Potential of mixed hydraulic barriers to remediate seawater intrusion.

Remediation measures are crucial to prevent or reverse seawater intrusion deteriorating coastal fresh groundwater resources. The mixed hydraulic barrier approach, as a combination of positive and negative hydraulic barriers, holds promising advantages especially for arid areas because extracted water provides a resource for injection after treatment. However, transient remediation mechanisms and impact of parameters are still unsatisfyingly understood. Therefore, the feasibility and optimal management of mixed hydraulic barriers as well as a comparison to single positive and negative barriers are explored with a synthetic 2D variable-density model of an already salinated, unconfined coastal aquifer using SEAWAT and FloPy. The hydraulic conductivity, porosity, injection and extraction rate, barrier locations, injection salt concentration, and reduction of pumping stress are varied jointly to determine the parameters' impact and interdependencies. The hydraulic conductivity controls the overall remediation potential as a hydrogeological component. Reduced inland abstractions of supply wells and the injection rates of the positive barrier show the largest remediation effects. However, locating the positive barrier within the salt wedge poses the risk of trapping salt landside. A sole negative barrier did not improve remediation substantially. This study thus shows that remediation with mixed hydraulic barriers can be feasible if implemented according to local conditions.