Hydrogeochemical and statistical assessment of groundwater in Pithoragarh, Lesser Himalaya

Abstract

Groundwater quality (subsurface groundwater) in the Lesser Himalaya is controlled by the interplay of geogenic and anthropogenic processes. This study assessed 32 spring-water samples from the Pithoragarh district during pre-monsoon and post-monsoon seasons, integrating major ions and trace metals (Cr, Pb, Cu, Fe, Mn, Zn, U) to elucidate hydrogeochemical processes and implications for drinking and agricultural use. The results indicate that groundwater ranges from mildly acidic to alkaline in nature and is primarily dominated by HCO₃⁻ and Cl⁻ among anions and Mg²⁺ and Ca⁺ among cations. Elevated HCO₃⁻ concentrations and high HCO₃⁻/(HCO₃⁻ + SO₄²⁻) ratios (>0.5) indicate that carbonic acid weathering is the primary driver of solute chemistry. Gibbs and Piper diagrams further confirm that rock–water interaction is the dominant hydrogeochemical process, with localized influence from anthropogenic activities. Quantitative assessment indicates that rock–water interaction accounts for around 71.9% of the governing processes, while Mg²⁺ and Ca²⁺ together contribute more than 75% of the total cation concentration. Similarly, HCO₃⁻ and Cl⁻ collectively account for nearly 90% of the total anion concentration. Seasonal shifts in hydrochemical facies (Ca–Mg–HCO₃, Ca–Mg–SO₄, Na–K–Cl, and mixed ion types) reflect variable water–rock interaction intensities. Irrigation suitability is generally favorable, though site-specific salinity and magnesium hazards may impair long-term use. Multivariate analysis showed that 82.82% of pre-monsoon variance was controlled by Mg²⁺, HCO₃⁻, TDS, EC, and Ca²⁺, underscoring their geochemical significance. Overall, the findings advance our understanding of Himalayan aquifer vulnerability under seasonal and environmental stressors, with implications for groundwater management, sustainability, and public health in complex mountain terrains.