Project Update: Gold Mine Site Reclamation
The following is an update on the project status for the reclamation work planned for the former Long Lake Gold Mine. The update reflects the completion of the detailed design drawings and construction specifications. The Report and data collected for the Phase I Site Characterization and Conceptual Rehabilitation Plan is still available on the weblink shown below.
The last update was March 4, 2016.
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The Phase 1 Site Characterization Work and Conceptual Reclamation Plan was completed in 2014 by CH2M Hill. The Site Characterization Report and supporting documentation has been provided in the weblink shown below:
Phase 1 Weblink – Site Characterization and Conceptual Remediation Plan
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The Phase 2 Detailed Design was initiated in the fall of 2014 by SNC Lavalin and will be completed this summer (2017).
The Detailed Design completed by SNC Lavalin expanded on the initial site characterization work and conceptual design completed in 2014 (Phase 1). The Design Report and the supporting appendices are provided on the Phase 2 weblink. The Design Report has been broken up into individual sections to make downloading easier. The contents of the Design Report is briefly described below. Costing information and some species at risk data has been removed from the Report provided as it remains confidential.
• Appendix A: Biological Survey In 2015, field surveys were undertaken to identify species at risk to support application for permitting under the Provincial Endangered Species Act (ESA)and Federal Species at Risk Act (SARA). Species identified as a potential concern within the project areas included Blanding’s turtles, Massasauga rattle snakes and Eastern Whip-poor-wills. In addition a breeding bird survey was completed for both forest and marsh species. Results of the surveys identified both Blanding’s turtles and Whip-poor-wills within the project site area. Although Massasauga habitat was identified, no rattle snakes were observed during the surveys. Appropriate avoidance and mitigative measures have been incorporated into the construction specifications. Federal and Provincial permit applications to the Ministry of Natural Resources and Forestry and Environmental Canada have been submitted. • Appendix B: Lake Bathymetry: Contours of the lake bottom in the area the tailings delta in Long Lake have been prepared to facilitate the removal of tailings and contaminated material from this area. The contours show that water depth is relatively shallow (less than 4 m) for about 100 m before dropping off steeply to in excess of 15m. Submerged tailing and contaminated material with less than 2 m of water cover will be removed and relocated to the new tailings impoundment located at TA-01. Contaminated material below this depth will be left in place. The arsenic in the tailings and contaminated sediment is stable when submerged and will not leach into the water column.
• Appendix C1, C2 and C3: Geotechnical Investigation: The geotechnical investigation was carried out in the TA-01 tailings area (the largest tailings area) to support the design and construction of the new Tailings Impoundment. The investigation involved the advancement of several boreholes in the TA-01 tailings area to characterize underlying soil stratigraphy and depth to bedrock. Analyses of the underlying soils in TA-01 identified very soft soil conditions at depth with limited bearing capacity. The soft soil conditions required the expansion of the impoundment area to cover most of TA-01 tailings area. The soft soils are also predicted to settle as much as 1.5 m. The construction schedule and design of the cap has had to accommodate the predicted settlement in order to ensure that settling does not cause water to pond on the cover.
• Appendix E: Tailings and Contaminated Sediments Removal: Removal options for tailings and contaminated sediment in Long Lake were reviewed. Excavation and dredging were found to be comparable options when comparing cost, environmental risk, feasibility and effectiveness. Based on this assessment the tender process will allow bidders to propose their preferred approach and this will be evaluated as part of the tender process.
• Appendix D1 and D2: Characterization of Contaminated Material: Detailed sampling was conducted across the contaminated areas identified in the Phase 1 Site Characterization work to identify the extent of the tailings and contaminated soil. During 2015 over 400 samples were collected and sent for laboratory analyses. Although tailings volumes were found to be similar to what was identified during the earlier site characterization work, arsenic contamination was found to have migrated into surrounding soils, to a greater extent than was expected.
o Although the maximum tailings depth in the main tailings area (TA-01) is about 3 m, elevated arsenic concentrations were identified in the underlying native soils to a depth of 8 m.
o In the wetland area, arsenic contamination was believed to be predominantly around the main drainage channel (Luke Creek). However, subsequent sampling has shown the arsenic contamination extends to more than 100 m beyond the creek channel, substantially increasing the quantify of contaminated material that will require excavation from the Wetland (as well as clean backfill that must be brought in).
o Elevated arsenic levels in the sediment in Long Lake was found to extend well out into the south bay of Long Lake, beyond the exposed tailings delta, which was not unexpected. Removal of tailings from Long Lake will be limited to material that is submerged with less than a 2 meter water cover, as was described previously in the Phase 1 Site Characterization Report (2014). The feasibility of removing arsenic contaminated sediment from the deeper areas of the lake is poor. In addition, the arsenic material that is submerged is stable provided it remains flooded and is not exposed to anoxic conditions.
o Sampling in the upper tailings areas (TA-02 and 03) determined that contaminated material in this area can be
completely removed due to the relatively shallow depth to bedrock.
• Appendix F1, F2 and F3: Water Management: Historic precipitation patterns in the Sudbury area were reviewed to support the design of temporary water diversion channels required during construction, as well as the design of permanent drainage channels as part of the site restoration. During construction, drainage channels have been sized to pass the 1 in 25 year flood. Following site reclamation, the permanent drainage features have been sized to pass a 1 in 1000 year flood. The Water Management assessment also determined the expected runoff that will occur from work areas during reclamation to help in sizing the required water treatment infrastructure. Groundwater seepage from the TA-01 Impoundment was also assessed and will be managed through a subsurface drainage system.
• Appendix G1 and G2: Water Treatment Options: Runoff from areas of active excavation, as well as water that collects in the impoundment during construction will be treated prior to being release to the environment. The plan is to use a package (mobile) treatment system with effluent that meets Provincial Water Quality Objectives. Several vendor were contacted to determine feasibility and cost to treat water to PWQO.
• Appendix H: Design Criteria: The design criteria requirements as specified in the original request for proposal have been summarized.
• Appendix I: Final Cover Selection: Several geosynthetic materials were reviewed to cover the TA-01 Impoundment once completed. High Density Polyethylene (HDPE) was identified as the preferred cover material.
• Appendix J: Settlement: Soft soil conditions within the TA-01 tailings areas are expected to experience significant consolidation after the tailings impoundment is constructed over this area. Samples were collected and laboratory analyses completed to quantify the extent of settlement expected and the time required before the underlining material is finished consolidating. Maximum settlement was determined to be on the order of 1.5 m and could take up to 5 years before settlement is completed. This resulted in delaying the installation of the Impoundment cover until the end of the project, and varying the design to accommodate the predicted settlement to ensure the impoundment cover continues to provide positive drainage.
• Appendix K: Technical Specifications: Project specific construction specifications as well as the generic Ontario Provincial Standard Specifications (OPSS) are provided in a separate folder. These provide specific instructions to the contractor with regard to material types, placement and handling of materials specified in the design documents, as well as environmental controls, QAQC requirements, etc.
• Appendix L: Material Quantities: This document includes the Basis of Cost Estimate and proposed Construction Schedule. The costing information has been removed.
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Next Public Meeting Summer/Fall of 2017
We are planning to tender the reclamation work late this summer and awarded by the end of 2017. Work is expected to begin in 2018.
The reclamation work is expected to result in some disturbance to area residents located along the south side of Long Lake. Some of the activities of concern are described below:
1. Site access improvement will include the widening of sections of Lakes End Road as well as the Mine Access Road (beyond the gate). Some of this work will be occurring within the Eden Township Forest Conservation Reserve and will result in the removal of trees. Red pine and white cedar are protected within the reserve boundaries and all such trees that require removal will be marked for approval by MNRF before being harvested.
2. Construction activity during 2018-2020 could interfere with the snow mobile trial running along the Mine Access Road and through the site. There will be no public access to work areas during active construction due to public health and safety concerns.
3. A significant quantity of backfill, gravel and topsoil will be required to restore excavated areas and construct the cover over the tailings area. Every effort will be made to source this material as close to the site as possible, however it is expected that significant amounts of material will have to be transported to site using area municipal roads, particularly along the south side of Long Lake. This will result in increased truck traffic during certain periods of the reclamation program.
4. Most of the excavation work will take place inland from the shore of Long Lake, or in the case of the Wetland area, in the winter. This should help to reduce construction noise at the lake shore. The exception to this will be the removal of tailing from Long Lake. This work has to take place during the ice free period and there will be no barrier to equipment noise.
5. Vandalism has been an ongoing issue at the Long Lake Gold site. Damage to monitoring wells, as well as the potential for ATV damage to the capped tailings impoundment and drainage channels is a concern. Options to protect the rehabilitation from vandalism include: limiting access to the site or fencing areas requiring protection will need to be discussed.
A meeting with area residents and stakeholders will be schedule this summer to review the details of the reclamation plan and discuss these and other issues, as well as potential mitigation to reduce their impact on area residents. Residents will be notified of the meeting date and the venue location once those details are confirmed.
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University of Waterloo working on site:
Researchers from the University of Waterloo in collaboration with the University of Ottawa have initiated a field and laboratory based research project at the Long Lake Gold Mine, in November 2016. The objectives of this project are to:
1) evaluate controls on arsenic biogeochemistry in tailings at the Long Lake site; and
2) evaluate passive-treatment approaches for the remediation of arsenic in tailings-impacted groundwater.
A total of 31 piezometers and soil-water solution samplers were installed. The research team completed one round of groundwater sampling from the wells installed in December 2016. The research team will complete two to three additional rounds of water sampling during the 2017 field season, and will characterize the water samples as above.
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Should you have any questions or concerns, please contact me at the email address or phone number provided below.
Regards,
Steve Reitzel, P.Eng Sr. Project Engineer Ministry of Northern Development and Mines 933 Ramsey Lake Road Sudbury, ON P3E 6B5