Résumé
Groundwater plays a dominant role in the eco-environmental protection of arid/semi-arid areas, on which depends human geo-economic development and survival. Recent environmental changes and anthropogenic impact render groundwater severely vulnerable. Groundwater in Grombalia region, NE Tunisia, is facing a similar situation. This study aims to investigate the hydrogeochemical processes that control the groundwater quality. Various graphical plots and statistical analyses have been carried out using chemical data to deduce a hydrochemical evaluation of both the shallow and deep aquifer based on the ionic constituents, water types, hydrochemical facies and factors controlling groundwater quality. According to these methods, it has been demonstrated that the high groundwater salinity is due to the water/rock interaction, the effect of the irrigation return flow, the industrial discharges influence and the salted water seepage below Sebkhat El Maleh. Furthermore, the high groundwater salinity (5814 mg/l) observed in coastal fringe is explained by intense agricultural irrigation activities, sea spray aerosols and diffusion from sea salt toward shallow fresh water. These processes of salinity are justified by the high chloride concentrations, the HFE-D diagram, the presence of reverse ionic exchange reactions and a sodium chloride facies. The freshwater-saltwater mixture is highly modified by geochemical interactions: precipitation/dissolution phenomena and cation exchange. Overall, the findings indicate that the groundwater resources quality of the Grombalia Basin are highly impacted by natural and anthropogenic constraints and require adequate intervention by decision-makers in terms of management and protection of groundwater resources to ensure their sustainability.