— Dozens of well owners near coal ash ponds across North Carolina will have to wait longer to learn whether their drinking water contains a cancer-causing compound primarily found in industrial waste.

Since late last year, state environmental regulators have been working with private laboratories to test about 300 wells located within 1,000 feet of the unlined dumps where Duke Energy stores the byproduct of electricity generation. The state was still waiting on about half of those results as of April 30, and based on testing, has already recommended that 123 well owners no longer drink the water.

But nearly one-third of the wells need to be sampled all over again because the labs couldn't determine exactly how much of a compound called hexavalent chromium is in the water.

Hexavalent chromium is notable because, unlike many of the elements on the testing list, experts say it rarely occurs naturally. It's also commonly found in coal ash.

Mobile and toxic

A known carcinogen, hexavalent chromium can cause skin irritation and allergic reactions in high concentrations. It was also the pollutant involved in an environmental lawsuit brought by citizens of Hinkley, Calif., against an energy company that settled in 1996 for $333 million, an event that formed the basis for the 2000 film Erin Brockovich.

Hexavalent chromium moves easily through groundwater, according to Gerald LeBlanc, professor and director of North Carolina State University's environmental and molecular toxicology program, making it of particular concern to people.

"It gets around, and as a result, it can cause significant contamination," LeBlanc said.

There's no state groundwater standard for the pollutant, which is just one form of the element chromium. But the state does have a standard for total chromium set at 10 micrograms per liter. By comparison, the U.S. Environmental Protection Agency sets its limit for total chromium at 100 mcg/L.

Yet state officials at the North Carolina Department of Health and Human Services set a much lower screening threshold specifically for hexavalent chromium at 0.07 mcg/L. State Epidemiologist Dr. Megan Davies said, at that level, experts would expect one case of cancer resulting from hexavalent chromium exposure given a population of 1 million people.

"It takes into account only any potential health effect," Davies said. "It doesn't try look at how expensive is it going to be to get water down to that level or how feasible is it to get water down to that level."

California, by comparison, set its standard specifically for hexavalent chromium at 10 mcg/L.

DHHS officials set the level for the contaminant in January, after environmental regulators had already chosen which labs would do the testing and had started the sampling process. While some factors, such as murkiness of the water sample, can affect the precision of measurement, DENR spokeswoman Sarah Young said many of the labs weren't capable of measuring to the DHHS standard.

Moving forward, Young said, regulators will use only two of the nine original labs.

As laid out in the Coal Ash Management Act, which state lawmakers passed in 2014, well-water tests near coal ash ponds would normally be billed to Duke.

The company is paying to retest a majority of the 94 wells that need resampling – mostly for hexavalent chromium along with a handful of other substances. But in the case of at least 42 wells that need resampling, the state will foot the bill, at a cost of about $20,000.

DENR officials said that's because there's no state standard specifically for hexavalent chromium.

"Duke has satisfied the requirements of the Coal Ash Management Act," Young said. "But because we have our state health organization saying these wells need to be resampled, we're going to do what they're telling us to do."

DENR officials point out they'll use a special coal ash fund created with Duke fees to pay for the resampling, meaning taxpayers won't technically be on the hook.

But the extended wait has left well owners such as Jeri Cruz-Segarra, of Arden, with unanswered questions. The paperwork she received a few weeks back contained a handwritten note saying state health officials couldn't make a health recommendation without another test for hexavalent chromium and other inorganic substances, scheduled to take place in about a month.

She said Duke has offered to supply bottled water and to meet with her and her husband to answer questions. What she wants, she said, is safe drinking water.

"This whole situation has left a bad taste in my mouth," she said.

Coal ash ponds found all across state

More than 30 coal ash ponds can be found at 14 existing or retired Duke power plants across North Carolina.

Contamination a question of risk

Of 33 wells that could be measured precisely enough to compare to the DHHS screening level, 21 of those exceeded it. Concentrations ranged from just above the standard to as high as 8.4 mcg/L.

The well with the highest measured level belongs to Sandra Avery, who has lived in her Belmont home with her husband for more than 40 years, before Duke even began digging some of the ash pits at the Allen Steam Station. The couple received a do-not-drink recommendation from DHHS a few weeks ago, and Duke has since begun delivering bottled water.

"We were quite shocked and still are a little bit shocked," Avery said. "It's a shame we had to go this long without knowing what was happening to us."

Her well also exceeded state standards for iron and vanadium as well, which can also be potentially toxic.

But LeBlanc said the concentration of hexavalent chromium in well tests so far hasn't been enough to cause serious alarm.

"In terms of health, no one would get excited about those numbers," LeBlanc said. "We think about chromium as being a nasty metal. But again, it's an issue of dose."

That's one reason why health officials are only issuing recommendations – and encouraging well owners to consult with state toxicologists for one-on-one consultations.

"We're not seeing levels that would cause us to call people up immediately and say 'You're going to become acutely ill if you keep drinking your water,'" Davies said. "It's much more a conversation about risk with exposure over time."

Substance not often found in nature

Unlike many of the elements the wells have been tested for, hexavalent chromium is not commonly found in the natural environment, LeBlanc said.

"Usually when we see hexavalent chromium, we say, 'Ah, human activity,'" he said. "The take-home message is: It's coming from somewhere, but it's not a natural occurrence."

That matters, because many of the elements that have prompted the state to issue do-not-drink recommendations occur naturally in soil and geologic formations absent any intervention from humans.

DENR officials, who will be tasked in the coming months with determining whether groundwater contamination can be linked directly to Duke's ash ponds, have noted the naturally occurring nature of these elements in their communication with well owners and the public.

So has Duke.

Company spokeswoman Erin Culbert said that, although there's still more work to be done to test background levels of these elements, the well tests so far haven't indicated the presence of common coal ash "tracers," most notably boron and sulfate. She said there's even geologic evidence to support the existence of some suspect elements in high concentrations across the state independent of the coal ash.

"Based on the data, it doesn't appear that plant operations have impacted a vast majority of these wells," Culbert said.

She also said some scientific literature shows hexavalent chromium can be naturally occurring in certain circumstances.

D.J. Gerken, an attorney with the Southern Environmental Law Center, said he doesn't buy the company's explanation.

His group has taken legal action against Duke over the coal ash ponds and has pressured the state to do more to require the energy company to clean them up.

"Duke's answer to this contamination has been, 'This is all attributable to background,'" Gerken said. "We're continuing to hear them say it to the public and the state, but there are years of data indicating these coal ash ponds are impacting groundwater."

As for the tracer elements, he said the 32 ponds sprinkled across the state contain coal ash generated over many decades and are far from uniform.

"They are a witch's brew of constituents from all over the place," Gerken said. "I don't know if there's one fingerprint that can rule this in or out."

Just this week, Duke pleaded guilty in federal court to environmental crimes for illegally releasing pollution from coal ash dumps at five North Carolina power plants. The case was prompted by a February 2014 spill that dumped 40,000 tons of the substance into the Dan River north of Greensboro, coating the waterway in gray sludge for 70 miles.

The $102 million the company will pay for cleanup is the largest federal criminal monetary penalty in state history.

If regulators link well contamination to Duke, the coal ash management law says the utility will have to pay to treat the water.

Some residents say they've already made up their minds.

"Duke Power is responsible for this, so we're going to let Duke Power do whatever it takes to clean up our wells," Avery, the well owner near the company's Allen plant, said.

She said she's already received information about companies who she could pay to treat her well, the only source of drinking water for the home.

Susan Massengale, a DENR spokeswoman, said that's certainly an option for residents who are looking for a longer-term option than the bottled water arriving at their homes every few weeks.

"All I know is that the Coal Ash Management Act says Duke will be responsible for that if the contamination is linked to them," Massengale said. "If I were putting in a filtering system now, I'd save my receipts."