Hydrogeological and Isotopic Assessment of the Pampeano Aquifer and the Balcarce Formation in the Southern Periurban Area of Mar del Plata

Abstract

The southern periurban sector of Mar del Plata relies on the Pampeano aquifer for domestic water supply, although its limited saturated thickness and increasing demand have encouraged the drilling of the Balcarce Formation as a potential complementary source. This study characterizes both units by integrating hydrochemical and isotopic analyses, pumping tests, and numerical groundwater modeling to evaluate their hydraulic behavior and exploitation potential. Three wells were surveyed: two screened in the Pampeano aquifer and one completed in the fractured quartzitic bedrock of the Balcarce Formation. Hydrochemical data indicate similar sodium-bicarbonate facies in both units, although the Balcarce well exhibits higher electrical conductivity and chloride values, suggesting longer residence times or slower circulation. Stable isotope compositions show a shared meteoric origin and reveal vertical connectivity controlled by fractures. Pumping tests demonstrate contrasting hydraulic responses: the Pampeano aquifer shows transmissivity and recovery rates consistent with a detrital, unconfined system capable of sustaining typical domestic yields, whereas the Balcarce Formation displays low transmissivity, rapid drawdown, and slow recovery, reflecting strong dependence on the continuity of fractures. A calibrated numerical model reproduced the dominant influence of a nearby wetland as the main discharge area and showed that distributing pumping between two wells significantly reduces drawdown compared to extraction from a single well. The results indicate that the Balcarce Formation does not behave as an independent aquifer but rather as a secondary reservoir recharged by downward flow from the Pampeano aquifer. Sustainable groundwater management in the area requires distributed extraction, protection of recharge zones, and regular monitoring of groundwater levels and quality.