The utility intends to challenge the fines through a formal appeal with the North Carolina Office of Administrative Hearings by April 9.

The fines were imposed earlier this month by the North Carolina Department of Environment and Natural Resources (NC DENR).

Duke Energy North Carolina state president Paul Newton said: "This is a difficult step, but we cannot allow this level of regulatory overreach to go unchallenged.

"The actions by NC DENR send a chilling message to the North Carolina business community."

The firm opines that NC DENR had exceeded its jurisdiction or authority, failed to act according to law and had not adhered to the state rules and procedures in imposing the fine.

The fine was imposed on the utility as water samples and monitoring revealed that it had allowed coal ash contaminants from the Wilmonton facility leach into groundwater for several years.

DENR secretary Donald R. van der Vaart said: "In addition to holding the utility accountable for past contamination we have found across the state, we are also moving expeditiously to remove the threat to our waterways and groundwater from coal ash ponds statewide."

The Sutton Plant began operation as a coal-fired electric generating station in 1954. The three coal units were retired in 2013 after a new natural gas-fired unit came online at the site.

"We take very seriously our responsibility to care for the communities around our facilities. That’s why we monitored groundwater at the Sutton plant, routinely shared data with the state, and voluntarily acted to ensure local residents continue to have a high-quality water supply," Newton added.