Migration of dissolved contaminants through subsurface environments may be enhanced by mobile colloidal particles. Lindqvist and Enfield <1992> have demonstrated that bacteria are capable of adsorbing and accelerating the movement of dichlorodiphenyltrichloroethane (DDT) through columns containing sand. In the work reported here, a mathematical model for describing this bacteria-facilitated transport is presented. Our results indicate that the experimental data of Lindqvist and Enfield <1992> are most closely described by a model that incorporates a Freundlich isotherm equation for DDT adsorption to the bacteria, a second-order rate law for bacterial deposition, and a two-site, kinetic formulation for DDT adsorption by the porous medium. ¿ American Geophysical Union 1996