North Carolina ranks fourth-highest in the nation for the number of people who are likely to have high levels of arsenic in their drinking water wells, a new federal study shows.
Up to 187,000 state residents are likely to have potentially toxic levels of arsenic, the U.S. Geological Survey and the Centers for Disease Control and Prevention reported.
Most North Carolina wells where arsenic has been detected are in the central Piedmont, state authorities said. State data shows that 20 percent of wells sampled in Union County, just east of Charlotte, have potentially unhealthy arsenic levels. Fewer than 1 percent of those in Mecklenburg County have those risks.
About 2.1 million people across the U.S. might be drinking arsenic-tainted water, the federal agencies said.
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Arsenic has no color, odor or taste in water. Drinking arsenic-tainted water for many years can increase risks of diabetes, high blood pressure, and several types of cancer, according to the CDC.
Most of the arsenic documented in the new report is believed to occur naturally in rocks and minerals through which water flows. Federal researchers developed maps showing where groundwater concentrations exceed 10 parts per billion, the maximum amount allowed in public water supplies.
“While we’re confident our research will help well owners understand if they live in an area of higher risk for arsenic, the only way for them to be certain of what’s in their water is to have it tested,” Joe Ayotte, a USGS hydrologist and lead author of the study, said in a statement.
While the highest arsenic concentrations are in the western half of the U.S., North Carolina ranks behind only Michigan, Ohio and Indiana for the number of people potentially at risk. That’s largely because so many people in the state – about one-third of its 10 million residents – rely on wells for their drinking water in rural areas.
While municipal and other public water systems are required to meet federal safety standards, well owners in North Carolina are largely on their own in ensuring that their water is safe. State law requires only that newly built private wells be tested for contaminants, although local health departments test wells for a fee.
The state Division of Public Health recommends that well owners get their water tested regularly, either through their local health department or a state-certified commercial lab. The division has more information and recommendations online.
North Carolina’s highest arsenic levels in groundwater are found in the “Slate Belt” of ancient volcanic rock that slices from southwest to northeast across the central Piedmont. The Division of Public Health has collaborated with UNC to study the average concentrations of contaminants including arsenic.
The most common solutions to arsenic in well water are treatment systems, state environment department officials said. The National Ground Water Association, a trade association, also offers information on arsenic, interpreting test results and treatment options.
The federal researchers used samples from more than 20,000 wells to estimate where high arsenic levels are likely. They combined that information with census data to estimate the number of people who might be exposed in each county.