Federal environmental officials said Thursday that they have reached a deal with Duke Energy to clean up its mess from a massive coal ash spill into the Dan river.

The US Environmental Protection Agency announced it had finalized an enforceable agreement with the nation's largest electricity company over the February 2 accident. The spill coated 70 miles of the river in North Carolina and Virginia with toxic gray sludge.

EPA will oversee the cleanup in consultation with federal wildlife officials under provisions in the Superfund law. Duke will reimburse the federal government for its oversight costs, including those incurred in the emergency response to the spill.

"EPA will work with Duke Energy to ensure that cleanup at the site, and affected areas, is comprehensive based on sound scientific and ecological principles, complies with all Federal and State environmental standards, and moves as quickly as possible," said Heather McTeer Toney, the EPA Regional Administrator based in Atlanta. "Protection of public health and safety remains a primary concern, along with the long-term ecological health of the Dan River."

Duke has already begun vacuuming out three large deposits of ash found in the river, including a pocket that collected at the bottom of a dam in Danville, Va. The byproduct left behind when coal is burned to generate electricity, the ash contains numerous toxic substances, including arsenic, selenium, chromium, thallium, mercury and lead.

Separately, North Carolina lawmakers are debating a measure about what to do with Duke's 33 ash dumps at 14 power plants in North Carolina, which are located along rivers and lakes that cities and towns rely on for drinking water. State environmental officials say all of Duke's unlined waste pits, which contain more than 100 million tons of ash, are contaminating groundwater.

Environmental groups are calling for Duke to be forced to remove the ash to lined landfills licensed to handle hazardous waste. Duke has agreed to remove ash from four sites, including the plant on the Dan River. But it has asked state officials for flexibility to consider other options at the other 10 sites, including leaving the ash in place cover with plastic sheeting and a layer of soil.