More than three-quarters of private drinking water wells tested in Iredell County had levels of Chromium 6 above the state health screening level, but the source of the compound is unknown.

Scientists from UNC Chapel Hill and Virginia Tech, who conducted the sampling, announced the results at a community meeting in Mooresville Thursday night. The researchers tested the well water for several chemicals and compounds, including lead, vanadium, cadmium, nickel and copper.

Of the 786 household wells, 79 percent had Chromium 6 above 0.07 parts per billion. That is the health screening level set by the NC Department of Health and Human Services at which the lifetime risk of developing cancer is 1 in 1 million. There is no EPA standard for Chromium 6.

The average level detected in Iredell County was an 0.84 ppb –12 times higher than the health screening level.

Chromium 6 is commonly found in well water at various levels. However, the Iredell County percentage is higher than in other locations that have been studied. By comparison, a previous DHHS survey of 192 wells in North Carolina showed that 58 percent had levels above the health screening level.

Kelsey Pieper, the Virginia Tech scientist who co-led the project, said compared to sampling conducted in other parts of the US, the levels “don’t appear unusually high.”

Scientists also tested the wells for vanadium, another chemical found in coal ash. More than 85 percent of Iredell County wells had levels above 0.3 ppb, the state’s interim maximum concentration for groundwater. The average was 4.2 ppb, with a maximum of 39.4 ppb.

Pieper said these levels are similar to those found in studies of school water outside of North Carolina.

Wilson Mize, an environmental health specialist with DHHS, said filters will remove Chromium 6, vanadium. lead and other chemicals from drinking water. The filters should be NSF-certified, Mize said, and can be installed on single faucets or in whole-house systems. Alternately, flushing the faucets for five minutes can also remove lead and copper that settles overnight in the pipes.

Some homes also tested above EPA standards for several other chemicals:

Copper, 10.8 percent

Lead, 7.5 percent

Cadmium, 0.4 percent

Nickel, 15 percent

The high percentage of wells with nickel could be due to plumbing changes in those homes. Many homeowners are switching out their lead pipes for those made of copper and nickel.

Duke Energy’s coal-fired Marshall Steam Station is about 10 miles west of Mooresville. While Chromium 6 and vanadium are often found in coal ash, they are also naturally occurring.

The well testing occurred earlier this year after Pieper received a grant from the EPA and the National Science Foundation to study the effects of hurricane flooding on private water supplies. The cost of the sampling and analysis was $350,000.

Pieper and UNC scientist Andrew George also conducted well water sampling in Robeson and Chatham counties. The Robeson results were announced in January; Chatham’s are due later this spring.