The evolution of the field saturated hydraulic conductivity of four covers located on a reclaimed saline-sodic shale overburden from oil sands mining is presented. Three covers consisted of a surface layer of peat/glacial topsoil over a mineral, soil. and one cover was a single layer of mixed peat and mineral soil. Measurements of the field saturated hydraulic conductivity of the cover and shale materials were made with a Guelph permeameter between 2000 and 2004. The hydraulic conductivity of the cover materials in the multilayered covers increased by one to two orders of magnitude over the first few monitoring seasons. The hydraulic conductivity of the single-layer cover system, which was placed three years before the multilayered covers, marginally increased from 2000 to 2002 and then remained relatively unchanged. The hydraulic conductivity of the shale underlying all four covers increased approximately one order of magnitude. Soil temperature measurements indicated that one freeze/thaw cycle occurred each year within all cover soils and the surficial overburden. This suggests that freeze/thaw effects were the cause of the observed increases in hydraulic conductivity, as previously observed by other researchers working on compacted clays.

Three prototype covers were constructed on a saline-sodic shale overburden fill at the Syncrude oil sands mine in Fort McMurray, Alberta, Canada in 1999. The covers are comprised of a surface layer of peat/mineral mix over glacial mineral soil placed over a sloping saline-sodic shale surface. The covers are designed to provide moisture storage for vegetation over the arid summer season while minimizing the impact of salt release from shale. The evolution of the hydraulic performance of the covers was evaluated through repeated testing of in situ hydraulic conductivity (K) over time. These changes are related to changes in monitored interflow collection rates. The mean K of the cover material increased approximately two orders of magnitude during the first three years following placement and then remained relatively constant. The interflow collection volumes have increased each year with the magnitude of interflow offset from the measured K values by two to three years. It appears that the interflow volumes which are critical for flushing salt from the covers are dependent on both the K of the cover and yearly climatic variability.