Data for karst groundwater vulnerability determined by modeled age and residence time tracers

Groundwater samples collected from the Edwards aquifer in south-central Texas were analyzed for water-quality data to assess aquifer susceptibility to contaminants. Water-quality data included environmental tracers of groundwater age (tritium, tritiogenic helium-3, sulfur hexafluoride, carbon-14, and radiogenic helium-4), calibrated to lumped parameter models (LPMs). Groundwater samples were collected from monitoring wells, domestic-supply wells, and public-supply wells during 2017 and 2018. This data release includes seven tables detailing these data. The final estimates for mean groundwater ages determined for samples from 65 wells ranged from 4 years to 45,400 years, with a median of 25 years. Table 1 provides site information and ancillary data for the wells and sample locations, and summarizes water-quality and mean groundwater age data. Sixty-five wells were sampled for environmental age tracers and a suite of other water-quality constituents; an additional twenty-one wells were sampled for water-quality constituents that did not include environmental age tracers. Tables 2 through 5 provide results in support of mean groundwater ages shown in Table 1. Table 2 reports detailed results for the calibration of dissolved gas models. Calibrated dissolved gas models provide the optimal water temperature, excess air, entrapped air, fractionation of gases, and excess nitrogen gas that explain the measured dissolved gases in a sample. Table 3 reports measured concentrations and the detailed calculations of environmental tracer concentrations derived from the dissolved gas modeling results in Table 2. Table 4 details calibrated lumped parameter models that provide the optimal mean age and mixing parameter(s) used to compute the distribution of ages based on the tracer concentrations in a sample. Table 5 reports data for carbon-14 corrections caused by dissolution of carbonate minerals in the soil and saturated zone; dilution of the carbon-14 atmospheric record was inferred from modern groundwater samples. In addition to these five tables, two ancillary tables (Tables 6 and 7) are included to provide more detailed information about the fields and the abbreviations used in tables 1-5. For more information about the data collection and interpretation, please refer to the process steps provided in this metadata (xml) file and citations therein.