Identification of the geochemical processes in coastal groundwater using hydrogeochemical and isotopic data: A Case study of the Gadilam river basin in southern India

The Gadilam river basin in Tamilnadu is characterized by different geological formation viz. Archaean, Cretaceous, Tertiary to Recent Alluvium and groundwater serves as the major source for domestic, agriculture and other water-related activities. Forty-four groundwater samples were collected during summer and post monsoon. Twenty-three samples were analysed for stable isotopes (d super(18)O and dD). Geochemical signatures of groundwater were used to identify the chemical processes that control hydrogeochemsitry. Chemical parameters of groundwater such as pH, EC, TDS, Na super(+), K super(+), Ca super(+), Mg super(+), HCO super(-) sub(3), SO super(-) sub(4), PO super(-) sub(4) and H sub(4)SiO sub(4) were determined. Interpretation of hydrogeochemical data ascribes that secondary leaching, saline water intrusion and anthropogenic impact in this regime. Interpretation of d super(18)O and dD indicates recharge from the meteoric water in Tertiary aquifer and from evaporated water in Alluvium aquifer.