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U.S. EPA Proposes Tougher SO2 Air Standard


By Andy Bowman, Attorney, Bingham Greenebaum Doll LLP

On November 16, 2009, U.S. EPA issued a notice of proposed revisions to the National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO2). U.S. EPA proposes replacing the current 24 hour standard of 140 ppb and annual standard of 30 ppb with a single one-hour standard to be set within a range between 50 ppb and 100 ppb. U.S. EPA will accept comments on the appropriate level for the new one-hour standard and other aspects of the proposed standard for a period of 60 days after the notice is published in the Federal Register. According to U.S. EPA, the largest sources of SO2 emissions are from fossil fuel combustion at power plants (66 percent) and other industrial facilities (29 percent).

U.S. EPA estimates that the new one-hour standard would provide health benefits valued between $16 billion and $100 billion. U.S. EPA has concluded that there is insufficient scientific evidence demonstrating an association between long-term exposure to SO2 and public health effects. As a result, U.S. EPA is proposing to revoke the current annual primary SO2 standard. U.S. EPA believes the one-hour standard will prevent SO2 concentrations from exceeding the current 24-hour standard.

U.S. EPA first set NAAQS standards for SO2 in 1971. The last review of the SO2 NAAQS was completed in 1996 and U.S. EPA chose not to revise the standards. The decision not to set a five-minute standard in 1996 was challenged successfully by the American Lung Association, and the court remanded the standards back to U.S. EPA in 1998. U.S. EPA had not taken any formal action with regard to the remand until this proposal. Under the terms of a judicial consent decree, U.S. EPA must complete its review of the primary SO2 standard by June 2, 2010.

U.S. EPA expects to issue final attainment and nonattainment designations in June 2012. States will have until the winter of 2014 to submit their state implementation plan revisions. Attainment with the one-hour standard will be required by summer 2017.

Based on 2006-2008 monitoring data, U.S. EPA believes that 13 Indiana counties (Daviess, Floyd, Fountain, Gibson, Jasper, Lake, Marion, Morgan, Porter, Vanderburgh, Vigo, Warrick and Wayne) will be in nonattainment if the one-hour standard is set at the lowest level of 50 ppb. Currently all Indiana counties are in attainment with the existing 24-hour and annual SO2 standards.

The proposed rule can be found at


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