Innovative design and deep trench excavation for a groundwater collection improvement project : Part 2 of 2 case study from the former Sullivan Mine, Kimberley BC Schneider, Daniel R.; Peterson, Ryan
SNC-Lavalin Inc. conducted detailed hydrogeological investigations and subsequent remedial activities to assess and improve the collection of seepage of acid rock drainage from two large waste rock dumps located in the Mark Creek valley, in what is called the Lower Mine Yard at Teck’s former Sullivan Mine Operations in Kimberley, British Columbia. A remedial options analysis was completed to assess potential long-term solutions, ranging from source removal to in-situ passive treatment. A detailed review of the options included a series of pre-screening questions, evaluation using a project-specific scoring matrix, and a series of technical workshops. The resulting preferred option was an interception trench system with a down gradient physical barrier. The design employed passive gravity flow to a central collection vault followed by pumping into nearby infrastructure for conveyance to an existing treatment facility. SNC-Lavalin developed the design basis and detailed design for installation of a 600-metre long interception trench that consisted of perforated drain pipes and a low permeability liner installed up to approximately six to ten metres below ground surface. Phase I construction of the system for the South Waste Rock Dump occurred between November 2016 and May 2017. Construction of Phase II commenced in April 2019 and was substantially completed by end of July 2019. Based on the Performance of Phase I, the same design was adapted to upgrade an existing seepage collection system along the toe of the North Waste Rock Dump. Trench stability, especially in areas with higher groundwater elevations and inflows, was a primary concern for both constructability and worker safety. This was addressed by the use of trench box shoring systems, limiting the lengths of open trench, and adapting liner installation methods to different ground conditions encountered. Potential for low oxygen conditions required continuous air monitoring and ventilation to ensure a safe work environment. The potential for worker exposure to low oxygen conditions during system operation and maintenance was mitigated through building and pump system design that eliminated confined space entry for routine inspections. Results of a performance monitoring program indicate that the system is functioning as designed to collect acid rock drainage affected shallow groundwater. Seepage into Mark Creek has not been observed since upgrades have been completed.
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