Assessment of groundwater salinization using PEST and sensitivity analysis: case of Zeuss-Koutine and Mio-Plio-Quaternary aquifers

Groundwater is the main source of water in arid regions. In the Southeast of Tunisia, Zeuss-Koutine and Mio-Plio-Quaternary underflow aquifers of Jeffara plain are considered the main source of water supply for drinking, agriculture, and industry. The study area is characterized with several known groundwater pollution sources (industrial and wastewater effluents, domestic wastes, etc.). This paper explains how sensitivity analysis can be useful tools in risk assessment of groundwater salinization. The main concern is whether the contamination sources threaten the drinking and irrigation water wells of the area. The groundwater flow and transport model of salts is set up to answer this question using MODFLOW, MT3DMS, and PEST tools. The preliminary results of the model are associated with large uncertainty. Thus, the effect of boundary conditions, dispersivity and porosity, on the migration of pollutants was investigated to estimate this uncertainty and build confidence in the model results. All variables and parameters were given a value from a range of realistic values. The sensitivity analyses show that the model is more sensitive to the salinity of the infiltrated water and the dispersivity. The results showed that the salinization process affects the areas close to the Mediterranean Sea and the Sebkha of Oum Zessar. The recharge areas have the low salinity values ranging from 1 to 2.5 g/l. High salinity reaching 3 g/l in the southeast of the Zeuss-Koutine aquifer is due to the inflow from the Triassic aquifer through Tajra fault.