Determination of the major geochemical processes of groundwater along the Cretaceous-Tertiary boundary of Trichinopoly, Tamilnadu, India

The hydrogeochemical variations in groundwater are mainly influenced by lithology, residence time of water in the aquifer matrix, and anthropogenic activities. This study was focused on the geochemical variations of groundwater in different lithological units (Archaean, Cretaceous, Tertiary, and Quaternary) by understanding the major factors governing the geochemical variations in each lithology. The 71 groundwater samples were collected from these rock types, namely, Archaean (14), Cretaceous (37), Tertiary (11), Quaternary (9). The collected samples were measured for major ions and they were used for preparation of standard geochemical plots and ionic ratios. Factor analysis and factor score were used to identify the major factors controlling the hydrochemistry and their spatial distribution in the study area. In addition, geochemical model, WATEQ 4F was used to determine the saturation condition of carbonate and sulphate minerals in the groundwater. Na-Cl and mixed Ca-Na-HCO3 were the dominant hydrochemical facies irrespective of lithological units. The overall interpretation of geochemical data revealed that leaching of secondary salts, weathering and ion exchange reaction along the groundwater flow path through various lithological units, and anthropogenic influence from domestic sewages and agricultural activities constitute the major geochemical processes in the study area. Hence, this study brings out the multiple hydrogeochemical process in the complex geological terrain along the Cretaceous-Tertiary boundary.