Effects of Saltwater Intrusion on Coastal Groundwater Quality and Aquifer Sediments

Abstract

Saltwater intrusion is a major challenge in coastal regions across the globe. The present study aims to (i) understand the geochemical processes controlling coastal water chemistry, (ii) identify potential freshwater regions in saltwater-intruded areas, and (iii) evaluate the impact of periodic fluctuation of the freshwater-seawater interface on groundwater chemistry and aquifer sediments. The first two objectives were achieved through integrated geochemical, statistical, and geospatial techniques in coastal regions of Puri, India. Seasonal groundwater and surface water samples were collected and analyzed for various physicochemical parameters. The water quality parameters show wide spatial variations with limited temporal variations in the area. Geochemical processes such as seawater-freshwater mixing, ion-exchange, and sulfate reduction are found to control the coastal water chemistry. It has been calculated that just 1% mixing of seawater is sufficient to raise the TDS content of groundwater above the WHO permissible limit. Owing to high water quality index values and very high sodium and salinity hazards, around 30-47% of groundwater and most surface water samples are unsuitable for drinking and irrigation purposes. Interestingly, saline groundwater is located in inland areas and patches of fresh groundwater near the coast. Existing geomorphic features are acting as perched aquifers to store freshwater near the coast. newlineFor the third objective, conditions similar to the natural coastal system were simulated in sediment-filled columns by injecting freshwater and seawater periodically. The experiment was continued for around 1 year, and pore water samples from the columns were collected at regular intervals. The pore waters were analyzed for various physicochemical parameters, while the pre- and post- experiment column sediments were measured for elemental concentrations, grain size distribution, porosity, and permeability.