An environmental advocacy group has published a report stating a cancer-causing substance could be in water systems servicing more than two-thirds of the U.S., including Grand Forks and wider North Dakota.

The Environmental Working Group released its national findings on chromium-6, a carcinogen produced by industrial practices, on Sept. 20. Chromium-6 is a variant of the element chromium, which was spotlighted in the 2000 film "Erin Brockovich."

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Though notorious, the substance is not regulated by the EPA, though chromium itself is regulated under the federal Safe Drinking Water Act.

California is the only state in the U.S. with enforceable standards for chromium-6 in sources of drinking water.

Greg Wavra, manager of North Dakota's Drinking Water Program, said the EWG's findings are correct, but need to be placed in context.

The environmental group's report drew from data gathered through the third Unregulated Contaminant Monitoring Rule, a nationwide sweep conducted by agencies like the North Dakota Department of Health to provide data on unregulated contaminants to see if future EPA action may be required.

Results from that national study found chromium-6 contamination in water systems serving more than 200 million U.S. residents. In many of those cases, the level of contamination was higher than the state of California's public health goal of 0.02 parts per billion-the equivalent of 1 microgram of chromium-6 in 1 liter of tap water.

"That's a goal, and yes, there are a lot of goals, but that doesn't mean that that's where the (maximum contaminant level) would be set by the EPA at all," Wavra said. "That's a number that you could say is unrealistic."

Laboratories that read water samples for such contaminants, he added, typically state they can accurately read levels down to 0.03 ppb-meaning that the health goal is lower than what can possibly be reported at the current time.

California's current enforceable limit for chromium-6 is set to 10 ppb. Both that limit and the public health goal were set using research conducted by the California Office of Environmental Health Hazard Assessment.

The EWG challenges the regulated limit for chromium-6 in its report, stating the level is the result of "aggressive lobbying by industry and water utilities." The working group maintains that the public health limit is a better measure for determining risk of harm through long-term consumption.

Wavra said the EPA usually takes research conducted in California into account when considering national regulations.

Still, he believed that state-which he described as "very conservative," in terms of environmental regulations-might overshoot the federal government when it comes to chromium-6.

"Even at 10 ppb," Wavra said, "the EPA would probably be higher than that."

The EWG study examined data which drew an average for multiple samples collected in water systems throughout individual counties.

Though some individual systems-none in North Dakota-showed signs of contamination levels much higher than the California limit, only a handful of counties produced average numbers that surpassed 10 ppb.

That number included Yolo and Merced counties, of California, and Cleveland and McClain counties, of Oklahoma. Cleveland County reported the highest average level of chromium-6 contamination in the country at 29.59 ppb.

In North Dakota, the highest recording in the state came from Ward County, where state health officials tested water from Minot and Minot Air Force Base. The countywide average for chromium-6 levels was 1.40 ppb across a range of eight water samples.

Grand Forks County had an average chromium-6 level of 0.381 ppb across a range of eight water samples. Cass County was lower still at 0.213 ppb.

When it comes to chromium itself, Wavra said the federal limit is 100 ppb.

The highest detected level in North Dakota that he knew of was a finding of about 36 ppb, which was discovered in a rental housing complex in Watford City.

Still, given the relative lack of manufacturing centers that typically contribute to both chromium and chromium-6 contamination, Wavra said the substances are not prevalent throughout the state.

"There were very few that had anything at all," he said.