Hydrologic investigations of waste rock test piles in a permafrost environment

• Main Author: Zak, Jordan
• Format: Thesis
• Language: English
• Published: University of British Columbia 2017
• Subjects: Diavik Diamond Mine; Rock Pile; Ice; permafrost
• Online Access: http://hdl.handle.net/2429/61301

Three 14 m tall waste rock test piles were constructed at the Diavik Diamond Mine, NWT, located in a region of continuous permafrost. Since 2006, instrumentation in the piles has been used to develop datasets characterizing the long-term geochemical, hydrologic, and thermal evolution of the waste rock. This thesis focuses on the hydrologic behaviour of two of the waste rock test piles; the Type III pile, considered as PAG material, and the Type I pile which was deconstructed in 2014, considered as NAG material. Complexity in the dataset is added by freeze-thaw processes occurring in this climate. The distribution of ice was mapped during the deconstruction of the Type I pile. Ice was found primarily in the batter regions, the cause of this was related to the infiltration profile across the crest and batters. Wind redistribution of snow results in a substantial snowpack on the batters with little on the crest. Infiltration through the crest occurs from rainfall alone, which is often low frequency and low magnitude. Snowmelt infiltration to the batters of the Type III pile was determined using an isotopic mass balance (????D and ????¹⁸O)- an estimated 77 mm/year representing a significant component of the water budget, about 74% of the annual outflow. Evidence of ice formation in this pile was provided by evaluating the storage of rainwater and trends in deuterium excess. A bromide tracer test on the Type III pile exhibited a breakthrough curve with a long tail and 46% mass recovery after ten years. The average pore water velocity was estimated to be 2-3 cm/day. Hypotheses were examined to explain low recovery of the tracer and the observed tailing, including the possibility of multirate mass transfer which assumes tailing is related to diffusion. Comparison of late time bromide behaviour to the migration of conservative blasting residuals suggests that tailing may also be influenced by low velocity flow paths. Concentration/mass loading histories from the two basal drains and basal collection lysimeters were highly variable, suggesting the solute transport system in the heterogeneous waste rock pile is complex and is potentially influenced by the presence of ice. Science, Faculty of Earth, Ocean and Atmospheric Sciences, Department of Graduate