Seawater intrusion and associated processes: Case of the Korba aquifer (Cap-Bon, Tunisia)

It has been established that intensive agricultural activities, usually, increase the risk of groundwater quality degradation through high groundwater pumping rates. In fact, the uncontrolled groundwater extraction causes a modification of natural flow systems and induces seawater intrusion from the coast and causes the groundwater quality deterioration. The Korba aquifer is located in the North-East of Tunisia, where a semi-arid Mediterranean climate prevails. The dry season is pronounced and this aggravates the situation, given that the highest water demand usually coincides with the drought period (dry weather conditions). The principal aim of this study is to characterize the hydrochemistry of this coastal aquifer, identifying the main processes that occur in the system, and to determine the extent of marine intrusion in the aquifer. In order to achieve this aim, geophysical and chemical parameters were measured, such as vertical electrical soundings (VES), electrical conductivity, pH, temperature, anions and cations concentrations. The analytical results obtained in the hydrochemistry study were interpreted using ion correlations with chloride and SO42-/Cl− and Mg2+/Ca2+ ratios, in conjunction with calculations of the ionic deviations and the saturation indexes. Saturation indexes are calculated with the PHREEQC 2.8 software used for mineral saturation modelling of the aquifer seawater-freshwater mixture. The high groundwater salinity anomaly observed in Diar El Hajjej, Garaet Sassi and Takelsa-Korba zones was explained by the presence of seawater intrusion in these areas. This hypothesis is based on high chloride concentrations, the inverse cation exchange reactions, and the lower piezometric level compared to sea level.