A Duke University-led study of coal ash contaminants, published Oct. 16, found high levels of toxic arsenic in Mountain Island Lake.
The study reported ash contaminants downstream of coal-fired power plant ash settling ponds in the 11 lakes and rivers sampled. It was published Monday in the journal Environmental Science & Technology.
Concentrations tended to be highest in small bodies of water, such as 2,914-acre Mountain Island Lake.
Water flowing into the lake from the Riverbend power plant’s ash ponds had arsenic concentrations up to nine times higher than the federal drinking water standard, the study said.
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It also found arsenic at levels that could harm aquatic life in water at the lake bottom. That suggests arsenic could accumulate in fish tissue, said Duke scientist Avner Vengosh, who contributed to the study.
The findings did not surprise Mecklenburg County water quality officials.
The county has sampled lake water near the Riverbend discharge point eight times a year since mid-2009, and detected arsenic above the state water quality standard five times, said water quality official David Caldwell. Concentrations have been up to three times higher than the state standard.
Mecklenburg does not test sediment, Caldwell said, but assumes the heavy metal would be found there, too.
The county has not found elevated arsenic levels in fish. Fish contaminated by chemicals called PCBs, which are not linked to coal ash, led to a state advisory for Mountain Island in 2011.
Caldwell said there is no indication that the drinking water Charlotte draws from Mountain Island is at risk.
Duke Energy, which runs Riverbend and other power plants alluded to in the study, said metals such as arsenic routinely meet water quality standards in Mountain Island and lakes Norman and Wylie near Charlotte. Duke says its testing shows fish and drinking water are safe.
Fish tissue analyses “tell us arsenic is not bioaccumulating in aquatic life,” spokeswoman Erin Culbert said.
Still, Mecklenburg officials had asked the state’s environmental agency to set tougher standards when permits for ash-pond discharges on the three Charlotte-area lakes were renewed in early 2011.
Mecklenburg County asked the state to set limits on a range of metals in Riverbend’s ash discharge. The county asked that Mountain Island’s water be tested upstream and downstream of the discharge, and that fish be analyzed once a year.
Instead, N.C. officials included new limits only for copper and iron at Riverbend but ordered more sampling of water and fish near the power plants on all three Charlotte-area lakes. The new sampling has raised no red flags, Duke’s Culbert said.
The plants also have to sample their discharges for arsenic, mercury and selenium, but don’t have fixed limits on those elements. Vengosh said that means power plant owners don’t have to take action if they see high readings.
The Duke study also found high levels of contamination in the French Broad River in Asheville, and in Hyco and Mayo lakes near the Virginia line. Lakes Norman and Wylie were among other water bodies studied.
The study also reported that plants equipped with “scrubbers” to control air pollution often discharged water high in selenium, which is toxic to fish in high doses. “It’s common sense, because the contaminants have to no place to go,” Vengosh said.
The study was led by former student Laura Ruhl, who now teaches at the University of Arkansas at Little Rock.