LAUSR

Groundwater samples were collected from 36 wells during summer and monsoon seasons in a coastal region in Tamil Nadu, India in 2011. The chemical analysis of groundwater samples indicated that groundwater in the region was fresh to saline with cationic concentrations in the order Na+ > Ca2+ > Mg2+ > K+ and anionic concentrations in the order Cl−  > HCO3−  > SO42−  > NO3−. Most of the groundwater samples had a chemical composition dominated by sodium and chloride ions. Scatter plots suggested that the principal processes influencing groundwater quality in the area are likely to be: ion exchange; reverse ion exchange; silicate weathering and evaporation. A Gibbs plot indicated that evaporation was the dominant process influencing groundwater salinity in the summer season, whereas both water–rock interactions and evaporation influenced the chemical composition and salinity of groundwater in the monsoon season. A principal component analysis of the data shows four principal components for the monsoon and three components for the summer seasons, which account for 85% and 87% of the total variance, respectively. The assessment has indicated that there is widespread seawater intrusion in coastal aquifers, which has led to changes in hydrochemical processes in the study area.