Hydrogeochemical evaluation of groundwater of Bhaktapur Municipality, Nepal

Abstract

The present study aims to evaluate groundwater hydrogeochemistry of Bhaktapur Municipality, Nepal with respect to water types, chemical elements and their statistical variability. Samples were collected in pre-monsoon (April–June), monsoon (July–August) and post-monsoon (October–November) seasons in 2007. Laboratory analysis of samples revealed inter-seasonal variability, primarily attributed to hydrogeochemical processes. All or most of the samples exceeded the World Health Organization (WHO) guideline value (GLV) for iron, conductivity and turbidity, while none of the samples exceeded WHO GLV for hardness and arsenic with minor fraction exceeding GLV for chloride content. Higher ammonia content in well water and highest phosphate concentration occurred for stone spout in pre-monsoon season. Principle component analysis highlighted three principle components while the dendrogram divided the sampling sites into four and two clusters, respectively, for well water and stone spout water sampling sites. Saturation index computed through WATEQ4F model revealed that ferrihydrite, siderite, strengite and vivianite minerals were in under-saturated state, while goethite was in supersaturated condition for each type of samples (well water and stone spout water) in both pre- and post-monsoon seasons depicting their tendency to precipitate. High degree of supersaturation in goethite mineral indicated response to temperature gradient of the reactions, while under-saturation for other minerals indicated the effect of dilution.