ABSTRACT
Contaminants sorbed onto colloidal particles in water in either the unsaturated or saturated zone. Water in both the saturated and unsaturated zones is included with regard to transport on colloids. Without considering water:colloid partitioning of contaminants, water:soil partitioning models may overestimate the mass of immobilized contaminants. Dissolved organic carbon content is usually much higher in the pore water of the unsaturated zone, particularly near the surface. This suggests that facilitated transport of contaminants in locus 9 may be significantly greater vertically downward in mobile pore water of the unsaturated zone than in groundwater. As the figure shows, the importance of colloidal particles on mobility of contaminants diminishes as the octanol-water partition coefficient decreases. In the unsaturated zone, enhanced fixation of colloidal particles through pH or ionic strength adjustments will introduce considerable amounts of water to the subsurface.
