Groundwater in southwestern Buenos Aires, Argentina: conditioning factors of the phreatic sandy aquifer for the supply to the town of Médanos

Abstract Groundwater quality and quantity are critical issues in semi-arid regions, where it often serves as the sole water source. The study area is located in the Villarino district, Buenos Aires, Argentina, featuring a dune chain with high infiltration capacity, leading to variable hydrochemical conditions. The town of Médanos relies on a phreatic aquifer within this eolian dune chain for its supply, with water quality being influenced by well location and depth, with the occasional presence of undesirable ions. This study aims to determine the hydrogeological conditions and limitants of the aquifer in the area, using well surveys, in-situ measurements, physicochemical analyses, and electrical resistivity tomographies (ERT). Results indicate a hydrochemical stratification, with low salinity water lens overlying more saline water. Groundwater conductivity varies, with lowest values in central and southwestern preferential recharge areas and higher values near discharge zones. Chloride content follows a similar pattern. Saturated thicknesses of fresh water, determined by means of ERTs, vary significantly, revealing potential paleochannels that could act as preferential zones for future wells. Analysis of existing pumping fields shows that well location and depth critically affect water yield and quality. The Mascota pumping field, with the highest fresh water saturated thickness, provides the best water quality and yield, while Las Escobas field faces issues of low yield (due to low saturated thickness) and interference among wells. This emphasizes the importance of these kind of studies for the strategic well placement and depth to improve water supply quality and sustainability for the town of Médanos.