A continuous simulation model that considers interactions of pesticides in surface runoff (in water and on eroded sediment, advection in percolating water, molecular diffusion, dispersion, uptake by plants, sorption to soil, and biological and chemical degradation) is described. The model was partially performance tested for aldicarb using data from field sites in New York, Florida, and Wisconsin. The model was successfully tested with observed data at the sites using selected values for 1st-order degradation rate constants and sorption coefficients. The model was successfully calibrated to the observed data at the New York site using selected values for 1st-order degradation rate constants and sorption coefficients. (Copyright (c) 1985 Elsevier Science Publishers).