Characterizing the spatial variability of the hydraulic conductivity of reclamation soils using air permeability

• Field Ks values are estimated from air permeability (AP) measurements.
• The estimated Ks values are compared to Guelph permeameter (GP) measurements.
• The Ks from the AP compares well with the GP when corrected to field capacity.
• The AP measurements enhance our ability to map the spatial variability of Ks.
• The spatial dependency of Ks within a constructed mine waste dump was weak.

The saturated hydraulic conductivity (Ks) is a key property in the design of reclamation soils, influencing key aspects of the water balance including infiltration and net percolation. The conventional field method of measuring Ks for reclamation soils has been the use of water infiltration tests such as the Guelph permeameter (GP). However, the time required to conduct a large number of water infiltration tests can make it difficult to obtain a sufficiently large dataset to define the spatial variability of the large areas associated with mine site reclamation. The objectives of this study were: (1) to compare the Ks estimated from air permeability measurements with those measured using a GP and (2) to use air permeability measurements to characterize spatial variations of Ks for two reclamation sites, one on a lean oil sands dump at the Aurora oil sands mine in Northern Alberta, and a second on a waste rock storage area at the Key Lake Uranium Mine in Northern Saskatchewan. The results indicated that the Ks values estimated from air permeability measurements were similar to those measured using a GP if the air permeability measurements were adjusted for differences between in situ water contents and field capacity water contents. The probability distributions of Ks values obtained from both measurement methods were also found to be similar at a 0.01 level of confidence. Geostatistical analysis revealed a weak spatial dependency in Ks values, with an effective range of 158 m for the Aurora site and a non-significant spatial structure for Ks at the Key Lake mine site. This paper provides a practical example of how air permeability measurements combined with a limited program of GP testing can be used to characterize spatial variability of Ks on reclamation soils.