Geology and Structure of the University of Texas at San Antonio Campus Within the Balcones Fault Zone and Edwards Aquifer Recharge Zone in Bexar County, Texas




Harwick, Heidi E.

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This project is a study of the University of Texas at San Antonio (UTSA) campus, which lies within the Balcones Fault Zone and the Edwards Aquifer. It used integrated methods to gather data using geographic information systems (GIS), geological mapping, well information, and geophysical methods to characterize the structural geology that governs the water flow into the aquifer. This case study provides information on recharge pathways into the aquifer, as well as showing how integrated methods can more effectively describe a study area's hydrogeology using combined geoscientific tools and methods. This study used electrical resistivity, electromagnetic, and ground penetrating radar near surface geophysical methods plus field mapping and GIS to determine the structural framework and stratigraphy of the UTSA campus. It was found that the study area contains four fault blocks separated by three faults, with a central fault block tilting to the southwest that constitutes a relay ramp. Karst features are present in outcropped area of the Person Formation of the Edwards Group. They also act as point recharge features on the northern portion of the campus and play an important role in groundwater flow. Fractures are present throughout the Person Formation with orientations consistent with Balcones faulting and provide avenues for water infiltration. Groundwater recharges through the Edwards rocks in the recharge zone in the northern campus, with a large amount of recharge occurring through fractured streambeds. Groundwater travels from the surface to the aquifer through solution features and fractures, along faults, or along the relay ramp between faults. In the southeastern portion of campus, in the contributing zone where the upper confining zone outcrops, water travels overland into streams contributing to Leon Creek.


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Edwards Aquifer, Groundwater, Integrated methods, Karst, Geographic information systems