Development of an automated sampling technique for estimation of pesticides concentrations in drainage flow

In 1998, the Danish Government initiated the Pesticide Leaching Assessment Programme (PLAP), an intensive monitoring programme aimed at evaluating the,leaching risk of pesticides under field conditions. The PLAP, which includes six different field sites, is intended to serve as an early warning system providing decision-makers with advance warning if approved pesticides - applied in accordance with the current regulations - leach to the groundwater in unacceptable concentrations. The monitoring programme includes sampling of water drained through a tile drainage system. The automated sampling of drainage water is designed to give peak concentrations of leached pesticides and tracers, but also to estimate a yearly average concentration. A sampling strategy combining time and flow proportional sampling models have been designed. The flow proportional model is a conceptual/empirical model, which is parameterised based on local experience including the time varying hydraulic response of the site. The question is how successful the initial parameterisation has been and how eventually to optimise the model parameters. An analysis of this problem is presented for two different clay sites with the use of measured drainage flow and modelling.