EPA Backs Missouri's St. Louis Ozone Control Measures Proposal
Published Date: 8/14/2026
Proposed Rule
Summary
The Environmental Protection Agency (EPA) is proposing to approve portions of a state implementation plan (SIP) revision submitted by the State of Missouri on September 6, 2023, as meeting Clean Air Act (CAA) requirements for the 2015 8-hour ozone national ambient air quality standards (NAAQS) in the Missouri portion of the St. Louis, MO-IL bi-state nonattainment area. Specifically, the EPA is proposing approval of the submitted vehicle inspection and maintenance (I/M) program, nonattainment new source review (NNSR) program, and reasonably available control technology (RACT) determinations for major sources of volatile organic compounds (VOC) and Nitrogen Oxides (NO<INF>X</INF>) SIP elements as meeting applicable Moderate nonattainment area requirements for the 2015 8-hour ozone NAAQS. The EPA will address the remaining SIP elements in a separate action.
Analyzed Economic Effects
5 provisions identified: 3 benefits, 1 costs, 1 mixed.
Five major plants get enforceable limits
EPA proposes to approve five source-specific consent agreements into Missouri's SIP, making their VOC and NOX emission limits federally enforceable for the Missouri portion of the St. Louis area. Examples in the agreements include Anheuser Busch process-loss limits (8% monthly, 6% rolling 12-month), Elementis requirements to operate its RTO at 1500°F with at least 95% destruction efficiency, Ameren Labadie NOX limit of 0.12 lb/mmBTU (30-day averaging), Ameren Sioux NOX limit of 0.18 lb/mmBTU (ozone season), and Ameren Meramec NOX limit of 0.055 lb/mmBTU.
St. Louis drivers remain in I/M program
If you own a light-duty vehicle in the Missouri portion of the St. Louis nonattainment area, EPA proposes to approve Missouri's 2023 vehicle inspection and maintenance (GVIP) plan and to replace the 2019 I/M plan. The GVIP requires on-board diagnostic (OBD) testing for gasoline vehicles 1996 model year and newer and diesel vehicles 1997 model year and newer, uses biannual testing frequency, and affirms inclusion of Jefferson County vehicles. EPA's review (using 2023 modeling) shows the GVIP reduces NOX by 0.67 tons per July weekday and VOC by 0.31 tons per July weekday compared to the Federal Basic I/M benchmark.
Force majeure clauses treated as defense
EPA proposes to approve the five consent agreements' "force majeure" provisions and interprets them as complete affirmative defenses that can excuse liability (monetary or injunctive) if a qualifying event prevents performance and the source follows notice procedures. The consent agreements require sources to notify the State within five business days after the force majeure event begins.
Enhanced air monitoring plan approved
Missouri submitted an enhanced monitoring plan (EMP) for the St. Louis area on October 11, 2024, with an update on January 29, 2026; EPA approved the 2025 monitoring network plan and EMP by letter on December 19, 2025. The State will maintain and quality-assure the ozone and precursor monitoring network in the Missouri portion of the St. Louis area in accordance with 40 CFR part 58.
Clean-data finding may suspend planning
EPA notes a proposed clean data determination published on February 26, 2026, for the St. Louis area; if finalized, that determination would suspend certain SIP planning requirements (attainment demonstrations, RACM, RFP plans, contingency measures, and other attainment-related submissions) for as long as the area continues to attain the 2015 ozone NAAQS.
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