At 1,100 acres, Sutton Lake is home to schools of largemouth bass, catfish and crappie. However, the lake also contains high levels of selenium, both in the surface water and in muscles of fish, a consequence of years of coal ash discharge from Duke Energy power plant near its shores.
Duke University scientists at the Nicholas School of the Environment announced the results of a study yesterday that showed levels of selenium were elevated in two of the three lakes sampled.
In Sutton Lake, 85 percent of all fish muscle samples examined contained selenium levels above the EPA’s threshold of 11.3 parts per million. In Mayo Lake near the Roxboro plant, 27 percent of samples exceeded EPA criteria. Levels were below the EPA criteria in Mountain Island Lake near the Riverbend plant in Charlotte.
All of the surface water samples in Sutton tested above the EPA threshold of 1.5 parts per billion. At Mayo, there was just one water exceedance, in “pore water” collected from sediment near the power plant.
Selenium is naturally occurring, but is also a main component of coal ash. It often enters surface water through discharges from power plants. Each day, millions of gallons of wastewater, which is treated, but far from pristine, are discharged into the lakes — popular destinations for boating, swimming and fishing.
“Across the board, we’re seeing elevated selenium levels in fish from lakes affected by coal combustion residual effluents,” said Jessica Brandt, a doctoral student in environmental health at the Nicholas School who led the study.
Brandt and her colleagues Emily Bernhardt, Gary Dwyer and Richard Di Giulio published their peer-reviewed study Feb. 6 in the journal Environmental Science & Technology. The samples were taken over three months in 2015.
Duke Energy spokesperson Erin Culbert said utility officials have not seen the study, but noted that it “diligently meets permit limits that were designed to protect the environment.”
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.
“We’re less worried about human effects at these levels,” Brandt said. “We’re more worried about the fish and birds.”
Exacerbating the problem, Sutton Lake is nearly a closed system, Brandt said, and gets freshwater from the Lower Cape Fear only from an intake pump operated by the utility. There is no way for water to leave the lake except by evaporation. That means water in the lake has what’s known as a “long residence time.”
The Sutton plants no longer burns coal and its ash basins are being closed. In 2013, Duke Energy converted the plant to natural gas. However, in the past Sutton Lake had received unregulated discharges from adjacent coal ash ponds, and that residue has settled at the bottom of the lake. “Moreover, there is an immense repository of selenium in the lake’s sediments that seems to be increasing with time,” the study says.
By comparison, Mountain Isle has what is known as a “short retention” time, meaning water circulates more frequently in and out of the lake. That might have contributed to its lower selenium levels; the Riverbend coal-fired plant has also been retired and its basins are also being closed.
Sutton Lake was built in 1972 by Progress Energy to supply cooling water for its coal-fired power plant. The NC Wildlife Resources Commission now manages the lake. Culbert said that “fish populations are thriving in these reservoirs.” In the 30 years of sampling and observing hundreds of thousands of fish at Sutton, Culbert said, “Duke Energy biologists have not observed health effects. Catch rates, reproduction and relative weight all demonstrating a thriving fish population in Sutton Lake.”
The utility’s contention contradicts the wildlife commission’s 2014 Sutton Lake Sportfish Assessment, which says “the conditions of largemouth bass, bluegill, redear sunfish and flathead catfish are all low.”
The commission attributed the conditions in part to metals entering the lake from the ash ponds. During the mid-1990s when levels of selenium in fish tissue were elevated, the assessment states, largemouth bass reproduction was low, “suggesting that some relationship between heavy metal loading and juvenile fish survival may exist.” From 2008 to 2010, the largemouth bass population declined by 50 percent, the assessment said.
Similar die-offs occurred in Belew’s Lake within less than a decade of a coal-fired power plant being built. In fact, 16 fish species had disappeared.
Duke Energy still operates its coal-fired Roxboro plant near Mayo Lake and has a permit to discharge water into it. Environmental advocates and many residents living hear Mayo Lake told state DEQ officials last fall that they opposed draft discharge permits over concerns that more contaminants would enter the lake.
As NCPW reported last year, Hope Taylor, executive director of Clean Water for North Carolina, spoke against the discharge permits in part because the state’s monitoring requirements are weak. For example, the permit would allow the utility to discharge as much as 2 million gallons of water per day from the top of the ash pond into Mayo Lake. Only weekly sampling would be required.
Even Mayo Lake also has a long residence time, sampling showed lower (but still high) levels of selenium in fish muscle than Sutton. The study theorizes that the structure of the reservoirs and their ecosystems could account for some of the variability.
Culbert of Duke Energy said that annual largemouth bass monitoring shows “healthy, robust fish.”
Brandt said researchers plan to further study other heavy metals and contaminants in the lakes, as well as the effects of bioaccumulation on birds that eat the fish.The only way for the fish and ecosystem in Sutton Lake to recover is for selenium to stop entering the water Click To Tweet
In 2013, the Southern Environmental Law Center, representing several conservation groups, sued Duke Energy alleging groundwater pollution at Sutton violated the Clean Water Act. In a settlement last fall, the utility agreed to contribute $1 million to protect the lower Cape Fear River, Sutton Lake near Wilmington and wetlands.
The only way for the fish and ecosystem in Sutton Lake to recover, the study says, is for selenium to stop entering the water. But under the terms of the Coal Ash Management Act and discharge permits, selenium will be allowed to flow into Sutton, Mayo and Mountain Isle for years.