Application of isotopic and hydrogeochemical techniques to evaluate mixing processes in groundwater systems from a coastal area in Argentina

Groundwater plays a fundamental role in supporting productive, domestic, and touristic activities in the Lobería District. In this region, two aquifers coexist: a regional aquifer (Pampeano Aquifer) and a local aquifer confined to the coastal dunes, referred to in this study as the Sand-dune Aquifer. To investigate their interaction, an End-Member Mixing Analysis (EMMA) was performed using conservative tracers, including hydrochemical data and stable water isotopes, based on measurements from 32 extraction wells. The results reveal significant groundwater exchange between the Sand-dune and Pampeano Aquifers, with notable contributions in both directions. Well G251 in the Sand-dune Aquifer receives 68% of its contribution from the Sand-dune Aquifer and 32% from the Pampeano Aquifer. Conversely, wells G1027 and G1028 in the Pampeano Aquifer have contributions of 32% and 49% from the Sand-dune Aquifer and 68% and 51% from the Pampeano Aquifer, respectively. However, stable water isotopes were ineffective as tracers for quantifying mixing due to shared recharge conditions and similar isotopic signatures. These findings enhance our understanding of groundwater interactions and provide valuable insights for the integrated management of groundwater resources.