Erin Brockovich, the consumer advocate made famous in a 2000 Julia Roberts movie, cited North Carolina's dispute over coal ash Tuesday to urge federal regulators to set new drinking-water limits for hexavalent chromium.

The cancer-causing form of chromium can occur naturally but is most often released by industries, including in coal ash. It's the most worrisome contaminant found in nearly 400 private wells near Duke Energy power plants, although Duke says its ash isn't the source.

North Carolina's state epidemiologist, Dr. Megan Davies, resigned last week over state officials' depiction of a subordinate's "unprofessional approach" for defending a strict testing limit for hexavalent chromium.

Davies and state toxicologist Kenneth Rudo have testified in legal depositions that they felt pressure from environmental officials to soften written advisories to well owners.

In a letter Tuesday to the Environmental Protection Agency, Brockovich and the nonprofit Environmental Working Group said the North Carolina conflicts "exemplify the discord that has resulted in the absence of federal action."

EPA regulates only total chromium but is studying whether to set a separate standard for its hexavalent form. Brockovich and the Environmental Working Group want the agency to take action.

"It is clear that the delay is sowing confusion among state and local regulators, utilities and the public about how much hexavalent chromium is safe in drinking water," they wrote.

An EPA spokeswoman responded that the agency "has not made any decision regarding revising the drinking water regulations for chromium or establishing regulations for hexavalent chromium. EPA is actively engaged in an evaluation of the available literature regarding the potential health effects that may occur as a result of exposure to hexavalent chromium."

Brockovich and hexavalent chromium go back a long way -- to 1993, when she helped uncover drinking water in Hinkley, Calif., that was contaminated by Pacific Gas and Electric's power plant cooling towers.

The Environmental Working Group says federal records show hexavalent chromium is in drinking water systems in all 50 states, including Charlotte's. .

Unresolved is how much is too much.

North Carolina scientists, including Rudo, used a .07 parts per billion limit -- the amount that would cause one cancer in 1 million people over a lifetime of drinking tainted water -- in assessing private wells near Duke's power plants.

Charlotte Water reported .096 ppb in water from its Dukes treatment plant in 2014.

State environmental officials say the more appropriate benchmark is the federal standard for total chromium: 100 ppb.

California, where Brockovich rose to fame, set an even lower "goal" of no more than .02 ppb of hexavalent chromium in drinking water. But its enforceable standard for hexavalent chromium is 10 ppb.

Bruce Henderson: 704-358-5051, @bhender

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