ARSENIC AND OTHER HEAVY METALS IN SURFACE WATER AND GROUNDWATER IN MUSTANG VALLEY, NEPAL HIMALAYA

Elevated levels of As in groundwater in the floodplain of the Ganges River in Bangladesh, West Bengal (India) and southern Nepal have been well-documented over the past 15 years. Recent studies have shown that elevated As in groundwater occurs even in Kathmandu Valley in Nepal, a tectonic valley well upstream of the floodplain of the Ganges River. Moreover, studies in Kathmandu Valley showed surface water As to be statistically indistinguishable from groundwater As, which led to the fluvial recharge model in which elevated groundwater As results from losing streams with elevated As, which is a consequence of rapid erosion caused by a combination of monsoon climate, tectonic uplift and deforestation. The objective of this study was to further test the fluvial recharge model and other existing models in Mustang Valley, another tectonic valley in the Nepal Himalaya far upstream from the floodplain of the Ganges River. In May 2011 water samples were collected from 24 streams, four canals or pipes fed by streams, 5 public faucets fed by streams, 10 springs, and 14 public faucets fed by springs, for a total of 57 samples. No wells were found anywhere in Mustang Valley. Electrical conductivity, pH and water temperature were measured on-site. Water samples are currently being analyzed for As, sulfate, and the transition elements Fe, Cu, Ni, Co, Mn, Zn and Cr using the Hach DR-2700 Spectrophotometer. Thus far, samples have been analyzed for three streams, four public faucets in the capitol city of Lo-Manthang, and the two springs that feed the public faucets in Lo-Manthang. The As concentration in the public faucets (geometric mean As = 0.103 mg/L) was considerably higher than in the springs that feed the faucets (geometric mean As = 0.014 mg/L), suggesting the possibility of pipe contamination. The streams also had elevated As (geometric mean As = 0.034 mg/L), which is consistent with the fluvial recharge model. All As analyses to date have exceeded the WHO As Standard (As = 0.01 mg/L). Further results will be reported at the meeting.