North Carolina environmental regulators said this week that Duke Energy, the nation's largest electric company, will be fined $6.6 million for a 2014spill of liquefied coal ash that polluted the state's Dan River.

Duke Energy admitted to violations of federal pollution crimes at hearings nine months ago. The large fine will cover those violations, and the company has also agreed to pay $102 million in fines and restitution, North Carolina's Department of Environmental Quality said. There could be additional civil penalties stemming from the 2014 coal ash spill that polluted the water near the company's Dan River plant in Eden, the agency added.

In this Thursday, Jan. 14, 2016, photo, a drainage pipe that was the original culprit of the coal ash spill is shown at the Dan River Steam Station in Eden, North Carolina.

(AP Photo/Gerry Broome)

"Having been made aware on numerous occasions of the potential" that toxic coal ash could pollute waterways, state Division of Water Resources Director S. Jay Zimmerman wrote in explaining the penalties, "Duke failed to take all reasonable steps to minimize or prevent any discharge or sludge disposal."

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Coal ash is the residue left after coal is burned to generate electricity. It has been collecting in holding basins for decades. It can contain toxic chemicals including arsenic, chromium and lead.

North Carolina officials began pursuing stronger regulations and enforcement after a burst pipe released coal ash from a holding pit at Duke Energy's power plant, coating 70 miles of the Dan River in more than 30,000 tons of sludge.

Duke Energy is reviewing whether to challenge the fine, the company said in a statement.

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The company last year contested the state agency's proposed $25 million fine over persistent groundwater pollution at a Wilmington power plant, the state's largest-ever penalty for environmental damage. That was later reduced to $7 million in a settlement that state regulators said also covered groundwater contamination at all 32 of Duke Energy's coal ash basins around North Carolina.

Water quality in the Dan River returned to normal quickly after the spill, and harm to fish or other aquatic life hasn't yet been observed, Duke Energy's statement said.

The Dan River spill, the third-largest in U.S. history, pushed North Carolina legislators to force the company to stop storing coal ash in unlined pits by 2029. New U.S. Environmental Protection Agency rules that took effect last year are expected to force similar cleanup at coal ash pits around the country.

MORE ON WEATHER.COM: Dan River Coal Ash Spill, 2014

In this January 14, 2016, photo, a drainage pipe that was the original culprit of the coal ash spill is seen at the Dan River Steam Station in Eden, North Carolina. The state's top public health official acted unethically and possibly illegally by telling residents living near Duke Energy coal ash pits that their well water is safe to drink when it's contaminated with a chemical known to cause cancer, a state toxicologist said in sworn testimony.