In coastal aquifers, seawater intrusion is a significant groundwater issue. The research paper contributes to the understanding of the consequences of seawater intrusion in the Chennai coastal aquifer from Foreshore Estate to Thirunilai along the coastline. 110 groundwater samples were collected and analyzed for physicochemical parameters such as pH, (EC), (TDS), (TH), major anions (Cl−, NO3−, HCO32−, and SO42−), and cations (Ca2+, Mg2+, Na+, and K+) during the pre-monsoon (June 2014) and post-monsoon (January 2015) seasons. Stable isotopic analyses of 18O were performed on 24 groundwater samples collected from various locations throughout the research region based on EC, TDS, Na, and Cl− concentrations for both seasons. The stable isotopic composition of 18O and Deuterium in groundwater samples was determined for the study region. According to the Correlation matrix and Factor analysis, the main contributors to groundwater salinity as a result of seawater intrusion into the coastal aquifer are EC, TDS, Na+, and Cl−. GMWL exhibits a similar pattern, and the samples have been classified into various molar ratio diagrams to identify seawater intrusions for better evaluation. The result revealed that seasonal, geogenic, and anthropogenic factors always make a significant contribution to the heterogeneous chemistry of groundwater.
