SUPPLEMENTARY INFORMATION:

Table of Contents

I. The EPA's Final Action

II. Background

III. The EPA's Evaluation of Kentucky's SIP Submittal

A. Attainment Emissions Inventory

B. Maintenance Demonstration

C. Monitoring Network

D. Verification of Continued Attainment

E. Contingency Plan

IV. Final Action

V. Statutory and Executive Order Reviews

( printed page 60841)

I. The EPA's Final Action

In accordance with the CAA, the EPA is approving the second 10-year maintenance plan for the Kentucky portion of the Campbell-Clermont, KY-OH Area for the 2010 1-hour SO₂ NAAQS, submitted by DAQ as a revision to the Kentucky SIP on February 20, 2025. The second maintenance plan is designed to maintain the 2010 1-hour SO₂ NAAQS within the Area through the end of the second 10-year portion of the maintenance period beyond redesignation (through 2037). The EPA is approving the plan because it meets all applicable requirements under CAA sections 110 and 175A.

II. Background

On June 2, 2010, the EPA revised the primary SO₂ NAAQS, establishing a new 1-hour SO₂ standard of 75 parts per billion (ppb).^[1] The 2010 1-hour SO₂ NAAQS is met at a monitoring site when the 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations is less than or equal to 75 ppb, as determined in accordance with 40 CFR part 50, appendix T.^[2] Ambient air quality monitoring data for the 3-year period must meet a data completeness requirement.^[3]

Upon promulgation of a new or revised NAAQS, CAA section 107(d) requires the EPA to designate as nonattainment any area that does not meet (or that contributes to ambient air quality in a nearby area that does not meet) the NAAQS. The EPA designated the Area as nonattainment for the 2010 1-hour SO₂ NAAQS, effective on October 4, 2013, based on a violating 2009-2011 design value of 89 ppb at the Highland Heights ambient air monitor (Air Quality System (AQS) ID: 21-037-3002) in Campbell County, Kentucky.^[4 5] The Area consists of a portion of Campbell County, Kentucky and Pierce Township in Clermont County, Ohio.^[6] Under CAA section 192(a), SO₂ nonattainment areas must attain the NAAQS as expeditiously as practicable but not later than five years after the effective date of the designation.^[7] The Area's attainment date was no later than October 4, 2018. The EPA's nonattainment designation for the Area established a requirement for Kentucky and Ohio to submit an attainment SIP within 18 months following the effective date of designation (October 4, 2013).^[8]

When the EPA designated the Area as nonattainment for the 2010 1-hour SO₂ NAAQS, the EPA determined that operations at the Walter C. Beckjord Generating Station (Beckjord) were the major contributor to the SO₂ NAAQS violations at the Highland Heights monitor in Campbell County.^[9 10] In 2014, operations at Beckjord ceased, and the facility was permanently shut down.^[11] The source is no longer authorized to operate and cannot restart without meeting the State of Ohio's prevention of significant deterioration (PSD) permitting requirements. The shutdown reduced SO₂ emissions in the Area from approximately 90,851 tons per year (tpy) ^[12] in 2011 to 38 tpy ^[13] in 2016, resulting in a significant improvement in monitored air quality.

On March 31, 2015, DAQ submitted a request to the EPA for a clean data determination (CDD) for the Area based on the then-certified 2012-2014 SO₂ monitoring design value showing attainment of the SO₂ NAAQS. On February 22, 2016, DAQ submitted a redesignation request and first 10-year maintenance plan for the Kentucky portion of the Area. On March 10, 2017, EPA finalized approval of the Commonwealth's CDD, redesignation request, and first 10-year maintenance plan.^[14 15] The purpose of Kentucky's February 20, 2025, submittal is to fulfill the second 10-year maintenance plan requirement for the Kentucky portion of the Area pursuant to CAA section 175A(b) to ensure compliance with the 2010 SO₂ NAAQS through 2037.^[16]

III. The EPA's Evaluation of Kentucky's SIP Submittal

CAA section 175A sets forth the elements of a maintenance plan for areas seeking redesignation from nonattainment to attainment. Under CAA section 175A(a), the plan must demonstrate continued attainment of the applicable NAAQS for at least 10 years after the Administrator approves a redesignation to attainment. The September 4, 1992, memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment” outlines the key elements of a maintenance plan, which includes an attainment emissions inventory, a maintenance demonstration, monitoring network requirements, verification of continued attainment, and contingency plan elements.^[17] CAA section 175A(b) requires that eight years after the redesignation, the Commonwealth must submit a revised (second) maintenance plan demonstrating continued attainment of the relevant NAAQS for 10 years following the initial 10-year period. To address the possibility of future NAAQS violations, the maintenance plan must contain contingency measures deemed necessary to assure prompt correction of any future 2010 1-hour SO₂ violations.

Kentucky's February 20, 2025, submission provides a plan for continued maintenance of 2010 SO₂ NAAQS for the Kentucky portion of the Area through the end of the second 10-year maintenance period in 2037. The EPA has determined that Kentucky's second maintenance plan meets all the requirements established at CAA section 175A and is thus approving DAQ's February 20, 2025, SIP submission. The following is a summary of the EPA's interpretation of the CAA section 175A requirements and the EPA's evaluation of how Kentucky's SIP submission meets each requirement.

A. Attainment Emissions Inventory

For the second maintenance plan, DAQ, in consultation with the EPA Region 4 and the Ohio Environmental ( printed page 60842) Protection Agency (Ohio EPA), selected 2016 as the base year ( i.e., attainment emissions inventory year). Also, in consultation with Ohio EPA, Kentucky's SIP relies on the 2016v2 Emissions Modeling Platform (EMP) ^[18] inventory as the preferred source of the 2016 base year and future year projected emissions data to demonstrate maintenance of the SO₂ NAAQS. The 2016v2 EMP draws on data from the 2017 National Emissions Inventory (which was updated to represent the year 2016 through the incorporation of 2016-specific State and local data) and includes emissions data for all criteria pollutants (and precursors) for electric utility generating unit (EGU) point sources, non-EGU point sources, on-road and non-road (mobile) sources, commercial marine vessels, and fires for the U.S., Canada, and Mexico. The 2016v2 EMP projects future year emissions for modeling years 2016, 2023, 2026, and 2032.^[19] Area source, on-road, and non-road emissions were compiled from the 2016v2 EMP for both 2016 and 2037 (with the 2032 modeling year used as a surrogate for 2037) for the Ohio and Kentucky portions of the Area.^[20] Kentucky's SO₂ emissions for Campbell County used county-wide SO₂ emissions data rather than scaling down emissions to the portion of Campbell County in the Area for each source sector (Ohio EPA's approach for Clermont County).

On September 16, 2025, DAQ transmitted to the EPA a clarification letter ^[21] to the Commonwealth's February 20, 2025, SIP submission, correcting typographical errors, base year and future year source sector emissions data, and clarifying how the Commonwealth developed the source sector emission inventories from the 2016v2 EMP data files. Specifically, Kentucky's supplement corrects footnote 14 in the February 20, 2025, SIP submission to reference Appendix D rather than Appendix C for additional information on emission inventory development. The supplement also identifies the three 2016v2 EMP input data files the Commonwealth used to develop the Campbell County SO₂ source-sector spreadsheet included in Appendix D of the SIP submission, including weblinks for each data file. Last, Kentucky's supplement corrects source sector emissions and documentation for Table 3—Kentucky Portion SO₂ Emission Inventory Totals for 2016 Base Year and 2037 Second Maintenance Year (tpy) of Kentucky's February 20, 2025, SIP submission including:

(1) Adding residential wood combustion and point fire emissions to the calculation for 2016 and 2037, changing the area source totals from 15.46 tpy for both years to 20.61 tpy for 2016 and 20.39 tpy for 2037;

(2) Updating the non-EGU point source-sector emissions for the 2016 inventory from 2.06 tpy to 2.07 tpy, and;

(3) Clarifying that the non-road source-sector emissions for 2016 and 2037, (0.85 tpy and 0.43 tpy emissions, respectively) were calculated as a total of the commercial marine vehicles, railroads, and non-road emissions from the 2016v2 EMP to ensure a comprehensive accounting of non-road emissions in Campbell County.

Kentucky's corrections to the source-sector SO₂ emission values in Table 3 of the submittal changed the 2016 base year total emissions from 22.90 tpy to 28.06 tpy and the 2037 future year total emissions from 20.63 tpy to 25.56 tpy. Kentucky provided a revised Table 3 in the supplemental September 16, 2025, letter clarifying that the source-sector emission updates do not affect the Commonwealth's conclusion in its February 20, 2025, SIP revision that the Kentucky portion of the Area demonstrates maintenance of the SO₂ NAAQS for the second 10-year maintenance period. Kentucky's revised Table 3 source-sector corrections are reflected in the Campbell County 2016 base year inventory emission data in Table 1, below.^[22]

Table 1 shows that 2016 SO₂ emissions in the Kentucky portion of the Area were at 28.06 tpy (based on county-level data), with emissions for the Ohio portion at 10.18 tpy. At the time of the EPA's 2013 nonattainment designation, there were no SO₂ point sources in the portion of Campbell County within the Area, and the Beckjord powerplant in Clermont County was the only SO₂ EGU point source in Ohio found to cause a violation at the Campbell County Highland Heights monitor.^[23] Since the EPA redesignated the Kentucky portion of the Area in 2017, there are no EGU and major point or non-point SO₂ emitting sources that could cause a violation of the SO₂ NAAQS at the Highland Heights monitor (AQS ID 21- ( printed page 60843) 037-3002) as reflected in the 2023-2025, 3-year design value of 6 ppb.^[24]

B. Maintenance Demonstration

States may generally demonstrate maintenance by either performing air quality modeling to show that the future mix of sources and emission rates will not cause a violation of the NAAQS or by showing that projected future emissions of a pollutant and its precursors will not exceed the level of emissions during a year when the area was attaining the NAAQS ( i.e., the 2016 base or attainment year inventory in Kentucky's SIP submission).^[25] Kentucky's submission establishes that the 2037 projected inventory is below the level of the 2016 base year inventory thus demonstrating maintenance through 2037. The 2037 future year is appropriate because it is 10 years beyond the first 10-year maintenance period. Kentucky projected 2037 future year emissions for non-EGU point, area, on-road,^[26] and non-road source categories using the 2016v2 EMP 2032 model year emissions case as a surrogate for 2037. See Appendix D of Kentucky's SIP submission. The 2016 base year and 2037 future year SO₂ emission inventory totals for the Area were developed consistent with the EPA guidance and are summarized in Tables 2 and 3, below.

The 2014 permanent and enforceable shutdown of the Beckjord facility in Ohio resulted in significant SO₂ emission reductions in the Area. As shown in Table 4 below, the design values since attainment have steadily decreased with the latest design value being 92 percent below the NAAQS, demonstrating continued maintenance. Tables 2 and 3 show no base and future year EGU point source emissions and low non-EGU point source emissions. See Appendix D of Kentucky's February 21, 2025, SIP revision for additional emissions inventory information. Currently, there are no large EGU or non-EGU SO₂ point sources located in either the Kentucky or Ohio portions of the Area with the potential to cause a monitored violation.

Additionally, while neither the Commonwealth nor Ohio have projected significant growth in their respective counties, any potential new major stationary source that seeks to construct during the second 10-year maintenance period would be subject to each State's ( printed page 60844) SIP-approved PSD program permitting requirements. Given the low design values for the Area, the EPA does not anticipate any future monitored violation of the SO₂ NAAQS for the Area. For the reasons discussed above, Kentucky's February 20, 2025, SIP submission demonstrates maintenance of the 2010 SO₂ NAAQS for the Area.

C. Monitoring Network

The Highland Heights SO₂ monitor (AQS ID: 21-037-3002) located in Campbell County is the only SO₂ monitor operating in the Area. The 3-year design values ^[27] since the shutdown of the Beckjord facility in Ohio in 2014 have remained well below the 75 ppb 2010 1-hour SO₂ NAAQS. See Table 4 below and Figure 2 in Kentucky's February 20, 2025, SIP submission. The most recent complete and certified 3-year design value (2023-2025) for Highland Heights is 6 ppb. In its SIP revision, Kentucky has committed to continue to operate an EPA-approved ambient air quality network, in compliance with 40 CFR part 58 and has thus addressed the requirement for the monitoring. The EPA approved Kentucky's 2025 Annual Ambient Air Monitoring Network Plan on October 28, 2025.^[28]

D. Verification of Continued Attainment

An air agency should ensure that it has the legal authority to implement and enforce all measures necessary to attain and maintain the NAAQS. Additionally, the air agency should establish how it will track progress of the maintenance plan for the area. Kentucky, through DAQ, has the legal authority to enforce and implement the maintenance plan for the Kentucky portion of the Area. This includes the authority to adopt, implement, and enforce any subsequent contingency measures determined to be necessary to correct future attainment issues for the 2010 SO₂ NAAQS. In addition, Kentucky requires major point sources in all counties to submit SO₂ emissions information annually and assists in the preparation of new periodic inventories for all source sectors every three years in accordance with the Air Emissions Reporting Rule, 40 CFR part 51 subpart A. Kentucky will compare emissions information to the attainment year and the 2037 projected maintenance year inventories to assess emission trends and to ensure continued compliance with the standard. Lastly, as mentioned in section II.C above, the Commonwealth will continue to operate an EPA-approved ambient air quality network in accordance with monitoring requirements at 40 CFR part 58.

E. Contingency Plan

CAA section 175A(d) requires that a maintenance plan include such contingency measures as the EPA deems necessary to assure that the State will promptly correct a violation of the NAAQS that occurs after redesignation. The maintenance plan should identify the contingency measures to be adopted, a schedule and procedure for adoption and implementation, and a timeframe for action by the State. A State should also identify specific indicators to be used to determine when the contingency measures need to be implemented. The maintenance plan must include a requirement that a State will implement all measures with respect to control of the pollutant that were contained in the SIP before redesignation of the area to attainment in accordance with CAA section 175A(d). With the 2014 permanent shutdown of the Beckjord Generating Station, there are no EGU point sources in the Area, and thus DAQ does not anticipate future monitored violations of the 2010 SO₂ NAAQS.

Kentucky has an enforcement program to address NAAQS violations and will continue to identify violations of the SO₂ NAAQS and undertake an aggressive follow-up, if a violation occurs, to ensure compliance and enforcement of the standard. Ambient air SO₂ monitoring data will serve as the primary trigger for any response to prevent or correct a NAAQS violation in the area. Kentucky has established warning and action level responses with specific triggering indicators. DAQ commits to adopt and expeditiously implement necessary corrective actions in the event of a warning or action level trigger.

A warning level trigger occurs whenever an annual average 99th percentile maximum daily 1-hour SO₂ concentration greater than 75 ppb occurs in a single calendar year within the Area.^[29] A warning level response will consist of a study to evaluate the Area's emission inventory for all source sectors, exceptional events, and best practices for implementing the State's PSD permitting program at any new stationary source and/or new or modified area source. The study will determine if the monitored SO₂ concentrations indicate a trend toward higher values and/or if SO₂ emissions appear to be increasing. The study will evaluate whether any such trend is likely to continue and, if so, what control measures are necessary to reverse the trend. Implementation of controls will take place as expeditiously as possible, but no later than 12 months from the conclusion of the most recent calendar year.

An action level trigger occurs whenever a two-year average of the 99th percentile maximum daily 1-hour SO₂ concentration greater than 75 ppb ( printed page 60845) occurs within the Area. A violation of the NAAQS (the three-year average of the 99th percentile maximum daily 1-hour value SO₂ concentration of 75 ppb or greater) shall also prompt an action level response. In the event that the action level is triggered and is not found to be due to an exceptional event, malfunction, or noncompliance with a permit condition or rule requirement, DAQ in conjunction with the metropolitan planning organization or regional council of governments, will determine additional control measures needed to assure future attainment of the 1-hour SO₂ NAAQS. Measures that can be implemented in the short term will be selected for implementation within 18 months from the close of the calendar year that prompted the action level response. The Commonwealth will also consider the timing of an action level trigger and determine if additional, significant new regulations not currently included as part of the maintenance provisions will be implemented in a timely manner and will constitute the response.

If the Commonwealth determines that a new control measure that is already promulgated and scheduled to be implemented will be sufficient to address a violation of the SO₂ NAAQS, additional local measures may be unnecessary. DAQ will submit to the EPA an analysis to demonstrate that the proposed control measures are adequate to return the Area to attainment. If adoption of control measures is necessary, they will be subject to Kentucky's administrative and legal process. This process will include publication of notices, an opportunity for public hearing and comment, and other measures required by State law for revisions to the SIP. The selection of control measures will be based on cost-effectiveness, emission reduction potential, economic and social considerations, or other factors that the Commonwealth deems appropriate.

IV. Final Action

The EPA is approving the second maintenance plan for the Kentucky portion of the 2010 1-hour SO₂ Campbell-Clermont, KY-OH Area for the reasons discussed above. Approval of Kentucky's SIP revision will make certain commitments related to maintenance of the 2010 1-hour SO₂ NAAQS in the Kentucky portion of the Campbell-Clermont, KY-OH Area federally enforceable as part of the Kentucky SIP.

V. 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.^[30] 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 approves State law as meeting Federal requirements and does not impose additional requirements beyond those imposed by State law. For that reason, this action:

• Is not a significant regulatory action subject to review by the Office of Management and Budget underExecutive Order 12866 (58 FR 51735, October 4, 1993);
• Is not anExecutive Order 14192 (90 FR 9065, February 6, 2025) regulatory action because this action is not significant under Executive Order 12866;
• Does not impose an information collection burden under the provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
• 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.);
• 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);
• Does not have federalism implications as specified inExecutive Order 13132 (64 FR 43255, August 10, 1999);
• Is not subject toExecutive Order 13045 (62 FR 19885, April 23, 1997) because it approves a State program;
• Is not a significant regulatory action subject toExecutive Order 13211 (66 FR 28355, May 22, 2001); and
• 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.

In addition, the SIP is not approved to apply on any Indian reservation land or in any other area where the 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.^[31]

This action is subject to the Congressional Review Act, and the EPA will submit a rule report to each House of the Congress and to the Comptroller General of the United States. This action is not a “major rule” as defined by 5 U.S.C. 804(2).

Under CAA section 307(b)(1), petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by November 24, 2026. Filing a petition for reconsideration by the Administrator of this final rule does not affect the finality of this action 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. Parties with objections to this direct final rule are encouraged to file a comment in response to the parallel notice of proposed rulemaking for this action published in the proposed rules section of this Federal Register , rather than file an immediate petition for judicial review of this direct final rule, so that the EPA can withdraw this direct final rule and address the comment in the proposed rulemaking. This action may not be challenged later in proceedings to enforce its requirements.^[32]

For the reasons stated in the preamble, the EPA amends 40 CFR part 52 as follows:

91 FR 60840