| The disposal of radionuclide wastes to the subsurface environment at Hanford Site has led us to environmental anxiety. It is not only liquid and gas phases that are responsible for contaminant transport in subsurface media, but also the solid phase itself, i.e., subsurface colloids. In the vadose zone, air-water interfaces play key roles in colloid mobilization and transport, but knowledge as to how exactly these interfaces affect colloid transport behavior is still inadequate. This dissertation reports on theoretical and experimental studies of colloid interactions with a moving air-water interface in porous media. The specific objectives of this dissertation were to (1) quantify the effect of advancing and receding air-water interfaces on detachment of colloidal particles from a solid surface, (2) quantify the effect of particle shape on particle detachment from a solid surface by a moving air-water interface, and (3) determine the effect of capillary fringe fluctuations on the behavior of colloidal particles. The major results of this work showed that air-water interfaces play a dominant role in colloid detachment surfaces. Advancing interfaces are more important in removing colloids from a stationary surface than are receding interfaces. Colloid shape affects how air-water interfaces can get pinned and angular particles are significantly better removed by moving air-water interfaces than spherical, smooth particles. These findings also apply to porous media, i.e., capillary fringe phenomena. |
