A multivariate statistical approach to evaluate the hydro-geochemistry of groundwater quality in the middle Ganga river basin, Patna, India

The study of groundwater samples from Patna, which is in the middle Ganga River basin in the state of Bihar, was done to evaluate the hydrogeochemical nature of groundwater and figure out the controlling factors that affect its ionic chemistry. This study’s groundwater samples were taken seasonally from 20 Patna, Bihar locations from 2019 to 2020 and analyzed for their physical and chemical properties using APHA’s standard methods. Multivariate statistical techniques, such as Correlation matrix, Principal Component Analysis and Hierarchical cluster analysis, were carried out on the analytical variables, followed by interpreting the groundwater’s geochemical nature using Durov Plot, Piper plot, ion-scatter plots and Gibb’s diagram. The results obtained were compared with water quality standards prescribed by the Bureau of Indian Standards. The study revealed that groundwater’s alkaline nature and water’s total hardness varied from hard to very hard categories. Total dissolved solids range from 158 to 575 mg/l, where 31.66% of samples have exceeded the desirable TDS limit for drinking water. The abundance of anions was observed in decreasing order (HCO3− > Cl− > SO42−) during all seasons and cations as Ca2+ > Na+ > Mg2+ > K+ in pre-monsoon and post-monsoon, whereas in monsoon season, it was observed as Mg2+ > Na+ > Ca2+ > K+. Ca2+–Mg2+–HCO3− type water was revealed as the significant hydrogeochemical facie, and the reverse ion exchange process was observed to be the governing factor in 77% of the total groundwater samples. Gibbs’s diagram showed rock–water dominance as a major factor in groundwater ionic composition during all seasons.