Evaluation of hydro-chemistry in a phreatic aquifer in the Vindhyan Region, India, using entropy weighted approach and geochemical modelling

Groundwater quality monitoring and geochemical characterization in the phreatic aquifer are critical for ensuring universal and equitable access to clean, reliable, and inexpensive drinking water for all. This research was intended to investigate the hydrogeochemical attributes and mechanisms regulating the chemistry of groundwater as well as to assess spatial variation in groundwater quality in Satna district, India. To accomplish this, the groundwater data comprising 13 physio-chemical parameters from thirty-eight phreatic aquifer locations were analysed for May 2020 by combining entropy-weighted water quality index (EWQI), multivariate statistics, geochemical modelling, and geographical information system. The findings revealed that the groundwater is fresh and slightly alkaline. Hardness was a significant concern as 57.89% of samples were beyond the permissible limit of the World Health Organisation. The dominance of ions were in the order of Ca²⁺  > Na⁺  > Mg²⁺  > K⁺ and HCO₃⁻ > SO₄²⁻ > Cl⁻ > NO₃⁻ > F⁻. Higher concentration of these ions is mainly concentrated in the northeast and eastern regions. Pearson correlation analysis and principal component analysis (PCA) demonstrated that both natural and human factors regulate groundwater chemistry in the region. The analysis of Q-mode agglomerative hierarchical clustering highlighted three significant water clusters. Ca–HCO₃ was the most prevalent hydro-chemical facies in all three clusters. Geochemical modelling through various conventional plots indicated that groundwater chemistry in the research region is influenced by the dissolution of calcite/dolomite, reverse ion exchange, and by silicate and halite weathering. EWQI data of the study area disclosed that 73.69% of the samples were appropriate for drinking. Due to high salinity, Magnesium (Mg²⁺), Nitrate (NO₃⁻), and Bicarbonate (HCO₃⁻) concentrations, the north-central and north-eastern regions are particularly susceptible. The findings of the study may be accomplished by policymakers and groundwater managers to achieve sustainable groundwater development at the regional scale.