Nitrate Pollution in Ground Water of Shallow Aquifer of Kathmandu Valley, Nepal

The Kathmandu Valley, the urban center of Nepal faces a plethora of problems regarding drinking water availability and its quality. Due to the inadequate and intermittent piped water supply, people largely rely on ground water sources to meet daily water needs and the situation is further exacerbated by rapid urbanization in Kathmandu. Nitrate contamination is one of the major concerns in the shallow aquifer of Kathmandu resulting from more intensive use of fertilizers in agriculture fields and seepage from sewage lines and septic tanks. To control and manage the elevated level of contamination in ground water, the characterization of ground water contamination and identification of the factors affecting the contaminants are significant. In this study, water was sampled from 100 sources from ground water of shallow aquifer of Kathmandu, including shallow tube wells, dug wells and stone spouts (locally called dhunge dharas). 16% of the sampled sites had nitrate results greater than the World Health Organization (WHO) guidelines of 10 mg/l as nitrate-nitrogen; however, another 33% wells have impacted levels of nitrate between 2 and 10 mg/l. Concentrations of nitrate in ground water are not uniform across the Valley. Nitrate is rarely detected in tube wells while contamination levels are generally higher in stone spouts and dug wells with lower depth. Interestingly, almost all samples from stone spouts exceed WHO guidelines. In addition, the study indicates that higher nitrate concentrations are more frequently observed in old urban areas than in agricultural areas, which may conclude that the nitrate contamination resulting from poorly managed sewer lines and septic tanks is worse than the contamination problems created by agriculture. The aim of this study is also to establish the relationship between hydogeological parameters that pertinent to ground water contamination and contaminant concentration in the study area.