Geochemical and Isotopic Investigations to Study the Origin of Mineralization of the Coastal Aquifer of Sousse, Tunisia

In the Tunisian Sahel near one of the seaside resorts, the water quantity and quality are an even greater problem than in southern/central Tunisia. The groundwater of the Oued Laya aquifer system occurs mainly at two levels, a shallow aquifer at depths to about 60 m whose reservoir is mainly formed by Mio-Pliocene sediments (with gypsum lenses dispersed within the geological formations), and a deep aquifer situated between 100 and 250 m depth, located in the Miocene sandstone formations. The results of geochemical and isotopic studies have shown that groundwater salinity does not seem to be linked with increasing water well extraction. Rather, water mineralization seems to be acquired by dissolution of minerals in the aquifer system, especially halite and gypsum. Moreover, ion exchange processes also play an important role in groundwater mineralization. The stable isotope data do not support the hypothesis of mixing with seawater.