Study of Rejim Maatoug groundwater in southern Tunisia using isotope methods

The Rejim Maatoug aquifer, which located in south-western Tunisia, constitutes a good example of overexploited resources. Hydrogeological and geochemical data were examined to determine the main factors and mechanisms controlling the groundwater chemistry and the hydrodynamic functioning of this aquifer based on a multi-tracer approach. Thirty-one groundwater samples from the CT Miocene aquifer of Rejim Maatoug and Djerid regions were collected in 2010 for major chemical element analysis. Physical parameters such as temperature, pH and electrical conductivity (EC) were measured in the field. Three groundwater samples were selected for 14C measurements. Four groundwater samples were chosen for 3H measurements. The chemical data indicates that dissolution of evaporate minerals, evaporation and cation exchange processes seem to be the main factors controlling groundwater mineralization. The geological and hydrogeological studies show the important role of the deep existing faults in controlling the hydrodynamic functioning of the aquifer systems in southern Tunisia. The isotopic data shows that groundwater in this area is a mixture of recent shallow waters located in the Mio-Plio-Quaternary sands and paleo-deep waters of the carbonate Senonian aquifer. Low 3H and 14C contents, observed in some sampled wells (3H = 0.15 TU in C1N1, 14C = 8.8 pmc in Matr2), indicates that the recharge of the Miocene aquifer occurs mainly through upflow leakage of Senonian deep aquifer while there is no evidence of significant recharge in major part of the plain and mountains piedmonts that can be observed.