MEASURED AND PREDICTED TRANSPORT OF 2 S-TRIAZINE HERBICIDES THROUGH SOIL COLUMNS

Effluent concentration of chloride and two pesticides (prometon and at razine) were measured during column displacement experiments at two wa ter flow rates. A constant suction of approximately 1300 Pa was mainta ined in the packed soil columns which were positioned vertically on to p of a vacuum chamber enclosing an automatic fraction collector. Measu red breakthrough curves (BTC's) were analyzed in terms of two solute t ransport models: the standard two-parameter convection-dispersion equa tion (CDE), and a four-parameter two-site/two-region nonequilibrium mo del (TRM). Calculations obtained with the TRM model were found to be i n better agreement with measured BTC's than predictions using the CDE model. Column retardation factors for prometon and artrazine calculate d from equilibrium batch sorption coefficients were comparable to thos e estimated from the observed BTC's only when the nonequilibrium TRM m odel was used.