U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division



Arsenic is a naturally occurring element, generally found at higher concentrations in sedimentary rocks than in other rock types. Arsenic is also commonly associated with sulfide deposits. In the continental United States a higher than average arsenic concentration is associated with sandstones, shales and coal located in Colorado, Utah, South Dakota, and Wyoming and with phoshorites in Arkansas, Idaho, Montana, South Carolina, and Wyoming. Shales, clays, and sedimentary iron and manganese oxides can also be rich in arsenic. Groundwater concentrations of arsenic tend to be higher in the west, especially parts of Arizona, Idaho, Nevada, New Mexico, Oregon, Utah, and Washington, than in the east. Parts of the Midwest states including Indiana, Michigan, and Wisconsin can also have relatively high concentrations of naturally occurring arsenic in groundwater.

Major anthropogenic sources of arsenic in the environment include smelting operations and chromated copper arsenate (CCA), a variety of pesticide used in pressure treating wood for construction purposes. When used as a wood preservative, CAA has the potential to leach out of the wood over time. As a result, the wood treating industry has made a decision to eliminate all arsenical wood preservatives from residential use by the end of 2003.

Organic arsenical pesticides are widely used for weed control. Inorganic arsenicals were largely used in the past to control specific insects, but for the most part, their registrations have been cancelled. They do, however, persist in fields and orchards where they were applied. Since arsenic is associated with sulfide deposits, which are in turn associated in many cases with non-ferrous ores, contamination can occur from mining operations and wastes. The smelting of non-ferrous ores has often resulted in air deposition of arsenic and other heavy metals (1). Arsenic is listed as the highest priority contaminant on the ATSDR/EPA priority list of hazardous substances at Superfund sites (ATSDR list).

From a world-wide perspective:
"Mean total arsenic concentrations in air from remote and rural areas range from 0.02 to 4 ng/m3. Mean total arsenic concentrations in urban areas range from 3 to about 200 ng/m3; much higher concentrations (> 1000 ng/m3) have been measured in the vicinity of industrial sources, although in some areas this is decreasing because of pollution abatement measures. Concentrations of arsenic in open ocean seawater are typically 1-2 µg/litre. Arsenic is widely distributed in surface freshwaters, and concentrations in rivers and lakes are generally below 10 µg/litre, although individual samples may range up to 5 mg/litre near anthropogenic sources. Arsenic levels in groundwater average about 1-2 µg/litre except in areas with volcanic rock and sulfide mineral deposits where arsenic levels can range up to 3 mg/litre. Mean sediment arsenic concentrations range from 5 to 3000 mg/kg, with the higher levels occurring in areas of contamination. Background concentrations in soil range from 1 to 40 mg/kg, with mean values often around 5 mg/kg. Naturally elevated levels of arsenic in soils may be associated with geological substrata such as sulfide ores. Anthropogenically contaminated soils can have concentrations of arsenic up to several grams per 100 ml." (2)


Equal-area map: Arsenic concentrations found in at least 25% of ground-water samples within a moving 50km radius [View]

County map: Arsenic concentrations found in at least 25% of ground-water samples in each county [View]

Data map: 31,350 ground-water arsenic samples collected in 1973-2001 [View]

For Further Information

Arsenic Contribution from Dietary Sources
E. Pellizzari, J. Raymer, C. Clayton, R. Fernando, and L. Milstein.
IWA Pub., London. AwwaRF Report 90969F, ISBN: 1843398745, 412 pp, 2004 [Originally released to Awwa Research Foundation subscribers in 2003]

Provides the results from cooking studies, a market basket survey, a food diary analysis, and the relationships between environmental and biological media; to be used in scenario-based models that predict arsenic exposures.

Arsenic in Ground Water: Geochemistry and Occurrence
A. Welch and K. Stollenwerk
Kluwer Academic Publishers, 2002

Adobe PDF LogoArsenic in Ground Water in Sanilac County, Michigan
U.S. Geological Survey Fact Sheet FS-132-00, 2 pp, 2000
Contact: Sheridan Haack,

Arsenic in Ground Water of the United States
United States Geological Survey

Arsenic in Ground Water of the Willamette Basin, Oregon
Henkel, S. and D. Polette
Water-Resources Investigations Report 98-4205, United States Geological Survey, 1999

Arsenic: Medical and Biological Effects of Environmental Pollutants
National Research Council, National Academy of Sciences Press, 1977

Adobe PDF LogoArsenic Occurrence in Public Drinking Water Supplies
U.S. EPA, Office of Water.
EPA 815-R-00-023, 156 pp, 2000.
Contact: Andrew Schulman,

Elements and Their Compounds in the Environment: Occurrence, Analysis and Biological Relevance, Second Edition
E. Merian, M. Anke, M. Ihnat, and M. Stoeppler (eds.).
John Wiley & Sons, New York. ISBN: 3-527-30459-2, 3 Vols, 2004.

Adobe PDF LogoElement Concentrations in Soils and Other Surficial Materials of the Conterminous United States
H. Shacklette and J. Boerngen.
U.S. Geological Survey Professional Paper 1270, 63 pp, 1984.

A digital version of the data can be obtained from David Smith,

Estimating the High-Arsenic Domestic-Well Population in the Conterminous United States
Ayotte, J.D., L. Medalie, S.L. Qi, L.C. Backer, and B.T. Nolan.
Environmental Science & Technology 51(21):12443-12454(2017) [Open Access]

A logistic regression model of the probability of having arsenic >10 µg/L (high arsenic) in wells at the county, state, and national scales was developed using As concentrations from 20,450 U.S. domestic wells. The population in the conterminous U.S. using water from domestic wells with predicted As concentration >10 µg/L is 2.1 million people (95% CI is 1.5 to 2.9 million). Although some parts of the U.S. were underrepresented with As data, by predicting to all of the conterminous U.S., the investigators were able to identify areas of high and low potential exposure in areas of limited As data, which can be viewed as potential areas to investigate further or to compare to more detailed local information.

Estimating Inorganic Arsenic Exposure from U.S. Rice and Total Water Intakes
Mantha, M., E. Yeary, J. Trent, P.Z. Creed, K. Kubachka, T. Hanley, N. Shockey, D. Heitkemper, et al.
Environmental Health Perspectives 125(5):(2017)

Researchers estimated Americans' inorganic arsenic exposures from drinking water and rice—a food that may contain arsenic—and concludes that rice consumption might account for as much inorganic arsenic exposure as drinking water in some U.S. populations. See also J.R. Barrett's commentary on the article in the following issue of EHP, Rice versus Drinking Water: Estimating the Primary Source of Arsenic in the U.S. Diet, at

Geochemical Landscapes of the Conterminous United States: New Map Presentations for 22 Elements
N. Gustavsson, B. Bølviken, D.B. Smith, and R.C. Severson.
U.S. Geological Survey Professional Paper 1648, 44 pp, 2001.

Adobe PDF LogoThe Influence of Geology and Land Use on Arsenic in Stream Sediments and Ground Waters in New England, USA
G.R. Robinson Jr. and J.D. Ayotte, USGS.
Applied Geochemistry, Vol 21, p 1482-1497, 2006

Adobe PDF LogoA Retrospective Analysis on the Occurrence of Arsenic in Ground-Water Resources of the United States and Limitations in Drinking-Water-Supply Characterizations
M.J. Focazio, A.H. Welch, S.A. Watkins, D.R. Helsel, and M.A. Horn.
U.S. Geological Survey Water-Resources Investigations Report 99-4279, 27 pp, 2000.
Contact: Michael Focazio,

State Arsenic Information Pages

Illinois Department of Natural Resources
Maine Bureau of Health
Maryland Department of Environment
Michigan Department of Environmental Quality
Adobe PDF LogoMinnesota Department of Health
North Carolina Department of Environment and Natural Resources
Washington State Department of Health
Wisconsin Department of Natural Resources

Study of State Soil Arsenic Regulations
L. Baldwin, and H. McCreary
Association for the Environmental Health of Soils, 40 pp, 1998

The Materials Flow of Arsenic in the United States
J. Roger Loebenstein.
U.S. Bureau of Mines Information Circular 9382, 18 pp, 1994.

This report presents a study of the flow of arsenic-containing materials in the United States, based on the best data available in 1991. It includes a consideration of arsenic as a byproduct of the processing of nonferrous metals, the fate of arsenic in manufacturing wastes, the quality of arsenic used in products, the fate of arsenic in dissipative uses, and the useful life of discarded products. Where possible, estimates are given of the amounts of arsenic lost from the materials flow.

USGS Arsenic Studies Group
United States Geological Survey

1. M. Focazio, et al. 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-Resources Investigations Report 99-4279, 2000.

2. Environmental Health Criteria 224: Arsenic and Arsenic Compounds
United Nations Environment Programme, the International Labour Organization, and the World Health Organization, 2001.