National Water-Quality Assessment

U.S. Geological Survey
Fact Sheet 063-00

Arsenic in Ground-Water Resources of the United States

By Alan H. Welch, Sharon A. Watkins, Dennis R. Helsel, and Michael J. Focazio


Arsenic is a naturally occurring element in rocks, soils, and the waters in contact with them. Recognized as a toxic element for centuries, arsenic today also is a human health concern because it can contribute to skin, bladder, and other cancers (National Research Council, 1999). Recently, the National Research Council (1999) recommended lowering the current maximum contaminant level (MCL) allowed for arsenic in drinking water of 50 µg/L (micrograms per liter), citing risks for developing bladder and other cancers. The U.S. Environmental Protection Agency (USEPA) will propose a new, and likely lower, arsenic MCL during 2000 (U.S. Environmental Protection Agency, 2000). This fact sheet provides information on where and to what extent natural concentrations of arsenic in ground water exceed possible new standards.

Table of Contents

The maps in this fact sheet have been superseded. The new maps were published in the November 2001 issue of Geotimes, and are available on the USGS Arsenic in Ground Water page.

Frequently Asked Questions

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Reader, it is available for free download from Adobe Systems Incorporated.

Download the report (PDF, 0.7 MB)

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For further information about this report, contact the National Water-Quality Assessment Program office.

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