Raleigh, N.C. — State environmental regulators announced Friday that tests of surface water found thallium, a highly toxic metal, near two coal ash ponds.
According to a release from the North Carolina Department of Environment and Natural Resources, tests of surface water near coal ash ponds at Duke Energy's Cliffside plant in Gaston County found levels of thallium that exceeded recommended water quality standards for drinking water supplies.
The Cliffside test showed the toxin at 0.35 parts per billion – well above the federal recommended standard of 0.24 parts per billion for drinking water.
The agency said a second water sample taken downstream, near the Broad River, showed the level of the poison had fallen to 0.13 parts per billion, safely below the recommended threshold.
At Duke's Asheville plant, a test of water coming out of a coal ash pond showed 0.67 parts per billion of thallium.
The river the Asheville site drains into, the French Broad, is classified as recreational water rather than a drinking water supply, so its recommended thallium standard is higher – 0.47 parts per billion. Three other samples near the Asheville plant showed levels of thallium below that mark.
Thallium is a metal that's produced when some coal is burned. It was commonly used as a rat poison until the U.S. banned it for consumer use in 1975, due to its very high toxicity.
In the 20th century, it was known as "the poisoner's poison" because it's colorless and odorless and its compounds dissolve easily in water.
The agency news release did not note thallium's poisonous properties, describing it only as a "by-product of burned coal."
According to DENR, "No downstream municipalities have reported problems meeting EPA drinking water standards." Municipal water systems are required to test for the toxin at least once per year.
Under the Environmental Protection Agency's Drinking Water Act, thallium levels can legally be as high as 2 parts per billion – nine times higher than the recommended level.
"This information and additional data collected at these sites will be used to develop an overall evaluation of the facilities and direct further actions by DENR and the EPA," the release said. "As part of the ongoing investigation, DENR will make additional water-quality testing results public as these results are processed."
DENR also announced it has issued Duke a citation for the large crack that formed in a coal ash dam at its Cape Fear plant in Chatham County.
Duke made emergency repairs to the dam. State regulators say no waste leaked through the crack, and they don't believe it's in danger of failing. But DENR is requiring Duke to turn over engineering reports and plans by April 7, as well as an "emergency action plan" in case of dam failure.
"The utility could face a fine if it does not meet the April 7 deadline or the dam fails and results in loss of life, property or environmental damage," DENR announced.