On July 14, 2015, the Sixth Circuit Court of Appeals ruled that the Sierra Club had standing to challenge EPA’s determination that the Cincinnati metropolitan area had reached attainment status for particulate matter (PM 2.5). Sierra Club v. EPA, — F.3d —-, 2015 WL 4231713 (6th Cir. 2015). After granting the Sierra Club the right to challenge, the court held that EPA had failed to implement “reasonably available control measures” applicable to non-attainment areas, and therefore vacated the EPA’s determination that the Cincinnati metropolitan area was in attainment for PM 2.5. The court’s rejection of the attainment status was made notwithstanding the fact that the Cincinnati metropolitan area’s real time data showed that the National Ambient Air Quality Standard for particulates had been met. The Sixth Circuit found that meeting the particulate standard was not enough. EPA also had to implement reasonably available control measures under Section 107(d)(3)(E)(ii) of the Clean Air Act even if those measures were not necessary to meet the particulate standard. In so holding, the Sixth Circuit reasoned in accord with recent U.S. Supreme Court holdings granting less deference to EPA in interpreting statutory provisions under the two-step test announced in Chevron, U.S.A., Inc. v. Natural Res. Def. Council, Inc., 467 U.S. 837, 842 (1984).

The Sixth Circuit’s decision places EPA and its state counterpart, Ohio EPA, in a quandary, namely, how to unring the bell and “fix” the prior failure to implement reasonably available control measures. Should EPA require Ohio EPA to re-submit a state implementation plan that includes requirements for reasonably available control measures for particulates? If so, how long must that approved plan be in place before the Cincinnati area can reapply for attainment designation?

The Sixth Circuit’s decision may not be the end of the judicial process. The court disagreed with the conclusion of the Seventh Circuit Court of Appeals that the phrase “applicable implementation plan” could refer to a plan other than the pre-attainment state implementation plan. The applicability of a different plan would likely have led to a different conclusion by the court. This disagreement establishes a conflict among the circuit courts that could be accepted for review by the U.S. Supreme Court.