Disposal of toxic ash from coal-fired electric power plants will be controlled under national regulations for the first time through an EPA proposal that was issued on May 4. Currently, coal ash is held in some 900 impoundments located in almost every state, without national standards, EPA says. Only 300 of these are dry storage landfills, which are more stable and less likely to allow leachate from the ash to migrate to groundwater. But the majority of ash is in wet slurry impoundments. In its proposal, the agency says it will determine whether the waste—which contains mercury, cadmium, and arsenic—will be subjected to more rigorous specific standards under hazardous waste regulations or treated as a solid waste, which has to meet less stringent performance-based standards. Such regulation, EPA says, would be under provisions of the Resource Conservation & Recovery Act and could include requirements for impoundment liners and groundwater-monitoring systems. However, EPA intends to exempt from regulation coal waste that is used for “beneficial purposes,” such as aggregate for cement or wallboard. In an assessment of coal-ash impoundments, which followed a massive 2008 Tennessee Valley Authority spill that spread millions of yards of ash over land and water, EPA found that most impoundments have a high or significant risk of structural failure (C&EN, Feb. 23, 2009, page 44).