Sä Dena Hes Tailings Management Facility Decommissioning Design Report

Transcription

1 Sä Dena Hes Tailings Management Facility Decommissioning Design Report Prepared for Teck Resources Limited Prepared by SRK Consulting (Canada) Inc. 1CT March 2014

2 Sä Dena Hes Tailings Management Facility Decommissioning Design Report March 2014 Prepared for Prepared by Teck Resources Limited 601 Knighton Road Kimberley, BC V1A 3E1 SRK Consulting (Canada) Inc West Hastings Street Vancouver, BC V6E 3X2 Canada Web: Tel: Web: Project No: File Name: 1CT SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ Copyright SRK Consulting (Canada) Inc., 2013

3 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page ii Table of Contents 1 Introduction Background Scope of Work Project Area Description Location Regional Geology Surficial Geology Climate Hydrology Hydrogeology Existing Conditions South Dam Reclaim Dam North Dam North Creek Dyke Camp Creek Diversion Dam Decommissioning Design Criteria Overview Dam Classification Design Flood Stability Analyses Design Earthquake Design General Sediment Retaining Structure (SRS) Drainage Channels Erosion Protection Soil Covers Reclaim Pond Drawdown and Dam Decommissioning South Pond Drawdown and Dam Decommissioning Sideslopes of the Notch Excavation Construction Water Balance Preparatory Activities IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

4 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page iii Sediment Load Assessment in the Reclaim Pond Prepare Construction and Spoil Areas Stockpile Required Materials Construction Activities Water Management Excavation of the Breach Sediment Control Structure Excavation of the Drainage Channels Soil Covers Riprap Placement Removal of the Pump House, Decant Tower and Pipe Construction Quality Assurance and Quality Control General Construction Monitoring and Responsibilities Post Construction Monitoring Reporting Construction Schedule Construction Quantities Erosion and Sediment Control Plan General Surface Roughening Flow Controls Check Dams Silt fences Temporary Sedimentation Basin Floating Turbidity Curtains Flocculation Revegetation Inspection and Maintenance Air Quality Plan Environmental Monitoring During Construction References...34 IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

5 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page iv List of Drawings All drawings can be found in Appendix A. Drawing Number SDH-DR-00 Engineering Drawings for Sä Dena Hes Project, Tailings Management Facility Decommissioning, Revision 2, IFT Drawing Number SDH-DR-01 Existing Conditions, Revision 1, IFT Drawing Number SDH-DR-02 Location Map, Revision 1, IFT Drawing Number SDH-DR-03 South Dam Plan and Profile, Revision 1, IFT Drawing Number SDH-DR-04 South Dam Cross Sections, Revision 2, IFT Drawing Number SDH-DR-05 Sediment Retaining Structure Plan, Revision 1, IFT Drawing Number SDH-DR-06 Sediment Retaining Structure Sections, Revision 2, IFT Drawing Number SDH-DR-07 Reclaim Dam Plan and Profile, Revision 1, IFT Drawing Number SDH-DR-08 Reclaim Dam Cross Sections, Revision 1, IFT Drawing Number SDH-DR-09 Drainage Channel Plan, Revision 2, IFT Drawing Number SDH-DR-10 Drainage Channel Sections, Revision 2, IFT Drawing Number SDH-DR-11 Areas to be Capped General Arrangement, Revision 1, IFT Drawing Number SDH-DR-12 Tailings Drainage Channel Plan, Profile and Section, Revision 2, IFT Drawing Number SDH-DR-13 Materials Zoning in South Dam, Revision 1, IFT Drawing Number SDH-DR-14 Materials Zoning in Reclaim Dam, Revision 1, IFT List of Tables Table 1: CDA (2007) Dam Classification in Terms of Consequences of Failure... 9 Table 2: CDA (2007) Inflow Design Flood (IDF) and Consequence Classes Table 3: Factors of Safety for Static Assessment (CDA, 2007) Table 4: Interim Guidelines for Minimum Design Factor of Safety Waste Rock Dumps Table 5: Reclamation Areas to Be Capped Table 6: Results of Stability Analysis Notch Sideslope Table 7: Inflow volumes to be managed (m 3 /day) Table 8: Free Board Levels at Reclaim Dam during Flood Events (2012 Datum) Table 9: Riprap Quantity Summary Table 10: Summary of Fill Quantities for the South and Reclaim Dams Appendices Appendix A: Drawings Appendix B: Technical Specifications Appendix C: Seismic Hazard Analysis Appendix D: Flood Hydrology Appendix E: Environmental Monitoring Plan Appendix F: Stability Analyses Appendix G: Drawdown Schedule Appendix H: Water Licence IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

6 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 1 1 Introduction 1.1 Background Teck Resources Limited retained SRK Consulting (Canada) Inc. to prepare a design report for the decommissioning of the tailings management facility (TMF) and the associated surface water management system located at their Sä Dena Hes mine. A site plan of the TMF location is provided in Drawing SDH-DR-01 (Appendix A). Mineralization at the Sä Dena Hes property was discovered in Several exploration companies conducted prospecting and exploratory drilling at the site between 1979 and 1988, leading to an estimated zinc-lead-silver mineral inventory of over 5 million tonnes in a number of zones. In 1989, the Mount Hundere Joint Venture purchased the property and started production in August 1991, mining the Jewelbox and Main Zone ore bodies using open pit and underground mining methods. Exploration and underground development work was also conducted in the Burnick ore body area, but no actual ore was extracted. During the 16 months of production, approximately 700,000 tonnes of ore were mined and processed. Concentrate was trucked in covered containers to Skagway for shipment to overseas smelters. A sharp downturn in metal prices forced the mine to shutdown in December 1992 at which time the property was put on care and maintenance eventually going into receivership. In March 1994, the current owners (joint venture between Teck Metals Limited, Teck Resources Limited, and Pan Pacific Metal Mining Corp., a wholly owned subsidiary of Korea Zinc) purchased the property through the receiver according to a court order. The property has been kept on care and maintenance except for a brief period in the winter of 1998 when Teck began preparations for reopening. A downturn in metal prices forced a re-evaluation and subsequent suspension of work. In February 2013, the owners made the decision to permanently close the mine. The closure objectives for the site are summarized below: Protection of public health and safety, Implementation of environmental protection measures to prevent adverse impacts, Ensuring land use commensurate with surrounding lands, Post closure site monitoring to assess effectiveness of closure measures for the long- term, and Passive post closure monitoring and management of the site where applicable. As part of the current mine site decommissioning, the Reclaim Dam and the South Dam would no longer be needed. Therefore, both these dams would be decommissioned, which would involve either partial removal of the dam fill or complete removal. The dam decommissioning would also involve the relocation of the existing Camp Creek Diversion to the original creek alignment. The IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

7 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 2 material excavated as part of the dam decommissioning would be used as soil cover material for both the tailings and other areas of the site that would be reclaimed. This report provides the final design for the decommissioning of both dams including a description of the current situation at and around the TMF, the design criteria for the removal of the dams supporting analyses, and the design drawings. The report contains the design drawings (reduced by 50%), also prepared as D-sized drawings. The D-sized drawings were prepared for use in the development of issued for construction drawings. The topographic contours and aerial photos used to generate the figures in this report were provided by McElhanney and are based on an August 15, 2012 LiDAR survey. The coordinate system is UTM NAD 83 Zone 9V. The original designs and as-built drawings for the TMF were based on a datum set in The recent topographic survey by McElhanney was based on a new datum that was about 2 m higher than the original datum. The drawings provided in this report and the recently issued for tender drawings were adjusted to the new datum. All elevations referenced in this report are based on the new datum. 1.2 Scope of Work The scope of work presented in this report includes: Engineering designs for the decommissioning of the South and Reclaim dams, Engineering designs for the construction of a sediment retaining structure (SRS) to replace the decommissioned South Dam, Engineering designs for permanent drainage channels to manage post closure design inflows and surface water management, and The preparation of engineering drawings (Appendix A) and technical specifications (Appendix B) for the decommissioning and construction works. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

8 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 3 2 Project Area Description 2.1 Location The Sä Dena Hes property is located in the upper basin of the Liard River close to Yukon s southern border with British Columbia. The property is approximately 70 km by road from Watson Lake, 25 km of which is gravel access road extending from the Robert Campbell Highway to the property. The mineralization lies above tree level in the alpine zone at elevations ranging between 1,200 and 1,500 m. The mill site is located below the mine workings while the TMF occupies the valley bottom at the water divide between Camp Creek and North Creek, with dam crest elevations around 1,090 m. 2.2 Regional Geology The Sä Dena Hes property is underlain by Paleozoic metasedimentary rocks with some igneous intrusions of limited size. The sedimentary strata are complexly folded with several sets of faults. The mineralization consists mainly of coarse grained galena and spharelite disseminated in skarns that have oxidized into soft incompetent clay. 2.3 Surficial Geology The mountainous area around Mount Hundere is part of the Hyland Plateau physiographic unit. To the west, the Hyland Plateau gives way to the Liard Plain, a broad southeasterly trending intermontane basin that contains the Liard and Frances rivers. 2.4 Climate Snowfall at the Sä Dena Hes property is approximately 230 cm/yr and temperatures vary from an average of 26.3 C in January to an average of 14 C in July. Using Watson Lake Airport (elevation of 689 m and mean annual precipitation (MAP) of 490 mm) as a base and applying the observed regional precipitation gradient, the estimated MAP for the TMF (elevation of 1,090 m) was about 690 mm. Mean annual runoff for the site was estimated to be in the range from 266 to 330 mm. 2.5 Hydrology The Sä Dena Hes mine is located in the drainage basin of False Canyon Creek, a left bank tributary of the Frances River. False Canyon Creek has a total catchment area of 492 km 2 and discharges some 55 km above the Frances River and Liard River confluence. Access to the mine development is from the south across the drainage basin of Tom Creek, a left bank tributary of the Liard River. The open pits, underground workings, and waste rock dumps associated with the Jewelbox ore zones are located near the drainage divide between Tom and False Canyon creeks. All drainage from the Jewelbox development is directed to Camp Creek, a steep-gradient tributary of False Canyon Creek that drains the eastern flank of Mount Hundere. The mill site is also located in the IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

9 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 4 catchment of Camp Creek. The Burnick development is entirely confined to the headwaters of another False Canyon Creek tributary, the west fork of tributary E. The TMF is spread across the drainage divide, with the former cofferdam being located on the divide. Since the tailings are deposited against the North Dam, runoff from the tailings area is now draining south towards the South Dam. 2.6 Hydrogeology Historically, there has been seepage along an 80 m zone of the downstream toe of the North Dam on both sides of the valley. This seepage is collected at a monitoring station referred to as MH-02 and is a combination of groundwater discharge from the surrounding hillsides to the west and minor seepage flow from the impoundment. There are a number of piezometers along the crest of the North Dam, which are recorded monthly when the piezometers are accessible. Locations of the piezometers are shown on Drawing SDH-DR-01 (Appendix A). The seasonal fluctuations recorded over the last few years have been generally consistent and are within acceptable tolerance limits. Piezometers are also located in the South and Reclaim dams as shown on Drawing SDH-DR-01 (Appendix A). The levels in these piezometers fluctuate with the water level in the South Dam pond and the Reclaim Pond, making management of the pond levels critical to the stability of the dams. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

10 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 5 3 Existing Conditions 3.1 South Dam The South Dam constructed in 1991, is approximately 17 m high with a crest length of about 400 m. The crest elevation varies from 1,098 m on the upstream side to 1,099 m on the downstream side. In 1997 and 1998 a zoned granular buttress was constructed along the toe of the dam to add additional stability. Three finger drains were constructed in localized toe areas to improve internal drainage. Adjacent to the upstream face of the South Dam is a decant tower, which during mine operation decanted supernatant water into the Reclaim Pond through a 0.6 m diameter corrugated steel pipe. The decant pipe was sealed off in 2001 and a siphon system (4 x 100 mm diameter pipes) was installed in 2003 to release water to the Reclaim Pond. Each year between April and October, the siphons draw the ponded water in behind the South Dam down as low as is practical in preparation for inflow from the spring runoff. An emergency spillway is also located in the west abutment of the South Dam consisting of two 900 mm Corrugated Steel Pipes (CSP) s with invert elevations at about 1,096 m. The culverts were originally designed to accommodate the 200 year flood event; however, the spillway can accommodate the peak discharge during a 1,000 year event without overtopping. The instantaneous peak of the incoming flood hydrograph for the 1,000 year event at the South Dam was estimated to be 5.4 m 3 /s. The combined outflow through the two culverts would peak at 1.6 m 3 /s, or 30% of the incoming flood peak. During passage of the flood, a volume of 53,000 m 3 of water would be temporarily stored within the TMF. The water level in the TMF would peak at an elevation of 1,096.9 m, which is roughly at the crown of the two culverts. 3.2 Reclaim Dam The Reclaim Dam was built in 1991 (elevation of 1,084 m) to detain the supernatant water decanted through the decant tower from the tailings pond. As part of mine operation the detained water was recycled through the mill under a controlled discharge, which when required discharged annually into Camp Creek from April to October The Reclaim Dam is approximately 16 m high, with a crest elevation of 1,084 m, a crest length of about 250 m and a crest width of 10 m. The Reclaim Pond has the capacity to store approximately 270,000 m 3 of water at an elevation of 1,082 m which is the elevation of the existing overflow spillway. Camp Creek is currently diverted into a channel along the west side of the Reclaim Pond and discharges through two 1.2 m diameter culverts into a riprap lined exit chute. The invert of these culverts is about 1, m. In March 1992, Curragh Resources, the previous owners of the mine, placed additional limestone rock over the existing inverted filter along the toe of the Reclaim Dam to build a toe buttress that would increase the factor of safety of the dam. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

11 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 6 Each year between April and October, a second set of siphons draw down the ponded water in behind the Reclaim Dam to maintain a safe pond level (elevation of m). An emergency spillway is located along the western perimeter of the Reclaim Pond. The spillway is a riprapped lined open channel with a base width of 4 m and an invert elevation of 1,082 m. 3.3 North Dam The North Dam is approximately 15 m high with a crest elevation of 1,100 m, a crest length of about 260 m, and a crest width of 10 m. When the facility was shutdown in 1992, the tailings at the dam s west end were almost level with the adjacent dam crest. To control the migration of wind-blown tailings, Teck placed a 50 to 75 mm cover of 20 mm minus gravel over a 150 x 80 m area adjacent to the northwest corner of the TMF. Teck also removed most of the windblown tailings on the downstream face of the North Dam. At the east end of the North Dam, the surface of the tailings behind the dam is 1.5 m below the crest. Most of the tailings lie within the northern half of the TMF, north of the cofferdam. Following spring melt, water historically ponds over about 40 to 70% of the northern tailings surface and extends all the way to the cofferdam. This excess water has historically been released to the southern half of the tailings pond through a gated culvert in the cofferdam. However, Teck breached the cofferdam in 2012 which lowered the pond level. However, while there is now uncontrolled discharge to the southern half of the impoundment, ponded water still occurs. The North Dam would be retained as part of the TMF decommissioning. The cofferdam would be removed. 3.4 North Creek Dyke The North Creek Dyke is located approximately 1 km north of the tailings pond as shown in Drawing SDH-DR-11 (Appendix A). The dyke was constructed in 1991 to provide a reservoir from which water was pumped to the northern end of the TMF in preparation for the start-up of the mill. The pump station is located on the north bank of the creek, upstream of the dyke. The dyke has a maximum height above original ground of about 5 m and is about 50 m in length. The volume of silty sandy till used to construct the dyke is estimated to be about 2,000 m 3. A 600 mm diameter outlet pipe at the base of the dyke allows for the North Creek to pass through the dyke. Three other culverts varying in size from 600 to 1,000 mm in diameter provide enough capacity to pass the 200 year flood event. These three culverts discharge onto the downstream face of the dyke, which has been riprapped in the vicinity of the culvert outlets. The lower culvert discharges further downslope of the upper culverts into the riprap lined channel. This dyke and the culverts would be removed as part of the site decommissioning. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

12 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Camp Creek Diversion The Camp Creek Diversion Channel diverts Camp Creek flows along the west side of the Reclaim Pond as shown in Drawing SDH-DR-01 (Appendix A). The diversion channel discharges its flow through two 1,200 mm diameter corrugated steel pipe culverts into a riprap lined exit chute downstream of the Reclaim Dam. From the exit chute, the flow returns to the original Camp Creek downstream of the Reclaim Dam. The diversion channel is designed to accommodate the peak instantaneous flow during the 200 year flood event. The two 1,200 mm diameter pipes are also designed for the 200 year peak instantaneous flow based on a catchment area of 4.47 km 2 and assuming all interceptor ditches are breached. The two culverts can also accommodate the peak flow from the 1,000 year event with a reduced freeboard. In passing this flood, it was estimated that about 66,000 m 3 of water would have to be temporarily stored in the Reclaim Pond, another 36,000m 3 would be stored in the tailings pond, and the water level behind the Reclaim Dam would rise to an elevation of m, leaving a freeboard of about 0.9 m below the dam crest. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

13 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 8 4 Dam Decommissioning 4.1 Design Criteria Overview Teck intends to decommission the TMF by the removal of the South Dam and the Reclaim Dam with the North Dam remaining in place. This would also involve the removal of the emergency spillway in the South Dam, the decant tower and decant pipe through the dam. The material removed from the dams would be used as a source of capping for reclamation of disturbed areas around the site including the tailings located in the north end of the TMF. The depth of the capping would vary from 0.4 to 0.6 m. The decommissioning plan also includes the construction of a 5 m (approx.) high sediment retaining structure (SRS) along the upstream toe of the removed South Dam to contain any sediment erosion from the tailings cover during the early stages of reclamation/revegetation. Any material in the dams that remain after completing the capping would be reshaped to provide positive runoff drainage. A small amount of tailings was deposited in the south half of the TMF during the operation of the mine. This area would also be capped and revegetated. Runoff from the capped tailings would drain to the sediment retaining structure and discharge over a riprapped lined spillway built into the dyke. Flow through the spillway would then be fed into a riprapped channel that would eventually discharge back into Camp Creek below the location of the removed Reclaim Dam. The Camp Creek Diversion channel along with the associated spillway and exit chute would also be decommissioned. The creek would be realigned back into the old creek bed via a new riprapped channel. The flow from the reclaimed tailings area would converge with this new channel. The drawings shown in Appendix A reflect the overall approach to the TMF decommissioning as discussed above. However, it is expected that the TMF decommissioning would likely take place in several stages. It is anticipated that the initial stage would involve removal of the material at the east abutment of the Reclaim Damdown to a point through the maximum section of the dam. This would involve the excavation of a notch through the dam with an east sideslope at the grade of the original ground and a west sideslope of about 2.5H:1V. The South Dam would remain in place throughout the excavation of the notch. Once the Reclaim Dam notch is completed, work would begin on a similar notch at the South Dam followed by the construction of the drainage channels and the eventual relocation of the Camp Creek back to its original predevelopment condition. Once both notches are complete and Camp Creek has been restored to its original alignment, work would focus on the removal of the remaining section of the dams. For the purposes of this report, the following sections focus on the staged approach to the decommissioning plan: the excavation of the embankment notches at the east abutment of both dams, water management during decommissioning, technical specifications, and QA/QC procedures. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

14 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Dam Classification Assessing safety acceptance requires the selection of appropriate design loading events that the structures must safely withstand. The design, construction, operation, and monitoring of dams, including tailings dams in Yukon have to be completed in accordance with appropriate Provincial and Federal regulations and industry best practices. The primary guidance document in this regard, is the 2007 Dam Safety Guidelines (CDA 2007) published by CDA. A key component of the guidelines is classifying the dam(s) in question into hazard categories (Dam Class), which establishes the appropriate geotechnical and hydro-technical design criteria. Table 1, is a reproduction of the recommended dam classification as presented in the CDA guidelines. Determining the appropriate hazard rating is subjective and is dependent on sitespecific circumstances and may require an agreement between the proponent, regulator, and stakeholders. Table 1: CDA (2007) Dam Classification in Terms of Consequences of Failure Dam Class Population at Risk [note 1] Incremental Losses Loss of Life [note 2] Environmental and Cultural Values Low None 0 Minimal short-term loss Significant Temporary only Unspecified No long-term loss No significant loss or deterioration of fish or wildlife habitat Loss of marginal habitat only Infrastructure and Economics Low economic losses; area contains limited infrastructure or services Losses to recreational facilities, seasonal workplaces, and infrequently used transportation routes Restoration or compensation in kind highly possible High Permanent 10 or fewer Significant loss or deterioration of important fish or wildlife habitat. Very high Permanent 100 or fewer Extreme Permanent More than 100 Restoration or compensation in kind highly possible Significant loss or deterioration of critical fish or wildlife habitat Restoration or compensation in kind possible but impractical Major loss of critical fish or wildlife habitat Restoration or compensation in kind impossible High economic losses affecting infrastructure, public transportation, and commercial facilities Very high economic losses affecting important infrastructure or services (e.g., highway, industrial facility, storage facilities for dangerous substances) Extreme loss affect critical infrastructure or services (e.g., hospital, major industrial complex, major storage facilities for dangerous substances) Note 1. Definitions for population at risk: None There is no identifiable population at risk, so there is no possibility of loss of life other than through unforeseeable misadventure. Temporary People are only temporarily in the dam-breach inundation zone (e.g., seasonal cottage use, passing though on transportation routes, participating in recreational activities). Permanent The population at risk is ordinarily located in the dam breach inundation zone (e.g., as permanent residents); three consequence classes (high, very high, extreme) are proposed to allow for more detailed estimates of potential loss of life (to assist in decision-making if the appropriate analysis is carried out). Note 2. Definitions for population at risk: Unspecified The appropriate level of safety required at a dam where people are temporarily at risk depends on the number of people, the exposure time, the nature of their activity, and other conditions. A higher class could be appropriate, depending on the requirements. However, the design flood requirement, for example, might not be higher if the temporary population is not likely to be present during the flood season. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

15 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 10 Based on an the assessment by Klohn Crippen in 2003, the North Dam, the South Dam, and the Reclaim Dam were classified in the Low Consequence category. However, following the release of the revised 2007 guidelines, all three dams were re-classified to the significant category Design Flood The design flood affects the sizing of riprap erosion protection of the slopes at the spillway in the SRS, the diversion channels and the channel through the base of the removed Reclaim Dam. As shown in Table 2 below, the CDA (2007) recommends that the inflow design flood (IDF) for a significant consequence dam class is between the 1/100 and 1/1,000 year event. Table 2: CDA (2007) Inflow Design Flood (IDF) and Consequence Classes Consequence Class Low IDF 1/100-year Significant Between 1/100 and 1/1,000 year (Note 1) High 1/3 between 1/100 year and peak maximum flood (PMF) (Note 2) Very High 2/3 between 1/100-year and PMF (Note 2) Extreme PMF Note 1. Selected on basis of incremental flood analysis, exposure and consequence of failure. Note 2. Extrapolation of flood statistics beyond 1/1,000 year flood AEP is generally discouraged. The PMF has no associated AEP. The flood defined as 1/3 between the 1/1,000 year and PMF or 2/3 between 1/100 year and PMF has no defined AEP. As the Reclaim Dam and the South Dam will be removed as part of the TMF decommissioning, and as no structures such as spillways or diversion ditches will be constructed that would impact the North Dam, the above criteria does not apply to post closure. However, the 1000 year event was selected as an appropriate criteria for the design of the permanent diversion channels and spillways that would remain post closure Stability Analyses The excavation of both the South Dam and the Reclaim Dam would change the classification of these structures. The areas where stability would remain important during and following the dam removals include: The upstream stability during reservoir drawdown, The upstream and downstream stability of the dam at the end of drawdown and in the long term, and The stability of the sideslopes of the embankment notch. Reservoir Drawdown Generally, a decrease in retained pond levels increases the factor of safety for embankment dams, although not in all cases. Terzaghi and Peck (1967) note that for some dams, the stability of the upstream slope may be more critical at an intermediate level, known as partial pool, than IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

16 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 11 when the reservoir is full. Furthermore, if the reservoir is lowered too quickly, there is a risk that the upstream slope can fail due to what is known as rapid drawdown. The CDA (2007) recommendations for the factors of safety applicable to static stability analyses of embankment dams, including rapid drawdown, are summarised in Table 3. These guidelines are applicable prior to the dam removal. Table 3: Factors of Safety for Static Assessment (CDA, 2007) Loading Conditions Minimum Factor of Safety Slope Long-term (Steady state seepage, normal reservoir level) 1.5 Downstream Full or partial rapid drawdown 1.2 to 1.3 [a] Upstream End of construction before reservoir filling 1.3 Downstream and upstream [a] Higher values may be required if drawdown occurs frequently during operations. In consideration of Table 3, the target factor of safety against failure of the upstream face of the dam during reservoir lowering of 1.2 was selected. Upstream and Downstream Slopes Given that the South Dam and the Reclaim Dam would no longer be dams following the proposed removals and that the dams are part of a mining project, it is reasonable to base the stability criteria for the upstream and downstream slopes on factors of safety applicable to waste rock dumps. A typical example of minimum factors of safety for waste rock dumps is provided in Table 4, the source of which is the guidelines published by the BC Mine Waste Rock Pile Research Committee in The partially removed dams would fit with Case B, as the consequences of a failure of either the upstream or downstream slope are not severe. Table 4: Interim Guidelines for Minimum Design Factor of Safety Waste Rock Dumps Stability Condition Case A More Severe Case B Less Severe Stability of Dump Surface Short term (active) Long term (closure) Overall Stability (deep-seated) Short term (active) Long term (closure) Pseudo-static * Applicable to the South and Reclaim Dams * * 1.0* In consideration of Table 4, the appropriate factors of safety against failure of the upstream and downstream face of the dam in the long term are 1.1 at the dam face (shallow failure), 1.3 for a deep-seated failure, and 1.0 under pseudo-static loading conditions, i.e., in response to the design earthquake. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

17 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 12 Sideslopes of Embankment Notches During the excavation of both notches, the appropriate factor of safety for the sideslopes corresponds to what is known as the end of construction phase. This case is noted in Table 6-1 of the CDA (2007) guidelines, which indicates that the minimum factor of safety is 1.3. This value is higher than the short-term value (1.1) for the stability of the dump face because of safety concerns for men and equipment working at the toe of the slope and because of the potential consequences to the works at the toe of the slope. In the long term, it is reasonable to base the stability criteria for the sideslopes of the embankment notch on minimum factors of safety of 1.3. Therefore, the appropriate factors of safety against failure of the sideslopes in the notch in the long term are 1.3 for at the slope face (shallow failure), 1.3 for a deep-seated failure, and 1.0 under pseudo-static loading conditions Design Earthquake The 2010 National Building Code of Canada lists the Sä Dena Hes mine as having a peak ground acceleration (PGA) of g with a recurrence interval of 1 in 2,475 years (i.e., a 2% probability of exceedance in 50 years). Details are provided in Appendix C. The three dams at the Sä Dena Hes mine have been classified as significant consequence dams. As shown in the CDA (2007) guidelines the usual minimum criteria for design earthquake for significant class dam would have the ground motion corresponding to the annual probability of exceedance of 1 in 1,000 or In consideration of both codes, the design earthquake for the dams with a PGA of g, with a recurrence interval of 1 in 2,475 years (i.e., a 2% probability of exceedance in 50 years) was selected. 4.2 Design General The decommissioning of the TMF at the Sä Dena Hes mine would ultimately involve the partial or complete removal of the dam fill of the South Dam and the Reclaim Dam. The TMF decommissioning would also involve the relocation of the existing Camp Creek Diversion to its original creek alignment. The material excavated as part of the dam decommissioning would be used as soil cover material for both the tailings and other areas of the site that would be reclaimed. However, as stated earlier, the TMF decommissioning is expected to take place in several stages. It is anticipated that the initial stages would involve partial excavation of the Reclaim Dam and the South Dam down to a predetermined level. At the base of the excavation, a riprapped channel would be formed to match the hydraulic performance of the originally planned spillway or channel. The following sections discuss the designs of each element of the TMF decommissioning. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

18 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Sediment Retaining Structure (SRS) The SRS would be constructed by leaving in place a portion of the South Dam fill along the upstream toe of the dam. During the removal of the dam fill material, the engineer would assess the suitability of the exposed material as fill for the structure. If some of the material is found to be unsuitable, it would be removed and replaced with acceptable dam fill. The spillway at the base of the excavation has been designed to accommodate the 1,000 year runoff event. The peak inflow for this event, 5.4 m 3 /s, was recently updated by SRK in the 2013 update to the Detailed Decommissioning and Reclamation Plan (DDRP) (Appendix D). The SRS would have a crest elevation of 1,086.7 m and the spillway through the dyke would have a finished invert elevation of 1,085.0 m. The upstream face would be built with a 2H:1V slope. The downstream slope would be constructed to 2.5H:1V. As shown in Drawing SDH-DR-03 (Appendix A), the spillway would be built with a base width of 4 m and sideslopes of 2H:1V. A freeboard of 1 m would be allowed for above the maximum flow depth of 0.7 m during the 1,000 year design inflow event. The bottom and sides of the spillway would be protected by installing riprap with a D50 of 0.3 m. The approach apron to the spillway would have a D50 of 0.3, but the D50 for the exit chute from the spillway would be increased to 0.5 m. If it is found that seepage at the SRS s downstream toe is impacting the structural integrity of the dyke, a rock buttress would be built along the downstream toe. Details of this buttress would be addressed in the field by the engineer. As discussed further in Section 4.2.6, the location of SRS may vary during the initial stages of the partial excavation of the South Dam. The planned location of the SRS would be along the upstream toe of the current dam, but may be changed depending on final construction schedule. Irrespective of the location of the SRS, a riprapped lined channel or spillway at the base of the excavation would be constructed Drainage Channels Three drainage channels would be constructed as part of the decommissioning of the TMF. One channel would be built from the outfall of the SRS to a convergence with the realigned Camp Creek channel. The second would be built from a point upstream of the existing Camp Creek Diversion in the original Camp Creek channel as shown on Drawing SDH-DR-09 (Appendix A). The start point of this channel would be determined in the field. The third would be built from a point above the Tailings Pond extending to the SRS pond as shown in Drawing SDH-DR-09 (Appendix A). The following design criteria were used for design of the channels: The design inflow is based on the 1,000 year runoff event, The embankments would be built to minimize long term erosion, and Drainage channels should conform to the natural topography. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

19 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 14 The design of the realigned Camp Creek drainage channel shows a channel about 940 m long, starting at the head of the original confluence with Camp Creek at an approximate elevation of 1,107 m and ending at the outflow of the existing Camp Creek Diversion channel downstream of the Reclaim Dam. As discussed above the actual channel start point and final length of the channel would be determined in the field however the channel would have a variable grade, ranging from 1.5% in the lower reaches to about 8% at the upstream end. The variable grade is dictated by the natural terrain configuration and the extent of each section is detailed on Drawing SDH-DR-09 and SDH-DR-10 (Appendix A). The flow from the SRS spillway at the South Dam would discharge into a 200 m long drainage channel that merges with the realigned Camp Creek. Details of the constructed sections and grades are detailed on Drawing SDH-DR-05, SDH-DR-06 and SDH-DR-10 (Appendix A). As the realigned Camp Creek diversion is double the width of the constructed spillway channel from the SRS spillway, a plunge pool or equivalent energy dissipation structure was not considered necessary at the confluence of the two channels. A Tailings Drainage (North Diversion) Channel would be constructed around the northern and eastern sides of the deposited tailings beach located at the north end of the South Dam tailings pond. The channel would direct runoff to the SRS sedimentation pond as detailed on Drawing SDH-DR-12 (Appendix A). Channel Cross-Section The cross-sections of the channels were designed to pass the 1 in 1,000 year design flow event. The peak flows were estimated based on the catchment areas for each diversion channel. The realigned Camp Creek Diversion channel catchment was estimated to be 4.47 km 2, resulting in an estimated peak flow of 15.9 m 3 /s expected at the downstream end of the channel. The SRS spillway and channel was designed based on a peak flow of 5.4 m 3 /s and the North Diversion Channel for a peak flow of 3.0 m 3 /s. Detailed sections for all individual reaches are provided on Drawing SDH-DR-06, SDH-DR-10, and SDH-DR-12 (Appendix A) Erosion Protection Channel erosion protection would be provided by placing riprap over the sideslopes and base of the channels as shown in Drawings SDH-DR-03, SDH-DR-05, SDH-DR-06, SDH-DR-09, SDH-DR-10 (Appendix A). The D50 of the riprap was determined based on the open channel geometry and the calculated flow velocities. The riprap armoring depth is determined by 1.5 times the section specific D50. There are three specified riprap types: Type I (300 mm D50), Type II (400 mm D50) and Type III (500 mm D50). Riprap armoring thickness is measured normal to all slopes. Geotextile filter fabric would be used on all channels prior to riprap placement. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

20 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Soil Covers In accordance with the current reclamation plan, the exposed tailings would be capped with soil to prevent wind erosion, to minimize the impact of dust, and to provide growth medium for vegetation. The cap is not designed as a low infiltration barrier. The cover, however, would reduce surface ponding and promote runoff of non-contact water. Several other areas requiring revegetation were identified throughout the property. Some of these areas would be scarified and seeded (access roads), while others would require capping to provide a growth medium for vegetation. Table 5 provides a summary of these areas and an estimate required fill quantities based on a 0.5 m thick cap. The tailings cap would be constructed by placing material excavated from the South and Reclaim dams. The soil would be placed in a single lift to a depth of between 0.4 to 0.5 m. Placement would be achieved by end dumping and levelling with a low ground pressure dozer (D6 or smaller) or by broadcasting with an excavator. Unnecessary soil layer compaction should be avoided. The cap surface would be re-contoured to a minimum grade of 2% to promote runoff and prevent ponding. The edges of the cover would be terminated flush with the crest of the North Dam, or where downgradient terrain is encountered, it would be graded to no steeper than 2H:1V. The cap would be revegetated by hydroseeding and tree and shrub planting as soon as possible after placement. Local vegetation would be favoured and the density would be limited initially to allow the colonization by local volunteer species to be established from the areas surrounding the caps. The soil capping of the areas other than the tailings would be constructed in a similar manner and contoured to blend in with the natural terrain where possible. Table 5: Reclamation Areas to Be Capped Description Footprint Cap Thickness Quantity (m 2 ) (m) (m 3 ) Tailings Area Large Tailings Area (north of the cofferdam) 61,523 Small Tailings Area (south of the cofferdam) 9,935 Subtotal 71, ,729 Borrow Areas Borrow B 12,031 Borrow C (landfill site) 28,319 Borrow D 43,943 Subtotal 84, ,147 Burnick Zone 1200 Portal and Waste Rock Dump 3, Portal and Waste Rock Dump 2,870 Subtotal 6, ,383 Mill/Camp Area IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

21 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 16 Description Footprint (m 2 ) Cap Thickness (m) Quantity (m 3 ) Mill Building 3,855 Mill Storage 557 Mill Stockpiles 7,306 Subtotal 11, ,859 Jewelbox Area Jewelbox Pit 6,581 Jewelbox Waste Rock Dump 2,518 Subtotal 9, ,550 Main Zone Area Main Zone Pit 4,808 Main Zone Waste Rock Dump 23,869 Subtotal 28, ,339 Total 212, ,006 Once the Reclaim Dam and South Dam have been drawn down, an inspection for tailings in the reservoir area may deem it necessary to construct an additional earthen cap to the areas indicated above. The decision to increase the capping area would be determined by the Engineer. Drawing SDH-DR-11 (Appendix A) displays the exposed areas that require capping and the potential additional areas beneath the ponded reservoirs. The draw down zone of the South and Reclaim Dam could increase the capping area by 23,668 m 2 and 60,084 m 2 respectively or a total potential capping volume of 41,876 m Reclaim Pond Drawdown and Dam Decommissioning Once the Reclaim pond has been drained, the Reclaim Dam can then be excavated. Because the Reclaim Dam was constructed with a sand and gravel upstream face rapid drawdown of the ponded water is not of considerable concern. During the excavation of an initial notch, the new Camp Creek channel can be constructed through the main section of the Reclaim Dam. The constructed channel is designed having a base width of 2 m and sideslopes of 2H:1V, to accommodate the 1 in 1,000 year event with a peak flow of 15.9 m 3 /s. Design Drawings SDH-DR-7, SDH-DR-9, and SDH_DR-10 present the constructed channel alignment and cross section South Pond Drawdown and Dam Decommissioning As discussed in section 4.1.4, if the South Pond is lowered too quickly, there is a risk that the upstream slope can become unstable due to what is known as rapid drawdown. The upstream face of the South Dam was not designed to retain ponded water that fluctuates seasonally. However since the mine shut down in 1992, water has ponded up against this face and each year has experienced seasonal fluctuation without any noticeable stress on the dam. The fluctuations normally range from an elevation of 1,096 m (the culvert invert) to a low of 1,089 m in May of In any given year the maximum rate of drawdown has been about 2 m over a one month IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

22 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 17 period. In 2013, the pond level on June 7 was at an elevation of 1,096 m and by July 10, the level was down to about an elevation of 1,093 m, a drop of 3 m over a one month period. During the decommissioning of the South Dam, as the pond level to drops, the rate of drop would increase with the added risk of a surficial slope failures. SRK completed a stability analyses (Appendix F) under this rapid drawdown condition. The results indicate that when the pond level drops below an elevation of 1,088 m, the factor of safety becomes less than 1.2. As a consequence, SRK is recommending that when the pond levels reach an elevation of 1,087 m during the discharge from the tailings pond to the reclaim pond, daily observations of the slope for any signs of instability should be carried out. It is anticipated that excavation of the South Dam at the eastern end would be undertaken as the pond continues to be drained. This has the added benefit of reducing the driving force on the slope and increasing the factor of safety. The plan is to lower the pond level to an elevation of 1,084.7 m to allow construction of the spillway in the dyke. Once the South pond has been drained an initial notch excavation of the South Dam will commence. As discussed in Section 4.2.2, the initial excavation of the South Dam would likely extend from the east abutment to the maximum section of the dam. This notch would be excavated to a base elevation of 1,086.7 m. A spillway channel would be built to a finished invert grade of 1,085 m, with a width of 4 m and sideslopes of 2H:1V. The spillway was designed to handle the 1 in 1,000 year flood event for design flow of 5.4 m 3 /s. The invert elevation was selected to provide storage for the containment of sediment Sideslopes of the Notch Excavation Stability analyses were performed to assess the stability of the west sideslope of the excavation notch of the South Dam and Reclaim Dam. The analyses considered the critical section through the exposed core of the dam and used conservative strength properties representative of the soils within that section. The piezometric levels used in the analyses were based on based on a seepage analysis and assumed permeability of the soils. The analysis was performed for the following conditions: Static analysis immediately post-construction, with high piezometric conditions within the dam, Static analysis long-term conditions, with the expected long-term piezometric conditions, and Pseudo-static analysis of earthquake loading and long-term piezometric conditions. Stability modelling was completed using Rocscience s Slide 6.0. The modelling results suggest that the critical slip surfaces would be present as skin failures down face of the notch. With slopes modelled at 2H:1V the factor of safety is greater than the recommended value of 1.3 under static conditions; however, the long term pseudo-static stability was below the recommended 1.0 factor of safety. Once the models were adjusted to a 2.5H:1V slope, the stability modelling results achieved the recommended minimum safety factors. The results for the case where the core of the dam has a friction angle of 33 are summarized in Table 6. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

23 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 18 Table 6: Results of Stability Analysis Notch Sideslope Condition Calculated Factor of Safety Sideslope of Notch 2.0H:1V 2.5H:1V Minimum Factor of Safety Static, immediately post-construction Static, long term Pseudo-static (g=0.203), long term One bench, having a width of 2 m, is planned at an elevation of about 1,090 m. The bench would limit erosion by breaking up the constant slope and limiting the runoff velocity due to direct rainfall. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

24 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 19 5 Construction 5.1 Water Balance The current schedule for the decommissioning of the Tailings Management Facility (TMF) has work commencing in early spring 2014 and ending in late October. The focus of the work would be the removal of the following two dams: the Reclaim Dam and the South Dam. Draining of the ponded water behind both dams would be required prior to their removal. Historically, both ponds at the TMF are drawn down over the summer months to provide sufficient storage for the runoff from the spring freshet each year. Water is pumped from the South Dam pond to the Reclaim pond and water is simultaneously pumped from the Reclaim Pond into Camp Creek. The discharge from the Reclaim pond to Camp Creek is governed by the following conditions of the current water licence: The period of active discharge is not to exceed a cumulative total of 90 days; The discharge rate to Camp Creek is not to exceed a rate of 228 m 3 /hr or. The total volume discharged is not to exceed a 490,000 m 3 a year. To assess water management options for the dam decommissioning, SRK prepared a water balance model (Appendix G) and a drawdown schedule based on assumed start volumes at the beginning of the discharge, estimated inflows from precipitation and groundwater seepage, expected pumping rates from the tailings pond to the reclaim pond and permitted discharge rates (228m 3 /hr) to Camp Creek. The schedule requires the draining of the Reclaim Pond first, to allow decommissioning of the Reclaim Dam and work at the drainage channels to proceed as early as possible. The current plan is to begin drawdown of the South pond once the Reclaim Pond is drained. However, earlier discharge from the South pond may be required if the capacity of the pond is insufficient to handle spring melt flows and water begins discharging through the recently opened 600 mm dia. culvert that runs from the decant tower to the toe of the dam. The invert of the decant pipeline in the decant tower is El m. However the outflow control from the South Pond is the sill of the decant tower which would provide a storage volume of about 93,000m 3. SRK has prepared a water balance model to illustrate the new scenario as shown on Figures 1 and 2. The model assumes that if the South pond water level reaches the sill elevation of the decant tower (EL 1092) prior to the start of the Reclaim Pond drawdown, the plan is to allow water to exit the pond via the decant pipeline (which has a lower invert elevation) into the Reclaim pond. However, this would be on condition that there is no visual evidence of unusual turbidity in the outflow from the decant pipeline that might indicate the CSP is damaged. Once drawdown of the Reclaim pond begins, the South Pond would be allowed to continue to drain into the Reclaim pond. If there is evidence that the decant pipeline is blocked or has collapsed, the intake in the tower would be closed off and the pond level would be allowed to rise up to the level of the overflow spillway. Once the Reclaim pond is drained, pumping from the South pond would commence via a HDPE pipeline running along the east side of the pond, discharging into Camp creek. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

25 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 20 Based on these assumptions, it is expected that the Reclaim pond would be completely drawn down by the end of June or about 46 days after pumping starts and complete drawdown of both ponds by about July 25, 2014 or 71 days after the initial pump start. It should be noted that management of the inflow to both the South and the Reclaim ponds would still be required until the construction season ends. An estimate of the monthly inflows for the period July to November is summarised in Table 7. Table 7: Inflow volumes to be managed (m 3 /day) Area July August September October November South Pond 1, Reclaim The estimated drain down schedule above assumes average precipitation conditions and an average snowpack. To evaluate the impact on the dam removals due to an unusually high runoff event, SRK superimposed 5 flood events at three different pond levels to assess the resulting freeboard at the Reclaim Dam spillway. The results of the analysis are shown in Table 8. Table 8: Free Board Levels at Reclaim Dam during Flood Events (2012 Datum) Scenario Reclaim Pond Initial Elevation (m) Return Period (yr) Peak Discharge (m³/s)* Max Elevation (m) Spillway Culvert Freeboard at Reclaim Dam (m) 1, , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , Notes: * Peak Discharge at the Reclaim Dam Culverts While any one of these flood events could occur, the analysis indicated that if the Reclaim pond was at say El 1080 when a 200 year event storm hits, a freeboard of 1.3 m could be maintained with no risk of overtopping. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

26 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Preparatory Activities Sediment Load Assessment in the Reclaim Pond Staging the partial removal of the Reclaim Dam before the removal of the South Dam has the advantage of being able to assess the amount of sediment that may have collected over the years in the bottom of the Reclaim Pond. If the exposed soil indicates the potential for significant sediment release into Camp Creek, measures to control the release would be implemented prior to final removal of the Reclaim Dam Prepare Construction and Spoil Areas The depleted former borrow areas provide space for temporary stockpiles and staging areas. As shown in Drawing SDH_DR_01 (Appendix A), Borrow Area D is conveniently located near the South Dam, while Borrow Area G is located in the immediate vicinity of the Reclaim Dam. Both borrow areas are flat and have sparse vegetation, thus minimal area preparation would be required. It is expected that a portion of Borrow Area D would be used as the contractor s work area. This area would require only minor preparation for the construction offices, storage facilities, and fuelling area. Fuelling equipment in this area will be done in accordance with the appropriate regulations for fuelling near water sources. No new fuel tanks are proposed as the existing fuel tanks at the mine would be used. Transportation of fuel from the mine would be performed using truck mounted storage tanks as needed. Spill contingency plans would be prepared as part of the final design and would be the contractor s responsibility. No soils resulting from excavation of the South and Reclaim dams would be spoiled. All excavated soils would be used to construct soil caps over the tailings area and other disturbed areas. Riprap recovered from the excavation of the South Dam would be temporarily stockpiled in Borrow Area D, while the riprap recovered from the Reclaim Dam would be stockpiled in Borrow Area G. As the riprap is devoid of fines, no sediment transport issues are expected Stockpile Required Materials All drawings referred to in this subsection are found in Appendix A. Materials required (excluding locally derived common fill) for erosion protection of the spillways and channels for sediment control would include: Type I Riprap: 300mm D50 material is required for providing erosion protection of: Section Q-Q (South Dam Drainage Channel, Drawing SDH-DR-10) Section U-U (Camp Creek Channel, Drawing SDH-DR-10) Section X-X (Tailings Drainage Channel, Drawing SDH-DR-12) Spillway Section (Sediment Retention Structure, Drawing SDH-DR-06) IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

27 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 22 Upstream Face (Sediment Retention Structure, drawings SDH-DR-05 and SDH- DR-06) All riprap material would be obtained by selecting the rock excavated from the toe buttress of the South Dam, Reclaim Dam or blasted and screened from the Mile 17 Quarry. Type II Riprap: 400mm D50 material is required for providing erosion protection of: Section P-P (South Dam Drainage Channel, SDH-DR-10) Section J-J (South Dam Drainage Channel, SDH-DR-06) Section S-S (Camp Creek Channel, Drawing SDH-DR-10) Section T-T (Camp Creek Channel, Drawing SDH-DR-10) Section R-R (Camp Creek Channel, Drawing SDH-DR-10) All riprap material would be obtained by selecting the rock excavated from the toe buttress of the South Dam, Reclaim Dam, or blasted and screened from the Mile 17 Quarry. Type III Riprap: 500mm D50 material is required for providing erosion protection of: Section H-H (Sediment Retaining Structure, Drawing SDH-DR-06) All riprap material would be obtained by selecting the rock excavated from the toe buttress of the South Dam, Reclaim Dam or blasted and screened from the Mile 17 Quarry. Hay bales: would be required for construction of erosion protection devices, including the temporary sedimentation basin; Silt fencing: required for construction of sediment control devices along the excavated drainage channels and any other areas requiring sediment control measures; and Geotextile: required to act as a separation layer between the riprap and the adjacent soil. 5.3 Construction Activities Water Management During construction, measures would be required to manage total suspended solids (TSS) in the discharge of surface water from the site. It is anticipated that the construction of the diversion channels for the Camp Creek relocation would occur once the Reclaim pond has been drained and while the dam is being excavated. A small sump would be excavated within the drained Reclaim Pond area to collect any sedimentladen runoff. Once an acceptable TSS level is achieved, water would be pumped into the relocated Camp Creek channel. During the excavation of the reclaim notch, measures to control the release of sediment to Camp Creek would be put in place as discussed in Section 6. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

28 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 23 The existing interceptor ditches on the eastern hillside, as well as the Camp Creek diversion on the west side of the Reclaim pond would continue to collect and divert clean runoff during the Reclaim dam excavation. Following construction of the drainage channels and the removal of the Reclaim dam, these ditches would be breached and Camp Creek would be redirected into the new channel. The two 1,200 mm diameter culverts and the exit chute at the Reclaim Dam would also be decommissioned and the emergency spillway removed. The PVC piezometers and steel drill casing embedded into the South Dam and Reclaim Dam will be removed Excavation of the Breach Excavated material from the dams would be loaded into haul trucks and transported directly to the locations designated for capping. The dam fill material is typically a sandy silt or a silty sand and is considered suitable for growth medium. However, to confirm any potential for metal leaching in the dam fill material, two representative soil samples from each dam will be collected during excavation and sent to a laboratory in Vancouver for acid base accounting (ABA) and metals testing (ICP). In the event that the results indicate any sign of metal leaching, a selective fill placement method would be adopted. It should be noted however that over the last 24 years since the dams were built there has been no indication of metal leaching from the dam fill and the likelihood of finding such material is low. Following excavation of the required volume of material for capping, any remaining fill material would be reshaped to provide positive drainage. The surface would be scarified and subsequently seeded and revegetated to provide erosion protection and to restore the area to land use consistent with established land use Sediment Control Structure A sediment collection pond would be established during the excavation of the South Dam. Currently it is planned to excavate the eastern end of the South Dam down to an elevation of 1,086.7 m and then construct a riprapped channel with an invert elevation of 1,085 m. The design details of this structure are discussed in Section Excavation of the Drainage Channels The area along the alignment of the drainage channels would be cleared and grubbed as appropriate. The channels would then be excavated to the grades and profiles as shown in Drawing SDH-DR-03, SDH-DR-06, SDH-DR-10 and SDH-DR-12 (Appendix A). Spoil from the excavation would be cast onto both sides of the channel, blended in with the surrounding topography and revegetated. A temporary access road would be built on one side of the channel provide vehicular access for construction and maintenance Soil Covers The soil cover on the tailings area would begin at the North Dam crest and proceed in a southerly direction. Material would be hauled by truck from the dam excavations end dumped, and pushed out over the tailings by a light dozer. The cover would be placed in such a manner as to create a final hummocky surface. No compaction of the soil covers would be performed. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

29 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Riprap Placement Placement of the riprap would be performed using an excavator or other appropriate mechanised equipment. The riprap recovered from the dam decommissioning or the obtained from the quarry would be hauled to the work area and placed as shown in the design Drawings SHD-DR-6, 9, 10, and 12 (Appendix A). Geotextile filter fabric would be placed on the slopes and base of the channel prior to placement of the riprap. Table 9 presents a summary of the rock riprap required for the constructed channels. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

30 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 25 Table 9: Riprap Quantity Summary Camp Creek Drainage Channel Section Armoring Thickness (m) D50 (m) Volume (m 3 ) U T S R South Dam Spillway and Drainage Channel Section Armoring Thickness (m) D50 (m) Volume (m 3 ) P Q J H Spillway Section Upstream Face North Runoff Diversion Channel Section Armoring Thickness (m) D50 (m) Volume (m 3 ) Y Discharge Area Total Riprap Volume Required 8,100 Source: P:\01_SITES\Sa_Dena_Hes\1CT _Quarry Development\!020_Project_Data\010_SRK Removal of the Pump House, Decant Tower and Pipe The decant tower located near the upstream toe of the South Dam would be demolished and the debris would be buried on-site. The exposed rebar would be cut into suitable length pieces and salvaged or buried. The decant pipe would be removed as part of the dam decommissioning and demolition. The pump house would be removed. 5.4 Construction Quality Assurance and Quality Control General Work should be carried out according to the drawings (Appendix A) and the technical specifications (Appendix B) Construction Monitoring and Responsibilities Prior to initiation of construction, evaluate the piezometric levels and the stability of the sideslopes of the notch of the South Dam. Monitor the setup of construction area including laydown areas, spoil areas, fuelling site, establishment of drainage and sediment control measures for construction. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

31 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 26 Monitor the siphoning and pumping operations for the pond and inflow water, ensuring that the permit discharge volumes and rates are not exceeded. Establish protocols (in conjunction with the environmental monitoring plan) for monitoring and verifying construction water quality prior to the discharge of construction water to the environment. Ensure that the constructed works meet the requirements described in the contract documents and the design intent described in this design report. Provide ongoing advice to the owner and contractor on technical elements of the works undertaken Post Construction Monitoring Evaluate the conditions of the constructed works after the 2014 and the 2015 freshet (in the fall of 2014 and 2015). Prepare a report on the performance as compared to the expected performance and recommend any necessary repairs. Evaluate the riprap protection of the drainage channels and make recommendations for any remediation work required Reporting Resident engineer would maintain suitable records and photographs throughout the construction phase. Weekly reports that summarize work activities (and incidents or issues) would be submitted to Teck. Any significant changes in construction methods or stream channel design, monitoring procedures, etc. would be presented to Teck. A report on the construction phase is required within three months of the completion of the construction work and should include photo documentation of the construction activities and summary of significant incidents (as-built report). A report on the assessment of the performance of the drainage channel, dam breach, and soil covers after the first freshet, along with recommendations for additional work or any remedial action taken would be submitted by December Construction Schedule No details are currently available for the construction schedule at time of this was written Construction Quantities Both dams were constructed using locally available sandy and silty till, as well as sand and gravel for drainage and blasted rock for toe stabilization. The design of the dams differed due to the nature and function of each dam. The South Dam was required to retain tailings and the Reclaim Dam was designed to retain water. While a silty till core was incorporated into each dam the upstream face of the Reclaim Dam had an outer shell of the more permeable sandy till. The downstream faces of both dams were constructed of a more erosion resistant sand and gravel as IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

32 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 27 shown in Drawings SDH-DR-13 and SDH-DR-14 (Appendix A). A drainage blanket of sand and gravel was incorporated in the base of each dam. Toe buttresses were also constructed along the downstream toe of both dams to improve slope stability. These toe berms were constructed largely of blasted rock material and processed gravel. Table 10 presents the estimated available quantities of material that could be used for capping material including recoverable riprap material from the toe buttresses. Table 10: Summary of Fill Quantities for the South and Reclaim Dams Structure Till (m³) Sand and Gravel (m³) Riprap (m³) Total Volume (m³) Reclaim Dam 71,566 33,560 3, ,125 South Dam 92,609 51, ,436 Total: 164,174 84,786 3, ,561 Source: L:\01_SITES\Sa_Dena_Hes\1CT _Dam_Decommissioning\!080_Deliverables\Design Report\020_Tables\Till_SandGravels_Quantity _Estimate_ML_IM_Rev2.xlsx IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

33 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 28 6 Erosion and Sediment Control Plan 6.1 General The undisturbed areas surrounding the TMF show variable slopes and are covered with some vegetation. The outer surface of both the South and the Reclaim dams were naturally colonised by the indigenous species since they were constructed and the original creek bed of Camp Creek is overgrown with thick vegetation. The areas exposed by the receding waters in the Reclaim and South pond may be susceptible to erosion and potential sediment transport. The nature and thickness of the sediment blanket would be determined by field investigation assessing the sediments once they are exposed by the lowering of the water level. Following the initial excavation of the eastern end of both dams, the newly exposed surfaces would be susceptible to erosion due to the relatively steep slopes (2H:1V) until such time as the work begins on removal of the dam fill or vegetation is fully established. During the initial phase of decommissioning, the South Dam would be left intact while the Reclaim pond is dewatered. Erosion and sediment control measures would be implemented to control sediments at the source before they enter the receiving environment. Best available practices would be implemented where practical to control the release of sediment-laden water. Erosion and sediment control can be implemented by controlling flow velocities. Some of flow control measures are already incorporated into the design by building gentle final slopes with smooth transitions. The length of continuous slopes would be limited by addition of swales or berms. The following sections provide methods of the various erosion and sediment control, which could be implemented during construction. 6.2 Surface Roughening Surface roughening is the process of creating small disturbances in the smooth overall sloped surface and should be applied on all sloped surfaces steeper than 4H:1V in conjunction with revegetation. Surface roughening should be applied following the completion of final grading. The purpose of this method is to create a series of horizontal depressions in close succession which would act to reduce flow velocity, trap sediments, and enhance infiltration. A side benefit of this method is an increase of establishment of vegetation on the steeper slopes, by preventing the seeds being washed away by runoff. Surface roughening can be done by running a dozer up and down the slope. The cleats of the dozer tracks would create a set of grooves parallel to the slope. Ploughing the surface parallel to the slope contour could be used as an alternative, but the application of this method is limited to IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

34 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 29 less steep slopes. The depression should be at least 50 mm deep and spaced at no more than 150 mm apart. The soils cover over the tailings area would be constructed by placing the cover soils in closely spaced small (300 mm high) hummocks. This would create a field of peaks and ponds that is analogous to the surface roughening described above. 6.3 Flow Controls During the excavation of the initial notch in the South dam, a spillway would be constructed with a finished invert elevation of 1,085 m. The bottom and the lower portion of the sideslopes of the spillway would be riprapped for erosion protection. The invert of the spillway was selected in order to develop a temporary sedimentation pond. If it is found that addition storage is needed, a rock plug or a cofferdam may be constructed at the upstream end of the spillway to raise the invert. Water held in the pond would be pumped into the Camp Creek Diversion. The cofferdam or rock plug would be removed once all the drainage channels are completed and the Reclaim Dam has been removed. 6.4 Check Dams Temporary check dams would be installed on drainage channel reaches exceeding 5% slope (Sections S and R in the upper reach of Camp Creek channel) prior to installation of the final riprap channel protection. The check dams would provide protection against excessive channel erosion prior to riprap placement and provide some opportunity for settlement of suspended solids through detention. The check dams would be constructed of clean rock (devoid of fines), with bottom layer consisting of smaller stones to a height of 0.45 m and larger stones making up the top layer of 0.15 m. A layer of non-woven geotextile would be placed between the upper and lower layers, extended upstream at least 1 m, and anchored using larger rocks. The maximum upstream slope is 2H:1V while the downstream slope should not be steeper than is 4H:1V. The spacing between the check dams should be such that the crest of the downstream check dam should be at same elevation as the toe of the upstream check dam. A small sump (300 mm deep) should be excavated immediately upstream of the check dam to act as a stilling basin. The check dams would be removed once the final riprap protection is installed, and the rock material from the dams would be used as part of the riprap protection elsewhere. 6.5 Silt fences The purpose of silt fences is to retain suspended sediments by ponding the water and allowing the sediments to settle out but do not filter sediments. Silt fences would be installed as temporary measures until the vegetation is established, which would then provide the permanent erosion control. Silt fences would be installed along the excavated drainage channels, at the base of the newly exposed surfaces of the dam notches, and the base of any steeper slope or toe of any soil stockpile. Within the footprint of the dewatered ponds, silt fences would be installed to retain the IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

35 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 30 fines from the freshly exposed barren soil. Several rows of silt fencing may be necessary, depending on site conditions and amount of sediments that could be mobilized. Prefabricated silt fences are commercially available in various sizes or can be fabricated on site using rolls of polyethylene woven geotextile and wood or metal posts. As a minimum the installed silt fence shall be no less than 0.6 m high with posts no more than 8 m apart. The posts shall be 25 x 50 mm wood stakes or equivalent, and shall be driven into the ground a minimum of 300 mm. To prevent water and sediments travelling under the fence, the bottom portion of the geotextile must be keyed in by excavating a 150 x 150 mm trench on the upstream side, placing the geotextile in the trench and backfilling with the excavated soil. Compaction of the fill should be performed if possible. Where joints between silt fence panels are necessary, adjacent length of geotextile are rolled together around the end posts. 6.6 Temporary Sedimentation Basin A temporary sedimentation basin would be used downstream of the Reclaim Dam during excavation of the dam. The basin would be developed by constructing a temporary dam about 1.2 m high, out of hay bales. Depending on the water quality (TSS), water collected in this basin may need to be pumped back upstream of the former South Dam. The base of the hay bales would be keyed in by excavating a trench equal in width with the hay bales and depth of about one third of the height of a hay bale, but a minimum of 150 mm. A nonwoven geotextile may be draped over the upstream side of this dam for added performance. The hay bale wall would be removed once all channel construction and dam decommissioning work is completed and the vegetation is sufficiently established on the newly exposed areas to act effectively to control erosion. 6.7 Floating Turbidity Curtains During drawdown of the water from the Reclaim Pond a floating turbidity curtain may need to be installed to manage suspended solids near the siphon intake point located at the deepest point in the pond. The turbidity curtains are available commercially as pre-assembled units including floaters, geotextile, load lines, and bottom ballast. The curtain would be deployed as a loop around the intake point, and ballasted to keep the geotextile vertical. As the water level decreases in the pond, the geotextile would be folded up but would continue to provide essentially the same filtration surface area. Once the drawdown of the pond is complete, the turbidity curtain would be recovered and disposed of in an appropriate manner. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

36 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page Flocculation During the drawdown of the ponds behind the South and Reclaim Dams, it is anticipated that the sediment may be mobilised by inflowing groundwater and/or runoff. Due to the nature of the fine sediments, settling of fine sediments may take several weeks or even months. In these cases chemical flocculants may be added to the water, in compliance with permit requirements, to speed up the settling process and allow the discharge of water in compliance permit requirements. The type and dosing of the flocculants would be determined based on field trials and a non-toxic variety would be chosen once the type is determined. The flocculant could be deployed either passively by placing a solid block in the drainage path and allowing it to dissolve or actively by building a manifold system and pumping a flocculant solution into the muddy water. 6.9 Revegetation Revegetation of the tailings cover, exposed till slopes, and barren pond footprint areas would be performed as soon as possible after construction and pond dewatering. Revegetation with grasses and legumes would be performed by hydroseeding using a mix of plant seeds, fertilizer, and paper mulch or other stabilizing agent and tree planting would also be performed. The paper mulch would create a crust on the barren soil, which would provide erosion protection in the first growing season while the vegetation is getting established. The paper mulch would gradually degrade and disappear. Hydroseeding should be done before planting because it can crush and damage newly planted trees and choke out a small plants ability to photosynthesize. The seed mix would be composed of agronomic and indigenous species as specified in the DDRP (Teck 2013). Tree seedlings from seed collected from the indigenous alder, poplar, and willow population would be planted in the tailings cover and the former pond areas Inspection and Maintenance All erosion and sedimentation control measures deployed on site would be inspected regularly and following each significant rainfall event. During prolonged rainfall events, some of the areas may require daily inspection. The inspection would include the roughened surfaces and the condition of the slopes to identify excessive erosion, slumping, cracking, or any early indicators of imminent slope failure. The active sediment control measures like the silt fences, the temporary sedimentation basin, and the check dams would require maintenance in the form of removal of the accumulated sediments once they reach one third of the height of the sediment control device. Regular visual inspection of the floating turbidity curtain would be performed from ashore with close inspection from a boat or a raft to be performed if considered necessary. The growth of vegetation and survival rate of the tree seedlings would be monitored, with reseeding being performed where required. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

37 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 32 7 Air Quality Plan Closure and remediation work at the site would require a fleet of equipment. To reduce emissions, the fleet would be sized for the work required, which would also reduce unnecessary idling. Additionally, proper maintenance would ensure the equipment is running efficiently. Excavation, transfer, and placement of soils, along with haul truck traffic on gravel roads, may cause dust emissions. Should dust control be required, water would be applied to road surfaces. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

38 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 33 8 Environmental Monitoring During Construction During the Sä Dena Hes closure activities, the water quality at the site would be monitored to ensure compliance with the conditions of the Water License (QZ99-045). Ground disturbance during closure may potentially result in increased sediment loading to runoff and surface water. The purpose of this Environmental Monitoring Plan is to describe how the site would be monitored during closure. The focus of water quality monitoring is the presence of Total Suspended Solids (TSS) and to a lesser extent total and dissolved metals. The goal of the proposed monitoring is to ensure that impacts to water quality during closure activities are limited to within the mining lease boundary. Details of the monitoring plan are provided in Appendix E. As part of this program, a flow gauge would be established in the overflow spillway at the west perimeter of the Reclaim Pond to monitor any overflow during or after the spring freshet. Presence of wildlife on and around the site would be monitored. Bird nests would be surveyed before construction activities begin in a specific area. If eggs are found, the nest would either be moved or construction would be delayed, if possible, until the eggs hatch and the chicks can be relocated safely. This report, Sä Dena Hes Tailings Management Facility Decommissioning Design Report, was prepared by Iozsef Miskolczi, PEng Consultant and reviewed by Peter Healey, PEng Principal Consultant All data used as source material plus the text, tables, figures, and attachments of this document have been reviewed and prepared in accordance with generally accepted professional engineering and environmental practices. Disclaimer SRK Consulting (Canada) Inc. has prepared this document for Teck Resources Limited. Any use or decisions by which a third party makes of this document are the responsibility of such third parties. In no circumstance does SRK accept any consequential liability arising from commercial decisions or actions resulting from the use of this report by a third party. The opinions expressed in this report have been based on the information available to SRK at the time of preparation. SRK has exercised all due care in reviewing information supplied by others for use on this project. Whilst SRK has compared key supplied data with expected values, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the supplied data. SRK does not accept responsibility for any errors or omissions in the supplied information, except to the extent that SRK was hired to verify the data. IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

39 SRK Consulting Sä Dena Hes TMF Decommissioning Design Report Page 34 9 References [BCMOE] British Columbia Ministry of Environment General BMP s and Standard Project Considerations. Available at: (accessed June 5, 2013) Teck Sä Dena Hes Operating Corporation Sä Dena Hes Mine Detailed Decommissioning & Reclamation Plan March 2013 Update. Prepared by Teck Resources Limited. March IM/PMH SDH Dam Decomissioning_DesignReport_1CT _SDM_PMH_ March 2014

40 Appendices

41 Appendix A: Drawings

42 Engineering Drawings for Sa Dena Hes Project, Tailings Management Facility Decommissioning ACTIVE DRAWING STATUS DWG NUMBER DRAWING TITLE REV. DATE STATUS OLD/REPLACED REVISIONS SDH-DR-00 Engineering Drawings for Sa Dena Hes Project, 1 Tailings Management Facility Decommissioning Mar. 3, 2014 Issued for Tender Rev.0, Feb.14, 2014 SDH-DR-01 SDH-DR-02 SDH-DR-03 SDH-DR-04 SDH-DR-05 SDH-DR-06 SDH-DR-07 SDH-DR-08 SDH-DR-09 SDH-DR-10 SDH-DR-11 SDH-DR-12 SDH-DR-13 SDH-DR-14 Existing Conditions Location Map South Dam Plan and Profile South Dam Cross Sections Sediment Retaining Structure Plan Sediment Retaining Structure Sections Reclaim Dam Plan and Profile Reclaim Dam Sections Drainage Channel Plan Drainage Channel Sections Areas to be Capped General Arrangement Tailings Drainage Channel Plan, Profile and Section Materials Zoning in South Dam Materials Zoning in Reclaim Dam 1 Mar. 3, Mar. 3, Mar. 24, Mar. 24, Mar. 3, Mar. 24, Mar. 3, Mar. 3, Mar. 24, Mar. 24, Mar. 3, Mar. 24, Mar. 3, Mar. 3, 2014 Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Issued for Tender Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.1, Mar.3, 2014 Rev.1, Mar.3, 2014 Rev.0, Feb.14, 2014 Rev.1, Mar.3, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.1, Mar.3, 2014 Rev.1, Mar.3, 2014 Rev.0, Feb.14, 2014 Rev.1, Mar.3, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 Rev.0, Feb.14, 2014 PROJECT NO: 1CT Issued for Tender Revision 2 March 24, 2014 Drawing No. 0

43 J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR-01.dwg E E Reclaim pipeline (To be removed) Borrow Area G (Depleted) 1125 Reclaim Pond Spillway and exit Chute CAMP CREEK km to Borrow Area F MH-06A 1100 GW-1 To Mill TH TH Toe buttress RDW-1 MH-07 RDW N MH-06B RDW N Camp Creek Diversion Reclaim Pond El m (October 2013) Reclaim Pond Emergency Spillway 1130 Reclaim Dam Crest El. 1084m South Dam Spillway MH-01A 1095 SDW SDW Toe Buttress 1145 To Mill Decant tower MH-01B Toe of Dam Tailings Pond El m (October 2013) South Dam Crest El. 1099m N N FLOW Borrow Area D (Depleted) Cofferdam 1115 Culvert FLOW N N Borrow Area B (Depleted) East Interceptor Ditch NOT FOR CONSTRUCTION Borrow Area A (Depleted) Gravel Tailings Cover NOTE Topographic contour data and aerial photos were obtained from McElhanney and are based on August 15, 2012 LiDAR survey. Elevations were correctect based on October 2013 YES Survey. Coordinate system is UTM NAD 83CSRS zone 9V Scale in Metres Sä Dena Hes Project To Mill Tailings Surface El m NDW-2 LEGEND NDW-3 TH NDW-1 NDW-4 MH N N Covered Tailings Contours interval 5m Edge of Road Water Pipe Tailings Line Creeks 1.3 km to Borrow Area C E North Dam Crest El. 1100m TMF Decommissioning Existing Conditions E Standing Pipe Piezometers Water Sampling Location SDH-DR-01 1

44 N N N N IBY1 E: N: Z: (See Note 4) Existing Camp Creek Diversion (to be removed) E E South Dam North Dam Decant Tower Sediment Retaining Structure FLOW FLOW W FLO FL O W North Diversion Channel Reclaim Dam C102 E: N: Z: Unknown Coffer Dam (Breached in 2012) East In te r Dit rcepto ch FLOW FLOW See Tailings Drainage Channel Plan on Drawing SDH-DR-12 See South Dam Plan on Drawing SDH-DR-03 See Drainage Channel Plan on Drawing SDH-DR E N LEGEND N See Reclaim Dam Plan on Drawing SDH-DR N N J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg E NOTES Sedimentation Pond Covered Tailings (Existing) Existing Crest Topographic contour data was obtained from McElhanney and is based on August 15, 2012 LiDAR Survey. 2. Coordinate system is UTM NAD 83 CSRS Zone 9V. 3. Contours shown behind the Reclaim Dam and the South Dam were interpreted from historical survey data. 4. This Benchmark datum is currently used to monitor settlement gauges on the dam and was used as the benchmark in construction of the dam. The elevation has been adjusted from m to the current LiDAR Survey elevation. Proposed Crest Existing Edge of Road Proposed Tailings Cover Proposed Edge of Road Dams to be Decommissioned Creek Drainage Channel Borrow Area to be covered and Revegetated 1. Tailings Pipeline Minor Contours (1m interval) Potential Tailings Cover Area Major Contours (5m interval) Survey Benchmark 5. The tie-in from the existing natural channel to the riprapped channel will be determined in the field as directed by the Engineer. 6. Potential Tailings Cover Area will be determined by sampling directed by the Engineer. NOT FOR CONSTRUCTION Scale in Metres Topographic Contour Interval 1m TMF Decommissioning Sä Dena Hes Project Location Map SDH-DR-02 1

45 See Sediment Retaining Structure Plan on Drawing SDH-DR-05 FLOW PLAN LEGEND Survey Benchmark Minor Contours (1m) Major Contours (5m) Existing Crest Proposed Crest Existing Edge of Road Decant Tower Access Road Existing Upstream Toe Proposed Edge of Road Drainage Channel Tailings Pipeline Reclamation Area Sediment Pond (See Note 6) Existing Crest (Varies El m m) PROFILE AND DETAIL LEGEND Pre-Existing Ground Existing Ground Non-woven Geotextile Access Road Material to be removed (see Note 3) Camp Creek Drainage Channel Existing Downstream Toe NOTES Rip-rap 1. Assume 1m freeboard for spillway. FLOW PLAN Scale in Metres South Drainage Channel FLOW NOT FOR CONSTRUCTION 2. Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 3. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. 4. Rip-rap from downstream toe buttress shall be salvaged to be used on the Sediment Retaining Structure and drainage channels. 5. Decant Tower shall be demolished and the debris disposed of. 6. This Benchmark datum is currently used to monitor settlement gauges on the dam and was used as the benchmark in construction of the dam. The elevation has been adjusted from m to the current LiDAR Survey elevation. J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg Original Topography (before Dam Construction) A - Dam Crest El m m Sediment retaining structure Profile A - A' 2.5x Vertical Exaggeration Horizontal: Scale in Metres Vertical: Scale in Metres El m El m 1.00m (see Note 1) 0.70m (see Note 2) 1 - Sä Dena Hes Project 7. The Geotextile will be non-woven, 12 ounces/square yard or equivalent. The geotextile will exceed the riprap limits by a minimum of 0.3m. 0.3m 0.3m 1 2 El m El m 0.45m 4.0m Detail 1 Spillway N.T.S. South Dam Plan and Profile SDH-DR Rip-rap (D 50 =0.3m) Geotextile TMF Decommissioning 2

46 LEGEND South Dam (to be removed) Existing Ground Pre-existing Ground Sediment Retaining Structure Material to be removed (See Note 1) B 04 CROSS SECTION Station NOTES 1. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. South Dam (to be removed) 2. Riprap to be salvaged. C 04 CROSS SECTION Station El m El m Accumulated sediments Sediment Retaining Structure South Dam (to be removed) Buttress (See Note 2) D 04 CROSS SECTION Station J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg E 04 CROSS SECTION Station South Dam (to be removed) Sä Dena Hes Project NOT FOR CONSTRUCTION South Dam Cross Sections SDH-DR Scale in Metres TMF Decommissioning 2

47 LEGEND Minor Contours (1m) Major Contours (5m) Edge of Road Drainage Channel Material to be removed (see Note 4) Rip-rap Till (left in place from Original Dam) South Dam Toe Sedimentation Pond Sediment Retaining Structure Crest El m Spillway Invert El m NOTES 1. Assume 1m freeboard. 2. Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 3. Riprap depth is 1.5 times D Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. 5. Riprap from downstream toe buttress shall be salvaged to be used on the Sediment Retaining Structure and drainage channels. Proposed Road Proposed Road Existing Crest Lines FLOW J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg Section Q Drawing SDH-DR-10 South Drainage Channel Sä Dena Hes Project NOT FOR CONSTRUCTION TMF Decommissioning Sediment Retaining Structure Plan SDH-DR-05 Scale in Metres 2

48 LEGEND Pre-existing Ground Existing Ground Sediment Retaining Structure Non-woven Geotextile Material to be removed (see Note 4) Rip-rap Till (left in place from Original Dam) NOTES 1. Assume 1m freeboard. 2. Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 3. Riprap depth is 1.5 times D Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. 5. Riprap from downstream toe buttress shall be salvaged to be used on the Sediment Retaining Structure. G 05 SECTION G - G' SPILLWAY PROFILE Scale in Metres Sediment Retaining Structure Riprap Volume Summary Table Location D50 (m) Armoring Depth (m) Volume (m3) Section Q Section J Section H Spillway Detail Upstream Face J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DRbak.dwg F 05 El m Original Ground Horizontal: Vertical: SECTION F - F' Scale in Metres Scale in Metres Note: Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 0.3m 0.3m 0.7m 0.3m 0.4m m 4.0m H SECTION H - H' 05 N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.5m) Dam Face Note: Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 0.3m 0.8m m 0.3m 0.3m 1.2m 4.0m J SECTION J - J' 05 N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.4m) Original Ground Sä Dena Hes Project NOT FOR CONSTRUCTION TMF Decommissioning Sediment Retaining Structure Sections SDH-DR-06 2

49 LEGEND Minor Contours (1m interval) Major Contours (5m interval) Edge of Road South Dam Toe Pipe Creek Existing Crest Drainage Channel Reclamation Area Material to be removed (see Note 4) Camp Creek Drainage Channel Existing Camp Creek Diversion (to be removed) South Drainage Channel NOTES 1. Dam fill shall be removed to original ground. 2. Final surface shall be smooth and blend with upstream and downstream topography. 3. Positive drainage must be ensured to prevent ponding areas. 4. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. NOT FOR CONSTRUCTION Existing Upstream Toe Key Trench Reclaim Dam Dam Crest (El m) J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg PLAN Scale in Metres Existing Dam Crest (El m) Existing Downstream Toe K - Profile K - K' Horizontal: Scale in Metres Vertical: Scale in Metres Sä Dena Hes Project Original Ground (before dam construction) TMF Decommissioning Reclaim Dam Plan and Profile SDH-DR-07 1

50 LEGEND Reclaim Dam (to be removed) Pre-existing Ground Existing Ground Material to be removed (see Note 2) L 07 CROSS SECTION Station NOTE 1. Key Trench fill shall be left in place. 2. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. Reclaim Dam (to be removed) Key Trench M 07 CROSS SECTION Station Reclaim Dam (to be removed) Key Trench N 07 CROSS SECTION Station J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg O 07 CROSS SECTION Station Reclaim Dam (to be removed) Sä Dena Hes Project NOT FOR CONSTRUCTION Scale in Metres TMF Decommissioning Reclaim Dam Cross Sections SDH-DR-08 1

51 LEGEND W' 10 Section R N N N Covered Tailings Reclamation Area Rip-rap R' 10 R 10 Sedimentation Pond Minor Contours (1m interval) Major Contours (5m interval) Camp Creek Diversion to be removed Proposed Crest Existing Edge of Road Proposed Edge of Road Creek Drainage Channel ns Potential Tailings Cover Area Sec tio Camp Creek Drainage Channel (see Note 2) E Existing Crest IBY1 E: N: Z: (See Note 1) FLOW NOTES South Dam (to be removed) S This Benchmark datum is currently used to monitor settlement gauges on the dam and was used as the benchmark in construction of the dam. The elevation has been adjusted from m to the current LiDAR Survey elevation. 2. The tie-in from the existing natural channel to the riprapped channel will be determined in the field as directed by the Engineer S' 10 V' 10 Riprap Apron See Detail 2 V 10 H Q 10 P 10 Culverts to be removed Sediment Retaining Structure H' 06 North Diversion Channel Q' 10 Riprap D50=0.30m Q FLOW C102 E: N: Z: Unknown m 10 Section 9.6 m 0 40 T' T 0+ Exit chute to be removed n io ct Se P' T 10 Reclaim Dam (to be removed) 8.6 m Channel 0+ c Se 0 20 nu tio E U E 2 - Discharge Area Scale in Metres W 10 U' J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg Thickness = 0.45m NOT FOR CONSTRUCTION Scale in Metres TMF Decommissioning S Dena Hes Project Drainage Channel Plan SDH-DR-09 2

52 Re-Alignment W - W' LEGEND Section U Section T Section S Section R Top of Drainage Channel Profile Pre-existing Ground Existing Ground Elevation (m.a.s.l.) Reclaim Dam (to be removed) 4.65% 5.60% 7.70% Elevation (m.a.s.l.) Sediment Retaining Structure Non-woven Geotextile Material to be removed (see Note 1) Rip-rap Till (left in place from Original Dam) % Note: Depth of flow based on design flow of 15.9m 3 /s (1000 year event). 0.3m 0.3m 1.7m 0.5m 1.2m m U m SECTION U- U' Camp Creek Channel N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.3m) 0.5m 1.1m m T m SECTION T- T' Camp Creek Channel N.T.S. W 09 Profile W - W' Camp Creek Channel Horizontal: Vertical: 1 2 Geotextile Riprap Size (D 50 = 0.4m) Scale in Metres Scale in Metres Note: Depth of flow based on design flow of 15.9m 3 /s (1000 year event). Note: Depth of flow based on design flow of 15.9m 3 /s (1000 year event). Note: Depth of flow based on design flow of 15.9m 3 /s (1000 year event). 0.3m 0.3m 0.3m 0.3m 0.3m 0.3m 1.6m 1.5m 1.5m 0.5m 1.0m m S m SECTION S - S' Camp Creek Channel N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.4m) 0.5m 1.0m m R m SECTION R - R' Camp Creek Channel N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.4m) m m Q 09 NOTE 1. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. Note: Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 0.3m 1.2m 1.0m SECTION Q - Q' South Dam Drainage Channel N.T.S. 1 2 Geotextile Riprap Size (D 50 = 0.3m) Varies J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg Elevation (m.a.s.l.) Section P 1.39% 1.6% Section Q Profile V - V' South Dam Drainage Channel V 09 Horizontal: Vertical: Scale in Metres Scale in Metres 2.7% 6.6m South Dam (to be removed) Spillway Section Section J H 3.4% Upstream Face Sediment Retaining Structure Elevation (m.a.s.l.) NOT FOR CONSTRUCTION Sä Dena Hes Project Note: Depth of flow based on design flow of 5.4m 3 /s (1000 year event). 0.3m 1.2m Varies m m P 09 Drainage Channel Riprap Volume Summary Table Location 1.0m SECTION P - P' South Dam Drainage Channel N.T.S. D50 (m) TMF Decommissioning Drainage Channel Sections SDH-DR Geotextile Riprap Size (D 50 = 0.4m) Armoring Depth (m) Volume (m³) Section U Section T Section S Section R Section P

53 LEGEND Areas to be capped Potential Capping Area Sedimentation Pond J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR_11.dwg NOTES 1. Topographic contour data and aerial photos were obtained from McElhanney and are based on August 15, 2012 LiDAR survey. Coordinate system is UTM NAD 83CSRS zone 9V. 2. Extent of soil capping to be determined in the field as directed by the Engineer. NOT FOR CONSTRUCTION Scale in Metres CONTOUR INTERVAL=10m TMF Decommissioning Sa Dena Hes Areas to be Capped General Arrangement SDH-DR-11 1

54 NOTES 1. Assume 1m freeboard for spillway. 2. Depth of flow based on design flow of 3.0m 3 /s (1000 year event). 3. Dam fill material required for capping shall be excavated and any remaining material shall be reshaped to provide a smooth and positive drainage. 4. Rip-rap from downstream toe buttress shall be salvaged to be used on the Sediment Retaining Structure and drainage channels. 5. The Benchmark datum is currently used to monitor settlement gauges on the dam and was used as the benchmark in construction of the dam. This benchmark does not agree with the recent Lidar Survey. 6. The Geotextile will be non-woven, 12 ounces/square yard or equivalent. The geotextile will exceed the riprap limits by a minimum of 0.3m. PLAN LEGEND Minor Contours (1m) Major Contours (5m) Existing Edge of Road Drainage Channel Tailings Pipeline Existing Ground Design Ground Non-woven Geotextile Covered Tailings Rip-rap Sedimentation Pond NOT FOR CONSTRUCTION Note: Depth of flow based on design flow of 3.0m 3 /s (1000 year event). 0.3m 0.3m 1.0m 0.3m 0.7m m 1.0m 1 2 Geotextile Riprap Size (D 50 = 0.30m) PLAN Section Y - Y' Tailings Drainage Channel N.T.S. Scale in Metres J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR.dwg X - Profile X - X' 2x Vertical Exaggeration Horizontal: Vertical: Scale in Metres Scale in Metres Sä Dena Hes Project TMF Decommissioning Tailings Drainage Channel Plan, Profile and Section SDH-DR-12 2

55 1100 DAM CREST ELEV m Of Dam SILTY TILL(1992) EXISTING CREST ELEV m (approximated from 2013 YES Survey) EXISTING EMBANKMENT SURFACE (SEE NOTE 2) ELEVATION (m) WATER ELEVATION October, 2013 (ELEV m) 1 2 SILTY TILL(1990) SANDY TILL(1990) SAND AND GRAVEL BLANKET DRAIN(1990) STRIPPED GROUND SURFACE(1990) SAND AND GRAVEL SAND AND (1990) 1 GRAVEL (1992) EXCAVATED TRENCH AT TOE TO EXPOSE ORIGINAL GEOTEXTILE IN DRAIN BLANKET 12 m X X X X X X X X X X X X X X X X X X X X X X X X GEOTEXTILE & BEDDING SAND (SEE NOTE 3) X X X AS BUILT TOP OF SAND & GRAVEL CAP ELEV m 1.5 m X X X X X X X X X X X X X X X X X X X X X X X X SHOT ROCK (SEE NOTE 4) TOP OF DRAIN ROCK ELEV m SUB-EXCAVATED EXTENT OF SOFT MATERIAL (1-1.5 m) TOE OF DRAIN ROCK ELEV m ORIGINAL GROUND SURFACE EDGE OF SHOT ROCK ELEV m DRAINAGE DITCH ELEVATION (m) STATION J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR-13.dwg ELEVATION (m) WATER ELEVATION October, 2013 (ELEV ) DAM CREST ELEV m 1 2 SILTY TILL(1990) Of Dam SILTY TILL(1992) SAND SAND AND AND GRAVEL GRAVEL (1990) (1992) SANDY TILL(1990) SAND AND GRAVEL BLANKET DRAIN(1990) STRIPPED GROUND SURFACE(1990) STATION EXISTING CREST ELEV m (approximated from 2013 YES Survey) EXISTING EMBANKMENT SURFACE DRAIN ROCK TRENCH (SEE NOTE 3) ORIGINAL GROUND SURFACE SHOT ROCK TOE BUTTRESS (1994) (SEE NOTE 4) ELEVATION (m) NOT FOR CONSTRUCTION Sa Dena Hes LEGEND Till NOTES 1. STRIPPED GROUND SURFACE AND EXISTING DAM ZONES FROM Y.E.S. AS-BUILT DRAWINGS, JULY EXISTING DAM SURFACE FROM SURVEY COMPLETED AUGUST DRAIN ROCK FILTER CRITERIA - 5mm < D < 25mm m THICK BEDDING LAYER OF PIT RUN SAND AND GRAVEL OVER SHOT ROCK PLATFORM. 4. SHOT ROCK CONSISTS OF BLASTED LIMESTONE FROM JEWELBOX PIT. Sand and Gravel Riprap TMF Decommissioning Materials Zoning in South Dam SDH-DR-13 1

56 Of Dam M Dam Crest Elev m (approximated from 2013 YES Survey) Spillway Elev Elevation (m) Elev M (October, 2013) Sandy Till (fill) Silty Till (fill) Sandy Till (fill) 1 Riprap Toe Buttress Inverted Gravel Filter (riprap) Elevation (m) 1070 Stripped Ground Surface Sand & Gravel (drainage Blanket) Original Ground (before Dam Construction) Section Reclaim Dam M Dam Crest Elev m (approximated from 2013 YES Survey) Of Dam LEGEND J:\01_SITES\Sa_Dena_Hes\1CT _Dams_Decommissioning\!040_AutoCAD\Construction Drawings\IFT\1CT008035_SDH-DR-14.dwg Elevation (m) Elev M (October, 2013) -40 Spillway Elev Sandy Till (fill) Silty Till (fill) Sand & Gravel (drainage Blanket) Sandy Till (fill) Geotextile Filter Fabric (nilex C54 Or Equivalent) Stripped Ground Surface Section Reclaim Dam 18 M (min.) Existing Inverted Filter (rip Rap) M Riprap Toe Buttress 60 Drilling Pad Glacial Till Fill Sa Dena Hes Elevation (m) Till Sand And Gravel Riprap NOT FOR CONSTRUCTION TMF Decommissioning Materials Zoning in Reclaim Dam SDH-DR-14 1

57 Appendix B: Technical Specifications

58 Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Revision B Issued for Tender Prepared for Teck Resources Ltd. Prepared by SRK Consulting (Canada) Inc. 1CT March 2014

59 Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Revision B Issued for Tender March 2014 Prepared for Prepared by Teck Resources Ltd. 550 Burrard St Vancouver, BC V6C 3L9 Canada SRK Consulting (Canada) Inc West Hastings Street Vancouver, BC V6E 3X2 Canada Tel: Web: Tel: Web: Project No: File Name: 1CT (SDM Riprap Review) TechnicalSpecifications_Report_1CT _PMH_IM_MMM_ Copyright SRK Consulting (Canada) Inc., 2013

60 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page ii Table of Contents 1 General Requirements Documents Revision Summary Definitions Summary of Works Contradictions Contractors Responsibilities Engineers Responsibilities Codes and Standards Quality Control Quality Assurance Submittals Construction Schedule Construction Drawings Construction Specifications Recontouring and Covering Tailings Surface Construct Riprapped Channel for Camp Creek and Spillway Flow Clearing, Grubbing and Stripping General Documents Definitions Description Submittals Permits and Regulations Protection Execution Preparation Clearing Grubbing Stripping Finished Surface Disposal Quality Control Quality Assurance Excavation and Water Control...13 PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

61 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page iii 4.1 General Documents Definitions Description Exclusions Procedures Submittals Execution Preparation Common Excavation Methods Excavation in Borrow Areas Dam Fill Excavation Spillway Excavation Control of Water Scaling, Slope Stability and Safety Quality Control Quality Assurance Drilling and Blasting General Documents Definitions Description Submittals Products and Personnel Execution Drilling Blasting Quality Control Quality Assurance Material Specifications Part 1 General Documents Description Submittals Part 2 Product General Cover Material PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

62 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page iv Riprap Geosynthetics Fill Placement General Documents Description Codes and Standards Submittals Execution Snow Removal Equipment Foundation Preparation General Fill Placement (All Products) Type I Riprap Placement Type II Riprap Placement Type III Riprap Placement Till Cover Material Placement Geotextile Deployment Tolerances Sediment and Runoff Control Quality Control Quality Assurance PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

63 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page v List of Figures Figure 6.1: Gradation Specification for Till Cover Material Figure 6.2: Gradation Specification for Type I Riprap Figure 6.3: Gradation Specification for Type II Riprap Figure 6.4: Gradation Specification for Type III Riprap List of Tables Table 1.1: Revision history of this Technical Specification... 1 Table 1.2: List of QA/QC testing standards... 4 Table 6.1: Nonwoven geotextile specifications (typical product) Table 7.1 List of QA/QC testing standards Table 7.2: Required QC testing during placement of construction materials Table 7.3: Required QA testing during placement of construction materials PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

64 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 1 1 General Requirements 1.1 Documents This Technical Specification forms part of the Contract Documents and is to be read, interpreted, and coordinated with all other parts. 1.2 Revision Summary Table 1.1 provides a summary of the revision history of this Technical Specification. Table 1.1: Revision history of this Technical Specification Revision Status Date Major Changes A Draft Owner Submittal June 2013 N/A B Issue for Tender March 2014 Rip-Rap Type I Size Increase 1.3 Definitions The following definitions and interpretations shall apply to these Technical Specifications: 1. PROJECT means the total Sä Dena Hes Project contemplated, of which the Works described in this Document may be the whole or part of. 2. WORKS is defined as the entire completed construction and decommissioning as defined by this Document, or the various separately identifiable parts thereof. 3. CONTRACT DOCUMENTS are defined as the agreement, the addenda, the Contractor s bid when attached as an exhibit to the agreement, the bonds, the general conditions, the supplementary conditions, these Specifications, the Drawings, together with all Modifications issued after the execution of the agreement. 4. SPECIFICATIONS are defined as this Document of Specifications. These Specifications are to be read, interpreted, and coordinated with all Drawings and Modifications, or any other relevant documents produced by the Engineer. 5. DRAWINGS are defined as all Engineering Drawings, plans, sketches, figures and maps issued with these Specifications, or subsequently, as deemed necessary by the Engineer. 6. MODIFICATIONS are defined as changes made to the Specifications and/or Drawings, which have been approved by the Engineer in writing. These modifications can be issued any time, including after issuance of these Specifications and any accompanying Drawings and/or other Modifications. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

65 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 2 7. SUBMITTALS are defined as any documentation, as outlined in this Document that are used as formal means of communication during execution of the Works; are originated by any of the Responsible Parties. 8. Responsible Parties: (a) OWNER is defined as Teck Resources Ltd. (b) ENGINEER (also ENGINEER-OF-RECORD) is defined as a representative appointed and authorized by the Owner for those Works described in this Document. (c) CONTRACTOR is defined as the party or appointed representative of the party that has an agreement with the Owner to execute the Works defined in this document. (d) SUB-CONTRACTOR is defined as a party or appointed representative of the party that has an agreement with the Owner to execute specialized components of the Works that cannot be carried out by the Owner. (e) ENVIRONMENTAL MONITOR is defined as the party or appointed representative of the party that has an agreement with the Owner to act as Environmental Monitor for the Project. (f) SURVEYOR is defined as the party or appointed representative of the party that has an agreement with the Owner to act as Site Surveyor for the execution of the Works defined in this document. (g) QUALITY CONTROL TEAM is defined as the individual(s) to perform on-site Quality Control (QC) for Works defined in this Document. (h) QUALITY ASSURANCE TEAM is defined as the individual(s) to perform on-site Quality Assurance (QA) for the Works defined in this Document. 9. ON-SITE MATERIAL is defined as borrow materials obtained from designated on-site facility excavations. 10. OFF-SITE MATERIAL is defined as material obtained from sources other than on-site. 11. RECORD DOCUMENTS are defined as the documents prepared and certified by a Land Surveyor, Material Testing Technician, Quality Control and Quality Assurance Personnel, Specialist Professionals, or any other parties documenting any aspects of the Works. 12. PRODUCTS are defined as processed fill material, machines, components, equipment, fixtures and systems forming the Works. Products may also include existing material or components required for reuse. 13. SLOPES are defined in all instances in the Specifications and on Drawings in terms of horizontal distance to vertical distance (i.e. 3H:1V shall read 3 Horizontal to 1 Vertical). 14. EQUIPMENT means all construction mobile equipment that will be used for the Works. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

66 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Summary of Works The Owner will be responsible for ensuring that all the Works defined in this Document will be executed in accordance with all appropriate permits and approvals. The Works covered by this Specification includes, but is not limited to the following: 1. Decommissioning of the South and Reclaim dams. 2. Decommissioning of the North Creek dyke. 3. Construction of Sediment Retaining Structure and spillway. 4. Construction of riprapped channel for Camp Creek realignment. 5. Construction of riprapped Tailings Drainage Channel. 6. Capping the tailings by placement of soil covers. 7. Clean-up of the construction, borrow, and stockpile areas and make safe all work areas upon completion of the Works. The construction of the Tailings Drainage Channel and the drainage of the ponded water above the South Dam shall be completed prior to removal of the South Dam. Drainage of the Reclaim pond shall be carried out prior to removal of the Reclaim Dam. Decommissioning of the Camp Creek diversion shall be carried out following the completion of the removal of the South and Reclaim dams and completion of the drainage channels. 1.5 Contradictions Should any contradictions, either implied or real, exists between the Specifications and Drawings, the Owner shall: 1. Notify the Engineer. 2. Stop all the Works that concern the contradiction until contradiction is clarified by the Engineer. The decision of the Engineer is final. 1.6 Contractors Responsibilities The Contractor, in the context of the Works defined in this Document, shall: 1. Comply with Teck s health and safety regulations and any other relevant required health and safety regulations. 2. Become familiar with the relevant regional and site specific conditions that deviate from the Specifications and Drawings, and inform the Engineer when a problem or delay is anticipated. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

67 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 4 3. Be responsible for making his own measurements and installing the Works to fit the conditions encountered. 4. Before proceeding with the Works, examine all Drawings and Specifications and report to the Engineer any apparent discrepancies or interferences. The Engineer shall at all times retain the right to make revisions to the Drawings and the Specifications. 1.7 Engineers Responsibilities The Engineer, in the context of the Works defined in this Document, shall: 1. Comply with Teck health and safety regulations and any other relevant required health and safety regulations. 2. Provide the Owner with Drawings and Specifications, including Revisions and Modifications, to be able to conduct the Works defined in this Document. 3. Provide, as needed, full-time site Engineer(s) representation during construction of the Works as defined in this Document. The Engineer will monitor construction activities to ensure that the Works are completed in accordance with the Drawings and Specifications. 4. Ensure timely response as defined in this Document, to Submittals pertaining to the Drawings or Specifications submitted by the Owner. 1.8 Codes and Standards The Quality Control and Quality Assurance Program (QC/QA) as described in this Document, shall use testing procedures from, but not limited to, the list of American Society of Testing and Materials Standards (ASTM) as summarized in Table 1.2. Table 1.2: List of QA/QC testing standards Test ASTM D2487 ASTM D422 ASTM D854 ASTM D698 Procedure A, B or C Topic Classification of Soils for Engineering Purposes. Particle Size Analysis of Soils. Specific Gravity of Soils. Laboratory Compaction Characteristics of Soil Using Modified Effort (Modified Proctor Density test). 1.9 Quality Control 1. The Contractor will carry out Quality Control (QC) for the Works defined in this document, and will undertake testing at a frequency and at the locations specified in these Specifications and Drawings. 2. All QC or other test data collected by the Contractor shall be made available to the Engineer on request. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

68 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 5 3. The Contractor shall provide all necessary equipment and technicians for material and product testing required to execute the QC program. 4. QC shall be done continuously, as specified in this Document, to ensure the quality of Products and Works. 5. The Contractor s QC shall be done independently from the Engineer s Quality Assurance (QA). 6. Geochemical testing of any construction material will be the responsibility of the Owner Quality Assurance 1.11 Submittals 1. The Engineer will carry out Quality Assurance (QA) for the Works defined in this Document, and will undertake testing at a frequency and at the locations specified in these Specifications and Drawings. The Engineer may undertake any additional testing which he deems necessary on any part of the Works. 2. This Document and the Drawings outline the Engineer s QA program and is subject to review by the Owner. 3. All QA or other test data, collected by the Engineer, shall be made available to the Owner on request. 4. The Contractor shall render such assistance as is necessary to enable QA sampling and testing to be carried out expeditiously, and provide all the necessary equipment. 5. The Engineer s QA shall be done independently from the Contractor s QC. 6. QA or any other form of performance testing by the Engineer shall in no way relieve the Contractor of its sole responsibility for completing the Works in accordance with the specified requirements. 7. Geochemical testing of any construction material will be the responsibility of the Owner. 1. The Contractor shall submit information as specified and requested from the Engineer. All submittals required by the Engineer will be requested from the Contractor. 2. The Engineer has the right to request as a Submittal any other information deemed necessary throughout execution of the Works. This includes information not currently defined as Submittal information on the Drawings and Specifications Construction Schedule 1. Construction scheduling is the responsibility of the Contractor Construction Drawings 1. Drawings will be issued by the Engineer specific to construction needs prior to commencement of the Work. Drawings shall be reviewed by the Contractor to ensure all aspects of the construction needs are covered and report to the Engineer any discrepancies and interferences. The Contractor shall notify the Engineer of construction PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

69 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 6 progress and Drawing requirements four (4) weeks prior to commencement of any Works. 2. Only Drawings specifically marked with the following words are considered acceptable for Construction: ISSUED FOR CONSTRUCTION, or IFC Construction Specifications 1. Specifications will be issued by the Engineer specific to construction needs prior to commencement of the Work. Specifications shall be reviewed by the Contractor to ensure all aspects of the construction needs are covered and report to the Engineer any discrepancies and interferences. The Contractor shall notify the Engineer of construction progress and Specification requirements four (4) weeks, or at a mutually agreed timeframe prior to commencement of any Works. 2. Only Specifications specifically marked with the following words are considered acceptable for Construction: ISSUED FOR CONSTRUCTION, or IFC END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

70 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 7 2 Construction 2.1 General This section of the Specifications forms part of the Contract Documents and is to be read, interpreted and coordinated with all other parts. The contents of this section are intended to make the Contractor aware of facts and design considerations that may well be beneficial to the execution of the Works. 2.2 Decommissioning of South Dam, Reclaim Dam and Cofferdam General The South and Reclaim Dams are two of several dams which make up the tailings management facility on site. The South and Reclaim dams are to be decommissioned as part of reclamation and closure activities. The decommissioning entails: 1. Removal or partial removal of the Reclaim dam fill to original ground elevation. 2. Removal or partial removal of the South Dam fill to an elevation of m. 3. Construction of a sediment retaining structure with spillway along the South Dam alignment. The Cofferdam was breached in 2012 by Teck. The remainder of the cofferdam requires regrading Excavation and Material Relocation 1. Material excavated from the dams will be salvaged for construction material for reclamation and closure activities. 2. Suitable Dam Fill material will be used for tailings cover material. 3. Suitable Dam toe buttress material will be used as Riprap for the spillway and drainage channels. 4. If there is an excess of Dam Fill material removed from the dams, this material will be stockpiled and revegetated. 5. The final depth of excavation will be at the discretion of the Engineer. 2.3 Recontouring and Covering Tailings Surface General 1. Tailings material will be recontoured to prevent ponded water, and capped with a Till cover to reduce infiltration and to prevent dust. 2. The final surface of the tailings should have positive drainage towards the south. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

71 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Till Cover 1. The Till Cover must be graded to shed water from the surface of the cover. 2. The Till Cover will be constructed with Till Cover Material salvaged from the South and Reclaim Dams. 2.4 Construct Riprapped Channel for Camp Creek and Spillway Flow General 1. Camp Creek will be realigned into the old creek bed. 2. The channel in the old creek bed will be riprapped and designed for a 1000 year event flow. 3. Channel from spillway will connect with Camp Creek channel END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

72 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 9 3 Clearing, Grubbing and Stripping 3.1 General Documents This section of the Specification forms part of the Contract Documents and are to be read, interpreted and coordinated with all other parts Definitions The following words and terms, unless the context otherwise requires, in this Specification, shall have a meaning set out below: Description Submittals 1. CLEARING means works involved in the removal of the ice and snow on natural ground or sub-grade surface to the satisfaction of the Engineer. 2. GRUBBING means removal of all trees, stumps, roots, logs, vegetation, debris and all other surface obstructions to the satisfaction of the Engineer. 3. STRIPPING means Works involving excavation and removal of unsuitable material including but not limited to organics and ice rich materials. 1. The Works covered in this section consist of supplying all labour, materials, and equipment, and performing all Works necessary for clearing, grubbing and stripping. 2. The works shall involve clearing, or clearing and grubbing, and stripping the Works areas as required, but not limited to: drainage channels, borrow areas, disposal areas, stockpile areas, laydown areas, water management areas, foundation zones and between individual lifts of fill placement, as shown on the Drawings, or inferred by these Specifications or as directed by the Engineer. 3. Clearing and stripping in all areas shall require approval by the Engineer before such Works begins. 4. It is the Owner s responsibility to identify and acquire all necessary permits and approvals for stockpiling and storage of materials removed through the process of clearing and/or stripping. 1. At least seven (7) days prior to clearing, or clearing and grubbing, or clearing, grubbing and stripping in any specific area, the Contractor shall submit to the Engineer, for approval, a Clearing, Grubbing and Stripping Work Plan describing the schedule, locations and extent of the clearing, grubbing and stripping and the proposed methods for disposal of said products. 2. Work shall not start until applicable approvals are obtained from the Engineer in writing. 3. Approval of submittals shall not relieve the Contractor of its sole responsibility to construct the Works in accordance with specified requirements. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

73 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Permits and Regulations Protection 3.2 Execution Preparation Clearing Grubbing Stripping 1. The Works shall be conducted in accordance with the Owner s and all applicable Federal, Territorial, Local or Landowner regulations and licences regarding the disposal of materials from clearing, grubbing and stripping. 2. It is the Contractor s responsibility to be familiar with all said regulations, conditions and permits. 1. Unless otherwise instructed, the Contractor is to take all necessary precautions to prevent damage to natural and man-made features, including, but not limited to monuments, survey marks, monitoring instrumentation, and existing infrastructure. 2. The Contractor may not perform any Works outside of the permitted and pre-approved construction area. 1. The Contractor shall confirm the clearing, grubbing, and stripping limits by having his surveyor layout and flag the extents of work, prior to commencement of clearing, grubbing and stripping. The Engineer will inspect these demarcated areas and confirm all clearing, grubbing and stripping limits before giving the Contractor approval to proceed. 2. The Contractor shall inspect the Works site and verify with the Engineer, any restrictions within or adjacent to the clearing limits. 1. Snow and ice shall be removed from all construction footprint areas, prior to undertaking any work in that area, with a maximum tolerance of 10 cm of snow left above natural ground, or as otherwise approved by the Engineer. 2. Should snow fall on previously cleared, grubbed, or stripped surfaces that have been prepared and approved for construction, including between individual lifts of fill placement, the Contractor will carry out any additional clearing as requested by the Engineer. 3. The Contractor shall take all necessary precautions to prevent damage to natural ground, unless otherwise specified by the Engineer. 1. Trees and shrubs, including their complete root system shall be removed from all construction footprint areas, prior to undertaking any work in that area. 1. Where required and as a minimum in areas to be excavated, areas subject to clearing and grubbing shall undergo stripping to the depth necessary to remove all soil and other PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

74 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 11 organic material necessary to expose bedrock, or other suitable foundation conditions as directed by the Engineer. 2. Should blasting be required to facilitate stripping, the Contractor will comply to all Specifications associated with blasting, in addition to those listed in this Section Finished Surface Disposal 1. The Contractor shall leave the cleared, grubbed and/or stripped surface clear, smooth, debris- and snow-free, in a condition suitable for inspection by the Engineer. 1. Snow and ice cleared off the construction area shall be stockpiled downstream and outside of the construction area where it will not affect the construction or any constructed elements during thaw. The stockpile area shall be proposed by the Contractor and approved by the Engineer. A water management plan, prepared by the Contractor, and approved by the Engineer, must be in place prior to stockpiling snow and ice in the specified area. 2. Trees, shrubs, and roots grubbed from construction areas shall be stockpiled in designated areas approved by the Owner. 3. Soil and organic material stripped off the construction areas shall be stockpiled in designated areas approved by the Owner with proper sediment control as instructed in permit requirements. 3.3 Quality Control 1. Contractor shall submit a Clearing, Grubbing, and Stripping Work Plan as defined in this Document. 2. Contractor is responsible to confirm that all Permits and Approvals are in place prior to commencing any work. 3. The Contractor shall physically demarcate, for review and approval by the Owner and Engineer, the Works area that will be cleared, grubbed and/or stripped using proper survey control. Within this zone clearly identify natural and man-made features that require protection as defined in this Document. 4. The Contractor shall implement measures, including spotters as needed, to allow visual inspection of clearing, grubbing and/or stripping activities during execution to ensure it is done in accordance with the Specifications as defined in this Document. 5. The Contractor shall conduct field surveys and submit As-Built Drawings, in electronic format, of any cleared, grubbed and/or stripped areas, as requested by the Engineer. 3.4 Quality Assurance 1. The Engineer shall review the Contractor s Clearing, Grubbing, and Stripping Work Plan as defined in this Document and submit review comments back to the Contractor. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

75 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page The engineer shall visually inspect the demarcated zone prepared by the Contractor for clearing, grubbing and/or stripping and inform the Contractor if changes are required. 3. The Engineer shall visually inspect the cleared, grubbed, and/or stripped areas and inform the Contractor if changes are required. 4. The Engineer shall review As-Built Drawings submitted by the Contractor of cleared, grubbed, and/or stripped areas and inform the Contractor if any changes are required END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

76 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 13 4 Excavation and Water Control 4.1 General Documents Definitions Description 1. This section of the Specifications forms part of the Contract Documents and is to be read, interpreted and coordinated with all other parts. 1. The following words and terms, unless the context otherwise requires, in this Specification, shall have the meanings set out below: (a) SOIL and OVERBURDEN meaning is interchangeable and means general overburden material including clays, silty clays, sand, gravel, till and any combination of these materials. (b) DRAINAGE ROCK means poorly graded gravel drainage material salvaged from the toe of the South Dam or Reclaim Dam or from a different source. (c) ROCK means quarried material from a designated quarry site. (d) DAM FILL means material salvaged from the South Dam, Reclaim Dam, or North Creek Dyke. (e) UNSUITABLE MATERIAL means any soil or rock that does not meet the Specifications for the use of this project. (f) BLASTED MATERIAL means any material produced by production blasting at all quarry or excavation sites that is deemed to be suitable for construction material. (g) NEAT LINE means the final grade to which an excavation or backfill is to be performed. (h) BORROW AREA means the area from which material for construction use is excavated. (i) COMMON EXCAVATION means excavation of all materials, including rock, waste rock, weathered bedrock, soil, and unsuitable material by mechanical means. 1. The excavation Works entails excavation of soil, dam fill, and other materials below existing ground surface to neat lines and grades as indicated on the Drawings. 2. The Works to be done under this Section consists of furnishing all labour, plant and equipment, and the performance of all Works necessary to carry out rock, dam fill, and soil excavation as shown on the Drawings, and as specified herein. 3. The works shall also include the loading, transportation and permanent disposal of all excavated materials which are deemed by the Engineer to be surplus, or unsuitable for PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

77 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Exclusions Procedures Submittals use as construction material, and the loading, transportation and possible temporary stockpiling and re-handling of acceptable materials to locations where they can either be used as part of the temporary or permanent structures, or stockpiled in readiness for future temporary or permanent use. 4. The Contractor will be responsible to locate suitable stockpile locations for any excavated material, whether temporary or permanent. The Engineer will however have the right to reject any identified sites, if in his opinion it may interfere with any of the Works. 1. The Contractor is responsible for borrow area development. The Engineer does however reserve the right to request modifications to the borrow area development plan if the materials being produced do not meet Specifications. 1. The details of the surface excavations shown on Drawings represent an engineered design encompassing drainage under particular assumed conditions. Variations in site conditions may require adjustments to the excavation shape, slope reinforcement, and drainage at the Engineer s discretion. 2. If, in a specific area, a plan that has previously been adopted does not fit the site conditions in accordance with the requirements of the specifications, the Engineer shall submit a revised plan to the Contractor before continuing excavation in identified areas. 3. Water management measures shall be constructed and implemented by the Contractor for all Common Excavations. 1. The Contractor shall submit a detailed excavation plan to the Engineer outlining his intended methods for excavation within a given area at least seven (7) days prior to the commencement of the Works including but not limited to the following details: (a) Typical equipment deployment. (b) Sediment and runoff control around the intended Works area. (c) Water control and dewatering plan for Works where ground water of surface water runoff could occur. (d) Typical blast method including hole size, depth, spacing, burden and loading details for production, buffer, and pre-split holes, if required. (e) The Contractor s excavation plan must be approved by the Engineer. (f) Work shall not start until applicable approvals are obtained from the Engineer in writing. 2. Approval of submittals shall not relieve the Contractor of its sole responsibility to construct the Works in accordance with specified requirements. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

78 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Execution Preparation 1. Prior to beginning a grading or excavation operation in any area, all necessary clearing, grubbing, snow clearing and/or stripping in that area shall have been performed in accordance with the Specifications. 2. The Contractor shall satisfy himself as to the character, quantity, and distribution of all the material to be excavated. 3. The Contractor shall have a contingency plan for sudden unforeseeable change of weather conditions in place prior to excavation commencement. The Contractor shall have a daily Works plan in relation to the weather conditions, equipment, operator availability, area of Works, and schedule. 4. The Contractor shall be responsible for sediment and runoff control around the construction area to ensure there is minimal impact on the natural state of the surrounding environment in accordance to all issued regulations, licenses and permits. 5. The Contractor shall be responsible for all dewatering and water control as appropriate Common Excavation Methods 1. Common excavation of dam fill and soil shall be performed to the lines, grades, and elevations as indicated on the Drawings, or as directed by the Engineer, and shall be finished to a reasonable smooth and uniform surface. 2. Should the Contractor, through carelessness or other fault, excavate beyond the designated grades, he shall replace the excavation in an approved manner, with approved materials, in accordance with the Specification, or any modification thereof as directed by the Engineer. 3. All excavated material determined unsuitable by the Engineer shall be disposed of as directed by the Engineer. 4. At all times during construction, the Contractor shall adopt excavation procedures such that at no time shall the stability of any slope be impaired. The Engineer reserves the right to stop work if he deems the conditions to be unsafe Excavation in Borrow Areas 1. Borrow excavation shall be performed to the lines, grades and elevation as indicated on the Drawings or as directed by the Engineer. 2. Borrow development will be the responsibility of the Contractor in accordance with staged plans submitted to the Engineer for approval prior to undertaking the Works. 3. Methods of access and excavation in the borrow areas will be determined by the Contractor, unless otherwise directed by the Engineer. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

79 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page The Contractor shall use appropriate blasting methods to control the height of each bench and associated material gradation. The Contractor is responsible for fragmentation and throw of the material to ensure ease of excavation. 5. Excavation in the borrow area should be optimized by the Contractor for safety of equipment operation, water control, and bench stability. 6. Prior to excavation of the material, certified personnel must inspect the blast pattern to ensure all blasting agents were ignited and none were left behind Dam Fill Excavation Tolerances 1. Excavation shall be to the lines and grades shown on the Drawings, or in the absence thereof to a vertical tolerance of m and a horizontal tolerance of +0.5 m. 2. Slopes shall not be steeper than those specified and shown on the Drawings. 3. Deviations from stated tolerances must be approved by the Engineer Spillway Excavation Tolerances 1. Excavation shall be to the lines and grades shown on the Drawings, or in the absence thereof to a vertical tolerance of m and a horizontal tolerance of +0.5 m. 2. Slopes shall not be steeper than those specified and shown on the Drawings. 3. Deviations from stated tolerances must be approved by the Engineer Control of Water 1. Surface water flows shall be directed away from the Works by means of diversion berms, ditches or other acceptable means and, in any case, all surface flows on the Works area shall be satisfactorily controlled, and to the environmental standards specified. 2. Any inflow of ground water or surface runoff water into the excavation must be controlled using suitably placed and sized sumps and pumps. 3. Any water collected in the sumps must be discharged in an approved manner to a designated area away from the construction activities. A pump and discharge contingency plan should be discussed with and submitted to the Engineer for approval prior to construction. 4. The construction, operation, and maintenance of the sump(s) and pump(s) are the responsibility of the Contractor Scaling, Slope Stability and Safety 1. Immediately following excavation and at any time during the Works, all loose material on slopes, which appears to be unsafe or to endanger workers, structures or equipment, shall be scaled and removed. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

80 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page All slope stability measures will be considered incidental to the Works, and will be the responsibility of the Contractor with inspections done by the Engineer. 4.3 Quality Control 1. The Contractor shall submit an Excavation Plan (including a Water Management and Dewatering Plan, if required) as defined in this Document. 2. Contractor to confirm that all Permits and Approvals are in place prior to commencing any work. 3. The Contractor shall physically demarcate, for review and approval by the Engineer, the Works area that will be excavated using proper survey control. 4. The Contractor shall implement measures, including spotters and frequent survey control as needed, to allow visual inspection of excavation activities during execution to ensure it is done in accordance with the Drawings and Specifications as defined in this Document. 5. The Contractor shall implement measures to ensure adequate water management and dewatering as necessary. 6. The Contractor shall advise the Engineer when an excavation has been completed and is ready for inspection and/or approval. Interim survey control may be requested by the Engineer to confirm lines and grades have been met. 7. The Contractor shall conduct a field survey, and submit As-Built Drawings in electronic format of any excavated area, for submittal to the Engineer. 4.4 Quality Assurance 1. The Engineer shall review the Excavation Plan (including a Water Management and Dewatering Plan, if required) as defined in this Document and submit review comments back to the Contractor. 2. The Engineer shall visually inspect the demarcated zone, and any associated survey files prepared by the Contractor for excavation, and inform the Contractor if changes are required. 3. The Engineer shall visually inspect the excavated areas, and any associated survey files, and inform the Contractor if changes are required. 4. The Engineer shall visually inspect water management and dewatering if required, and inform the Contractor if changes are required. 5. The Engineer shall review As-Built Drawings submitted by the Contractor of excavated areas and inform the Contractor if any changes are required END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

81 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 18 5 Drilling and Blasting 5.1 General Documents Definitions Description 1. This section of the Specifications forms part of the Contract Documents and are to be read, interpreted and coordinated with all other parts. 1. The following words and terms, unless the context otherwise requires, in this Specification, shall have the meanings set out below: (a) CERTIFIED PERSONNEL means a suitably qualified person that hold current blasting certificates issued by all necessary Territorial and Federal Regulatory agencies for the Project. (b) CHEMICAL BLASTING AGENTS means any form of explosive agents, and components that are suitable for use in the Project. 1. All blasting operations must be performed in accordance with the Contractors Environmental Management and Procedures Manual and all Federal and Provincial Regulations and Licenses. 2. Blasting near water bodies frequented by fish, will require lower powder factors, as determined by Guidelines issued by the Department of Fisheries and Oceans. 3. The Contractor will be responsible to familiarize himself with all appropriate conditions that would apply to blasting. 4. The Works to be done under this Section consists of supplying all labour, materials, plant and equipment, and performing all Works necessary to carry out drilling and blasting with certified personnel and chemical agents as shown on Drawings and specified herein. 5. The Works shall include; but is not limited to: (a) Provide a typical list of safety protocols, chemical blasting agents, blast patterns and powder factors that will be suitable for carrying out the Works, and for producing the specified construction materials. (b) Drilling with appropriate equipment, to appropriate depth and grade to execute the Works, develop rock quarries and any other common excavation as shown on the Drawings, or as directed by the Engineer. (c) Provide suitably qualified personnel, with current blasting certificates to carry out all required safety protocols for blasting regulations prior to ignition. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

82 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Submittals 1. The Contractor shall submit a Drilling and Blasting Plan to the Engineer describing the schedule, and proposed methods for borrow development and common excavation, at least seven (7) days prior to the commencement of Works. 2. Work shall not start until applicable approvals are obtained from the Engineer in writing. 3. Approval of submittals shall not relieve the Contractor of its sole responsibility to construct the Works in accordance with specified requirements. 5.2 Products and Personnel 5.3 Execution Drilling Blasting 1. The Contractor is responsible to procure all necessary supplies and equipment for drilling and blasting operations, including the chemical blasting agents, detonators and detonator cords. 2. The Owner is responsible to acquire all required licenses and notifications from Territorial and Federal Regulatory Agencies. 3. The Contractor is responsible to have appropriately qualified and certified persons to handle all aspects of the drilling and blasting Works, including, but not limited to management of inventory, mixing of explosives, storage of explosives, transportation of explosives, placing of charges, ignition of explosives, and clearing of explosives after ignition. 4. The Contractor is responsible for management, maintenance and security of the Explosives Facility, whether temporary or permanent. 1. The Contractor will lay out the appropriate blast pattern for the specified material grade required, at appropriate locations. 2. The Contractor will drill blast holes in accordance with the blast pattern requirements, taking due care to prevent over-breaking. 3. The Contractor will ensure that the appropriate surface water containment and management procedures are followed when drilling. 1. The Contractor s Health and Safety Plan, list of blasting agents, technician s certificates, and proposed methods of blasting will be provided by the Contractor prior to blasting operation, for record keeping purposes. 2. The Contractor will provide appropriately qualified and certified personnel to manage all aspects of the blasting. 3. The Contractor will be responsible for notifying all air and land traffic of the time and location of any blast at least 24 hours in advance. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

83 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page The Contractor will be responsible for putting in place all protocols and physical barriers to warn and prevent land and air traffic from entering the designated blast zone, according to all applicable Territorial and Federal Regulations and the Contractor s Health and Safety Plan. 5. The Contractor will use controlled blasting methods to ensure production of specified materials, ease of excavation and to minimize processing requirements. 6. Certified Personnel must inspect the blast pattern post blasting to ensure there are no unexploded agents and explosives left behind prior to excavation. If unexploded material is found in the pattern, Certified Personnel must remove the danger material according to normal practice and the Contractor s Health and Safety Plan. 5.4 Quality Control 1. Contractor shall submit a Drilling and Blasting Plan as defined in this Document. 2. Contractor must confirm that all Permits and Approvals are in place prior to commencing any work. 3. Contractor shall physically demarcate, for review and approval by the Engineer, the Works area that will be drilled and blasted using proper survey control. 4. Contractor shall implement and follow appropriate established protocols prior to and immediately following any Blast in compliance with all appropriate Rules and Regulations. 5.5 Quality Assurance 1. The Engineer shall review the Drilling and Blasting Plan as defined in this Document and submit review comments back to the Contractor. 2. The Engineer shall visually inspect the demarcated zone, and any associated survey files prepared by the Contractor for drilling and blasting, and inform the Contractor if changes are required END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

84 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 21 6 Material Specifications 6.1 Part 1 General Documents Description Submittals 1. This section of the Specification forms part of the Contract Documents and is to be read, interpreted, and coordinated with all other parts. 1. The sources and borrow areas of all fill will be designated on-site by the Owner and the Engineer. The material types required for the completion of the Works are labelled as: (a) Capping; (b) Riprap; and (c) Drainage Rock. 2. All construction material shall be non-acid generating, free of snow and ice, organic matter or similar impurities. 3. The Contractor is responsible for supplying, installing, operating and maintaining all the necessary plant, equipment, materials, labour, and supervision to produce and test the suitability of the specified construction material on site. 4. The Contractor must process all materials to meet the gradations specified herein. 1. The Contractor shall submit the information requested in the Quality Control program listed in this section to the Engineer in a timely manner, understanding that approvals to proceed with the Works may be contingent on review and approval of these submittals. 2. Work shall not start until applicable approvals are obtained from the Engineer in writing. 3. Approval of submittals shall not relieve the Contractor of its sole responsibility to construct the Works in accordance with the specified requirements. 6.2 Part 2 Product General 1. Fill, required for the Works, shall be obtained and/or manufactured by the Contractor from designated borrow areas as shown on the Drawings, and from salvage of material from the South Dam and the Reclaim Dam. The North Creek Dyke may be a source of capping material if required. 2. The parent rock sources for all fill materials must be inspected by the Engineer throughout the material processing and construction activities to ensure the requirements stated herein are being met. 3. Unsuitable material from an excavation of the Works shall be disposed of in a designated on-site disposal area as directed by the Engineer. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

85 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Cover Material 4. If the Contractor proposes to obtain fill from an area not within the excavations or designated areas shown on the Drawings, he shall communicate his intention to the Engineer. The Contractor shall first obtain the necessary approvals and permits to carry out such sub-surface investigation and obtain and submit such samples, as are required, to enable the Engineer to assess the suitability of the fill for the Works. 5. The Contractor shall keep accurate exploration records of any test pit, trench or drill hole which it makes for the purpose of investigating borrow material, and a copy of such records shall be submitted to the Engineer within seven (7) days of the completion of exploration Works. 6. The Contractor shall give the Engineer no less than 14 days notice of his intention to develop any potential borrow area not shown on the Drawings. 7. The Contractor shall make his own determination of the adequacy of any borrow source he intends to exploit. 1. Cover material shall consist of well graded material sourced from South Dam or Reclaim Dam, and shall be free of frozen soil, snow and ice and conforms generally to these specifications as shown in Figure The maximum allowable grain size for the cover material is 300 mm. Boulders larger than the maximum diameters shall be removed at source or scalped from the fill during placement and pushed away from the working area. 3. The Owner shall take random samples of the dam fill materials during excavation to assess metal leaching potential. The testing program will not interfere with the excavation schedule. In the event that material with metal leaching is encountered, fill placement may be modified so that this material is place in the initial lifts. 4. Drainage Rock is not suitable Till Cover material. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

86 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 23 Percent Passing (%) Min. Particle Size (mm) Max. Particle Size (mm) Figure 6.1: Gradation Specification for Till Cover Material Riprap 1. Riprap material shall consist of competent non-acid generating material from a designated quarry or salvaged from the Reclaim and South Dams or from the North Creek dyke, and that is free of organic matter, frozen soil, snow and ice. 2. Basic screening or manual selection may be used to achieve the desired gradation. 3. The Owner shall sample and test the Riprap material to ensure it is within permit limits for blast residue. 4. Riprap material shall be clean with no fine grained material. Type I Riprap (D 50 = 0.3 m) 1. The gradation of the Type I Riprap shall meet the Specifications shown in Figure 6.2. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

87 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 24 Percent Passing (%) Min. Particle Size (mm) Max. Particle Size (mm) Figure 6.2: Gradation Specification for Type I Riprap Type II Riprap (D 50 = 0.4 m) 1. The gradation of the Type II Riprap shall meet the Specifications shown in Figure 6.3. Percent Passing (%) Min. Particle Size (mm) Max. Particle Size (mm) Figure 6.3: Gradation Specification for Type II Riprap PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

88 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 25 Type III Riprap (D 50 = 0.5 m) 1. The gradation of the Type III Riprap shall meet the Specifications shown in Figure 6.4. Percent Passing (%) Min. Particle Size (mm) Max. Particle Size (mm) Figure 6.4: Gradation Specification for Type III Riprap PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

89 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Geosynthetics 1. The geosynthetics shall be a nonwoven needle-punched geotextile fabric with a nominal weight of 12 ounces per square yard and must satisfy the Specifications listed in Table 6.1. Table 6.1: Nonwoven geotextile specifications (typical product) Parameter Standard LP12 Grab Tensile ASTM D4632 1,330 N Elongation ASTM D % Tear ASTM D N CBR Puncture ASTM D N AOS ASTM D microns Permittivity ASTM D sec -1 Water Flow ASTM D l/min/m 2 UV (500 hrs) ASTM D % Nominal Thickness ASTM D mm Roll size N/A 4.57 x 91.4 m Roll Weight 1 N/A 181 kg END OF SECTION Typical values. All other values are minimum average roll values (MARV) PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

90 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 27 7 Fill Placement 7.1 General Documents Description 1. This section of the Specifications forms part of the Contract Documents and is to be read, interpreted and coordinated with all other parts. 1. The Works specified in this section includes furnishing all supervision, labour, materials, tools and equipment for placement of fill material to the lines and grades shown on the Drawings and specified herein. 2. The Works shall include, but is not limited to the following: (a) Foundation preparation to receive fill. (b) The supply, hauling, placing, and compacting of the specified fill materials as shown on the Drawings. (c) All related surveys for layout and control of the Works. (d) Assisting the Engineer when necessary for the performance of QA testing. (e) All QA testing and submission of QA results to the Engineer. (f) Maintenance of haul roads (as applicable) including snow and ice removal. (g) The development, maintenance, and restoration of fill material borrow areas. (h) Any other related Works not covered elsewhere. 3. Fill material required to be placed include, but are not limited to the following: Codes and Standards (a) Haul and place Riprap as an erosion protection or wave energy dissipation layer. (b) Haul and place Till Cover material as soil cap. (c) Haul and place Sand and Gravel material as soil cap. (d) Regrade surplus Dam Fill material. 1. The Quality Control and Assurance Program (QA/QC) shall use testing procedures from, but not limited to the list of American Society of Testing and Materials Standards in Table 7.1. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

91 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page 28 Table 7.1 List of QA/QC testing standards Test Topic ASTM D2487 Classification of Soils for Engineering Purposes. ASTM D2216 Water (Moisture) Content in Soil and Rock. ASTM C136 Standard Test Method for Sieve Analysis of Fine and Coarse Aggregates. ASTM D854 Specific Gravity of Soils Submittals 1. The Owner shall submit the information requested below to the Engineer. Works shall not start until applicable approvals are obtained. 2. The Owner shall ensure that the Contractor work qualities are in accordance with this Specification and the Drawings. 3. Testing: 7.2 Execution Snow Removal Equipment (a) Quality Control testing will be done by the Contractor. (b) Quality Assurance testing will be done by the Engineer. (c) The Owner is responsible to ensure the Contractors work meet the Specifications as demonstrated by test results or otherwise specified by the Engineer. (d) The Engineer s testing shall not relieve the Contractor of his sole responsibility to construct the Works in accordance with specified requirements. 1. Care shall be taken when clearing snow adjacent to previously placed capping material to avoid compaction or other disturbance. Any material, which, in the opinion of the Engineer, has been disturbed, shall be removed and replaced. 2. If deemed necessary by the Engineer, the Contractor shall use hand labour to clear snow Foundation Preparation 1. The Contractor shall prepare an acceptable foundation surface to receive the specified fill material. An acceptable foundation surface is a surface which is clean, sound and firm, and which does not contain any loose, softened or disturbed foundation material as determined by the Engineer. 2. Dense foundation surfaces to receive fill shall be free from uncompacted fill, snow, ice or other unsuitable materials. The surfaces shall be inspected by the Engineer, who may direct proof rolling with a loaded haul truck, and/or local over excavation and backfilling with approved material. Placement shall be completed as outlined in the applicable sections of these Specifications. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

92 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Where depressions or holes exist in the foundation material, acceptable fill shall be placed in depressions, as directed, and compacted as specified herein. Special techniques, handwork and the like shall be required as necessary. 4. Fill shall not be placed on the prepared foundations until they have been inspected and approved by the Engineer General Fill Placement (All Products) 1. Construction must be performed in accordance with the best modern practice and with equipment best adapted to the work being performed. Materials must be placed so that each zone is homogenous, free of stratifications, ice chunks, lenses or pockets, ruts, and layers of material with different texture or grading not conforming to the requirements stated herein. 2. No fill material shall be placed on any part of the foundation until it has been prepared as specified herein and approved by the Engineer. The placement of fill material must conform to the lines, grades and elevations shown on the Drawings, as specified herein or as per the direction of the Engineer. Fill placement must be conducted in such a manner that mixing of fill materials with fill materials in the adjacent zones is avoided. 3. Construction shall not proceed when the work cannot be performed in accordance with the requirements of the Specifications. Any part of the Works that have been damaged by the action of rain, snow or any other cause must be removed and replaced with the appropriate material conforming to the requirements stated herein before subsequent layers are placed. 4. Stockpiling, loading, transporting, dumping, and spreading of all materials shall be carried out in such a manner to avoid segregation or any other condition that does not meet the requirements stated herein. Segregated materials must be removed and replaced with materials meeting the requirements stated herein and receiving the Engineer s approval. 5. The Contractor must remove all debris, vegetation or any other material not conforming to the requirements stated herein. The Contractor must dispose of these materials in an area approved by the Owner. 6. Unless otherwise specified construction material maximum lift thicknesses and compaction requirements shall be as indicated herein or otherwise specified on the Drawings Type I Riprap Placement 1. The Type I Riprap must be placed in lifts not exceeding 450 mm thickness. Any rock pieces exceeding the top size specification must be removed. 2. The Type I Riprap material must be compacted with the bucket of an excavator Type II Riprap Placement 1. The Type II Riprap must be placed in lifts not exceeding 600 mm thickness. Any rock pieces exceeding the top size specification must be removed. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

93 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page The Type II Riprap material must be compacted with the bucket of an excavator Type III Riprap Placement 1. The Type C Riprap must be placed in lifts not exceeding 750 mm thickness. Any rock pieces exceeding the top size specification must be removed. 2. The Type III Riprap material must be compacted with the bucket of an excavator Till Cover Material Placement 1. The Till Cover material must be placed in lifts not exceeding 300 mm thickness. The placement method must ensure that segregation and nesting of coarse particles is avoided. 2. The Till Cover material shall not be compacted. Haul truck traffic must be routed to minimize travel of loaded haul trucks over the placed till cover material Geotextile Deployment Tolerances 1. The Contractor shall submit a proposed panel layout 14 days prior deployment for Engineer s approval. 2. The Contractor shall have sufficient amount of ballast weight, such as sand bags, during the deployment to hold and keep deployed panels in place as protection against wind. 3. The geotextile shall be unrolled as smoothly as possible on the prepared subgrade in the direction of construction traffic. 4. Geotextile rolls shall be overlapped in the direction of sub-base placement. 5. The geotextile shall be 450 mm minimum overlapped and stitched or heat bonded together. The Engineer will inspect the stitching or heat bonding to ensure quality of Works. 6. On curves, the geotextile may be folded or cut and overlapped to conform to the curve. 7. The geotextile shall not be excessively dragged across the subgrade. 8. Damaged geotextile, as identified by the Engineer, shall be repaired immediately. A geotextile patch extending 1 m beyond the perimeter of the damage in all directions shall be installed as directed by the Engineer. 9. A method of attaching the geotextile patch may be required over soft subgrade as directed by the Engineer. 1. Fill shall be placed in horizontal lifts to the lines and levels shown on the drawings or in the absence thereof to a vertical tolerance of m and a horizontal tolerance of +0.5 m. 2. Slopes shall not be steeper than those specified and shown on the Drawings. 3. Deviations from stated tolerances must be approved by the Engineer. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

94 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Sediment and Runoff Control 1. The Contractor is responsible to provide and construct facilities such as silt fences, diversion berms, sediment ponds, and other measures as are required to prevent the discharge of fines from construction areas and from entering any natural water courses downstream of the Works during the season immediately following construction. 2. In general, when placing fill material, the Contractor shall slope the surfaces toward collection channels for surface water management. 7.3 Quality Control 1. The Contractor shall be responsible for the quality of fill as described in this Document. 2. The Contractor shall conduct regular topographic surveys to demonstrate the placement of fill to specified lines, levels, grades and tolerances. The Engineer may from time to time conduct check surveys. Survey results shall be reported to the Engineer within 24 hours of the completion of each survey. 3. The Contractor shall carry out Quality Control testing during fill placement as outlined in Table 7.2 Table 7.2: Required QC testing during placement of construction materials Material Type Sample Location Sample Type Test Type Test Location Expected Turnaround Time QC Test Frequency Submittal Riprap In-Place N/A Particle Size Analysis (Visual) N/A N/A Ongoing None Riprap In-Place N/A Lift Thickness (Survey Control) N/A Hold Point Before Next Lift is Placed Every Lift Survey Report Till Cover In-Place Grab Particle Size Analysis (ASTM C136) Off Site 5-days One per 1,000 m 3 Test Certificate Till Cover In-Place Grab Lift Thickness (Survey Control) N/A Hold Point Before Next Lift is Placed Every Lift Survey Report 7.4 Quality Assurance 1. QA testing shall be carried out across the full length, width and depth of various fill zones so as to fully represent the overall quality of the structure. 2. The Contractor shall conduct regular topographic surveys to demonstrate the placement of fill to specified lines, levels, grades and tolerances. The Engineer may from time to time conduct check survey. Survey results shall be reported to the Engineer within 24 hours of the completion of each survey. PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

95 SRK Consulting Technical Specifications for Tailings Dam Decommissioning Sä Dena Hes Project Page Final acceptance of earthworks will be made only after fill materials have been dumped, spread, moisture conditioned, and compacted, and tests and surveys have demonstrated compliance with the Specifications. 4. If on the basis of the sampling and testing, or if in the opinion of the Engineer, an area of the fill does not meet the specified requirements; such fill shall be removed and replaced with conforming material. Rejection of fill material by the Engineer may be made at source, in transporting vehicles, or in place. 5. The Engineer can re-inspect previously approved areas for damages and instruct the Contractor to repair said damages in accordance with the Specifications. 6. The Engineer shall carry out Quality Assurance testing during fill placement as outlined in Table 7.3. Additional testing may be conducted at the discretion of the Engineer Table 7.3: Required QA testing during placement of construction materials Material Type Sample Location Sample Type Test Type Test Location Expected Turnaround Time QC Test Frequency Submittal Riprap In-Place N/A Particle Size Analysis (Visual) N/A n/a Ongoing None Riprap In-Place N/A Lift Thickness (Survey Control) N/A Hold Point Before Next Lift is Placed Every Lift Survey Report Till Cover In-Place Grab Particle Size Analysis (ASTM C136) Off Site 5-days One per 1,000 m 3 Test Certificate Till Cover In-Place Grab Lift Thickness (Survey Control) N/A Hold Point Before Next Lift is Placed Every Lift Survey Report END OF SECTION PMH/IM/MMM TechnicalSpecifications_Report_1CT _PMH_IM_MMM_SDM_ March 2014

96 Appendix C: Seismic Hazard Analysis

97 Sa Dena Hes From: alea/simphaz eng.php, accessed on June 7, 2013

98 2010 National Building Code Seismic Hazard Calculation INFORMATION: Eastern Canada English (613) français (613) Facsimile (613) Western Canada English (250) Facsimile (250) Requested by:, SRK Consulting Site Coordinates: North West User File Reference: Sa Dena Hes June 07, 2013 National Building Code ground motions: 2% probability of exceedance in 50 years ( per annum) Sa(0.2) Sa(0.5) Sa(1.0) Sa(2.0) PGA (g) Notes. Spectral and peak hazard values are determined for firm ground (NBCC 2010 soil class C - average shear wave velocity m/s). Median (50th percentile) values are given in units of g. 5% damped spectral acceleration (Sa(T), where T is the period in seconds) and peak ground acceleration (PGA) values are tabulated. Only 2 significant figures are to be used. These values have been interpolated from a 10 km spaced grid of points. Depending on the gradient of the nearby points, values at this location calculated directly from the hazard program may vary. More than 95 percent of interpolated values are within 2 percent of the calculated values. Ground motions for other probabilities: Probability of exceedance per annum Probability of exceedance in 50 years Sa(0.2) Sa(0.5) Sa(1.0) Sa(2.0) PGA % % % References National Building Code of Canada 2010 NRCC no ; sections 4.1.8, , , , and Appendix C: Climatic Information for Building Design in Canada - table in Appendix C starting on page C-11 of Division B, volume 2 User s Guide - NBC 2010, Structural Commentaries NRCC no (in preparation) Commentary J: Design for Seismic Effects Geological Survey of Canada Open File xxxx Fourth generation seismic hazard maps of Canada: Maps and grid values to be used with the 2010 National Building Code of Canada (in preparation) See the websites and for more information 60.5 N km Aussi disponible en français W 129 W W

99 Appendix D: Flood Hydrology

100 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS 3.0 WATER RESOURCES 3.1 SURFACE WATER HYDROLOGY Hydrological Setting The Sä Dena Hes mine is located in the drainage basin of False Canyon Creek, a left bank tributary of the Frances River. False Canyon Creek has a total catchment area of 492 km 2 and discharges some 55 km above the Frances River and Liard River confluence. Access to the mine development is from the south across the drainage basin of Tom Creek, a left bank tributary of the Liard River. Figure 2-1 shows the location of the mine in relation to the major rivers and lakes of the region. The open pits, underground workings and waste rock dumps associated with the Jewelbox ore zones are located near the drainage divide between Tom and False Canyon Creeks. All drainage from the Jewelbox development is directed to Camp Creek, a steep-gradient tributary of False Canyon Creek that drains the eastern flank of Mount Hundere. The mill site is also located in the catchment of Camp Creek. The Burnick development is entirely confined in the headwaters of another False Canyon Creek tributary, which has been designated Tributary D. The tailings impoundment is constructed in a saddle that lies along the drainage divide between Camp Creek and Tributary E. Figure 3-1 shows the locations of the major mine elements relative to the catchments of False Canyon and Tom Creeks. Figure 3-2 is a larger scale map showing the drainage basin for the Tailings Management Facility. MARCH

101

102

103 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Available Data As was done for the climate analysis, the hydrology of the minesite was first characterized in 1990 as part of the mine s permitting studies. The hydrology was then updated in 1999 and 2005 to support preparation of the DDRP. The hydrology was estimated using a mix of site-specific and regional data. At the point of updating the hydrology in 1999, no automated streamflow gauging stations had been operated at the minesite. The site-specific data largely comprised spot measurements made by a current meter. In 2002, Access Mining Consultants established an automated water level recorder in the Camp Creek Diversion upstream of the spillway from the Reclaim Pond. At the time of the latest update to the hydrology assessment (2005), this streamflow gauging station had been operated for four open water seasons. A total of 12 direct flow measurements had been made at the station with a current meter. Operation of this station has continued and the streamflow data collected since 2005 will be incorporated into an updated hydrological assessment for the mine, slated for The flows collected at the Camp Creek Diversion from 2002 to 2005 are presented in Figures 3-3 to 3-5. The corresponding daily rainfall records collected at the mill site, where available, are also shown on these figures. The flow hydrographs for Camp Creek have one distinctive feature: they are subdued. This suggests that the groundwater contribution to streamflow is large. Large rainfalls (e.g., see July 9, 2002 event on Figure 3-3) appear to cause only minor increases in flow in Camp Creek. The groundwater-dominated nature of the hydrology may, at least partly, be a result of the limestone geology within the stream s catchment. The annual peak was probably missed in the first two years of record and may have also been missed in However, it is very likely that the 2005 peak was measured, as evidenced by the streamflow record of a regional streamflow gauging station (Big Creek). This regional station experienced its annual peak just days after the peak was observed in Camp Creek (see Figure 3-5). MARCH

104 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS The 2005 peak flow for Camp Creek is shown on Figure 3-5 to be about 0.5 m 3 /s. However, it is strongly suspected that the true discharge was less than this value. On the day preceding the occurrence of the peak, the stream was largely covered by ice and snow. This cover may have partially still been in existence at the time of the flow peak, resulting in a higher stream level for a given flow rate than would occur if the channel was completely free of ice and snow. The shape of the water level record exhibits abrupt increases and decreases in stream depth just prior to and following the apparent peak in discharge, which suggests the stream channel may have been temporarily dammed by ice and snow. Further discussion of the Camp Creek flow data is given in Section MARCH

105 Minesite Rainfall Jun 18 Jun 25 Jul 02 Jul 09 Jul 16 Jul 23 Jul 30 Aug 06 Aug 13 Aug 20 Aug Daily Rainfall (mm) Discharge Computed from water level readings Measured with a current meter Jun Jun Jul Jul Jul Jul Jul Aug Aug Aug Aug 27 Hourly Average Discharge (m 3 /s) 2002 Sep 03 Date VANCOUVER Camp Creek Flow Record and Minesite Rainfall Record Job No: Filename: 1CT Figure 2_Camp Cr Flow Record_ ppt Sä Dena Hes Detailed Decommissioning and Reclamation Plan Date: Dec Approved: Figure: 3-3

106 2003 Discharge Record Hourly Average Discharge (m 3 /s) Computed from water level readings Measured with a current meter Discharge Record May May May Jun Jun Jun Jun Jul Jul Jul Jul Jul Aug Aug Aug Aug Sep Sep May Jun Jun Jun Jun Jul Jul Jul Jul Aug Aug Aug Aug Aug Sep Sep Sep Sep 27 Date Hourly Average Discharge (m 3 /s) Computed from water level readings Measured with a current meter Date Job No: Filename: 1CT VANCOUVER Figure 3_hr flow Record Camp Cr_ ppt Sä Dena Hes Detailed Decommissioning and Reclamation Plan Hourly Flow Record for Camp Creek 2003 and 2004 Date: Dec Approved: Figure: 3-4

107 Minesite Rainfall Discharge Quarter-Hourly Average Discharge (m 3 /s) May May May Jun Jun Jul Jul Aug Aug Sep Sep Oct Oct 16 May 01 May 15 May 29 Jun 12 Jun 26 Jul 10 Jul 24 Aug 07 Aug 21 Sep 04 Sep 18 Oct 02 Oct Daily Rainfall (mm) The tipping bucket was installed on May 16 during a rainfall event. Accordingly, the total rainfall on that day was greater than the measured value of 27.1 mm. The tipping bucket operated until October 24, Camp Creek (computed from automated water level readings) Camp Creek (measured by current meter) Big Creek (provisional data from WSC) The true peak flow for Camp Creek was probably less than computed from the water level record. In the day preceding the peak, the stream was still covered by ice and snow. This cover probably collapsed, causing an artificially high water level at the gauge at the time of the peak flow. The rating curve for this station was based on measurements taken with minimal or no backwater effects caused by ice conditions. The float on the automated water level recorder became stuck on June 7 and remained that way until the datalogger was retrieved on September 20. It is likely that the flow during this period remained below what was observed on June 7 (i.e., 90 L/s). If the water level had risen above that experienced on June 7, then the float would likely have become dislodged. Hourly Average Discharge (m 3 /s) 0 Date VANCOUVER Camp Creek Flow Record and Minesite Rainfall Record Job No: Filename: 1CT Figure 4_Camp Cr Flow Record-05_ ppt Sä Dena Hes Detailed Decommissioning and Reclamation Plan Date: Dec Approved: Figure: 3-5

108 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Average Flow Estimates As indicated in Section 2.4, elevation generally accounts for a large proportion of the variation in mean annual precipitation within a mountainous region. It follows, therefore, that mean annual runoff (MAR) would also be a function of elevation. Figure 3-6 shows how this observation was exploited to estimate the average flows of the minesite streams. The vertical axis of this figure displays values of MAR expressed as equivalent depths of water. The horizontal axis shows values of median elevation, which is the variable adopted to quantify the elevation characteristics of the regional and minesite catchments. The 18 pairs of MAR and median elevation values assembled in Table 3-2 for the WSC stations were plotted on this figure. These data demonstrate a reasonably strong relationship between the two variables. The data plotted on Figure 3-6 were used to develop a relationship that was believed to represent the conditions at the minesite. Two steps were undertaken to develop the relationship. Firstly, a linear regression was fitted to all 18 data points. This defined a straight line with a slope of 0.60 mm per m. Secondly, the intercept of this straight line was adjusted to force the line through the data point for Tom Creek. This adjustment was based on the premise that, of all the WSC catchments, the one for Tom Creek is probably the most representative of the conditions within the False Canyon Creek catchment. These two catchments share a significant portion of their respective drainage divides and also possess similar elevational characteristics. Expressed as an equation, the adopted relationship between mean annual runoff (MAR in mm) and catchment median elevation (E in m) is: MAR = 0.60 E 397 The above relationship was derived exclusively from the regional data. The site-specific data collected at Station MH-11 were reserved for validation purposes. The streamflow record for this station comprises a series of spot flow measurements made over a 10-year period. MARCH

109 Lened Cottonwood Hyland (10AD002) 600 Mac Flat Mean Annual Runoff (mm) True MAR of Station MH-11 is likely contained in this range Hyland (10AD001) Frances Coal Liard Blue Rancheria Beaver King Adopted relationship for estimating MAR of minesite catchments 200 Smith Tom Teeter Big 100 Geddes Catchment Median Elevation (m) SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN REGIONAL RELATIONSHIP BETWEEN MEAN ANNUAL RUNOFF AND CATCHMENT MEDIAN PROJECT 1CC DATE AUG APPROVED FIGURE 3-6

110 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS To provide a greater degree of confidence in the estimate, the observed flows at Station MH-11 were correlated with the coincidental flows of neighbouring WSC Stations. Three stations were selected for this purpose, Station 10AA005 on Big Creek, Station 10AA004 on Rancheria River and Station 10AA002 on Tom Creek. Figure 3-7 is a graphical presentation of the correlations. These correlations were performed on log-log graphs in recognition of the differences between the flow regimes of small and large catchments. Station MH-11 commands a much smaller catchment than the three WSC Stations and, accordingly, is expected to experience a more erratic flow regime (i.e., the ratio between the highest and lowest flow for Station MH-11 should be greater than the corresponding ratios for the other three stations). The correlations were used to make estimates of the MAR at Station MH-11. Table 3-1 summarizes the results. These correlations provided estimates that fall in a fairly narrow range from 266 mm to 330 mm. To validate the adopted relationship between MAR and elevation, this range was plotted on Figure 3-6. As can be seen, the adopted relationship passes through the range believed to contain the true MAR of Station MH-11. This suggests that the relationship is reasonably accurate, at least for catchments with similar median elevations as Station MH-11 (1140 m). The above discussion centred on finding a means of determining the average annual runoff volume at an ungauged site. The remainder of this section presents a technique for distributing this annual volume amongst the twelve months of the year. To implement this technique, an examination was made of the average monthly hydrographs observed at the regional gauging stations. The top plot on Figure 3-8 graphically presents the distributions for five regional stations. The average monthly flows for these distributions have been expressed as percentages of MAR to facilitate comparisons amongst the distributions. Of all the 18 WSC stations selected for the hydrology study, the five selected ones were judged to be the most representative of the minesite catchments, largely on the basis of a similarity in catchment median elevation. MARCH

111 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Table 3-1 Estimated Streamflow Characteristics at Station MH-11 Streamflow Characteristic Location Mean Annual Runoff a As a Flow (m 3 /s) As a Depth (mm) 7-Day Low Flow for the following Return Periods: 2-Year (m 3 /s) 10-Year (m 3 /s) 50-Year (m 3 /s) Big Creek at WSC Station 10AA Station MH-11 (estimated using regression between MH-11 and 10AA005) Rancheria River at Station 10AA Station MH-11 (estimated using regression between MH-11 and 10AA004) Tom Creek at WSC Station 10AA Station MH-11 (estimated using regression between MH-11 and 10AA002) Average estimate for Station MH Note: a) Based on the complete daily record of the WSC Station, a daily streamflow record was synthesized for Station MH-11. This was done by applying the regression equation to every observed daily flow value in the record of the WSC station. The MAR of Station MH-11 was then taken to equal the average of the synthesized record. MARCH

112 Spot Discharge at MH-11 (m 3 /s) y = x R² = Daily Average Discharge at WSC Station10AA005 on Big Creek (m 3 /s) Spot Discharge at MH-11 (m 3 /s) y = x R² = Daily Average Discharge at WSC Station 10AA004 on Rancheria River (m 3 /s) Spot Discharge at MH-11 (m 3 /s) y = 0.036x R² = Daily Average Discharge at WSC Station 10AA002 on Tom Creek (m 3 /s) SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN CORRELATION BETWEEN SITE AND REGIONAL STREAMFLOW DATA PROJECT 1CC DATE AUG APPROVED FIGURE 3-7

113 Average Monthly Runoff (% of MAR) Observed Streamflow Distributions at Regional WSC Stations Stream Name and Catchment Median Elevation Beaver (1020 m) Tom (1020 m) Coal (1130 m) Big (1210 m) King (1310 m) 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Average Monthly Runoff (% of MAR) Estimated Streamflow Distributions for Minesite Streams Catchment Median Elevation 950 m 1050 m 1150 m 1250 m 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN AVERAGE MONTHLY STREAMFLOW DISTRIBUTIONS PROJECT 1CC DATE AUG APPROVED FIGURE 3-8

114 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS The distributions for the five selected stations are characterized by high spring flows during snowmelt and low winter flows during prolonged freezing conditions. All five distributions are remarkably similar over the period August to April, especially considering they represent runoff from significantly different catchment areas ranging from 13.7 km 2 to 9190 km 2. The major difference that exists amongst the five distributions is the proportion of runoff that occurs during the months of May, June and July. Examination of these distributions and the characteristics of their associated catchments revealed that median elevation is a reasonably good predictor of the shape of the average monthly hydrograph. As expected, low-elevation catchments generally experience earlier peaks than high-elevation catchments. The median elevations for the catchments of the five stations are shown in the legend of the top plot. The observed relationship between hydrograph shape and catchment median elevation was used to estimate the shape of the average monthly hydrograph at ungauged locations around the minesite. The bottom plot on Figure 3-8 shows how this was implemented. The normalized distributions for Tom Creek and King Creek were used to establish the hydrograph shape at median elevations of 1020 m and 1310 m, respectively. Interpolation between the shapes of these two hydrographs was used to estimate the distribution for intermediate median elevations. Figure 3-8 shows the estimated shapes of the hydrographs for four distinct elevations Low Flow Estimates Low flows in southeastern Yukon occur in the winter months due to the prolonged freezing conditions. This is a consistent phenomenon, as evidenced by the WSC streamflow records assembled for this study. For 16 of the 18 records, the annual minimum daily flow was observed to always occur in the period November to early May. Even for the other two records, low flows outside this period were infrequent. For the Cottonwood River, the annual minimum was outside the winter period on only one occasion over a total of 35 years of record. In the case of Geddes Creek, the annual minimum was outside the winter period a total of four times in a 17-year record. The magnitude of low flows at the minesite was estimated using Regional Analysis. To apply this technique, three steps were undertaken. Firstly, the annual series of 7-day low flows was extracted from each of the 18 WSC streamflow records assembled for this hydrology study. For the purpose of selecting the annual low-flow values, the year was defined as the period June 1 to MARCH

115 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS May 31. Use of a calendar year was rejected for this purpose to avoid missing any low-flow periods that might span the period from late December to early January. It is interesting to note that the annual low flows for durations of 1, 3, 10 and 30 consecutive days have values very close to the 7-day low flow. This is a consequence of the low flows occurring in the winter rather than the late summer. The winter flows originate from storage releases (lake and groundwater) and, accordingly, vary only slightly over lengthy periods of time. The second step involved fitting a theoretical frequency distribution (Log-Pearson Type III) to each annual series to estimate the magnitude of extreme low flow events. This step and the previous one were performed using a suite of computer programs developed by the U.S. Geological Survey (Jones and Fahl, 1994) for processing hydrological data (viz., IOWDM2.4, SWSTAT3.2 and ANNIE2.5). Table 3-2 summarizes the results obtained from these programs. Estimates of the 7-day low flow are presented for return periods of 2, 5, 10, 20, 50 and 100 years. Because the 18 WSC stations measure the flow from a wide range of catchment areas, some method was sought to normalize the low flow values so that comparisons amongst the stations could readily be made. The method adopted was to express the values as percentages of the mean annual runoff. For example, the table indicates that the 7-day, 50-year low flow for the Blue River station is 6.3% of MAR. This corresponds to a flow rate of 1.1 m 3 /s (i.e., 6.3% of 18.2 m 3 /s). The third and final step entailed finding a way of transposing the low flow values in Table 3-2 to the minesite. To accomplish this, an examination was made of the relationship between low flow and the physical characteristics of the catchments that generated the flow. Two such characteristics were investigated: catchment median elevation and catchment area. Correlation with the former characteristic was poor but catchment area was discovered to help explain at least some of the variation in the low-flow characteristics of the WSC stations. A relationship with catchment area is plausible because channel storage and floodplain area tend to increase as drainage area increases. Increases in these two features of a catchment provide a larger unit storage of water from which to sustain the baseflow. MARCH

116 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Table 3-2 Estimated Low Flow Magnitudes at Regional Streamflow Gauging Stations Streamflow Gauging Station Catchment Area (km 2 ) Mean Annual Runoff (m 3 /s) Annual Minimum 7-Day Discharge as a Percentage of Mean Annual Runoff ID No. Name 2-Year 5-Year 10-Year 20-Year 50-Year 100-Year 10BD001 Beaver River below Whitefish River AA005 Big Creek at km Alaska Highway AC004 Blue River near the mouth BC001 Coal River at the mouth AC005 Cottonwood River above Bass Creek EA002 Flat River at Cantung Camp AB001 Frances River near Watson Lake BE008 Geddes Creek at the mouth AD002 Hyland River at km Nahanni Range Road AD001 Hyland River near Lower Post AB003 King Creek at km 20.9 Nahanni Range Road EB003 Lened Creek above Little Nahanni River AA001 Liard River at Upper Crossing EB002 Mac Creek near the mouth AA004 Rancheria River near the mouth BE013 Smith River above Smith Falls BE009 Teeter Creek near the mouth AA002 Tom Creek at km 34.9 Robert Campbell Highway MARCH

117 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Figure 3-9 is a graphical presentation of the analysis involved in the third step. This figure shows three plots, one each for the 2-year, 10-year and 50-year events. The vertical axis of each plot shows values of 7-day low flow expressed as a percentage of MAR. The horizontal axis presents the independent variable, or catchment area. At first glance, the data on these plots appear to exhibit considerable scatter. However, the situation improves when the data points for Geddes Creek, Smith River and Teeter Creek are removed from further consideration (denoted by open diamonds on the plots). The catchments of these streams are probably substantially underlain by carbonate bedrock that promotes the development of substantial groundwater storage. This storage results in an attenuated hydrograph shape with very high baseflows. Even with the removal of these three high-yield catchments, a significant amount of scatter still remained. Given this scatter, the decision was made to develop a prediction equation that would provide conservative estimates of low flow for the minesite streams. To do this, the remaining 15 WSC stations were separated into two groups. The first group comprised the stations that, in effect, formed a lower-bound envelope on all the data. This group was designated the low-yield catchments (solid squares on the plots of Figure 3-9). The second group was named the moderate-yield catchments and covered the stations lying just above the first group (open squares on the plots). To provide a convenient means of estimating the low flows at ungauged locations, a set of logarithmic regressions were fitted to the data from the first group. These logarithmic regressions appear as straight lines on the three plots of Figure 3-9. In equation form, these lines are expressed as: Q 7, 2 = Q MAR ( log A ) Q 7, 10 = Q MAR ( log A ) Q 7, 50 = Q MAR ( log A ) where: Q 7, 2 = annual minimum 7-day flow with 2-year return period (m 3 /s); Q 7, 10 = annual minimum 7-day flow with 10-year return period (m 3 /s); Q 7, 50 = annual minimum 7-day flow with 50-year return period (m 3 /s); Q MAR = mean annual runoff (m 3 /s); and, A = catchment area (km 2 ). FEBRUARY

118 Discharge (% of MAR) 7-Day Low Flow with 2-Year Return Period Low yield catchment Moderate yield catchment 40 High yield catchment 30 MH-11 (Estimated) Best-fit curve Catchment Area (km 2 ) Discharge (% of MAR) Day Low Flow with 10-Year Return Period Catchment Area (km 2 ) Discharge (% of MAR) Day Low Flow with 50-Year Return Period Catchment Area (km 2 ) SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN REGIONAL RELATIONSHIPS BETWEEN 7-DAY LOW FLOW AND CATCHMENT AREA PROJECT 1CC DATE AUG APPROVED FIGURE 3-9

119 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS These equations suggest that the flow in small catchments (i.e., with areas less than about 10 to 50 km 2 ) may completely freeze-up at a return period of 10 years. As was done for average flows, the stream flow record of Station MH-11 was used as a check on the low-flow analysis. Extreme low flow events for this station were estimated using the correlations developed in Section The mechanics of computing the low flow events are set out in Table 3-1. The estimated 7-day low flows at Station MH-11 for return periods of 2, 10 and 50 years have been plotted on the graphs of Figure 3-9. As can be observed, the MH-11 values suggest that the moderate-yield catchments, rather than the low-yield catchments, may better represent the Upper False Canyon Creek. However, this observation must be viewed with caution because none of the flow measurements at MH-11 were conducted in the period January to April, or the period most likely to contain the annual minimum flow. Until such measurements become available, the equations based on the low-yield catchments should be used to estimate the lowflow characteristics of the minesite streams. Based on the preliminary comparison made with the MH-11 data, these equations will likely provide conservative (i.e., low) estimates for the Upper False Canyon Creek. This is not necessarily the case for locations further downstream in False Canyon Creek. It is noteworthy that the data point for Tom Creek falls within the group of lowyield catchments Flood Estimates A Dam Safety Review was conducted in A key finding was that failure of the tailings dams does not pose a significant risk to the public health and safety after closure. Also, the environmental impact would be limited. For these reasons, the required design flood for closure was deemed to be the 1000-year event, or the same event specified as a requirement in the water licence. This section describes the analysis undertaken to estimate the 1000-year flood magnitudes at key locations around the mine development. For comparison purposes, this section also provides estimates of the mean annual flood(maf) and the 200-year return period flood. Three techniques were used to estimate the mine s flood regime, namely the Rational Method, Regional Analysis and application of a hydrological model. FEBRUARY

120 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Rational Method For small catchments in the Yukon, most of the annual floods are caused by snowmelt, as evidenced by the high frequency of annual flood peaks occurring in the months of May and June. Despite this observation, the most extreme floods on small catchments can be generated by another mechanism, namely intense rainstorms. In recognition of the importance of this second mechanism, the Rational Method was adopted to assess the design floods for the minesite streams. The Rational Method is essentially a modeling technique that simulates the magnitude of floods caused by intense rainstorms. The Rational Method entails applying the following formula: Q= CIA/3.6 Where: Q is the peak instantaneous discharge of the flood (m 3 /s); C is a runoff coefficient (dimensionless); I is the average rainfall intensity which causes the flood (mm/h); and A is the catchment area (km 2 ). The runoff coefficient specifies the proportion of the rainfall that quickly runs off the catchment to form the flood hydrograph. The remainder of the rainfall is retained on the catchment for subsequent evaporation or slow release to the catchment's streams. The value of the runoff coefficient varies from storm to storm depending on the initial moisture content of the soils and the extent of frozen soils within the catchment. For rural catchments, such as those at the minesite, standard practice is to assume a low runoff coefficient for frequent floods and a high coefficient for rare events. Accordingly, values of 0.3, 0.9, and 0.95 were adopted to represent the "wetness" of the study catchments during, respectively, the mean annual flood, the 200-year flood, and the 1000-year flood. A value of C equal to 0.95 implies a very wet catchment in which practically all of the rainfall is converted to flood runoff. In order to apply the Rational Method, it was necessary to estimate a characteristic of each study catchment known as the "time of concentration". This is a measure of the response time of the catchment. It may be interpreted as the time it takes for the most remote portion of the catchment to contribute to the flow at the outlet of the catchment. The time of concentration was estimated FEBRUARY

121 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS using empirical relationships that depend on the physical characteristics of the catchment (Leopold, 1991 and McCuen, 1982). Information on design storm rainfalls likely to be experienced at the minesite was obtained from the "Rainfall Frequency Atlas for Canada" (Hogg and Carr, 1985). The data extracted from this publication are presented in Figure 3-10 in the form of an intensity-duration-frequency relationship. The curves on this figure represent the characteristics of rainfall storms with return periods of 2.33 (i.e., mean annual), 200 and 1000 years. The calculation of flood peaks using the Rational Method is set out in Table 3-3. Note that the basic premise of the Rational Method is the largest flood will occur when the selected rainfall intensity has a duration exactly equal to the time of concentration. Furthermore, the computed flood peak is assumed to have the same frequency of occurrence as the causative rainfall intensity. Table 3-3 Flood Peak Estimates Using the Rational Method Tailings Dam Item Catchment Drainage area (A) - km Lag time (T L ) h 1.00 Time of concentration (T c ) - h 1.66 Time of concentration (T c ) - min 100 Rational coefficient (C) Mean annual maximum year maximum year maximum 0.95 Rainfall intensity (I) - mm/h (for duration = T c ) Mean annual maximum year maximum year maximum 16.0 Flood peak (Q) - m 3 /s (Q = CIA/3.6) Mean annual maximum year maximum year maximum 5.6 Notes: 1.T L = 0.89 A T c = 1.67 T L FEBRUARY

122 1000 Rainfall Intensity (mm/h) Hour Duration Return Period 1000 Years 200 Years 2.33 Years 1 Data Source: Rainfall Frequency Atlas for Canada (Environment Canada, 1985) Duration (min) SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN ESTIMATED RAINFALL INTERSITY-DURATION- FREQUENCY CURVES FOR MINE SITE PROJECT 1CC DATE AUG APPROVED FIGURE

123 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Regional Analysis The region encompassing the minesite is served by a reasonably dense network of streamflow gauging stations. The data collected at these regional stations were used to estimate the flood hydrology of the minesite streams by a variation on the technique used to estimate the average and low flows. Application of this approach involved four steps, as outlined below. The first step entailed data gathering. A total of 25 regional streamflow gauging stations were selected to provide the necessary data for the Regional Analysis. Table 3-6 provides details of these stations. The WSC operated 18 of the selected stations while Environment Yukon was responsible for the remainder. From the streamflow record of each of the 25 stations, an annual series of flood peaks was extracted. The length of these annual series ranged from 2 to 41 years. The second step involved a statistical analysis of the assembled data. For each station, the average of its annual series of flood peaks was calculated to provide an estimate of the mean annual flood. The annual series was then fitted to a theoretical frequency distribution (Generalized Extreme Value) to provide an estimate of the flood events. Table 3-4 presents the estimated mean annual, 200-year and the 1000-year floods for the regional streamflow gauging stations. The third step involved transposing the above-mentioned flood estimates to the minesite. This was done by exploiting a well-known observation that flood discharge is correlated with catchment area. The most useful way of examining this correlation was to prepare a logarithmic plot of "unit" discharge versus catchment area. Unit discharge means the flood peak is expressed as a flow rate per unit area (i.e., the absolute flood value is divided by the contributing catchment area). Figure 3-11 presents the plots used to examine the relationship between unit discharge and catchment area for the mean annual, the 200-year and the 1000-year floods. Examination of these plots reveals that the data exhibits the expected inverse trend between unit flood discharge and catchment area (i.e., the unit flood discharge increases as catchment area decreases). FEBRUARY

124 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Table 3-4 Estimated Flood Magnitudes at Regional Streamflow Gauging Stations Streamflow Gauging Station a Sample Size (No. of years) Catchment Area (km 2 ) ID No. Name Mean Annual Flood Estimated Maximum Instantaneous Discharge (m 3 /s) 200- Year Flood Year Event Estimated Maximum Instantaneous Unit Discharge (L/s/km 2 ) Mean Annual Flood 200- Year Flood Year Event 10BD001 Beaver River below Whitefish River AA005/30AE Big Creek at km Alaska Highway b AC004 Blue River near the mouth BC001 Coal River at the mouth AC005 Cottonwood River above Bass Creek EA002/10EA Flat River at Cantung Camp c AD005 Flood Creek at km Nahanni Range Road 10AB001 Frances River near Watson Lake BE008 Geddes Creek at the mouth AD002 Hyland River at km Nahanni Range Road 10AD001 Hyland River near Lower Post AD001 Jackpine Creek at km 62.2 Nahanni Range Road 10AB003 King Creek at km 20.9 Nahanni Range Road 10EB003 Lened Creek above Little Nahanni River AA001 Liard River at Upper Crossing EB002 Mac Creek near the mouth AA001 Meister River above Liard River AE003 Partridge Creek at km Alaska Highway 10AA004 Rancheria River near the mouth FEBRUARY

125 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Streamflow Gauging Station a Sample Size (No. of years) Catchment Area (km 2 ) ID No. Name Mean Annual Flood Estimated Maximum Instantaneous Discharge (m 3 /s) 200- Year Flood Year Event Estimated Maximum Instantaneous Unit Discharge (L/s/km 2 ) Mean Annual Flood 10BE013 Smith River above Smith Falls AD004 South Moose Creek at km 84.8 Nahanni Range Road 30AE001 Spencer Creek at km Alaska Highway 30AD002 Spruce Creek at km 66.4 Nahanni Range Road 10BE009 Teeter Creek near the mouth AA002 Tom Creek at km 34.9 Robert Campbell Highway Notes: a) DIAND recently established a gauging station on Contact Creek (30BE001), located some 60 km east of Watson Lake. The period of record for this station was too short to include in the present analysis. This station commands a small catchment and, accordingly, will be a valuable resource in the future for characterizing the flood hydrology of small basins. b) This station was originally operated by DIAND from 1978 to 1988 (30AE002). The WSC assumed responsibility for this station in 1989 and gave it a new identification number (10AA005). This station was active in c) The WSC has operated two stations on Flat Creek in the vicinity of the Cantung Mine. The first station (10EA002) was operated from 1973 to 1988 and commanded a catchment area of 128 km 2. The second station (10EA004) was located 3 km downstream of the first, was operated from 1988 to 1992, and controlled a total area of 160 km 2. Owing to the closeness in their catchment areas, the flood data for the two stations were combined to create a single record spanning 19 years. The flood values at 10EA004 were scaled by a factor of (128/160) 0.75 to make them representative of the conditions at 10EA Year Flood Year Event FEBRUARY

126 Unit Discharge (L/s/km 2 ) Mean Annual Peak Instantaneous Flood Envelope curve Best-fit curve Representative flood regime Unrepresentative flood regime Year Peak Instantaneous Flood Unit Discharge (L/s/km 2 ) Year Peak Instantaneous Flood Unit Discharge (L/s/km 2 ) Catchment Area (km 2 ) SA DENA HES DETAILED DECOMMISSIONING AND RECLAMATION PLAN REGIONAL RELATIONSHIPS BETWEEN FLOOD DISCHARGE AND CATCHMENT AREA PROJECT 1CC DATE AUG APPROVED FIGURE 3-11

127 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Two different approaches are commonly used to quantify the correlation between flood discharge and catchment area. One is to fit a power regression to the data and the other is to draw an upperbound curve which envelops all of the data. Both approaches were used in this study. The respective curves are shown on the plots of Figure 3-8. It is interesting to note that the three upper-bound curves possess a slope close to on the logarithmic plot. This same slope is common to flood envelope curves for other parts of the Yukon and for British Columbia.The fourth and final step entailed using the curves on Figure 3-8 is to provide flood estimates for ungauged points on the minesite. For any ungauged point, this was done by planimetering the catchment area controlled by the point of interest. The best fit curves in the plots on Figure 3-11 were used to determine a unit discharge for the given catchment area. The product of unit discharge and catchment area was then calculated to provide the required flood estimates. MARCH

128 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Hydrological Model The two flood techniques presented above are aimed at estimating the instantaneous peaks of flood events. This section introduces a flood estimation technique that examines the full flood hydrograph, not just its peak. The third technique was introduced in 2005 as a direct result of the 2003 Dam Safety Review. Following recommendations in that report, Teck initiated a study to determine whether the TMF and the Reclaim Dam have the capacity to deal with the 1000-year flood during the temporary closure status. As the tailings impoundment South Dam emergency spillway was designed for the 1 in 200 year flood, a study was conducted to determine if the current spillway at the TMF (comprising two 900 mm culverts) and the road crossing of the Camp Creek Diversion (comprising two 1200 mm culverts) could accommodate the 1000-year flood. In performing the study, it was recognized that storages within the TMF and the Reclaim Pond would probably have to be relied upon to temporarily store a portion of the incoming flood waters so that the capacities of the culverts would not be exceeded during passage of the extreme flood event. The results of this study are presented below and are still considered valid. To examine the effects of storage on flood magnitude it was necessary to turn to a rainfall/runoff model that simulates the full flood hydrograph and that provides flood routing capabilities. The model selected for this purpose was developed by the U.S. Corps of Engineers and is known as HEC-HMS. Figure 3-12 shows the results of applying the HEC-HMS model to the TMF. Key assumptions of the modeling are: The 1000-year flood would be generated by an intense thunderstorm (1000-year, 24-hour total rainfall = 81 mm) falling on a ripe snowpack that, in the days preceding the storm, was melting at a high rate (20 mm/d); The spillway would be comprised of the existing two 900 mm culverts; All interceptor ditches around the TMF would fail, allowing the full catchment runoff to enter the impoundment; and MARCH

129 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS The culverts would be flowing prior to the arrival of the storm, so that storage below the invert level of the culverts would not be available to store a portion of the incoming flood hydrograph. The rainfall intensities associated with the 1000-year storm for durations of 5 minutes to 24 hours were estimated from the intensity-duration-frequency (IDF) curve presented in Section (see Figure 3-10). The record of annual maximum daily precipitation at the Watson Lake Airport climate station was used as a check on the estimated 24-hour rainfall total for the 1000-year event. A theoretical frequency distribution was fitted to the 66 values of annual maximum daily precipitation observed at the climate station. The resulting estimate of 1000-year daily precipitation was close to the value derived from the IDF curve. The instantaneous peak of the incoming flood hydrograph was estimated to be 5.4 m 3 /s. The combined outflow through the two culverts would peak at 1.6 m 3 /s, or 30% of the incoming flood peak. During passage of the flood, a volume of 53,000 m 3 of water would be temporarily stored within the TMF. The water level in the TMF would peak at an elevation of m, which is roughly at the crown level of the two culverts. Figure 3-13 shows the simulated flood hydrology for the two culverts at the road crossing of the Camp Creek Diversion. Key assumptions of the modeling are: The 1000-year flood would be generated by the same conditions outlined above for the TMF; The interceptor ditches around the TMF would function in such a way as to maximize the peak flow of water to the Camp Creek Diversion (i.e., the West Interceptor Ditch would survive but one of the East Interceptor Ditches would develop a breach and empty into the Reclaim Pond); and The TMF spillway and the Reclaim Pond spillway would both be flowing prior to the arrival of the storm so that storage below the crests of these spillways would not be available to store a portion of the incoming floodwaters. The instantaneous peak of the hydrograph generated by the Camp Creek catchment would be 12.7 m 3 /s, including outflows from the TMF. The combined outflow through the two culverts at the road crossing would be an estimated 6.0 m 3 /s, or roughly half the peak of the incoming flood. In passing this flood, some 66,000 m 3 of water would be temporarily stored in the Reclaim Pond. MARCH

130 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS Another 36,000 m 3 would be stored in the TMF. The water level would rise to m behind the Reclaim Dam, leaving a freeboard of about 0.9 m below the dam s crest. In addition to examining the flood hydrology of the mine during the temporary closure status, HEC- HMS was used to provide additional estimates of flood magnitude for the permanent closure status. Figure 3-14 shows the estimated 1000-year flood that would have to be conveyed by the permanent spillway for the TMF. The situation is identical to the conditions modeled in Figure 3-12 except it was assumed that no storage attenuation would occur within the TMF. Thus, the peak of the outflow hydrograph is identical to the peak of the inflow hydrograph, or 5.4 m 3 /s. Figure 3-15 shows the estimated 1000-year flood for the proposed breach in the Reclaim Dam. Without the benefit of storage within either the Reclaim Pond or the TMF, the flood peaks at an estimated 15.6 m 3 /s. The simulated flood peaks in Figures 3-12 to 3-15 were checked for reasonableness by comparing them against maximum observed floods in the Yukon. Figure 3-16 presents the maximum observed floods at all government-operated streamflow gauging stations within the territory (87 operated by the Water Survey of Canada and 97 by Environment Yukon.) To facilitate comparison of the flood values from the widely different drainage areas, the flood magnitudes have been normalized (i.e., the absolute flood value has been divided by the contributing drainage area). Examination of Figure 3-16 reveals that none of the floods in the Yukon have attained a unit discharge greater than 1.0 m 3 /s/km 2. The estimated 1000-year floods for the mine, for both temporary and permanent closure scenarios, all plot above the maximum observed floods in the Yukon. Even the attenuated peaks through the TMF culverts and the Camp Creek culverts are large relative to the floods that have thus far been measured in the territory. It should be noted that model parameters were selected for HEC-HMS that would generate hydrograph shapes typical of steep, forested catchments. This probably results in an overestimation of the true 1000-year flood peaks that could be generated within the Camp Creek catchment. The flow monitoring station at the minesite has revealed that groundwater contributions to the streamflows of Camp Creek are large. Thus, the 1000-year flood hydrographs MARCH

131 SÄ DENA HES OPERATING CORP., SÄ DENA HES MINE UPDATE TO DDRP APPENDIX B ENVIRONMENTAL BASELINE UPDATE AND TECHNICAL BASIS FOR CLOSURE ASSUMPTIONS for this stream may be substantially more subdued than simulated by the HEC-HMS model. Further monitoring of the flows in Camp Creek may provide enough evidence to allow the estimated flood peaks to eventually be reduced. In summary, using the conservative 1000-year flood event, the recent hydrological evaluation confirms that both the current facilities as well as the permanent closure designs proposed in the 2000 DDRP are adequate and do not require upgrading. The closure design currently proposed is a revised version of one of those proposed in the 2000 DDRP (refer to Section 10-3), and as the revisions will not significantly alter the design criteria relevant to the hydrological evaluation, based on the climate and flow data available up to 2005, the permanent closure design is adequate and does not require upgrading. MARCH

132 6 Flow (cms) Peak of inflow hydrograph = 5.4 m 3 /s Peak outflow through two spillway culverts = 1.6 m 3 /s 1 Stor (THOU M3) Peak volume of water temporarily stored in TMF during passage of flood = 53,000 m 3. Water level rises to m in TMF, or 0.9 m above the inverts of the two spillway culverts :00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00 01Jun Jun Jun Jun2005 TAILINGS RUN 1 FLOW TAILINGS POND RUN 1 FLOW TAILINGS POND RUN 1 STORAGE Job No: Filename: 1CT VANCOUVER Figure 5_Sim 1000yr_Tailings_ ppt Sä Dena Hes Detailed Date: Decommissioning and Reclamation Plan Dec Simulated 1000-Year Flood in Tailings Management Facility- Temporary Closure Status Approved: Figure: 3-12

133 14 12 Peak of hydrograph generated by Camp Creek catchment = 12.7 m 3 /s Flow (cms) Stor (THOU M3) Water rises above spillway crest and begins to back up into Reclaim Pond Peak outflow through two culverts at road crossing of Camp Creek Diversion = 6.0 m 3 /s Peak volume of water temporarily stored in Reclaim Pond during passage of flood = 66,000 m 3. Another 36,000 m 3 would be temporarily stored in TMF. Water level rises to m behind Reclaim Dam, or about 0.9 m below the dam's crest. 0 00:00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00 01Jun Jun Jun Jun2005 RECLAIM DAM RUN 2 FLOW-COMBINE RECLAIM DAM REVISED FLOW RECLAIM DAM RUN 2 STORAGE Job No: Filename: 1CT VANCOUVER Figure 6_Sim 1000yr_Camp Cr_ ppt Sä Dena Hes Detailed Date: Decommissioning and Reclamation Plan Dec Simulated 1000-Year Flood for Camp Creek Diversion - Temporary Closure Status Approved: Figure: 3-13

134 6 5 Peak of hydrograph = 5.4 m 3 /s (or unit discharge of 4.1 m 3 /s/km 2 ) Flow (cms) 4 3 Key assumptions: 1) All interceptor ditches around TMF develop a breach 2) A 1000-year storm (24-h precipitation = 81 mm) falls on a ripe snowpack that, in the days preceding the storm, was melting at a high rate (20 mm/d) :00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00 01Jun Jun Jun Jun2005 TAILINGS RUN 3 FLOW Job No: Filename: 1CT VANCOUVER Figure 7_Sim 1000yr_Spillway_ ppt Sä Dena Hes Detailed Date: Decommissioning and Reclamation Plan Dec Simulated 1000-Year Flood at Spillway of Tailings Management Facility - Permanent Closure Status Approved: Figure: 3-14

135 16 14 Peak of hydrograph = 15.6 m 3 /s (or unit discharge of 3.5 m 3 /s/km 2 ) 12 Flow (cms) Key assumptions: 1) A 1000-year storm (24-h precipitation = 81 mm) falls on a ripe snowpack that, in the days preceding the storm, was melting at a high rate (20 mm/d) 2) The catchment has a moderately flashy response to rainfall events (which is probably a conservative assumption given that the flow monitoring in the Camp Creek Diversion suggests a groundwater dominated system) :00 12:00 00:00 12:00 00:00 12:00 00:00 12:00 00:00 01Jun Jun Jun Jun2005 JUNCTION-1 RUN 3 FLOW VANCOUVER Simulated 1000-Year Flood at Breach in Reclaim Dam - Permanent Closure Status Job No: Filename: 1CT Figure 8_Sim 1000yr_Breach_ ppt Sä Dena Hes Detailed Date: Decommissioning and Reclamation Plan Dec Approved: Figure: 3-15

136 4.5 4 Peak outflow through TMF permanent spillway Maximum observed floods in Yukon Estimated 1000-year floods (temporary closure status) Estimated 1000-year floods (permanent closure status) 3.5 Peak inflow to TMF Peak flow at breach in Reclaim Dam Unit Discharge (m 3 /s/km 2 ) Peak outflow through TMF temporary spillway Peak flow generated by Camp Creek catchment (incl. outflows from TMF) Peak outflow through two culverts at road crossing of Camp Creek Diversion Catchment Area (km 2 ) Job No: Filename: 1CT VANCOUVER Figure 9_Comparison 1000yr_ ppt Sä Dena Hes Detailed Date: Decommissioning and Reclamation Plan Dec Comparison of Estimated Year Floods with Maximum Observed Floods in Yukon Approved: Figure: 3-16

137 Appendix E: Environmental Monitoring Plan

138 SRK Consulting (Canada) Inc. Suite West Hastings Street Vancouver, BC V6E 3X2 T: F: Memo To: Peter Healey Client: Teck Metals Ltd. From: Tom Sharp Kaitlyn Kooy Project No: 1CT Cc: Date: July 18, 2013 Subject: Sa Dena Hes Mine Decommissioning Environmental Monitoring Plan 1 Introduction Teck Metals Ltd. (Teck) retained SRK Consulting (Canada) Inc. (SRK) to prepare an Environmental Water Quality and Flow monitoring plan (EMP) to be implemented during activities associated with the decommissioning of the Sä Dena Hes mine site, located near Watson Lake in the Yukon. Closure activities would be carried out in accordance with the Detailed Decommissioning and Reclamation Plan (DDRP) (Teck 2013) and would include mill and plant demolition, removal of the Reclaim and South Dams, rerouting of Camp Creek to its original channel, and reshaping of the waste rock dumps, where necessary. This memorandum presents the monitoring program that would be undertaken before, during and after closure activities at the site. During the decommissioning phase, water quality at the site will be monitored to ensure compliance with the conditions of the Water License (QZ99-045). Proposed earthworks may potentially result in increased sediment loading in the runoff and surface water. The purpose of this EMP is to describe how the site will be monitored. The primary focus of the EMP is to ensure adequate control of Total Suspended Solids (TSS) and to a lesser extent total and dissolved metals. 2 Water Quality Limits All discharges from site are expected to meet the Effluent Quality Standards in the Water License (Table 1). Closure activities could potentially increase turbidity and TSS concentrations downstream of areas disturbed. The turbidity and TSS limits in the Water License are 15 Jackson Turbidity Units (JTU) and 50 mg/l, respectively. The Water License refers to turbidity units as JTU but turbidity has been commonly measured and reported in Nephelometric Turbidity Units (NTU) at the site. The two units are approximately equivalent and for the purpose of developing this monitoring plan the two are used interchangeably. K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

139 SRK Consulting Page 2 Table 1 Effluent Water Quality Standards Parameter Concentration All Waste Discharge Standards Suspended Solids 50 mg/l ph Not less than 6.0 Colour 20 PT-CO Units Turbidity 15 JTU Floating Solids None Floating oils or grease None Visible Grab Sample Analysis Standards Ammonia (as total N) 3.50 mg/l Arsenic (dissolved) 0.05 mg/l Cadmium (total) 0.02 mg/l Copper (total) 0.20 mg/l Cyanide (as total CN) 0.5 mg/l Cyanide (as WAD CN)* 0.2 mg/l Lead (total) 0.20 mg/l Selenium (total) 0.05 mg/l Silver (total) 0.10 mg/l Zinc (total) 0.50 mg/l *Analysis for weak acid dissociable cyanide (WAD CN) is a requirement of Water Licence QZ only in the event that results of analysis for total CN exceed a concentration of 0.2 mg/l. If total CN concentration exceeds 0.2 mg/l then analyses are required for both WAD CN and Total CN. Source: Yukon Territory Water Board Water License QZ Turbidity and Total Suspended Solids Turbidity can be measured in the field and the results are available quicker than TSS which is measured in the laboratory. It takes about 10 business days to receive TSS and metal results after the samples are sent to the laboratory. Because of this delay between sample collection and receiving the results, field measurements of turbidity will be used as an indicator of TSS concentrations. Historical TSS and turbidity data from the site were used to evaluate the relationship between turbidity and TSS. The turbidity was measured in the laboratory and the samples generally had exceeded the holding time limit for turbidity measurements. TSS and turbidity data from eight water quality monitoring locations were used. Figure 1 shows the relationship between turbidity and TSS. The data predominately show that when the turbidity is less than 15 NTU the TSS concentrations were nearly always less than 50 mg/l. K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

140 SRK Consulting Page 3 TSS_Turb.xlsx \\VAN-SVR0\Projects\01_SITES\Sa_Dena_Hes\1CT _Dam_Decommissioning\!080_Deliverables\Design Report\030_Appendices\Appendix E Environmental Monitoring Plan\SDH Figure 1. Turbidity versus TSS. 4 Monitoring 4.1 Initial Baseline Monitoring Acute toxicity testing and water chemistry analysis will be conducted in accordance with the Water License prior to the start of closure activities. These data and historic data will be used to establish baseline conditions. 4.2 Closure Activity Monitoring During construction activities water quality will be monitored at the sampling locations listed in Table 2. These monitoring locations were selected to assess the potential impact of closure activities. Four of the monitoring locations are part of the water license monitoring network. One monitoring locations (MH-28A) is new and would be located in Camp Creek about 100 m downstream from the Reclaim dam but above Portal Creek. This station was added because it is more accessible than the nearest Water License station (MH-11) in Camp Creek. While there would be closure activity at times at the Jewelbox area and the Mill site, the drainage from these areas has been historically dry and consequently no regular sampling is proposed for Portal Creek. Similarly conditions are found at the Burnick Waste Rock Dump area and consequently K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

141 SRK Consulting Page 4 no regular sampling is proposed for this area. However, if high runoff conditions do occur during activity at these locations and measurable flow is detected, water quality samples would be taken at MH-28 and below the Burnick Dump. Table 2 Water Quality Monitoring Locations Sampling Location MH-01B MH-02 MH-04 MH-06A/B MH-28A Description Tailings Ponded Water North Dam Seepage Upper Camp Creek Reclaim Pond Spillway/Ponded Water Camp Creek above Portal Creek Daily field turbidity, temperature, conductivity and ph measurements will be taken at these locations during closure activities. Site conditions in areas where there is construction activity will be monitored and recorded daily. These daily inspections will include observations of pooling water, runoff, seepage and signs of erosion. Water samples will be collected weekly from the locations listed in Table 2. All the samples will be analyzed for ph, conductivity, alkalinity, hardness, sulphate, TSS, TDS, and total and dissolved metals. All results and observations will be reviewed daily to compare this information to site objectives and assess if conditions warrant mitigation. Water quality results will be compared to site water quality objectives as the data become available. Water License compliance monitoring will also continue during closure. The monitoring program outlined below will be used to supplement the compliance monitoring and ensure that closure water quality objectives are met. 4.3 Freshet Monitoring During freshet (late May to early June), flow and water quality will be monitored in the Reclaim Pond. Siphons or pumps would discharge the water into Camp Creek. In the event that flow exceeds the pump capacity, a pressure transducer will be installed in the overflow spillway on the west side of the Reclaim pond to monitor the flow over the spillway. A stage discharge curve for the spillway will be used to convert water level into flow. Water quality samples will be collected weekly and analyzed for ph, conductivity, alkalinity, hardness, sulphate, TSS, TDS, and total and dissolved metals. 5 Data Reporting The EMP would be initiated once closure activities begin. Once sample results become available they shall be compiled and compared to the Water License water quality limits. K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

142 SRK Consulting Page 5 Monthly reports of the compiled monitoring results will be submitted to the Yukon Water Board and to YEMR for review. 6 Contingency Plan During decommissioning of the site, MH-28A has been identified as the ultimate compliance point. The primary parameter of concern is expected to be total suspended solids (TSS) from the dam removal. Field turbidity measurements will provide early indication of potential TSS exceedance. While normal erosion and sediment control measures would be implemented during the closure activities, if field turbidity measurements at upgradient stations exceed 15 NTU and if unacceptable levels of sediment remain in the Reclaim Pond preventing discharge, the ponded water would be pumped back to the sediment pond constructed in behind the control dyke that would remain following the removal of the South Dam. As discussed in Section 4.2 water quality samples would be collected at MH-28 in Portal Creek and at the toe of Burnick Dump, if there is sufficient flow. SRK Consulting (Canada) Inc. Kaitlyn Kooy Engineering Intern Tom Sharp, Ph.D., P.Eng. Principal Consultant Disclaimer SRK Consulting (Canada) Inc. has prepared this document for Teck Metals Ltd.. Any use or decisions by which a third party makes of this document are the responsibility of such third parties. In no circumstance does SRK accept any consequential liability arising from commercial decisions or actions resulting from the use of this report by a third party. The opinions expressed in this report have been based on the information available to SRK at the time of preparation. SRK has exercised all due care in reviewing information supplied by others for use on this project. Whilst SRK has compared key supplied data with expected values, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the supplied data. SRK does not accept responsibility for any errors or omissions in the supplied information, except to the extent that SRK was hired to verify the data. K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

143 SRK Consulting Page 6 7 References Teck 2013a. Sä Dena Hes Mine Detailed Decommissioning & Reclamation Plan March 2013 Update. Prepared by Teck Resources Limited. March Teck 2013b. SDH Dam Decommissioning Design Report_ K/TRS SDH Environmental Monitoring Plan_PMH_ docx July 2013

144 Appendix F: Stability Analyses

145 SRK Consulting (Canada) Inc. Suite West Hastings Street Vancouver, BC V6E 3X2 T: F: Memo To: Gerry Murdock, Teck Resources Limited Client: Teck Resources Ltd. From: Murray McGregor, Peter Healey Project No: 1CT Cc: Cam Scott, SRK Date: March 28, 2014 Subject: Stability Analysis for Rapid Drawdown and Dam Excavation 1 Introduction Teck Resources Limited (Teck), retained SRK Consulting (Canada) Inc. to prepare a design report for the decommissioning of the Tailings Management Facility (TMF) and the associated surface water management system located at their Sä Dena Hes mine near Watson Lake, Yukon. As part of the TMF decommissioning, two dams will be removed. The dam removal will be staged with an initial excavation of notch in the dams to allow the water to pass followed by complete removal of the dams in subsequent stages. This memo provides an assessment of the stability of the various slopes during the staged removal of the dams. Stability analyses were completed in accordance with Canadian Dam Association (CDA 2007), guidelines. Two scenarios were considered; the stability of the South and Reclaim Dams under rapid drawdown conditions and the stability of sideslopes of a partially removed dam. 2 Slope Stability Assessment 2.1 Method For the slope stability assessment, Factor of Safety (FOS) values were utilized for performance evaluation. The seepage and slope stability analyses were completed using Rocscience s Slide software version 6.0. The slip surfaces were evaluated using both Spencer and Morgenstern-Price methods. Grid and radius searches were completed on select models to confirm the suitability of the auto locate. In each case, the results were comparable. 2.2 Model Setup The geometry used for the dam was based on the as-built construction report (SRK 1992a) and 2013 YES survey. The dam foundations consist of silty tills and Sand and gravels. The basic design for both the Reclaim and South dams was a zoned embankment consisting of silty tills and Sandy tills, with a Sand and gravel drainage blanket. The sideslopes for the embankment MJM/PH DamStability_Memo_1CT _PMH_mjm_ _rev1 March 2014

146 SRK Consulting Page 2 excavation were modelled at 2:1 H:V and 2.5:1 H:V with a 2 m bench midway down the slope. The upstream slope of the south dam used for rapid drawdown calculations was based on the asbuilt slope of 2:1 H:V while the upstream slope of the Reclaim Dam was modelled at 2.5:1 H:V. For both sets of models, a seepage analysis was completed prior to stability such that appropriate phreatic surfaces could be generated. The phreatic surfaces from the seepage analysis were adjusted so they remained consistent with actual piezometer data collected from site. For the Reclaim and South Dam rapid drawdown calculations, a seepage analysis was performed to assess the phreatic surface at several stages of drawdown. The pond level drawdown is dependent on the pond bathymetry and the rate of discharge. A preliminary model was completed assuming a rate of discharge equal to the maximum allowable rate of 228m 3 /hour. The theoretical pond level drawdown curve is presented in Figure 1 below. Figure 1: Projected drawdown schedule The piezometric results from the seepage analyses were then applied to the stability analyses. 2.3 Material Properties Density and shear strength parameters were taken from the stability analysis that was completed for the South Dam extension (SRK 1992b). Assumed dam fill permeability values were derived from our experience with similar soils and the results of permeability test that were presented in MJM/PH DamStability_Memo_1CT _PMH_mjm_ _rev1 March 2014

147 SRK Consulting Page 3 the South Dam as-built report (SRK 1992b). Table 1 presents the material properties used for the models. Table 1: Material Properties Material Unit Weight (kn/m 3 ) Effective Angle of Friction (degrees) Effective Cohesion (kpa) Assumed Permeability (m/s) A Tailings N/A B Silty Till E-07 C Sand and Gravel E-05 D Sandy Till E-07 E Sand and Gravel Blanket Drain E-05 F Sandy Gravelly Silt (low PP) E-07 G Sandy Gravelly Silt (high PP) E-07 H Sand and Gravel E-05 I Bedrock E-10 J Sand and Gravel Cap E-05 K Drain Rock E-03 L Shot Rock E Seismic Analysis Seismic analysis was not performed for rapid drawdown calculations since the duration the conditions exist is relatively short. For the excavated area slopes, seismic calculations were completed using a horizontal loading of 0.203g, the value for peak ground acceleration based on the 2010 National Building Code of Canada. 3 Results The results of the rapid draw down analyses for the South Dam indicated that when the pond level drops below EL. 1088, the Factor of Safety of the upstream slope of the dam drops below the design criteria of 1.2. Assuming no change in the discharge rate, the model indicated that the FOS drops to just below 1 at the EL 1086 increasing the risk of surficial sloughing on the slope. The results of the rapid draw down analyses for the Reclaim Dam indicated that the slope would be stable with a FOS of at least 1.2 throughout the drawdown period. Graphical results of the Reclaim and South Dam rapid drawdown analyses are presented in Attachment 1. The results of the notch stability for the South and Reclaim Dams are presented in Table 2 below and graphical results are presented in Attachment 2. MJM/PH DamStability_Memo_1CT _PMH_mjm_ _rev1 March 2014

148 SRK Consulting Page 4 Table 2: Stability Analysis Results, Notch Sideslopes Condition Calculated Factor of Säfety Side Slope of Notch 2.0H:1V 2.5H:1V Minimum Factor of Safety Static, immediately post-construction Static, long term Pseudo-static (g=0.203), long term Recommendations To minimize the risk of slope failure on the upstream face of the South dam during drawdown of the South Pond, daily monitoring of the upstream face, the pond level and the water level in the dam piezometers is required once the pond drops below elevation 1087 m. Any slumping, excessive water bleeding or appearance of tension cracks on the face should be reported as soon as possible so that mitigative measures can be taken. It is currently planned to begin excavation of the dams at the east abutments as the pond is drawdown. This has an added benefit of reducing the driving force of deep seated slip surfaces.. The results of the stability analyses for the embankment notch indicated that a 2.5:1 H:V side slope with intermediate 2 m bench would be appropriate. SRK Consulting (Canada) Inc. Murray McGregor, E.I.T. Consultant Reviewed by: Peter Healey, P.Eng Principal Consultant Disclaimer SRK Consulting (Canada) Inc. has prepared this document for Teck Resources Ltd.. Any use or decisions by which a third party makes of this document are the responsibility of such third parties. In no circumstance does SRK accept any consequential liability arising from commercial decisions or actions resulting from the use of this report by a third party. The opinions expressed in this report have been based on the information available to SRK at the time of preparation. SRK has exercised all due care in reviewing information supplied by others for use on this project. Whilst SRK has compared key supplied data with expected values, the accuracy of the results and conclusions from the review are entirely reliant on the accuracy and completeness of the supplied data. SRK does not accept responsibility for any errors or omissions in the supplied information, except to the extent that SRK was hired to verify the data. MJM/PH DamStability_Memo_1CT _PMH_mjm_ _rev1 March 2014

149 SRK Consulting Page 5 5 References SRK Consulting (Canada) Inc. (1992a). As-Built Construction Report - North, South and Reclaim Dams, Sä Dena Hes Mine Yukon Territory. Project number: Report submitted to Curragh Resources Inc. Sä Dena Hes. SRK Consulting (Canada) Inc. (1992b). Design Report South Dam Extension, Sä Dena Hes Mine Yukon Territory. Project number: Report submitted to Curragh Resources Inc. Sä Dena Hes. Canadian Dam Association (2007). Dam Safety Guidelines. Library and Archive Canada, Ottawa, ON. MJM/PH DamStability_Memo_1CT _PMH_mjm_ _rev1 March 2014

150 Attachment 1: Rapid Drawdown Analysis

151 Rapid Drawdown Stability Analysis South Dam Pond Level 1092 m Job No: 1CT Date: Sa Dena Hes Filename: Attachment A Rapid Drawdown Analysis.ppt March 28,2014 Approved: MJM Attachment: 1.1

152 Rapid Drawdown Stability Analysis South Dam Pond Level 1088 m Job No: 1CT Date: Sa Dena Hes Filename: Attachment A Rapid Drawdown Analysis.ppt March 28,2014 Approved: MJM Attachment: 1.2

153 Rapid Drawdown Stability Analysis South Dam Pond Level 1086 m Job No: 1CT Date: Sa Dena Hes Filename: Attachment A Rapid Drawdown Analysis.ppt March 28,2014 Approved: MJM Attachment: 1.3

154 Rapid Drawdown Stability Analysis South Dam Pond Level 1085 m Job No: 1CT Date: Sa Dena Hes Filename: Attachment A Rapid Drawdown Analysis.ppt March 28,2014 Approved: MJM Attachment: 1.4

155 Rapid Drawdown Stability Analysis Reclaim Dam Pond Level 1078 m Job No: 1CT Date: Sa Dena Hes Filename: Attachment A Rapid Drawdown Analysis.ppt March 28,2014 Approved: MJM Attachment: 1.5

156 Rapid Drawdown Stability Analysis Reclaim Dam Fully Drained Job No: Filename: 1CT Attachment A Rapid Drawdown Analysis.ppt Sa Dena Hes Date: March 28,2014 Approved: MJM Attachment: 1.6

157 Attachment 2: Dam Notch Stability

158 Dam Notch Stability Analysis 2:1 Slopes Static Stability Job No: Filename: 1CT Attachment A Rapid Drawdown Analysis.ppt Sa Dena Hes Date: July 12, 2013 Approved: MJM Attachment: 2.1

159 Dam Notch Stability Analysis 2:1 Slopes Pseudo-Static Stability Job No: Filename: 1CT Attachment A Rapid Drawdown Analysis.ppt Sa Dena Hes Date: July 12, 2013 Approved: MJM Attachment: 2.1

160 Dam Notch Stability Analysis 2.5:1 Slopes Static Stability Job No: Filename: 1CT Attachment A Rapid Drawdown Analysis.ppt Sa Dena Hes Date: July 12, 2013 Approved: MJM Attachment: 2.3

161 Dam Notch Stability Analysis 2.5:1 Slopes Pseudo-Static Stability Job No: Filename: 1CT Attachment A Rapid Drawdown Analysis.ppt Sa Dena Hes Date: July 12, 2013 Approved: MJM Attachment: 2.4