The Use of in Situ Measurement of Hydraulic Conductivity to Provide an Understanding of Cover System Performance Over Time

Abstract

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.

Snow hydrology of a constructed watershed in the Athabasca oil sands region, Alberta, Canada

“…Because reclamation soil covers are designed to promote water storage, they are generally a combination of organic peat and mineral soils (termed 'peat/mineral mix') obtained by over-stripping of natural peat deposits on glacial soils (Meiers et al, 2006). These soil covers typically exhibit strong soil water retention characteristics (Shurniak and Barbour, 2002) that are influenced by the proportion of clay, sand and organic matter (Leatherdale et al, 2012).…”

“…In addition to the regional climate, the storage properties of the reclamation soil materials also influence the availability of water for aquifer recharge. Many reclamation soil covers are designed to maximize available water holding capacity for vegetation growth and to minimize seepage into deeper soil layers (Meier and Barbour, 2002;Shurniak and Barbour, 2002;Meiers et al, 2006;Carrera-Hernández et al, 2012). Consequently, downslope interflow from surface mine waste deposits reclaimed using typical soil cover prescriptions occurs infrequently during the summer months (Kelln et al, 2006), and reclaimed slope landforms are largely considered water storage features in the reconstructed landscape.…”

Controls on the spatial distribution of soil moisture and solute transport in a sloping reclamation cover

“…Meiers et al (2006) found that the saturated hydraulic conductivity (K s ) of the clay-rich cover soil increased by approximately two orders of magnitude within 3-4 years after cover placement. The large increase in K s was attributed to the development of macroporosity caused by freeze-thaw cycles (Chamberlain and Gow 1979;Chamberlain et al 1990;Benson and Othman 1993;Benson et al 1995;Chamberlain et al 1995).…”

Postconstruction Changes in the Hydraulic Properties of Water Balance Cover Soils

“…During design, however, hydraulic properties are typically determined on laboratory-compacted specimens and may not reflect the condition of cover soils following long-term exposure to local environmental conditions. Postconstruction processes (freezing and thawing, wetting and drying, root growth and death, and burrowing of worms and insects) often form larger pores between existing peds (Buol et al 1997, Hillel 1998, altering the hydraulic properties of the soil and the hydrology of the cover (Suter et al 1993, Benson and Othman 1993, Chamberlain et al 1994, Waugh et al 1999, Albrecht and Benson 2001, Ayers et al 2004, Henken-Mellies et al 2001, Meiers et al 2006). …”