also cited Attachment A to the March 2018 memorandum along
with an interpretation of EME Homer City to argue that EPA cannot
require reductions that would result in a reduction greater than an
upwind state's portion of the difference between the NAAQS and a
maintenance receptor's projected maximum design value. EGLE claimed
that Michigan's apportioned contribution to three linked receptors,
when distributed proportionally among other states that also contribute
more than 1 ppb to those receptors, is less than 0.12 ppb, but that
Michigan's responsibility to the exceedance is actually substantially
less than that amount when the home state's responsibility is
considered. EGLE also stated Michigan's apportioned contribution is at
less than 0.05 ppb of the projected maintenance exceedance at the
Sheboygan receptor, which is less than the variation among the modeled
maximum design values by both LADCO and EPA. EGLE concluded that
because of built-in modeling noise it would be ``difficult'' to either
verify that Michigan contributed 0.05 ppb to the Sheboygan, Wisconsin
receptor or for Michigan to require any additional reduction from
sources in the state.\54\ EGLE speculated it was quite likely that the
three linked receptors would maintain the NAAQS without any emissions
reductions from Michigan at all because the projected exceedances were
small.
---------------------------------------------------------------------------

    \54\ Michigan's SIP submission at 27.
---------------------------------------------------------------------------

    The state also stated that Michigan has downward emissions trends
(44% and 18% reduction in industrial point source NOX and
VOC emissions from 2008 through 2016, respectively) that are expected
to continue to decline or stay consistent over time due to projected
reductions in emissions from point sources of NOX and VOCs
EGUs, mobile sources and through other Federal measures. For EGUs, EGLE
pointed out that the shutdown of the Marquette Board of Light & Power
Shiras Steam Plant shut down was not included in either EPA or LADCO
modeling and that the U.S. Energy Information Agency's Annual Energy
Outlook anticipates growth in renewable energy in Michigan in 2019 and
a decline in coal beginning in 2022. EGLE also provided a list of
additional coal-fired EGUs that they stated were expected to retire by
2023. To support the conclusion that emissions will further be reduced
from mobile sources and through other Federal action, EGLE listed
several on the books and on the way Federal regulations. Finally, EGLE
noted existing controls on the oil and gas sector (applicable Federal
standards), non-EGUs (subject to the NOX SIP Call), and EGUs
(subject to CSAPR Update).
4. Information Provided by Michigan Regarding Step 4
    EGLE concluded it would be unreasonable for Michigan to take
further actions to address its obligations under the good neighbor
provisions for the ozone NAAQS, and so at Step 4 EGLE determined that
no permanent and enforceable measures to reduce emissions were
necessary.

D. Minnesota

    Minnesota Pollution Control Agency (MPCA) submitted a SIP revision
to address CAA Section 110(a)(2)(D)(i)(I) on October 1, 2018. The
submission utilized both EPA modeling released with the March 2018
memorandum and LADCO modeling results previously mentioned. Minnesota
followed the 4-step interstate transport framework and used an analytic
year of 2023 to describe Minnesota's lack of contributions to out of
state receptors and assess emission reduction considerations. The
following sections will summarize MPCA's submission and the information
provided for each step in the process.

1. Information Provided by Minnesota Regarding Step 1
    For Step 1 in the 4-step framework, MPCA identified monitoring
sites that are projected to have problems attaining and/or maintaining
the 2015 ozone NAAQS in 2023 according to LADCO modeling and EPA
modeling released in the March 2018 memorandum.\55\ As previously
mentioned, the LADCO modeling efforts used the same technique as EPA to
calculate future year design values which are used to identify
maintenance and nonattainment receptors. The submittal expressed MPCA's
opinion that the ERTAC EGU tool used in LADCO's modeling is superior to
EPA's 2023en modeling platform because the ERTAC EGU tool addresses
economic factors, preserves system reliability, and includes controls
or emissions reductions measure justified through some legal framework.
---------------------------------------------------------------------------

    \55\ MPCA's SIP submittal at Tables 2 and 3, pages 8-9.
---------------------------------------------------------------------------

2. Information Provided by Minnesota Regarding Step 2
    MPCA's submittal at Step 2 presented Minnesota's projected 2023
ozone contributions to maintenance and nonattainment receptors
identified by both LADCO modeling and EPA modeling released in the
March 2018 memorandum.\55\ The submittal noted there were differences
in identified receptors between the two modeling results, and that the
LADCO results overall yielded slightly lower projected contributions to
downwind receptors from Minnesota sources than EPA modeling.
    Minnesota relied on a contribution threshold of 1 percent of the
ozone NAAQS (0.70 ppb) to define linkages for a state's contribution to
downwind air quality problems. Both the LADCO modeling and the EPA
modeling released in the March 2018 memorandum projected that Minnesota
contributes less than 1 percent of the NAAQS to all downwind receptors.
MPCA showed in Table 2 of its submission that the highest projected
contribution to a receptor in 2023 was 0.40 ppb, based on EPA modeling
released in the March 2018 memorandum, or 0.45 ppb, based on LADCO ``no
water'' modeling, to the Milwaukee, Wisconsin receptor (Site ID: 55-
079-0085). Based on this analysis, MPCA concluded that Minnesota was
not linked above 1 percent of the NAAQS to any downwind receptor, and
therefore would not contribute to nonattainment or interference with
maintenance in other state with respect to the ozone NAAQS.
3. Information Provided by Minnesota Regarding Step 3
    Despite concluding Minnesota was not linked at Step 2, MPCA
proceeded with a Step 3 analysis. MPCA provided air quality data in
Step 3 to justify that no additional emissions reductions are necessary
to satisfy their transport obligations. MPCA provided evidence of
decreasing ambient ozone concentrations in Minnesota from the mid-1990s
through 2017 as well as decreasing NOX and VOC emissions
from the state from 2002 through 2015 to further support their
conclusion.\56\
---------------------------------------------------------------------------

    \56\ See Minnesota's SIP submittal Figures 1-3, pages 10-11.
---------------------------------------------------------------------------

    The state concluded that decreasing ambient ozone concentrations in
the state point to Minnesota contributing less to ozone in downwind
states as time goes on. Minnesota provided an analysis of
NOX and VOC emissions levels in the state from 2002 through
2015 to further support this point. According to MPCA, NOX
emissions have been steadily declining in the state from all sectors
and especially from EGUs due to emission limits and reductions required
in that category. MPCA also asserted that VOCs emissions have also seen
a similar decline in Minnesota in the years reported. MPCA concluded
that decreasing emissions in the state would make it unlikely for the
state to contribute significantly to nonattainment or interference with
maintenance in downwind states.
4. Information Provided by Minnesota Regarding Step 4
    Citing declining emissions and their conclusion that Minnesota was
not projected to contribute above 1 percent of the NAAQS to any
receptor, MPCA concluded that no additional permanent or enforceable
measures would be needed to address ozone transport contribution from
Minnesota sources. MPCA determined the existing emission controls would
be sufficient to maintain Minnesota's continued contribution of less
than 1 percent of the NAAQS to downwind receptors. In support of this
argument, Minnesota provided a list of several Federal and State
emissions regulations applicable to sources in Minnesota, including
Part 70 permits, the CSAPR NOX trading programs, Mercury and
Air Toxics Standards, and various state standards for SO2,
particulate matter, NOX, NO2, and VOC. Hence,
Minnesota declined to consider any new permanent and enforceable
measures to reduce emissions as part of the Step 4 analysis.

E. Ohio

    On September 28, 2018 the Ohio Environmental Protection Agency
(OEPA) submitted a revision to the Ohio SIP addressing interstate
transport of air pollution for the 2015 ozone NAAQS. OEPA stated that
its submittal, which relied on an analytic year of 2023, conforms with
EPA's four-step framework. The following sections will describe what
OEPA provided for each step.
1. Information Provided by Ohio Regarding Step 1
    For Step 1 in the 4-step framework, OEPA first identified 10
monitoring sites in the Northeast and Midwest that are projected to be
nonattainment, nonattainment/maintenance, or maintenance-only receptors
for the 2015 ozone NAAQS in 2023 based on LADCO's modeling and EPA's
method for defining nonattainment and maintenance receptors (See Table
1 below, reproduced from OEPA's submission).

                                          Table 1--Ohio's Projected 2023 Nonattainment and Maintenance Monitors
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                                2023
                                                      2015-2017       2023                       OH                         Maintenance    Status  (TX
      Site ID               County          State         DV       Average DV  2023 Max DV  contribution       Status          DV (TX       approach)
                                                                                approach)
--------------------------------------------------------------------------------------------------------------------------------------------------------
36-103-0002........  Suffolk............  NY                  76         71.6         73.1          1.75  Nonattainment/           69.7  Nonattainment.
                                                                                Maintenance.
09-001-9003........  Fairfield..........  CT                  83         71.4         74.2          1.58  Nonattainment/           73.7  Nonattainment/
                                                                                Maintenance.                   Maintenance.

24-035-1001........  Harford............  MD                  75         71.0         73.3          2.83  Nonattainment/           67.0  Nonattainment.
                                                                                Maintenance.
36-085-0067........  Richmond...........  NY                  76         70.9         72.4          2.24  Maintenance.....         68.0  Attainment.
55-117-0006........  Sheyboygan.........  WI                  80         70.5         72.8          1.17  Maintenance.....         71.1  Maintenance.
09-009-9002........  New Haven..........  CT                  82         69.9         72.6          1.12  Maintenance.....         72.6  Maintenance.
09-001-3007........  Fairfield..........  CT                  83         69.8         73.7          1.84  Maintenance.....         73.7  Maintenance.
36-081-0124........  Queens.............  NY                  74         69.2         71.0          1.88  Maintenance.....         70.1  Attainment.
09-001-0017........  Fairfield..........  CT                  79         68.9         71.2          1.05  Maintenance.....         71.2  Maintenance.
26-005-0003........  Allegan............  MI                  73         68.8         71.5          0.19  Maintenance--Not         71.5  Maintenance--No
                                                                                Linked.                        t Linked.
--------------------------------------------------------------------------------------------------------------------------------------------------------

    OEPA then claimed that EPA's methodology for determining
maintenance-only receptors is inappropriate because it is more
stringent than EPA's methodology for identifying nonattainment monitors
and is inconsistent with the CAA. In OEPA's view, EPA's methodology
results in greater emissions reduction requirements to address
maintenance receptors than nonattainment receptors. Citing stakeholder-
identified potential flexibilities that were listed in an attachment to
EPA's March 2018 memorandum, OEPA used an alternative method developed
by the Texas Commission for Environmental Quality (TCEQ) to identify
maintenance receptors. This method determines a future year design
value (DV) for purposes of identifying maintenance-only receptors by
applying the model-predicted relative response factor (RRF) to the most
recent 3-year design value (i.e., 2011-2013 design value) within the
five-year base period (i.e., 2009-2013), rather than the highest 3-year
DV in the same 5-year base period, which is used in EPA's approach.
OEPA stated that using the TCEQ approach accounts for emissions
reductions over the five-year period, while also accounting for
meteorological variability, since the design value is calculated based
on monitoring data from a three-year period. By using the TCEQ
approach, Ohio concluded that four monitors which would be either
nonattainment/maintenance receptors under EPA's method would, under the
TCEQ method, actually be nonattainment-only receptors (i.e., sites
261030002 in Suffolk, New York, 240251001 in Harford, Maryland) or
monitors in attainment (i.e., sites 360850067 in Richmond, New York,
and 360810124 in Queens, New York) in 2023.\57\
---------------------------------------------------------------------------

    \57\ Ohio's SIP submission, Table 1.
---------------------------------------------------------------------------

    OEPA's submittal provided information on inter-annual
meteorological variability, ozone design value trends at the four
monitoring sites that the state eliminated as receptors, as well as
recent and projected trends in NOX and VOC emissions to
support the use of an alternative definition of maintenance receptors.
The meteorological information provided in OEPA's submission included
nationwide maps showing the maximum temperature anomaly (i.e.,
departure from the long-term average or ``normal'') for the period May
through October in the years 2011, 2012, and 2013. OEPA concluded from
these maps that temperatures in the Northeast and Midwest were above or
much above average during May through October in each of the years
2011, 2012, and 2013. OEPA examined trends in ozone design values at
each of the four monitoring sites in question and concluded that design
values at these sites have declined substantially from 2000 through
2017 and that although there has been a slight leveling off or increase
in recent years, this is no greater than the normal year to year
variability. In addition, based on the emissions trends data, OEPA
stated that NOX emissions have declined in concert with
these trends in design values and are projected to continue to decline
through 2028 for the continental U.S. as well as those states that were
projected to be linked to the four monitors eliminated under the TCEQ
approach. Based on their analysis of the meteorological and ozone and
emissions trends data, OEPA concluded that the four monitoring sites
identified previously are not reasonably expected to have difficulty
maintaining the standards in 2023.
2. Information Provided by Ohio Regarding Step 2
    OEPA's submittal presented the projected 2023 ozone contributions
from Ohio to ten maintenance and nonattainment receptors in the
Northeast and Midwest using data from the LADCO source apportionment
modeling. LADCO's contribution data identified a total of nine
receptors in 2023 (3 nonattainment and 6 maintenance-only) with modeled
contributions from emissions in Ohio that exceed both a one percent of
the 2015 NAAQS threshold (i.e., 0.70 ppb) and a 1 ppb contribution
threshold (Table 1). Despite acknowledging Ohio was linked to the same
number of receptors under either a 1 percent of the NAAQS or 1 ppb,
OEPA maintained they had concerns about both thresholds being too
stringent, noting that Ohio would have two linkages if the threshold
were 3 percent and zero linkages if the threshold were 4 percent.
    As noted above, OEPA applied the TCEQ method for identifying
maintenance-only receptors, and concluded that four of the receptors to
which Ohio was linked would not have difficulty maintaining the NAAQS
in 2023. However, after eliminating these four monitoring sites as
having maintenance issues, OEPA acknowledged that Ohio would still be
linked to seven receptors in 2023.
3. Information Provided by Ohio Regarding Step 3
    OEPA provided what they characterize as a weight of evidence
analysis in Step 3 to justify their conclusion that no additional
emissions reductions are necessary to satisfy Ohio's interstate
transport obligations under the 2015 ozone NAAQS. OEPA argued that
their analysis demonstrated that any additional controls beyond those
on the books or already planned would result in overcontrol of sources
in Ohio, likely at cost-prohibitive levels.
    First, OEPA attempted to show that NOX and VOC 2023
emissions from EGU, nonEGU, and onroad sectors had been overestimated
by 21,761 tons of NOX and 3,240 tons of VOC annually, and
7,040 tons of NOX and 878 tons of VOC per ozone season. The
submittal performed an evaluation of the ERTAC EGU Tool, emphasizing
that projected 2023 EGU emissions from eight facilities

were overestimated, analyzed through a comparison of actual emissions
data obtained from EPA's Clean Air Markets Database (CAMD) and CSAPR/
CSAPR Update allocations obtained from EPA's CSAPR website with
projected emissions in 2023 obtained from ERTAC EGU tool. OEPA also
based its conclusions on an expected increase of natural gas sources
projected by the U.S. Energy Information's Annual Energy Outlook 2018
and recently permitted natural gas facilities not reflected in the
ERTAC EGU tool. Further, OEPA evaluated emissions from nine non-EGU
sources to claim EPA's 2023 projected emissions were overestimated. For
this analysis, OEPA compared actual emissions data trends from Ohio's
Emissions Inventory System18 with projected emissions from EPA's Air
Emissions Modeling Platform 2011v6.319 to conclude EPA's projections
overestimated non-EGU emissions. OEPA also asserted that EPA's
projections of vehicle miles traveled (VMT) were higher than the local
projections.
    OEPA's submittal also looked at NOX and VOC emissions
trends, and asserted that from 2011 to 2016, NOX emissions
declined while VOC emissions remained steady. Additionally, based on
state-specific data, OEPA posited that Ohio's VOC emissions will
decrease even more rapidly than predicted by EPA because the large
growth in the State's oil and gas sector had begun to level off. OEPA
attributed the trends it identified to several Federal and State
programs, including SIP approved state programs, non-SIP approved
programs such as NOX RACT, Architectural and Industrial
Maintenance (AIM) Coatings rules, Ohio's Beneficiary Mitigation Plan
for the Volkswagen settlement, and Federal programs such as CAIR and
CSAPR, NOX SIP Call, the National Emission Standards for
Hazardous Air Pollutants (NESHAP), the Regional Haze Rule, BART,
SO2 Data Requirements Rule, and MATS.
    In addition to emissions trends data, OEPA noted LADCO modeling
projected downwind trends in design values at the ten receptors from
2000 through 2017 and included a reference to ``a May 14, 2018
presentation, U.S. EPA Office of Air Quality Planning and Standards
(OAQPS)''.\58\ OEPA also stated that LADCO sector-based source
apportionment modeling indicates a significant contribution from onroad
sources at nine receptors. OEPA argued that local onroad emissions
should be addressed by EPA before EPA requires additional reductions
from upwind states. OEPA also suggested EPA should take into account
the impact on ozone of the proposed Safer Affordable Fuel-Efficient
(SAFE) Vehicles Rule before taking final action on SAFE. Further, OEPA
asserted that Ohio's contribution to nine monitors is in the 1 or 2 ppb
range while the home state and initial and boundary contributions are
each up to 19 ppb, and the contribution from Canada/Mexico is in the
same range as Ohio's. OEPA argued that ignoring international emissions
sources and placing all responsibility for addressing receptors on
upwind states would result in overcontrol.
---------------------------------------------------------------------------

    \58\ Ohio's SIP submission at 43.
---------------------------------------------------------------------------

    OEPA concluded that there were no cost-effective measures to be
taken for EGU or non-EGU sources in Ohio. To support this claim, OEPA
pointed to the cost effectiveness threshold of $1400/ton from the CSAPR
Update (81 FR 74508, October 26, 2016), and while OEPA recognized that
it was developed for the 2008 ozone standard, OEPA stated they believed
it is a reasonable cost-effectiveness level for the 2015 ozone NAAQS.
As for non-EGUs, OEPA asserted that those sectors were adequately
controlled by the Boiler MACT and numerous other MACT categories, BART,
SO2 Data Requirements Rule and other Federal regulations.
4. Information Provided by Ohio Regarding Step 4
    OEPA concluded, based on its weight of evidence analysis, that no
additional emissions reduction measures beyond existing and planned
controls are necessary to address ozone transport contribution from
Ohio sources for the 2015 ozone NAAQS.

F. Wisconsin

    Wisconsin Department of Natural Resources (WDNR) submitted a SIP
revision to address CAA Section 110(a)(2)(D)(i)(I) on September 14,
2018. The submittal notes state and Federal rules applicable to sources
in Wisconsin that are relevant to interstate transport, as well as
Wisconsin's participation in LADCO. WDNR identified CAIR, CSAPR, CSAPR
Update, Wisconsin's regional haze SIP applicable for the 2008-2018
planning period, and state PSD programs. Further, WDNR cited continued
consultation with LADCO, three Wisconsin Administrative Code statutes
that could be relied on ``[i]f needed'' to address disagreements for
SIP development in other states' nonattainment areas, and an adequate
PSD program.\59\ The statues mentioned include Wisconsin Administrative
Code, Natural Resources (Wis. Admin. Code, NR), subsections 285.11,
285.13 and 285.15. The first two address air pollution control
department duties and powers. The third, Wisconsin Statute 285.15,
entitled Interstate Agreement, gives the governor the authority to
enter an agreement to solve interstate pollution transport with
Illinois, Indiana and Michigan if the area includes portions of both
Wisconsin and Illinois.\60\ WDNR does not explicitly reach the
conclusion that Wisconsin has satisfied the good neighbor provision for
the 2015 ozone NAAQS, but it is implied. WDNR did not reference the 4-
step framework. WDNR did not rely on any modeling, identify any
receptors, or determine whether Wisconsin contributes any amount of
ozone precursor emissions to downwind states. The submittal does not
include an analysis of potential NOX controls. WDNR did not
rely on any EPA memoranda. No supporting documentation was provided.
Apart from the cited rules and LADCO membership, WDNR provided no
discussion or analysis to determine whether they have any obligations
under the 2015 ozone NAAQS.
---------------------------------------------------------------------------

    \59\ Wisconsin's SIP submission at 4.
    \60\ See Wis. Admin. Code NR 285.15 (2021), available at https://docs.legis.wisconsin.gov/statutes/statutes/285/ii/11.
---------------------------------------------------------------------------

III. EPA Evaluation

    EPA is proposing to find that the Illinois, Indiana, Michigan,
Minnesota, Ohio, and Wisconsin's SIP submissions do not meet the
states' 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 EPA's evaluation of
the SIP submissions using the 4-step interstate transport framework,
and EPA is therefore proposing to disapprove Illinois, Indiana,
Michigan, Minnesota, Ohio, and Wisconsin's SIP submissions.

A. Illinois

1. Evaluation of Information Provided by Illinois Regarding Step 1
    For Step 1 in the 4-step framework, IEPA identified monitoring
sites that are projected to have problems attaining or maintaining the
2015 ozone NAAQS in 2023. As previously mentioned, the LADCO modeling
efforts used the same technique as EPA to calculate future year design
values used to identify maintenance and nonattainment receptors. IEPA
presented the LADCO results with water cells, which identified five
monitors with 2023 maximum design values greater than the

2015 ozone standard, or maintenance receptors, and seven monitors with
2023 average design values greater than the 2015 ozone standard, or
nonattainment receptors. Since new modeling has been performed by EPA
with updated emission data, EPA proposes to rely on the most recent
modeling to identify nonattainment and maintenance receptors with
linkage to Wisconsin in 2023. Nonetheless, the alternative modeling
relied on by IEPA also identified a number of nonattainment and
maintenance receptor sites in 2023. See Table CC on page 15 of IEPA's
submittal. Thus, even under the alternative modeling of 2023, IEPA
acknowledges in its submittal the existence of several nonattainment
and maintenance receptors.
2. Evaluation of Information Provided by the State Regarding Step 2
    Although Illinois relied on alternative modeling to EPA's modeling,
Illinois acknowledged in their SIP submission that it is linked to one
or more downwind receptors above either a 1 percent of the NAAQS or a 1
ppb contribution threshold in 2023. Because the alternative modeling
relied on by the state also demonstrates that a linkage exists between
the state and downwind receptors at step 2, EPA need not conduct a
comparative assessment of the alternative modeling; the state concedes
that it is linked. IEPA's analysis corroborates the conclusion in EPA's
most recent modeling in that the modeling demonstrates the State to be
linked above 1 percent of the NAAQS to a downwind receptor, as
described in the next section.
    IEPA, relying on a concept listed in Attachment A to the March 2018
memorandum, attempted to justify the use of a 1 ppb threshold at step 2
to identify whether the state was ``linked'' to a projected downwind
nonattainment or maintenance receptor. As explained in Section I above,
the concepts presented in Attachment A to the March 2018 memorandum
were developed by outside parties; they are neither guidance nor
determined by EPA to be consistent with the CAA. However, EPA's August
2018 memorandum also addressed possible alternative thresholds and
suggested that, with appropriate additional analysis, it may be
reasonable for states to use a 1 ppb contribution threshold, as an
alternative to a 1 percent of the NAAQS threshold, at Step 2 of the 4-
Step interstate transport framework for the purposes of identifying
linkages to downwind receptors.
    As an initial matter, EPA does not accept Illinois' argument that a
1 percent of the NAAQS contribution threshold at Step 2 is
``inappropriate'' for the 2015 ozone NAAQS due to modeling biases and
errors.\61\ The explanation for how the 1 percent contribution
threshold was originally derived is available in the 2011 CSAPR
rulemaking. See 76 FR 48208, 48237-38. Further, in the CSAPR Update,
EPA re-analyzed the threshold for purposes of the 2008 ozone NAAQS and
determined it was appropriate to continue to apply this threshold. EPA
compared the 1 percent threshold to a 0.5 percent of NAAQS threshold
and a 5 percent of NAAQS threshold. EPA found that the lower threshold
did not capture appreciably more upwind state contribution compared to
the 1 percent threshold, while the 5 percent threshold allowed too much
upwind state contribution to drop out from further analysis. See Final
CSAPR Update Air Quality Modeling TSD, at 27-30 (EPA-HQ-OAR-2015-0596-
0144). If EPA were to apply this analysis to the 2015 ozone NAAQS using
the updated modeling based on the 2016v2 emissions platform, a 5
percent of the NAAQS contribution threshold (i.e., 3.5 ppb) only
captures approximately 50 percent of the total upwind contribution.
Compared to a 1 percent threshold, a 5 percent threshold would, on
average, forgo 27 percent of the total upwind contribution. As EPA
noted in the August 2018 memorandum, the use of even a 2 ppb
contribution threshold under the modeling released with the March 2018
memorandum would only capture about 55 percent of all upwind
contributions, and therefore ``emission reductions from states linked
at that higher threshold may be insufficient to address collective
upwind state contribution to downwind air quality problems.'' \31\
---------------------------------------------------------------------------

    \61\ Illinois' SIP submission at 8, 14.
---------------------------------------------------------------------------

    With these figures in mind, IEPA's claims that the contribution
threshold should be substantially higher than 1 or even 2 ppb solely on
the basis of modeling uncertainty cannot be accepted. First, both
LADCO's and EPA's modeling techniques are sufficiently reliable and fit
for the purpose to measure upwind contribution levels down to at least
one percent of the NAAQS. EPA's recommended model attainment test is
based on application of the model in a relative sense rather than
relying upon absolute model predictions.\62\ All models have
limitations resulting from uncertainties in inputs and scientific
formulation. To minimize the effects of these uncertainties, the
modeling is anchored to base period measured data in EPA's guidance
approach for projecting design values. Notably, EPA also uses our
source apportionment modeling in a relative sense when calculating the
average contribution metric (used to identify linkages). In this method
the magnitude of the contribution metric is tied to the magnitude of
the projected average design value which is tied to the base period
average measured design value. EPA's guidance has not established a
bright line criteria for judging whether or not statistical measures of
model performance constitute acceptable or unacceptable model
performance. So, contrary to what Illinois appears to be claiming with
regards to modeling biases, there are no EPA recommended measures of
allowable error. Although EPA does not typically focus on using
particular benchmarks as the sole criteria for model performance, EPA
notes that the model performance for the updated modeling based on the
2016v2 emissions platform is generally within the benchmarks
recommended by Emery.\63\
---------------------------------------------------------------------------

    \62\ See Section 4.1' ``Overview of Modeled Attainment Test in
EPA Modeling Guidance for Demonstrating Air Quality Goals for Ozone,
PM2.5, and Regional Haze. November 2018. EPA 454-R-18-
009. https://www.epa.gov/scram/sip-modeling-guidance-documents.
    \63\ Christopher Emery, Zhen Liu, Armistead G. Russel, M. Talat
Odman, Greg Yarwood and Naresh Kumar (2017). Recommendations on
statistics and benchmarks to assess photochemical model performance,
Journal of the Air & Waste Management Association, 67:5,582-598,
DOI: 10.1080/10962247.2016.1265027.
---------------------------------------------------------------------------

    EPA has successfully applied a 1 percent of NAAQS threshold to
identify linked upwind states in three prior rulemakings. And the D.C.
Circuit has declined to establish bright line criteria for model
performance. In upholding EPA's approach to evaluating interstate
transport in CSAPR, the D.C. Circuit held that they would not
``invalidate EPA's predictions solely because there might be
discrepancies between those predictions and the real world. That
possibility is inherent in the enterprise of prediction.'' EME Homer
City Generation, L.P. v. EPA, 795 F.3d 118, 135 (2015). The court
continued to note that ``the fact that a `model does not fit every
application perfectly is no criticism; a model is meant to simplify
reality in order to make it tractable.''' Id. at 135-36 (quoting
Chemical Manufacturers Association v. EPA, 28 F.3d 1259, 1264 (D.C.
Cir. 1994).
    Finally, EPA's August 2018 memorandum provided that whether use of
a 1 ppb threshold is appropriate must be based on an evaluation of
state-specific circumstances, and no such evaluation was included in
the

submission. IEPA did not conduct such an analysis. EPA's experience
with the alternative Step 2 thresholds is further discussed in Section
I.D.3.i. As discussed there, EPA is considering withdrawing the August
2018 memorandum.
    However, based on both the state's alternative modeling and EPA's
updated modeling, the state is projected to contribute greater than
both the 1 percent and alternative 1 ppb thresholds. While EPA does
not, in this action, approve of the IEPA's application of the 1 ppb
threshold, based on Illinois' 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 this SIP submittal.
3. Results of EPA's Step 1 and Step 2 Modeling and Findings for
Illinois
    As described in Section I, EPA performed air quality modeling using
the 2016v2 emissions platform to project design values and
contributions for 2023. These data were examined to determine if
Illinois 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 2, the data \64\ indicate that in 2023,
emissions from Illinois contribute greater than 1 percent of the
standard to nonattainment or maintenance-only receptors in
Wisconsin.\65\
---------------------------------------------------------------------------

    \64\ Design values and contributions at individual monitoring
sites nationwide are provide in the file:''
2016v2_DVs_state_contributions.xlsx'' which is included in docket ID
No. EPA-HQ-OAR-2021-0663.
    \65\ These modeling results are consistent with the results of a
prior round of 2023 modeling using the 2016v1 emissions platform
which became available to the public in the fall of 2020 in the
Revised CSAPR Update, as noted in Section I. That modeling showed
that Illinois 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 ID No. EPA-HQ-
OAR-2021-0663.

                      Table 2--Illinois Linkage Results Based on EPA Updated 2023 Modeling
----------------------------------------------------------------------------------------------------------------
                                                                   2023 Average    2023  Maximum     Illinois
         Receptor ID               Location       Nonattainment/   design value    design value    contribution
                                                   maintenance         (ppb)           (ppb)           (ppb)
----------------------------------------------------------------------------------------------------------------
550590025....................  Kenosha, WI.....  Maintenance....            69.2            72.3           18.55
550590019....................  Kenosha, WI.....  Nonattainment..            72.8            73.7           18.13
551010020....................  Racine, WI......  Nonattainment..            71.3            73.2           13.86
----------------------------------------------------------------------------------------------------------------

    Therefore, based on EPA's evaluation of the information submitted
by IEPA, and based on EPA's most recent modeling results for 2023, EPA
proposes to find that Illinois 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. EPA will
proceed to Step 3 of the 4-step interstate transport framework to
assess the arguments the state presented as to why, despite this
linkage, the state should not be considered to significantly contribute
to nonattainment or interfere with maintenance of the NAAQS in any
other state.
4. Evaluation of Information Provided Regarding Step 3
    At Step 3 of the 4-step interstate transport framework, a state's
emissions are further evaluated, in light of multiple factors,
including air quality and cost considerations, to determine what, if
any, emissions significantly contribute to nonattainment or interfere
with maintenance and, thus, must be eliminated under CAA section
110(a)(2)(D)(i)(I).
    To effectively evaluate which emissions in the state should be
deemed ``significant'' and therefore prohibited, states generally
should prepare an accounting of sources and other emissions activity
for relevant pollutants and assess potential, additional emissions
reduction opportunities and resulting downwind air quality
improvements. 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 EPA has not directed states that
they must conduct a Step 3 analysis in precisely the manner 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 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. IEPA did not conduct
such an analysis in Illinois' SIP submission.
    IEPA argued that Illinois' contributions to the nonattainment
monitors in the LADCO domain, namely the Allegan and Sheboygan
receptors, EPA can be fairly and adequately addressed through Illinois'
participation in LADCO. Though IEPA suggested that LADCO may be
partially responsible for decreases in ambient ozone concentrations in
the Lake Michigan area, LADCO is not a regulatory agency responsible
for implementing emissions controls. Furthermore, Illinois did not
provide any information on any planned emission reductions, or
evaluation of control strategies that the LADCO states intend to
implement within their domain, that would reduce either the ozone
concentrations or Illinois' contributions at the nonattainment or
maintenance monitors to which IEPA identified Illinois as linked.
IEPA's basis for concluding that LADCO participation may relieve
Illinois of any good neighbor obligations to downwind receptors is
entirely unsubstantiated and does not present any basis on which EPA
can approve IEPA's SIP submittal. As such, EPA proposes to find
Illinois' LADCO participation as inadequate to resolve Illinois' good
neighbor obligations for the 2015 ozone NAAQS.

    The submittal also stated that Illinois is developing new
NOX RACT standards for the Chicago area that, in conjunction
with existing regulations and future Federal reductions, are estimated
to reduce NOX emissions by up to 20,000 tons/year which had
not yet been reflected in modeling to 2023. However, Illinois failed to
provide any information on the control measures or implementation
schedule that would achieve the estimated 20,000 tons/year in
reductions. IEPA did not quantify how the emissions reductions they
estimated would impact air quality at downwind receptors or Illinois'
contributions. In fact, Illinois has not yet finalized the
NOX RACT rule for Chicago. In general, any changes in the
emissions inventory and on-the-books controls relevant to emissions in
2023 have now been incorporated into EPA's modeling using the 2016v2
emissions platform, which projects a continuing contribution from
Illinois to out of state receptors above a threshold of 1 percent of
the NAAQS (at Steps 1 and 2) despite these measures. Therefore, IEPA's
SIP submission should have evaluated the availability of additional air
quality controls to improve downwind air quality at nonattainment and
maintenance receptors at Step 3.
    Additionally, states may not rely on non-SIP measures to meet SIP
requirements. See CAA section 110(a)(2)(D) (``Each such [SIP] shall . .
. contain adequate provisions . . . .''). See also CAA section
110(a)(2)(A); Committee for a Better Arvin v. U.S. E.P.A., 786 F.3d
1169, 1175-76 (9th Cir. 2015) (holding that measures relied on by state