Application and comparison of EPA wellhead protection delineation methods for karst aquifers, Centre County, Pennsylvania

Five out of six USEPA recommended wellhead delineation methods, i.e., arbitrary fixed radius, calculated fixed radius, analytical, hydrogeologic mapping, and numerical flow/transport and the DRASTIC models were used to define groundwater quality protection zones for unconfined karst aquifers within Nittany Valley, near State College, Pennsylvania.;The arbitrary fixed radius and three calculated fixed radius methods tend to overprotect the downgradient and lateral areas when compared to the adequately delineated upgradient protection area. Use of the analytical method results in a better resolution than either the arbitrary fixed radius or calculated fixed radius method. The analytical method does not account for the anisotropic properties of the karst aquifers. The hydrogeologic mapping method combined with the upgradient extent should provide a conservative result but less favored to be overprotective of the lateral area defined by groundwater divides.;Numerical model results show the delineated WHPA, with one year of travel time and average 5% aquifer porosity in the Big Hollow area, is a narrow, elongate shape due to a fast flow field that exists in the wellfield area. A buffer zone to widen the lateral extent to 1,000 feet would be prudent to ensure added protection of groundwater quality. DRASTIC model shows potential pollution is most likely to occur along stream areas where the groundwater is located closer to land surface.;The spatial distribution of calibrated hydraulic conductivity values in the modeled area range from 10;Particle forward tracking analyses show that groundwater within Penn State's Gameland wastewater treatment area will flow much faster than within Penn State's Radio Astronomy wastewater treatment area in the downgradient direction. Chemical transport modeling results show that the downgradient area of the Gameland wastewater treatment site will received a significant annual nitrate loading assuming that nitrate loading rates are maintained in steady state for 18 years.;Pollution vulnerability mapping combined with flow boundary definition should provide a useful tool for defining pollution potential of a given area, verifying these concepts and for management purpose. Among the five delineation methods, hydrogeologic mapping and numerical flow/transport models should be the two best methods for WHPA delineation for the unconfined karst aquifers in the study area.