Hydrochemical evaluation of Rangit river, Sikkim, India: using Water Quality Index and multivariate statistics

This study is aiming to focus on hydrogeochemical investigation of water samples from Rangit river basin and assessment of water quality for human consumption and agricultural purposes. River water is neutral to mildly alkaline, with dominance of K + , Ca 2+ , HCO 3 − , and SO 4 2− in ionic strength. K + –Ca 2+ –Mg 2+ –HCO 3 − is the major hydrochemical facies in upstream river water, whereas Ca 2+ –K + –Mg 2+ –HCO 3 − water-type dominates in downstream stretches of river. The weathering of rock-forming minerals mainly controls the solute acquisition process. The high equivalent ratios of (Ca 2+ + Mg 2+ )/(Na + + K + ) and the low ratio of (Na + + K + /TZ + ) reveal that the chemical composition of river water is mostly determined by carbonate weathering with partial contribution from silicate weathering. An evaluation of Water Quality Index of sampled river water indicates that the majority of the water samples are good–moderate for human consumption and domestic usages. Irrigation suitability of river water in relation to EC content, SAR, and RSC values suggests that river water is good–excellent type for agricultural applications.