A FUGACITY MODEL OF PESTICIDE RUNOFF TO SURFACE-WATER - DEVELOPMENT AND VALIDATION

Real field data for pesticide release to surface water are compared wi th data obtained by simulations of a fugacity-derived model. This was done for several herbicides, applied on to two basins, characterized b y different soil properties. The basin were hydraulically isolated and data for water input (rainfall and irrigation), output (outflowing su rface water) were recorded, together with concentration of the investi gated pesticides in the outflowing water. A fugacity model was develop ed to take into account the unsteady-state condition of the actual fie ld treatments, since pesticides are typically applied once or twice on the same ares. The model allows for several pesticide applications on different areas of the basin at different times and for different rea ction half lives, that may change during the simulation time, dependin g on environmental conditions. A ''user friendly'' program for Window( R) was written, allowing for calculations and plotting of the results. The comparison between predicted and measured concentrations indicate d that the model is a useful tool for the prediction of surface water concentration.