Groundwater and saline water interaction is the most common processes in the coastal aquifers that alters the quality of aquifer waters. The quaternary alluvium aquifer system is a significant water resource of southeast coastal Tamil Nadu that provides water supplies for industrial, agriculture, and domestic utilities. Hydrogeochemical investigations were attempted to analyze groundwater-saline water interactions for which a total of three hundred and sixty samples representing surface water, pore water, and groundwater samples collected from three significant locations (location A, B, and C) and analyzed for major ion concentrations. Piper plot infers surface and pore water samples representing saline water type (Na-Cl) in all the three locations due to tidal variation and sand dominant surface layer. Groundwater samples represent (Ca-HCO3) type at location A due to fresh groundwater discharge, mixed or subterranean estuary (Ca, Mg-Cl, HCO3) at location B due to conversion of freshwater (Ca-HCO3) at low tide to saline water (Na-Cl) at high tide, and saline (Na-Cl) water at location C due to proximity and influence of tides. The Cl-/HCO3- vs. Cl- plot represents two water types, such as fresh groundwater (0.5) and strongly affected by seawater intrusion (6.6). The plot (Ca2++Mg2+)/(K++Na+) vs. log Cl- represents freshwater in location A, mixing in location B, and saline water in location C. Groundwater samples observed to be fresh in location A (20.0 km away from the coast), recirculated in location B (9.0 km away from the coast), and saline in location C (0.5 km away from the coast).
Keywords: Freshwater; Hydrochemical facies; Ionic ratio plots; Saline water; Subterranean estuary.