The D.C. Circuit Court of Appeals upheld EPA’s 2012 rule setting emission standards for coal and oil-fired electric utility steam generating units, denying the challenge from utilities and industry groups that EPA exceeded its authority under the Clean Air Act.
The rule, establishing limits for mercury and other hazardous air pollutants (HAPs), are based on authority granted under the 1990 amendment to § 112 of the Clean Air Act. The amended Act requires EPA to implement maximum achievable control technology (MACT) standards for certain HAPs when they find such regulation appropriate and necessary based on a study of their hazards to public health. The MACT standards cannot be less stringent than the average emission limitation achieved by the best performing sources, regardless of cost or considerations other than the study of their hazards.
The groups opposing 
EPA’s MACT standard argued that the phrase “appropriate and necessary” in § 112(b)(1)(A) limits EPA’s ability to regulate emissions from electric utilities, and that EPA exceeded its authority by considering factors other than public health. The Court disagreed, explaining despite the statutory ambiguity of the phrase, EPA’s “commonsense” construction–which considered the HAPs hazards generally but within the context of the requisite study on public health–was permissible, satisfying Chevron’s two-part test, and within the bounds of its discretion.
According to an EPA spokesperson, the MACT standards will eliminate 90 percent of mercury pollution from coal-fired power plants.