A comparison of wellhead protection area delineation methods for public drinking water systems in Whatcom county,...

Groundwater protection is a critical issue on a global scale. A relatively recent strategy for reducing the potential for contamination has been to establish wellhead protection areas on the land surface above aquifers. One method of delineating groundwater flow around public supply wells is the calculated-fixed-radius (CFR) method. The purpose of this study was, with a geographic information system (GIS), to create spatial-data overlays based on CFRs and to compare the areas captured with the results of more complex methods (i.e., analytical methods, hydrogeologic mapping, and numerical flow/transport models). The overlays showed that as distance from the well decreased, the areas captured by the CFRs became more similar to those captured by the noncircular (more complex) methods. In the one-year overlay, only 20 percent of the noncircular areas were not captured by the CFR method, while 42 percent were not captured in the 10-year overlay. The one-year CFR had a 57 percent overcapture area outside the noncircular area, while the 10-year over-captured was very high, at 75 percent. Study results indicate that local health departments can successfully incorporate both existing formal wellhead protection areas and CFRs into various land use permitting processes, with emphasis placed on six-month and one-year time-of-travel areas. Where time, money, and personnel are limited, the CFR method is an effective starting point for improved protection of groundwater quality.