Environment

After studying Sutton Lake, Duke University scientists say, “Impact of coal ash in environment far larger than previously thought”

A Duke University study released today suggests there have been “multiple unmonitored coal ash spills” in Sutton Lake, even before Hurricane Florence struck the coast last year.

Avner Vengosh, professor of geochemistry and water quality at Duke University’s Nicholas School of the Environment, said the spills could have been caused by floods, accidental releases or past dumping practices.

As a result, levels of some metals in the lake could be toxic to fish and wildlife. “A coal ash spill is not a one-time contamination,” Vengosh said in a Duke University press release. “It builds up a legacy in the environment. Even if you close the site, the legacy and threat remain, as our research has revealed at Sutton Lake and other coal ash spill sites such as Kingston, Tennessee. Collectively, these findings imply that the distribution and impact of coal ash in the environment is far larger than previously thought.” 

Sutton Lake, which is in Wilmington, served as a cooling lake for Duke Energy’s coal-fired power plant from the 1970s to 2013. There are two unlined coal ash impoundments at the plant, which are being excavated, and one lined landfill, where much of the ash is being deposited.

“The levels of coal ash contaminants we detected in Sutton Lake’s sediments, including metals with known environmental impacts, are similar to or higher than what was found in stream sediments contaminated by the 2008 Tennessee Valley Authority coal ash spill in Kingston, Tennessee, or the 2014 Dan River spill here in North Carolina,” Vengosh said.

The metals included arsenic and cadmium — both carcinogens — as well as selenium, copper, nickel, antimony, vanadium and thallium.

Duke Energy downplayed Vengosh’s findings as “nothing new.” “It is ludicrous to compare decades-old ash at the bottom of a manmade wastewater facility to anything found in conventional lakes and rivers,” Norton said. “This wastewater facility did exactly what it was designed to do, serve as a buffer between our former coal plant and the Cape Fear river to keep the public and environment safe.”

The Duke University team studied bottom sediments collected in October 2018 from seven sites in Sutton Lake and three in the adjacent Cape Fear River. They compared those sediments to samples collected from Sutton Lake in 2015, as well as Lake Waccamaw, which has never been a coal ash impoundment.

Duke Energy’s Sutton plant in Wilmington. Rains from Hurricane Florence caused a slope at an on-site coal ash landfill to collapse. (File photo: Duke Energy)

A geochemical analysis also found high levels of the contaminants in water between the grains of sediment — known as pore water — and in water extracted from the sediment itself. Pore water from 2015 in Sutton Lake showed metal concentrations that were higher than what was detected in Lake Waccamaw.

During Hurricane Florence in 2018  floodwaters breached the lake’s cooling dam and submerged a steel wall that separated ash from the lake. As flooding intensified, coal ash moved from the 1971 ash basin to the cooling lake and into the Cape Fear River.

“The findings from the study imply that unmonitored coal ash spills may be more common than previously realized,” the study says, “and other lakes near coal ash storage facilities, particularly in areas susceptible to hurricane events or frequent flooding may also be impacted. … Future studies should verify whether water resources throughout the southeastern US and elsewhere are impacted by unmonitored coal as spills.”

Sutton Lake is used not only for cooling water for the utility, but also for boating and fishing. The lake’s water quality has been more stringently regulated since 2014, when the Southern Environmental Law Center successfully sued the utility in federal court. A judge determined that the lake qualified as a navigable water and thus entitled to protections under the Clean Water Act.

Duke University’s most recent findings showed contaminant levels in Sutton Lake exceeded ecological guidelines for freshwater lakes. Previous Duke University studies showed 85 percent of fish muscle samples contained selenium higher than the EPA threshold of 11.3 parts per million. Fish and other aquatic life exposed to high levels of selenium can develop deformities, and in extreme cases, die. Their growth and reproduction can also be impaired. Because selenium accumulates in the food chain, it also can be toxic to birds that eat aquatic animals containing high levels.

Norton said Duke Energy has “monitored fish community for many years and our data indicates a healthy, self-sustaining and balanced fish community.”

However, state wildlife studies contradict the utility’s assertion. In 2014, the NC Wildlife Resources Commission issued a Sutton Lake Sportfish Assessment that said “conditions of largemouth bass, bluegill, redear sunfish and flathead catfish are all low.”

The WRC said it was unlikely the poor conditions were the result of overfishing. “While heat from the power plant creates a long growing season in the lake, high water temperatures during the summer may prevent the accumulation of old, large fish in the population,” the assessment reads. “Additionally, metals entering the lake from the ash ponds may have adverse impacts on the fish community. During the mid–1990s when levels of selenium in fish tissue were higher than normal, largemouth bass reproduction was low suggesting, that some relationship between heavy metal loading and juvenile fish survival may exist.”

Duke University’s peer-reviewed study appears in the journal Science of the Total Environment. Vengosh led the six-person research team: Ellen Cowan, Rachel Coyte, Andrew Kondash, Zhen Wang, Jessica Brandt and Gary Dwyer.

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