Geoelectric and Seismic Data acquired in the Precambrian Granite Gravel Aquifer, Llano Uplift, Central Texas, May 2017 - August 2018

This data release contains geophysical data and well and borehole driller's logs acquired at a small field site in the Llano Uplift of central Texas. The field site is underlain by the unconfined Precambrian Granite Gravel aquifer and the Precambrian Town Mountain Granite bedrock from which the Granite Gravel Aquifer was derived through chemical and mechanical weathering. The data set consists of five types of data in the quantities indicated: (1) 1 time-domain electromagnetic sounding, (2) 441 self-potential measurements, (3) 2 electrical resistivity tomography profiles, (4) 2 seismic refraction tomography profiles, and (5) 4 driller's logs (obtained from 2 wells and 2 shallow boreholes). The data were collected primarily from within a 100-meter (m) by 100-m survey area to characterize the geoelectric and seismic properties of the Granite Gravel Aquifer. Emphasis was placed upon evaluating the successes of time-domain electromagnetic sounding and seismic refraction tomography to map the water-table and bedrock depths, respectively, in the shallow subsurface. This emphasis provided the catalyst for a more extensive geophysical characterization of the aquifer to provide enough contrasting data to reduce uncertainty in the interpretations made from the electromagnetic and seismic data. Geophysical properties of the aquifer were measured and correlated to driller's logs from local wells and boreholes to interpret the water-table and bedrock depths beneath the survey area. Correlations between geophysical data and driller's logs enabled a hydrogeophysical characterization of the Granite Gravel Aquifer and Town Mountain Granite beneath the survey area at the field site.