S. M. Shrestha and K. Rijal

Central Department of Environmental Science, Tribhuvan University, Kirtipur, Kathmandu, Nepal

M. R. Pokhrel

Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal

A study was conducted in forty-one deep groundwater and twenty shallow groundwater wells of Kathmandu Valley, Nepal to assess heavy metal distribution and relationships between pH, EC and heavy metals. Groundwater samples were collected during premonsoon season in 2012. Atomic absorption spectrometer (AAS) was used to measure the concentration of iron (Fe), manganese (Mn), zinc (Zn) and arsenic (As). The maximum concentrations of Fe, Mn, Zn and As measured in deep groundwater were 17.9 mg/L, 1.04 mg/L, 0.95 mg/L and 0.143 mg/L, respectively. Likewise, the maximum concentrations of Fe, Mn, Zn and As  observed in shallow groundwater were 36.2 mg/L, 1.73 mg/L, 0.60 mg/L and 0.005 mg/L respectively. There is strong positive correlation between Fe and Mn concentration in both deep and shallow groundwater (r = 0.701, p < 0.01; r = 0.669, p < 0.01). Arsenic is positively correlated to Mn and Fe in deep groundwater (r=0.492, p<0.01; r = 0.373, p < 0.05). The t-test revealed significant difference in concentration of Fe in between deep and shallow groundwater at p < 0.05. Similarly, there is significant difference in concentration of Mn in between deep and shallow groundwater at p < 0.05. Furthermore, there is significant difference in concentration of As in between deep and shallow groundwater at p < 0.01. Based on the similarities in groundwater quality the hierarchical cluster analysis classified groundwater wells into cluster I and cluster II which were characterized as groundwater wells of low mineralization zone and high mineralization zone, respectively. The groundwater wells mainly in the central groundwater district were classified in cluster II.