Implication of Hydrogeological and Hydrodynamic Setting on Water Quality of the Complex Terminal Aquifer in Kebili (Southern Tunisia): The Use of Geochemical Indicators and Modelling

Abstract The Complex Terminal Aquifer in Kebili basin (CTAK) is one of the most important deep groundwater reserves in the North West Aquifer Sahara System (NWASS). It plays a crucial role in the regional socio-economic development as it represents the main source of water supply in the region. However, the exploitation increases given rise to a grave water quality degradation and a gradual hydraulic head lowering. Using geostatistical and modelling methods and geochemical tools, this investigation aims to: (i) improve the understanding of hydrogeological structure of the aquifer through more precise maps; (ii) evaluate the quality of the CTAK groundwater and their compliance with international standards; (iii) develop an integrated hydrogeological conceptual model able to describe the hydrodynamic functioning of the aquifer. The calculated recharge and flow rates, using carbon 14 activities, are very low confirming the long residence time of CTAK groundwater. The use of quality indicators proves that 51% of the groundwater samples show poor quality for drinking purposes. In terms of agricultural activities, only 6% of waters are good to permissible for irrigation purposes, while 44% are doubtful for use. Based on this multidisciplinary analysis, the established hydrogeological conceptual model will provide a required basis for futures numerical groundwater flow models used in the management strategies under these conditions.