Michigan's St. Clair Area Gets EPA Nod for Cleaner SO2 Air
Published Date: 4/10/2026
Proposed Rule
Summary
Good news for folks in southeast Michigan! The EPA wants to officially say the St. Clair area now meets clean air standards for sulfur dioxide (SO2) and approve Michigan’s plan to keep it that way. This means cleaner air near the DTE Belle River Power Plant, with rules to limit pollution and a chance for the community to weigh in by May 11, 2026.
Analyzed Economic Effects
6 provisions identified: 4 benefits, 1 costs, 1 mixed.
Planned Gas Conversion Slashes Emissions
Michigan's submissions state the St. Clair Power Plant shut down in 2022 and the Belle River facility plans to convert from coal to natural gas by 2027. Permit APP-2024-0273 projects Belle River actual SO2 emissions falling from a baseline 21,470 tons per year to 24 tpy after conversion, and modeled post-2022 emissions total 9,268 lbs/hr resulting in a modeled design value of 62.8 ppb (below the 75 ppb standard).
St. Clair Redesignated Attainment
The EPA is proposing to redesignate the Partial St. Clair area in southeast Michigan from nonattainment to attainment for the 2010 1-hour sulfur dioxide (SO2) standard (75 ppb). This is the EPA's proposed action based on monitoring and modeling showing a design value of 62.8 ppb and is open for comment through May 11, 2026.
Belle River Limits Become Federally Enforceable
The EPA proposes to incorporate Michigan Permit to Install 51-22 into the State Implementation Plan, making Belle River Power Plant SO2 limits federally enforceable. The permit establishes limits of 0.680 lbs/MMBtu (30-day rolling average) and 1.2 lbs/MMBtu (3-hour average) for each boiler (permit approved April 26, 2022; revised May 25, 2023).
Local Monitors Discontinued; Annual Reports Instead
DTE discontinued its two on-site SO2 monitors at the end of 2022; Michigan's monitoring network does not include a monitor inside the St. Clair nonattainment area. Michigan commits to provide the EPA an annual emissions report for the Belle River Power Plant to verify continued attainment per the SO2 Data Requirements Rule.
PSD Permits Apply to New/Modified Sources
If the St. Clair area is redesignated to attainment, Prevention of Significant Deterioration (PSD) permitting requirements under the Clean Air Act will apply to any new sources or major modifications in the area. PSD requirements govern permitting for projects that could increase air pollutant emissions.
Contingency Measures with Public Input
Michigan's maintenance plan includes a list of potential contingency measures (for example: require alternative fuel, add-on SO2 controls, reduced operating hours, or SO2 offsets) to correct any future SO2 standard violations. Michigan will solicit input from affected persons and provide full public participation before implementing any contingency measure.
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