Characterization of hydrogeological processes of karst-influenced multi-layered aquifers of basin edge using statistical and geochemical approaches (northern Aquitaine basin, France)

This study aims to characterize the regional hydrodynamic and hydrochemical variability of multi-layer carbonate aquifers of basin edge by considering their karst feature. The study area is the northern edge Aquitaine Basin in Southwest France, which is characterized by two main Upper Cretaceous and Jurassic reservoirs. A dataset of water levels and physico-chemical analyses in 65 springs/shallow wells and 94 boreholes was collected from French public database. A statistical approach was conducted in order to differentiate aquifer compartments in relation with their hydrogeological context. First results show a contrasted physico-chemical signature between Jurassic and Upper Cretaceous aquifers, which is explained by the lithological properties, the aquifer depth and the residence time. Nevertheless, some locations present temperature and hydrochemical anomalies. Likely hypothesis are the karst influence due to localized recharge from fast river losses, as well as the karstification degree in unconfined and confined compartments.