HYDROCHEMISTRY AND GROUNDWATER FLOW OF JEFFARA-GABES NORTH AQUIFER SYSTEM

The main aquifers (Complexe Terminal) include sand layers within Mio-Plio-Quaternary sequences and fractured bedrocks in the underlying limestones of Senonian age. The Senonian aquifer is recharges to the West by Continental Intercalaire hot groundwaters (70°C) via the El Hamma network fault N-S and NW-SE direction, then water temperatures diminish to 22°C in the Northeastern area of the basin following the groundwater flow direction. These groundwaters are saturated or even supersaturate in aragonite, calcite and dolomite. Gypsum is generally under saturation or close to saturation indicating saturation of sulphate in groundwaters. Moreover, geochemical indicate that water table with low salinity are dominated by Ca-Na-SO4 type while waters with high total dissolved salts belong to Na-(Mg)-Ca-SO4-Cl type. The latter hydrochemical facies characterizes the Continental Intercalaire. Chemical analyses supported by geological data and thermodynamic calculus prove that it exists a lateral communication between Continental Intercalaire aquifer and the Jeffara system aquifer through the El Hamma active faults. Also, the results show a mixing and an upward leakage from the Senonian aquifer to the uppermost mio-plio-quaternary reservoir via NE-SW and E-W oriented master faults.