Experiments on the movement of pesticides in sandy soils to groundwater : prospects of testing preferential transport models

Many agricultural areas with humic-sandy and loamy-sandy soils are used also for the extraction of water for drinking-water supply. Model concepts have been developed for the fast preferential transport of plant protection products (pesticides) in such soils, e.g. by fingered and funneled flow. An inventory is given of experiments that may be suitable for the testing of preferential transport models for cultivated sandy soils (without macropores). The pesticide concentrations per depth in soil are highly variable, due to local differences in transport, adsorption and transformation. Measurements in both the subsoil and in the upper groundwater are scarce, also due to sampling problems. Suggestions are given to improve the characterisation of soil profiles and weather conditions. Sampling methods for soil and soil solution can easily miss the preferential transport pathways. The methods of pesticide analysis in soils samples are often not sensitive enough to measure concentrations relevant for groundwater quality. The present study serves as the starting point for selecting the most suitable data sets for model testing and for the design of more complete and detailed data sets in the future.