Closure and rehabilitation detailed design for a tailings storage facility: case study of a gold mine in Quebec, Canada

Authors: Ouchebri, I; Göksu, A; Junqueira, F Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2152_34

Cite As:
Ouchebri, I, Göksu, A & Junqueira, F 2021, 'Closure and rehabilitation detailed design for a tailings storage facility: case study of a gold mine in Quebec, Canada', in AB Fourie, M Tibbett & A Sharkuu (eds), Mine Closure 2021: Proceedings of the 14th International Conference on Mine Closure, QMC Group, Ulaanbaatar, https://doi.org/10.36487/ACG_repo/2152_34



Abstract:
The preservation of ecosystems surrounding mine sites and the rehabilitation of disturbed ecosystems due to mine activities is a key responsibility of mine operators. In Canada, federal and provincial regulations are established to control mining activities and assist mine operators in developing a successful management system for tailings facilities, through planning, construction, operation and closure. A Closure and Rehabilitation Plan has been prepared for an acid-generating tailings storage facility (TSF) in Quebec (Canada) as part of the mine’s progressive reclamation effort and in order to meet regulatory closure requirements. This article presents background information on the TSF, the main closure objectives and the rehabilitation strategy, concepts and design principles. Details for the rationale behind various choices made throughout the planning and design phases, as well as a description of the design, are presented with regards to the cover system and water management strategy. Based on research conducted at the mine site, a 1.4-m thick cover with a capillary barrier effect (CCBE) has been designed to limit oxygen diffusion and water infiltration into the acid-generating tailings. The cover was designed to be constructed using materials available at or close to the site. Numerical simulations indicated that the proposed CCBE design could reduce surface water infiltration by 85% and significantly reduce oxygen diffusion into the mine tailings, thereby limiting acid generation and metal leaching in the long term. To validate design assumptions and monitor long-term performance of the cover and associated water management infrastructure, an instrumentation and monitoring plan was elaborated as part of the TSF closure plan, in compliance with mining Directive 019 (MELCC 2012) and the guidelines for preparing mine closure plans in Quebec (MERN 2017). This paper includes discussions on how the cover will be instrumented with moisture and temperature sensors, suction sensors and oxygen probes, as well as observation wells and surface water sampling stations. The paper also presents the water management plan as an essential component of the reclamation and closure of the TSF. The water management plan aims to reproduce a hydrographic network, mimicking natural conditions: surface regrading will create topographic ridges and valleys, resulting in a stable “natural type” condition over the long term. Runoff water from the cover will flow over the surface of the TSF through engineered internal ditches built at the bottom of constructed valleys. These ditches extend into a discharge channel that will convey surface water runoff to the downstream natural watercourse. Water will only be released into the environment once water quality criteria are met. These water management structures are designed to create a robust system protecting the cover and dams from erosion in the long term. A new network of perimeter ditches and pumping stations was designed to collect and pump seepage and runoff water from around the TSF during the post-mining period. A staged construction schedule was also defined to minimize disturbance to the environment

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