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Zeuss-Koutine aquifer, located in southeastern Tunisia, has been used intensively as a primary source to meet the growing needs of the various sectors. Detailed knowledge of the geochemical evolution of groundwater and water quality can enhance understanding of the hydrochemical system, promoting sustainable development and effective management of groundwater resources. To this end, a hydrochemical and statistical investigation was conducted. Groundwater samples have been collected from 13 wells from 1995 to 2005; to understand the sources of dissolved ions and assess the chemical quality of the groundwater. Results demonstrate that among the cations, only the mean concentrations of Na( + ) exceed guideline values set by the World Health Organization (WHO). Regarding the analyzed anions, the concentration of SO(2-)(4) and Cl( - ) are above the WHO allowable concentrations. Total dissolved solids in most groundwater samples are greater than 1,000 mg l(-1), the limit set by the WHO, indicating slightly saline or moderately saline water. In general, a significant increase in the degree of water mineralization was observed in the direction of southwest to northeast following the regional flow direction. Calculated saturation indices show that all water samples were oversaturated with respect to aragonite, calcite, and dolomite, and undersaturated with respect to anhydrite, gypsum, and halite. Based on hydrochemical facies, two types of water predominate in the study area. The first is Ca-Na-SO(4)-Cl in type and located in the southwest which corresponds to the recharge part of the aquifer. The second type is Na-Ca-Cl-SO(4) and located in the east, which corresponds to the discharge part.

Coastal aquifers are at threat of salinization in most parts of the world. This study was carried out in coastal shallow aquifers of Aousja-Ghar El Melh and Kalâat el Andalous, northeastern of Tunisia with an objective to identify sources and processes of groundwater salinization. Groundwater samples were collected from 42 shallow dug wells during July and September 2007. Chemical parameters such as Na(+), Ca(2+), Mg(2+), K(+), Cl(-), SO4 (2-), HCO3 (-), NO3 (-), Br(-), and F(-) were analyzed. The combination of hydrogeochemical, statistical, and GIS approaches was used to understand and to identify the main sources of salinization and contamination of these shallow coastal aquifers as follows: (i) water-rock interaction, (ii) evapotranspiration, (iii) saltwater is started to intrude before 1972 and it is still intruding continuously, (iv) irrigation return flow, (v) sea aerosol spray, and finally, (vi) agricultural fertilizers. During 2005/2006, the overexploitation of the renewable water resources of aquifers caused saline water intrusion. In 2007, the freshening of a brackish-saline groundwater occurred under natural recharge conditions by Ca-HCO3 meteoric freshwater. The cationic exchange processes are occurred at fresh-saline interfaces of mixtures along the hydraulic gradient. The sulfate reduction process and the neo-formation of clays minerals characterize the hypersaline coastal Sebkha environments. Evaporation tends to increase the concentrations of solutes in groundwater from the recharge areas to the discharge areas and leads to precipitate carbonate and sulfate minerals.

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