Key Contacts
Tenth Circuit Clarifies Diligent Prosecution Bar to Citizen Suits under Clean Air Act
The U.S. Court of Appeals for the Tenth Circuit issued a decision on August 3, 2026, which clarified the scope of the diligent prosecution bar to citizen suits under the Clean Air Act (“CAA”). The decision was a partial victory for the environmental organizations that brought the lawsuit and adds to the body of appellate decisions aiming to elucidate this heavily litigated area of the law.
The case, GreenLatinos et al. v. Suncor Energy (U.S.A.), Inc., No. 25-1243 (10th Cir.), was filed by several environmental groups that alleged petroleum refineries in Commerce City, Colorado, were violating the CAA and its implementing regulations. The statute provides a cause of action for citizens to sue based on violations of “an emission standard or limitation” under the CAA. But these “citizen suits” are precluded where “the [EPA] Administrator or [a] State has commenced and is diligently prosecuting a civil action in a court of the United States or a State to require compliance with the standard, limitation, or order.” 42 U.S.C. § 7604(b)(1)(B).
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