Over the past several years, the EPA and states have wrestled with the highly controversial question of how to manage ash and other residual materials produced by the combustion of coal in coal-fired power plants. These so-called “coal combustion residuals” (“CCR”) have been traditionally managed in large man-made ponds at many power plant sites. While discharges from these impoundments directly to surface waters are regulated by permits issued under the Clean Water Act, the impoundments themselves have been regulated under state waste management programs. In 2015, EPA fundamentally changed the regulatory landscape for these facilities when it promulgated a federal rule setting national standards for design, operation and closure of CCR impoundments. EPA, Hazardous and Solid Waste Management System; Disposal of Coal Combustion Residuals from Electric Utilities, 80 Fed. Reg. 21,302 (Apr. 17, 2015).