The Environmental Protection Agency on May 4 unveiled a draft rule to regulate for the first time coal ash under the Resource Conservation and Recovery Act (RCRA). Under the proposal, coal plants would be required to retrofit existing impoundments, which typically store the ash in liquid form, with composite liners. The proposal also would provide strong incentives for utilities to eventually close the surface impoundments and shift to dry storage in landfills, EPA says. The potential regulation of coal ash has been highly anticipated by environmental groups, who say that contaminants in coal ash—such as mercury cadmium and arsenic—can leach
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.