Isolation of hazardous soil contaminated by DU (depleted uranium) from groundwater

Cappings of waste piles conventionally contain a drain layer over a low permeable clay liner composed of smectite minerals. The rate of percolation of the clay liner, once it has been largely water saturated, determines the downward migration of water into and through the underlying waste. In a desert climate, cyclic variation in the degree of hydration of the clay takes place, from desiccated to largely water saturated conditions. Clays of smectite type effectively seal off the underlying waste but the content must be low for preventing contraction and expansion causing a reduced isolation potential of the liner. Penetration of the liner, implying wetting of the waste, starts when the top liner is largely water saturated but the hydration followed by dehydration is confined to take place only to a limited depth according to the assumed wetting mechanism. The rate of wetting usually follows a log time law. For an ideal composition and density of the upper clay liner there will be no percolation and wetting of the underlying waste. This paper is focused on the mechanisms involved in hydration/dehydration of a top clay liner prepared by mixing clay and ballast material for providing a basis for design, construction and maintenance of well performing cappings.