EPA also expressed reservations about details of how Duke would be required to test for contaminants in the wastewater flowing out of its dumps into rivers and lakes, suggesting more stringent monitoring requirements. The federal agency also questioned provisions allowing pollution leaking from the earthen dikes holding back the coal ash to be included under the company's wastewater discharge permits issued by the state.

State officials made modest technical changes to the settlement proposal in response to the EPA's concerns, but did not increase the amount of the fines.

In the wake of the massive Feb. 2 coal ash spill, state officials have been defending their earlier deal with Duke even as they have sought to distance themselves from it.

The state agency asked a judge to pull its own proposed settlement, the day after an Associated Press story in which environmentalists derided the agreement as a "sweetheart deal" intended to shield nation's largest electricity from a costly cleanup of its dumps.

North Carolina Gov. Pat McCrory worked at Duke for more than 28 years and the company and its executives have remained generous contributors to his campaign and GOP groups that support him. McCrory, a Republican, denies Duke received any special treatment from his administration.