Teck Coal Ltd. Elkview Operations. Dam Safety Inspection Report Independent Third Party Review. November 2014 M09963A01.730

Transcription

1 November 2014 M09963A01.730

2 November 28, 2014 Teck Coal Limited Sparwood, British Columbia Mr. Adam Walker Geotechnical Engineer ear Mr. Walker: Please find attached the Third Party Review of the am Safety Inspection (SI) Report for the Elkview Operations Tailings Facilities. The review concludes that the SI meets the requirements of the Ministry of Mines Guidelines for Annual 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 LT. Harvey McLeod, P.Eng., P.Geo. Principal HM/W:dl R Elkview 3rd Party Review.docx M09963A Klohn Crippen Berger Ltd Virtual Way Vancouver BC V5M 4X6 CANAA t f

3 cover.docx

4 TABLE OF CONTENTS 1 INTROUCTION BACKGROUN INFORMATION AN SITE VISIT Site Visit and ocument Review Facility escription Site Conditions REVIEW OF AM SAFETY INSPECTION REPORT General Consequence Classification Review Instrumentation Review Stability Review REVIEW OF TAILINGS FACILITY STEWARSHIP SUMMARY CLOSING List of Tables Table 2.1 EVO esign ocuments and Construction Records... 3 Table 2.2 Summary of Tailing Facility Features... 6 Table 2.3 TSF esign Flood and esign PGA... 7 Table 3.1 Summary of SI Conformance... 8 Table 3.2 am Classifications... 9 Table 5.1 Summary of 2014 SI Recommendations () List of Figures Figure 2.1 Location Plan Lagoons A, B, C and... 5 Figure 2.2 Location Plan WFTF R Elkview 3rd Party Review.docx Page i

5 1 INTROUCTION This report presents the results of an of the am Safety Inspection (SI) Report for the (EVO) tailings storage facilities. The SI was prepared by Environment and Infrastructure (). The Klohn Crippen Berger (KCB) review included a site visit by the Review Engineer, Mr. Harvey McLeod, P.Eng., P.Geo. The Elkview Mine is located in south eastern British Columbia near the town of Sparwood. The open pit mine produces approximately 5.5 Mt to 6.0 Mt per year of clean coal. Fine coal refuse has been stored in 5 historic tailings facilities (Lagoons A, B, C, and ) and are currently being stored in the West Fork Tailings Facility (WFTF). Lagoon is used for contingency storage only. The SI Report covers the five facilities. 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: ams must be designed in accordance with the criteria provided in the Canadian am Association, am Safety Guidelines (HSRC ). The Operation, Maintenance and Surveillance (OMS) manual must be revised regularly during operations (HSRC ). Annual (HSRC ) must be carried out and submitted to the Ministry of Mines. The MEM website provides the document Guidelines for Annual am Safety Inspection Reports. There must be an Emergency Preparedness Plan for any dam with a consequence classification of High or Very High. (HSRC ). KCB have been informed that the Engineer of Record (EOR) for these tailings facilities is Andy Small, P.Eng. of, responsible for the design and performance of the dam including: 1) dam safety inspections; 2) construction monitoring and quality assurance/quality control; 3) instrumentation planning, design and review; and, 4) design modifications. On August 18, 2014, the Chief Inspector s office of the MEM issued orders mandating that the 2014 am Safety Inspection (SI) of tailing dams be completed, and that the report be reviewed by a third party Professional Engineer, and submitted ecember 1, The order required that the third party review: to assess if the SI report meets the requirements of MEM; and the consequence classification of the dam(s) R Elkview 3rd Party Review.docx Page 1

6 2 BACKGROUN INFORMATION AN SITE VISIT 2.1 Site Visit and ocument Review Site Visit The site visit was carried out on October 17, 2014, and included: Mr. Harvey McLeod and Mr. Lowell Constable of KCB; Mr. Adam Walker (Engineering), Mr. Zane Leonard (Engineering) and Laura Gislason (Engineering Superintendent) of EVO; and, Mr. Andrew Bidwell of Teck Coal. The site tour included inspection of Lagoons A, B, C, and, and the West Fork Tailings Facility (WFTF). The relevant observations from the site visit include the following: Tailings are currently being discharged into the southwest corner of the WFTF, and observations in this area include: Tailings beach slopes are approximately 0.5% towards the northeast, where the pond is located. The pond has approximately 300,000 m 3 of decant water. The west (right) flank of the WFTF comprises the Adit Waste Rock ump, which is well above the tailings pond level. EVO staff indicated that there were historic occasions of tailings migrating into the waste rock and, therefore, current practice is to push a dozer road along the waste rock/tailings beach contact using a finer gradation material excavated from a separate location south of the WFTF. EVO indicated that the purpose of the road is to place a finer gradation material between the tailings beach and the Adit waste rock dump toe that is resistant to tailings migration and/or piping. The upstream slope of the main dam section has been graded to an approximate slope of 3H:1V, with a secondary objective of mixing the waste rock particles on the surface to produce a well graded material that could be resistant to piping. The majority of the surface appears to contain well graded material however there were a number of sections of exposed coarse rockfill. Lagoon is used for auxiliary tailings storage. Observations of Lagoon include the following: There was a wide (25 m minimum) zone upstream of the crest in which tailings were spigotted to produce a segregated tailings material in the outer dam shell. The dam slopes were in good condition with no major erosion channels. The west dam slopes are close to the railway line and the Elk River. Lagoons A and B are small tailing ponds that were used for initial start up of the mine and are not active; relevant field observations include: Minor erosion in Lagoon A occurred in the 2014 freshet due to overflow of a 2 m high portion of the dam. The dams have limited ability to pond any significant volumes of water. The ponds are overgrown with cattails and grasslands R Elkview 3rd Party Review.docx Page 2

7 The consequences of failure are low. Lagoon C is inactive for tailings storage and is periodically used for storage of sludge from settling ponds; relevant observations include: The impoundment was dry with no ponded water. The dam slopes are in good condition with no major erosion channels. The west dam slope is close to the railway line and the Elk River. Water is not stored in the impoundment however it does have the ability to store water during extreme flood events. ocument Review The documents listed in Table 2.1 were provided to KCB. The review of documentation was carried out at a high level to obtain an understanding of the design and site conditions. Items of interest, relevant to dam safety are noted. Table 2.1 EVO esign ocuments and Construction Records ate Prepared By Title July 1972 June 1982 March 1985 Phillips, Barratt, Hillier, Jones & Partners Consulting Engineers Golder Associates Golder Associates Report on Tailings Holding Lagoon for the Elkview Coal Preparation plan raft Preliminary Report to Swan Wooster Engineering Co. Ltd. Long Term Refuse Storage B.C. Coal Ltd. Elkview Plant Borehole and CPT Location Plan Lagoon C and Inspection (I), esign () or Construction I Key Items of Interest Lab results, design analysis, hydrology Site conditions, geology, sub surface conditions, test pit logs, grain size analysis June 1986 Golder Associates Interim Report No.3 To Westar Mining Ltd. On Long Term Raising of Lagoons C and Above Elevation 3705 Site Investigations and recommendations includes slope stability analysis, lab testing results, record of boreholes and gradations, CPT results, strength and deformation characteristics, liquefaction potential, collapse potential August 1986 Golder Associates Report to Westar Mining Ltd. On Geotechnical Engineering Study Lagoon E Includes field and lab investigation, recommendations for design and construction, record of boreholes and test pits February 1987 Golder Associates Final Report to Westar Mining Ltd. On Long Term Raising of Lagoons C and Above Elevation 3705 Includes Site Investigation, subsurface conditions, long term analysis and design, construction recommendations, boreholes and gradations, CPT results, strength and deformation characteristics, liquefaction potential, collapse potential R Elkview 3rd Party Review.docx Page 3

8 ate Prepared By Title June 2002 October 2003 May 2004 March 2008 March 2010 March 2011 January 2012 January 2012 January 2012 January 2012 January 2012 March 2012 October 2013 March 2013 March 2014 (a) July 2014 (b) November 2014 (c) Teck Teck Teck Teck Teck Short Term Coal Refuse Management Utilizing Lagoon and CCR umps West Fork Tailings Storage Facility esign Report FINAL West Fork Storage Facility Addendum to esign Report Issued 28 October, 2003 Coal Refuse Facilities Report on 2007 Annual Geotechnical Inspection Final Report Coal Refuse Facilities Report on 2009 Geotechnical inspection Final Report Coal Refuse Facilities Report on 2010 Geotechnical inspection Final Report OMS Inactive Tailings Facilities Lagoons A, B, C, and Inactive Tailings Facilities, EPP & ERP for Flood Emergencies Lagoon Tailings Facility, EPP & ERP for Flood Emergencies OMS tailings eposition West Fork Facility OMS Tailings eposition Lagoon Coal Refuse Facilities Report on 2011 Annual Geotechnical Inspection Final Report Tailings Storage Facilities Lagoon C and 2013 am Safety Review Elkview Coal Refuse Facilities 2012 Geotechnical Inspection West Fork tailings Facility evelopment to El As Built Report West Fork Tailings Facility Results of 2013 Site Inspection Tailings Storage Facilities West Fork Tailings Facility and Lagoons A, B, C, and 2014 am Safety Inspection Final Report Inspection (I), esign () or Construction I I I I C C C C C I I C I I Key Items of Interest Liquefaction of tailings and foundation concluded dam stable for g (975 year return period). eveloped trigger levels for piezometers for static liquefaction for dam raising. Recommended an average Su/P =0.1 CCR/MCR dump cross sections, instrumentation details, refuse facilities inspection reports, inundation evaluation CCR/MCR dump cross sections, instrumentation, refuse facilities inspection reports, OMS manuals, Truck Shop yke esign CCR/MCR dump cross sections, instrumentation, refuse facilities inspection reports CCR/MCR dump cross sections, instrumentation, refuse facilities inspection reports SR prepared under CA Guidelines CCR/MCR dump cross sections, instrumentation, refuse facilities inspection reports, geotechnical drilling program, OMS manuals and ERP s Climate data, instrumentation readings, results of SI, dam safety assessment, recommendations R Elkview 3rd Party Review.docx Page 4

9 2.2 Facility escription The EVO fine tailings storage facilities include five tailings facilities: Lagoons A, B, C, and ; and, the West Fork Tailings Facility (WFTF). The four Lagoons are located in the Elk River floodplain as shown on Figure 2.2. The WFTF is located in the Upper Erickson Valley, upstream of the Erickson am and ump, as shown on Figure 2.2. Elk River N Figure 2.1 Location Plan Lagoons A, B, C and R Elkview 3rd Party Review.docx Page 5

10 West Fork TSF Figure 2.2 Location Plan WFTF Lagoons A and B were the initial storage facilities for the mine when it opened in 1969, until the early 1970 s when two ring dyke tailings dams were constructed, Lagoons C and. From 1985 to 2006, Lagoon served as the primary tailings facility while Lagoon C was used as an emergency water attenuation facility. Table 2.2 provides a summary of the tailings facilities, along with their respective storage capacity, heights and volumes. Table 2.2 Structure Summary of Tailing Facility Features Status Max Embankment Height (m) Approx. Footprint Area (ha) Impounded Tailings Volume (m 3 ) Impounded Water Volume (m 3 ) Lagoon A Inactive , Lagoon B Inactive ,700 0 Lagoon C Inactive* ,658,600 0 Lagoon Secondary storage facility ,004, ,000 WFTF Primary storage facility ,500, ,000 *Note: (1) Lagoon C is used for periodic storage of sludge from settling ponds. The WFTF commenced operation in 2006, taking over as the principle storage facility. The WFTF is bounded by the Adit Waste and West Fork umps to the west and south, respectively. Cowboy Ridge, a massive limestone ridge, bounds the east side of the facility. Lagoon is only used when either the wash plant is producing more coal, which exceeds the pipeline capacity to the WFTF, or if the pumping system to the WFTF is down for maintenance. A second pipeline is currently under construction which will provide the capacity to pump all of the tailings to WFTF and Lagoon would only be used if both pipelines to the WFTF were down R Elkview 3rd Party Review.docx Page 6

11 Lagoons C and are the only two facilities currently classified as major dams and major impoundments under the HSRC. The WFTF is classified as major impoundment but not a major dam as it is currently an infill of a pre existing depression formed between natural ground and waste dumps and has not reached the height designated for a major dam. Lagoons A and B are neither major dams nor major impoundments. Lagoons C and both have operational criteria based on the seismic design and the Inflow esign Flood (IF) criteria, as summarized in Table 2.3. Table 2.3 TSF esign Flood and esign PGA Tailings Facility Classification Seismic Criteria Flood Criteria (IF)* Lagoon C High Consequence 1/2500 (PGA = 0.13 g) 1/3 between the 1/1000 and Probable Maximum Flood (PMF) Lagoon Very High Consequence 1/5000 (PGA = 0.18 g) 2/3 between the 1/1000 and Probable Maximum Flood (PMF) *Note that the assumed duration of the inflow design flood is 24 hours 2.3 Site Conditions The site has warm, dry summers and cool winters. Temperatures range from an average daily maximum of 24 C in the summer to an average daily minimum of 12 C in the winter. Average annual precipitation is on the order of 450 mm. General site topography includes moderate to steep slopes on rolling to gullied terrain, with small streams interspersed throughout the property. The area is moderately seismic and the 1/5000 year return period earthquake is a magnitude M7 and a peak ground acceleration (PGA) of 0.18 g R Elkview 3rd Party Review.docx Page 7

12 3 REVIEW OF AM SAFETY INSPECTION REPORT 3.1 General The contents of the SI have been compared against the MEM Guidelines for Annual SI Reports and the results are summarized in Table 3.1. Table 3.1 Executive Summary Summary of SI Conformance Requirement Classification of the dam(s) in terms of Consequence of Failure in accordance with Table 2 1 of the CA am 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 am Safety Review (SR) in accordance with Table 5 1 of the CA am Safety Guidelines (2007). Formal SRs are required every 5 to 10 years (depending on consequence classification) and differ from annual dam safety inspections. The SRs 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. Summary of past years construction (if any) with a description of any problems and stabilization. Plan and representative cross sections. Site Photographs. Review of climate data. Included in SI KCB Observations Latest revision is January 2012 Update is required. Reviewed revision is January 2012 Update for November 2014 is in preparation Last SR completed 2013 and the next SR is scheduled for 2018 Water balance review. Not completed for Lagoons A and B Low consequence structures Freeboard and storage availability (in excess of the design flood). Water discharge system, volumes, and quality. NA The tailing ponds do not discharge water. EVO is developing a site wide water balance Seepage occurrence and water quality. Water quality reported to Ministry of Environment Surface water control and surface erosion Erosion discussed on each structure Phreatic surfaces Piezometer readings given Instrumentation Review Settlement Only Lagoon Lateral movement Only Lagoon R Elkview 3rd Party Review.docx Page 8

13 3.2 Consequence Classification Review The Canadian am Association am Safety Guidelines (2007, revised in 2013) provide a classification of dams based on the consequences of failure, which is based on the following: population at risk: none, temporary or permanent; loss of life; environmental and cultural values; and infrastructure and economics. The dam consequence classifications for the various structures are summarized in Table 3.2. Table 3.2 am Classifications Structure Status Consequence Classification MEM Classification (CA, 2013) (HSRC) Lagoon A ecommissioned Low N/A* Lagoon B ecommissioned Low N/A* Lagoon C ecommissioned High Major am and Major Impoundment Lagoon Secondary storage facility Very High Major am and Major Impoundment WFTF Primary storage facility N/A** Major Impoundment Notes: *not classified as major impoundment or major dam *note: does not fall under CA classification KCB agree with the dam classifications, however, for record purposes, EVO should explicitly document the supporting information that provides the basis for dam classification for each of the consequence categories. 3.3 Instrumentation Review The instrumentation program is appropriately summarized and presented in the SI. KCB observations on the piezometer instrumentation include the following: Piezometers and standpipes located in Lagoon indicate that significant portions of the tailings are drained, with a low phreatic surface within most of the perimeter dam. There are numerous perched water levels associated with different stages of construction and, as a result, it is difficult to interpret the spatial extent of the phreatic surface. The relatively low phreatic surface supports the static stability of the structure. The water levels in the standpipes located in WFTF are rising with the associated rise in the tailings surface, which confirms a direct hydraulic connection. Piezometers and standpipes located in Lagoon C indicate that the phreatic surface is just above the original ground surface indicating a well drained structure. The piezometric levels reported do not indicate any dam safety concerns R Elkview 3rd Party Review.docx Page 9

14 The deformation monitoring program is appropriately summarized in the SI. eformation monitoring in Lagoon included two inclinometers, which are showing acceptable horizontal movements. There are no visual signs of deformation in any of the facilities. 3.4 Stability Review The SI indicates that the dams are stable under the design conditions. Lagoon and Lagoon C have been constructed by the upstream construction method and, consequently, contain significant deposits of loose saturated tailings that could liquefy under seismic loading. The stability of Lagoon was addressed in the (2004) report, which indicated that the structure was stable under seismic loading. The SI recommends reassessment of the seismic stability based on an updated understanding of the current seismicity and KCB agree with this recommendation. Lagoons C and comprise outer dam shells constructed of compacted coarse refuse, which is filter compatible with the fine refuse, consequently there is a low risk of piping. The waste rock dumps that abut the west and south slopes of the WFTF comprise mine waste rock that may not be filter compatible with the fine refuse tailings. The SI Report does not consider that the WFTF is yet a dam as the impoundment level is still below the natural ground surface and the piping potential is not addressed. However, the structure will be raised in the future to become a major dam and, accordingly, this aspect should be addressed. The impoundments at Lagoons A, B, C, and and WFTF do not have spillways and flood protection is provided by storage capacity for the Inflow design flood (IF), which is achieved with a freeboard requirement for each impoundment. The SI report provides documentation for freeboard capacity R Elkview 3rd Party Review.docx Page 10

15 4 REVIEW OF TAILINGS FACILITY STEWARSHIP EVO has a good team in place for managing and constructing the facilities and for providing oversight on the technical, environmental and social aspects. EVO manage and maintain the facility adequately and procedures are well documented. The OMS Manual is complete and procedures are in place to manage and respond to emergencies. As part of the KCB preliminary overview of the OMS, we have the following suggestions for improvement: Prepare a separate organization chart that clearly defines the EVO person responsible for the tailings facility, e.g. Tailings Engineer, who is responsible for the tailing facilities. Identify who the person reports to and what other persons report to the Tailings Engineer for matters pertaining to the tailing facilities. ocument the 4 components of the dam consequence classification, in conjunction with the review of the Inundation Study and any other relevant studies R Elkview 3rd Party Review.docx Page 11

16 5 SUMMARY The assessment of the physical conditions of the dams and associated works is thorough and comprehensive and no significant concerns have been identified. Management systems are in place, including OMS Manual and EPPs. The SI Report is compliant with the MEM Guidelines. For reference purposes the recommendations from the SI Report are summarized in Table 5.1. The SI Report does not consider that the WFTF is yet a dam as the impoundment level is still below the natural ground surface. However, the structure will be raised in the future to become a major dam and, accordingly, KCB recommend that the potential for tailings migrating (piping) into the rockfill be assessed and documented by the Engineer of Record by ecember Table 5.1 Summary of 2014 SI Recommendations () No. Recommendation Summary Source of Recommendation Status/Action Timeline Priority 1 etailed risk assessment New Review of development plan 2013 SI None Survey of upstream slope of development area Tailings header pipeline back from edge Flood routing/water management study 6 Repair slumped areas New 7 No discharge spillway or channel and very little freeboard New Jun New ec New ec SI Permission From Geotechnical. epartment Prior to discharge 8 Removal of overhead pipelines 2013 SI Ongoing Prior to spring 2015 Asrequired 2 N/A Comments This Recommendati on is still applicable EVO currently developing a site wide environmental water management model Closed 4 Still applicable 9 Monitor riprap protection 2013 SI+SR OMS updated Closed 10 Assess design evaluations 2013 SR None Still applicable 11 Stability analysis on westembankment 2013 SR None ec Still applicable 12 Compare slopes of lagoons to dam raise designs 2013 SR None ec Still applicable 13 Check standpipes 2013 SR Updating OMS Closed R Elkview 3rd Party Review.docx Page 12

17 No. Recommendation Summary Source of Recommendation Status/Action Timeline Priority 14 Update OMS, EPP, ERP 2013 SR In progress 2014/ Establish reference lines 2013 SR Reference lines marked Comments Updating EPP, ERP and OMS Superseded by no Method for monitoring deformation along reference New ec lines 17 Prepare water balance 2013 SR None Still applicable 18 Piezometer reading frequency 2013 SR Reduced frequency adopted outside of freshet 19 Lagoon C SR 2013 SR None Remove or grout unused buried pipes Continued monitoring of unused pipes Remedial work on Cossarini Creek Consider rerouting Cossarini Creek 2013 SR New 2013 SR 2013 SR Repairs performed in 2013 Culvert upgrade designs completed OMS to be updated in ec Closed Will be completed tentatively by 2018 Superseded by no. 21 Closed 24 Plot piezometer data 2013 SR one Closed Upgrades designed but not implemented 25 Update OMS, EPP, ERP 2013 SR In progress 3 Refer to no Seismic stability analysis of embankments 2013 SR None ec Still applicable 27 Reference lines to replace Ref. lines have Superseded by 2013 SR observation stations been marked no Method for monitoring ground deformation New ec Flood routing study 2013 SR None Reduced 30 Piezometer reading frequencies 2013 SR frequency N/A Closed adopted 31 Lagoon SR 2013 None EVO has planned to complete next SR by R Elkview 3rd Party Review.docx Page 13

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19 REFERENCES Note that additional references are included in Table 2.1. Environment and Infrastructure () Tailings Storage Facilities West Fork Tailings Facility and Lagoons A, B, C and 2014 am Safety Inspection. November 7, Environment and Infrastructure () West Fork Facility evelopment to El m As Built Report. March 7, Environment and Infrastructure () West Fork Tailings Facility Results of 2013 Site Inspection. July 4, Canadian am Association (CA) Technical Bulletin. am Safety Guidelines (update 2013). Teck Coal (Teck Coal) Inactive Tailings Facilities Emergency Preparedness Plan (EPP) & Emergency Response Plan (ERP). January, Teck Coal (Teck Coal) Lagoon Tailings Facility Emergency Preparedness Plan (EPP) & Emergency Response Plan (ERP). January, Teck Coal (Teck Coal) Operating, Maintenance, and Surveillance Manual Inactive Tailings Facilities Lagoons A, B, & C. January, Teck Coal (Teck Coal) Operating, Maintenance, and Surveillance Manual Tailings eposition Lagoon. January, Teck Coal (Teck Coal) Operating, Maintenance, and Surveillance Manual Tailings eposition West Fork Facility. January, R Elkview 3rd Party Review.docx Page 15