Regional information can be used to identify potential offsite sources of contamination and to provide background information on regional geology, hydrology, surface soils, and meteorology. This information can provide insight into the complexities of the groundwater contamination and help guide future site investigations.
A regional inventory of potential offsite sources of contamination can be developed through aerial photographs, land-use maps, and field inspections. Old aerial photographs are especially useful because they may be the only means of identifying abandoned facilities such as old landfills, lagoons, and industrial facilities. Land-use maps can identify unsewered residential areas that can be a potential source of contamination, especially where organic chemical septic tank cleaners have been used. Topographic maps can identify surface drainage patterns that can carry contaminants to the plant site and recharge the underlying groundwater system.
Regional geologic reports, maps, and cross sections can provide details on the regional subsurface geology including areal extent, thickness, composition, and structure of the geological units present in the region. Regional hy-drogeologic reports can provide information on the regional groundwater flow direction and quality as well as the groundwater usage in the region. A survey of state files can reveal long-term groundwater quality problems in the general area of the plant site.
Soil maps can be used to evaluate the migration potential of contaminants through the unsaturated zone. Climatological data can be used to determine precipitation rates and patterns as well as surface runoff and ground-water recharge rates. In addition, climatological data can be used to determine evapotranspiration rates from shallow groundwater tables and their effect on the gradient and direction of groundwater.
An inventory of regional information is available from state and federal agencies such as the U.S. Geological Survey (USGS), the U.S. EPA, the U.S. Department of Agriculture (USDA), and the Soil Conservation Service (SCS). Other sources of information include computerized databases on environmental regulations and technical information on a variety of chemical compounds (Lynne et al. 1991). Examples of these databases include the Computer-Aided Environmental Legislative Data System (CELDS), which provides a collection of abstracted federal and state environmental regulations and standards; HAZARDLINE, which provides information on over 500 hazardous workplace substances as defined by the Occupational Safety and Health Administration (OSHA); and the Chemical Information System (CIS), which provides a variety of subjects related to chemistry.
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