Summary: This action responds to the U.S. Supreme Court decision in Michigan v. EPA, 135 S. Ct. 2699 (2015), and explains how the Environmental Protection Agency (EPA) has taken cost into account in evaluating whether it is appropriate and necessary to regulate coal- and oil-fired electric utility steam generating units (EGUs) under section 112 of the Clean Air Act (CAA). The EPA requested comment on all aspects of its approach to considering cost through a proposed supplemental finding and on a companion Legal Memorandum available in the rulemaking docket. After consideration of public comments, the EPA, in this final supplemental finding, concludes that a consideration of cost does not cause us to change our determination that regulation of hazardous air pollutant (HAP) emissions from coal- and oil-fired EGUs is appropriate and necessary and that EGUs are, therefore, properly included on the CAA section 112(c) list of sources that must be regulated under CAA section 112(d).

… In May 2011, in conjunction with the proposed MATS, the EPA conducted additional technical analyses to reaffirm the appropriate and necessary finding, including peer-reviewed risk assessments on human health effects associated with mercury and non-mercury HAP emissions from EGUs, focusing on risks to the most exposed and sensitive individuals in the population. These analyses found that mercury and non-mercury HAP emissions from EGUs remain a significant public health hazard and that EGUs are by far the largest U.S. anthropogenic source of mercury, selenium, hydrogen chloride, and hydrogen fluoride emissions, and a significant source of other metallic HAP emissions including arsenic, chromium, and nickel (8).

… The EPA also previously concluded that EGUs are by far the largest remaining source of mercury, selenium, hydrogen chloride, and hydrogen fluoride emissions, accounting for half or more of all U.S. anthropogenic emissions of such HAP, and that EGUs contribute a considerable percentage of all U.S. anthropogenic emissions of arsenic, chromium, nickel, and other metallic HAP emissions. The agency also confirmed the availability of controls to reduce these HAP emissions from EGUs.

Reference:

8. Specifically, the EPA estimated that in 2005 (the most recent inventory year available during the MATS rulemaking), U.S. EGUs emitted approximately 50 percent of total domestic anthropogenic mercury emissions, 62 percent of total arsenic emissions, 39 percent of total cadmium emissions, 22 percent of total chromium emissions, 82 percent of total hydrogen chloride emissions, 62 percent of total hydrogen fluoride emissions, 28 percent of total nickel emissions, and 83 percent of total selenium emissions. Docket ID No. EPA-HQ-OAR-2009-0234-19914.

Read full finding in the Federal Register