Salifu, KF, Woosaree, J, Wells, S & Anderson, B 2011, 'Innovative techniques to improve reclamation practices in Alberta oil sands', in AB Fourie, M Tibbett & A Beersing (eds), Proceedings of the Sixth International Conference on Mine Closure
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Suncor Energy is in the process of reclaiming one of its consolidated tailings ponds (Pond 5). In order to deal with residual soft tailings (aqueous solution of silt, sand, clay and bitumen) still contained within the pond area, a capping and dewatering system is being used. Petroleum coke is used to create the primary, floating trafficability cap, with vertical strip drains then installed to dewater and strengthen the underlying tailings. As these tailings dewater, additional loading is required in order to ensure dewatering of the top of the tailings column under the cap. This loading is to be accomplished through the placement of a layer of tailings sand on top of the coke. The need for a temporary reclamation cover over tailings sand has been identified to stabilise the sand against water and wind erosion prior to the final reclamation cover being established. A peat/mineral amendment is usually used to mitigate poor water retention in the sand, but rather than using stockpiled cover soil in the establishment of the temporary cover (and potentially lost to future use), an alternative amendment was desired. Barley (Hordeum vulgare), an annual species has been the cover crop of choice for years. To evaluate the possibility of establishing a temporary reclamation cover on tailings sand, a program was initiated to identify appropriate grass species, and to evaluate the use of alfalfa pellets (Medicago sativa) as an amendment. It is proposed that alfalfa pellets may improve soil structure and moisture storage, and serve as a slow release fertiliser providing nutrition to plants. This study screens a series of native grasses [fringed brome grass (Bromus ciliatus), June grass (Koeleria macrantha), a mix of native grasses along with barley and oats (Avena sativa) for suitability to grow and stabilise tailing sands. First year observations showed remarkable growth of native species on tailings sand. Plant height, plant cover and total nitrogen were similar across the tested alfalfa pellets application rates of 5, 10 and 20 t/ha. Despite the shorter plant height and lower vigour of the fringed brome grass and June grass compared to barley and oats, the native grasses exhibited greater nitrogen (N) uptake, which may be explained by extensive root growth and development. Additionally, the perennial native grasses have potential to provide adequate cover against erosion for a longer portion of the year and in subsequent years. The application of alfalfa pellets at the rate of 5 t/ha improved moisture retention and bulk density, but to a lesser extent than at 20 t/ha. Experimental plots will be monitored in 2011 to quantify residual N in soils that could be potentially available to plants. Generally, study results suggest the studied native species can be used to stabilise tailings sand against water and wind erosion.
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