Deciphering the groundwater–saline water interaction in a complex coastal aquifer in South India using statistical and hydrochemical mixing models

Abstract

Hydrogeochemical investigations were carried out in a coastal aquifer along the East coast of Cuddalore district in Tamil Nadu, Southern India, to analyse the groundwater–seawater interactions. Multiple techniques including Hydrochemical Facies Evaluation Diagram (HFE-D), principle component analysis (PCA), ionic ratios, hydrochemical ionic changes models and salinity mixing index (SMI) models were applied to refine the results and exactly understand the salinization process. EC and Ionic constituents along with the Gibbs plot showed controls of evaporation and the rock–water interaction o hydrogeochemistry, which is later proved by the bivariate plots. Major ions listed under PC1 (Na, Mg, Cl and SO4) and PC2 (Ca, HCO3, and CO3) showing the influence of seawater and carbonate dissolution processes go together with cation exchange. Definitive results, shown by HFE-D plot than the piper plot, indicate that 58% of the samples either completely fall in the seawater zone or on the mixing line. Results of the ionic changes calculation indicate that 6 wells (50%) have a positive seawater fraction in the groundwater. Analogous results were observed for the SMI values (>1) in these wells, except in sample number 3. Encouragingly, after each method the results significantly rectified. Impact of seawater mixing with fresh groundwater is found in the entire starch (perpendicular to coast) of samples in the southern end of the aquifer, and samples located in very near to the coast in the central part. Good quality groundwater in the northern end indicate that the aquifer was unaffected by the seawater mixing.