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Raleigh, N.C. • All coal-ash pits in North Carolina maintained by Duke Energy power plants pose enough of an environmental risk that they should be excavated and moved by 2024, state environmental regulators said Wednesday.

But the state Department of Environmental Quality said it's asking for a change in state law that would allow it to reconsider its risk assessment in 18 months. The agency was required to submit its risk rankings by Wednesday under a state law passed in 2014 after a spill at a Duke Energy coal-ash pit coated 70 miles of the Dan River in a toxic sludge.

Fewer pits would have to be excavated if repairs to dams retaining the liquefied waste are finished and neighbors who last year were warned against drinking their well water are provided a "permanent alternative" supply, the agency said.

Duke Energy in 2014 floated a potential cost to excavate coal ash from all 14 of its coal-burning power plants at $10 billion. The company has said it expected to ask state utilities regulators to allow it to pass along its coal-ash bill to electricity customers.

The reevaluation would allow regulators to see if fewer pits would need excavation

"The deadlines in the coal ash law are too compressed to allow adequate repairs to be completed," state environment secretary Donald van der Vaart said in a statement. "The intent was not to set pond closure deadlines based on incomplete information. Making decisions based on incomplete information could lead to the expenditure of billions of dollars when spending millions now would provide equal or better protection."

The environmental agency said in December that pollution is leaking into underground water deposits from unlined coal-ash pits at all 14 power plants run by the country's largest electric company. Coal ash contains toxic elements including arsenic, lead and chromium.

Duke Energy says its coal ash pits aren't polluting water supplies.

Last May, Duke Energy pleaded guilty to federal environmental crimes and agreed to pay $102 million in fines and restitution for years of illegal pollution leaking from coal-ash dumps at five North Carolina power plants.