The residuals of coal combustion in power plants that are captured by pollution control technology, such as scrubbers, are often referred to as coal ash. The waste includes fly ash, bottom ash, boiler slag, flue gas desulfurization gypsum, and other byproducts and contains low concentrations of arsenic, selenium, lead, and mercury. After collection at a power plant, coal ash is often impounded in a surface storage pond or in a landfill.
Like other waste products, coal ash is governed under the Resources Conservation and Recovery Act (RCRA) and is currently considered to be a non-hazardous waste under that law. Through a rulemaking process, EPA is considering whether this designation should be changed.
Coal-fired power plants in the U.S. produced 136 million tons of coal ash in 2008. Fifty-five percent of that total was disposed of in 584 landfills or surface impoundments nationwide. However, coal ash has some useful purposes; 45 percent of the waste is now recycled into products like concrete and bricks and as filler for abandoned mines and highway berms. New coal ash disposal regulations would affect the 60 million tons of coal ash annual that is disposed of and not recycled, reused, or reclaimed.
EPA decisions in 1993 and 2000 determined that coal ash should be regulated as a non-hazardous waste under Subtitle D of RCRA, the same classification as household garbage and other nonhazardous industrial wastes. EPA develops guidelines to assist in planning, managing, and implementing disposal of these wastes, although state and local agencies take primary responsibility.
The classification of coal ash as non-hazardous waste has been challenged by recent events. In December 2008, a dam holding a wet storage pond of coal ash from power plants broke in Kingston, Tennessee, spilling about one billion gallons of coal ash-polluted water over 300 acres into the nearby community and waterways. Another spill in October 2011 sent coal ash-polluted water into Lake Michigan. These accidents, along with long held concerns about leaching of pollutants from impoundments to ground water, have led to some advocates to call for a designation as a hazardous waste under RCRA, and EPA proposed rulemaking on the issue in June 2010.
EPA issued a final rule on coal ash disposal on December 14, 2014 in accordance with a court order. Under the rule coal ash will be treated as a non-hazardous waste under Subtitle D of RCRA with certain minimum requirements for storage in both new and existing sites. Storage requirements are targeted to maintaining integrity of containment structures, reducing effects on groundwater, strengthened operating requirements, and closure requirements. Monitoring reports, corrective actions, and other information about coal ash sites must be posted on the internet to allow for citizen oversight. The rule will require the closure of active sites that fail to meet engineering and structural standards, but it does not affect coal ash containment for power plants that are no longer in use. The designation of coal ash as a non-hazardous substance will allow its continued recycling and use in products like cement and wallboard.
Read more from EPA  on coal ash disposal.