Colloid Transport in the Vadose Zone: Unresolved Issues and the Importance of the Air-Water Interface.

Colloids can enhance the transport of otherwise immobile contaminants in soils and sediments. Particularly radionuclides are prone to mobilized and transported by colloids, because many radionuclides are strongly sorbed by soil and rock minerals. In the unsaturated vadose zone, the transport of colloids is strongly affected by the presence of the gas phase. This presence of the gas phase has several implications for colloid transport, and these implications are being discussed in this talk. It will be shown that capillary forces acting at the air-water interface are of paramount importance for fate and transport of colloids in the vadose zone.