APPLICATION OF 2D AND PSEUDO-3D ELECTRICAL RESISTIVITY TOMOGRAPHY IN CHARACTERIZING SUBSURFACE PREFERENTIAL PATHWAYS IN KARST AQUIFERS

The management of karst aquifers requires extensive knowledge of subsurface preferential groundwater pathways such as fractures and conduits. These heterogenous karstic conduits can cause groundwater flow to vary in magnitude and direction and may also favor contaminant transport in the karst system. Furthermore, because of the complex nature of the subsurface dissolution in karst terrain, the connectivity of these conduits is usually unknown and challenging to assess. Therefore, to improve understanding of subsurface pathway connectivity in karst aquifers, this study integrated Lidar data with 2D and 3D Electrical Resistivity Tomography on two sites in the Northern Segment of the Edward Balcones Fault Zone (BFZ) Aquifer. The first site is located within the springshed of Robertson Spring located adjacent to an urbanized area along Interstate Highway 35 in Bell County, Texas. Because the spring serves as habitat for a federally threatened species (Eurycea chisholmensis), there are concerns about spring protection and its recharge pathways. The second location is an Archeological Site where results from a pumping test suggested the well intercepted a void near the water table. However, the extent and orientation of the void and its connection to nearby springs is unknown. The combination of these methodologies is used to investigate the connectivity of conduits serving as preferential flowpaths and emphasis is placed on using Electrical Resistivity Tomography to determine the location, extension, alignment, proximity, continuity, and dip direction of low-resistivity conduit zones at these two sites. Since this research is the first attempt at using a geophysical technique to characterize the preferential groundwater flow path at the two sites, the result from this study is important to water resource managers, and agencies tasked with managing karst aquifers and their springs sustainably.