Analytical modelling of pesticide transport from the soil surface to a drinking water well

A model for the coupled unsaturated/saturated soil system was developed, based on analytical solutions for each zone. The model was used to identify the processes and parameters with the greatest impact on the fraction of applied pesticide reaching a drinking-water well. For representative sandy soils under average Dutch rainfall conditions, processes in the unsaturated zone had a much greater impact on pesticide arrival in the wells than processes in the saturated zone. Protection zones reduced pesticide transport to wells substantially if their half-life was much smaller than the characteristic travel time of the pesticide in the aquifer.