Proposed Rule2026-02841
Air Plan Approval; Oklahoma; Interstate Transport Requirements for the 2010 SO2 NAAQS
Primary source
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Published
February 12, 2026
Issuing agencies
Environmental Protection Agency
Abstract
Pursuant to the Clean Air Act (CAA or the Act), the Environmental Protection Agency (EPA) is proposing to approve the portion of the State Implementation Plan (SIP) submittal from the state of Oklahoma demonstrating that the State satisfies the interstate transport requirements of section 110, also known as the "good neighbor" provision of the Clean Air Act (CAA or Act), for the 2010 1- hour sulfur dioxide (SO<INF>2</INF>) primary National Ambient Air Quality Standard (NAAQS). The good neighbor provision requires each State's implementation plan to contain adequate provisions prohibiting the interstate transport of air pollution in amounts that will contribute significantly to nonattainment, or interfere with maintenance, of a NAAQS in any other State.
Full Text
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<title>Federal Register, Volume 91 Issue 29 (Thursday, February 12, 2026)</title>
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[Federal Register Volume 91, Number 29 (Thursday, February 12, 2026)]
[Proposed Rules]
[Pages 6575-6581]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-02841]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R06-OAR-2025-2270; FRL-13190-01-R6]
Air Plan Approval; Oklahoma; Interstate Transport Requirements
for the 2010 SO2 NAAQS
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
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SUMMARY: Pursuant to the Clean Air Act (CAA or the Act), the
Environmental Protection Agency (EPA) is proposing to approve the
portion of the State Implementation Plan (SIP) submittal from the state
of Oklahoma demonstrating that the State satisfies the interstate
transport requirements of section 110, also known as the ``good
neighbor'' provision of the Clean Air Act (CAA or Act), for the 2010 1-
hour sulfur dioxide (SO<INF>2</INF>) primary National Ambient Air
Quality Standard (NAAQS). The good neighbor provision requires each
State's implementation plan to contain adequate provisions prohibiting
the interstate transport of air pollution in amounts that will
contribute significantly to nonattainment, or interfere with
maintenance, of a NAAQS in any other State.
DATES: Written comments must be received on or before March 16, 2026.
ADDRESSES: Submit your comments, identified by Docket ID No. EPA-R06-
OAR-2025-2270, at <a href="http://www.regulations.gov">http://www.regulations.gov</a>. For comments submitted at
<a href="http://Regulations.gov">Regulations.gov</a>, follow the online instructions for submitting
comments. Once submitted, comments cannot be edited or removed from
<a href="http://Regulations.gov">Regulations.gov</a>. The EPA may publish any comment received to its public
docket. Do not submit electronically any information you consider to be
Confidential Business Information (CBI) or other information whose
disclosure is restricted by statute. Multimedia submissions (audio,
video, etc.) must be accompanied by a written comment. The written
comment is considered the official comment and should include
discussion of all points you wish to make. The EPA will generally not
consider comments or comment contents located outside of the primary
submission (i.e., on the web, cloud, or other file sharing system). For
additional submission methods, please contact the person identified in
the FOR FURTHER INFORMATION CONTACT section. For the full EPA public
comment policy, information about CBI or multimedia submissions, and
general guidance on making effective comments, please visit <a href="https://www.epa.gov/dockets/commenting-epa-dockets">https://www.epa.gov/dockets/commenting-epa-dockets</a>.
Docket: The index to the docket for this action is available
electronically at <a href="http://www.regulations.gov">www.regulations.gov</a>. While all documents in the
docket are listed in the index, some information may not be publicly
available due to docket file size restrictions or content (e.g., CBI).
FOR FURTHER INFORMATION CONTACT: Ms. Nevine Salem, EPA Region 6 Office,
Air and Radiation Division, Infrastructure and Ozone Section, (214)
665-7222, <a href="/cdn-cgi/l/email-protection#2f5c4e434a4201414a5946414a6f4a5f4e01484059"><span class="__cf_email__" data-cfemail="0d7e6c6168602363687b6463684d687d6c236a627b">[email protected]</span></a>. We encourage the public to submit
comments via <a href="https://www.regulations.gov">https://www.regulations.gov</a>. Please call or email the
contact listed above if you need alternative access to material indexed
but not provided in the docket.
SUPPLEMENTARY INFORMATION: Throughout this document wherever ``we,''
``us,'' or ``our'' is used, we mean the EPA.
I. Background
A. Infrastructure SIPs
On June 2, 2010, the EPA established a revised primary 1-hour
SO<INF>2</INF> NAAQS with a level of 75 parts per billion (ppb), based
on a three-year average of the annual 99th percentile of daily maximum
1-hour average concentrations.\1\ CAA section 110(a)(1) requires all
states to submit, within three years after promulgation of a new or
revised NAAQS, SIP submissions to provide for the implementation,
maintenance, and enforcement of the NAAQS.\2\ The EPA has historically
referred to these SIPs as ``infrastructure SIPs.'' Specifically,
section 110(a)(1) provides the procedural and timing requirements for
SIP submissions. Section 110(a)(2) lists specific elements that all
states must meet related to a newly established or revised NAAQS, such
as requirements for monitoring, basic program requirements, and legal
authority that are designed to assure attainment and maintenance of the
NAAQS.
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\1\ See 75 FR 35520 (June 22, 2010).
\2\ In 2012, the EPA retained the current secondary NAAQS for
SO<INF>2</INF>. Thus, the CAA section 110(a)(1) requirement to
submit an infrastructure SIP for this secondary standard was not
triggered. The secondary SO<INF>2</INF> standard is 500 ppb averaged
over three hours, not to be exceeded more than once per year. See 77
FR 20218 (April 3, 2012).
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Section 110(a)(2)(D)(i)(I) of the CAA requires a state's SIP to
include provisions prohibiting any source or other type of emissions
activity in the state from emitting any air pollutant in amounts that
will contribute significantly to nonattainment, or interfere with
maintenance, of the NAAQS in any other state. The EPA has long
interpreted this language to enact a ``functional prohibition'' on
certain emissions from upwind states, necessitating the EPA's
independent assessment of whether those emissions will occur or have
been adequately controlled in the state where they originate.\3\ The
EPA often refers to these requirements as Prong 1 (significant
contribution to nonattainment of the NAAQS) and Prong 2 (interference
with maintenance of the NAAQS). We are addressing Prongs 1 and 2 in
this action. All other applicable infrastructure SIP requirements of
the Oklahoma SIP submission are addressed in separate rulemakings.
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\3\ See Genon Rema LLC v. EPA, 722 F.3d 513, 520-24 (3d Cir.
2013); Appalachian Power Co. v. EPA, 249 F.2d 1032, 1045-47 (D.C.
Cir. 2001); see also 71 FR 25328, 25335 (April 28, 2006) (explaining
that the SIP/FIP process under section 110 and the petitioning
process for direct federal regulation under section 126 provide
independent means of effectuating the same ``functional
prohibition'' found in CAA section 110(a)(2)(D)(i)(I)).
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B. 2010 1-Hour SO2 NAAQS Designations Background
In this proposed action, the EPA has considered information from
the 2010 1-hour SO<INF>2</INF> NAAQS designations process which is
discussed in more detail in section III.C of this notice. For this
reason, a brief summary of the EPA's designations process for the 2010
1-hour SO<INF>2</INF> NAAQS is included here.\4\
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\4\ While designations may provide useful information for
purposes of analyzing transport, particularly for a more source-
specific pollutant such as SO<INF>2</INF>, EPA notes that
designations themselves are not dispositive of whether upwind
emissions are impacting areas in downwind states. EPA has
consistently taken the position that CAA section 110(a)(2)(D)(i)(I)
requires elimination of significant contribution and interference
with maintenance in other states, and this analysis is not limited
to designated nonattainment areas. Nor must designations for
nonattainment areas have first occurred before states or the EPA can
act under section 110(a)(2)(D)(i)(I). See, e.g., Clean Air
Interstate Rule, 70 FR 25162, 25265 (May 12, 2005); Cross State Air
Pollution Rule, 76 FR 48208, 48211 (Aug. 8, 2011); Final Response to
Petition from New Jersey Regarding SO<INF>2</INF> Emissions From the
Portland Generating Station, 76 FR 69052 (Nov. 7, 2011) (finding
facility in violation of the prohibitions of CAA section
110(a)(2)(D)(i)(I) with respect to the 2010 1-hour SO<INF>2</INF>
NAAQS prior to issuance of designations for that standard).
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[[Page 6576]]
After the promulgation of a new or revised NAAQS, the EPA is
required to designate areas as ``nonattainment,'' ``attainment,'' or
``unclassifiable'' pursuant to section 107(d)(1)-(2) of the CAA. The
process for designating areas following promulgation of a new or
revised NAAQS is contained in section 107(d) of the CAA. The CAA
requires the EPA to complete the initial designations process within
two years of promulgating a new or revised standard. If the
Administrator has insufficient information to make these designations
by that deadline, the EPA has the authority to extend the deadline for
completing designations by up to one year.
The EPA promulgated the 2010 1-hour SO<INF>2</INF> NAAQS on June 2,
2010. See 75 FR 35520 (June 22, 2010). The EPA Administrator signed the
first round \5\ of designations; ``Round 1'' \6\ for the 2010 1-hour
SO<INF>2</INF> NAAQS on July 25, 2013, designating 29 areas in 16
States as nonattainment for the 2010 1-hour SO<INF>2</INF> NAAQS. See
78 FR 47191 (August 5, 2013). The EPA Administrator signed Federal
Register notices for Round 2 designations \7\ on June 30, 2016 (81 FR
45039 (July 12, 2016)) and on November 29, 2016 (81 FR 89870 (December
13, 2016)). Round 3 designations \8\ were signed on December 21, 2017
(83 FR 1098 (January 9, 2018)) and March 28, 2018 (83 FR 14597 (April
5, 2018)). Round 4 designations \9\ were signed on December 21, 2020
(86 FR 16055 (March 26, 2021)) \10\ and April 8, 2021 (86 FR 19576
(April 14, 2021)).\11\
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\5\ The term ``round'' in this instance refers to which ``round
of designations.''
\6\ The EPA and state documents and public comments related to
the Round 1 final designations are in the docket at regulations.gov
with Docket ID No. EPA-HQ-OAR-2012-0233 and at EPA's website for
SO<INF>2</INF> designations at <a href="https://www.epa.gov/sulfur-dioxide-designations">https://www.epa.gov/sulfur-dioxide-designations</a>.
\7\ The EPA and state documents and public comments related to
the Round 2 final designations are in the docket at regulations.gov
with Docket ID No. EPA-HQ-OAR-2014-0464 and at EPA's website for
SO<INF>2</INF> designations at <a href="https://www.epa.gov/sulfur-dioxide-designations">https://www.epa.gov/sulfur-dioxide-designations</a>.
\8\ The EPA and state documents and public comments related to
Round 3 final designations are in the docket at regulations.gov with
Docket ID No. EPA-HQ-OAR-2017-0003 and at EPA's website for
SO<INF>2</INF> designations at <a href="https://www.epa.gov/sulfur-dioxide-designations">https://www.epa.gov/sulfur-dioxide-designations</a>.
\9\ The EPA and state documents and public comments related to
Round 4 final designations are in the docket at regulations.gov with
Docket ID No. EPA-HQ-OAR-2020-0037 and at EPA's website for
SO<INF>2</INF> designations at <a href="https://www.epa.gov/sulfur-dioxide-designations">https://www.epa.gov/sulfur-dioxide-designations</a>.
\10\ The Round 4 2010 1-hour SO<INF>2</INF> NAAQS designations
action was signed by former EPA Administrator Andrew Wheeler on
December 21, 2020, pursuant to a court-ordered deadline of December
31, 2020. For administrative purposes only, and in compliance with
requirements of the Office of the Federal Register, former Acting
Administrator Jane Nishida re-signed the same action on March 10,
2021, for publication in the Federal Register.
\11\ On August 21, 2015 (80 FR 51052), EPA separately
promulgated air quality characterization requirements for the 2010
1-hour SO<INF>2</INF> NAAQS in the Data Requirements Rule (DRR). The
DRR requires state air agencies to characterize air quality, through
air dispersion modeling or monitoring, in areas associated with
sources that emitted in 2014 2,000 tons per year (tpy) or more of
SO<INF>2</INF>, or that have otherwise been listed under the DRR by
EPA or state air agencies. In lieu of modeling or monitoring, state
air agencies, by specified dates, could elect to impose federally
enforceable emissions limitations on those sources restricting their
annual SO<INF>2</INF> emissions to less than 2,000 tpy, or provide
documentation that the sources have been shut down. EPA used the
information generated by implementation of the DRR to help inform
Round 4 designations for the 2010 1-hour SO<INF>2</INF> NAAQS.
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For Oklahoma, the EPA designated Choctaw County, as unclassifiable/
attainment in round 2, based on modeling submitted by Oklahoma
Department of Environmental Quality (ODEQ). On January 9, 2018 (83 FR
1098), the EPA designated Kay, Le Flore, and Rogers Counites as
attainment/unclassifiable based on modeling submitted by ODEQ. In the
EPA's multiple rounds of SO<INF>2</INF> designations, all Oklahoma's
counties were designated attainment/unclassifiable. At the time of this
action, there are no designated nonattainment areas in Oklahoma or in
any other states within 50 km of the Oklahoma border.
II. Relevant Factors Used To Evaluate 2010 1-Hour SO2 Interstate
Transport SIPs
Although SO<INF>2</INF> is emitted from a similar universe of point
and nonpoint sources as directly emitted fine particulate matter
(PM<INF>2.5</INF>) and the precursors to ozone and PM<INF>2.5</INF>,
interstate transport of SO<INF>2</INF> is unlike the transport of
PM<INF>2.5</INF> or ozone, which disperse over a wide area and can
contribute to nonattainment or maintenance issues hundreds of miles
from precursor-emitting sources or activities. SO<INF>2</INF> emissions
usually do not undergo long-range transport in the atmosphere. The
transport of SO<INF>2</INF> relative to the 2010 1-hour SO<INF>2</INF>
NAAQS is more analogous to the transport of lead (Pb) relative to the
Pb NAAQS in that emissions of SO<INF>2</INF> typically result in 1-hour
pollutant impacts of greatest concern near the emissions source.
However, ambient 1-hour concentrations of SO<INF>2</INF> do not
decrease as quickly with distance from the source as do 3-month average
concentrations of Pb, because SO<INF>2</INF> gas is not removed by
deposition as rapidly as are Pb particles. Emitted SO<INF>2</INF> has
wider-ranging impacts than emitted Pb, but it does not have such wide-
ranging (far downwind) impacts that treatment in a manner similar to
ozone or PM<INF>2.5</INF> would be appropriate. Accordingly, the
approaches that EPA has adopted for ozone or PM<INF>2.5</INF> transport
are too regionally focused, and the approach for Pb transport is too
tightly circumscribed to the source, to be appropriate for assessing
SO<INF>2</INF> transport. SO<INF>2</INF> transport is therefore a
unique case and necessitates an analytical approach that examines
potential impacts that are further from the source than would be
examined for Pb transport but less regional in scope than ozone or PM
transport.
In this proposed rulemaking, and consistent with prior
SO<INF>2</INF> transport analyses, the EPA focused on a 50 kilometer
(km)-wide zone around sources of interest because the physical
properties of SO<INF>2</INF> result in relatively localized pollutant
impacts near an emissions source that drop off with distance. Given the
properties of SO<INF>2</INF>, the EPA believes that significant impacts
in a downwind state are unlikely at distances greater than 50 km from a
source and thus, we are focusing our review on areas within 50 km of
the state lines. This scale of analysis is consistent with the ``urban
scale'' which is the largest appropriate spatial scale for
SO<INF>2</INF> monitors and is useful for assessing SO<INF>2</INF>
transport and trends in area-wide air quality.\12\
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\12\ For the definition of spatial scales for SO<INF>2</INF>,
see 40 CFR part 58, Appendix D, section 4.4 (``Sulfur Dioxide
(SO<INF>2</INF>) Design Criteria''). For further discussion on how
the EPA applies these definitions with respect to interstate
transport of SO<INF>2</INF>, see the EPA's proposed rulemaking on
Connecticut's SO<INF>2</INF> transport SIP. See 82 FR 21351, 21352,
21354 (May 8, 2017).
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Oklahoma certified that its 2010 SO<INF>2</INF> SIP meets the
transport Prong 1 and 2 infrastructure obligation for the 2010 Primary
SO<INF>2</INF> NAAQS and has no sources or activities within Oklahoma
contribute significantly to nonattainment or interfere with
maintenance, in any other state. The EPA elected to review and assess
other available information regarding SO<INF>2</INF> emissions and air
quality in Oklahoma to assist in our own evaluation. We independently
analyzed such information to determine whether Oklahoma meets the
interstate transport requirements described in the CAA.\13\
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\13\ This proposed approval of Oklahoma SIP submission under CAA
section 110(a)(2)(D)(i)(I) is based on the information contained in
the administrative record for this action and does not prejudge any
other future EPA action that may make other determinations regarding
Oklahoma's air quality status and downwind states. Any such future
actions, such as area designations under any NAAQS or action on
petitions submitted under CAA section 126(b), will be based on their
own administrative records and EPA's analyses of information that
becomes available at those times. Future available information may
include, and is not limited to, monitoring data and modeling
analyses conducted pursuant to EPA's Data Requirements Rule (80 FR
51052, August 21, 2015) and information submitted to EPA by states,
air agencies, and third-party stakeholders such as citizen groups
and industry representatives.
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[[Page 6577]]
Consistent with our prior evaluations of other states'
SO<INF>2</INF> transport obligations, we conducted a weight of evidence
(WOE) analysis evaluating several sources of information, including
current air quality data from monitors as well as available emissions
and/or source modeling for sources in Oklahoma and in neighboring
states within 50 km of the Oklahoma border. A WOE approach can be
appropriate in instances, such as this case, to determine whether
SO<INF>2</INF> emissions from Oklahoma contribute to nonattainment or
maintenance issues in adjoining states. A WOE analysis that is based
solely on available data may not be sufficient in all instances for
evaluating interstate SO<INF>2</INF> transport, and additional analysis
may be necessary. Further, the term ``WOE'' does not establish the
legal or technical meaning for what constitutes significant
contribution to nonattainment or interference with maintenance for the
2010 SO<INF>2</INF> NAAQS. Rather, the term refers to the gathering and
consideration of a wide range of information, on a case-by-case basis,
to make a determination regarding whether a statutory or regulatory
requirements met.
In other SO<INF>2</INF> transport actions, the EPA has typically
been able to use a WOE analysis to reach a conclusion that there are no
SO<INF>2</INF> nonattainment or maintenance issues in the relevant
areas of other states, or that no sources in the upwind state are
contributing to those issues. If the available evidence indicated,
however, that an upwind source, sources, or emissions activities were
contributing to an out-of-state SO<INF>2</INF> nonattainment or
maintenance problem, then further analysis and a regulatory
determination would be necessary concerning what amount of those
emissions, if any, constituted ``significant contribution'' under Prong
1 or Prong 2 of the good neighbor provision.
We find that there is sufficient information to support the EPA's
proposed determination that, under baseline conditions and likely
future emissions scenarios, no Oklahoma sources are contributing or
will contribute to any out-of-state SO<INF>2</INF> nonattainment or
maintenance concerns, and therefore it is not necessary for the
purposes of this action to render a determination concerning what
amount of emissions would be ``significant'' and therefore subject to
prohibition under the good neighbor provision.\14\
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\14\ Cf. Genon Rema v. EPA, 722 F.3d 513 (3d Cir. 2013)
(upholding EPA grant of CAA section 126(b) petition and
establishment of direct federal emissions control requirements on
SO<INF>2</INF> source in Pennsylvania found to be significantly
contributing to nonattainment and interfering with maintenance of
the 2010 SO<INF>2</INF> NAAQS in New Jersey).
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III. Oklahoma's SIP Submission and EPA's Analysis
A. State Submission
On January 28, 2015, Oklahoma submitted the 2010 SO<INF>2</INF>
NAAQS infrastructure SIP (i-SIP) submittal addressing how the existing
Oklahoma SIP provides for the implementation, maintenance and
enforcement of the 2010 1-hour SO<INF>2</INF> NAAQS.\15\ On December 9,
2016 (81 FR 89008), the EPA approved most elements of the Oklahoma
SO<INF>2</INF> i-SIP but took no action on elements of Section
110(a)(2)(D)(i)(I), prongs 1 and 2, regarding the contribution to
nonattainment and interfere with maintenance of the 2010 SO<INF>2</INF>
NAAQS in other states. On a letter dated May 28, 2021, the EPA received
Oklahoma's revised certification of Transport Prong 1 & 2 elements for
the 2010 Primary 2010 SO<INF>2</INF> NAAQS under CAA Section
110(a)(2).\16\
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\15\ See fn #13.
\16\ On April 2, 2021, the State of Oklahoma submitted the 2010
SO<INF>2</INF> interstate transport SIP without a public notice or
an opportunity to request a hearing. ODEQ's revised SO<INF>2</INF>
Interstate Transport SIP submittal letter on May 28, 2021, to the
EPA, Region 6 serve to withdraw and replace the submittal made by
the State of Oklahoma on April 2, 2021.
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In its submittal, Oklahoma certified that its 2010 SO<INF>2</INF>
SIP meets the transport Prong 1 and 2 infrastructure obligation for the
2010 Primary SO<INF>2</INF> NAAQS and has no sources or activities
within Oklahoma contribute significantly to nonattainment or interfere
with maintenance, in any other state. Public notice for the Oklahoma
submittal was posted on the Oklahoma Department of Environmental
Quality (ODEQ) website on April 21, 2021, to allow the opportunity to
provide comments and to request a public hearing scheduled May 24,
2021, at ODEQ's offices. No hearing requests or written comments were
received during the 30-day comment period.
EPA elected to review and assess other available information, as
described below and in more detail in the TSD for this action,
regarding SO<INF>2</INF> emissions and air quality for sources in
Oklahoma to assist in our evaluation and to fully assess whether
Oklahoma was meeting its CAA good neighbor obligations for the 2010
SO<INF>2</INF> NAAQS.
B. EPA's Evaluation Methodology
For this CAA section 110 (a)(2)(D)(i)(I) evaluation of the 2010
SO<INF>2</INF> NAAQS, the EPA conducted a WOE analysis for Prong 1 and
Prong 2 separately,\17\ evaluating available information such as air
quality, emission sources, modeling, and emission trends in Oklahoma
and the states that border Oklahoma. To identify which sources and
emissions activities in Oklahoma could potentially impact downwind air
quality in other states with respect to the 2010 1-hour SO<INF>2</INF>
NAAQS, the EPA used information in the EPA's National Emissions
Inventory (NEI) \18\ and Emissions Inventory System (EIS).\19\ The NEI
is a comprehensive and detailed estimate of air emissions for criteria
pollutants, criteria pollutant precursors, and hazardous air pollutants
from air emissions sources, updated every three years using information
provided by the states and other information available to the EPA. For
analyses, we largely relied on data from the 2020 NEI, because it is
the most recently available, complete, and quality assured dataset.
However, in evaluating emissions trends, both state-wide and at the
facility level, the EPA also considered data from prior NEI reports and
EIS queries, as part of the overall WOE analysis.
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\17\ In North Carolina v. EPA, 531 F.3d at 910-911 (D.C. Cir.
2008), the D.C. Circuit explained that the
regulating authority must give Prong 2 ``independent
significance'' from Prong 1 by evaluating the impact of upwind state
emissions on downwind areas that, while currently in attainment, are
at risk of future nonattainment.
\18\ EPA's NEI is available at <a href="https://www.epa.gov/air-emissions-inventories/national-emissions-inventory">https://www.epa.gov/air-emissions-inventories/national-emissions-inventory</a>.
\19\ The EIS Gateway was developed to provide only registered
EPA, State, local, and Tribal users with access to emission
inventory data for sources in their jurisdiction.
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As shown in Table 1, the majority of SO<INF>2</INF> emissions in
Oklahoma originate from point sources. In 2020, total SO<INF>2</INF>
emissions from point sources in Oklahoma comprised approximately 79
percent of the total SO<INF>2</INF> emissions in the State. Non-point
sources, on road, and non-road emissions sources contribute to a much
smaller portion of total SO<INF>2</INF> emissions; these emissions are
also more dispersed throughout the State and are therefore unlikely to
contribute to high ambient concentrations of SO<INF>2</INF> when
compared to point source contributions. Further analysis \20\ shows
[[Page 6578]]
that facilities with reported emissions greater than 100 tons per year
(tpy) represent approximately less than 2 percent of the total number
of Oklahoma SO<INF>2</INF> point sources but are responsible for 25,889
tons of SO<INF>2</INF> or 94 percent of the total 2020 SO<INF>2</INF>
emissions.\21\ Based on this analysis, the EPA focused our WOE analysis
on SO<INF>2</INF> emissions from Oklahoma's larger point sources (i.e.,
point sources emitting over 100 tpy of SO<INF>2</INF>) that are located
within 50 km of one or more state borders.
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\20\ See EPA's TSD for a more detailed discussion.
\21\ See Table 8 in the EPA's TSD.
Table 1--Summary of SO2 Data for Oklahoma by Source Category
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2020 Emissions Percent of total
Category (tpy) SO2 emissions
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Point............................. 27,534 79
Nonpoint.......................... 7,281 21
On road........................... 149 0
Nonroad........................... 12 0
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SO2 Emissions Total........... 34,976 100
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As described in this section, the EPA proposes that an assessment
of Oklahoma's satisfaction of the Prong 1 and 2 requirements under CAA
section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO<INF>2</INF> NAAQS may
be reasonably based upon several factors. These factors include
evaluation of the predicted downwind impacts projected in previous
relevant modeling studies for the source and nearby areas, assessment
of Oklahoma's SO<INF>2</INF> point source emissions of more than 100
tpy of SO<INF>2</INF> per facility that are located within
approximately 50 km of another state, assessment of other states' point
sources emitting more than 100 tpy of SO<INF>2</INF> located within
approximately 50 km of Oklahoma, and assessment of federal regulations
and SIP-approved regulations affecting Oklahoma's SO<INF>2</INF>
sources. The EPA's evaluation is informed by all available data at the
time of this rulemaking.\22\
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\22\ EPA notes that the evaluation of other states' satisfaction
of section 110(a)(2)(D)(i)(I) for the 2010 1-hour SO<INF>2</INF>
NAAQS can be informed by similar factors found in this proposed
rulemaking but may not be identical to the approach taken in this or
any future rulemaking for Oklahoma, depending on available
information and state-specific circumstances.
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1. EPA's Prong 1 Evaluation--Contribute Significantly to Nonattainment
Prong 1 of the ``good neighbor'' provision requires states' plans
to prohibit emissions that will contribute significantly to
nonattainment of the NAAQS in another state. The EPA's evaluation \23\
of whether Oklahoma has met its Prong 1 transport obligations was
accomplished by considering all available information, including the
following: SO<INF>2</INF> ambient air quality in Oklahoma and
neighboring states; SO<INF>2</INF> emissions trends for Oklahoma and
neighboring states; potential ambient impacts of SO<INF>2</INF>
emissions from certain facilities \24\ in Oklahoma on neighboring
states; Oklahoma's SIP-approved regulations specific to SO<INF>2</INF>
emissions and permit requirements; and other SIP-approved or federally
enforceable regulations which may reduce SO<INF>2</INF> emissions
either directly or indirectly.
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\23\ A detailed review of the EPA's evaluation of emissions, air
monitoring data, other technical information, and rationale for
proposed approval of this SIP revision as meeting CAA section
110(a)(2)(D)(i)(I) for the 2010 1-hour SO<INF>2</INF> NAAQS may be
found in the TSD.
\24\ The physical properties of SO<INF>2</INF> result in
relatively localized pollutant impacts very near the emissions
source. Therefore, the EPA selected a spatial scale with dimensions
up to 50 km from point sources.
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Based on the EPA's analysis, we propose to determine that there are
no SO<INF>2</INF> nonattainment concerns in the relevant areas in other
states bordering Oklahoma, and as such the EPA proposes to determine
that Oklahoma's SIP satisfies the requirements of Prong 1 of CAA
section 110(a)(2)(D)(i)(I). This proposed determination is based on the
following considerations:
<bullet> There are no monitors within 50 km of the Oklahoma border
recording violations of the 2010 SO<INF>2</INF> NAAQS, all these
monitors have design values (DV) that are below the 75 ppb standard.
Current DVs for Oklahoma's AQS SO<INF>2</INF> monitors within 50 km of
another State's border remained below the 2010 1-hour SO<INF>2</INF>
NAAQS from 2019-2024, similarly, SO<INF>2</INF> monitors in neighboring
states (Arkansas, Texas, Kansas, and Missouri) within 50 km of Oklahoma
have 2023 DVs (2021-2023) below the 2010 1-hour SO<INF>2</INF> NAAQS;
<bullet> Downward SO<INF>2</INF> emissions trends in Oklahoma and
surrounding States (Arkansas, Texas, Kansas, and Missouri), when
considered with other factors discussed as part of EPA's WOE analysis,
further support that Oklahoma's sources will not significantly
contribute to any State's nonattainment of the 2010 1-hour
SO<INF>2</INF> NAAQS.
<bullet> Source-specific analyses of every Oklahoma source emitting
100 tpy or more and located within 50 km of the state border indicate
that the sources do not contribute to nonattainment in other states.
These analyses draw upon available emissions data, monitoring data, air
quality modeling, control requirements and/or unit retirement, wind
rose data, and other relevant information to assess the likelihood of
air quality impacts from these sources to areas in surrounding states.
A detailed discussion of each source-specific analysis is contained in
Section IV.B.1 of the TSD accompanying this action.
Below, we summarize the principal evidence that provides overall
support for the EPA's proposed conclusion that SO<INF>2</INF> emissions
from the five Oklahoma sources with annual emissions greater than 100
tpy and located within 50 km of another state are not likely to pose a
transport concern.
River Valley Generating Station, Le Flore County
The EPA reviewed SO<INF>2</INF> emissions for River Valley
Generating Station (formally, AES Shady Cogeneration Plant), whose
emissions have been modeled, for the Round 3 SO<INF>2</INF>
designations process, shows compliance with the standard, there are no
other sources within Le Flore County that emit at or above 100 tpy,
based on 2014-2020 NEI.\25\ Additionally, the EPA confirmed that there
were no other sources in Le Flore County or near its borders that were
likely to cause or contribute to a violation of the NAAQS within Le
Flore County or other states. The absence of nearby SO<INF>2</INF>
sources in neighboring states that could interact with the annual
SO<INF>2</INF> emissions emitted from River Valley Generating Station,
the distance to any SO<INF>2</INF> sources in
[[Page 6579]]
nearby states, modeling results, and air monitoring values make it very
unlikely for this source to be a transport concern for its neighboring
states.
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\25\ Most recent (2022-2023) NEI data emissions show no other
SO<INF>2</INF> emission sources at or above 100 tpy in Le Flore
County.
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Hugo Power Station, Choctaw County
The Hugo Power Plant was included in Oklahoma's 2015 modeling for
the Round 2 SO<INF>2</INF> designations process.\26\ The EPA found in
our referenced TSD that modeling submitted by the State for the Hugo
Power Station showed attainment of the NAAQS and no significant impact
upon adjacent or surrounding states. Additionally, the EPA has
confirmed that there are no other sources in Choctaw County or near its
borders that are likely to cause or contribute to a violation of the
SO<INF>2</INF> NAAQS in Choctaw County or nearby adjacent states. The
absence of violations from monitoring or modeling, the distance between
the Hugo Power Plant and SO<INF>2</INF> sources in Arkansas and Texas,
and the predominant wind pattern blowing towards Oklahoma from Texas,
suggest that Hugo Power Plant source is not causing any air quality
concerns for SO<INF>2</INF> transport in any state.
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\26\ Summaries of Hugo Power Plant modeling can be found in
EPA's ``Final Technical Support Document, Oklahoma, Area
Designations for the 2010 SO<INF>2</INF> Primary National Ambient
Air Quality Standard'', located at <a href="https://www.epa.gov/sites/default/files/2016-07/documents/r6_ok_final_designation_tsd_06302016.pdf">https://www.epa.gov/sites/default/files/2016-07/documents/r6_ok_final_designation_tsd_06302016.pdf</a> and <a href="https://www.regulations.gov/document/EPA-HQ-OAR-2014-0464-0408">https://www.regulations.gov/document/EPA-HQ-OAR-2014-0464-0408</a>. The TSD
containing our detailed review of Oklahoma's modeling submission for
Choctaw County can be found in the preliminary determination page at
<a href="https://www.epa.gov/sulfur-dioxide-designations/so2-designations-round-2-oklahoma-state-recommendation-and-epa-response">https://www.epa.gov/sulfur-dioxide-designations/so2-designations-round-2-oklahoma-state-recommendation-and-epa-response</a> as ``EPA
Response to Oklahoma Round 2 Recommendations--Attachment (pdf)''
(downloadable file titled ``ok-epa-tsd-r2.pdf''). See p. 25-38 for
the Choctaw County review.
---------------------------------------------------------------------------
Cardinal Glass Plant, Bryan County
The Cardinal Glass Plant manufactures flat glass and is a
relatively small SO<INF>2</INF> source that emitted between 100-160 tpy
in the most recent four years. Given its low emissions in combination
with its 17 km distance to Texas, no nearby sources either in Oklahoma
or Texas, and the predominant winds in the direction of Oklahoma, we
conclude that the Cardinal Gas Plant source is not causing any air
quality concerns for SO<INF>2</INF> transport in any state.
Healdton Gas Plant, Carter County
The Healdton Gas Plant, a small SO<INF>2</INF> source of gas
extraction in Carter County, Oklahoma, is located approximately 32 km
north of the OK-TX border, reported relatively low emissions of 183 and
176 tpy in 2022 and 2023, respectively. Based on the relatively low
emissions of the source, the large distance between the Healdton Gas
Plant in Oklahoma and two SO<INF>2</INF> sources in Texas, and the fact
that these sources are aligned in directions that are some of the least
frequent wind directions (WSW and ENE) such that these emissions would
very rarely comingle, the EPA proposes to find that it is very unlikely
that emissions from Healdton Gas Plant contributes to SO<INF>2</INF>
nonattainment or maintenance concerns in Texas.
Continental Carbon Black Production Facility (Continental Carbon), Kay
County
Continental Carbon was identified as a DRR source and chose to
comply with DRR via modeling in Round 3 of SO<INF>2</INF> designation.
The state of Oklahoma provided through modeling an assessment and
characterization of air quality impacts from this facility and other
nearby sources \27\ that may have a potential impact in the area where
the 2010 SO<INF>2</INF> NAAQS may be exceeded.\28\ We evaluated the
EPA's TSD, which was a review of Oklahoma's submittal, noted that the
source was modeled at its 2014 SO<INF>2</INF> emissions of 5,893 tpy,
and noted that at a distance of 10 km north of the source that the
maximum concentration was approximately 80 g/m\3\ (NAAQS level at 196
[mu]g/m\3\). We concluded at that time that none of the sources in Kay
County or near its borders were likely to cause or contribute to a
violation of the NAAQS.
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\27\ The state included all SO<INF>2</INF> sources within 50 km
with emissions greater than 1 tpy.
\28\ Detailed modeling information and EPA's assessment for
Continental Carbon Black and nearby SO<INF>2</INF> sources in Kay
County can be found in the technical support document for the Round
3 SO<INF>2</INF> designation documents: 33_ok_so2_rd3-final.pdf
---------------------------------------------------------------------------
2. EPA's Prong 2 Evaluation--Interference With Maintenance
Prong 2 of the ``good neighbor'' provision requires state plans to
prohibit emissions that will interfere with maintenance of a NAAQS in
another state. The EPA's evaluation of whether Oklahoma has met its
Prong 2 transport obligations was accomplished by considering all
available information, with a focus on current air quality data,
SO<INF>2</INF> emissions trends for Oklahoma and neighboring states,
and how existing and future sources of SO<INF>2</INF> are addressed
through existing SIP-approved and federally enforceable regulations.
This evaluation builds upon the analysis conducted for significant
contribution to nonattainment (Prong 1), which evaluated SO<INF>2</INF>
ambient air quality in Oklahoma and neighboring states and potential
ambient impacts of SO<INF>2</INF> emissions from certain facilities in
Oklahoma on neighboring states.
Based on the EPA's analysis, we propose to find that SO<INF>2</INF>
levels near the Oklahoma border in neighboring states do not indicate
an inability to maintain the 2010 SO<INF>2</INF> NAAQS that could be
attributed in part to sources in Oklahoma, and as such, the EPA
proposes to determine that Oklahoma' SIP submittal satisfies the
requirements of Prong 2 of CAA section 110(a)(2)(D)(i)(I). This
determination is based on the following considerations:
<bullet> Current 2021-2023 DVs for monitors in Oklahoma within 50
km of another state's border and in neighboring states (Arkansas,
Texas, Kansas, Louisiana, and Missouri) within 50 km of Oklahoma'
border are below the standard, indicating that these areas are
currently in attainment of the 2010 1-hour SO<INF>2</INF> NAAQS;
<bullet> State-wide emissions trends in Oklahoma indicate generally
declining SO<INF>2</INF> emissions and consequently declining impacts
to the relevant areas;
<bullet> Source-specific analyses show that in most cases facility-
level emissions are decreasing as a result of emissions unit control
technology installation or shut down, indicating that emissions are not
anticipated to increase relative to baseline emissions;
<bullet> Current Oklahoma statutes, SIP-approved measures, and
federal emissions control programs control SO<INF>2</INF> emissions
from certain sources with Oklahoma; and
<bullet> Oklahoma's SIP-approved PSD, major New Source Review (NSR)
regulations and minor source NSR permit programs address future and new
modified SO<INF>2</INF> sources above major and minor permitting
thresholds with the intent of ensuring that the SO<INF>2</INF> NAAQS
will not be exceeded as a result of new facility construction or
existing facility modification within the state or surrounding states.
Based on the evaluation outlined in our TSD for this action, the
EPA proposes to find that SO<INF>2</INF> emissions from Oklahoma will
not interfere with maintenance of the 2010 1-hour SO<INF>2</INF> NAAQS
in any other state.
IV. Impact on Areas of Indian Country
Following the U.S. Supreme Court decision in McGirt v. Oklahoma,
140 S. Ct. 2452 (2020), the Governor of the State of Oklahoma requested
approval under Section 10211(a) of the Safe, Accountable, Flexible,
Efficient Transportation Equity Act of 2005: A Legacy for Users, Public
Law 109-59, 119 Stat. 1144, 1937 (August 10, 2005) (``SAFETEA''), to
administer in certain
[[Page 6580]]
areas of Indian country (as defined at 18 U.S.C. 1151) the State's
environmental regulatory programs that were previously approved by the
EPA outside of Indian country. The State's request excluded certain
areas of Indian country further described below. In addition, the State
only sought approval to the extent that such approval was necessary for
the State to administer a program in light of Oklahoma Dept. of
Environmental Quality v. EPA, 740 F.3d 185 (D.C. Cir. 2014).\29\
---------------------------------------------------------------------------
\29\ In ODEQ v. EPA, the D.C. Circuit held that under the CAA,
states have the authority to implement a SIP in non-reservation
areas of Indian country in the state, unless there has been a
demonstration of tribal jurisdiction. Under the D.C. Circuit's
decision, the CAA does not provide authority to states to implement
SIPs in Indian reservations.
---------------------------------------------------------------------------
The EPA has approved Oklahoma's SAFETEA request to administer all
of the State's EPA-approved environmental regulatory programs in the
requested areas of Indian country. As requested by Oklahoma, the EPA's
approval under SAFETEA does not include Indian country lands, including
rights-of-way running through the same, that: (1) qualify as Indian
allotments, the Indian titles to which have not been extinguished,
under 18 U.S.C. 1151(c); (2) are held in trust by the United States on
behalf of an individual Indian or Tribe; or (3) are owned in fee by a
Tribe, if the Tribe (a) acquired that fee title to such land, or an
area that included such land, in accordance with a treaty with the
United States to which such Tribe was a party, and (b) never allotted
the land to a member or citizen of the Tribe (collectively ``excluded
Indian country lands'').
The EPA's approval under SAFETEA expressly provided that to the
extent the EPA's prior approvals of Oklahoma's environmental programs
excluded Indian country, any such exclusions are superseded for the
geographic areas of Indian country covered by the EPA's approval of
Oklahoma's SAFETEA request.\30\ The approval also provided that future
revisions or amendments to Oklahoma's approved environmental regulatory
programs would extend to the covered areas of Indian country (without
any further need for additional requests under SAFETEA).
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\30\ The EPA's prior approvals relating to Oklahoma's SIP
frequently noted that the SIP was not approved to apply in areas of
Indian country (except as explained in the D.C. Circuit's decision
in ODEQ v. EPA) located in the State. See, e.g., 85 FR 20178, 20180
(April 10, 2020). Such prior expressed limitations are superseded by
the EPA's approval of Oklahoma's SAFETEA request.
---------------------------------------------------------------------------
As explained above, the EPA is proposing to approve the portion of
the State SIP submittal from the state of Oklahoma demonstrating that
the State satisfies the interstate transport requirements of section
110(a)(2)(D)(i)(I), for the 2010 1-hour SO<INF>2</INF> NAAQS which will
apply statewide in Oklahoma. Consistent with the D.C. Circuit's
decision in ODEQ v. EPA and with the EPA's SAFETEA approval, these SIP
revisions will apply to areas of Indian country as follows: (1)
pursuant to the SAFETEA approval, the SIP revisions will apply to all
Indian country in the State of Oklahoma other than the excluded Indian
country lands as described above; and (2) pursuant to the D.C.
Circuit's decision in ODEQ v. EPA, the SIP revisions will also apply to
any Indian allotments or dependent Indian communities that are located
outside of any Indian reservation over which there has been no
demonstration of tribal authority.
V. Proposed Action
The EPA is proposing to approve the prong 1 and prong 2 portions of
Oklahoma's May 28, 2021 revised certification submittal addressing
interstate transport for the 2010 1-hour SO<INF>2</INF> NAAQS. Based on
the EPA's WOE analysis, more thoroughly discussed in the TSD, the EPA
proposes to determine that emissions from Oklahoma will not contribute
significantly to nonattainment in, or interfere with maintenance of,
any other state with respect to the 2010 1-hr SO<INF>2</INF> NAAQS. We
therefore propose to find that Oklahoma' SIP contains adequate
provisions consistent with CAA section 110(a)(2)(D)(i)(I).
VI. Statutory and Executive Order Reviews
Under the CAA, the Administrator is required to approve a SIP
submission that complies with the provisions of the CAA and applicable
Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). Thus, in
reviewing SIP submissions, the EPA's role is to approve state choices,
provided that they meet the criteria of the CAA. Accordingly, this
action merely proposes to approve state law as meeting Federal
requirements and does not impose additional requirements beyond those
imposed by state law. For that reason, this action:
<bullet> Is not a ``significant regulatory action'' subject to
review by the Office of Management and Budget under Executive Orders
12866 (58 FR 51735, October 4, 1993);
<bullet> Is not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because State Implementation Plan approvals under the
CAA are exempt from review under Executive Order 12866:
<bullet> Does not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> Is certified as not having a significant economic impact
on a substantial number of small entities under the Regulatory
Flexibility Act (5 U.S.C. 601 et seq.);
<bullet> Does not contain any unfunded mandate or significantly or
uniquely affect small governments, as described in the Unfunded
Mandates Reform Act of 1995 (Pub. L. 104-4);
<bullet> Does not have Federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Is not an economically significant regulatory action based
on health or safety risks subject to Executive Order 13045 (62 FR
19885, April 23, 1997);
<bullet> Is not a significant regulatory action subject to
Executive Order 13211 (66 FR 28355, May 22, 2001);
<bullet> Is not subject to requirements of Section 12(d) of the
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272
note) because application of those requirements would be inconsistent
with the CAA; and
This proposed approval of the Oklahoma 2010 SO<INF>2</INF>
Interstate Transport that requires each state SIP contain adequate
provisions prohibiting the interstate transport of air pollution in
amounts that will contribute significantly to nonattainment, or
interfere with maintenance, of a NAAQS in any other State, will apply,
if finalized as proposed, to certain areas of Indian county throughout
Oklahoma as discussed in the preamble, and therefore has tribal
Implications as specified in as specified in E.O. 13175 (65 FR 67249,
November 9, 2000). However, this action will neither impose substantial
direct compliance costs on federally recognized Tribal governments, nor
preempt tribal law. This action will not impose substantial direct
compliance costs on federally recognized Tribal governments because no
actions will be required of Tribal governments. This action will also
not preempt Tribal law as no Oklahoma tribe implements a regulatory
program under the CAA, and thus does not have applicable or related
Tribal laws. Consistent with the EPA Policy on Consultation with Indian
Tribes (December 7, 2023), the EPA has offered consultation to Tribal
governments that may be affected by this action and provided
information about this action.
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
[[Page 6581]]
reference, Sulfur dioxide, Reporting and recordkeeping requirements.
Authority: 42 U.S.C. 7401 et seq.
Dated: February 3, 2026.
Walter Mason,
Regional Administrator, Region 6.
[FR Doc. 2026-02841 Filed 2-11-26; 8:45 am]
BILLING CODE 6560-50-P
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This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.