Abstract
The paper is concerned with thermal disturbances in continuous permafrost due to open pit mining and tailings impoundment in the cold regions of Northern Canada. Numerical simulations were conducted to investigate issues of thermal regime changes and permafrost degradation in both the short term and the long term in connection with the proposed Kiggavik project in Nunavut, Canada. The results of numerical simulations indicate that no open talik would form below the East Zone and Center Zone pits during the estimated mining and milling operation period of 14 years, although a thin thawed zone would develop surrounding the open pits. For the Main Zone pit where the excavation would break through permafrost, the open talik remains following an extended operation period of 25 years with a 5 to 30 m thawed zone along the pit side walls. In the long term, with a plausible climate change scenario of 5 °C increase in the mean annual ground surface temperature during the next 100 years, the permafrost surrounding the in-pit tailings management facilities (TMFs) would reduce greatly in about 500 years. However, an approximately 40 m thick permafrost layer would remain on the top of the TMFs, which is impervious and would prevent any tailings pore water from migrating upward to reach the ground surface.
Highlights
The presence of permafrost and its susceptibility to naturally freeze and thaw under changes in the environment, whether natural or anthropogenic, is one of the major concerns in cold regions such as Northern Canada
Both the short-term and the long-term evolution of the permafrost surrounding the open pits/tailings management facilities (TMFs) are simulated under two-dimensional conditions using COMSOL Multiphysics (2012) software (4.3a, COMSOL Inc., Los Angeles, CA, USA) with the consideration of climate change in the long term
The analyses results indicate that the initial tailings temperature has little impact on the permafrost evolution, the time needed to reach the freezing point is slightly longer for tailings with higher (i.e., 10 ◦ C) initial temperatures
Summary
The presence of permafrost and its susceptibility to naturally freeze and thaw under changes in the environment, whether natural (climate change) or anthropogenic (engineering activities), is one of the major concerns in cold regions such as Northern Canada. This paper presents a case study analyzing both the short-term and the long-term impacts of mining activities and tailings management with the consideration of climate change on the underlying permafrost at a proposed uranium mine, the Kiggavik project, in Nunavut, Canada. An independent study was initiated by Canadian Nuclear Safety Commission (CNSC) as a nuclear regulator to understand the potential disturbance in permafrost surrounding the pits/TMFs during the open pit mining and the subsequent long-term tailings management. The results obtained from the study provide valuable independent knowledge to assess the potential long-term impact of mining and tailings management in northern environments, and to the proposed Kiggavik project, should it proceed to the licensing phase under the Nuclear Safety and Control Act
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