On August 7, the U.S. Court of Appeals for the Sixth Circuit rejected EPA’s definition of “adjacency” used to determine when to aggregate emissions from oil and gas drilling operations for major source permitting purposes under the Clean Air Act. In a 2-1 ruling in the case of Summit Petroleum Corporation v. EPA, the Sixth Circuit held that the word “adjacent” has a plain and unambiguous meaning, and EPA’s effort to stretch the meaning to include dispersed emission sources based on functional interrelatedness was unreasonable and unlawful.