Influence of pumping saline groundwater on land-sourced solute transport in coastal aquifers

Coastal aquifers serve as key conduits for land-sourced solutes released into the ocean, impacting coastal water quality and ecology. Saline groundwater (SGW) pumping, or negative hydraulic barriers, is widely used to mitigate seawater intrusion (SWI) and alter groundwater behavior, but its effect on land-sourced solute fate is unclear. This study investigated the mechanisms of SGW pumping on land-sourced solute migration, using a variable-density, multi-species transport model to optimize SGW pumping design for SWI control and pollutant reduction. Findings indicate that SGW pumping, while effective in controlling SWI, increased the depth and area of land-sourced solute plumes by redirecting their migration downward to the well. This resulted in a broader dispersion zone near the well and a 13% increase in solute residence time compared to non-pumping conditions. Lower pumping rates and reduced distances between the well and sea boundary further intensified solute accumulation in coastal areas. Sensitivity analysis revealed that dispersivity primarily affected solute enrichment, while hydraulic conductivity had a greater influence on residence time. These findings provide valuable insights for SGW pumping design aimed at balancing SWI mitigation and reducing land-sourced pollutant buildup in coastal aquifers.