A manmade lake in front of a power plant sits behind a chain link fence designed to keep boats away from the site.
High levels of coal ash solids in sediments from North Carolina’s Sutton Lake suggest that it has been contaminated by multiple coal ash spills, most of them apparently unmonitored and unreported. Credit: Avner Vengosh, Duke University

Today Sutton Lake in North Carolina, on the Cape Fear River, is known for year-round largemouth bass fishing, but the lake’s history is not pristine: The 4.5-square-kilometer lake was originally created in the 1970s as an impoundment for a coal-fired power plant.

A new study looking at sediments from the lake bottom has found evidence of repeated spills from an adjacent pile of coal ash tailings. The implications for consuming fish caught in the lake and the ecological health of the Cape Fear River are still unknown.

When Hurricane Florence made landfall on the coast of North Carolina in September 2018, it brought record high storm surges and rainfall that triggered unprecedented flooding. In the aftermath, geochemist Avner Vengosh of Duke University and colleagues were interested to see whether the storm event had mobilized coal ash into Sutton Lake.

“It’s clear that there is a long legacy of coal ash getting into the lake and not just during the recent storm event.”

“We thought we might see traces of coal ash in the lake bottom sediments, but the levels we found were surprisingly high,” Vengosh says.

The team used multiple lines of evidence to identify the presence of coal ash solids in the sediments, including strontium isotope ratios, heavy-metal distributions, magnetic susceptibility analyses, and visual observation of coal ash particles in the microscope, they reported in Science of the Total Environment.

But then the team also tested sediment samples collected in 2015, before Florence, and found similar levels of contamination. “It’s clear that there is a long legacy of coal ash getting into the lake and not just during the recent storm event,” Vengosh says.

Coal ash is no longer produced by the Duke Energy power plant, which was converted to natural gas in 2013, but decades’ worth of coal combustion residuals are stored on site in several impoundments and an open landfill next to the lake. The setting is typical of outdated coal ash storage facilities found all over the United States, says James Hower, a geochemist at the University of Kentucky in Lexington who was not involved in the new study.

“These impoundments were constructed to the standards of the time, but we have since learned that these standards are not adequate to contain this material long term,” Hower says.

Some of these loose piles have since been deposited into modern landfills that are lined and covered with soil and vegetation. “If properly drained and monitored, they are quite stable,” Hower says.

“The topic of Sutton Lake’s sediment is not new. We’ve shared similar sediment results going back to the mid-90s with the North Carolina Wildlife Resources Commission, so these findings are not at all surprising. We strongly disagree with the study and how it characterizes Sutton Lake. Sutton Lake’s fish are healthy, thriving and safe from coal ash impacts,” says Bill Norton, director of corporate communications for Duke Energy.

Coal Ash Contamination

But the majority of coal ash impoundments and landfills in the United States are not lined, Vengosh says. A 2019 report found that groundwater and surface water adjacent to hundreds of coal ash disposal sites are contaminated by coal ash.

Coal ash contains high levels of toxic and carcinogenic compounds that can pose ecological and human health risks if not properly contained, Vengosh says. Coal-fired power plants in the United States continue to produce about 100 million tons of coal ash a year, about half of which is stored in landfills or impoundments. Because coal-fired power plants require copious amounts of water in their operations, these plants and landfills are often located near lakes and rivers.

“What’s happened at Sutton Lake highlights the risk of large-scale unmonitored spills occurring at coal ash storage sites nationwide.”

The other 50 million tons are used by the cement industry in their products. Despite its known toxicity, the Environmental Protection Agency has historically been reluctant to classify coal ash as a hazardous waste because it may impact the cement industry’s willingness to utilize it, Vengosh says. “Then the environmental impact of coal ash could be even larger.”

Sutton Lake serves as a case study that represents a much bigger problem of improper coal ash storage.

“What’s happened at Sutton Lake highlights the risk of large-scale unmonitored spills occurring at coal ash storage sites nationwide,” Vengosh says. “The risks are especially high in the Southeast where we have a large number of coal ash impoundments in flood-prone areas and tropical storms and hurricanes are common occurrences.”

Whether the coal ash is making its way downstream into the Cape Fear River in significant quantities is a potential topic for further research, Vengosh says. Several studies have detected high levels of selenium in fish caught in Lake Sutton. “The health risk for people who eat these fish has not been studied yet.”

—Mary Caperton Morton (@theblondecoyote), Science Writer

9 July 2019: This article has been updated to include a response from Duke Energy.


Morton, M. C. (2019), A North Carolina lake’s long legacy of coal ash spills, Eos, 100, https://doi.org/10.1029/2019EO127227. Published on 08 July 2019.

Text © 2019. The authors. CC BY-NC-ND 3.0
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