Like the one in Tennessee, most of these dumps, which reach up to 1,500 acres, contain heavy metals like arsenic, lead, mercury and selenium, which are considered by the Environmental Protection Agency to be a threat to water supplies and human health. Yet they are not subject to any federal regulation, which experts say could have prevented the spill, and there is little monitoring of their effects on the surrounding environment.
A 2007 report by EPA identified 63 sites in 26 states where the water was contaminated by heavy metals from coal ash dumps, including three other Tennessee Valley Authority sites.
