STOCHASTIC SIMULATION OF THE REGIONAL PESTICIDE TRANSPORT INCLUDING THE UNSATURATED AND THE SATURATED ZONE

New drinking water standards in the European Community allow a maximum total pesticide concentration of 0.5 mu g/l. Water works and environmental agencies at the local, state and federal level are forced to rigidly assess the contamination potential of pesticides under a great variety of natural conditions. A large number of pesticide studies were therefore initiated, mostly either at laboratory scale using column or lysimeter experiments or at catchment scale using groundwater quality data. However, there is also a need for coupled approaches, where laboratory data are integrated into regional catchment studies taking into account the spatial and temporal variability and/or uncertainty of the governing transport parameters. This paper presents a stochastic approach where a numerical, one-dimensional pesticide transport model has been coupled with a numerical, three-dimensional groundwater flow and transport model. The variability of the soil parameters is taken into account through multiple realizations of the one-dimensional parameter sets at a scale of individual agricultural fields. The regional heterogeneity of the aquifer (saturation zone) can be described from borehole and structural data either deterministically or as shown here using a random field generator (e.g. Turning Bands method). Based on a set of soil data from the literature, the importance of different soil parameter distributions was analysed with respect to concentration breakthrough curves at an assumed groundwater extraction well. This analysis is aimed towards an optimization of data collection strategies for future pesticide leachate risk assessments. Using the described coupled stochastic modelling approach, the sensitivity of pesticide concentrations in the production well was estimated as a result of varying soil and aquifer transport properties.