Aller and 4 co-authors created a methodology in 1987 which was described that will allow the pollution potential of any hydrogeologic setting to be systematically evaluated anywhere in the United States. The system has two major portions:
- the designation of mappable units, termed hydrogeologic settings, and
- the superposition of a relative rating system called DRASTIC.
Hydrogeologic settings form the basis of the system and incorporate the major hydrogeologic factors which affect and control ground-water movement
including depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone media and hydraulic conductivity of the aquifer.
These factors, which form the acronym DRASTIC, are incorporated into a relative ranking scheme that uses a combination of weights and ratings to produce a numerical value called the DRASTIC Index.
Hydrogeologic settings are combined with DRASTIC Indexes to create units which can be graphically displayed on a map. The application of the system to 10 hydrogeologica11y variable counties resulted in maps with symbols and colors which illustrate areas of ground-water contamination vulnerability. The system optimizes the use of existing data to rank areas with respect to pollution potential to help direct investigations and resource expenditures and to
prioritize protection, monitoring and clean-up efforts.
This report was submitted in partial fulfillment of Contract No. Ck-81071S-01 by the National Water Well Association under the sponsorship of the Robert S. Kerr Environmental Research Laboratory, Ada, Oklahoma. This report covers a period from October, 1983 to March, 1987, and work was completed as of April, 1987.
The basic conceptual foundation for this system is modeled after a waste disposal site evaluation technique developed by Harry LeGrand. The geographic
framework for the presented system is developed within ground-water regions as defined by Ralph C. Heath. A special note of acknowledgement and gratitude is made to these two individuals for their inspiration and assistance in
developing this document.
In addition to the committee members, many individuals assisted in the demonstration mapping portion of the project. These individuals provided guidance in choosing ratings for DRASTIC factors, helped assemble information about the county, organized and assembled individuals for attendance at the county presentation on DRASTIC, provided vehicles for field checks, peer reviewed the pollution potential maps and participated in the field checking of
the county.
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