Mine site reclamation is a major concern for mining companies, especially when mine tailings are potentially acid generating mine drainage. For mine sites located in Arctic environments, many factors, such as climate change, the evolution of permafrost, remoteness, the availability of materials, and harsh climatic conditions, can make difficult the implementation of conventional rehabilitation methods. Therefore, it is necessary to design and develop reclamation approaches specific to these conditions. This study focuses on assessing the effectiveness of covers with capillary barrier effects, made of desulphurized tailings from Raglan mine (Nunavik region, Quebec). The approach would mitigate the risk of water contamination by simultaneously limiting oxygen migration into potentially acid-generating tailings, as well as reducing their temperature. The study involved a detailed characterization of the cover materials and the construction of two instrumented columns in a controlled-environment chamber (two residual sulphide level). Column tests demonstrated that capillary barrier effects induced a permanent high degree of saturation (>85%) in the moisture-retaining layer made of desulphurized tailings. This high degree of saturation impeded oxygen migration; the estimated oxygen fluxes passing through the moisture-retaining layer being lower than 5.5 x 10(-3) mol/m(2)/day for the two columns. The column containing the desulphurized tailings with the highest sulphide content was slightly more efficient in controlling the oxygen flux due to the greater oxygen consumption by residual sulphides. Results also showed that freeze-thaw cycles did not significantly affect the hydrogeological properties of the desulphurized tailings, thus indicating a stability in the long-term performance of the cover. (C) 2018 Elsevier Ltd. All rights reserved.

Permafrost can provide a containment medium for drilling wastes deposited to in-ground sumps. but tall shrubs may proliferate on covers causing snow to accumulate, active layers to deepen and the ground to thaw We evaluate these effects using a 2-dimensional heat transfer model to simulate the thermal evolution of sumps in warm (-3 0 degrees C mean annual ground temperatures (MAGT)) and cold (-6 0 degrees C MAGT) permafrost under varying snow and climate conditions characteristic of the Mackenzie Delta region Application of climate and snow normals for Inuvik, Northwest Territories, south of treeline, and Tuktoyaktuk, on coastal tundra, maintained wastes within frozen ground at temperatures below -1 5 degrees C in warm permafrost and -3 0 degrees C in cold permafrost. respectively A gradual increase in snow depth from 017 m to 1.5 m simulating the effect of shrub growth on snow accumulation, caused thawing by the third decade In the absence of shrub growth and increasing snow, moderate climate warming (0 09 degrees C/year) also caused sump thawing after 35 years for the warm scenario, but for the cold scenario wastes remained below - 2 degrees C through to year 40 Climate warming and increasing snow depths hasten thermal degradation Modeling results indicating sump degradation due to deepening snow were corroborated by snow and ground temperature measurements, observations of collapsed shrub covered sumps in the Mackenzie Delta region and the local absence of permafrost where deep snow accumulates over mineral soils. Although thawing increases the mobility of sump contents, the associated subsidence of the sump and adjacent areas may inhibit lateral movement of the wastes Several factors combine to influence the integrity of sumps in permafrost indicating the need for a long-term management strategy. Crown Copyright (C) 2010 Published by Elsevier BV All rights reserved