PREDICTING THE TRANSPORT OF ATRAZINE IN SOILS - 2ND-ORDER AND MULTIREACTION APPROACHES

As a follow-up to a previous paper (Ma and Selim, 1994a), this study was designed to further validate a modified second-order, two-site (SOTS) model for describing atrazine transport in column miscible experiments. Moreover, the capability of the SOTS model was compared with that of the multireaction transport model (MRTM) of Selim (1989). For both models the necessary parameters were derived from batch experiments and tritium tracer breakthrough results. The models were used solely to predict atrazine breakthrough curves (BTCs) for different experimental conditions. We also proposed an alternative way of analyzing tritium BTCs, where the hydrodynamic dispersion coefficient D and an effective solute transport length L(e) were used as fitting parameters. Tritium fitted D and L(e) were used in both models to arrive at atrazine BTC predictions. The SOTS model provided superior predictions over MRTM for all (14) atrazine BTCs regardless of (1) input concentration C-0, (2) soil column length L, (3) pore water velocity v, (4) multiple pulse applications, and (5) flow interruption (incubation). We conclude that the SOTS model was capable of describing chemical heterogeneity of atrazine retention and transport. BTC predictions lend credence to the transport parameter L(e) in predicting solute transport in soils.