The use of a GIS to compare the land areas captured by very basic and complex wellhead protection area models.

Geographic information systems (GIS) can be used in public health programs to better understand humans and their interactions with their environment. The Washington State Department of Health (WSDOH) estimates that over 65 percent of its citizens rely on groundwater as a source of drinking water, with some counties approaching 100 percent. In an effort to focus on groundwater protection, the department has recognized the delineation of wellhead protection areas in Whatcom County, Washington, as a proactive method for protecting the land areas around public water supply wells. At present, WSDOH accepts four methods for the delineation of these areas: 1) the calculated-fixed-radius (CFR) method, 2) the analytical method, 3) hydrogeologic mapping, and 4) the numerical flow/transport model. The objective of the study reported here was to utilize a GIS to compare the very basic CFR method with other methods in the following separate pairs for water systems in Whatcom County: CFR versus analytical method, CFR versus hydrogeologic mapping, and CFR versus numerical flow/transport modeling. Analytical, hydrogeologic, and numerical models are generally considered to be superior to the CFR model. The GIS overlay comparisons in the study, however, showed the CFR method having land capture areas that were most similar to those delineated by the more advanced hydrogeologic method and least similar to those delineated by the less advanced analytical method. The 1-, 5-, and 10-year overall comparison averages show that the CFR and hydrogeologic overlays were the most similar in each of the three study comparison areas. Similarly, the analytical method had the least similar overlays in each of the three study areas. This research further clarifies the usefulness of GIS in applying the CFR model around public supply wells for initial wellhead protection measures, especially for smaller water systems with limited funds or for larger systems as an interim protection measure. These measures can be successfully adopted by local and state public health agencies in various land use planning processes.