An environmental group claims the Santee Cooper power generating plant in Conway is polluting the Waccamaw River.
The Southern Environmental Law Center has filed notice that it plans to sue the utility for violating the federal Clean Water Act.
The environmental group says toxic waste on the site of the Grainger power plant is seeping into the river, wetlands and ground water.
The group's complaint says waste in Santee Cooper's coal ash lagoons has arsenic and other pollutants in it.
Santee Cooper says there is no indication from its monitoring wells that pollution is getting into the river.
A spokesperson for the state-owned utility says the environmental group has already filed two similar lawsuits about the Conway plant at the state level and there's nothing new about these latest allegations.
"We frankly find this another disruption in our efforts to develop a plan to close the ash ponds according to proper and appropriate regulatory processes," said Mollie Gore.
The Grainger plant is no longer in use and Gore says the utility plans to close the ash ponds as part of its larger effort to decommission the plant.
She says the utility is still working on options for closing the ash lagoons and hopes to file a plan with DHEC around the middle of March.
A press release from the environmental group says Santee Cooper has known for years that arsenic from the lagoons has polluted the river, but has done nothing to clean it up.