SUPPLEMENTARY INFORMATION:

Throughout this document “we,” “us,” and “our” refer to EPA.

Table of Contents

I. What is being addressed in this document?

II. Have the requirements for approval of a SIP revision been met?

III. The EPA's Response to Comments

IV. What action is the EPA taking?

V. Incorporation by Reference

VI. Statutory and Executive Order Reviews

I. What is being addressed in this document?

The EPA is approving revisions to the Missouri SIP received on April 23, 2025. The EPA proposed to approve these revisions on June 27, 2025 (90 FR 27491). In its submission, Missouri requested rescinding 10 CSR 10-6.260 “Restriction of Emission of Sulfur Compounds” and replacing it with a newer statewide regulation, 10 CSR 10-6.261 “Control of Sulfur Dioxide Emissions” (state effective date May 30, 2025) in the Missouri SIP. Specifically, the revisions resulting from this action include adding an exemption for units burning ultra-low sulfur diesel fuel; removing sulfur compound stack gas concentration limits for non-indirect heating units along with eliminating these sources from the rule's applicability; consolidating all facility-specific SO₂ emission rate limits into a single table and removing the limits that are no longer necessary; consolidating and clarifying reporting, recordkeeping, and testing requirements; and making a number of other minor changes and error corrections.

The revisions also reinstate SO₂ emission limits applicable to Ameren-Labadie and Evergy-Hawthorn power plants that Missouri had previously removed from 10 CSR 10-6.261, which addresses the deficiencies identified in the EPA's disapproval action finalized on January 4, 2023 (88 FR 291). Regarding the Hawthorn SO₂ emission limit for boiler 5A, the revisions incorporate requirements for natural gas usage and dry scrubber operation during periods of startup and shutdown, ensuring that a continuous limit is in place. In addition, because the Hawthorn boiler 5A numeric limit along with the necessary monitoring, record keeping, and reporting requirements are now fully incorporated into the SIP via this action, any potential deficiencies in the SIP with respect to Hawthorn have been addressed and the enforceability and protectiveness of the limit previously approved into the SIP have been enhanced.

Concurrent with approving these revisions to the Missouri SIP, the EPA is approving a negative declaration submitted on May 4, 2022 pursuant to the state's approved Clean Air Act (CAA) 111(d) plan for Sulfuric Acid Mist from Existing Sulfuric Acid Production Plants, which is codified at 40 CFR 62.6353. The negative declaration is necessary for Missouri to remove portions of 10 CSR 10-6.260 that are linked to the state's 111(d) plan for sulfuric acid production. The lone facility included in the state's 111(d) plan at 40 CFR 62.6353, W.R. Grace and Company, Joplin, Missouri, has permanently closed.

The proposed rule and the EPA's technical support document (TSD) included in this docket discuss our analysis of the Missouri SIP and 111(d) plan revisions in greater detail.

II. Have the requirements for approval of a SIP revision been met?

The State's submission has met the public notice requirements for SIP submissions in accordance with 40 CFR 51.102. The submission also satisfies the completeness criteria of 40 CFR part 51, appendix V. The State provided an initial 60-day public review and comment period on the Regulatory Impact Report, draft version of 10 CSR 10-6.261, and the CAA section 110(l) demonstration from February 2, 2024 to April 2, 2024. The State provided an additional public notice period from November 1, 2024 to December 12, 2024 and received zero (0) comments. A public hearing was held December 5, 2024. In addition, as explained in section III. of the proposed rule and in more detail in the TSD included in the docket for this action, the revisions meet the substantive SIP requirements of the CAA, including section 110 and implementing regulations.

III. The EPA's Response to Comments

The public comment period on the EPA's proposed rule opened June 27, 2025, the date of its publication in the Federal Register , and closed on July 28, 2025. During this period, the EPA received no comments.

IV. What action is the EPA taking?

The EPA is taking final action to amend the Missouri SIP by approving the State's request to incorporate 10 CSR 10-6.261 “Control of Sulfur Dioxide Emissions” and revise 40 CFR 62.6353.

V. Incorporation by Reference

In this document, the EPA is finalizing regulatory text that includes incorporation by reference. In accordance with requirements of 1 CFR 51.5, the EPA is finalizing the incorporation by reference of the ( printed page 42840) Missouri state rule 10 CSR 10-6.261 discussed in section I. of this preamble and as set forth below in the amendments to 40 CFR part 52. The EPA has made, and will continue to make, these materials generally available through https://www.regulations.gov and at the EPA Region 7 Office (please contact the person identified in the FOR FURTHER INFORMATION CONTACT section of this preamble for more information).

Therefore, these materials have been approved by the EPA for inclusion in the State Implementation Plan, have been incorporated by reference by EPA into that plan, are fully federally enforceable under sections 110 and 113 of the CAA as of the effective date of the final rulemaking of the EPA's approval, and will be incorporated by reference in the next update to the SIP compilation.^[1]

Also, in this document, as described in the amendments to 40 CFR part 52 set forth below, the EPA is removing provisions of the EPA-Approved Missouri Regulations and Statutes from the Missouri State Implementation Plan, which is incorporated by reference in accordance with the requirements of 1 CFR part 51.

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, EPA's role is to approve state choices, provided that they meet the criteria of the Clean Air Act. 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 under Executive Orders 12866 (58 FR 51735, October 4, 1993);
• Is not subject toExecutive Order 14192 (90 FR 9065, February 6, 2025) because SIP actions are exempt from review 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 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).

This action is subject to the Congressional Review Act (CRA), and 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 section 307(b)(1) of the CAA, petitions for judicial review of this action must be filed in the United States Court of Appeals for the appropriate circuit by November 4, 2025. 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. This action may not be challenged later in proceedings to enforce its requirements (see section 307(b)(2)).

For the reasons stated in the preamble, the EPA amends 40 CFR parts 52 and 62 as set forth below: