Assessment of groundwater chemistry in layered coastal aquifers using multivariate statistical analysis

This study presents statistical analysis of hydrogeochemical data of the groundwater samples collected from the layered formations of the Cretaceous, Tertiary (Lower Cuddalore and Upper Cuddalore) and Quaternary in Pondicherry region, South India. It focuses on the sources, controls and geochemical processes occurring in these formations. The results obtained from statistical analysis of 11 important hydrochemical parameters indicate dissimilar elemental correlations among aquifers. Quaternary aquifer exhibit good correlations among ion pairs Ca+–Cl− and Na+–Cl− indicating source controls like salts from unsaturated zone, fertilizers, industrial wastes and also processes like ion exchange. Upper and lower Tertiary aquifers have good correlations among ions as Ca2+–Mg2+–Na+–K+–Cl−–HCO32−—H4SiO4 indicating dominant role of silicate rock weathering processes, while Cretaceous formation show high correlations among Ca+–Mg2+–SO42−–HCO3− indicating carbonate and sulphate mineral contribution. High positive ion correlations among Na+–K+–Cl− observed in Cretaceous formation reflects contribution from marine sources. The study has also brought out the three major processes active in theses aquifers like parental, anthropogenic and mixing. The spatial distribution of the factor score for individual groundwater samples reveals the sources of the constituents that are in good agreement with those deduced from the geological and hydrogeological evidences. A conceptual geochemical model is developed to improve the understanding of this complex multi-layered aquifer system that would help the water authorities to plan for judicious exploitation of groundwater resources management without significantly hampering the groundwater quality. © 2017, Springer International Publishing Switzerland.