On Monday, the United States Supreme Court rejected an appeal from 20 states seeking to block the MATS rule from taking effect while the EPA undertakes a second determination whether regulating power plant mercury emissions is appropriate and necessary.  As previously discussed on this blog, the MATS rule was promulgated pursuant to Section 112 of the Clean Air Act to limit emissions of mercury and other hazardous air pollutants from coal-  and oil-fired electric utility steam generating units. To regulate hazardous air pollutants from electric utility steam generating units, Section 112 of the Act requires the EPA to evaluate hazards reasonably anticipated to occur from emissions occurring after other Clean Air Act mandates are in place, and determine whether regulating the emissions with a Section 112-based standard is appropriate and necessary. In June 2015, the Supreme Court ruled that the EPA failed to comply with the Clear Air Act when it made its “appropriate and necessary” determination without considering compliance costs. However, the Supreme Court remanded the case to the United States Court of Appeals for the District of Columbia for further proceedings, leaving it up to the Court of Appeals to decide what to do with the rule while the EPA corrects its error. In December 2015, the D.C. Circuit issued an Order that left the MATS rule in place while the EPA seeks to correct its error.  On Monday, the Supreme Court left this ruling in place.

On April 25, 2016, the EPA published a supplemental finding that regulating hazardous air pollutants from coal- and oil-fired electric utility steam generating units is appropriate and necessary.  In making this finding, the EPA considered compliance costs, and it advised that the finding completes its response to the Supreme Court’s direction.  The EPA made no change to the MATS rule, leaving it in place as originally promulgated. Murray Energy Corporation has filed a timely petition challenging the finding in court.