If the US District Court for the Eastern District of North Carolina approves the plea bargain – which includes a five-year probationary period with a court-appointed monitor to ensure compliance – Duke will pay $68.2 million in fines and restitution and pay $34 million for community service and projects to help reduce the effects of the pollution.

The New York-listed company emphasised that the $102.2 million would come from shareholders, not utility customers.

It took five days for Duke to halt the leak after a broken storm water pipe was discovered at the retired Dan River plant on February 12 last year, as an estimated 39,000 tonnes of coal ash in 102 million litres of coal-ash slurry was spilled, making it as the third-largest ash spill in US history.

"We are accountable for what happened at Dan River and have learned from this event," Duke CEO Lynn Good said. "We are setting a new standard for coal ash management and implementing smart, sustainable solutions for all of our ash basins.

“Our highest priorities are safe operations and the well-being of the people and communities we serve."

Duke said In regulatory filings in December that it had found 200 leaks and seeps at its 32 coal ash dumps state-wide that together leak more than 11 million litres of contaminated waste water a day.

A state law passed in August requires Duke to clean up or permanently cap all of its ash dumps in North Carolina by 2029.

North Carolina Department of Environment and Natural Resources spokesman Drew Elliot said the state agency had no information on whether federal authorities were still looking into the state's relationship with Duke.

“We just know we will continue to cooperate with any investigation," he says.

He said the department was pleased to see that federal officials had completed a thorough investigation of the charges against Duke, adding that the agreement did not settle civil cases that the state has filed against Duke.