Hydrogeophysical Characterization of Karstic Limestone Within the Valley and Ridge Province at the Dickinson College Farm

With a changing global climate, it is increasingly important to understand and characterize Earth's groundwater resources, especially karst aquifers that supply groundwater to roughly 25% of Earth's population. Groundwater, specifically in karst systems, flows within spatially heterogeneous pore space. Geophysical methods such as electrical resistivity, seismic refraction, ground-penetrating radar, and borehole geophysics can help inform understanding of flow patterns across karst landscapes. Here we present a hydrogeophysical characterization of the karst system at Dickinson College Farm in Carlisle, PA. The Dickinson College Farm lies within a limestone valley in the valley and ridge province in Appalachia whose lands are dominated by agribusiness. The Dickinson College Farm sources its irrigation water from five wells that were drilled in 1996 and have been characterized by downhole methods that describe lithology, resistivity, temperature, diameter, and natural gamma radiation. One drill site was also cored and described in detail. The well field is cored into the Elbrook Formation, a Cambrian formation composed of argillaceous limestone, shale, calcareous shale, dolomite, siltstone, and calcareous sandstone, with limestone as the dominant lithology in our study area. Here we combine indirect geophysical methods with the direct observations from boreholes including pump tests, cores, and geophysical well logs. Our preliminary results indicate void spacings in the strata that are possible flow paths from aquifers to the well sites. These depths correspond to decreases in resistivity. These spacings occur between 80ft-100ft and 100ft-120ft deep in each well. We will present results from complementary seismic surveys and GPR which further investigate water table depth as well as from a slug test that further characterizes the near-well aquifer characteristics of void spacings and low resistivities.