In September it was reported that more than 200 million Americans have chromium-6 in their tap water. It is believed that most of the chromium comes from industrial contamination.  However, a study from Duke University surprised many people on the origins of chromium-6 contamination. The toxin is not only far more abundant in North Carolina’s water wells than previously thought. Chromium-6 is bleeding into the water from volcanic rocks.

In 2015, North Carolina officials issued temporary “do not drink” recommendations to residents living near coal-burning plants after tests detected potentially harmful levels of chromium-6 in well water. Coal is the leading element for energy consumption in North Carolina, according to the U.S. Energy Information Administration. Because of North Carolina’s large scale coal-burning facilities, it was assumed that the contamination was coming from leaking coal ash ponds. Other toxins that have been linked to coal ash are selenium, lead, and arsenic.

The Duke study revealed that the contamination is caused by the natural leaching “of mostly volcanic rocks in aquifers across the Piedmont region.” Results of the study were published in the journal Environmental Science and Technology Letters.

The study also shed light on very public debate among state officials over contaminated water. One official has already resigned. The back-and-forth accusations are at the heart North Carolina’s contamination woes.  PBS Newshour reported that Ken Rudo, North Carolina’s top public health official: “acted unethically and possibly illegally by telling residents living near Duke Energy coal ash pits that their well water is safe to drink when it’s contaminated with a chemical known to cause cancer, a state toxicologist said in sworn testimony.” That chemical is chromium-6.

Even though the Duke study points the pollution finger at Mother Nature that doesn’t absolve the coal-burning plants. The policy think tank, N.C. Policy Watch, reports that North Carolina’s coal-fired power plants are some of the biggest polluters in the country. Two of the plants are ranked in the top twenty and three rank among the fifty dirtiest plants in the nation. The three power plants emit 8 million cars’ worth of pollution each year. On its blog,, the institute also warns that thousands of private well owners—nearly a third of North Carolinians—may be exposed to chromium-6 from natural sources.

What makes the contamination ever more problematic is that no one is sure how much pollution comes from natural resources and how much comes from coal-fired plants. At best, North Carolinians should continue to avoid drinking well water.