Seasonal Variations of Groundwater Geochemistry in Coastal Aquifers, Pondicherry Region, South India

Abstract The overdrafting of groundwater in India due to the lack of adequate surface water resources necessitates the assessment of groundwater quality. Except the western part, which is covered by basement rocks, the Pondicherry region is a multilayered coastal aquifer system. The geochemical signature of groundwater in these formations was studied by collecting 98 groundwater samples representing the premonsoon (PRM) and postmonsoon (POM) seasons. The samples were collected from different aquifers, namely, the Alluvium, Upper Cuddalore, Lower Cuddalore, and Cretaceous aquifers. The physicochemical parameters, including electrical conductivity (EC), pH, and major ions, namely, Ca 2 + , Mg 2 + , Na + , K + , Cl − , HCO 3 − , NO 3 − , PO 4 3− , SO 4 2− ; stable isotopes, and tritium were analyzed. The higher electrical conductivity infers seawater intrusion in the southern part of the study area with Na-Cl and Na-HCO 3 as the dominant facies. The statistical analysis reveals that ion exchange, weathering, and anthropogenic activities are the major factors responsible for groundwater chemistry of the region during the postmonsoon season. A few samples during the premonsoon season reflected the impact of saline intrusion. The younger water is more contaminated than the older water, and the isotopic signature infers two distinct end members, saline and fresh.