Groundwater resources and recharge processes in the Western Andean Front of Central Chile

Abstract

In Central Chile, the increment of withdrawals together with drought conditions has exposed the poor understandingof the regional hydrogeological system. In this study, we addressed theWestern Andean Front hydrogeology by hydrogeochemical and water stable isotope analyses of 23 springs, 10 boreholes, 5 rain-collectors and 5 leaching-rocks samples at Aconcagua Basin. From the upstream to the downstream parts of the Western Andean Front, most groundwater is HCO3-Ca and results from the dissolution of anorthite, labradorite and other silicate minerals. The Hierarchical Cluster Analysis groups the samples according to its position along the Western Andean Front and supports a clear correlation between the increasing groundwater mineralization(31–1188 μS/cm) and residence time. Through Factorial Analysis, we point that Cl, NO3, Sr and Ba concentrationsare related to agriculture practices in the Central Depression. After defining the regional meteoric water line at 33°S in Chile, water isotopes demonstrate the role of rain and snowmelt above ~2000 m asl in the recharge of groundwater. Finally, we propose an original conceptual model applicable to the entire Central Chile. During dry periods,water releases fromhigh-elevation areas infiltrate in mid-mountain gullies feeding groundwater circulation in the fractured rocks of Western Andean Front. To the downstream, mountain-block and -front processesrecharge the alluvial aquifers. Irrigation canals, conducting water from Principal Cordillera, play a significant role in the recharge of Central Depression aquifers. While groundwater in the Western Andean Front has a high-quality according to different water uses, intensive agriculture practices in the Central Depression cause an increment of hazardous elements for human-health in groundwater.