Duke Energy has stopped draining coal ash ponds into Mountain Island Lake after recent county tests found elevated levels of arsenic in the water. State environmental regulators say they’re investigating whether Duke violated state law.
The Riverbend Steam Station is in Mount Holly, on the Gaston County side of Mountain Island Lake. Duke has been draining coal ash ponds there since January, under a federal permit issued in 2011.
Mecklenburg County officials have been monitoring the discharges, which are upstream from public water supplies for Charlotte, Gastonia and Mount Holly.
On June 20, tests found an arsenic level of 95 parts per billion. That’s nearly 10 times the federal limit of 10 parts per billion, said Rusty Rozzelle, of Mecklenburg Storm Water Services.
“This sampling was done 50 feet from the discharge pipe in the lake, but up in a cove. And we sampled at three locations downstream, and we didn't find any arsenic,” he said.
Rozzelle said more recent tests show arsenic has returned to previous levels. And he says levels were normal around drinking water intakes.
“I think the main point, and this is a very important point, is that the water supplies are safe,” Rozzelle said.
Duke's own tests also spotted the problem, so the utility stopped the draining that same morning.
A spokeswoman said Duke won't resume draining the coal ash ponds until it finishes a wastewater treatment system in the coming weeks.
Coal ash is the residue left after burning coal. It contains toxic heavy metals such as arsenic and chromium. Sam Perkins, the Catawba Riverkeeper, said coal ash has been leaking at Duke plants for decades.
This is the first major problem he's seen since cleanup began at Riverbend:
“So this is a good learning case for why we need to have additional treatment and filtration for what's being discharged into waterways that are also serving as drinking water reservoirs,” Perkins said.
The state Department of Environmental Quality has dispatched its own team to collect water samples from Mountain Island Lake. A spokesman said Thursday regulators will evaluate that and the county data to decide if Duke is guilty of any violations.