The present study area falls beside the coastal zone of Tamil Nadu, and Puducherry is characterized by varied geological formations that mostly contain groundwater resources that are primarily utilized for domestic, agricultural, industrial, and other utilities. The study aims to differentiate various hydrogeochemical processes responsible for disparities in water chemistry. Groundwater samples were collected from 66 sites during the two major seasons: pre-monsoon and post-monsoon. The analytical data were separated into terrain vice and utilized for preparing graphical plots as well as mathematical calculations to obtain the existing relationship among chemical constituents and water quality. The Ca-HCO3, Na-Cl, Ca-Na-HCO3, mixed Ca-Mg-Cl, Ca-Cl, and Na-HCO3 are the main hydrochemical facies observed from the groundwater samples. The ionic relationship among the samples indicates the control of direct and reverse ion exchange in the concentration of Ca2+, Mg2+, Na+, and K+ in groundwater. Moreover, silicate weathering contributes more in comparison with carbonate and evaporite dissolution. Gibbs plots reveal that water-rock interaction and evaporation processes are the main mechanisms controlling the water chemistry. The saturation index of different mineral phases indicates groundwater to be oversaturated with silicate mineral phases irrespective of the terrain. Statistical methods like correlation and principal component analysis were also performed to differentiate the specific association and possible source of the dissolved constituent in the groundwater. The study concludes the influence of multiple processes such as silicate weathering, direct and reverse ion exchange, secondary dissolution, saline water intrusion, and anthropogenic sources as the main reasons responsible for variation in groundwater chemistry.
Keywords: Ion exchange; Rock-water interaction; Saturation index; Silicate weathering; Tamil Nadu and Puducherry.