Measured and Predicted Transport of Two S-triazine Herbicides through Soil Columns *

Effluent concentration of chloride and two pesticides (prometon and atrazine) were measured during column displacement experiments at two water flow rates. A constant suction of approximately 1300 Pa was maintained in the packed soil columns which were positioned vertically on top of a vacuum chamber enclosing an automatic fraction collector. Measured breakthrough curves (BTC’s) were analyzed in terms of two solute transport models: the standard two-parameter convectiondispersion equation (CDE), and a four-parameter two-site/two-region nonequilibrium model (TRM). Calculations obtained with the TRM model were found to be in better agreement with measured BTC’s than predictions using the CDE model. Column retardation factors for prometon and artrazine calculated from equilibrium batch sorption coefficients were comparable to those estimated from the observed BTC’s only when the nonequilibrium TRM model was used.