1 The modeling of Reactive Solute Transport with Sorption to Mobile and Immobile Sorbents Part II: Model Discussion and Numerical Simulation K. U. Totsche 2 *, P. Knabner 1 and I. Kögel-Knabner 2 1 Institute for Applied Mathematics, University of Erlangen-Nürnberg, Martensstr. 3, D-91058 Erlangen, Germany. 2 Soil Science Group, University of Bochum, NA 6/134, D-44780 Bochum; *present address: Soil Physics Group, University of Bayreuth, D-95440 Bayreuth, Germany. ABSTRACT We analyze mathematically and numerically a model derived in Part I of this paper. The model deals with carrier influenced transport and besides advective and dispersive transport and equilibrium and nonequilibrium sorption takes into account both carrier facilitation and co-sorption. Guidelines are derived, whether the overall mobility is enhanced or reduced and various other properties of the model elucidated, in particular for varying carrier concentrations. We indicate how to modify existing numerical codes for the usual adsorption model and discuss simulations for experimental data sets. INTRODUCTION This paper is a sequel of Knabner et al. [1995], in the following referred to as part I. In part I based on a discussion of experimental findings, we have set up a mathematical model to describe the advective and dispersive transport of both a dissolved carrier, which undergoes possibly nonlinear equilibrium and nonequilibrium sorption to the soil, and the movement of a dissolved contaminant, which may get attached to the carrier, thus existing in solution in a free and a bound form, where both of these forms are also subject to all the transport mechanisms already mentioned. We always refer to the carrier as dissolved organic carbon (DOC) and to the contaminant as hydrophobic organic chemicals (HOC). In particular this model both takes into account facilitated transport of contaminants (co-transport) and the adsorption of the HOC attached to reactive carrier to the soil matrix (co-sorption), i. e. two competing mechanisms. A transformation in terms of total concentrations of contaminant and carrier simplifies the model, insofar the model now has the structure of the well-known equilibrium-nonequilibrium multiple site adsorption model, but with space and time dependent, implicitly defined isotherms and rate functions. They are called effective, as they combine the competing mechanisms. The effective isotherm resulting for linear isotherms has already been pointed out in part I. This part II assumes the knowledge of the basic notation and equations of part I. Its aim is to analyze the model mathematically and numerically, which in particular includes a comparison with the experimental data discussed in part I. The mathematical analysis is not directed towards closed form (analytical) solutions: These solutions are not available in the general case, but in some special cases quite obvious: If the carrier concentration is constant and the