Assessing the origin and processes controlling groundwater salinization in coastal aquifers through integrated hydrochemical, isotopic and hydrogeochemical modelling techniques

The origin of groundwater and the processes controlling its chemical composition in complex coastal aquifers are of interest, as about 44% of the world's population lives in coastal areas. Groundwater over-exploitation in the highly urbanized coastal regions has exerted pressure on these aquifers, leading to seawater intrusion. This study aimed to identify (1) the complex relationship between natural and anthropogenic factors, and (2) the hydrogeochemical processes controlling the groundwater chemistry in an over-stressed coastal aquifer of southern India. The results indicate an increase in the extent of seawater intrusion from 4 km in 1969 to 17 km in 2014. Major hydrogeochemical processes controlling the aquifers are evaporation, ion exchange and dissolution of aluminosilicates, gypsum, halites and calcites. The integrated use of field investigation with hydrochemical, isotopic and hydrogeochemical modelling techniques allowed a conceptual model of the groundwater salinization process over 46 years to be developed as a basis for designing sustainable management measures.