One of the big debates over the safety of drinking water wells near coal cash ponds is whether a carcinogenic chemical called hexavalent chromium is naturally-occurring. Duke Energy says it is, while environmentalists say Duke’s coal ash ponds are to blame for polluted wells. A new Duke University study shows the chemical does occur naturally and contamination likely isn’t from coal ash.

The chemical has been a concern for well owners around Duke Energy's coal ash storage ponds. A year-and-a-half ago, state officials told well owners not to drink their water after tests found high levels of the carcinogen and other toxic chemicals.

A study published Wednesday in the journal Environmental Science & Technology Letters says hexavalent chromium occurs naturally across the Piedmont in the Carolinas and Virginia. It can leak into groundwater and wells, even those not near a coal ash dump, said lead author Avner Vengosh, a Duke University professor of water quality and geochemistry.

“It's coming from rocks,” Vengosh said. “We see that some rocks contribute more chromium than others, so we have some idea to see where to look for it. But basically the data shows that it's coming from the interaction of the groundwater with rocks.”

The study is the first to show that coal ash contamination likely isn’t from coal ash.

Scientists tested 376 wells, both near and far from coal ash ponds. About 90 percent had hexavalent chromium, and many had unsafe levels, he says. He wants state and federal officials to set safety standards for the chemical, to protect public health.

That’s not to say coal ash basins are safe.

"Coal ash ponds are a serious threat to the health and to the environment North Carolina," Vengosh said.

He and colleagues published another paper in June that found unlined coal ash ponds leak high levels of other toxic heavy metals, such as arsenic and selenium.

Duke Energy says its own studies show it's not to blame.

“We were really confident that hexavalent chromium and other substances was not traveling in the direction of neighbors that are up-gradient, and this study today helps validate that,” spokeswoman Erin Culbert said.

Culbert says the new report – from an independent source - should reassure neighbors.

Neighbors still aren't sure. Amy Brown lives near Duke's Allen plant in Gaston County. She compares the latest news to March, when the state reversed its recommendation against drinking from wells near coal ash ponds.

“We won't go back to drinking our water this afternoon now that we know of this report. Just like when the rescinding of the do not drink letters happened and they took that recommendation,” Brown said.

Duke Energy has been supplying bottled water to households around some plants. And state law requires the company to provide a safe permanent water supply to plant neighbors by October 2018.

If you don’t live near a coal ash site and your well is contaminated, you’ll have to make your own arrangements.

Catawba Riverkeeper Sam Perkins favors removing coal ash. He says Vengosh’s research for years has outlined problems with unlined coal ash pits near waterways. He said in an email:

“There are still a lot of questions that will need to be scrutinized in the study. However, decades of research has concluded that hexavalent chromium 'rarely occurs naturally.' We should always continue to engage in research, especially when public health is of concern, and this is one more study that adds to our knowledge, but the science, engineering and experience thus far all demonstrate the need to clean up these unlined coal ash sites,” Perkins said.

RELATED LINKS

Oct. 26, 2016, Duke.edu, "Hexavalent Chromium is widespread in N.C. wells, but not linked to coal ash"

Oct. 26, 2016, Environmental Science & Technology Letters, "Origin of Hexavalent Chromium in Drinking Water Wells from the Piedmont Aquifers of North Carolina"

June 10, 2016, Duke.edu, "Coal Ash Ponds Found to Leak Toxic Chemicals"

June 10, 2016, Environmental Science & Techology, "Evidence for Coal Ash Ponds Leaking in the Southeastern U.S."