South Carolina's state-run utility company said Tuesday that mud from a coal ash pit was accidentally dumped into a local river, The Post and Courier reported.

Santee Cooper officials reportedly found a malfunctioning pump at a former coal-fired power plant, the Grainger Generating Station, in Conway, S.C.

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Company spokesperson Mollie Gore told The Post and Courier that employees found a pump had sucked all the water out of a pond and was dredging up sediment on Jan. 30.

That sediment, a mix of coal ash and soil, ended up in the nearby Waccamaw River.

“Sometime overnight, it was during the night, the pump was not monitored and the area that it was pumping was being dewatered,” Gore said.

Coal ash is a waste product from burning coal that contains harmful heavy metals. The river did not show significant levels of the toxic materials found in coal ash, such as arsenic, lead and mercury, according to Gore.

Gore said that since the incident Santee Cooper has increased its nighttime monitoring and installed stone under the water its pumps draw from.

Gore confirmed the report to The Hill.

Fears that coal ash from plants would be spilled into rivers after Hurricane Florence hit North and South Carolina has spurred companies into action.

No spills occurred in either state as a result of the hurricane, but according to Gore, Santee Cooper has accelerated its efforts to remove as much ash as possible from pits near rivers.

Updated at 4:19 p.m.