Spatial variability of hydrochemical characteristics and appraisal of water quality in stressed phreatic aquifer of Upper Ganga Plain, Uttar Pradesh, India

The present study deals with the characterization of hydrochemical parameters and their spatial variability, and suitability for drinking and irrigation purposes of groundwater from unconfined aquifer of Western Uttar Pradesh, India, encompassing an area of 57,342 km². The results confirm that groundwater is predominantly hard and exhibits neutral to alkaline nature. Groundwater were dominated by Na⁺ (6–5060 mg/L) followed by Ca²⁺, Mg²⁺, and K⁺ for cations, while Cl⁻, HCO₃⁻, and SO₄²⁻ were the dominating anions. The water facies belong to fresh (Ca–Mg–HCO₃ Na–HCO₃) to very saline (Na–Cl, Ca–Mg–Cl) water types, representing both geogenic and anthropogenic controls on groundwater chemistry. The spatial distribution pattern of the ions (Cl⁻, SO₄²⁻, F⁻, Ca²⁺, HCO₃⁻, Na⁺, and Mg²⁺) showed an increasing trend from the source to downstream. The correlation coefficients between hydrochemical parameters show a strong positive correlation of EC and TDS with all major ions, including NO₃⁻ and K⁺. This finding corroborated that chemicals originating from geogenic and anthropogenic causes contribute substantially to groundwater mineralization. Except for the unsuitability due to excessive salinity (9.2%) and hardness (19.2%), the main human-health-related concern is the high concentrations exceeding the permissible limits for NO₃⁻ (15.6%) and F⁻ (7.8%). The irrigation water quality parameters such as % Na, MH, TDS, RSC, SAR, PI, and KR revealed excellent to permissible quality. The unsuitable samples were derived mostly from the South and South-Western parts of the Yamuna and Ganga Rivers banks, requiring immediate salinity and NO₃⁻ contamination control measures.