A cancer-causing heavy metal found in water wells near coal ash pits and other industrial sites is much more widespread and naturally occurring than previously thought, university researchers said Wednesday.
The presence of hexavalent chromium is more related to volcanic rock found in North Carolina and nearby states than the pits used to store the waste left after burning coal, Duke University geochemistry professor Avner Vengosh said. Badly tainted groundwater was found in wells more than 18 miles from a coal ash storage basin in central North Carolina's Piedmont region, according to the study published in the American Chemical Society's publication Environmental Science & Technology Letters.
"The most import thing is to make sure the industry, the coal ash issue, is not off the table," Vengosh said. "Groundwaters near coal ash ponds are contaminated. We see evidence for that. But the issue with hexavalent chromium, we're finding, is unrelated and much larger than we thought."
The U.S. Environmental Protection Agency says hexavalent chromium is likely to be carcinogenic when ingested. The chemical was portrayed as poisoning residents in a California town in a Hollywood movie describing the work of former legal clerk and sleuth Erin Brockovich.
The findings mean it's urgent that the EPA set uniform safety limits for hexavalent chromium in drinking water, said Vengosh, who studies coal ash contamination at Duke's Nicholas School of the Environment.
The EPA's current standard for all variations of chromium is 100 parts per billion, while California's limit specifically for the more toxic hexavalent form is 10 parts per billion.
The heavy metal is at the center of concerns about whether massive coal ash basins are polluting nearby groundwater. North Carolina last year warned more than 300 neighbors of Duke Energy Corp. coal plants against drinking their well water. That was based on calculations by state scientists that ingesting water containing more than 0.07 parts per billion over the course of a lifetime created a one-in-a-million chance of causing cancer.
North Carolina officials reversed those warnings last spring as too strict, adding that if the same threshold were applied evenly statewide it would apply to about 900,000 wells and millions of people would be urged against drinking their groundwater.
Duke Energy, which is not related to the university, said the study bolstered its position that its coal ash pits are not responsible for groundwater pollution.
"When combined with previous research, there is overwhelming evidence that coal ash basins are not impacting water quality in neighbor wells," said Harry Sideris, Duke Energy's senior vice president of environmental, health and safety.
The country's largest electric company is required by state law to close all 14 of its North Carolina coal-burning power plants. About half could be dried out, covered with earth and left in place, but the company must provide alternative water supplies to neighbors who now use well water. It is also excavating and moving coal ash from its South Carolina pits.