Duke Energy engineers are working on at least two fronts at a North Carolina power plant as flood waters from Hurricane Florence forced the 625 megawatt natural gas-fired facility offline and caused coal ash byproducts to spill into the Cape Fear River.

(Click to enlarge.) Duke Energy diagram showing location of the Lake Sutton breach.The utility said that initial water tests from its L.V. Sutton Plant in Wilmington, N.C., suggest that discharges from a lake to the Cape Fear River are not harming water quality downstream. It also says that its coal ash basins on the site remain stable. The affected lake provided water to cool power plant equipment.

From 1954 until 2013, the site was home to a 575 MW coal-fired power plant. Following decommissioning, that plant was removed in 2017. Coal ash basins that date from 1971 and 1984 remain at the site.

Duke says that coal combustion byproducts known as "cenospheres" moved into the Cape Fear River after Hurricane Florence sent rivers to historic highs across the Carolinas. The utility company deployed booms to try to capture other material before it could leave the lake.

Duke Energy photo showing foam-like cenospheres leaving Lake Sutton and entering the Cape Fear River.Duke Energy says that cenospheres are lightweight, hollow beads made of alumina and silica. Even though cenospheres are included in the Environmental Protection Agency's Coal Combustion Residuals regulations, the EPA does not consider them to be coal ash, says a Duke Energy spokesperson.

Dam Breach

On September 21, the Cape Fear River began overtopping the north end of Sutton Lake, a 1,100-acre man-made reservoir built in 1972 to supply cooling water to the coal-fired power plant. Floodwaters caused a number of small cuts and a larger-scale breach where water from the lake flowed into the river. As flood waters from the hurricane continued to travel through the lake, the smaller breaches widened, the utility said.

(Click to enlarge.) Duke Energy photo showing Sutton Lake breach.Flooding resulted in about 12 inches of water throughout the new 625 MW combined-cycle gas power plant. The plant was shut down on September 24 and plant operators began assessing possible damage to equipment.

Duke Energy photo of its flooded 625 MW power plant.There are two coal ash basins at the site, which were being excavated and closed, and their dams remain stable, Duke Energy says. Water reportedly filled the 1971 basin and the company says that it believes the ash is being contained by a steel wall. The 1984 basin has not been affected.

Although too much water in Sutton Lake was a problem in late September, so is the possibility of too little water as flooding eases, said the spokesperson. The gas-fired power plant relies on water from the lake for cooling. That means crews are in a race to repair the breach to stop the lake from draining too much as flood waters recede.