Projects

Source Water Assessments at the Indiana Geological Survey

Overview by Denver Harper and Sally Letsinger

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The Safe Drinking Water Act Amendments of 1996 require that states identify the areas that are sources of public drinking water, assess the susceptibility of water-supply systems to contamination, and inform the public of the results. This program is referred to as the "Source Water Assessment Program" (SWAP).

The U.S. Environmental Protection Agency (EPA) permits the various states to conduct different types and levels of assessments for different types of Public Water Systems (PWSs). Personnel of the Office of Water Quality of the Indiana Department of Environmental Management (IDEM) have selected the Indiana Geological Survey (IGS) to conduct assessments for non-community, non-transient PWSs. These include approximately 650 schools, churches, and businesses whose water supplies are derived from ground-water wells that regularly serve at least 25 of the same individuals over 6 months per year.

The Indiana Geological Survey will develop a fact sheet for each individual PWS. The assessment will include a thorough hydrogeologic analysis of the area surrounding each water supply and an inventory of all possible contaminant sources in the area. Emphasis will be placed on an evaluation of source water susceptibility to potential sources of contamination. Explanatory materials will be developed to explain the sources of data and other technical information concerning SWAP. The explanatory materials and individual fact sheets will be provided in both digital form (to be posted on a web site) and as paper pamphlets.

Each fact sheet will discuss the importance of ground water and briefly describe the source water and hydrogeologic setting. Following guidelines provided by IDEM, source water susceptibility will be assessed on the basis of the hydrogeologic sensitivity of the area in which the well field is installed and the occurrence or nonoccurrence of any contaminants of concern in the area. Hydrogeologic sensitivity will be evaluated in two ways: (1) by estimating the time required for water to flow vertically through the unsaturated zone to the water table, and (2) by delineation of areas within the saturated zone through which water may be expected to flow horizontally during a five-year period. The data used for these estimates and delineations will include pumping data and lithologic descriptions from water wells. For each water supply, a diagram (see example below) will show the local hydrogeology based on 20 to 30 lithologic logs extracted from the edited Water Well Data Base of the Indiana Department of Natural Resources (IDNR).

Source water vulnerability will be assessed on the basis of whether contaminants of concern (as defined by the EPA), particularly point sources such as buried tanks, occur within an area of concern (i.e., within a 3,000-foot radius of the targeted system). Locations of potential contaminant sources will be derived from state and federal data sources such as Envirofacts and the Facility Index System (FINDS) Data Base. A map (see example below) will show modeled five-year capture zones for: (1) a heterogeneous aquifer, and (2) for an assumed homogeneous sand aquifer. The map will also show land use in the area and the locations of any potential point sources of contamination within the area of concern.

The project is sponsored by the Indiana Department of Environmental Management (IDEM). The term of this ongoing project is from March 2001 to March 2003.

For additional information about this project, contact Sally Letsinger (e-mail: sletsing@indiana.edu) at the Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47405