National Water-Quality Assessment (NAWQA) Program

Arsenic in groundwater is largely the result of minerals dissolving from weathered rocks and soils. Several types of cancer have been linked to arsenic in water. In 2001 the US Environmental Protection Agency lowered the maximum level of arsenic permitted in drinking water from 50 micrograms per liter (ug/L) to 10 ug/L.

The USGS has developed maps that show where and to what extent arsenic occurs in groundwater across the country. The current maps are based on samples from 31,350 wells. Widespread high concentrations were found in the West, the Midwest, parts of Texas, and the Northeast. See Ryker (2001) for more information. See Focazio and others (2000) for the use of available data for characterizing arsenic concentrations in public-water supply systems. See Gronberg (2011) for updated arsenic map.

Featured publications

United States

• Effects of human-induced alteration of groundwater flow on concentrations of naturally-occurring trace elements at water-supply wells: Applied Geochemistry, v. 20, issue 5, p. 747-762. (2011)
• Mapping arsenic in groundwater: A real need, but a hard problem: Geotimes Newsmagazine of the Earth Sciences, v.46 no.11, p.34-36. (2001) DATA
• Arsenic in ground-water resources of the United States: U.S. Geological Survey Fact Sheet 063-00. (2000)
• A retrospective analysis on the occurrence of arsenic in ground-water resources of the United States and limitations in drinking-water-supply characterizations: U.S. Geological Survey Water-Resource Investigations Report 99-4279. (2000)
• Arsenic in ground water supplies of the United States, in: Arsenic exposure and health effects, Elsevier Science, p. 9-17 (1998)