Effects of management policies, including artificial recharge, on salinization in a sloping aquifer: The Israeli Coastal Aquifer case

[1] Overexploitation of aquifers may impair groundwater quality and cause salinization, as occurs in the sloping Coastal Aquifer in Israel. The current management policy risks the future of the aquifer as the country's most important water reservoir. The paper examines a variety of policies and studies their impact on the salinization of the aquifer. Two quantitative approaches were applied: ( 1) a balance approach which was used to calculate the mean salinity of the aquifer water and (2) a 2-D numerical solution of the flow and transport equations in a 10 x 15 km cell representing a portion of the aquifer. The policy alternatives include desalination of imported freshwater ( 180 - 250 ppm Cl-), desalination of treated wastewater, and injection of the desalinated water. An increased pumping from the aquifer compensates for the injection of these waters. The results show that desalination of imported freshwater or wastewater with no injection would reduce the salinization rate of the aquifer only slightly, and that the effect would be noticeable only after a period corresponding to the retention time of the vadose zone. The alternatives that involve injection of desalinated water would stop the salinization process; the aquifer mean salinity would stabilize around the level that prevailed at the time of implementation of the injection policy. The numerical solution confirmed the conclusions of the balance approach while including the complex effect of the high-salinity boundary condition on the east and the role of thickness variations in a sloping aquifer. This approach addressed the influence of the spatial densities of pumping and of injection and showed that as the density increases, the numerical and balance solutions converge. It is shown that the numerical simulation should be used for future planning of the injection and pumping layout. Finally, calculations based on our results show that the alternatives involving injection of desalinated freshwater provide the lowest cost of improving the aquifer water salinity.