On December 11, a D.C. Circuit panel (Tatel, Brown, Griffith) granted in part environmental and state petitions for rehearing in Mississippi v. EPA (Nos. 08-1200 et al.), revising key language describing the court’s review of certain agency actions.  In July, the panel affirmed EPA’s 2008 revisions to the primary ozone National Ambient Air Quality Standards (“NAAQS”), while remanding the revised secondary ozone NAAQS for reconsideration. EPA set both the primary and secondary standards at the same level: 0.075 ppm (parts per million), revised downward from the 1997 level of 0.08 ppm.

Under Clean Air Act Section 109(b)(1), primary NAAQS set pollution levels that “allow[] an adequate margin of safety. . . requisite to protect the public health”; secondary NAAQS under Section 109(b)(2) set levels “requisite to protect the public welfare.” The court’s July opinion rejected arguments that EPA had improperly disregarded a recommendation from the Clean Air Science Advisory Committee (“CASAC”) that the primary standard be set between 0.060 and 0.070 ppm, but held that the agency erred in not making a separate determination as to the appropriate secondary standard. The rehearing order revises language in the July opinion, removing a phrase suggesting that the court will only disturb EPA’s judgment on NAAQS due to “egregious procedural errors” and substituting language clarifying that the court will correct “arbitrary[] and capricious[]” failures to appropriately consider, e.g., the vulnerability of “sub-populations” such as the young or elderly.

This revision grant signals that the court will continue to examine critically EPA departures from CASAC’s recommendations, and will remain open to arguments that EPA failed to explain the basis for an “adequate margin of safety” determination.