Water Storage and Preferential Flow In Layered Soil Covers with Abrupt and Long Interlayer Transition Zones.

Waste rock piles are exposed to chemical/physical weathering and emanate radon gas unless covered with uncontaminated material ― soil cover. Current research is focused on studies of preferential flow or water storage in soil covers with abrupt textural transitions at layers interface that rarely exist in nature and may lead to the overprediction of water storage. Therefore, the objective of this study is to investigate if there are differences in soil water storage capacity and the susceptibility to preferential flow between layered and nonlayered covers. Two-layered cover consists of finer sand overlaying coarser sand (#2), which are fractions of the same soil used for nonlayered cover (#1). The cover with interlayer transition (#3) is composed of thin layers with gradually increasing amounts of finer particles when ascending from the coarser to the finer layer. Infiltration of water and dye were implemented in the slab chamber under air-dried, unsaturated, and quasi-saturated conditions. Preferential flow and finger geometry were characterized from pore pressure distribution data and dye coverage. To verify water content data the latter was measured gravimetrically as well. Water storage of Cover#2 (14.4 cm) is considerably higher than that of the Cover#1 (9.8 cm). The water storage of Cover#3 is 1.7 cm lower than of Cover#2 due to reduced capillary barrier effect. Wetting front was uniform in all covers under air-dried conditions; however, at a higher water contents preferential flow was observed in all covers. Layering of sand with even slightly differing textures led to a considerable increase in water storage and preferential flow suppression under saturated conditions.