Why did the Court vacate the EPA rule?
The Courts opinion failed to reach the controversial questions of whether EPAs risk-based Health Thresholds and No Control Boiler MACT options are lawful, and instead vacated based on the scope of the boilers evaluated and covered under the rule. What troubled the D.C. Circuit was the fact that in another rule appealed in the same case, the Commercial and Industrial Solid Waste Incineration (CISWI) Rule, EPA narrowed the definition of incinerator to exclude units that burn any solid waste for energy recovery. The effect of this definition is to make fewer units subject to the CISWI, which applies to both area (minor) and major sources of Hazardous Air Pollutants (HAP). By statute, this change resulted in the regulation of those units under the Boiler MACT, which applies only to major HAP sources. The Court held this was inconsistent with Section 129 of the Clean Air Act, which only exempts co-generation facilities from the definition of incinerator. Because thousands of units that were
