What to know about arsenic in Charlotte’s water supply

It’s never good news that a substance known for ages as the “king of poisons” has found its way into a city’s water supply.

Mecklenburg County detected arsenic last month in Mountain Island Lake, Charlotte’s main source of water, at a level nearly 10 times higher than the Environmental Protection Agency says is safe in drinking water.

Arsenic was found near a discharge pipe from Duke Energy’s retired Riverbend power plant, which had been draining water from two coal ash ponds into the lake. Ash contains arsenic and other metals.

Duke acknowledges high levels of arsenic were in the water from the ponds, but said it stopped the discharge after the county reported its findings. Arsenic has not been detected in other parts of the lake, including Charlotte Water’s intake.

Duke said it will install by September a treatment system, to remove arsenic and other contaminants, before resuming drainage of the ponds.

Three things to know for now:

The arsenic poses no immediate risk to drinking water

“Arsenic’s a bad thing, no question,” said Dr. Stephen Keener, medical director of the Mecklenburg County Health Department. Long-term exposure can cause skin, hair and nail problems, and high doses over many years can lead to cancer.

Toxic doses are thousands of times higher than the 10 part per billion limit in drinking water set by the Environmental Protection Agency, Keener said.

“What’s important is continued monitoring at the (Charlotte Water) point of intake,” he said. “As long as that’s zero, there’s no indication of arsenic getting into the water supply.”

Charlotte Water reported that it detected no arsenic in drinking water in 2015.

Water will be drained from ash ponds statewide

Draining Riverbend’s ash ponds without contaminating water supplies is important because it will be repeated at 13 other power plants across the state, Catawba Riverkeeper Sam Perkins said.

“Whether Duke Energy is going to cap in place or move coal ash at all 14 of its sites, it’s going to have to (drain) these sites,” he said. “So this is going to happen 14 times over.”

Perkins and Duke University scientists detected arsenic in lake-bottom sediment near Riverbend several years ago. The element tends to settle to the bottom in water and stick to particles.

Mecklenburg County previously found elevated levels of arsenic in the lake near Riverbend in April, and in 2010 and 2011.

“I hope whatever treatment they get in place is thorough and will get the dissolved arsenic down as far as possible,” he said.

Duke Energy might, or might not, be in trouble

Duke got permission from state regulators last December to start draining water from ash ponds at Riverbend and six other power plants.

Among the conditions set in the permission letter was that Duke not break water quality standards. It required Duke to monitor levels of arsenic and other contaminants.

The N.C. Department of Environmental Quality, separately, issued Riverbend a permit in February to regulate the process. It included limits on arsenic in an area where water drained from the ash ponds would mix with lake water. Duke challenged the permit’s terms, so it is not yet in force.

“The current permit does not have specific limits for arsenic, because the state’s evaluation showed those were not necessary to protect the lake,” Duke spokeswoman Zenica Chatman said. “We wanted to conduct our work in the spirit of the forthcoming permit, and when we saw results trending above those levels, it caused us to pause and re-evaluate.”

DEQ, meanwhile, said it will collect its own water samples and evaluate Mecklenburg County’s data before deciding whether Duke should be cited.

“The department issued a permit in 2011 that requires Duke Energy to meet water quality standards for the lake, which is 10 ppb,” said DEQ’s Stephanie Hawco. “The department has authority under that permit and under state law to hold Duke accountable for meeting water quality standards.”

This story was originally published July 7, 2016 at 12:56 PM with the headline "What to know about arsenic in Charlotte’s water supply."