On Sunday, a storm water pipe broke beneath an ash basin at the retired Dan River Steam Station in Eden, N.C., causing a release of ash basin water and ash into the Dan River.
The ash basin dam along the river is secure and downstream municipal water supplies remain unaffected.
Crews are working on a plan to stabilize the area and to determine the volume of water and ash that reached the river.
The coal plant retired in 2012, so the basin was already at a lower level. The primary basin is about 27 surface acres.
Duke Energy has notified a water quality monitoring team. The N.C. Department of Environment and Natural Resources is also performing a site inspection.
The company has been looking for the most appropriate way to close the ash basins retired plant sites.