State regulators said Wednesday they detected no arsenic in Mountain Island Lake, Charlotte’s main water supply, after Mecklenburg County reported elevated levels.
The state Department of Environmental Quality tested the water on July 7. Those tests followed county findings in late June that found arsenic at 95 parts per billion, nearly 10 times higher than a federal safety standard, near Duke Energy’s retired Riverbend power plant.
Mecklenburg County officials say there is no threat to drinking water because arsenic was not detected in the lake, including at Charlotte’s water intake, other than near the power plant.
Riverbend, as required by state legislation, has been draining water from two ponds that hold 3.6 million tons of coal ash. Arsenic is among the metals found in ash.
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Once Mecklenburg County detected arsenic, Duke stopped draining the ponds. The county retested the water on June 24 and detected no arsenic.
The county will test again on July 18, with results expected one week later.
The DEQ findings reported Wednesday are consistent with the county’s results – no arsenic was detected once draining of the ponds stopped. The state tested lake water from four sites including near Riverbend, upstream of the power plant and near Charlotte’s water intake.
Duke says a treatment system to clean water from the ash ponds before it is drained into the lake will start operating in September. Discharges into the lake will resume then, she said.