EPA Redesignates Michigan's St. Clair Area to SO2 Attainment
The redesignation relieves local sources of Nonattainment NSR permitting requirements in favor of less restrictive standards.
The Environmental Protection Agency has redesignated the St. Clair nonattainment area in southeast Michigan to attainment for the 2010 sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS). This action changes the legal designation of the area and approves Michigan's maintenance plan to ensure continued air quality compliance.
Local sources in the area are now relieved of Nonattainment NSR permitting requirements. These entities are instead subject to the less restrictive Prevention of Significant Deterioration permitting requirements.
As part of the approval, the EPA incorporated Permit to Install 51-22 into the Michigan State Implementation Plan, which governs SO2 emissions for the DTE Belle River Power Plant. Modeling indicates that the emission limits in this permit, combined with the St. Clair Power Plant shutdown, result in a maximum SO2 concentration of 62.8 ppb, falling below the 75 ppb NAAQS threshold.
The maintenance plan approved by the EPA includes an attainment emissions inventory, a maintenance demonstration, a contingency plan, and commitments for continued air quality monitoring and verification.
This rule became effective on July 9, 2026.