NWT RESEARCH DATABASE

Tags: physical sciences, environmental assessment, land reclamation, revegetation, geotechnical survey

Objective(s): To return the site and affected areas to viable, and wherever practicable, self-sustaining ecosystems that are compatible with a healthy environment and with human activities.

Project Description: In accordance with the Mackenzie Valley Land and Water Board (MVWLB) Guidelines, the overarching closure goal for former mine sites is to return the site and affected areas to viable, and wherever practicable, self-sustaining ecosystems that are compatible with a healthy environment and with human activities. To meet this closure goal, companies must demonstrate that a site is physically stable, chemically stable, does not require long-term active care, and has potential for future use. This closure goal is consistent with Teck’s approach to responsible mine closure that focuses on returning the land to a stable state for post-mining land uses and healthy ecosystems. The closure goal may be modified through engagement with stakeholders during reclamation research, and the closure and reclamation plan update process. Several different types of field investigations will be done in 2019 and 2020 to better understand metals movement through the Tailings Impoundment Area (TIA) and to test options for closure planning. The field programs will include Environmental and Geotechnical Investigations, Passive Water Treatment Studies and Vegetation Trials, which are described in more detail below: The research team will conduct surface water, groundwater, soil, tailings, and berry sampling, and vegetation and soil surveys. These surveys are primarily non-invasive requiring 1 to 5 people temporarily onsite (possibly more if the community participates in berry sampling). Additional soil and tailings surveys require sampling via borehole/testpit investigation. Borehole investigation typically requires 3 to 5 people temporarily onsite. Tandem to environmental soil sampling, geotechnical boreholes are also planned to investigate soil characteristics of the tailings and the earthen dykes containing them. Boreholes can be drilled anywhere from 1 to 25 m deep, using a sonic (vibration-based) drilling method. Geotechnical instrumentation may also be installed to monitor groundwater, and subsurface soil qualities and properties. These instruments are installed in boreholes drilled during the geotechnical investigation. A selection of boreholes will be completed as groundwater monitoring wells. The wells will be accessed periodically for collection of water quality samples. All wells and boreholes will be plugged and sealed with bentonite clay and/or concrete grout to prevent vertical movement of water from surface or between soil strata. Surface and ground water sampling of the TIA, downstream wetland, and point-of-last-control will continue, requiring 1 to 3 people temporarily onsite. Added to this survey schedule will be monitoring of any future restoration plans, to evaluate compliance with the Water Licence. Surface water samples are collected using a manually powered boat. Waterbodies downstream from the water treatment facility are monitored annually. Access to these waterbodies is only by helicopter. The helicopter may land on the lease area. An on-site field trial will be performed to evaluate passive water treatment technologies. The areal extent of the passive water field trial will be approximately 1 hectare, or less. The field trial area will be located near the existing serpentine channel, which will serve as the source of water for the passive water treatment testing. The shrub vegetation will be shredded and larger logs will be used for the vegetation trial described below. The approximately 1 ha area will be cleared of vegetation and organic soil that will stripped to a depth of approximately 0.30 m. The area will be graded (deep to shallow) to direct water from the main pond to and through the constructed wetland, and back toward the serpentine channel. The organic soil that was stripped will be mixed with the shredded vegetation from site. Additional organic material including mulch, topsoil, manure and/or biosolids may be also be mixed in to create suitable wetland substrate. This additional organic material will be sourced from vendors. The substrate mix will be placed in a single lift across the constructed wetland trial area. The area will be vegetated using willow stakes and/or nursery-supplied seed or plugs of native wetland vegetation. Another method that will be used to determine the water treatment capacity of local wetland vegetation is to conduct an offsite mesocosm study. Working from the edge of the TIA dyke (to minimize impacts to the existing wetland area by equipment), three 1-m square patches will be carefully removed from the existing wetland. The patches, up to 0.3 m thick, will be placed into a tote and wrapped for off-site shipment. The patch area will be carefully regraded to promote re-establishment of vegetation. The patch will be shipped to a research facility/laboratory and used in a controlled wetland mesocosm study. The wetland mesocosm study will be a controlled experiment to determine the capacity of the patch to treat tailings-impacted water. A vegetation trial is being considered that will include the establishment of 3 to 5 plots of approximately 10 m x 10 m in size. Within these plots, weathered logs and fresh logs (from clearing done for the constructed wetland trial) will be scattered. A native grass seed mix will be used to establish growth quickly of non-invasive plants. The plots will be monitored for seed germination with respect to log placement. Flagged poles will be used to demarcate the plot areas, which will remain on the TIA until the trials are complete (one or two years). Results will be provided as a component of annual water licence reports submitted to MVLWB by March 31 each year. Community meetings will also occur in person at least once per year with results and next steps in the research, and ultimately input into a closure plan. The fieldwork for this study will be conducted from June 20, 2019 to December 31, 2019.