Chemical reaction and Co-60 retardation in unsteady, unsaturated soil water flow: the effect of clay content

The ability of the regolith to adsorb and retard radioactive and other noxi ous chemicals is important when selecting repository sites. Because of its surface charge and great specific surface, the clay in soil contributes sig nificantly to this retardation. This paper illustrates a novel analysis of unsteady water and solute flow in unsaturated soil that quantifies these ef fects. Analysis and experiments suggest that the use of a clay-based space- like coordinate permits us to generalise results to account for variation i n clay content and soil structure across many materials. Results imply that clay content, mineralogy, and charge permit quantitative material classifi cation according to their ability to retard cationic wastes. The approach a ppears to offer significant economies in selecting materials where adsorpti on and retardation of cation pollutants is desired.