Unsaturated sloping layered soil cover system: Field investigation

Abstract

Tallon, L. K., O'Kane, M. A., Chapman, D. E., Phillip, M. A., Shurniak, R. E. and Strunk, R. L. 2011. Unsaturated sloping layered soil cover system: Field investigation. Can. J. Soil Sci. 91: 161–168. Unsaturated soil cover systems are effective in minimizing the interaction of meteoric water with underlying mine waste. Studies detailing field-monitoring results of layered systems in sloping landscapes are scarce. The objective of this paper was to evaluate the field performance, defined as a reduction in percolation, of a sloping fine-over-coarse-layered cover system at a phosphate mine in the northwestern United States. Cover water content profiles were elevated in the underlying waste material during and after wet periods such as spring snow melt, suggesting that any layering effect of increasing storage capacity was lost. During dry periods, water content profiles suggested a slight benefit due to layering, as water contents were slightly elevated immediately above the cover/waste shale interface. Although there were incidental gains in performance due to layering, the majority of the infiltrating water was stored in the fine-textured layer. This layer was most responsible for limiting percolation into the underlying waste. There was little difference in performance due to slope position. The cover was sufficient in preventing net percolation into the underlying waste shale, and performance was at least partially improved by increased storage at layer interfaces.