RESPONSE TO BCMEM SCREENING COMMENTS QUANTITATIVE PERFORMANCE OBJECTIVES

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1 DATE January 27, 2016 REFERENCE No. TO Mr. Luke Moger Mount Polley Mining Corporation FROM Germán Pizarro and Terry Eldridge RESPONSE TO BCMEM SCREENING COMMENTS QUANTITATIVE PERFORMANCE OBJECTIVES 1.0 INTRODUCTION This Technical Memorandum addresses the screening comment regarding quantitative performance objectives included in the letter Re: Mines Act permit application Mount Polley Mine Return to Full Operations dated January 21, 2016 provided jointly by the Williams Lake Indian Band (WLIB), Xat sull First Nation (XFN) and the British Columbia Ministry of Energy and Mines (BCMEM) in response to the application for the return to full operations at the Mount Polley Mine. The comment, included under the Geotechnical grouping, is: Quantitative Performance Objectives (QPO s) consistent with Section of the 2015 IEEIRP Report on Mount Polley Tailings Storage Facility Breach were not found in the reviewed documents and are requested. The QPO s should be tabulated in one table. 2.0 QUANTITATIVE PERFORMANCE OBJECTIVES Table 1 presents the quantitative performance objectives for the Mount Polley Tailings Storage Facility (TSF). Design criteria related to regulatory compliance has not been included in this Technical Memorandum. Details of the design criteria for the design of the TSF are presented in Golder (2015). Golder Associates Ltd. Suite Virtual Way, Vancouver, BC, V5M 0C4 Tel: +1 (604) Fax: +1 (604) Golder Associates: Operations in Africa, Asia, Australasia, Europe, North America and South America Golder, Golder Associates and the GA globe design are trademarks of Golder Associates Corporation.

2 Table 1: TSF Quantitative Performance Objectives Quantitative Performance Objective Value Source / Comment Impoundment Filling Schedule TSF Capacity 970 m Tailings Elevation 27.8 million tonnes 20.6 million m 3 at 1.35 tonnes / m 3 and 1.0 % deposition angle. Mine plan (MPMC 2015a). Impoundment Filling 970 m Tailings Elevation Q Based on deposition starting on May 2016 and a Schedule 22,000 tonnes/day nominal tailings production rate. Beach Width Portion of beach above operating pond level. Minimum Beach Width 100 m Minimum during normal operating conditions after beach developed along Corner 1 embankment. Water Balance Operating Pond Minimum 1 million m 3 Provided by MPMC. Storage Volume Maximum 1.5 million m 3 Based on maintaining 100 m beach width. Provided by MPMC. Minimum 3 m Pond depth Minimum pond depth at barge location. Maximum 4 m Based on maintaining 100 m beach width. Construction Materials Availability and Schedule Construction Schedule To elevation 970 m Year 2 Golder (2015). Till (Zone S) 73,950 m 3 (to El. 970) As needed for construction Sourced from specific borrow areas or from the excavation of water management structures. Transition (Zone T), Filter (Zone F), Drain Rock and Filter Sand Upstream fill (Zone U) Tailings Sand or Rockfill 69,230 m 3 (to El. 970) 10,000 to 20,000 tonnes/day 424,200 m 3 (to El. 970) Rockfill (Zone C) 1,134,300 m 3 (to El. 970) 16,300 m 3 /day (tailings discharge) 11 million tonnes/year (direct haul run-of-mine waste rock) 11 million tonnes/year (direct haul run-of-mine waste rock) Sourced from crushing waste rock (mining operations or waste rock dumps) or from screening waste rock and filter from borrow sources. Sourced from tailings discharge. Additional tailings available within TSF. Provided by MPMC. Sourced from direct haul run-of-mine waste rock. Additional rock available from dumps/stockpiles Provided by MPMC. Sourced from direct haul run-of-mine waste rock. Additional rock available from dumps/stockpiles. 2/6

3 Quantitative Performance Objective Value Source / Comment Survey Monuments Trigger Levels for Response to Instrumentation Data gathering frequency Once every two weeks. Horizontal displacement measured perpendicular Horizontal and/or vertical to the embankment. displacement > 0.01m. Data gathering frequency Once every two weeks. Slope Inclinometers Slope Acceleration Arrays (SAAs) Data gathering frequency Downstream displacement > 3 mm in the glaciolacustrine unit (GLU). Downstream displacement > 5 mm in other units. Daily and submitted every two weeks. Displacement > 1 mm in the GLU. Displacement > 5 mm in other units. Wander plot to be used to confirm direction of movement. Data gathering frequency Once every two weeks. Piezometers Increase or decrease > 15 m from baseline elevation readings at corner 1 Upper GLU unit. Increase or decrease > 25 m from baseline elevation readings in GLU unit in other areas. Baseline elevation readings listed in OMS manual (MPMC 2015b). 3/6

4 The instrumentation reading frequency will be adjusted based on conditions and construction activities being carried out. If the trigger levels are exceeded, the instruments are to be re-read immediately. If the initial readings are proven accurate, the Engineer-of-Record (EoR) is to be contacted immediately. If a change below the trigger level is recorded in multiple instruments in a similar location, the EoR is to be notified immediately. Interpretation of the instrumentation readings is the responsibility of the EoR. Instruments reading data is to be submitted to the EoR for review every two (2) weeks. Interpretation and reporting of the readings will be completed twice a year in the spring after freshet and in the fall as part of the annual dam inspection. 3.0 CLOSURE The reader is referred to the Study Limitations, which follows the text and forms an integral part of this memorandum. We trust the above information adequately addresses the joint comments provided by the WLIB, XFN and BCMEM. If you have any questions or requirements, please contact the undersigned. GOLDER ASSOCIATES LTD. Germán Pizarro, P.Eng. Geotechnical Engineer Terry Eldridge, P.Eng. Principal, Engineering Manager GP/TLE/jc/ls/jc/bb Attachment: Study Limitations \\golder.gds\gal\burnaby\final\2014\dynamics numbers - mining division\ \ tm-rev0-8000\ tm-rev quantitative performance objectives 27jan_16.docx 4/5

5 REFERENCES Golder Associates Ltd. (Golder) Mount Polley Tailings Storage Facility Design Basis. Technical memorandum TM-Rev prepared for Mount Polley Mining Corporation. Submitted August 27, Mount Polley Mining Corporation (MPMC). 2015a. Mine plan. File received on October 13, Mount Polley Mining Corporation (MPMC). 2015b. Mount Polley Mine Tailings Storage Facility Operation, Maintenance and Surveillance Manual. Revision 15 dated December 15, /5

6 STUDY LIMITATIONS Golder Associates Ltd. (Golder) has prepared this document in a manner consistent with that level of care and skill ordinarily exercised by members of the engineering and science professions currently practising under similar conditions in the jurisdiction in which the services are provided, subject to the time limits and physical constraints applicable to this document. No warranty, express or implied, is made. This document, including all text, data, tables, plans, figures, drawings and other documents contained herein, has been prepared by Golder for the sole benefit of Mount Polley Mining Corporation (MPMC). It represents Golder s professional judgement based on the knowledge and information available at the time of completion. Golder is not responsible for any unauthorized use or modification of this document. All third parties relying on this document do so at their own risk. The factual data, interpretations, suggestions, recommendations and opinions expressed in this document pertain to the specific project, site conditions, design objective, development and purpose described to Golder by MPMC, and are not applicable to any other project or site location. In order to properly understand the factual data, interpretations, suggestions, recommendations and opinions expressed in this document, reference must be made to the entire document. This document, including all text, data, tables, plans, figures, drawings and other documents contained herein, as well as all electronic media prepared by Golder are considered its professional work product and shall remain the copyright property of Golder. MPMC may make copies of the document in such quantities as are reasonably necessary for those parties conducting business specifically related to the subject of this document or in support of or in response to regulatory inquiries and proceedings. Electronic media is susceptible to unauthorized modification, deterioration and incompatibility and therefore no party can rely solely on the electronic media versions of this document. 1/1