| Contents Notes |
Methods commonly used to delineate protection zones for water-supply wells are often not directly applicable for springs. This investigation focuses on the use of hydrogeologic mapping methods to identify physical and hydrologic features that control ground-water flow to springs to aid in delineating springhead protection zones. Two public-supply springs were selected as study sites to represent diversegeologic settings. One spring discharges from fractured dolomite and one from fractures siltstone, sandstone, and shale. Hydrogeologic mapping techniques, as applied in this study, are methods for mapping geologic or hydrologic features or geophysical/geochemical signatures of subsurface features. These data are often supplemented with information from subsurface investigations to aid in extrapolating surface results to aquifer depths. In this investigation, geologic mapping, fracture-trace analysis, topographic analysis, catchment area estimation, geochemical characterization, elemental isotope studies, and a tracer study were used to locate and describe potential ground-water flow boundaries and pathways and develop conceptual models for site hydrogeology. Results were integrated to estimate the zones of contribution to each spring and evaluated for use in the delineation of potential protection zones. Data from borings and hydraulic tests supported this characterization by providing direct and indirect information regarding susurface lithology and hydraulic parameters. In these case studies, results of hydrogeologic mapping allowed development of the conceptual model for site hydrology and evaluation of potential ground-water flow controls. Although definitive ground-water flow boundaries suitable for delineation of practicable protection zones could not be identified at either site, these techniques provided sufficient information to support an initial evaluation of potential protection zones. These results would also serve as a strong basis for additional investigations if more detailed or reliable delineations were warrented. |
