A study to evaluate the performance of reclamation soil covers placed over an oil sands fluid coke deposit

Coke, a by-product of petroleum extraction from oil sands, is considered a potential energy source and must be stored within the reclaimed landscape in a manner that allows it to be recovered in the future. Syncrude Canada constructed two instrumented watersheds at the Mildred Lake Settling Basin (tailings management facility) to study the effects of coke in the environment. The watersheds consisted of a “shallow” and a “deep” cover system with nominal thicknesses of 35cm and 100cm, overlying an approximate 5 m thick coke deposit. The two reclamation soil covers were constructed using peat-mineral mix placed over secondary (glacial till). The global objective of this research program was to evaluate the preliminary performance for each of the soil covers with respect to the available water holding capacity (AWHC). The specific objectives were to: a) install additional instrumentation to supplement the existing instrumented watersheds; b) characterize the properties of the covers on each watershed; and c) develop a preliminary, one-dimensional water balance for each watershed. Existing instrumentation on each cover (installed by others) included: a meteorological station; automated soil stations to monitor suction, water content and temperature; and, lysimeters to collect net percolation. Additional instrumentation was installed during this research program to track vertical and horizontal variations in soil conditions and included: access tubes for monitoring water content; temperature sensors; gas sampling points; and, standpipe piezometers to determine depth to the water table. The instrumentation generally performed well, with the exception of the lysimeters which did not appear to measure net percolation accurately. Through the measurement of soil parameters, interpretation of field monitoring data and laboratory testing, the covers were characterized for their relative ability to store water for plant growth. A water balance was determined for each watershed. Evaluation of the covers indicated that neither the deep nor the shallow covers were successful at storing sufficient water necessary for plant growth under dry conditions. However, the deep cover performed better than the shallow cover based on the overall cover performance, likely due to its higher AWHC