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EPA Proposes New Sulfur Dioxide Limits for Last Three Remaining Coal-Fired Power Plants in PA

The U.S. Environmental Protection Agency (EPA) recently published a proposed rule that will finally (we hope!) implement the 2010 National Ambient Air Quality Standard (NAAQS) for sulfur dioxide (SO2) in our region. 


Specifically, the proposed rule would approve a revision to Pennsylvania’s State Implementation Plan - the set of federally approved regulations that govern air quality in the state.


That revision will reduce hourly emission limits for sulfur dioxide from the region’s three remaining coal-fired electric generating units: The Conemaugh Generating Station in Indiana County, Keystone Generating Station in Armstrong County, and Seward Generating Station in Westmoreland County. 


The proposed rule also addresses operating limits at the Homer City Generating Station, even though that facility ceased operations in 2023. That’s because the facility has not yet surrendered its Title V Operating Permit. 


All four EGUs are located in the Indiana Nonattainment Area, which was designated as nonattainment for the 2010 SO2 NAAQS back in 2013.


“The history of the proposed rule shows just how long it can take for requirements imposed by the Clean Air Act to have real world impacts,” GASP senior attorney John Baillie said. “The rule’s background is nearly as convoluted as it is long.”


However, he said the key development was a 2021 decision by the Biden Administration’s EPA to reconsider, and revise, a 2020 decision by the Trump Administration’s EPA to approve hourly SO2 emission limits at the EGUs. 


As now proposed, the hourly emission limits for SO2 at the EGUs will be as follows:

  • at Conemaugh, SO2 emissions from its Units 1 and 2 will be limited to 3,080 lbs/hour, “combined in a three-hour block average,” down from 3,312 lbs/hour

  • at Keystone, SO2 emissions from its Boilers 1 and 2 will be reduced from 9,600 lbs/hour to 8,328 lbs/hour, measured on a “24-hour block average;” and

  • at Seward, SO2 emission from its two units will be reduced from 3,083.4 lbs/hour 2,895 lbs/hour, “based on a 30-day operating hours’ average rolling by one day.”

How much impact the proposed new limits will have - assuming they are finally approved and go into effect - remains to be seen,” Baillie added. “The SO2 monitors closest to the EGUs have been measuring attainment of the 2010 SO2 NAAQS for several years even with higher limits in place.”


EPA’s explanation of the proposed rule is available here


You can submit comments on the proposed rule at, referencing Docket ID No. EPA-R03-OAR-2024-0024, or by emailing


Editor’s Note: Looking ahead, both the Conemaugh Generating Station and the Keystone Generating Station have announced plans to shut down on or before Dec. 31, 2028, when new wastewater discharge rules for coal-fired EGUs go into effect.



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