A study was carried out to address distribution of some heavy metals in deep groundwater resources
of the Kathmandu Valley. Groundwater samples were analyzed for pH, ORP, EC, iron,
manganese, zinc, and arsenic in 41 deep groundwater wells during pre monsoon and post monsoon
seasons for two consecutive years. The study showed elevated concentrations of iron and
manganese in the groundwater of the valley. The occurrence of elevated concentrations of arsenic
was also exhibited and observed up to 0.160 mg/L. The spatial distribution patterns demonstrated
elevated levels of EC, iron, manganese, zinc, and arsenic in central groundwater district (CGWD) of
the valley. The monitored parameters except ORP are not significantly correlated with studied
time series, inferring similar distribution of the metals. Correlation analysis and principal component
analysis (PCA) were performed to find out relationships among examined parameters and
metals. The ORP has strong negative correlations with iron, manganese, and arsenic, suggesting
reductive mobilization mechanism of the metals in the groundwater. PCA results showed that iron
and manganese with high positive loading factors were due to common natural source of origin of
these metals in the groundwater, while negative loading factors of pH and ORP indicated that iron
and manganese mobilization was favorable in low pH and reducing environment. Cluster analysis
(CA) evidenced high mineralization in most of the wells in the CGWD.