National Water-Quality Assessment (NAWQA) Program

Updated maps

Equal-area map--
Arsenic concentrations found in at least 25% of samples within a moving 50km radius

County map--
Arsenic concentrations found in at least 25% of samples in each county

    > Original county map (Welch and others, 2000)

Data map--
31,350 ground-water samples collected in 1973-2001

    > Original data map (Welch and others, 2000)

Arsenic in ground water 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 ground water across the country. The current maps are based on samples from 31,350 wells. Widespread high concentrations were found in the West, the Midwest, and the Northeast.

Data

USGS data-- The maps at right are based on 31,350 arsenic samples. Of those samples, 20,050 were collected by USGS.

• Data updated to March 30, 2000:
  (6.8 mb, Excel file)
  (2.8 mb, text file)
• Data for 1973-1997, used in report WRI 99-4279 (superseded): (1.9 mb, text file)

State data--
Several state agencies contributed data to these maps, including:

• Minnesota
• Texas
• Wisconsin

Related publications

Map of arsenic in groundwater of the United States, updated 2011--

• Map of arsenic in groundwater of the United States Gronberg (2011)
• PNG

Fact Sheet--

• Arsenic in ground-water resources of the United States: U.S. Geological Survey Fact Sheet 063-00. (2000)
• Frequently asked questions

Detailed report--

• 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)
• May 2000 news release

Research--

• Arsenic in ground water supplies of the United States, in: Arsenic exposure and health effects, Elsevier Science, p. 9-17 (1998)

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U.S. Department of the Interior | U.S. Geological Survey
URL: http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/index.html
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Page Last Modified: Tuesday, 04-Mar-2014 14:45:30 EST