Keywords: 
• groundwater contamination /
• risk assessment /
• stochastic collocation method

Abstract: Groundwater contamination event is hardly observed,and its circumstance has various uncertainties.Risk assessment provides a quantitative approach to evaluate the potential hazard of the contamination.This study develops a new method for risk assessment by using the stochastic collocation method and the polynomial sampling technique.The uncertainties from hydraulic conductivity,porosity and dispersivity are considered simultaneously.The risk distribution is assessed in a complex groundwater system.It is shown that our proposed model avoids the large number of repetitive solutions to the diffusion-dispersion equation.The low-cost stochastic collocation method is able to determine the Lagrange polynomials expression of the concentration field.The concentration samples are thus obtained by zero-cost polynomial sampling technique.Comparing to the traditional analytical methods,the new model does not adopt any assumption to the concentration distribution and the proposed model has superior efficiency and convergence property compared to the Monte Carlo simulation.The distribution type of input variable has significant influence to risk distribution.