mpmc short-term effluent discharge tar (pdf)

May 29, 2015

MOUNT POLLEY MINE: SHORT TERM EFFLUENT DISCHARGE

Technical Assessment Report in Support of an Effluent Permit Amendment

REPO

RT

Reference Number: 1411734-030-R-Rev0-12000Distribution:Mount Polley Mining Corporation - 1 Electronic Copy Ministry of Environment - 1 Electronic Copy Ministry of Energy and Mines - 1 Electronic Copy Williams Lake Indian Band - 1 Electronic Copy Soda Creek Indian Band - 1 Electronic Copy Golder Associates Ltd. - 1 Hard Copy

Submitted to:Mount Polley Mining Corporation Box 12 Likely, BC V0L 1N0

MOUNT POLLEY MINE: TECHNICAL ASSESSMENT REPORT

May 29, 2015 Reference No. 1411734-030-R-Rev0-12000 i

EXECUTIVE SUMMARY

BACKGROUND The Mount Polley Mine is a copper-gold mine owned and operated by Mount Polley Mining Corporation (MPMC), a subsidiary of Imperial Metals Corporation. The mine site is located 56 km northeast of Williams Lake, British Columbia (BC). As a result of a foundation failure of the Tailings Storage Facility (TSF), mining and milling operations at the mine have been suspended since August 4, 2014, and currently all mine contact water is conveyed to and stored in the Springer Pit, which has a finite capacity. There is a predicted surplus volume of mine contact water and a resulting need to develop a short-term water management plan whether or not Return to Restricted Operations is permitted. Authorization of the discharge of treated effluent as a short-term water management strategy requires an amendment of Permit 11678. Amendment of this permit requires a technical assessment of the effluent discharge to identify whether or not receiving water uses are impaired. That assessment, contained in this Technical Assessment Report (TAR) is used by the Ministry of Environment (MoE) in their permitting decisions and is used by the discharger, in this case MPMC, as part of their due diligence to verify that they meet the requirements of the Environmental Management Act (EMA) and the Metal Mining Effluent Regulation (MMER).

APPROACH The TAR presented here describes the receiving environment, an options analysis of discharge locations and water treatment technologies, and predicted effluent and receiving environment quality for the proposed short-term water management system.

The water treatment system comprises lime addition and an active treatment process to remove particulate matter from the Springer Pit water, followed by discharge to Hazeltine Creek and subsequent conveyance by pipe from the upper sedimentation pond in lower Hazeltine Creek to Quesnel Lake. Dual pipes are proposed, with nominal discharge depths of 10 and 20 m to improve dilution. The selection of the water treatment technology and discharge location for short-term water management is a result of a Best Available Technology (BAT) assessment and preliminary modelling of options, followed by consultation with regulators, First Nations and the community. Consultation with the various parties on this effluent discharge permit amendment has been an ongoing process in the development of the TAR and further consultation (30 days) is a statutory requirement following submission of the application and supporting TAR. The application now being pursued has benefited from this early, voluntary consultation that MPMC have elected to undertake. However, Golder Associates Ltd. (Golder) notes that while the parties have provided helpful and constructive input during their participation, their comments were not final and all parties, including the public, may comment on the application during the 30 day public comment period.

Quesnel Lake and Quesnel River remain potential discharge options for long-term water management, and additional studies will be undertaken to determine which of these provides the highest overall level of environmental protection, as well as relative cost of the options. However, in the short term, treated effluent is proposed to be discharged to Hazeltine Creek and then Quesnel Lake via submerged pipe. This short-term discharge option will be replaced with the long-term option before Hazeltine Creek is rehabilitated as fish habitat.


May 29, 2015 Reference No. 1411734-030-R-Rev0-12000 ii

The technical evaluation of the short-term discharge option presented here involved the identification of BAT for effluent treatment, identification of proposed effluent permit limits, an evaluation of how an effluent at these permit limits would behave, and prediction of effluent dilution in the receiving environment to identify the potential for environmental impacts on receiving environment use.

The impact assessment was based on a structured and transparent process guided by MoE policy, guidance, and statute. For effluent discharges to aquatic receiving environments in BC, both federal and provincial environmental legislation applies. While a permit to discharge is required by the provincial government, there is no federal permit requirement. Federal requirements are imposed on a metal mine discharge by regulation. While this TAR has been prepared in support of a provincial permit amendment process, federal requirements have also been addressed in the evaluations carried out because MPMC must comply with both provincial and federal laws.

The common expectations under the MMER (federal) and EMA (provincial) are three-fold:

The effluent should not be acutely lethal. The effluent constituents must not exceed the numeric limits presented in the MMER (Schedule 4). Chronic sublethal effects should not occur outside of the initial dilution zone (IDZ). A lack of chronic

sublethal effects are (conservatively) predicted when the constituent of concern has a concentration lower than the BC ambient water quality guidelines (BC WQG).

The IDZ is the three-dimensional zone around the point of discharge where mixing of the effluent and the receiving water occurs. For Quesnel Lake, the IDZ was defined as a cylindrical body of water around the Hazeltine Creek pipe outfall with a lateral radius of 100 m. Predicted concentrations of constituents at the edge of the IDZ for the mixed effluent plume were compared to applicable ambient BC WQGs. Comparisons were made to the most conservative guideline for each constituent, representing the most sensitive receiving environment use relevant to the West Basin of Quesnel Lake. The ambient chemistry of Quesnel Lake was used to calculate applicable guidelines.

Typically, these were the BC WQGs for the protection of aquatic life. BC WQGs are considered to be conservative environmental quality benchmarks with built-in safety factors and therefore represent concentrations at which there is confidence that designated uses will not be adversely affected. Where a constituent concentration is predicted to be less than its applicable BC WQG, impacts on designated uses as a result of the effluent discharge are not predicted.

The permit limits proposed in this TAR represent upper-bound estimates of treated effluent quality predicted by computer simulation modelling based on conservative assumptions. Both the expected effluent quality predicted by the model and the proposed permit limits were evaluated to determine the potential for acute lethality at the point of discharge. To determine a priori whether the proposed permit limits would be protective of water quality and aquatic resources in the Quesnel Lake receiving environment, computer simulation modelling was undertaken to predict water quality at the edge of the IDZ. A conceptual receiving environment monitoring program has been proposed to confirm that the proposed permit limits are protective of water quality and aquatic resources in Quesnel Lake. It is anticipated that this will be modified to harmonize the permit monitoring program with the post-breach monitoring and the MMER Environmental Effects Monitoring program.


May 29, 2015 Reference No. 1411734-030-R-Rev0-12000 iii

PROPOSED EFFLUENT PERMIT LIMITS AND IMPACT ASSESSMENT FINDINGS The proposed effluent permit limits are below the MMER limits for total suspended solids, arsenic, copper, and zinc. Compliance with the permit will therefore simultaneously result in compliance with the limits contained within the MMER. The treated effluent itself is not predicted to be acutely lethal at the point of discharge to Hazeltine Creek, a finding supported by the absence of acute toxicity in the untreated water in the Springer Pit to rainbow trout and Daphnia magna. Adverse effects on aquatic life and other receiving environment uses (i.e., drinking water sources, recreational contact, wildlife) in Quesnel Lake are not expected based on the impact assessment. Expected and upper bound IDZ water quality estimates are lower than applicable BC WQGs or are not distinguishable from baseline concentrations in Quesnel Lake (less than a 20% difference). Therefore, pollution is unlikely to occur as a result of the proposed treated effluent discharge based on comparison to conservative receiving environment benchmarks.

UNCERTAINTY IN THE ASSESSMENT The assessment was necessarily a predictive exercise (there is at present no treated effluent discharge), with the objective of identifying whether or not the proposed treated effluent will result in adverse effects to the receiving environment. Assessing impact before the discharge occurs requires the use of various predictive tools, such as effluent dilution modeling and comparison to established benchmarks. While these tools are useful and provide a reasonable prediction of likely circumstances, it is important to identify the main uncertainties associated with a predictive assessment and to consider the implications of these uncertainties on predictions made. The main areas of uncertainty identified in the present assessment, which are described in greater detail in the report, are as follows:

Plume dilution and surface water quality are as predicted by the computer simulation models.

Background water quality concentrations were as identified in the data set available for Quesnel Lake.

Treated effluent concentrations from the proposed treatment system.

Implications of the interaction of contaminant mixtures with regard to toxicity.

When uncertainty is taken into consideration, the overall prediction that pollution will not occur remains unchanged.


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 iv

Statement of Limitations

This report was prepared for the exclusive use of MPMC. The inferences concerning the data, site and receiving environment conditions contained in this report are based on information obtained during investigations conducted at the site by Golder, other consultants and MPMC, and are based solely on the condition of the site at the time of the site studies and subsequent investigations and remediation and other information obtained by Golder, as described in this report. Soil, surface water and groundwater conditions may vary with location, depth, time, sampling methodology, analytical techniques and other factors.

In evaluating the subject site and water quality data, Golder has relied in good faith on information provided. The factual data, interpretations and recommendations pertain to a specific project as described in this report, based on the information obtained during the assessment by Golder on the dates cited in the report, and are not applicable to any other project or site location. Golder accept no responsibility for any deficiency or inaccuracy contained in this report as a result of reliance on the aforementioned information.

The findings and conclusions documented in this report have been prepared for the specific application to this project, and have been developed in a manner consistent with that level of care normally exercised by environmental professionals currently practising under similar conditions in the jurisdiction. Golder makes no other warranty, expressed or implied and assumes no liability with respect to the use of the information contained in this report at the subject site, or any other site, for other than its intended purpose.

Any use which a third party makes of this report, or any reliance on or decisions to be made based on it, are the responsibility of such third parties. Golder accepts no responsibility for damages, if any, suffered by any third party as a result of decisions made or action based on this report. All third parties relying on this report do so at their own risk. Electronic media is susceptible to unauthorized modification, deterioration and incompatibility and therefore no party can rely upon the electronic media versions of Golders report or other work product. Golder is not responsible for any unauthorized use or modifications of this report.

MPMC may rely on the information contained in this report subject to the above limitations.

Golder makes no other representation whatsoever, including those concerning the legal significance of its findings, or as to other legal matters touched on in this report, including, but not limited to, ownership of any property, or the application of any law to the facts set forth herein. With respect to regulatory compliance issues, regulatory statutes are subject to interpretation. These interpretations and the regulations themselves may change over time, thus MPMC should review these issues.

If new information is discovered during future work, including excavations, sampling, soil boring, predictive geochemistry or other investigations, Golder should be requested to re-evaluate the conclusions of this report and to provide amendments, as required, prior to any reliance upon the information presented herein. The validity of this report is affected by any change of site conditions, purpose, development plans or significant delay from the date of this report in initiating or completing the project.


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 v

LIST OF ABBREVIATIONS AND ACRONYMS 7Q2 2-year return period 7-day low flow + plus - minus > greater than < less than less than or equal to AP acid potential BAT best available technology BC British Columbia BC WQG British Columbia Water Quality Guideline CaCO3 calcium carbonate CCS Central Collection Sump CMN Community Mapping Network COSEWIC Committee on the Status of Endangered Wildlife in Canada COPC Constituent of Potential Concern CRA commercial, recreational or Aboriginal (Cr(VI)) chromium VI DOC dissolved organic carbon DFO Department of Fisheries and Oceans Canada EC Environment Canada EC25 25% effective concentration EEM environmental effects monitoring EMA Environmental Management Act FIM foreshore inventory and mapping Golder Golder Associates Ltd. HCT humidity cell test ICHwk2 interior cedar hemlock; wet cool; subzone 2 ICHmk3 interior cedar hemlock; moist cool; subzone 3 IDZ initial dilution zone LC50 concentration that is lethal to 50% of test population MDL method detection limit MAD mean annual discharge MAF mean annual flood masl metres above sea level MEM BC Ministry of Energy and Mines


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 vi

MoE BC Ministry of Environment MMER Metal Mining Effluent Regulation Minnow Minnow Environmental Inc. MPMC Mount Polley Mining Corporation NPA Navigation Protection Act N/A not applicable PAG potentially acid generating PEEIAR Post-Event Environmental Impact Assessment Report PEL probable effects level QA/QC quality assurance/quality control Q10 1:10-year flow Q100 1:100-year flow Q200 1:200-year flow SQG sediment quality guidelines TAR technical assessment report TDS total dissolved solids TEM terrestrial ecosystem mapping TIC total inorganic carbon TOC total organic carbon TOR terms of reference TSF tailings storage facility TSS total suspended solids USA United States of America WDR Waste Discharge Regulation WQG Water Quality Guideline YOY young-of-year


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 vii

UNITS % percent C degrees Celsius

s/cm micro Siemens per centimetre ha hectares h hour km kilometre km2 square kilometre m metre m2 square metre m3 cubic metres m3/s cubic metres per second mg/L milligrams per litre NTU nephelometric turbidity units


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 viii

Table of Contents

EXECUTIVE SUMMARY ............................................................................................................................................................ i

STATEMENT OF LIMITATIONS .............................................................................................................................................. iv

LIST OF ABBREVIATIONS AND ACRONYMS ........................................................................................................................ v

UNITS ...................................................................................................................................................................................... vii

1.0 INTRODUCTION ............................................................................................................................................................... 1

1.1 Background ......................................................................................................................................................... 1

1.2 Company Information and Property Description .................................................................................................. 2

1.3 Terms of Reference ............................................................................................................................................. 3

2.0 PROJECT DESCRIPTION ................................................................................................................................................ 5

2.1 Project Rationale ................................................................................................................................................. 5

2.2 Proposed Treatment and Discharge .................................................................................................................... 6

2.2.1 Options Analysis ............................................................................................................................................ 6

2.2.1.1 Water Treatment Technology Options ........................................................................................................ 7

2.2.1.2 Effluent Management Options .................................................................................................................... 7

2.2.2 Options Selected for Short-term Water Management .................................................................................... 9

2.2.3 Requirements for Sewage Disposal ............................................................................................................. 11

2.3 Regulatory Setting ............................................................................................................................................. 11

2.3.1 Environmental Management Act .................................................................................................................. 11

2.3.2 Fisheries Act ................................................................................................................................................ 12

2.3.3 Metal Mining Effluent Regulation ................................................................................................................. 12

2.3.4 Navigation Protection Act ............................................................................................................................. 12

2.3.5 Water Act and Regulation ............................................................................................................................ 12

2.3.1 Land Tenure ................................................................................................................................................. 13

3.0 RECEIVING ENVIRONMENT ......................................................................................................................................... 14

3.1 Outfall Location .................................................................................................................................................. 14

3.2 Physical Environment ........................................................................................................................................ 14

3.2.1 Site Geology ................................................................................................................................................ 14

3.2.1.1 Site Geochemistry .................................................................................................................................... 15


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 ix

3.2.1.1.1 Summary of Geochemical Findings ....................................................................................................... 16

3.2.1.2 Site Hydrogeology .................................................................................................................................... 17

3.2.2 Climate and Hydrology ................................................................................................................................. 17

3.2.2.1 Climate ..................................................................................................................................................... 17

3.2.2.1.1 Temperature .......................................................................................................................................... 18

3.2.2.1.2 Precipitation .......................................................................................................................................... 19

3.2.2.2 Local Hydrology ........................................................................................................................................ 19

3.2.2.2.1 Design Flows ......................................................................................................................................... 20

3.2.2.3 Hydrologic Capacity .................................................................................................................................. 20

3.2.3 Water and Sediment Quality ........................................................................................................................ 21

3.3 Biophysical Environment ................................................................................................................................... 27

3.3.1 Fish and Fish Habitat ................................................................................................................................... 27

3.3.2 Vegetation .................................................................................................................................................... 29

3.3.3 Wildlife and Wildlife Habitat .......................................................................................................................... 30

3.4 Receiving Environment Uses ............................................................................................................................. 31

3.4.1 Fisheries ...................................................................................................................................................... 31

3.4.2 Parks and Recreational Activities ................................................................................................................. 31

3.4.3 Agricultural ................................................................................................................................................... 32

3.4.4 Other Uses ................................................................................................................................................... 32

3.4.5 BC Water Quality Guidelines for End Uses .................................................................................................. 33

4.0 SPRINGER PIT EFFLUENT ........................................................................................................................................... 35

4.1 Untreated Source Water Quality ........................................................................................................................ 36

4.1.1 Source Water Quality ................................................................................................................................... 36

4.1.2 Effluent Discharge Constituents and Potential Effects ................................................................................. 38

4.1.2.1 pH ............................................................................................................................................................. 38

4.1.2.2 Total Suspended Solids ............................................................................................................................ 38

4.1.2.3 Nitrate ....................................................................................................................................................... 39

4.1.2.4 Sulphate ................................................................................................................................................... 39

4.1.2.5 Metals ....................................................................................................................................................... 39

4.1.3 Effluent Toxicity Testing ............................................................................................................................... 40


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 x

4.2 Treated Effluent ................................................................................................................................................. 40

4.2.1 Effluent Chemistry ........................................................................................................................................ 40

4.2.2 Proposed Effluent Permit Limits ................................................................................................................... 44

4.2.3 Potential for Indirect Exposure to Selenium and Molybdenum ..................................................................... 47

4.2.3.1 Molybdenum ............................................................................................................................................. 47

4.2.3.2 Selenium ................................................................................................................................................... 47

5.0 IMPACT ASSESSMENT ................................................................................................................................................. 48

5.1 Approach to Modelling Effluent Discharge ......................................................................................................... 48

5.1.1 Near-field ..................................................................................................................................................... 48

5.1.2 Far-field ........................................................................................................................................................ 48

5.2 Assessment of Impacts in Quesnel Lake ........................................................................................................... 49

5.2.1 Assessment Approach ................................................................................................................................. 49

5.2.2 Impact Assessment ...................................................................................................................................... 52

6.0 UNCERTAINTY ASSESSMENT ..................................................................................................................................... 53

7.0 MONITORING ................................................................................................................................................................. 55

7.1 Compliance Monitoring ...................................................................................................................................... 55

7.1.1 Monitoring .................................................................................................................................................... 55

7.1.2 Reporting ..................................................................................................................................................... 57

7.2 Receiving Environment Monitoring .................................................................................................................... 57

7.2.1 Monitoring .................................................................................................................................................... 57

7.2.2 Reporting ..................................................................................................................................................... 58

7.3 Quality Assurance .............................................................................................................................................. 59

8.0 CLOSURE ....................................................................................................................................................................... 60

9.0 REFERENCES ................................................................................................................................................................ 61


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 xi

TABLES Table 1: Concordance with Generic Terms of Reference for Technical Assessment Reports under the Environmental

Management Act ....................................................................................................................................................... 3

Table 2: Options Analysis Attendees ......................................................................................................................................... 6

Table 3: Local and Regional Climate Stations for the Mount Polley Mine ................................................................................ 18

Table 4: Likely Climate Station Monthly Temperatures (1974 1993) ..................................................................................... 18

Table 5: Design Flows for Potential Receiving Waters ............................................................................................................. 20

Table 6: Far-field Dilution Ratios for Potential Treated Effluent Discharge Locations .............................................................. 21

Table 7: Surface Water Quality in Quesnel Lake East of Cariboo Island, 8 August, 2014 to 16 December, 2014 ................... 24

Table 8: Documented Fish Species in Quesnel Lake ............................................................................................................... 28

Table 9: At-Risk Terrestrial Wildlife Species Potentially Present in the Hazeltine Creek Corridor ............................................ 30

Table 10: BC Water Quality Guidelines for Receiving Environment Uses ................................................................................ 33

Table 11: Water Quality Model Constituent List ....................................................................................................................... 36

Table 12: Summary of Predicted Untreated Springer Pit Water Quality ................................................................................... 37

Table 13: Summary of Predicted Treated Springer Pit Water Quality ...................................................................................... 41

Table 14: 95th Percentile Values for Springer Pit Water Quality and Proposed Effluent Permit Limits for the Short-Term Discharge of Treated Springer Pit Effluent to Quesnel Lake via Hazeltine Creek .......................................... 46

Table 15: Summary of Predicted Quesnel Lake Water Quality at the Edge of Initial Dilution Zone .......................................... 50

Table 16: Identified Uncertainties in the Technical Assessment Report for the Proposed Short-Term Effluent Discharge ................................................................................................................................................................ 53

Table 17: Overview of Monitoring Locations and Frequencies ................................................................................................. 55

Table 18: Parameters to be analyzed in the Discharge and Receiving Environment as part of the Proposed Monitoring Program .................................................................................................................................................................. 55

Table 19: Proposed Bioassay Sampling for the Effluent Discharge ......................................................................................... 57

FIGURES Figure 1: Study Area and Baseline Water Quality Monitoring Stations ...................................................................................... 4

Figure 2: Outfall Locations Options Analysis .............................................................................................................................. 8

Figure 3: Proposed Short-term Pipe Route from Hazeltine Creek to Quesnel Lake Subsurface. ............................................. 10

Figure 4: Post-event Instantaneous (A) and Rolling 30-day Average (B) Total and Dissolved Copper Concentrations in Stations QUL-66 (-54,-55,-56) and QUL-18 in the West Basin of Quesnel Lake. .................................................... 22

Figure 5: Post-event Instantaneous (A) and Rolling 30-day Average (B) Total and Dissolved Copper Concentrations in Stations QUL-120/A east of Cariboo Island in Quesnel Lake. ................................................................................. 23

Figure 6: Conceptual Springer Pit Model ................................................................................................................................. 35


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 xii

APPENDICES APPENDIX ASite Wide Water Balance

APPENDIX BWater Quality Modelling Report

APPENDIX CAdditional Predictions of Water Level and Seepage in the Springer Pit for May 2015 to December 2016

APPENDIX DMount Polley Options Analysis for Discharge Location and Water Treatment Technology

APPENDIX EConceptual Design of Diffusers in Quesnel Lake

APPENDIX FConceptual Diffuser Design and Near-field Modelling in Quesnel Lake

APPENDIX GProposed Water Treatment System for Short-term Water Management

APPENDIX HGeochemistry Reports

APPENDIX IDetailed Concordance Table


May 29, 2015 Report No. 1411734-030-R-Rev0-12000 1

1.0 INTRODUCTION The Mount Polley Mine is a copper-gold mine owned and operated by Mount Polley Mining Corporation (MPMC), a subsidiary of Imperial Metals Corporation. The mine site is located 56 km northeast of Williams Lake, British Columbia (BC) (Figure 1). As a result of a foundation failure of the Tailings Storage Facility (TSF) on August 4, 2014, mining and milling operations at the mine have been suspended and currently all mine contact water is conveyed to and stored in the Springer Pit, which has a finite capacity. There is a predicted surplus volume of mine contact water and a resulting need to develop a short-term water management plan whether or not Return to Restricted Operations is permitted. Authorization of the discharge of treated effluent as a short-term water management strategy requires an amendment of Permit 11678. Amendment of this permit requires a technical assessment of the effluent discharge to identify whether or not receiving water uses are impaired. That assessment, contained in this Technical Assessment Report (TAR) is used by the Ministry of Environment (MoE) in their permitting decisions and is used by the discharger, in this case MPMC, as part of their due diligence to verify that they meet the requirements of the Environmental Management Act (EMA) and the Metal Mining Effluent Regulation (MMER).

Golder Associates Ltd. (Golder) was retained by MPMC to prepare a TAR for an effluent permit amendment application for the short-term discharge of mine contact water. A long-term water management plan for the mine is being developed in parallel, and it is anticipated that amendment(s) for applicable permits will be sought in the future.

This TAR has been conducted in parallel with two (2) closely related undertakings. First, a permit amendment application has been submitted to the BC Ministry of Energy and Mines (MEM) and the MoE under the BC Mines Act and EMA for a Return to Restricted Operations (MPMC 2015). Second, the impacts of the TSF breach on the receiving environment are being evaluated separately as part of a Post-Event Environmental Impact Assessment. Efforts have been made to align the TAR with work being conducted for these initiatives.

1.1 Background The Mount Polley Mine operated from August 1997 to September 2001, at which point it was placed on care and maintenance due to low metal prices. The mine re-opened in March 2005 as a result of improved metal prices and the discovery of significant new ore reserves. A detailed description of the mine, including past mining and milling operations, waste and water management, and environmental management systems is available in MPMC (2009) and in the permit amendment application for a Return to Restricted Operations (MPMC 2015). The mine remained in operation from 2005 until the TSF breach occurred on August 4, 2014, and has not been in operation since that time.

It is the objective of MPMC to return Mount Polley Mine to full operation; however, this will be a staged process and additional permit amendments will be required. In the interim, a Return to Restricted Operations M-200 Permit Amendment Application (Revision 1) was submitted by MPMC to the BC MEM and MoE on March 20, 2015 (MPMC 2015). The purpose of the restricted operations application is to provide an option for MPMC that would mitigate detrimental effects that a prolonged shutdown would entail, including retention of skilled workers, while providing resources to continue remediation work. Under the proposed restricted operating conditions, open pit and underground mining activities and milling will resume largely as previously permitted, but will be limited to a maximum of 4,000,000 tonnes (t) of ore. Ore will be processed at



approximately half of the full operational throughput. Tailings generated as a result of this milling would be deposited in the Springer Pit, where they would be contained subaqueously in-pit. Depending on mine planning and permitting related to full restart of the mine, those tailings could be transferred to a reconstructed TSF at a later date. Details of the proposed mining, milling, process water source, and management of surplus process water and tailings are described in Return to Restricted Operations M-200 Permit Amendment Application Revision 1 of MPMC (2015).

Pre-breach, mine contact water was stored in the TSF or open pits per Section 2.4 of the EMA Permit 11678. Post-breach, site water management was modified to direct all mine contact water to the Springer Pit. To collect water that could not be directly conveyed to the Springer Pit, the Central Collection Sump (CCS) was excavated downstream of the open pits and waste dumps. Water from the TSF and other mine contact water from the breach are currently pumped to the CCS, from where it is conveyed to the Springer Pit via the Booster Station. This portion of the water management system became operational on September 4, 2014.

As described in Section 2.1, the Springer Pit is accumulating a surplus of water that will need to be discharged to minimize risk of future uncontrolled releases. This TAR describes the receiving environment, provides an options analysis of discharge locations and water treatment technologies, and provides predicted receiving environment quality and potential environmental impact for a proposed short-term water management system.

1.2 Company Information and Property Description Imperial Metals Corporation is a Canadian mining company active in the acquisition, exploration, development, mining and production of base and precious metals, with a focus on western North America. Key properties are: Mount Polley, an open pit copper-gold mine with a developing underground project in south-central BC (currently on care and maintenance); Huckleberry, an open pit copper/molybdenum mine (50% interest) in west-central BC; Red Chris, a commissioning stage copper-gold property in northwest BC; Sterling, a heap leach gold mine in Nevada, USA; and Ruddock Creek, a predevelopment stage zinc/lead property (50% interest) in southeast BC.

The main contact information for the company is:

Imperial Metals Corporation

Don Parsons, Chief Operating Officer 580 Hornby Street, Suite 200 Vancouver, BC V6C 3B6

Mount Polley Mine, located 56 kilometres northeast of Williams Lake, BC, is owned by MPMC, a wholly owned subsidiary of Imperial Metals Corporation. The property covers 18,931 hectares, consisting of seven (7) mining leases totaling 2,007 hectares, and 43 mineral claims encompassing 16,787 hectares.



1.3 Terms of Reference Generic Terms of Reference (TOR) outlined in the Technical Guidance 1: Environmental Management Act Applications (MoE 2014) are intended for proponents of major mine projects applying for an effluent discharge permit under the EMA. These TOR have been adapted to the current TAR and are listed in Table 1 to verify concordance with provincial guidance. A detailed concordance table is provided in Appendix H.

Consultation with regulators and key stakeholders on this effluent discharge permit amendment has been an ongoing process and will be documented in a consultation report prepared by MPMC under separate cover, on conclusion of the statutory consultation period.

An Application for Authorization to Discharge Waste under the Environmental Management Act will also be submitted separately to MoE.

Table 1: Concordance with Generic Terms of Reference for Technical Assessment Reports under the Environmental Management Act

Provincial Guidance Relevant Section in this Technical Assessment Report

Project description and overview

Introduction 1.0 Project description 1.0

Baseline information

Meteorology and climate 3.2.2 Geology 3.2.1 Topography, surface drainage features, natural hazards 3.2.2 Water quantity 3.2.2.2, 3.2.2.3 and Appendix A Water quality 3.2.3 and Appendix B Sediment quality 3.2.3 Aquatic resources 3.3.1, 3.4.1 and 5.2

Discharges and treatment

Specific information requirements for storage and effluent discharges 2.2 and 4.0

Information requirements for wastewater treatment plants 2.2 Site contamination Not applicable Requirements for sewage disposal 2.2.3

Environmental effects prediction

Groundwater quantity and quality 3.2.1.1 and Appendix B and C Surface water quantity and quality 4.0, 5.0, Appendix A and B Aquatic resources and other receptors 5.2.2 Safe discharge plans 4.2

Discharges and environmental monitoring requirements for EMA permits

Discharge monitoring 7.1 Receiving environment monitoring 7.2 Aquatic effects monitoring 7.2 Quality assurance requirements 7.3

Description of water quality thresholds

Water quality guidelines 5.2.1 Additional science-based water quality thresholds Not applicable

Risk assessment Section 5.2 Impacts to receiving environment Notes: as outlined by MoE (2014)

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

!(

QUESNEL LAKE

POLLEY LAKE

HAZELTINE CREEKEDNEYCREEK

QUESN EL RIVER

BOOTJACK LAKE

CARIBOOISLAND

TAILINGSSTORAGEFACILITY

MOUNTPOLLEYMINE SITEQUL-ZOO-8

QUL-ZOO-8a

QUL-19QUL-31a

QUL-40QUL-40a

QUL-79

QUL-87

QUL-112QUL-119

QUL-120QUL-120a

QUL-112a

PATH: \

\golde

r.gds\g

al\burn

aby\CA

D-GIS\C

lient\Im

perial_

Metals

_Corp\M

ount_P

olley_M

ine\99

_PROJE

CTS\1

411734

\02_PR

ODUC

TION\1

2000_W

ATER_M

ANAG

EMEN

T\MXD

\Repor

t\Techn

ical_As

sessme

nt\MP_1

411734

_Figur

e_01_S

tudy_A

rea_an

d_Base

line_W

ater_M

onitori

ng.mxd

IF THIS

MEAS

UREM

ENT D

OES N

OT MA

TCH W

HAT IS

SHOW

N, THE

SHEE

T SIZE

HAS B

EEN MO

DIFIED

FROM

: ANSI B

25mm

0

0 3 6

1:120,000 KILOMETRESCLIENTIMPERIAL METALSMOUNT POLLEY MINING CORPORATION

REFERENCES1. WATER MONITORING STATIONS OBTAINED FROM MOUNT POLLEY MINING CORPORATION.2. WATERCOURSE, LAKE AND KEY MAP DATA OBTAINED FROM CANVEC DEPARTMENT OFNATURAL RESOURCES CANADA. ALL RIGHTS RESERVED.3. PROJECTION: UTM ZONE 10; DATUM: NAD 1983PROJECTMOUNT POLLEY MINETECHNICAL ASSESSMENT REPORTTITLESTUDY AREA AND BASELINE WATER QUALITY MONITORINGSTATIONS1411734 12000 0 1

2015-05-22JVGRHJVBJVB

CONSULTANT

PROJECT NO. CONTROL REV. FIGURE

YYYY-MM-DDDESIGNEDPREPAREDREVIEWEDAPPROVED

LEGEND!(

WATER QUALITY MONITORING STATIONSUSED TO ESTABLISH BASELINEROADWATERCOURSEWATERBODYMOUNT POLLEY MINE SITE

!

!

!

!

!

!

!

!

!!

!

!

!

!

!

!

!

!

!

!

PROJECTLOCATION

WASHINGTONUSA

ALBERTA

VICTORIAVANCOUVER

KAMLOOPSKELOWNA

PRINCERUPERT

PORTHARDY

NANAIMO

CAMPBELLRIVER

HOPE TRAILCRANBROOK

REVELSTOKE

WILLIAMSLAKE

KITIMAT

BELLACOOLA

QUEENCHARLOTTE

FORT STJAMES

FORT STJOHN

TERRACE

NELSON200 0 200

1:17,500,000KILOMETRESSCALE:

KEY MAP



2.0 PROJECT DESCRIPTION 2.1 Project Rationale With the use of the Springer Pit for receiving mine contact water and that pits finite capacity, there is a need in the short term to address the water balance challenge that stems from this circumstance. This need is present whether or not the mine resumes operation under restricted restart conditions.

An upgraded, probabilistic site-wide water balance model (Appendix A) has been developed to provide a predictive tool that allows analysis of water balance under existing conditions, which assists in planning and management of short-term water management issues; however, the model is also sufficiently flexible that it can be used as an analytical tool to evaluate various water management scenarios, making this tool particularly useful to long-term water management planning. At present, mine contact water is collected into a single ultimate location, the Springer Pit. The existing mine site water management regime will generate a surplus of approximately 6 million m3 mine contact water because water management does not currently have a discharge component.

Hydrological and hydrogeological studies of the Springer Pit were recently updated (Appendix A and C) in support of the Return to Restricted Operation application. These studies suggest that a pit lake will form within the Springer Pit and eventually overtop at the 1050 m elevation and that groundwater outflow from the Springer Pit Lake into rock is anticipated at the 1030 m elevation. The volume of groundwater predicted to report to the Springer Pit per month is not expected to play a significant role in the Springer Pit filling rates or water chemistry during 2015, compared to the larger volumes of water from other sources being added to the Springer Pit. It is the intention of MPMC, to maintain the Springer Pit water level below the point at which ground water exfiltration would occur (1,030 m). Achievement of this goal will require removal of surplus water (as per the treatment and discharge system described in Section 2.2) and further development of a longer-term site water management plan. Deposition of tailings into the pit from the restricted operations does not significantly change the requirements for short- or long-term water management on site.

In the short-term, development of storage or discharge alternatives in an appropriate timeline are needed to manage the surplus volume of mine contact water. Predictions of the Springer Pit filling suggest that in the case of a 1-in-200-year wet site condition, a site discharge strategy for mine contact water would have to be approved and operational by July 2015 to maintain the water level below the 1030 m elevation. In a 1-in-25-year wet site condition, the 1030 m elevation will be reached by August or September 2015. Under both these high precipitation conditions, the deposition of tailings into the Springer Pit is predicted to have little impact on the overall storage capacity or timing (Appendix A).

Authorization of the discharge of treated effluent as a short-term water management strategy requires an amendment of Permit 11678. Amendment of this permit requires a technical assessment of the effluent discharge to identify whether or not receiving water uses are impaired. That assessment, contained in this TAR is used by the MoE in their permitting decisions and is used by the discharger, in this case MPMC, as part of their due diligence to verify that they meet the requirements of the EMA and the MMER.



2.2 Proposed Treatment and Discharge The proposed water treatment system comprises an active treatment process involving lime addition to water being conveyed to the Springer Pit via the mill and active treatment to remove particulate matter prior to discharge. Treated water is proposed to be discharged to the recently constructed channel in Hazeltine Creek. Water from the upper sedimentation pond, comprising a mix of treated effluent and Hazeltine Creek flow will be conveyed by pipe to Quesnel Lake. Initial modeling with a surface discharge from Hazeltine Creek indicated that during periods of sustained winds, the discharge would remain close to the shore where dispersion was insufficient. Subsequent investigation of a piped discharge to depth identified much better dispersion and for this reason, the piped option was selected at the end of Hazeltine Creek. Dual pipes are proposed, with nominal discharge depths of 30 and 40 m to better dissipate effluent (Section 5.0).

The selection of the water treatment technology and discharge location for short-term water management is a result of a Best Available Technology (BAT) assessment and preliminary modelling of options. MoE policy requires that prospective effluents be treated at source using BAT; dilution zones are not permitted as a treatment process, but are utilized in the assessment of impacts from a BAT-treated effluent. When examining prospective discharge options, it became apparent to Golder that the selection of a short-term option could pre-judge that option as the final, long-term, effluent discharge location where the short-term option has high capital cost such that it would be infeasible to decommission it in favour of a different long-term option. It was therefore necessary to consider this possibility in the selection of a short-term discharge location. The process of selecting an effluent discharge option was carried out openly with the involvement of MoE, MEM, Fisheries and Oceans Canada (DFO), First Nations and the Likely community.

2.2.1 Options Analysis A workshop meeting was held at the Golder office in Vancouver on May 8, 2015, to discuss and evaluate options for water treatment technologies and options for discharge of that treated effluent. A description of the initial list of options and a numeric ranking process intended for that meeting is attached in Appendix D.

Although the numeric options analysis was not concluded, valuable focussed discussion and important feedback was gathered to assist in the selection of a short-term discharge option. Feedback was received from the attendees, listed along with the organizations represented, in Table 2.

Table 2: Options Analysis Attendees Organization Representatives

Mount Polley Mining Corporation (MPMC) Art Frye, Luke Moger BC Ministry of Energy and Mines Tania Demchuk(a), Scott Jackson (Lorax Environmental) BC Ministry of Environment Hubert Bunce, Chris Swan(a), Brian Yamelst Fisheries and Oceans Canada Darryl Hussey(a) Soda Creek Indian Band Julia Banks Williams Lake Indian Band Kirk Dressler, Elmar Plate (LGL Limited), Willie Sellars Likely Community Douglas Watt(a) Golder Associates Ltd. Paul Beddoes, Robert Millar, Lee Nikl, Corn Pretorius, Jerry Vandenberg

(a)attended by teleconference



2.2.1.1 Water Treatment Technology Options Prior to the meeting, Golder undertook an extensive search to screen technologies down to a list of treatment options that comply with the principle of BAT and can be reasonably deployed within the time constraints set by the water balance forecasts (Appendix A). Commercial offerings from various suppliers were contemplated, including sand ballasted sedimentation, mobile dissolved air flotation and reverse osmosis. Five (5) water treatment technology options have been considered as BAT, given the current constraints of a short-term water management plan:

Passive settling.

Lime addition.

Veolia Actiflow system.

Veolia Actiflow with lime addition.

Pre-treatment and reverse osmosis (note that this option was selected in a previous TAR).

The Veolia Actiflow system has several advantages over the other options. It is portable and scalable, flexible to inflow characteristics, and has a proven performance at other mines in northern climates with higher total suspended solids (TSS) and flow rates than those anticipated at Mount Polley Mine. This option can also be combined with the lime addition option to further reduce total metals.

2.2.1.2 Effluent Management Options A preliminary analysis considered a number of potential locations for discharge:

Hazeltine Creek/Polley Lake.

Edney Creek.

Bootjack Lake/Morehead Creek.

Quesnel Lake/Quesnel River.

Of those options, only Quesnel Lake and Quesnel River provide adequate dilution (i.e., minimum of 10:1 based on average flows) to be considered a viable short-term option for effluent discharge, as described in Section 3.2.2.3. Potential pipeline routes to these locations are shown in Figure 2. These routes, selected by geospatial algorithms, are preliminary. Ground-truthing of the alignment and further assessment of the routing, including detailed engineering has not yet been carried out.

QUESNELLAKE

QUESNEL RIVER

POLLEY LAKE

BOOTJACK LAKE

HAZELTINE CREEKEDNEYCREEK

TAILINGSSTORAGEFACILITY

MOUNTPOLLEYMINE SITE

OUTFALL LOCATIONOPTION 1

OUTFALL LOCATIONOPTION 2

CLIENTIMPERIAL METALSMOUNT POLLEY MINING CORPORATION

LEGEND! SOURCE LOCATION!( LONG-TERM OUTFALL LOCATION

LONG-TERM PIPELINE ROUTE OPTIONSOPTION QL-BOPTION QR-COPTION QR-DROADWATERCOURSEWATERBODY

REFERENCES1. WATERCOURSE AND LAKE DATA OBTAINED FROM CANVEC DEPARTMENT OF NATURALRESOURCES CANADA. ALL RIGHTS RESERVED.2. ORTHOPHOTO OBTAINED FROM NASA 201402173. PROJECTION: UTM ZONE 10; DATUM: NAD 1983

PROJECTMOUNT POLLEY MINETECHNICAL ASSESSMENT REPORTTITLEOUTFALL LOCATIONS OPTIONS ANALYSISLONG-TERM

1411734 12000 0 2

2015-05-22JVGRHJVBJVB

1 in0PA

TH: \\g

older.g

ds\gal\b

urnaby

\CAD-G

IS\Clien

t\Imper

ial_Me

tals_Co

rp\Moun

t_Polle

y_Mine

\99_PR

OJECT

S\1411

734\02

_PROD

UCTIO

N\1200

0_WATE

R_MAN

AGEM

ENT\M

XD\Re

port\Te

chnical

_Asses

sment\M

P_1411

734_Fi

gure_0

2_Outfa

ll_Loca

tions_O

ptions_

Analysi

s_Long

Term.m

xd

IF THIS

MEAS

UREM

ENT D

OES N

OT MA

TCH W

HAT IS

SHOW

N, THE

SHEE

T SIZE

HAS B

EEN MO

DIFIED

FROM

: ANSI B

CONSULTANT



KILOMETRES

0 1.5 3

1:60,000



2.2.2 Options Selected for Short-term Water Management Based on initial hydrological evaluation and discussion at the May 8, 2015 workshop, it was clear that there are three (3) viable options for discharge, all of which entail water treatment. The viable discharge locations are:

Hazeltine Creek (short-term, while it is not fish habitat; not viable in the long-term, when it is fish habitat).

Quesnel Lake via pipe and diffuser.

Quesnel River via pipe and diffuser.

Other discharge locations were determined not to be viable, with the exception of retaining a distributed (multi-point) discharge option in the long-term. The feasibility of this option will depend on long-term water treatment and water management decisions to be made in the future.

From evaluations carried out prior to the May 8 workshop and the workshop discussions, it was decided that it would be imprudent to proceed with the Quesnel Lake via pipe and diffuser or Quesnel River via pipe and diffuser for the short-term discharge, because:

Once the infrastructure is installed for either of these discharge locations, the capital expenditure would be of a magnitude that would preclude an alternate option.

The time delay in sourcing sufficient pipe, obtaining land tenure and construction of either of these options would be longer than the Hazeltine Creek Option.

The short-term needs for a timely discharge solution would favour the Quesnel Lake option rather than the Quesnel River option because of distance and greater simplicity in land tenure and pipe routing options. It was considered that the selection of the options should be based on environmental considerations, cost, and factors other than the need for an expedient solution.

A discharge to Hazeltine Creek is the preferred short-term solution because it will not require extensive infrastructure that will bind a long-term option, and it will afford the time for sufficiently detailed studies of the other two (2) options to clearly identify which is the best overall for a long-term discharge. The short-term pipe route is shown in Figure 3. At the May 8 meeting, nominal depths of 10 m and 20 m discharges were proposed. Subsequent model simulations using both CORMIX (Appendix E) and H3D (Appendix F) indicated that the best overall mixing, considering both near- and far-field dynamics, would be achieved by placing the outfalls at 30 m and 40 m depths to avoid density trapping at the thermocline.

Treatment options were presented at the May 8 workshop and subsequent investigations of efficacy and cost were carried out. A combination of lime addition and solids removal using the Veolia Actiflow system was selected for the short-term treatment technology. This treatment technology and its basis for selection are presented in more detail in Appendix E and Appendix G. This treatment technology has been considered in the water quality model (Appendix B), which was used to generate untreated and treated effluent predictions (Section 4.2) and forms the basis for the environmental assessment (Section 5.2).

HAZELTINE CREEK

QUESNEL LAKE

CLIENTIMPERIAL METALSMOUNT POLLEY MINING CORPORATION

LEGEND!( SHORT-TERM OUTFALL LOCATION

INITIAL DILUTION ZONE (100m RADIUS)PIPELINE ROUTE (APPROXIMATE)ROADWATERCOURSEHAZELTINE CREEK SEDIMENTATION POND 1HAZELTINE CREEK SEDIMENTATION POND 2

REFERENCES1. ORTHOPHOTO OBTAINED FROM SNC LAVALIN 20142. PROJECTION: UTM ZONE 10; DATUM: NAD 1983

PROJECTMOUNT POLLEY MINETECHNICAL ASSESSMENT REPORTTITLEPROPOSED SHORT-TERM PIPELINE ROUTE FROMHAZELTINE CREEK

1411734 12000 0 3

2015-05-22JVBRHJVBJVB

1 in0PA

TH: \\g

older.g

ds\gal\b

urnaby

\CAD-G

IS\Clien

t\Imper

ial_Me

tals_Co

rp\Moun

t_Polle

y_Mine

\99_PR

OJECT

S\1411

734\02

_PROD

UCTIO

N\1200

0_WATE

R_MAN

AGEM

ENT\M

XD\Re

port\Te

chnical

_Asses

sment\M

P_1411

734_Fi

gure_0

3_Prop

osed_P

ipeline_

ShortTe

rm.mx

d

IF THIS

MEAS

UREM

ENT D

OES N

OT MA

TCH W

HAT IS

SHOW

N, THE

SHEE

T SIZE

HAS B

EEN MO

DIFIED

FROM

: ANSI B

CONSULTANT



KILOMETRES

0 0.1 0.2

1:5,000



2.2.3 Requirements for Sewage Disposal The Return to Restricted Operations and TAR applications do not affect the current sewage disposal location, the Mill Site Sump, which is pumped to the Springer Pit. This sump has been used historically, so potential effects due to sewage disposal are inherent in the historical dataset presented in Section 4.0 that was used to generate untreated and treated effluent conditions, and by extension, considered in the effects assessment in Section 5.0.

2.3 Regulatory Setting For effluent discharges to aquatic receiving environments in BC, the applicable legislation includes the federal Fisheries Act, which contains a general prohibition against the deposit of a deleterious substance into waters frequented by fish (Section 36), and the provincial EMA, which contains a general prohibition against causing pollution. Under the general provisions of the Fisheries Act, what constitutes a deleterious substance is a matter of expert opinion; however, for the purposes of discharges involving a metal mine, which applies to the current permit amendment application, what constitutes a deleterious substance is specifically defined in the MMER. While a permit to discharge is required by the provincial government, there isnt a federal permit requirement. Federal requirements are imposed on a metal mine discharge by regulation.

While this TAR has been prepared in support of a provincial permit amendment process, federal requirements have also been addressed in the evaluations carried out because MPMC must comply with both provincial and federal laws.

2.3.1 Environmental Management Act The EMA is BCs principal pollution control statute with regulations made pursuant to that Act for more specific regulatory purposes. The EMA prohibits causing pollution, and (per subordinate regulation) requires specified dischargers to obtain an effluent permit. Because federal legislation has no effluent permitting system contained within it, federal agencies (i.e., Environment Canada [EC] and Fisheries and Oceans Canada) utilize the provincial permit process to communicate their specific requirements to the proponent. However, the proponent remains responsible for compliance with the general prohibitions of those federal laws (described further below), notwithstanding the presence of a provincial permit. The permit for the short-term effluent discharge is being sought under the Waste Discharge Regulation (WDR), pursuant to EMA. The proposed amendment to the current discharge permit (Permit 11678) under EMA to allow for the discharge of treated water from the mine to the receiving environment would be considered under Schedule 1 of the WDR.

In the EMA, pollution is defined as, the presence in the environment of substances or contaminants that substantially alter or impair the usefulness of the environment. The common expectations under the EMA are two-fold:

Lethal conditions should not exist within the initial dilution zone (IDZ) or the effluent.

Chronic sublethal effects should not occur outside of the IDZ. A lack of chronic sublethal effects is (conservatively) predicted when the parameter of concern has a concentration lower than ambient water quality guidelines for BC (BC MoE 2015a).



The IDZ is the three-dimensional zone around the point of discharge where mixing of the effluent and the receiving water occurs. For a large water body, the IDZ is commonly defined as a cylindrical body of water around the outfall with a lateral radius the lesser of 100 m from the outfall or 25% the width of the body of water and extending upwards to the surface of the water column. This definition is consistent with the BC Municipal Wastewater Regulation (B.C. Reg. 87/2012; O.C. 230/2012); however, this is not a municipal wastewater effluent and the MoE will consider alternative proposals for IDZ boundary geometry. For Quesnel Lake, the waterbody width is greater than 400 m so the cylinder of water with a radius of 100 m has been applied as the IDZ in diffusion modelling (Section 5.1).

2.3.2 Fisheries Act With respect to the Fisheries Act, a deleterious substance is a substance that, if added to water, would degrade or alter or form part of a process of degradation and would likely be rendered deleterious to fish or fish habitat, or the use by man of fish that frequent that water. The specific properties defining a substance as being deleterious under the parent act are left to interpretation by experts, except where sector-specific regulations have been developed, such as the MMER (SOR/2002-222). EC may request more stringent requirements, if necessary, by communicating those requirements to the provincial permitting authority.

DFO also regulates the placement of physical structures within fish habitats. The determination of whether or not an Authorization is required for the placement of the pipes will be determined before placement.

2.3.3 Metal Mining Effluent Regulation The MMER is a sector-specific regulation that is written under the authority of subsections 34(2), 36(5) and 38(9) of the Fisheries Act and includes specific definition of what constitutes a deleterious substance in effluent from a metal mine. The MMER also contains a requirement to undertake an Environmental Effects Monitoring (EEM) program. Undertaking an EEM program provides assurances that the technology-based effluent limits specified in the MMER are sufficient to protect the aquatic receiving environment. The MMER Schedule 4 limits were used as one set of criteria for screening end-of-pipe concentrations in Section 4.2.

2.3.4 Navigation Protection Act Consideration should also be given to the Navigation Protection Act (NPA) that is concerned with promoting the safe navigation of vessels which includes verifying that the installation of physical structures does not impede navigation. With specific regard to subsurface pipes, this process leads to protection against damage to the pipe by restricting vessel anchoring at the location of a pipe. The need for an NPA permit for the short-term pipe placement, as well as the long-term placement of a diffuser, will be determined prior to installing infrastructure.

2.3.5 Water Act and Regulation The BC Water Act governs the use and diversion of streams for domestic, industrial and other uses. Section 4 of the Act is a general prohibition against unauthorized diversion, extraction, use or storage of water from a stream. Surface mines in BC require a license to divert, store and convey water to facilitate safe mining.



MPMC currently holds three licenses under the Water Act: 5002458, which authorizes the non-power storage of Hazeltine Creek (500,000 m3/y); C101763 which authorizes Polley Lake water to be stored (1,000,352.28 m3/y) and used for processing ore (454.609 m3/d); and C111741 which allows Polley Lake to be used for dust suppression (818.296 m3/d) and work camps (36.369 m3/d) (MoE 2015d).

Section 9 of the Water Act requires an Authorization for works in and about a stream, which includes a broader definition of stream in law than what is commonly understood to be a stream in ordinary use. In the present case, a stream would include Hazeltine Creek and would also include Quesnel Lake. There are certain activities that are authorized by regulation; however, because water will be diverted by pipe to Quesnel Lake, an written Authorization is likely needed to enable construction of the pipe.

2.3.1 Land Tenure The pipe routing (see Figure 3) will cross crown land. It may be necessary for MPMC to obtain tenure for this portion of the alignment.



3.0 RECEIVING ENVIRONMENT 3.1 Outfall Location Quesnel Lake is a large, deep fjord lake with a surface area of 266 square kilometres (km2); the lake is comprised of East, West and North Arms. It is the deepest fjord-type lake in the world with a maximum depth of more than 511 m in the East Arm (Laval et al. 2008). The West Basin is a shallower (113 m maximum depth) portion of the West Arm that is demarcated in the east by a shallow sill near Cariboo Island that is approximately 35 m deep (Laval et al. 2008). The lake drains to the west via the Quesnel River to the Fraser River. The Horsefly River, Mitchell River, and Niagara Creek are the main tributaries to Quesnel Lake, entering east of the sill (MPMC 2009).

Hazeltine Creek flows 9.2 km from Polley Lake into the West Basin of Quesnel Lake. At the present time, Hazeltine Creek is not fish habitat because fish access has been restricted with barriers during the ongoing rehabilitation activities. For the purpose of this TAR for a short-term discharge of effluent, Hazeltine Creek is not considered a receiving environment and will be considered as a conduit for surface water flow into Quesnel Lake. It is noted that this perspective is one that is intended to apply for the short-term only because the objectives for Hazeltine Creek rehabilitation include its future use by fish.

As described in Section 2.2.2 and shown in Figure 3, the proposed short-term discharge location from Mount Polley Mine is Quesnel Lake near the mouth of Hazeltine Creek, with dual pipelines conveying water from the upper sedimentation pond on Hazeltine Creek. The pipes would discharge at nominal depths of 30 m and 40 m to promote far-field mixing. An analysis of near-field and far-field mixing is presented in Section 5.1.

3.2 Physical Environment Characteristics of the physical environment at the mine site and in the receiving environment in the West Basin downstream of the potential discharge points are summarized below.

3.2.1 Site Geology The Mount Polley property is located on the eastern edge of the Fraser Plateau physiographic sub-division, characterized by rolling topography and moderate relief. Elevations range from 920 metres above sea level (masl) at Polley Lake to 1,266 masl at the summit of Mount Polley. Volcanic rocks generally underlay this part of the plateau with inclusions of intrusive rocks. Most of the area is covered by a deposit of unconsolidated till which contains fluvial, lacustrine and colluvial deposits. Some patches of organic soils are present in poorly drained areas (i.e., wetlands).

The Mount Polley deposit is an alkali porphyry copper-gold deposit hosted in the Central Quesnel Belt along the Intermontaine Belt of BC. The deposit is located between Polley Lake in the east and Bootjack Lake in the west, consisting of several alkali intrusions and hydrothermal breccias. The deposit can be subdivided into five (5) main zones: Cariboo Zone, Bell Zone, Springer Zone, Southeast Zone (SEZ), and Northeast Zone (NEZ). A detailed description of these zones is provided in Imperial Metals (2004); a summary of the mineralization in each zone follows:

Cariboo Zone: copper mineralization occurs mainly as disseminated chalcopyrite with minor chalcopyrite, bornite and trace covellite, chalcocite and digenite.



Bell Zone: copper mineralization consists of fine to coarse disseminated and veined chalcopyrite with minor copper sulphides including bornite, chalcocite, covellite and digenite.

Springer Zone: Copper mineralization occurs mainly as disseminated chalcopyrite with minor bornite and trace covellite, chalcocite and digenite.

Southeast Zone: Copper mineralization occurs mainly as finely disseminated chalcopyrite, and also in potassically altered and silicified plagioclase porphyry dykes.

Northeast Zone: mineralization is high grade consisting of coarse grained copper sulphides in a heterolithic intrusion breccia host rock with subordinate plagioclase porphyry dykes.

3.2.1.1 Site Geochemistry Several geochemical characterization studies have been completed at Mount Polley Mine between 2004 and 2014. Geochemical characterization studies included static testing (e.g., acid-base accounting [ABA], trace element analysis and leach testing) and kinetic testing (e.g., humidity cell tests [HCTs]) on waste rock and tailings samples. The following studies were available at the time this TAR was prepared:

2001 ML/ARD Waste Characterization Final Report (MPMC 2004).

Mount Polley Northeast Zone Geochemical Characterization of Waste Rock (SRK 2004).

Southeast Zone Acid Base Accounting Results DRAFT (SRK 2005).

2010 Review of Humidity Cell Data, Mount Polley Mine Final (SRK 2011).

2011 Review of Humidity Cell Data, Mount Polley Mine (SRK 2012).

2012 Review of Humidity Cell Data, Mount Polley Mine (SRK 2013).

The purpose of these reports was to assess the acid rock drainage (ARD) and metal leaching (ML) potential of materials to be mined at the Mount Polley Mine. The above reports are provided in Appendix H, with the exception of SRK (2011) and SRK (2012). SRK (2011), SRK (2012) and SRK (2013) are annual updates of the humidity cell testing program and therefore, only SRK (2013) is provided in Appendix H since this is the most recent technical memorandum in the series.

More recent geochemistry work by SRK for the PEEIAR was undertaken to understand how the chemical composition of rainwater and snowmelt would be affected by contact with the spilled tailings (i.e. the finely crushed rocks generated in the mine processing plant). Water in contact with the spilled tailings can be expected along the banks of Hazeltine Creek and on the bottom of Quesnel Lake.

The main finding of the investigation was that the risk of element release from the tailings is low, although at the time of this report some testing was still underway and the interpretations are therefore considered preliminary. Nevertheless, a low element release from the tailings generally indicates that the composition of contact rainwater and snowmelt would not change considerably.



The results available to date confirm previous assessments of the tailings in that they are not likely to generate acid rock drainage due to a low abundance of minerals that can produce acid when in the presence of air (i.e., sulphide minerals like pyrite). Moreover, the tailings contain a greater amount of acid-consuming minerals (i.e., carbonate minerals like calcite) than acid-generating minerals. As a result, considerations for leaching and release of elements are only under neutral pH conditions.

The tailings that are on the bottom of Quesnel and Polley lake are not expected to weather or dissolve at appreciable rates. This is because sulphide minerals need air to react and air is present at very low concentrations in water and often not present in the deeper portions of these lakes. Certain minerals can dissolve when oxygen is not present (i.e. iron hydroxides), but these minerals were not present in significant amounts in the tailings, with background (i.e. non-impacted) lake sediments often having a higher proportion of these minerals than the tailings.

3.2.1.1.1 Summary of Geochemical Findings Several studies have been completed to characterize the geochemical characteristics of waste rock and tailings at the Mount Polley Mine. These studies indicate the following:

The majority of the tailings samples are non-PAG.

Waste rock from the Cariboo Pit is non-potentially acid generating (non-PAG) (MPMC 2004).

Some of the waste rock mined from the Bell pit is classified as acid generating (AG) or potentially acid generating (PAG); however, these materials were not segregated during mining and were mixed with non-PAG waste rock in the waste rock dumps. A study of the blending of AG/PAG materials from the Bell Pit with non-PAG waste rock indicates the blending provides sufficient neutralization potential to offset acid generation from AG/PAG waste rock (MPMC 2004).

Waste rock samples from the Northeast Zone are non-PAG (SRK 2004).

The Southeast Zone is mainly PAG (SRK 2005); waste rock mined from this zone was placed in the Bell Pit and the Wight Pit for subaqueous deposition (MPMC 2015).

Humidity cell testing indicates it will take decades for Northwest zone samples to become acid generating but less time for the Southeast, Springer and Pond Zones (SRK 2011; 2012; 2013).

MPMC proposes to store PAG waste rock in the Temporary Northwest PAG Stockpile and re-handle these materials at closure for subaqueous disposal (MPMC 2015).

The results of the above studies were considered in the development of the conceptual model for the water quality predictions developed as part of the TAR. In addition to the above studies, a review of site water quality monitoring results was completed as part of the derivation of source terms for the water quality model. Details of this review are provided in Appendix B.



3.2.1.2 Site Hydrogeology The groundwater flow at the site occurs primarily in the bedrock units in response to recharge from precipitation in the area between the Polley Lake and the Bootjack Lake. Flow in the overburden is less significant due to its limited thickness and discontinuous nature. Prior to mining, the water table at the site generally followed the surface topography, but the water table was deeper below the topographic heights and shallower in the low areas. At that time, the direction of groundwater flow was inferred to be from the top of the ridge between Polley Lake and the Bootjack Lake towards the low lying areas associates with these lakes northeast and southwest from the ridge.

Mine dewatering altered the groundwater flow pattern at the site, with the open pit and underground workings acting as sinks for groundwater flow. Mine dewatering lowered the water table elevation and created radial patterns of groundwater flow towards these facilities. Following the formation of the pit lake in the Cariboo Pit, seepage from this pit started to provide a contribution to groundwater inflow to the Springer Pit. At present, the Springer Pit is being flooded and the pit lake continues to act as a groundwater sink. The currently available information suggests that some seepage from the Springer Pit lake towards Bootjack Lake could occur once the Springer Pit Lake level reaches 1020 m to 1030 m elevation. The implications of this potential seepage are described more fully in Appendix B.

3.2.2 Climate and Hydrology 3.2.2.1 Climate The Mount Polley Mine is located in the Cariboo region of BC. This region experiences high spatial climate variation due to its topographical complexity. The climate of the study area is influenced by the Quesnel Highlands, which borders the Fraser Plateau to the east (MPMC 2009).

MPMC has operated climate stations on site since 1995, although records are not continuous. The mine site previously had one (1) climate station at the Mill Site that measured and recorded rainfall and temperature. This station was replaced in 2012 by two (2) of the climate stations (near the Mill Site and adjacent to the TSF) that measure and record rainfall, temperature, wind speed and direction, relative humidity and solar radiation. The details of these stations are shown in Table 3 and the locations are shown in Appendix A. The climate of the Mount Polley Mine site was also characterized using the EC station in the nearby town of Likely.

During the winter, snowpack is measured at four (4) snow course sites at minimum frequency of once per month, with more frequent measurements typically taken during the melt phase. The details of these stations, including locations, durations and typical measured values, are provided in Appendix A.

Prevailing winds are from the northwest in the winter months and south and southwest during the summer months. Along Quesnel Lake, winds tend to be channeled by valleys along the path of the lake. This longitudinal wind pattern is the principal driver of lake turnover events, internal seiching and water transfers among basins, as described by Laval et al (2008) and Tetra Tech (2015).



Table 3: Local and Regional Climate Stations for the Mount Polley Mine

Station Name Northing (m N)(a) Easting (m E)(a)

Elevation (masl)(b) Data Type

Period of Record

Likely 5828785 599332 724 Temperature, Precipitation 1974 - 1993

Mill Site Weather Station 5822420 592495 1181 Rainfall, Temperature 1995 - 2012

Weather Station #1 5822420 592792 1171 Rainfall, Temperature, Relative Humidity, Solar Radiation, Wind Speed, Wind Direction

2012 - 2015

Weather Station #2 5819955 594059 964 Rainfall, Temperature, Relative Humidity, Solar Radiation, Wind Speed, Wind Direction

2012 - 2015

(a)UTM Coordinate system- Zone 10U (b)Elevation for on-site climate stations measured with handheld GPS device in meters above sea level (masl)

3.2.2.1.1 Temperature The town of Likely is located approximately 9 km northeast of the mine site at an elevation of 724 masl. The elevation of the mine ranges from about 920 masl to 1200 masl, and therefore the average temperatures are generally 0.3C to 1.0C cooler than recorded at Likely.

Monthly values for the Likely climate station are shown in Table 4. Temperatures at Likely are generally mild to cold, with average monthly temperatures ranging from -6.6C in January to 15.1C in July and August.

Table 4: Likely Climate Station Monthly Temperatures (1974 1993)

Month Temperature

(C) Average Maximum Minimum

January -6.6 -2.9 -11.1 February -4.5 0.6 -9.4 March -0.8 5.8 -6.0 April 4.0 11.3 -2.1 May 9.1 16.3 2.3 June 12.8 19.8 6.0 July 15.1 22.7 8.1 August 15.1 22.3 7.8 September 10.7 17.3 4.0 October 4.7 10.6 0.1 November -1.3 2.4 -4.8 December -5.6 -2.1 -9.2 Annual 4.4 10.3 -1.2



3.2.2.1.2 Precipitation Long-term precipitation time series representative of the climate conditions at Mount Polley Mine were derived using the regional data from the Likely station (1974 to 1993) and available local data from the three (3) on-site climate stations (1995 to 2015). The 1:25 year dry and wet, as well as the 1:200 year dry and wet precipitation values, were determined by distributing the average annual precipitation (derived based on Likely and on-site stations) among the months based on average percentage of precipitation for each month. These data are described in more detail in Appendix A.

The mine site experiences high summer precipitation (50 to 60 mm/mon) due to summer storms, with the lowest precipitation occurring in February to April (38 to 50 mm/mon). Precipitation typically occurs as snowfall starting in November and accumulates until March. Average annual precipitation at Mount Polley is estimated to be 670 mm.

3.2.2.2 Local Hydrology Mount Polley is drained by three (3) main watersheds: Hazeltine Creek (30.2 km2 at Quesnel Lake), Edney Creek (87.4 km2) at Quesnel Lake, and Morehead Lake (62.7 km2). The Hazeltine Creek watershed includes Polley Lake and conveys all water from Polley Lake, the east side of Mount Polley and the area surrounding the Mount Polley TSF. The Morehead Creek watershed includes the Bootjack Lake catchment area (11.2 km2).

Both the Hazeltine Creek and the Morehead Creek watersheds were significantly altered by historical water diversions. Bootjack Creek, a small remnant of which now flows into Polley Lake, historically conveyed water from Bootjack Lake into Hazeltine Creek. In 1913, flow from Bootjack Lake was reversed by damming the east end of Bootjack Lake and digging a new outlet westward to Morehead Creek. Around the same time, a control structure was also built at the outlet of Polley Lake (Hazeltine Creek), and Hazeltine Creek water was diverted to the previously existing Bullion Pit. Flow from Polley Lake to Hazeltine Creek was restored with the abandonment of mining at Bullion Pit during World War II. However, the flow from Bootjack Lake to Hazeltine Creek was never restored. In their current configuration, Edney Creek and Hazeltine Creek converge just prior to discharging into Quesnel Lake. Under the short term discharge scenario proposed, these flows will be separated because Hazeltine Creek will be directed to a submerged pipe,

mpmc short-term effluent discharge tar (pdf)

Documents