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Virginia Aquifer Susceptibility (VAS) graphic
   The U.S. Geological Survey (USGS), in cooperation with the Virginia Department of Health (VDH), conducted a study to determine the susceptibility of thePublic Ground-Water Supply regional aquifers in Virginia that serve as public water supplies. The information will be used to screen public ground-water supplies and identify those that require detailed source-water assessments. Over 150 sites were sampled between 1998 and 2000.

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.

Dating of groound water for source-water assessment subheading

   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.

Benefits subheading

   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 Public Ground-Water Supplysources. The Commonwealth of Virginia will be able to prioritize source-water investigations and to devote resources to water supplies that are potentially most susceptible to contamination.

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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Last update: 09/15/04 12:56