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The U.S. Geological Survey (USGS),
in cooperation with the Virginia Department of Health (VDH), conducted a study to determine the susceptibility of
the![]() The Safe Drinking Water Act (SDWA) Amendments of 1996 require the Commonwealth to develop and implement a comprehensive Source Water Assessment Program (SWAP). The VAS study is part of the Commonwealth's SWAP, which is coordinated by the VDH, Division of Water Supply Engineering. |
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The fundamental premise of the USGS study was to use age determinations as a guide for the classification of areas in terms of the susceptibility of ground water to near-surface contamination. Various environmental isotopes and tracers were used to determine the apparent age of ground water. Chlorofluorocarbons (CFC's, Freon), tritium (a product of above ground thermonuclear weapons testing), tritium/helium, and sulfur hexafluoride (SF6) techniques were used to date ground water that is less than 60 years old. Carbon-14 was used to date ground water that is older than 1,000 years. The average temperature of ground water at the time of recharge, which is used in the age-determination techniques, was estimated from analysis of dissolved gas samples. |
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The results of the VAS study will
allow the streamlining and focusing of the Source Water Assessment
program on public water supply systems that have the greatest susceptibility to contamination from near surface The apparent ages of ground water provided by the VAS study will greatly enhance the current understanding of Virginia's regional aquifer systems and will result in improved management of the Commonwealth's public water supplies.
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Last Updated on 2/4/2002 By David L. Nelms |
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Contact:
GS-W-VArmd_webmaster@usgs.gov
U.S. Department of
Interior, U.S. Geological Survey
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Last update: 09/15/04 12:56