New Gold Inc. Independent Third Party Review. Dam Safety Inspection Report. November 2014 M09783A04.730

Transcription

1 November 2014 M09783A04.730

2 November 28, 2014 New Gold Inc. New Afton Box 948 Stn. Main, Kamloops, British Columbia V2C 5N4 Mr. Scott Davidson Environment and Social Responsibility Manager Dear Mr. Davidson: Please find attached the Third Party Review of the Dam Safety Inspection (DSI) Report for the New Afton Tailings Facilities. The review concludes that the DSI meets the requirements of the Ministry of Mines Guidelines for Annual s and that the consequence classifications for the tailing dams are appropriate. This report documents our review and identifies areas for ongoing improvement. Yours truly, KLOHN CRIPPEN BERGER LTD. Harvey McLeod, P.Eng., P.Geo. Principal HM:cd R 3rd Party Review DSI.docx M09783A Klohn Crippen Berger Ltd Virtual Way Vancouver BC V5M 4X6 CANADA t f

3 Cover.docx M09783A November 2014

4 TABLE OF CONTENTS 1 INTRODUCTION BACKGROUND INFORMATION AND SITE VISIT Site Visit and Document Review Site Visit Document Review Facility Description Site Conditions REVIEW OF DAM SAFETY INSPECTION REPORT General Consequence Classification Review Instrumentation Review Piezometers Settlement Plates and Inclinometers Summary Geotechnical Review Stability Review Seepage Internal Erosion Hydrotechnical Review Mining Dam Considerations REVIEW OF TAILINGS FACILITY STEWARDSHIP General OMS Manual Emergency Preparedness and Response Plan SUMMARY CLOSING List of Tables Table 2.1 Design Documents and Construction Records Review Summary... 7 Table 3.1 Review of MEM Guidelines applicable to the 2014 Draft DSI Table 3.2 Summary of 2014 Piezometer Changes and Threshold Levels Table 4.1 OMS Checklist Table 4.2 Emergency Preparedness and Response Plan Checklist Table 5.1 Summary and Review of Key DSI Recommendations Table 5.2 Summary of 3 rd Party Review Recommendations R 3rd Party Review DSI.docx Page ii

5 TABLE OF CONTENTS (continued) List of Figures Figure 2.1 Orthophoto of New Afton (July 2013, BGC)... 8 List of Appendices Appendix I Appendix II MEM Order and Guidelines for Annual s CDA Consequence Complications R 3rd Party Review DSI.docx M09922A November 2014 Page iii

6 1 INTRODUCTION This report presents the results of an of the Dam Safety Inspection Report (BGC, 2014c) for the New Afton Tailings Storage Facility (TSF). The review included a site visit by the Review Engineer, Mr. Harvey McLeod, P.Eng., P.Geo., accompanied by Mr. David Willms, P.Eng. on November 10, The New Afton Mine is located just west of the city of Kamloops in central British Columbia. The facility consists of a 15,000 tonnes per day underground block cave mine and processing plant, which produces a copper gold concentrate. Tailings are stored within the New Afton tailings impoundment and the adjacent Pothook open pit that was converted to a tailings impoundment. The three cyclone sand impoundment dams (Dam A, Dam B, and Dam C) are currently up to 16.7 m high at centreline and join together for a total length of approximately 2 km. Two rockfill saddle dams (West Dam and South Dam) are up to 23 m high at centreline and are about 170 m long and 280 m long, respectively. The tailings impoundments are regulated under the Mines Act of British Columbia and must comply with the requirements of the Health Safety and Reclamation Code for Mines (HSRC) in BC (BC MEMPR 2008). The requirements related to tailings impoundments in the code include the following: Dams must be designed in accordance with the criteria provided in the Canadian Dam Association, Dam Safety Guidelines (HSRC ). The Operation, Maintenance and Surveillance (OMS) manual must be revised regularly during operations (HRSC10.5.2). Annual (HSRC ) must be carried out and submitted to the Ministry of Mines. The MEM website provides the document Guidelines for Annual Dam Safety Inspection Reports. There must be an Emergency Preparedness Plan for any dam with a consequence classification of High or Very High. (HRSC ). The Ministry of Energy and Mines (MEM) follows the guidance of the Canadian Dam Association, which has also recently published a Technical Bulletin entitled Application of Dam Safety Guidelines to Mining Dams (CDA, 2014). The Mining Dams Bulletin includes the need to consider seepage/groundwater quality impacts and the various stages of a tailings dam The current dam classification under the CDA Guidelines is Very High. The MEM classification under the HSRC is a major impoundment and major dams. KCB have been informed that the Engineer of Record (EOR) for the TSF is BGC Engineering Inc. (BGC), responsible for the design and performance of the New Afton and Pothook tailings facilities, including: 1) dam safety inspections; 2) construction monitoring and quality assurance; 3) instrumentation planning, design and review; and 4) design modifications. Quality control for earthworks construction is being carried out by AMEC Environment and Infrastructure (AMEC) R 3rd Party Review DSI.docx Page 4

7 On August 18, 2014, the Chief Inspector s office of the MEM issued orders (Appendix I) mandating that the 2014 Dam Safety Inspection (DSI) of tailing dams be completed, and that the report be reviewed by a third party Professional Engineer, and submitted by December 1, The order required that an independent party: Assess if the DSI report meets the requirements of MEM; and Review the consequence classification of the dam(s) R 3rd Party Review DSI.docx Page 5

8 2 BACKGROUND INFORMATION AND SITE VISIT 2.1 Site Visit and Document Review Site Visit The site visit was carried out November 10, 2014, and included Mr. Harvey McLeod and Mr. David Willms of KCB, and Mr. Scott Davidson (Environment), Matt Davis (Engineering) and Emily O Hara (Environment) of New Afton. The site tour included inspection of the New Afton and Pothook tailings facilities, as well as the current construction activities. The relevant observations from the site visit include the following: The dams were all in good condition with no evidence of cracking, subsidence or erosion. The water ponds in both the New Afton and Pothook tailings facilities were well below crest level, with over 5 m of freeboard. Sand and gravel stockpiles were in good condition, with no evidence of segregation. Placement of materials was being carried out in an orderly fashion and the materials, from a visual inspection, were suitable for dam fills. Compaction was being carried out with four 10 tonne smooth drum vibratory rollers. Cyclone operations were not active; however, observations of the sand indicated that it was a good clean product, suitable for dam construction. The fine filter and coarse filter zones consisted of well graded sand and fine gravel. Glacial till core material was being screened to 150 mm minus. Reported sinkholes in the right abutment ridge of Pothook Dam appear to be erosion channels and do not appear to be sinkholes that may have developed due to piping. Seepage ponds are small but the dams may high enough to be classified as dams Document Review The documents listed in Table 2.1 were provided to KCB. The review was carried out at a high level to obtain an understanding of the design and site conditions and, as such, does not represent a comprehensive review. Items of interest, relevant to dam safety, are noted R 3rd Party Review DSI.docx Page 6

9 Table 2.1 Design Documents and Construction Records Review Summary Date June 2008 Prepared By Vector Title Design Report for the Tailings Storage Facility at the New Afton Gold & Copper Mine Inspection (I), Design (D) or Construction (C) July 2012 New Gold TSF As Built Report C November 28, 2012 January 31, 2014 (a) March 28, 2014 (b) November 14, 2014 (c) November 14, 2014 (d) March 31, 2014 (a) March 31, 2014 (b) Geo Logic New Afton TSF Dam Audit Memorandum BGC 2013 Record of Construction C BGC BGC BGC New Gold New Gold 2014 (c) New Gold 2013 Annual Inspection Tailings Storage Facility 2014 Annual Inspection Tailings Storage Facility DRAFT New Afton Dam Break and Inundation Assessment Tailings and Water Management Facilities Operation, Maintenance and Surveillance Manual Tailings and Water management Facilities Emergency Preparedness and Response Plan Tailings, Heap Leach and Waste Rock Facilities Management Policy D I I I D Manual Plan Policy Key Items of Interest Dam design Very good QC documentation of Construction. Plans and cross sections Limited information on as built foundations and as built geometry. South and West Dams have redundant filters and drains upstream of the core zone. Fine filter not placed over glacial till. Visual observations. No documentation of construction or monitoring. Very good documentation of QC and construction. Downstream cyclone sand reported 5% fines, upstream 5% to 10%.Fine filter has < 5% fines. Coarse filter is 1 m thick over rockfill and 2 m thick over glacial till Discussion of construction activities and pond level Summary of instrumentation responses Plans and cross sections Discussion of construction activities and pond level Summary of instrumentation responses Inundation Assessment Instrument and pond level thresholds. Key personnel and response plan 2.2 Facility Description The New Afton TSF is located directly to the south of the Afton Pit, and east of the closed Teck TSF. A secondary, and smaller, tailings impoundment is Pothook Pit, located northeast of the New Afton TSF. The facilities are shown in plan on Figure R 3rd Party Review DSI.docx Page 7

10 Approximately 250 m N Pothook TSF Figure 2.1 Orthophoto of New Afton (July 2013, BGC) The New Afton TSF impoundment is formed by a series of dams. Three compacted till starter dams (Dam A, Dam B, and Dam C) were constructed in These dams have subsequently been connected to form one long dam currently up to 16.7 m high at centreline with a total length of approximately 2 km. Three seepage ponds (1, 2, and 3) collect seepage from Dam A, Dam B, and Dam C, respectively. The seepage is pumped back into the impoundment. Two rockfill saddle dams (West Dam and South Dam) are up to 23 m high at centreline and are about 170 m long and 280 m long, respectively., The impoundment covers 92.1 ha and has an up gradient catchment of 36.7 ha. Approximately half of the New Afton TSF is underlain by mine waste rock, which is up to 70 m thick, and was placed during previous mining of the Afton Pit and construction of the Teck TSF. Consequently, a linear low density polyethylene (LLDPE) geomembrane liner was placed over the majority of the New Afton TSF impoundment footprint to prevent excessive seepage and/or piping of R 3rd Party Review DSI.docx Page 8

11 tailings into the rockfill foundation. The dam design cross sections vary and include the following elements: The West and South Dams have a central glacial till core, keyed into the glacial till foundation. Fine filter and coarse filter zones were placed between the glacial till core and both the upstream and downstream rockfill shells. Dam A and Dam B have a central glacial till core, with a downstream chimney filter and compacted cyclone sand shells. Dam C comprises compacted cyclone sand with a LLDPE geomembrane which zigzags on 3H:1V slopes vertically along the centerline. A chimney filter is placed within the downstream cyclone sand shell, just downstream of the centerline. Dams A, B, and C have a blanket drain under the downstream cyclone sand shell. The blanket drain consists of a fine filter overlying a coarse filter, overlying glacial till foundation. Where the foundation is rockfill, a fine filter was placed over the rockfill. The Pothook TSF has a rockfill dam 10 m high at centreline and approximately 350 m long. A LLDPE liner was installed on the upstream face of the dam in 2011 to reduce seepage beneath the dam. Tailings and water are stored in Pothook Pit. Reclaim systems pump water back to the mill for use as process water. The main water reclaim barge is located in the southeast corner of the New Afton TSF and a smaller pump system is installed in Pothook TSF. Water from the seepage recovery ponds are pumped back to the New Afton TSF. 2.3 Site Conditions The New Afton project area is located in the Interior Plateau of British Columbia at an elevation of approximately 720 m above sea level. The climate is semi arid with warm to hot, sunny and dry summers, and mild to cold and dry winters. Average summer temperatures are about 19 C and average winter temperatures are about 6 C. Total annual precipitation is 305 mm. The drainage from the tailings facility is towards Afton Pit and the drainage from the overall site is ultimately towards Kamloops Lake. The area is moderately seismic. The surficial geology consists of a loose surface organic soil, overlying medium dense to dense glacial till (silt sand gravel, with clay). The glacial till can have occasional silty or gravelly interlayers which are typically discontinuous R 3rd Party Review DSI.docx Page 9

12 3 REVIEW OF DAM SAFETY INSPECTION REPORT 3.1 General KCB reviewed the DSI (BGC, 2014c). The document is comprehensive and addresses the MEM Guidelines for Annual DSI Reports and the consequence classification is appropriate. Our general comments are: The report should contain a summary of all recommendations in the document with priority items related to dam safety noted. The representative cross sections should include the measured piezometric levels and foundation soils. The contents of the DSI have been compared against the MEM Guidelines for Annual DSI Reports and the results in Table 3.1. Table 3.1 Review of MEM Guidelines applicable to the 2014 Draft DSI Executive Summary MEM Requirement Consequence Classification of the dam(s) in accordance with Table 2 1 of the CDA Dam Safety Guidelines (2007) Significant changes in instrumentation and/or visual monitoring records Included in 2014 DSI KCB Observations Very High Consequence is appropriate. Consequence categories should be explicitly documented to support the classification. More detail on the instrument locations would be helpful in following the discussion of instrument responses. None. Significant changes to dam stability and/or surface water control OMS Manual Latest revision is March 31, Emergency Preparedness Plan Latest revision is March 31, Scheduled date for the next formal Dam Safety Mid 2017 Review Summary of past years construction (if any) with a description No Construction observations are noted in the of any problems and stabilization Background Information for each dam. Plan and representative cross sections No Appendices for 2014 not received. Plan and cross sections are available in 2013 DSI. Site photographs Review of climate data Water balance review Last water balance update in July Water balance needs to be updated for increased mill throughput and new bathymetry. Freeboard and storage availability (in excess of the design flood) About 5 m freeboard. The design freeboard is 1.1 m. Water discharge system, volumes, and quality N/A Operated as closed facility ; seepage is collected in seepage ponds and pumped back R 3rd Party Review DSI.docx Page 10

13 MEM Requirement Included KCB Observations in 2014 DSI Seepage occurrence and water quality No Seepage discussed but not quantified. Clear seepage noted. Water quality reported by New Gold. Surface water control and surface erosion Routinely monitored. Phreatic surfaces Instrumentation review Phreatic surface not shown but piezometer readings included. Thresholds set according to select piezometer readings but these thresholds appear to be for the ultimate dam. Settlement Settlement plates (no guidelines or thresholds). Lateral movement Inclinometers (no guidelines or thresholds). 3.2 Consequence Classification Review The Canadian Dam Association Dam Safety Guidelines (2007, revised in 2013) provide a classification of dams based on the consequences of failure. The original design report (Vector 2008) assigned a classification of High based on CDA BGC updated the consequence classification based on CDA 2007 and the DSI reports a dam classification of Very High. KCB has reviewed the 2014 Dam Break Inundation Assessment (BGC, 2014d), which was carried out to assess the potential extent of a dam breach under both the sunny day (piping failure of dam with operational water pond) and the rainy day (overtopping under extreme flood conditions). The assessment is appropriate and the breach outflow extent supports the dam consequence classification of Very High. KCB also recommend, for record purposes, that New Afton explicitly document the four main consequence components contributing to the dam classification, as outlined in the 2007 CDA Dam Safety Guidelines: Population at Risk, Incremental Loss of Life, Environmental and Cultural Values, and Infrastructure and Economics (Appendix II). 3.3 Instrumentation Review The DSI (BGC, 2014c) contains a review of the instruments for Over the review period of November 29, 2013 to October 1, 2014 the tailings pond rose about 7 m from about 5726 m (mine grid elevation, which is 5000 m above ground elevation) to about 5733 m. Key observations regarding the instrumentation review are discussed in the following sections Piezometers Threshold values are set for some vibrating wire piezometers. These thresholds are all set at Elevation m (Table 3.2) which was determined for the ultimate dam. This is not appropriate for intermediate stages of construction and the threshold values will need to be modified to reflect the ongoing construction raising. The updated threshold values should be included in the OMS. The locations of the piezometers are not clearly documented or shown in plan and sections, and these details should be added to the piezometer plots to assist in interpretation. The operation fluctuation R 3rd Party Review DSI.docx Page 11

14 range discussed in the OMS Manual states: The Operational Fluctuation Range threshold is exceeded if any aggregate of readings between reviews by the EOR is equal to or exceeds the noted range. If exceeded, action is required. This requires clarification. Observations on the 2014 instrumentation are summarized as follows: Dam A: Piezometer VW29211, which is reported as being in the foundation ; increased approximately 5 m in 2014 and is approximately 1.5 m below pond level. This illustrates a positive hydraulic connection between the pond and the piezometer and it is necessary to provide a clear explanation of its genesis and significance. Dam B: Piezometers VW29220, VW29221 and VW26794, indicate slightly negative pore pressures. VW29221 increased about 1.2 m in July 2014 in response to cyclone sand placement which appears reasonable. Dam C: Piezometer VW29217 increased 6 m in 2014, the genesis and significance of the increased pore pressure should be clearly explained. South Dam, West Dam and Pothook Dam: Piezometer readings are stable and show modest increase with increasing pond level. Table 3.2 Summary of 2014 Piezometer Changes and Threshold Levels Piezometer ID Location Phreatic Surface* (Mine Grid (m)) Threshold Level* (OMS Manual) Operation Fluctuation Range (+/ m) Approximate Range for 2014 (BGC, 2014c) VW29211 Dam A VW29220 Dam B VW29221 Dam B VW29218 Dam B/C VW29214 Dam C VW29216 Dam C VW29217 Dam C *Note that threshold levels are based on the Ultimate Dam height Settlement Plates and Inclinometers Settlement plates and inclinometer plots for the dams at the New Afton TSF and the Pothook TSFindicate that there are no significant deformations of the dams Summary The instrumentation indicates that the structures are behaving according to the expected conditions and do not indicate dam instability. The two anomalies in VW29211 and VW29217, which appear to indicate a positive hydraulic connection with the pond, require further assessment. Low (m) High (m) Range R 3rd Party Review DSI.docx Page 12

15 3.4 Geotechnical Review Stability Review The dams are in good condition and no evidence of cracking, bulging, or deformations were observed during the KCB site visit or reported in the DSI. The dams have a 3H:1V downstream slope and are founded on either competent glacial till, bedrock, or waste rock. KCB have not completed a stability analysis, however, in our opinion this is a robust configuration that would be resistant to static and seismic loading There is some possibility of settling due to the waste rock foundation (under Dam B and Dam C) or due to deformation from the block cave, both of which are well monitored. The dam should be capable of tolerating some displacement Seepage The downstream shell of the dam appears to be well drained. However, the piezometric levels should be plotted on the cross sections and compared to the updated thresholds so it is clear that the phreatic surface is below the point where it would cause instability. With the chimney filter, drainage blanket, and a cycloned sand downstream shell, the probability of instability from a high phreatic surface is low Internal Erosion There was no evidence of piping reported in the DSI or observed on our site visit. Filters are in place against the core to provide protection from piping. The cyclone sand also acts as a filter to prevent fines migration. There is good tie in to the abutments. The probability of piping related instability is very low. 3.5 Hydrotechnical Review The tailings impoundments are operated on a no discharge basis with water recycled to the process plant. In addition to the tailings, the TSF is required to maintain storage for the IDF (0.26 Mm 3 ) which is the Probable Maximum Precipitation (PMP) plus a minimum 0.8 m emergency dam freeboard (BGC 2014c), for a total design freeboard of 1.1 m from the dam crest. In our review of the hydrotechnical components of the 2014 DSI we have the following comments: The pond is being operated with adequate freeboard to meet dam safety requirements. The TSF met storage requirements in 2014 and the 2014 crest elevation should provide storage until the end of 2015 (BGC, 2014c). The pond level threshold for the current dam crest should also be reported in the DSI. The pond thresholds for the dam raise schedule are reported in the OMS Manual R 3rd Party Review DSI.docx Page 13

16 3.6 Mining Dam Considerations The APEGBC Guidelines for Dam Safety Reviews (2014) and the CDA Technical Bulletin for Mining Dams (2014) introduce requirements for consideration of closure and environmental objectives of the dams. The CDA technical bulletin for Mining Dams (2014) recommends higher design criteria for closure passive care, which should be considered in the context of potentially reducing the consequence with a dry landform. This is the current closure plan for New Afton TSF, and is appropriate. Surface water quality is monitored at the following points: Plant Site Pond, Pothook Pit, the New Afton Tailings Storage Facility, Russell Slough, Tailings Perimeter Ditch, Afton Pit, and Muskrat Slough. (New Gold, 2014a) but is reported by New Gold separately from the DSI. Seepage from the TSF ultimately reports to the open pit or underground workings and there is not a concern, at this time, of seepage plumes bypassing the mine area R 3rd Party Review DSI.docx Page 14

17 4 REVIEW OF TAILINGS FACILITY STEWARDSHIP 4.1 General The New Afton and Pothook tailings facilities are well maintained and well documented by New Afton and BGC. New Afton has a good team for managing and constructing the facility; and for providing oversight on the technical, environmental and social aspects of the facilities. The OMS Manual and the EPRP are well documented and procedures are in place to manage and respond to emergencies. 4.2 OMS Manual New Afton has an Operation, Maintenance and Surveillance (OMS) Manual which is comprehensive and was updated in March, In our opinion, the OMS Manual meets the Mining Association of Canada s 2011 guideline for Developing an OMS Manual for Tailings and Water Management Facilities (MAC, 2011). Our observations on the OMS Manual are summarized in Table 4.1. Table 4.1 OMS Checklist Section as per MAC 2011 Included Comments Discussion on preparation of the OMS Manual including: Objectives, team, resources, scheduling, and document control. Roles and responsibilities including: org structure, individual responsibility, competency and training, and managing change Should clearly identify responsibility for TSF including an org chart with individuals responsible for QA, QC, EOR, and Tailings Management. Facility description including: facility overview, site conditions, facility components, regulatory requirements, basis of design and design criteria, construction history, and documents control. Operation of facility including: Objectives, tailings transport and deposition, dam and basin raising, water management, environmental protection, safety and security, documentation, and reporting. Maintenance including: Objective, parameters, routine and predictive maintenance, even driven maintenance, documentation, and reporting Surveillance including: objectives, parameter, and procedures. Thresholds should be defined for intermediate construction phases and operational range should be clarified Emergency Planning and Response 4.3 Emergency Preparedness and Response Plan New Afton has an Emergency Preparedness and Response Plan (EPRP) which is the framework for identifying and responding to emergencies and was updated March, The Health, Safety and Security Department have run desk top trial runs for emergency procedures. In our opinion, the EPRP meets the MEM Guidelines for Mine Emergency Response Plan (MEM, 2013). Our observations on the EPRP are summarized in Table R 3rd Party Review DSI.docx Page 15

18 Table 4.2 Emergency Preparedness and Response Plan Checklist Policy Directive Requirement Included Comments Mine Emergency Response Plan Coordinator and Planning Group Emergency Identification, Prevention and Protection Duties and Responsibilities of Personnel Emergency Notification Plan Emergency Management Organization Emergency Operations Centre Emergency Response Procedures Action Plans Mine Plan and Operation Maps Evacuation Plan and Map of Escape Routes Check in/check out Procedure for Emergencies No Should clearly identify tailings manager. TSF plan only. Consider adding map with all mine operations indicated. Not in EPRP. Maintained by Engineering Coordinator. Mine Rescue Equipment Inventory No Not included Mutual Aid Agreement First Responders Consultation Communication Services Public and Media Relations Training Plan Practice Drills Plan Plan for Review and Updating Costs No R 3rd Party Review DSI.docx Page 16

19 5 SUMMARY The assessment of the physical condition of the dam and associated works is comprehensive and no significant concerns have been identified or observed. Management systems are in pace, including OMS Manual and EPPs. The DSI report is generally compliant with the MEM Guidelines. For reference purposes the recommendations from the executive summary (BGC, 2014c) are summarized in Table 5.1 with comment from KCB. There are other recommendations in the DSI that should be summarized in a table with the status and schedule. Additional recommendations from KCB s Third Party Review are summarized in Table 5.2. Table 5.1 Summary and Review of Key DSI Recommendations Component Recommended Action (BGC, 2104c) KCB Comment Pothook A dam break inundation study should be completed for the Pothook Dam. Minor consequence compared to the New Afton TSF EPRP The EPRP should be updated to include the inundation maps created as part of the dam break inundation study. The recommended edits to the OMS and EPRP should be completed as part of the next revision to these documents planned for the first quarter of TSF The survey monuments removed as part of the 2014 construction activities should be re established as planned, and manual readings of the survey monuments for all dams should be taken monthly following completion of the 2014 construction activities. All instruments should be protected from vehicle traffic with barriers such as Lock Blocks. Pothook/Seepage Pond 1 Dam The vegetation on the Pothook Dam and Seepage Pond 1 Dam should be controlled using the measures utilized successfully at the South and West Dams. Pothook The damage to the LLDPE liner on the Pothook Dam should be completed as soon as possible. Pipelines and equipment should be kept from coming in direct contact with the LLDPE liner on the Pothook Dam. Pothook The Pothook Emergency Spillway assessment and any corresponding changes should be completed. The stability of the overburden along the north rim of the Pothook Pit should be Unlikely that slope failure, if it Pothook assessed. The discharge of water on this slope from the Afton Open Pit should be were to occur, stopped, and an alternate path to the impoundment in the Pothook Pit should be could create a utilized. wave that could overtop the dam TSF The leaking spigot valves on the tailings header pipe upstream of Dam C should be repaired as soon as possible. Procedures for monitoring and criteria for reacting to encroachment of the TSF subsidence zone toward the TSF should be established and incorporated into the OMS Manual R 3rd Party Review DSI.docx Page 17

20 Table 5.2 Summary of 3 rd Party Review Recommendations ID No. Component Recommended Action Schedule KCB14 1 OMS Set annual threshold levels for instrumentation and quantify the + 2 m operational criteria. Q KCB14 2 OMS Prepare a separate organization chart for the TSF that clearly identifies the New Afton Tailings Engineer responsible for the tailings facility. Identify who the person reports to and what other persons report to Q the Tailings Engineer for matters pertaining to the facility. KCB14 3 OMS On an annual basis, name the QA Engineer (e.g. Resident Engineer), who is responsible for QA for construction and signs off on the annual Q As Constructed Report. KCB14 4 DSI Assess the displacement tolerance of the dam and compare to measured displacement identify threshold levels to be included in the Q OMS. KCB14 5 DSI Document genesis and significance of piezometer readings from VW29211 and VW Q KCB14 6 DSI Indicate the location of instrumentation on sections and plans, and plot actual levels on an annual basis. Q KCB14 7 DSI DSI should contain a summary table of all recommendations in the document with the level of importance, schedule and status. Q KCB14 8 Design Document the 4 components of the dam consequence classification. Q Report KCB14 9 Design Review Seepage Ponds to confirm if they should be classified as dams. Q Report KCB14 10 Prepare a Consolidated Design Report that updates all design aspects, Design including: design criteria, stability assessment, design sections and Report geotechnical database. Q R 3rd Party Review DSI.docx Page 18

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22 REFERENCES Note that additional references are included in Table 2.1. British Columbia Ministry of Energy and Mines (BC MEM) Tailings Dams Independent Review of Dam Safety and Consequence Classification. August 18, British Columbia Ministry of Energy, Mines and Natural Gas Mines and Mineral Resources Division (BC MEM) Mine Emergency Response Plan Guidelines for the Mining Industry. February, British Columbia Ministry of Mines and Petroleum Resources. (BC MEMPR) Health Safety and Reclamation Code for Mines (HSRCM). Canadian Dam Association (CDA) Technical Bulletin Application of Dam Safety Guidelines to Mining Dams. Canadian Dam Association (CDA) Technical Bulletin. Dam Safety Guidelines (update 2013). The Mining Association of Canada (MACC) Developing an Operation, maintenance and Surveillance Manual for Tailings and Water management Facilities R 3rd Party Review DSI.docx Page 20

23 APPENDIX I MEM Order and Guidelines for Annual s R 3rd Party Review DSI.docx M09783A November 2014

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26 Ministry of Energy & Mines GUIDELINES FOR ANNUAL DAM SAFETY INSPECTION REPORTS Reference: Health, Safety and Reclamation Code for Mines in British Columbia (Code) Section : The manager shall submit an annual dam safety inspection report prepared by a professional engineer on the operation, maintenance and surveillance of the tailings and water management facilities and associated dams to the chief inspector. This Code reference applies to every operating and closed mine in BC. The report shall provide the following information: 1. Executive Summary (a) (b) (c) (d) (e) (f) Classification of the dam(s) in terms of Consequence of Failure in accordance with Table 2 1 of the CDA Dam Safety Guidelines (2007). Significant changes in instrumentation and/or visual monitoring records. Significant changes to dam stability and/or surface water control. For major impoundments, as defined in Part 10 of the Code, a current Operation, Maintenance and Surveillance (OMS) Manual is required. The annual report shall indicate the latest revision date of the OMS manual. For tailings dams classified as High, Very High, or Extreme Consequence, an Emergency Preparedness Plan (EPP) is required. The annual report shall indicate the latest revision date of the EPP document. Scheduled date for the next formal Dam Safety Review in accordance with Table 5 1 of the CDA Dam Safety Guidelines (2007). Formal Dam Safety Reviews are required every 5 to 10 years (depending on consequence classification) and differ from annual dam safety inspections. The requirements for Dam Safety Reviews are included in Section 5 of the CDA Dam Safety Guidelines. Dam Safety Reviews may be conducted by the Engineer of Record with third party review, or by an independent third party with involvement of the Engineer of Record.

27 Guidelines for Annual Dam Safety Inspection Reports August Summary of past years' construction (if any) with a description of any problems and stabilization. 3. Plan and representative cross sections. 4. Site photographs. 5. Review of climate data. 6. Water balance review. 7. Freeboard and storage availability (in excess of the design flood). 8. Water discharge system, volumes, and quality. 9. Seepage occurrence and water quality. 10. Surface water control and surface erosion. 11. Instrumentation review including: (a) (b) (c) Phreatic surfaces and piezometric data. Settlement. Lateral movement. The report shall be submitted by a qualified geotechnical engineer registered as a Professional Engineer (P.Eng.) in British Columbia. The professional engineer will be deemed the Engineer of Record for the facility unless another engineer is identified within the Dam Safety Inspection report as having this responsibility. Note, this document modified from the original by George Warnock, P.Eng. (Manager, Geotechnical Engineering) in August Original prepared by Chris Carr, P.Eng. (former Manager) in February 2002.

28 APPENDIX II CDA Consequence Classification R 3rd Party Review DSI.docx M09783A November 2014

29 Appendix II CDA Consequence Classification Table II-1 Dam Classification 1 Dam Class Population at Risk [note 1] Loss of Life [note 2] Incremental Losses Environmental and Cultural Values Infrastructure and Economics Low None 0 Minimal short-term loss. No long-term loss. Low economic losses; area contains limited infrastructure or services. Significant Temporary only Unspecified No significant loss or deterioration of fish or wildlife habitat. Loss of marginal habitat only. Restoration or compensation in kind highly possible. Losses to recreational facilities, seasonal workplaces, and infrequently used transportation routes. High Permanent 10 or fewer Very high Permanent 100 or fewer Extreme Permanent More than 100 Significant loss or deterioration of important fish or wildlife habitat. 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 losses affecting 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 through 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. Implication for loss of life: 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. 1 From the Canadian Dam Association, Dam Safety Guidelines, 2007, updated Appendix II.docx Page II-1 M09783A November 2014