A study released on Thursday finds that 39 sites in 21 states where coal-fired power plants dump their coal ash are contaminating water with toxic metals such as arsenic and other pollutants, and that the problem is more extensive than previously estimated.

The analysis of state pollution data by the Environmental Integrity Project, the Sierra Club and Earthjustice comes as the Environmental Protection Agency is considering whether to impose federally enforceable regulations for the first time. An alternative option would leave regulation of coal ash disposal up to the states, as it is now.

The EPA will hold the first of seven nationwide hearings about the proposed regulation Monday in Arlington, Va. A public comment period ends Nov. 19.

The electric power industry is lobbying to keep regulation up to individual states. Environmental groups say the states have failed to protect the public and that the EPA should set a national standard and enforce it.

"This is a huge and very real public health issue for Americans," said the director of the study, Jeff Stant of the Environmental Integrity Project. "Coal ash is putting drinking water around these sites at risk."