Fresh and saline groundwater ages and flow dynamics in a perturbed coastal aquifer

Abstract Excessive freshwater pumping in coastal areas result in an inland intrusion of the saltwater wedge underlying the freshwater aquifer, leading to salinization of coastal aquifers. While multiple approaches and techniques in the form of analytical solutions, numerical simulations, mass balance calculations and laboratory experiments have been used to study the flow dynamics of the density-driven circulation of saltwater, little is known regarding the groundwater ages in coastal aquifers and the process timescales. The current study makes use of multiple age tracers such as 3H, 85Kr and 39Ar, corroborated by radium isotopes, allowing to calculate both modern and sub-modern groundwater ages. The ages derived based on the measured tracer values were compared to a numerical flow simulations. The results indicate that seawater intrusion in the Nitzanim coastal reserve (prompted by excessive freshwater pumping upstream) has a different effect on the ages of the shallow groundwaters in comparison with the deeper groundwater. Close to the shoreline (