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 environm ental agencies at the local, state and federal level are forced to rig idly assess the contamination potential of pesticides under a great va riety 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 lab oratory data are integrated into regional catchment studies taking int o account the spatial and temporal variability and/or uncertainty of t he governing transport parameters. This paper presents a stochastic ap proach where a numerical, one-dimensional pesticide transport model ha s been coupled with a numerical, three-dimensional groundwater flow an d transport model. The variability of the soil parameters is taken int o account through multiple realizations of the one-dimensional paramet er sets at a scale of individual agricultural fields. The regional het erogeneity of the aquifer (saturation zone) can be described from bore hole and structural data either deterministically or as shown here usi ng a random field generator (e.g. Turning Bands method). Based on a se t of soil data from the literature, the importance of different soil p arameter distributions was analysed with respect to concentration brea kthrough curves at an assumed groundwater extraction well. This analys is is aimed towards an optimization of data collection strategies for future pesticide leachate risk assessments. Using the described couple d stochastic modelling approach, the sensitivity of pesticide concentr ations in the production well was estimated as a result of varying soi l and aquifer transport properties.