Hydrochemical evaluation of shallow groundwater aquifers: a case study from a semiarid Himalayan foothill river basin, northwest India

This paper describes the hydrochemical characteristics and ion exchange process in the groundwater of a semiarid climatic condition river basin located at Himalayan foothill, northwest India. Chemical testing results on pH, EC, TDS, hardness, major cations and anions revealed that the groundwater quality is suitable for potable use. High concentrations of Ca2+, SO4 (2-) and Cl- are observed in the alluvial plain, while low SO4 (2-) and Cl- concentrations are confined to the piedmont zone. Low and high concentrations of HCO3 (-) are distributed in the alluvial plain and in the piedmont zone, respectively. Aquifer panel diagram revealed that piedmont zone is dominated by gravelly sand layers, while alluvial plain is dominated by fine and medium sand layers. The scatter diagrams of (SO4 (2-) + HCO3 (-)) versus (Ca2+ + Mg2+) and Cl- versus Na+ show predominance of the ion exchange process. The scatter plot of (Ca2+ + Mg2+) versus total cations (TZ+) indicates that Ca2+ and Mg2+ are resulted from the weathering of silicate minerals. Stiff diagrams suggest that the alluvial plain has more concentration of ions than the piedmont area, suggesting longer evolutionary period of groundwater in the alluvial plain than in the piedmont area. Groundwater in the alluvial plain is characterized by Ca2+-Mg2+-HCO3 (-), Na2+-Ca2+-HCO3 (-) and Na2+-HCO3 (-) water types, while it is characterized by Ca2+-Mg2+-HCO3 (-) type in the piedmont area. The result of correlation matrices of groundwater suggests that the variations of ion relations are due to the impact of lithological and groundwater level variations in the alluvial plain and in the piedmont area.