Geochemical assessment of groundwater quality in the Dun valley of central Nepal using chemometric method and geochemical modeling

• Geochemical modeling is done to understand the aqueous speciation.
• Spatial distribution of nitrate pollution and its source distribution.
• Multivariate statistical techniques to deduce the sources of ions in the groundwater.
• GWQI for groundwater quality estimate and hydro-chemical indices to classify the groundwater suitability for various uses.

In order to assess the hydrogeochemistry for suitability of different purposes, a total of 45 groundwater samples in Dun valley of central Nepal has been collected and analyzed for various geochemical parameters. Geologically, the study area comprises of Quaternary alluvium composed of boulder, cobble, pebble, gravel and sand with intercalation of clays. All the physicochemical parameters were within the permissible limits except nitrate. 53% of groundwater samples shows more than permissible limit of nitrate concentration (>50 mg/l) as prescribed in the WHO are unsuitable for drinking purpose which may be due to local domestic effluents, leakage of septic tanks, nitrate fertilizer input and livestock excreta. On the basis of mineral stability diagram, groundwater appears to be stable within the kaolinite field suggesting weathering of silicate minerals. Piper diagram’s classification shows that majority of samples belong to Ca–Mg–HCO3 hydrochemical facies. Saturation index reveals undersaturation state of carbonate minerals which result in carbonate dissolution and Ca dominant waters along with direct exchange process. Groundwater quality index (GWQI) was calculated and found that majority of the area fall in excellent to good water for drinking uses. Evaluation of groundwater quality indicates that all samples are suitable for agricultural and industrial purposes, but around fifty percent samples are not suitable for drinking uses due to high nitrate concentration.

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