This map shows the number of wells on a county level that are likely contaminated with high levels of arsenic.
Many states keep tabs on arsenic in water wells, but normally in places where the chemical is already known to be a problem.
Rain patterns and how water flows through these rocks can release arsenic from their earthen homes and into a water well.
Ayotte’s team used USGS and other databases to compile arsenic measurements from 20,450 wells in the U.S. Map courtesy of Joseph Ayotte What they found: The USGS model, published in Environmental Science & Technology, predicts 2.1 million people drink from wells with arsenic at greater than 10 micrograms per liter of water, which is the maximum contaminant level allowed by the Environmental Protection Agency.
Overall, 44.1 million in the conterminous U.S. rely on wells for their water.
States like Maine, New Hampshire and Massachusetts registered high levels of arsenic on the map.
“I wish I knew why U.S. domestic well water quality is not regulated to meet the same drinking water standards as for other types of water supplies,” said Zheng, who has conducted regional studies of arsenic in water wells in the U.S., China and Bangladesh, where she was formerly a water and sanitation specialist with UNICEF on arsenic mitigation projects.
Her research leads her to believe the most effective way to reduce arsenic exposure and protect human health is a national screening program in the form of individual tests at domestic wells.
It offers a sense of where arsenic might be, but people will not know for sure if their wells are contaminated unless they test.
Once detected, arsenic can be removed through common water filters, but even this simple technological fix might be cost prohibitive in rural areas where water wells dominate.