We simulate column experiments of europium migration in humic-rich groundwater performed with different Darcy velocities to investigate the predictive capability of colloid-facilitated transport models for actinides. The simulation results indicate two retention mechanisms: sorption of dissolved contaminants and filtration of colloidal contaminants by the matrix. These interaction processes, which determine the breakthrough curves and their tailing behavior, are kinetically controlled. Sorption constants are derived from batch experiments. Sorption rates are obtained by the simulation and are compared with the values of the filtration rate predicted by the colloid filtration theory. ¿ 1998 American Geophysical Union