Air Plan Approval; Kentucky; Emissions Inventory and Nonattainment New Source Review for the Henderson-Webster Sulfur Dioxide Nonattainment Area

<RULE> ENVIRONMENTAL PROTECTION AGENCY <CFR>40 CFR Part 52</CFR> <DEPDOC>[EPA-R04-OAR-2025-0023; FRL-12899-02-R4]</DEPDOC> <SUBJECT>Air Plan Approval; Kentucky; Emissions Inventory and Nonattainment New Source Review for the Henderson-Webster Sulfur Dioxide Nonattainment Area</SUBJECT> <HD SOURCE="HED">AGENCY:</HD> Environmental Protection Agency (EPA). <HD SOURCE="HED">ACTION:</HD> Final rule. <SUM> <HD SOURCE="HED">SUMMARY:</HD> 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 <E T="52">2</E> ) national ambient air quality standard (NAAQS) for the Henderson-Webster SO <E T="52">2</E> nonattainment area (hereinafter “Henderson-Webster SO <E T="52">2</E> Nonattainment Area” or “Area”). EPA is approving these revisions pursuant to the CAA. </SUM> <EFFDATE> <HD SOURCE="HED">DATES:</HD> This rule is effective February 9, 2026. </EFFDATE> <HD SOURCE="HED">ADDRESSES:</HD> 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 <E T="03">regulations.gov</E> website. Although listed in the index, some information may not be publicly available, <E T="03">i.e.,</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 <E T="03">www.regulations.gov</E> 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 <E T="02">FOR FURTHER INFORMATION CONTACT</E> 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. <FURINF> <HD SOURCE="HED">FOR FURTHER INFORMATION CONTACT:</HD> 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 <E T="03">williamsmiles.pearlene@epa.gov.</E> </FURINF> <SUPLINF> <HD SOURCE="HED">SUPPLEMENTARY INFORMATION:</HD> <HD SOURCE="HD1">I. Background</HD> On June 2, 2010, EPA revised the primary SO <E T="52">2</E> NAAQS. Specifically, EPA established a 1-hour SO <E T="52">2</E> 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. <FTREF/> <SU>1</SU> <E T="03">See</E> 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. <E T="03">See</E> 75 FR 35520, codified at 40 CFR 50.17(a)-(b). <FTNT> <SU>1</SU>  This rule became effective on August 23, 2010, and also revoked the 24-hour and annual primary SO <E T="52">2</E> standards. </FTNT> Upon promulgation of a new or revised SO <E T="52">2</E> 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 is violating the NAAQS). As part of the designation process for the 2010 1-hour SO <E T="52">2</E> NAAQS, the Henderson-Webster SO <E T="52">2</E> Nonattainment Area was designated as a nonattainment area in the fourth round of designations on December 21, 2020. <E T="51">2 3</E> <FTREF/> These area designations became effective on April 30, 2021. <E T="03">See</E> 86 FR 16055 (March 26, 2021). States with nonattainment areas for the SO <E T="52">2</E> NAAQS must provide nonattainment SIP revisions meeting the applicable requirements of CAA sections 110(a), 172, 191, and 192  <SU>4</SU> <FTREF/> for the SO <E T="52">2</E> 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. <FTNT> <SU>2</SU>   <E T="03">See</E> Round 4 SO <E T="52">2</E> Designations at <E T="03">https://www.epa.gov/sulfur-dioxide-designations/epa-completes-fourth-round-sulfur-dioxide-designations.</E> <SU>3</SU>  The Henderson-Webster SO <E T="52">2</E> Nonattainment Area is comprised of a portion of Henderson County and a portion of Webster County. EPA designated the Henderson-Webster SO <E T="52">2</E> 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 <E T="52">2</E> concentrations in the Area. (The DRR may be found at 40 CFR 51.1205). The extent of the partial county Henderson-Webster SO <E T="52">2</E> Nonattainment Area was defined based on air dispersion modeling during round 4 SO <E T="52">2</E> designations in 2020. <E T="03">See</E> 40 CFR 81.318. </FTNT> <FTNT> <SU>4</SU>  Section 191(a) of the CAA directs states to submit SIPs for areas designated as nonattainment for the SO <E T="52">2</E> 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. </FTNT> 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 <E T="52">2</E> 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 <E T="52">2</E> Nonattainment Area). <SU>5</SU> <FTREF/> 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. <FTNT> <SU>5</SU>   <E T="03">See</E> CAA section 191(a). </FTNT> Specifically, Kentucky's January 26, 2024, SIP revision addresses NNSR permitting requirements for the 2010 1-hour SO <E T="52">2</E> NAAQS for the Henderson-Webster SO <E T="52">2</E> 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 <E T="52">2</E> 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 <E T="52">2</E> Nonattainment Area at section 172(c)(3) of the CAA by providing the required accounting of actual SO <E T="52">2</E> emissions for the Henderson-Webster SO <E T="52">2</E> 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 <E T="52">2</E> NNSR permit program requirements and the emissions inventory for Kentucky for the Henderson-Webster SO <E T="52">2</E> Nonattainment Area. <E T="03">See</E> 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. <HD SOURCE="HD1">II. Response to Comments</HD> <E T="03">Comment 1:</E> 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 fut ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Preview showing 10k of 25k characters. Full document text is stored and available for version comparison. ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━