A mathematical model was developed to simulate the transport and dissolution of colloidal particles with a water-soluble component in a porous medium. The model is based on mass balance equations describing the mass transport, dissolution, sorption, capture, and release of colloids in a three-phase medium consisting of a solid matrix, an aqueous phase, and colloids. Colloid dissolution, contaminant sorption on solid matrix, and colloid capture mechanisms are represented by first-order kinetics. A numerical comparison of the model of a water-soluble component associated with fly ash-mobilized transport and transport due only to dissolved component migration indicates that the presence of colloids significantly increases the aqueous phase contaminant concentration. ¿ 1999 American Geophysical Union