A thesis submitted in partial fulfillment of the requirements for the d egree of Master of Engineering in Water Engine ering and Management

Thesis (M.Eng.) - Asian Institute of Technology, 2015

Groundwater is the largest accessible resource but it is v e ry vulnerable to contamination . It has been reported from previous studies that groundwater of Kathmandu valley is highly vulnerable to pollution. So, the vulnerability and risk assessment can be useful tool for identifying the vulnerable and risk zones. T his study focus es on the evaluation of groundwater vulnerability and risk assessment by different methods for Kathmandu groundwater basin, Nepal. In this study, vulnerability assessment is carried out using three methods, index and overlay method (DRASTIC , GOD, SI), statistical method (Logistic regression) and process based method (M ODFLOW and MT3DMS) followed by spatial variability of groundwater quality assessment. Moreover, risk assessment is carried out by groundwater risk assessment mode l (GRAM). SI method of Index Overlay method gave good result for the study area . The result showed that about 80% of area is under high vulnerability . Also, 15 % of the area is under high risk and 5 9 % area is under moderate risk. Result from solute transport model show ed that there was negligible transport of contamination in eight years and the concentration decreases from 25.35 to 24.88 mg/l. The likely concentration for NO 3 - N in some places is still higher than the guideline of World Health organization (WHO) which i s 50mg/l of nitrate (equivalent to 11 mg/l as NO 3 - N; WHO, 2011a) . This study can provide some preliminary information about vulnerable zones, risk zones and the likely concentration of pollu tant in the context of Kathmandu groundwater basin. The findings of this study could be useful for the development, management and monitoring of groundwater resources.