Risk assessment of well contamination using a regional stochastic modelling approach

This paper presents a stochastic risk analysis approach for contamination of water supply wells in agriculturally dominated catchment areas, using a stochastic approach, where a numerical one-dimensional pesticide transport model has been coupled with a numerical three-dimensional groundwater flowand transport model. The risk analysis is based on Monte-Carlo simulations with multiple realizations of the entire parameter set at a scale of individual agricultural fields. For the generation of the parameter set in the saturated zone the turning band method was used according to the lognormal pdf. Based on a set of soil and aquifer data from literature, the importance of different soil parameter distributions and different agricultural area sizes, were analysed with respect to the variability of the concentration breakthrough curves as observed at an assumed groundwater supply well. Using the coupled stochastic modelling approach the risk of exceeding a given concentration limit was investigated as a result of spatially variable soil and aquifer transport properties.