Geochemical Evolution of Coastal Groundwater in Eastern Saudi Arabia: Insights from Lab-Scale Experiment and Inverse Geochemical Modeling

Abstract The study aims to understand the geochemical evolution of coastal groundwater in the eastern coastal region of Saudi Arabia using integrated lab-scale experimental and inverse geochemical modeling. The primary focus is on the geochemical processes occurring during seawater-groundwater mixing with emphasis on mineral dissolution/precipitation, cation exchange, adsorption, and trace element mobilization. 3D lab-scale physical experiments were carried out to simulate seawater intrusion in coastal aquifers using local aquifer materials, groundwater, and seawater. The lab experiments were conducted under various hydrogeological conditions and variable control factors to simulate groundwater dynamics in sandy coastal aquifers impacted by seawater intrusion. Post-experiment advanced geochemical analysis was performed to describe the chemical change of groundwater characteristics during seawater intrusion. Inverse geochemical modeling was performed to identify the geochemical processes that controlled the water chemistry during the seawater intrusion experiment. The lab experiment data were used to validate geochemical models. The integrated lab-scale experiment and inverse geochemical modeling reveal that the seawater intrusion in coastal aquifers has significantly impacted the groundwater quality through increasing salinity and trace element mobilization. The study showed that significant changes in groundwater quality occurred during low pumping and no recharge scenarios within high seawater mixing zones. The validated geochemical model offers a reliable prediction tool for groundwater quality under different hydrogeological scenarios. The study results underscore the importance of integrated lab experiments and modeling approaches to improve the understanding of seawater intrusion's impact on the geochemical evolution of coastal aquifers in arid regions.