Two January rulings by the U.S. Court of Appeals for the D.C. Circuit have imposed significant limitations on EPA’s ability to offer regulated parties flexibility in meeting the agency’s PM2.5 air quality regulations. In Nat. Res. Def. Council v. EPA, No. 08-1250, slip op. (D.C. Cir. Jan. 4 2013), the D.C. Circuit ruled that EPA improperly promulgated its 2007/2008 rule implementing the PM2.5 National Ambient Air Quality Standards (NAAQS) in non-attainment areas under the general implementation provisions of Subpart 1 of Part D of Title I of the Clean Air Act rather than the more stringent Subpart 4. The Court ordered the agency to revise the rules accordingly, a ruling which could call into question the legality of existing state air quality plans for meeting the 1997 standard. It is also unclear how the Court’s remand will affect EPA’s implementation of its December 2012 rule lowering the annual PM2.5 standard from the 1997 limit of ug/m3 to 12ug/m3.

The second D.C. Circuit decision, Sierra Club v. EPA, No. 10-1413, slip op. (D.C. Cir. Jan. 22, 2013), addressed two October 2007 EPA rules implementing the PM2.5 standard in the agency’s prevention of significant deterioration (PSD) permit program. The first rule established significant impact levels (SILs) for PM2.5; if a proposed project’s emissions are projected to be below the SIL, they are treated as negligible and can avoid stricter permit reviews. The second rule established PM2.5 significant monitoring concentrations (SMCs), threshold levels of

In this March 16, 2011  photo, exhaust rises from smokestacks in front of piles of coal at NRG Energy's W.A. Parish Electric Generating Station in Thompsons, Texas.  (AP Photo/David J. Phillip, originally viewed at www.onepennysheet.com)

In this March 16, 2011 photo, exhaust rises from smokestacks in front of piles of coal at NRG Energy’s W.A. Parish Electric Generating Station in Thompsons, Texas. (AP Photo/David J. Phillip, originally viewed at http://www.onepennysheet.com)

projected pollution below which a facility need not comply with a requirement to gather one year’s worth of air quality monitoring data to establish background concentration levels for measuring future emissions increases from the project. The Court remanded the SIL policy (partially at EPA’s request) but vacated the SMC policy entirely, basing both decisions on EPA’s lack of de minimis authority—at least to the extent EPA claimed—in light of how rigidly Congress wrote the relevant statutory requirements.

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