ASSESSING GROUNDWATER AGE IN CONFINED AQUIFERS FROM THE CENTRAL PAMPEAN PLAIN OF CORDOBA, ARGENTINA

In Cordoba Province, Argentina, the population uses groundwater from confined aquifer systems (CASs) for different activities. Therefore, it is necessary to carry out comprehensive studies in order to plan more sustainable use considering that groundwater renewal times can be of several thousands of years. The objective of this research is to evaluate groundwater age in confined aquifers based on hydraulic and isotopic methods. The CASs present variable extension, are multilayered and formed by thin (4-6m) sand-pebble lenses, and are linked to Neogene fluvial paleosystems. These layers are situated at different depths (120-400 m) and interbedded with thick clay strata. The interpretations made from H-2, O-18, and H-3 results and hydraulic calculations suggest that the groundwater is old. Furthermore, an age gradient was observed that increases with depth and flow direction. The C-14 ages obtained for the CASs labeled A2, C, and D were 3.6-1.1 ka BP, 10.8 ka BP, and 46.0-40.5 ka BP, respectively. These results indicate that A2 and C contain groundwater recharged during Holocene cold periods, between the Little Ice Age and the ending of the Holocene Climatic Optimum and during the last glaciation. The D CAS contains paleowater that was recharged during the Pleistocene.