Hydrochemical and statistical techniques to decode groundwater geochemical interactions and saline water intrusion along the coastal regions of Tamil Nadu and Puducherry, India.

Abstract

The study attempts to decipher saline water invasion and aided geochemical influences activated along the coastal zones of Tamil Nadu and Puducherry. Total 76 groundwater samples representing pre- and post-monsoon seasons were collected and examined for various parameters like Ca2+, K+, Na+, Mg2+, Cl-, HCO3-, NO3- and SO42-. Multiple techniques such as hydrochemical ionic changes, hydrochemical facies evolution model and seawater mixing index were incorporated to decipher the salinization process in the study area. Hydrochemical facies suggests 38.00% of groundwater samples representing CaHCO3 facies indicating fresh groundwater, mixed Ca-Cl groundwater by 26.00% of samples and about 36.00% samples suggest Na-Cl indicating saline water. Hydrochemical facies evolution diagram differentiated groundwater facies into freshening and intrusion phase irrespective of seasons. About 23.60% and 21.00% of samples during pre- and post-monsoon suggest samples influenced by seawater intrusion. Hydrochemical ionic changes of samples signify the positive fraction of seawater in both seasons, which shows the mixing of fresh groundwater with saline water. The seawater mixing index confirms a greater percentage of samples during post-monsoon (42.00%) have been influenced by seawater with values greater than one. Principle component analysis extracted three factors with a total variance of 67.31% and 62.03% during pre- and post-monsoon seasons, respectively. Factor 1 replicates the natural processes such as saline water intrusion and ion exchange, whereas factors 2 and 3 signify anthropogenic actions such as improper sewage disposal, use of fertilizers, domestic and industrial waste discharge influencing groundwater chemistry.