DC Circuit Vacates Boiler MACT
On June 8, the U.S. Appeals Court for the D.C. Circuit vacated the National Emission Standards for Hazardous Air Pollutants for Industrial, Commercial and Institutional Boilers and Process Heaters, 40 CFR Part 63, Subpart DDDDD ("Boiler MACT"). The Boiler MACT, which set a September 13 compliance deadline for existing sources, established hydrogen chloride, particulate matter, mercury and carbon monoxide emission limits for various new and existing units. The court did not reach most of the challenges to the Boiler MACT. Instead, it examined the interrelationship between the Boiler MACT and the Commercial and Industrial Solid Waste Incineration Rule ("CISWI Rule"), which was under review in a consolidated case. Under the Clean Air Act, these rules must be mutually exclusive. However, the court found that the U.S. Environmental Protection Agency ("EPA") had impermissibly narrowed the scope of units affected by the CISWI Rule, and that sources currently regulated under the Boiler MACT must instead be regulated under the CISWI Rule. Thus, the court vacated both rules to revise their respective applicability provisions.
The implications of the court's decision are unclear. Although the Boiler MACT has been remanded to EPA for revisions consistent with the decision on the CISWI Rule, EPA may also revise other aspects of the Boiler MACT subject to challenge in the D.C. Circuit. In particular, based on other D.C. Circuit MACT standard decisions, EPA may revisit its approach to set "no control" standards for certain affected unit subcategories. EPA has not indicated the content or timing of its revision process.