Assessing interactions between groundwater and surface water in a Pampean stream

In the south of Cordoba (Argentina), groundwater from the unconfined aquifer, presents scarce suitability due to high values of salts, sulfates, arsenic and fluorides. This situation makes it necessary to explore other possibilities, for example, conjunctive use of groundwater and surface water. The objective of this work was to describe the dynamic and geochemical relationships between surface water and groundwater in the medium-low basin of the Aji stream. The conceptual model was supported by the use of stable O-18/O-16 and H-2/H-1 isotopes and it was validated through numerical modeling and Rn-222 activity results. The stream water is sodium bicarbonate fresh type (460-1,400 mu S/cm). The aquifer presents fresh to salt water (720-14,000 mu S/cm), from sodium bicarbonate to sodium chloride type. The isotopic results show that there is a straight mixing line between surface water and groundwater samples. The geochemical numerical modeling revealed that in the mixing models between stream and aquifer, for hydraulically linked samples, the aquifer only provides 2% of the total stream flow. This was validated through Rn-222 results, which led us to the estimation of about 2% of groundwater supply in summer.