In a recent opinion, the US Court of Appeals for the District of Columbia Circuit upheld the Environmental Protection Agency's (EPA's) 2016 amended Clean Air Act regional consistency regulations. These regulations – located at 40 CFR Sections 56.1 to 56.7 – state in relevant part that the EPA will apply decisions of the US Supreme Court or DC Circuit on Clean Air Act matters uniformly across its 10 regions.

The DC Circuit's opinion held that the revised regional consistency regulations were a "permissible and sensible" way to satisfy the Clean Air Act's statutory mandate for national uniformity in implementation and enforcement while recognising that circuit courts of appeals may interpret the Clean Air Act differently. The 2016 regulations are the result of a lengthy history. In a 2012 opinion, the Sixth Circuit overturned an EPA interpretation of the definition of 'major source' under the Clean Air Act's Title V permitting programme. The EPA subsequently issued a memorandum stating that it did not intend to apply the Sixth Circuit's decision outside that circuit's boundaries, which was challenged and struck down by the DC Circuit.

For further information on this topic please contact Samuel B Boxerman or Jim Wedeking at Sidley Austin LLP by telephone (+1 202 736 8000) or email (sboxerman@sidley.com or jwedeking@sidley.com). The Sidley Austin LLP website can be accessed at www.sidley.com.

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