Characterization of groundwater in the reference of arsenic and nitrate mobilization, Kathmandu Basin, Nepal

The groundwater is an important source of drinking water in the Kathmandu Valley, and is presently fulfilling about forty five percent of the total demand of water supply. However, the deteriorating groundwater quality is an emerging issue of concern. In this study attempt has been done to characterize the groundwater for the fate of arsenic and nitrate contaminations. Physico-chemical parameters as pH, Electrical Conductivity (EC), Oxidation Reduction Potential (ORP), Chemical Oxygen Demand (COD), total arsenic (AsT), nitrate (NO3), iron (FeT) and phosphate (PO4) of sixty water samples were measured. The shallow and deep aquifers of the valley are contrast in groundwaterchemistry. ORP values are relatively lower in the deep aquifers compared to the shallow aquifers indicating the deeper part is under reducing condition. The shallow aquifers with high ORP values (up to 272 mV) is considered to be in aerobic and commonly contains elevated nitrate (up to 45 mg NO3-/L). In contrast to nitrate, arsenic is higher (>5 μg/L) in the deep aquifers than those in the shallow aquifers (<5 μg/L). The commonly existing * Corresponding author: Jaya Kumar Gurung E-mail: [email protected] Tel.: +81-852-32-6078; Fax: +81-852-32-6469