Evaluating Ground Water Pollution Potential in Ohio
A ground water pollution potential mapping program for Ohio was initiated in 1986 under the direction of the Ohio Department of Natural Resources, Division of Water. The DRASTIC mapping system, developed by Aller, et al, 1987, was chosen because it allows the pollution potential of an aquifer to be evaluated systematically using existing information. Vulnerability to contamination is a combination of hydrogeologic factors, anthropogenic influences, and sources of contamination for a given area. The DRASTIC system focuses on the hydrogeologic factors that influence ground water movement.
Click here for a link to order the DRASTIC Manual by Aller, et al.
The system consists of two major elements:
1. The designation of mappable units, termed hydrogeologic settings, and
2. The superposition of a relative rating system to determine the pollution potential.
How the Mapping Begins:
Hydrogeologic settings form the basis of the system and incorporate the major hydrogeologic factors that affect and control ground water movement and occurrence. These seven factors are:
Depth to Water
Impact of the Vadose Zone Media
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 ground water pollution potential index. Hydrogeologic settings are combined with the pollution potential indexes to create units that can be graphically displayed on a map. A report accompanies each map that includes general geologic and hydrogeologic information and describes the mapping process used to determine the ground water pollution potential of areas in the county.
Mapping the Results:
Demonstration mapping using the DRASTIC system in Madison County, Ohio, resulted in a map with symbols and colors which illustrate areas of ground water contamination vulnerability. The mapping program has been implemented on a county-wide basis across the state according to specific selection criteria. These criteria include the availability of basic geologic and hydrogeologic information, a completed, digitized soil survey, and adequately field located water well logs.
Applications of Pollution Potential Maps:
The ground water pollution potential mapping program optimizes the use of existing data to rank areas with respect to relative vulnerability to contamination from the surface. Ground water pollution potential maps may be used to assist planners, managers, and local officials in evaluating the potential for contamination from various sources of pollution. This information can be used to help direct resources and land use activities to appropriate areas, or to assist in protection, monitoring and clean-up efforts.
Example of a DRASTIC hydrogeologic setting.
This setting is 7D Buried Valley. Hydrogeologic settings describe areas of common geologic and ground water characteristics that directly affect the vulnerability of an aquifer to contamination from the surface.