Hydrodynamic groundwater modeling and hydrochemical conceptualization of the mining area of Moulares Redeyef (southwestern of Tunisia): New local insights

Abstract

The Moulares Redeyef Mining basin (MMR-B) is located on Southwestern of Tunisia. The problem of groundwater mineralization in this basin has long been attributed to the significant decline in groundwater reserves. In order to quantify the aquifers reserves and identify processes and factors governing the groundwater quality, a detailed multidisciplinary study was proposed in this study. The approach used various GIS databases, including hydrodynamic characteristics, geochemistry, geology and climatic parameters. A Modflow hydrodynamic model was developed over 67-year modeling period (1953–2020) and many simulations were performed. Water samples were collected from 39 boreholes from the deep aquifer and 13 wells from the superficial aquifer in Tabeddit area. The hydrogeological model shows a flow convergence zone around the Tabeddit area. The reserve of the aquifer system was simulated to 10 Mm3/year for 2020, while it was 26 Mm3/year in 2000. Yet, 61% of exploitable reserves was consumed in 20 years. The quality of groundwater showed that MMR-b is characterized by 4 main trends: Ca–Mg–HCO3, Ca–Mg–SO4, Na–Cl–NO3 and Na–Mg–HCO3. For the heavy metals, the 13 alluvial groundwater samples contain high concentration of Cadmium that exceed the Tunisian Standards. Finally, a Risk Index of Aquifer is elaborated based on the Modflow model and the geochemical quality. The index gives that the PQ layer is under very high risk and the M aquifer is in a moderate situation. Accordingly, it is recommended that the mining deciders revise their exploitation strategy urgently in order to preserve water resources for future use.