Hydrogeochemical characterization of the Continental Intercalaire aquifer (southern Tunisia)

The study of the Continental Intercalaire aquifer system of southern Tunisia, based on the interpretation of geochemical ( major elements) and isotopic ((18)O, (2)H, (13)C and (14)C) data, has aided the understanding of the hydrodynamics of this multi-layer aquifer system, which is greatly influenced by tectonics. The determination of the origin of groundwater salinization and the understanding of the hydrogeological and geochemical behaviour of this aquifer were achieved by studying the correlation between the major elements and total mineralization (TDS). By using isotopic tools, it was shown that the water of this aquifer has been recharged under cooler, palaeoclimatic conditions. The technique also made it possible to better understand the hydrodynamic functioning of the aquifer system: it showed that the relatively recent recharge of the aquifer has been by direct infiltration from carbonate and sandy outcrops of the Cretaceous and Miocene, respectively, located in the eastern and northeastern parts of the aquifer. The (18)O content was used to calculate the altitude of recharge basins. The isotopic gradient defined in this study is -0.5 delta(18)O %/100 m.