Assessment of Aquifer Mixing and Salinity Intrusion in the North-Western Sahara Aquifer System: A Hydrogeochemical Analysis- Algeria, Tunisia

Abstract

The North-Western Sahara Aquifer System is a complex multilayer leaky aquifer system providing water to Algeria, Tunisia, and Libya. Changing the hydrologic equilibrium through pumping can cause previously isolated saline water to mix with the fresh water in the pumped aquifers, resulting in increased salinity over time and, creating the potential for water-related conflict. The objective of this study is to identify areas where salinity intrusion is occurring now and could worsen in the future. To accomplish this, fourteen existing datasets were analyzed, yielding new insights into regional and local occurrences of salinity intrusion. Major ion chemistry and ratios of Br/Cl indicate that the source of salinity in the saline aquifers of the system, which intrude into the freshwater, is the dissolution of evaporates in the aquifer matrix. A complex geochemical system where due to the common ion effect gypsum dissolution sustains calcite saturation producing a water rich in Ca and SO4. Stable isotopes of oxygen and total dissolved solids were the best geochemical indicators of areas of salinity intrusion. Contour mapping of the Total Dissolved Solids and δ18O has shown that considerable aquifer mixing and salinity intrusion affect the aquifer system. At this time, five areas in the North-Western Sahara Aquifer system are subject to salinity intrusion.