National Water-Quality Assessment
National Analysis of Trace Elements

Arsenic in ground water of the United States

Publications

About the maps--
Mapping arsenic in ground water

Fact sheet--
Arsenic in ground-water resources of the US

Detailed report--
A retrospective analysis on the occurrence of arsenic in ground water of the US

Research--
Arsenic in ground water supplies of the US

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.

For help interpreting these maps, see:

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

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

> Original data map

Data

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

USGS data (1.8 Mb, tab delimited)

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

Arsenic links

World Health Organization-- Arsenic in drinking water

US Environmental Protection Agency-- Arsenic Standard pages and Q&A's

US Congressional Research Service-- Report for Congress on Arsenic

National Research Council-- Arsenic in drinking water and 2001 Update

West Bengal & Bangladesh Arsenic Crisis Information Centre