EVALUATION OF GROUNDWATER QUALITY IN THE EDWARDS AQUIFER AT NORTHWEST SAN ANTONIO, TEXAS, USING TRACE METAL AND RARE EARTH ELEMENT ABUNDANCES

Edwards Aquifer (EA) in south central Texas provides drinking water to over 2.5 million residents residing in the fast-growing San Antonio city and its surroundings. The quality of groundwater in this karst aquifer has been satisfactory so far. However, in recent years, with exponential growth in the contributing and recharge zones of the aquifer, new challenges have been posed to the aquifer quality. A few prior studies have characterized the regional groundwater quality by traditional means, such as quantifying the major ions and metals concentrations in the groundwater. This study focuses on quantifying the trace metal and rare earth element (REEs) abundances in the Edwards Aquifer’s groundwater to better understand the recharge process, the influence of host rock compositions, and anthropogenic activities on the groundwater quality under different land use patterns. Three distinct areas were selected for sampling over 2023 to cover the commercial, residential, and undeveloped land use patterns. Groundwater samples were collected from a control site at Edwards Aquifer Field Research Park (n = 21), as well as from the bore -wells in the contributing zones (n = 6) and the recharge zones (n = 6). Surface water samples (n = 30) were collected from the recharge zones for comparison to understand the recharge process in the aquifer. Field-based parameters (pH, conductivity, temperature) of the water samples were measured using a probe onsite. The concentrations of major cations, anions, trace metals, REEs, and dissolved organic carbon (DOC) were monitored in the water samples and measured using ion chromatography, inductively coupled plasma mass spectrometry, and a TOC analyzer at the University of Texas at San Antonio. Our current geochemical dataset, in conjunction with the previously published results show slight seasonal variation of major anions, cations, and temperature while conductivity and pH remained consistent. REE and trace metals were evaluated at the University of Nebraska-Lincoln via ICPMS and are in progress.