The U.S. Environmental Protection Agency on May 4 unveiled a draft rule to regulate coal ash, for the first time, under the Resource Conservation and Recovery Act. The proposal would require coal-fired powerplants to retrofit existing impoundments, which typically store ash in liquid form, with composite liners. It also would provide strong incentives to eventually close surface impoundments and shift to dry storage in landfills, EPA says. The new scrutiny follows a 2008 collapse of a Tennessee impoundment that spread ash over a 300-sq-mile area of land and water. Environmentalists claim contaminants in coal ash, such as mercury and arsenic,
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.