New USGS Fact Sheet Shows Arsenic in Nation's Ground Water

Note to Editors: U.S. Environmental Protection Agency will propose a new arsenic drinking-water standard in 2000.

A new U.S. Geological Survey (USGS) national map and fact sheet shows where and to what extent arsenic occurs in ground water across the Nation. Highest arsenic concentrations were found in ground-water samples analyzed throughout the West and in parts of the Midwest and Northeast. The USGS has been assessing arsenic in the Midwest, such as the deep glacial aquifer in central Illinois.

The widespread occurrence of this naturally occurring and toxic element underscores its importance as a top national priority to address in ensuring safe and livable communities for all our citizens, said USGS Chief Hydrologist Robert Hirsch. Arsenic was included in the amendments to the Safe Drinking Water Act by Congress in 1996 because of its known prevalence and possible adverse health effects, Hirsch said. The new publication, and the data base from which it was created, have substantially increased our understanding of arsenic occurrence and provide a snapshot view of where ground-water resources are at risk from arsenic contamination. Nationally, concentrations of arsenic in ground water presented in the USGS study were usually lower than the current U.S. Environmental Protection Agency (USEPA) drinking-water standard of 50 micrograms per liter (ug/L). However, this standard is under review and ma be lowered by USEPA. A recent USGS publication Analysis of nutrients, selected inorganic constituents, and trace elements in water from Illinois community-supply wells, 1984-91 by K.L. Warner describes arsenic in drinking water in Illinois. Most concentrations exceeding 50 ug/L are in the Quaternary (glacial drift aquifer). The deep glacial drift aquifer in central Illinois has a higher frequency of detection than most aquifers in other areas in Illinois. Arsenic is a drinking-water concern in the deep glacial drift aquifers like the Mahomet aquifer. Although the national map shows a small area of concern in central Illinois, we know that there are many areas in Illinois where not enough data are available to adequately define the extent of the arsenic problem, Warner said. The USEPA is in the process of designating a new drinking-water standard for arsenic. The USEPA is proposing to reduce the current arsenic standard from 50 parts per billion (ppb) to 5 ppb in drinking water. Additional information is available at http://www.epa.gov/safewater/arsenic.html. In a report released last year, the National Academy of Sciences recommended that the USEPA issue a lower concentration for the standard.

The information from the USGS study will help water managers and other users to better understand where and to what extent ground water may have limitations for public supply and other uses because of the concentrations of arsenic that are present, Hirsch said. In looking at where arsenic concentrations might exceed possible new standards, the USGS chose the international guideline for arsenic in drinking water of 10 micrograms per liter set by the World Health Organization (WHO). Approximately 10 percent of the samples in the USGS study exceed the WHO guidelines. A USGS study of arsenic in the deep glacial drift aquifer in central Illinois found 40 percent of the samples from privately owned wells had arsenic concentrations above 10 ug/L and 55 percent of the samples from public-supply wells in the deep glacial drift aquifer exceed 10 ug/L. The national map is based on ground-water samples collected from wells used for irrigation, industrial purposes and research, and public and private water supply, the mat shows in which counties wells might exceed 10 micrograms per liter and other lower concentrations. The countywide findings portrayed on the map were calculated from about 18,850 samples of potable ground water (which are not necessarily current sources of drinking water), and do not represent testing of every well or drinking-water supply system in a given county. The map is available at http://co.water.usgs.gov/trace/arsenic. Arsenic is a naturally occurring element in the environment. Its presence in ground water is largely the result of minerals dissolving naturally over time as rocks and soils weather. Several types of cancer have been linked to arsenic present in drinking-water concentrations higher than observed in U.S. drinking-water supplies. In addition, high levels of arsenic have been reported to affect the vascular system in people and have been associated with development of diabetes. Public-supply systems exceeding the present USEPA standard are required to either treat the water or find alternative sources of supply. People served by public-water supplies can obtain information on the quality of their drinking water, including arsenic concentrations, directly from their water supplier. Information about public water supplies in your community is available from the USEPA at http://www.epa.gov/safewater/dwinfo.htm. Data used in the national analysis and an accompanying USGS Fact Sheet, FS-063-00, Arsenic in Ground-Water Resources of the Unites States, are available at http://co.water.usgs.gov/trace/arsenic. Information about the USGS technical report, Analysis of nutrients, selected inorganic constituents, and trace elements in water from Illinois community-supply wells, 1984-91 is available by calling (217) 344-0037. As the Nation~Rs largest water, earth and biological science and civilian mapping agency the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every State by USGS scientists to minimize the loss of life and property from natural disasters, contribute to sound economic and physical development of the Nation~Rs natural resources, and enhance the quality of life by monitoring water, biological, energy, and mineral resources.

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In-depth information about water resources in Illinois may be found on the USGS, Illinois Water Science Center home page at http://il.water.usgs.gov.