Rule2026-00201
Air Plan Approval; Kentucky; Emissions Inventory and Nonattainment New Source Review for the Henderson-Webster Sulfur Dioxide Nonattainment Area
Primary source
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Published
January 8, 2026
Effective
February 9, 2026
Issuing agencies
Environmental Protection Agency
Abstract
The Environmental Protection Agency (EPA) is approving two State Implementation Plan (SIP) revisions submitted by the Commonwealth of Kentucky (Commonwealth), through the Energy and Environment Cabinet, Division of Air Quality (DAQ) on January 26, 2024, and February 15, 2024, to certify two requirements under the Clean Air Act (CAA or Act). These revisions establish that the Kentucky SIP satisfies the nonattainment new source review (NNSR) and base year emissions inventory requirements for the 2010 1-hour sulfur dioxide (SO<INF>2</INF>) national ambient air quality standard (NAAQS) for the Henderson-Webster SO<INF>2</INF> nonattainment area (hereinafter "Henderson-Webster SO<INF>2</INF> Nonattainment Area" or "Area"). EPA is approving these revisions pursuant to the CAA.
Full Text
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<title>Federal Register, Volume 91 Issue 5 (Thursday, January 8, 2026)</title>
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[Federal Register Volume 91, Number 5 (Thursday, January 8, 2026)]
[Rules and Regulations]
[Pages 609-612]
From the Federal Register Online via the Government Publishing Office [<a href="http://www.gpo.gov">www.gpo.gov</a>]
[FR Doc No: 2026-00201]
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ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 52
[EPA-R04-OAR-2025-0023; FRL-12899-02-R4]
Air Plan Approval; Kentucky; Emissions Inventory and
Nonattainment New Source Review for the Henderson-Webster Sulfur
Dioxide Nonattainment Area
AGENCY: Environmental Protection Agency (EPA).
ACTION: Final rule.
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SUMMARY: The Environmental Protection Agency (EPA) is approving two
State Implementation Plan (SIP) revisions submitted by the Commonwealth
of Kentucky (Commonwealth), through the Energy and Environment Cabinet,
Division of Air Quality (DAQ) on January 26, 2024, and February 15,
2024, to certify two requirements under the Clean Air Act (CAA or Act).
These revisions establish that the Kentucky SIP satisfies the
nonattainment new source review (NNSR) and base year emissions
inventory requirements for the 2010 1-hour sulfur dioxide
(SO<INF>2</INF>) national ambient air quality standard (NAAQS) for the
Henderson-Webster SO<INF>2</INF> nonattainment area (hereinafter
``Henderson-Webster SO<INF>2</INF> Nonattainment Area'' or ``Area'').
EPA is approving these revisions pursuant to the CAA.
DATES: This rule is effective February 9, 2026.
ADDRESSES: EPA has established a docket for this action under Docket
Identification No. EPA-R04-OAR-2025-0023. All documents in the docket
are listed on the <a href="http://regulations.gov">regulations.gov</a> website. Although listed in the
index, some information may not be publicly available, i.e.,
Confidential Business Information or other information whose disclosure
is restricted by statute. Certain other material, such as copyrighted
material, is not placed on the internet and will be publicly available
only in hard copy form. Publicly available docket materials are
available either electronically through <a href="http://www.regulations.gov">www.regulations.gov</a> or in hard
copy at the Air Regulatory Management Section, Air Planning and
Implementation Branch, Air and Radiation Division, U.S. Environmental
Protection Agency, Region 4, 61 Forsyth Street SW, Atlanta, Georgia
30303-8960. EPA requests that if at all possible, you contact the
person listed in the FOR FURTHER INFORMATION CONTACT section to
schedule your inspection. The Regional Office's official hours of
business are Monday through Friday 8:30 a.m. to 4:30 p.m., excluding
Federal holidays.
FOR FURTHER INFORMATION CONTACT: Pearlene Williams-Miles, Multi-Air
Pollutant Coordination Section, Air Planning and Implementation Branch,
Air and Radiation Division, U.S. Environmental Protection Agency,
Region 4, 61 Forsyth Street SW, Atlanta, Georgia 30303-8960. The
telephone number is (404) 562-9144. Ms. Williams-Miles can also be
reached via electronic mail at <a href="/cdn-cgi/l/email-protection#abdcc2c7c7c2cac6d8c6c2c7ced885dbcecad9c7cec5ceebcedbca85ccc4dd"><span class="__cf_email__" data-cfemail="3b4c525757525a56485652575e48154b5e5a49575e555e7b5e4b5a155c544d">[email protected]</span></a>.
SUPPLEMENTARY INFORMATION:
I. Background
On June 2, 2010, EPA revised the primary SO<INF>2</INF> NAAQS.
Specifically, EPA established a 1-hour SO<INF>2</INF> standard at a
level of 75 parts per billion (ppb), based on the 3-year average of the
annual 99th percentile of 1-hour daily maximum concentrations.\1\ See
75 FR 35520 (June 22, 2010). The 1-hour standard is met at an ambient
air quality monitoring site when the 3-year average of the annual 99th
percentile of daily maximum 1-hour average concentrations does not
exceed 75 ppb, as determined in accordance with appendix T of 40 CFR
part 50. See 75 FR 35520, codified at 40 CFR 50.17(a)-(b).
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\1\ This rule became effective on August 23, 2010, and also
revoked the 24-hour and annual primary SO<INF>2</INF> standards.
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Upon promulgation of a new or revised SO<INF>2</INF> NAAQS, section
107(d) of the CAA requires EPA to designate as nonattainment any area
that is violating the NAAQS (or that contributes to ambient air quality
in a nearby area that
[[Page 610]]
is violating the NAAQS). As part of the designation process for the
2010 1-hour SO<INF>2</INF> NAAQS, the Henderson-Webster SO<INF>2</INF>
Nonattainment Area was designated as a nonattainment area in the fourth
round of designations on December 21, 2020.<SUP>2 3</SUP> These area
designations became effective on April 30, 2021. See 86 FR 16055 (March
26, 2021). States with nonattainment areas for the SO<INF>2</INF> NAAQS
must provide nonattainment SIP revisions meeting the applicable
requirements of CAA sections 110(a), 172, 191, and 192 \4\ for the
SO<INF>2</INF> NAAQS. EPA's regulations governing nonattainment SIPs
are set forth at 40 CFR part 51, with specific procedural requirements
and control strategy requirements residing at subparts F and G,
respectively.
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\2\ See Round 4 SO<INF>2</INF> Designations at <a href="https://www.epa.gov/sulfur-dioxide-designations/epa-completes-fourth-round-sulfur-dioxide-designations">https://www.epa.gov/sulfur-dioxide-designations/epa-completes-fourth-round-sulfur-dioxide-designations</a>.
\3\ The Henderson-Webster SO<INF>2</INF> Nonattainment Area is
comprised of a portion of Henderson County and a portion of Webster
County. EPA designated the Henderson-Webster SO<INF>2</INF>
Nonattainment Area in 2020 based on a violating ambient air
monitor--the Sebree data requirements rule (DRR) monitor (Air
Quality System ID: 21-101-1011)--sited to characterize the maximum
1-hour SO<INF>2</INF> concentrations in the Area. (The DRR may be
found at 40 CFR 51.1205). The extent of the partial county
Henderson-Webster SO<INF>2</INF> Nonattainment Area was defined
based on air dispersion modeling during round 4 SO<INF>2</INF>
designations in 2020. See 40 CFR 81.318.
\4\ Section 191(a) of the CAA directs states to submit SIPs for
areas designated as nonattainment for the SO<INF>2</INF> NAAQS to
EPA within 18 months of the effective date of the designation. Under
CAA section 192(a) these SIPs are required to demonstrate that their
respective areas will attain the NAAQS as expeditiously as
practicable, but no later than 5 years from the effective date of
designation. In addition, sections 110(a) and 172(c), as well as EPA
regulations at 40 CFR part 51, set forth substantive elements each
SIP must contain to be approved by EPA.
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For EPA to fully approve a SIP revision as meeting the requirements
of CAA sections 110, 172, 191, and 192 and EPA's regulations at 40 CFR
part 51, the SIP for the affected area must demonstrate to EPA's
satisfaction that each of the requirements have been met. State air
agencies with nonattainment areas for the 2010 1-hour primary
SO<INF>2</INF> NAAQS are required to submit a SIP revision that
addresses these requirements within 18 months after an area is
designated nonattainment (no later than October 30, 2022, for the
Henderson-Webster SO<INF>2</INF> Nonattainment Area).\5\ Kentucky's
January 26, 2024, and February 15, 2024, SIP revisions address the air
agency's NNSR permitting and emissions inventory obligations pursuant
to section 172(c)(5) and 172(c)(3) of the Act, respectively.
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\5\ See CAA section 191(a).
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Specifically, Kentucky's January 26, 2024, SIP revision addresses
NNSR permitting requirements for the 2010 1-hour SO<INF>2</INF> NAAQS
for the Henderson-Webster SO<INF>2</INF> Nonattainment Area by
certifying that the version of 401 KAR 51:052 in the SIP satisfies the
federal NNSR requirements for the Henderson-Webster SO<INF>2</INF>
Nonattainment Area at CAA sections 172(c)(5) and 173 and 40 CFR 51.165,
and thus, a modification to the Commonwealth's SIP-approved regulations
at 401 KAR 51:052 is not necessary.
Additionally, Kentucky's February 15, 2024, SIP revision addresses
the base year emissions inventory requirements for the Henderson-
Webster SO<INF>2</INF> Nonattainment Area at section 172(c)(3) of the
CAA by providing the required accounting of actual SO<INF>2</INF>
emissions for the Henderson-Webster SO<INF>2</INF> Nonattainment Area.
On September 5, 2025, EPA published a notice of proposed rulemaking
(NPRM) proposing to approve the January 26, 2024, and February 15,
2024, SIP revisions regarding the 2010 1-hour SO<INF>2</INF> NNSR
permit program requirements and the emissions inventory for Kentucky
for the Henderson-Webster SO<INF>2</INF> Nonattainment Area. See 90 FR
42889. The September 5, 2025, NPRM provides additional detail regarding
the background and rationale for EPA's action. Comments on the
September 5, 2025, NPRM were due on or before October 6, 2025. EPA
received one set of adverse comments on the NPRM from a commenter. The
comments are posted to the docket for this action. EPA summarizes and
responds to the adverse comments below.
II. Response to Comments
Comment 1: The commenter asserts that Kentucky's 2018 point source
emissions inventory for the Area is a ``non-representative'' inventory
because it does not account for the conversion from coal to natural gas
at the Big Rivers Electric Corporation (BREC)--Robert D. Green Station
power plant (BREC-Green Station) that occurred since 2018, and thus,
violates the requirement to have a comprehensive, accurate, and current
inventory pursuant to section 172(c)(3) of the CAA. Specifically, the
commenter claims that the operational changes at BREC Green Station
mean the 2018 data does not represent the actual emissions baseline of
the Area. Further, the commenter states that because the emissions
inventory is the platform for ``all future modeling and control
strategy development,'' using this emissions data guarantees that
subsequent SIP elements will be flawed from the outset. The commenter
asserts that EPA failed its duty to ensure the SIP is ``built on a
technically sound foundation'' by proposing to approve an inventory
based on what the commenter describes as ``obsolete'' emission data for
a major source.
Response 1: EPA disagrees with this comment. Section 172(c)(3) of
the CAA states that nonattainment SIPs shall include a comprehensive,
accurate, current inventory of actual emissions from all sources of the
relevant pollutant or pollutants in the Area. As noted in the September
5, 2025, NPRM, the Commonwealth stated in its February 15, 2024, SIP
submission that it selected a 2018 base year emission inventory for the
Henderson-Webster SO<INF>2</INF> Nonattainment Area point sources
because: (1) 2018 was one of three years (2017, 2018 and 2019) used to
designate the Area as nonattainment, and (2) the Commonwealth's 2018
point source emission data set was more current than the most recent
comprehensive triennial inventory in this period, EPA's 2017 national
emissions inventory (NEI) point source data.
The commenter's claims are unsubstantiated and indicate a
misunderstanding of the section 172(c)(3) emissions inventory.
Kentucky's 2018 base year emissions inventory represents emissions in
the Henderson-Webster Area at the time it did not meet the 2010 1-hour
SO<INF>2</INF> NAAQS. Emission inventories provide emissions data that
inform a variety of air quality planning tasks, including establishing
baseline emission levels, calculating emission reduction triggers
necessary to attain the NAAQS, determining emission inputs for
SO<INF>2</INF> air quality modeling analyses, and tracking emissions
over time to determine progress toward achieving air quality and
emission reduction goal. As noted in EPA's NPRM, Kentucky has met this
requirement to provide a comprehensive, accurate, and current inventory
for the Area.
To demonstrate attainment of the NAAQS, the Commonwealth will have
to provide an updated emissions inventory that is representative of the
emissions in the Area at a time the air quality is attaining the NAAQS.
Furthermore, to be redesignated to ``attainment,'' the Commonwealth
would also have to provide a maintenance demonstration. The
Commonwealth would be required to either provide a projected inventory
that shows emissions will not increase during a 10-year period in a way
that endangers the continued maintenance of the NAAQS or modeling to
show that the future mix of sources and emission rates will not cause a
violation of the NAAQS. These base year attainment
[[Page 611]]
and maintenance inventories serve a different fundamental purpose than
the nonattainment base year inventory provided in the February 2024 SIP
submittal.
EPA has determined that Kentucky's emission inventory for the
Henderson-Webster SO<INF>2</INF> Nonattainment Area, including the 2018
base year inventory for all four point sources, is consistent with the
requirements established at section 172(c)(3) of the CAA for a
comprehensive, accurate, and current inventory of actual emissions. As
such, Kentucky's February 2024 SIP revision satisfies the emissions
inventory requirements for nonattainment plans at section 172(c)(3) of
the CAA. In addition, pursuant to CAA section 110(k)(3), EPA shall
approve a SIP submittal if it meets all the applicable requirements.
For these reasons, EPA has not failed its statutory duty.
Comment 2: The commenter asserts that EPA must consider the
interdependency of SIP elements and states that approving the NNSR
certification based on a flawed emission inventory creates regulatory
uncertainty. The commenter goes on to state that the NNSR program
applicability and stringency are tied to the accuracy of the emissions
inventory data because they determine major source thresholds and
significance levels for modifications. The commenter concludes that EPA
cannot reasonably determine that the NNSR program is adequate for the
2010 SO<INF>2</INF> NAAQS when the emissions inventory used to
calibrate the program is not representative. The commenter alleges that
approving a component that is critically dependent on another,
unresolved component is an arbitrary segmentation of the SIP process.
Response 2: EPA disagrees with this comment. As discussed in
Response 1, nonattainment SIPs must contain an emissions inventory that
meets the requirements of CAA section 172(c)(3), and EPA has determined
that the Commonwealth's SIP revision satisfies those requirements.
Separately, section 172(c)(5) of the CAA requires that SIPs require
permits for the construction and operation of new or modified major
stationary source anywhere in a nonattainment area in accordance with
section 173 of the CAA. EPA's implementing regulations at 40 CFR 51.165
and Appendix S to part 51 set forth detailed requirements for NNSR
programs and define a major stationary source as any stationary source
that emits, or has the potential to emit, 100 tons per year (tpy) or
more of SO<INF>2</INF>. A major modification of an existing major
stationary source of SO<INF>2</INF> is defined as a significant
emissions increase and significant net emissions increase of
SO<INF>2</INF> of 40 tpy. Because these regulations prescribe NNSR
requirements, including applicability thresholds, the section 172(c)(3)
inventories do not ``determine major source thresholds and significance
levels for modifications,'' do not impact the applicability or
stringency of NNSR, and are not used to ``calibrate'' NNSR.
EPA's proposed certification of Kentucky's NNSR program at 401 KAR
51.052 is based on the fact that the SIP is required to contain the
permitting criteria established at sections 172(c)(5) and 173 of the
CAA and EPA's implementing regulations at 40 CFR 51.165. The NNSR
program requirements are not dependent on the base year emission
inventory SIP requirements. Both SIP requirements are critical planning
elements of the collective nonattainment SIP pursuant to part D of the
CAA. Each is independent of the other and serves a unique purpose in
addressing air quality that does not attain the NAAQS. Neither the CAA
nor its implementing regulations require EPA to deem either a
nonattainment plan's NNSR or emissions inventory elements adequate in
order to approve the other. Furthermore, the commenter fails to explain
how these two elements are interrelated.
Comment 3: The commenter states that the emissions inventory EPA
evaluated is outdated and creates a ``flawed regulatory framework''
that introduces unnecessary risk and uncertainty for Century Aluminum's
operations and potential modernization plans. The commenter states that
EPA must consider the `` `extraordinary circumstance' '' of approving a
plan that governs a facility of ``strategic national importance.'' The
commenter then claims that the Century Aluminum facility in the
Henderson-Webster SO<INF>2</INF> Nonattainment Area produces material
that is critical to national defense and infrastructure, and thus, EPA
has a responsibility to ensure its actions do not undermine national
economic and strategic interests by inadvertently creating a legally
unstable and technically unsound permitting environment. The commenter
further states that a SIP subject to legal challenges creates
regulatory unpredictability that harms investments in critical
industries.
Response 3: EPA disagrees with this comment. For the reasons
explained in Response 1, EPA disagrees that Kentucky's selection of
2018 for its inventory of point sources in the nonattainment area is
outdated. Furthermore, the commenter's assertion that EPA's action
approving Kentucky's use of the 2018 base year for point sources as a
part of the inventory for the Area somehow undermines the economic
viability of an industry the commenter believes produces critical
materials is unsupported as is the claim that EPA must consider the ``
`extraordinary circumstance' '' of approving a plan that governs a
facility of ``strategic national importance.'' As discussed in
Responses 1 and 2, EPA has evaluated the SIP revisions and determined
that they meet the requirements of CAA section 172(c)(3) for the
emissions inventory and section 172(c)(5) for NNSR. Pursuant to CAA
section 110(k)(3), EPA shall approve a SIP submittal if it meets all
the applicable requirements. Therefore, EPA's actions to approve these
SIP submittals are consistent with the CAA, and it is therefore unclear
how these actions could create regulatory unpredictability that harms
investments in critical industries.
Comment 4: The commenter states that ``the proposal exhibits
significant flaws that require a more rigorous evaluation before a
finding of approval can be legally sustained'' as summarized in
Comments 1 through 3. The commenter concludes that EPA must withdraw
the proposal based on the comments summarized above, thoroughly analyze
the emission inventory to meet the ``current'' requirement of CAA
172(c)(3) and require Kentucky to submit a revised inventory, and
evaluate the NNSR certification in the context of a ``valid'' emissions
inventory.
Response 4: EPA disagrees with this comment for the reasons
discussed in Responses 1 through 3. Therefore, EPA is finalizing
approval of these nonattainment planning elements pursuant to CAA
sections 172(c)(3), 172(c)(5), and 173 and 40 CFR part 51.
III. Final Actions
For the reasons discussed above, EPA is approving Kentucky's
January 26, 2024, and February 15, 2024, SIP revisions containing a
certification that its existing SIP-approved NNSR program meets the
NNSR requirements for the 2010 SO<INF>2</INF> NAAQS and an emissions
inventory, respectively, for the Henderson-Webster SO<INF>2</INF>
Nonattainment Area.
IV. 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. See 42 U.S.C. 7410(k); 40 CFR 52.02(a).
[[Page 612]]
Thus, in reviewing SIP submissions, EPA's role is to approve state
choices, provided that they meet the criteria of the CAA. Accordingly,
these actions merely approve state law as meeting Federal requirements
and do not impose additional requirements beyond those imposed by state
law. For that reason, these actions:
<bullet> Are not significant regulatory actions subject to review
by the Office of Management and Budget under Executive Orders 12866 (58
FR 51735, October 4, 1993);
<bullet> Are not subject to Executive Order 14192 (90 FR 9065,
February 6, 2025) because SIP actions are exempt from review under
Executive Order 12866;
<bullet> Do not impose an information collection burden under the
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
<bullet> Are 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> Do 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> Do not have federalism implications as specified in
Executive Order 13132 (64 FR 43255, August 10, 1999);
<bullet> Are not subject to Executive Order 13045 (62 FR 19885,
April 23, 1997) because they approve a state program;
<bullet> Are not significant regulatory actions subject to
Executive Order 13211 (66 FR 28355, May 22, 2001); and
<bullet> Are 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.
In addition, the SIP is not approved to apply on any Indian
reservation land or in any other area where EPA or an Indian tribe has
demonstrated that a tribe has jurisdiction. In those areas of Indian
country, the rule does not have Tribal implications and will not impose
substantial direct costs on Tribal governments or preempt Tribal law as
specified by Executive Order 13175 (65 FR 67249, November 9, 2000).
These actions are subject to the Congressional Review Act, and EPA
will submit a rule report to each House of the Congress and to the
Comptroller General of the United States. These actions are not a
``major rule'' as defined by 5 U.S.C. 804(2).
Under section 307(b)(1) of the CAA, petitions for judicial review
of these actions must be filed in the United States Court of Appeals
for the appropriate circuit by March 9, 2026. Filing a petition for
reconsideration by the Administrator of this final rule does not affect
the finality of these actions for the purposes of judicial review nor
does it extend the time within which a petition for judicial review may
be filed, and shall not postpone the effectiveness of such rule or
action. These actions may not be challenged later in proceedings to
enforce its requirements. See section 307(b)(2).
List of Subjects in 40 CFR Part 52
Environmental protection, Air pollution control, Incorporation by
reference, Intergovernmental relations, Sulfur oxides.
Dated: December 29, 2025.
Kevin McOmber,
Regional Administrator, Region 4.
For the reasons stated in the preamble, EPA amends 40 CFR part 52
as follows:
PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS
0
1. The authority citation for part 52 continues to read as follows:
Authority: 42 U.S.C. 7401 et seq.
Subpart S--Kentucky
0
2. In Sec. 52.920(e), amend the table by adding new entries for ``2010
1-hour SO<INF>2</INF> NAAQS Nonattainment New Source Review
Requirements'' and ``Emissions Inventory for the 2010 1-hour
SO<INF>2</INF> NAAQS'' at the end of the table, to reads as follows:
Sec. 52.920 Identification of plan.
* * * * *
(e) * * *
EPA-Approved Kentucky Non-Regulatory Provisions
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Applicable
Name of non-regulatory SIP geographic or State submittal
provision nonattainment date/effective EPA approval date Explanations
area date
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* * * * * * *
2010 1-hour SO2 NAAQS Portions of 1/26/2024 1/8/2026, 90 FR
Nonattainment New Source Henderson and [Insert citation
Review Requirements. Webster Counties of publication].
in Kentucky.
Emissions Inventory for the Portions of 2/15/2024 1/8/2026, 90 FR
2010 1-hour SO2 NAAQS. Henderson and [Insert citation
Webster Counties of publication].
in Kentucky.
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[FR Doc. 2026-00201 Filed 1-7-26; 8:45 am]
BILLING CODE 6560-50-P
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