British Columbia Mine Reclamation Symposium

Pinchi Lake mine closure : demolition debris disposal Marsland, Rob; Unger, Michelle; Donald, Bruce 2013

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PINCHI LAKE MINE CLOSURE ? DEMOLITION DEBRIS DISPOSAL   Rob Marsland, P.Eng.1, Michelle Unger, B.Sc.2, Bruce Donald, P.Eng.2   1Marsland Environmental Associates Ltd,  203 West Beasley St.,  Nelson, BC  V1L 3K4  2Teck Resources Limited,  601 Knighton Road,  Kimberley, B.C.  V1A 1C7    ABSTRACT  The Pinchi Lake mine operated from 1940 to 1944, and again between 1968 and 1975.  Between 2010 and 2012, the mine underwent decommissioning and reclamation.  This paper reviews the development of the plans for on-site disposal of demolition debris from decommissioning of the infrastructure including the ore processing and roasting facilities. This paper describes: the investigations by Teck to evaluate disposal options, including identification of the challenges associated with the recycling of scrap metal that could potentially be contaminated with mercury; the involvement of local First Nations in the process; and, the subsequent evaluation of on-site disposal options.  The selected on-site disposal option of backfilling part of an open pit with the debris and waste rock was accepted by the First Nations and was also approved by the regulators.  The design of the landfill, the waste testing and emplacement requirements and the results of the environmental monitoring are provided.  Key words: Landfill, permitting, reclamation, decommissioning, monitoring, mercury   INTRODUCTION AND BACKGROUND  The Pinchi Lake mine, which produced mercury from cinnabar ore, initially operated from 1940 to 1944, and all structures were subsequently demolished. It was then redeveloped with new facilities and operated again from 1968 to 1975, at which time the facility was placed on care and maintenance.  The property is located approximately 25 km northwest of Fort St James, British Columbia.  Between 2010 and 2012, the Pinchi Lake mine underwent decommissioning and reclamation.    The mill demolition and disposal aspect of the mine closure plan greatly benefited from input by members of the Pinchi Mine Technical Working Group (TWG), which is composed of members/advisors of the Tl?azt?en Nation and the Nak?azdli Band (hereafter referred to as the First Nations) and Teck.  The Environmental Management Act (Part 5, Section 65(1)) recognizes the existence of ?core? areas at mines, where waste rock or tailings have been placed. At a mine, the ?background? concentrations of substances in the ore and waste are much higher than generic numerical standards considered under the Contaminated Sites Regulation.  Section 11(3) of Part 5 of the CSR recognizes that the definition of a contaminated site does not apply as long as the concentration of the substance is not greater than the local background concentration.  Furthermore, Section 2(8) of Part 1 of the Hazardous Waste Regulation recognizes that a facility containing mine tailings or mine waste rock is not a hazardous waste facility. Core materials at the site would include the various forms of mercury, arsenic and antimony related to ore, waste rock, tailings and concentrates.   CHARACTERIZATION OF BUILDING MATERIALS  The mill buildings (Photo 1) had been standing unused since 1975 and most of the original equipment still remained.  The mill contained mercury sulphide (cinnabar) as dust and rubble throughout the facilities.  While cinnabar is chemically and environmentally stable, it was an impediment to off-site disposal of debris.  Structures in and near the roaster area were observed to have elemental mercury contamination.  In addition, asbestos was used for insulation in some equipment (and pipe joints) and several permitted Polychlorinated biphenyl (PCB) transformers (oils had been drained but shells were contaminated) as well as PCB containing light ballasts were present on-site.  As part of the closure planning process, a hazardous materials assessment was conducted by AMEC.   In addition to typical hazardous materials such as PCB, lab chemicals, asbestos, etc., concentrations of total mercury warranting classification as industrial waste (if not located at a mercury mine) were identified in virtually all building materials and crushed rock or rock dust in the  Photo 1. Pinchi Mill Buildings  crusher, change house, mill and roaster areas.  For off-site handing or disposal, the Toxicity Characteristic Leaching Procedure (TCLP) concentrations would warrant classification of portions of the crusher and mill buildings as hazardous (leachable) waste.  Furthermore, all building materials and rock dust from the roaster area, based on TCLP concentrations, would be considered hazardous (leachable) waste, if removed from the site. Elemental mercury was present on the floor and on equipment throughout the roaster area (AMEC, 2007).  Swab samples collected from surfaces of various materials throughout the site, including the building materials in the shop, change house and power house (as well as the office and warehouse) passed TCLP tests.  However, surfaces of various building materials within the mill and roaster areas had quantities of mercury that were indicative of potential for classification as leachable waste (based partially on TCLP analysis from bulk samples in these areas) (AMEC, 2007).    EVALUATION OF OFF-SITE DISPOSAL OPTIONS  In considering disposal options for the building materials, an option favoured by the First Nations was to remove material for off-site recycling to extent practicable.  However, the potential contamination of steel with mercury is an obstacle for recyclers due to their customer requirements, and therefore the option was not consistent with responsible material stewardship.  Furthermore, studies (Lee, 2004) had shown that removal of mercury, even from structural steel such as I-beams is surprisingly difficult, requiring mechanical abrasion (e.g., sand blasting), to remove any mill scale or rust, which could potentially remobilize the mercury.  Even with the aggressive cleaning, detectable mercury was reported to remain.  This finding rendered the prospect of beneficial reprocessing of the steel to be untenable.  Teck also had significant concerns related to allowing mercury contaminated materials to be re-used off-site, in particular with the idea of allowing local contractors and home owners to remove the sheet metal cladding from the roofs and walls of the buildings.  There were also concerns by the local community regarding the number of truck loads of material that would need to be hauled away ? most as far as Fort St. John, especially given that the haul route would be right through Fort St. James.  The end result was that the off-site disposal option was basically limited to a select few specialized waste disposal locations depending on material type and degree of contamination, as summarized in Table 1.  In all cases, materials with contaminants not related to the local geology (e.g., PCBs, lab chemicals, etc.) would be shipped off site.  Table 2 presents the materials that would still need to be shipped off-site.   ON-SITE DISPOSAL OPTIONS  As part of a trade-off study on the disposal options for the building debris, the issue of where on the site the materials should be interred was considered.  The basic options for on-site disposal were: ? standard industrial landfill without burning of combustibles (e.g., wood potentially contaminated with volatile mercury); ? standard secure (hazardous waste) landfill located in till with liner and leak detection; and, ? landfill contained within the West Zone pit.  The Pinchi mine site is generally covered with a thick layer of low permeability glacial till, so is an ideal location for a landfill.  Table 1 Option for Off-Site Disposal of all Demolition Debris Item Tonnage (t) NotesClean steel for disposal with municipal waste 600 Haul to Fort St James municipal landfill Steel classified as Industrial Waste 500 Haul to Silverberry in Fort St. John Steel classified at Hazardous Waste (e.g., roaster) 200 Haul to Pembina in Alberta - may require cleaning prior to off-site disposal Concrete - non-hazardous 500 Haul to Fort St James municipal landfill Concrete - Hazardous 100 Haul to Silverberry in Fort St. John Wood - non-hazardous 40 Haul to Fort St James municipal landfill Wood - Hazardous 10 Haul to Silverberry Drywall - non-hazardous 10 Haul to Silverberry in Fort St. John Drywall - hazardous 5 Haul to Silverberry in Fort St. John Asbestos - non-hazardous 8 Haul to Fort St James municipal landfill Asbestos - hazardous 8 Haul to Silverberry in Fort St. John - note if can't separate hazardous portion from inert will need to take everything to Silverberry Fibreglass insulation - non-hazardous 10 Haul to Fort St James municipal landfill Fibreglass insulation - hazardous 5 Haul to Silverberry in Fort St. John - note if can't separate hazardous portion from inert will need to take everything to Silverberry Liquid Mercury 0.25 Haul to Clean Harbours in Ontario Various other hazardous materials  51 Most gets hauled to Silverberry in Fort St. John - some goes to specialist processing facilities (Swan Hills, etc.). TOTAL 2047Note: Between 250 and 600 truck loads could have required off-site disposal, in addition to the ?conventional? hazardous materials.  Table 2 Off-Site Disposal Required even with Demolition Debris in West Zone Pit Landfill Item Tonnage (t) NotesSteel classified at Hazardous Waste (e.g., roaster) <200 May require some cleaning to meet MLEP for on-site disposal.  If can?t clean adequately, haul to Pembina in Alberta - may still require cleaning prior to off-site disposal Drywall - non-hazardous 10 Haul to off-site landfill permitted to take drywall material.  Assume Silverberry in Fort St. John. Drywall - hazardous 5 Haul to Silverberry in Fort St. John Asbestos - hazardous 8 Haul to Silverberry in Fort St. John - note if can't separate hazardous portion from inert will need to take everything to Silverberry Fibreglass insulation - hazardous 5 Haul to Silverberry in Fort St. John - note if can't separate hazardous portion from inert will need to take everything to Silverberry Liquid Mercury 0.25 Haul to Clean Harbours in Ontario Various other hazardous materials  51 Most gets hauled to Silverberry in Fort St. John - some goes to specialist processing facilities (Swan Hills, etc.). TOTAL 79Note:  Only ~10 truck loads required for off-site disposal of <130 tonnes of material. The option of using the existing West Zone pit as a landfill site would allow backfilling of a significant portion of the pit and elimination of a large portion of the adjacent waste dump ? both of which had considerable appeal to the local First Nations.  In the process, the demolition debris containing trace amounts of mercury, antimony and arsenic associated with the natural mineralization would be buried back in the ground.    DESIGN OF WEST ZONE PIT LANDFILL  The West Zone open pit is a side cut into the steeply sloping hillside, with the majority of the pit volume located above grade (see Photo 2). Nevertheless, a substantial volume of the pit is below original ground level.  While there are near surface underground workings beneath the pit, any major openings had been previously filled with waste rock during mine operations, to facilitate the safe mining of the pit. The West Zone Pit bottom did not accumulate standing water. Examination of the mine plans indicated that the bottom of the West Zone Pit is open to a combination of underground level workings, raises, and mined stopes that have been backfilled but remain porous. The 750-Level portal is the lowest exit from the mine and therefore is the natural drainage location for all of the mine workings.  The lower part of the West Zone Pit had been identified as the most suitable on-site permanent disposal area for demolition debris from the rest of the site. This process would result in a portion of the West Zone Pit below the access ramp being filled with a combination of demolition debris and waste rock.  The West Zone Pit Landfill was designed such that seepage through the building demolition debris is minimized. Figure 1 illustrates the engineering design.  Seepage reduction features include: - 1.5m thick drainage layer at the bottom of the pit;  - 10m thick layer of waste rock to ensure the landfill debris is not in contact with the drainage layer;  - keeping building debris a minimum of 5 m away from any sidewalls of the pit;  - 1.0m (minimum) thick low permeability till cap (2% minimum slope) placed over top of the building debris; and  - top cover till cap (also minimum 1 m thick with 2% minimum slope) to reduce seepage into the waste rock and landfill debris and serve as a base for growth media.   The West Zone Pit landfill is a till-capped facility, and any seepage drains to the underground workings of the mine and discharges from the 750-level portal, where it can be readily monitored.   At the request of First Nations, Teck agreed to move additional waste rock to incrementally fill the pit above the elevation of the debris and re-contour the landscape. The till cap has been re-vegetated with agronomic grasses and legumes mixed with islands and corridors to facilitate re-vegetation with native trees and shrubs. Maintenance fertilizer treatments will be conducted as required to promote the establishment of a self-sustaining plant community.  The closure cost estimates indicated that there would be no cost savings associated with the selected on-site landfill option relative to off-site disposal, because of the large volume of waste rock that would need to be relocated (Table 3).  Figure 1 West Zone Pit Landfill As-built Plan, Profile and Cross-Sections Table 3 Estimated Material Quantities for the West Zone Pit Landfill Material Type Quantity (m3) Till Cap 12,000 Drainage Layer and Waste Rock 100,000 Demolition Debris and Waste Rock 12,000 Filter Layer 2,500 TOTAL 126,500 Debris contaminated with Hg, Sb or As, which originated from site, to be stored on-site as a core material, as long as waste criteria was met.  PERMITTING  The first stage of the permitting process was to develop a design that was agreeable to the First Nations.  It needed to provide for secure, long term storage that could be adequately monitored and that could be reclaimed to fulfill the land use objectives of the Pinchi Mine Decommissioning and Reclamation Plan (MEA 2009).  Once the design was accepted by the TWG, it was incorporated in to the Decommissioning and Reclamation Plan (or Closure Plan) and submitted to the Ministry of Energy and Mines (MEM) in support of the necessary Mines Act Permit amendment. Near the end of the review process for the Reclamation Plan, an application was submitted to the Ministry of Environment (MoE) Environmental Protection Division to formally request a temporary Approval under the Environmental Management Act to operate the landfill in the West Zone pit.  The application was accompanied by a Technical Assessment Report, which described the landfill design, operations and monitoring in detail (MEA, 2010).  A supporting document describing the debris management and mercury removal processes for cleaning and testing the debris prior to landfilling was also prepared and submitted to MoE.  One of the key features of the permitting process was the testing of the building materials prior to demolition and the testing of the demolition debris prior to landfilling.  The First Nations and regulators agreed to the building materials being segregated based on three categories as follows: 1. Roaster; 2. Process buildings and process equipment; and  3. Non-process buildings.   A second key feature was the recognition that the standard TCLP test was not an appropriate test for characterizing the waste to be deposited in the demolition debris landfill, since organic acids would not be present in the landfill.  Instead the MoE accepted the use of the Modified Leachate Extraction Procedure (MLEP) as described in Schedule 4 of the BC Hazardous Waste Regulation.  The test was used to demonstrate that none of the materials placed in the landfill could be considered a leachable hazardous waste.  The key parameters of interest were arsenic and mercury with the limits based on the Leachate Quality Standards in Table 1 of Schedule 4.  Confirmatory testing was then conducted at the sampling frequency outlined in Table 4.  Note that the sampling was completed as proposed in the Landfill Technical Assessment Report with the exception of testing the structural steel supporting the Roaster. The sampling frequency of the structural steel was considered to be classified as ?process building and equipment? based on the material thickness, Table 4: Sampling Frequency  Roaster EquipmentProcess Buildings and EquipmentNon-ProcessOne sample conducted for every: 1 tonne of material 10 tonnes of material 100 tonnes of material  expected volume (62 tonnes), and the very low initial MLEP test results. However, the steel equipment supports were considered separate from the structural steel and were treated as part of the ?roaster equipment?. In addition, any process or roaster equipment that was identified within the auxiliary areas was sampled at a higher frequency as required.  A detailed calculation for the weight of materials was conducted prior to the demolition and is outlined below in Table 5. The weight of materials was used to develop the number of confirmatory samples required for the West Zone Pit materials. For those materials that did not pass the acceptable MLEP concentration and were then drummed for offsite disposal, the estimated weights of these materials are included as a subtraction in the calculations.  LANDFILL OPERATIONS  The preparation and filling of the West Zone Pit with debris and fill initiated in November 2010 and the final cap was completed in November 2011.  A summary discharge report as required under Approval AR-104969 was submitted to MoE in February 2012 (Teck, 2012). The decommissioning of the mill area buildings and auxiliary buildings was completed from October 2010 through to December 2010.  Prior to the decommissioning, testing of building materials was completed by AMEC Environment and Infrastructure (AMEC).  Sumas Environmental Services Inc. (Sumas) was the onsite hazardous waste contractor for the completion of the Hazardous Waste building abatement and decontamination prior to the demolition and disposal of the buildings.  In 2010 and 2011, a total of 288 samples were analyzed for leachable mercury, of which 217 samples passed the applicable leachable mercury standard. The final sample results indicated that all the structural components, building materials, and equipment were suitable for onsite disposal in the West Zone Pit with the exception of a few items.  The roaster, condensers and other areas noted to contain free, liquid mercury were handled as hazardous waste.  Approximately 5 L of elemental mercury collected during the dry phase de-contamination was shipped offsite.  In addition, approximately 200 x 45 gallon drums of mercury-containing Hazardous Waste were also shipped off-site.  The drums include soot and refractory from the Roaster oven, dirt and debris from the Roaster dry phase decontamination, old mercury canisters, and demolition debris that did not pass the MLEP testing. Prior to the demolition, a number of other hazardous materials were identified within the building structures (e.g., transformers containing PCBs, old lab chemicals, asbestos, hydrocarbons, etc.).  A total of 27,420 L and 75,505 kg were contained, manifested, and shipped off site for proper disposal at licensed facilities in 2010 and 2011.  Photo 2 illustrates the West Zone pit before and after landfilling.  Table 5 Quantity of Building Demolition Debris and Confirmatory Sampling  Area Structural Steel (tonnes) Equipment (tonnes) Building Material (tonnes) Total (tonnes) Sample Frequency required (per tonne)1  Total number of confirmatory samples required Total number of confirmatory  samples analyzed2 Crusher  34 164 41  239 1/10 24 24 Conveyors  111 23 134 1/10 13 15 Mill Building  179 376 115  670 1/10 67 73 Roaster    Equipment  ? 83  ? 83  1/1 83 38?Building materials  39  25 64 1/10 6 22?Subtract materials removed from site as Hazardous Waste3  -45 -2 -47  -45 - Roaster subtotal 39 38 23 100 As above 44 60 TOTAL 363 578 202 1,143  148 172 1 Based on building material category and sample frequency in Table 3. 2 This only includes the number of samples for materials that passed the MLEP testing and does not include samples that initially failed the MLEP and were resubmitted after washing.   3 Materials that failed the MLEP testing and removed from site include roaster soot and refractory, wood, lead skirting, plastic pipes and insulation.   Photo 2 West Zone pit before and after backfilling  MONITORING  As part of the closure permit and landfill approval for the West Zone Pit, monthly monitoring and sampling of the 750-level portal was required during landfilling activities to verify that the buried debris was not affecting mine drainage and, ultimately, lake water quality. The monthly sampling was initiated in November 2010 and continued until June 2012 to track any potential changes after the West Zone Pit was filled. The field sampling was conducted by EcoFor, under the direction of Azimuth Consulting Group (Azimuth), and was reported by Azimuth (Teck, 2012) and summarized below.   Monitoring of the 750-level adit chemistry had been undertaken by Teck since at least 1993, episodically during the open water season (May-October). Over this time the collection location has not changed and the same laboratory (ALS) has been used.  Flow varies only slightly seasonally, from approximately 0.6 L/s to 1.4 L/s, averaging around 1 L/s, with no long term trends.    The parameters of particular attention in adit water include a select group of metals that are associated with the Pinchi ore body in particular mercury, antimony and arsenic, which are the main contaminants of potential concern (COPC) in the Pinchi Mine Ecological Risk Assessment (Azimuth 2009). In addition to these, total suspended solids concentration is of interest because of its relationship with metals concentrations in general, as well as those parameters that can influence the methylation of mercury including pH, and sulphate concentrations, as well as methyl mercury itself.  The allowable discharge concentrations are dictated by Ministry of Environment Discharge Effluent Permit PE 224-P.  Examination of these select parameters in adit water over the nearly 20 years prior to capping of the WZP, is useful to put current concentrations into historical perspective. To assist in a visual depiction of all data dating back to 2000, Figures 2 to 6 show the temporal trends of sulphate (SO4), antimony (Sb), arsenic (As), total mercury (Hg), and methyl mercury (MeHg). Key results are as follows: ? Historic data (>1993) show that pH was relatively consistent ranging from 7.5 to 8.4 with few exceptions. Mean pH during this period was 7.9 with no difference in adit water pH between pre- and post-reclamation. This is less than the average pH limit of 8.1 as specified in the Pinchi mine discharge permit.  ? Alkalinity and sulphate (Figure 2) were also reasonably consistent, averaging 246 mg/L and 165 mg/L, respectively, with no apparent trends and very consistent concentrations in both parameters over time.  ? TSS concentrations were also low and generally below the detection limit (typically <3 mg/L) during all monitoring events prior to and after reclamation.  This is well below the maximum TSS limit of 20 mg/L as specified in the Pinchi mine discharge permit.  ? There were 13 metals that were either not detected or detected in very low concentrations (e.g., aluminum, cadmium, chromium, lead, strontium, zinc). A further four metals (barium, lithium, iron, nickel) were consistently detected but at relatively low and consistent concentrations over time. These results suggest that for the majority of metals, concentrations have been quite consistent, with no noticeable reduction or increase in concentration over a long period of time.  ? Arsenic (As) averaged 0.008 mg/L (0.005 ? 0.015 mg/L) over the course of the study. The average arsenic concentration in the last four monitoring episodes prior to reclamation was 0.010 mg/L and averaged 0.007 mg/L in the most recent four episodes. Figure 3 illustrates that aside from a small increase prior to initiation of remediation, concentrations changed very little over time. The Pinchi discharge permit does not specify a limit for arsenic, but the measured values are well below the standard Metal Mines Effluent Regulations (MMER) limit of 0.5 mg/L.  ? Antimony (Sb) averaged 0.37 mg/L and ranged up to 1.01 mg/L prior to remediation. During the course of the remedial period antimony averaged 0.23 mg/L (0.10 ? 0.42 mg/L). The average antimony concentration in the four monitoring episodes prior and in the final four episodes post-remediation was 0.25 mg/L. A time series plot (Figure 4) of antimony showed some variation during capping, although the magnitude of change was within 0.2 mg/L. The Pinchi mine discharge permit does not specify limits for antimony, nor does the MMER. To reach the BC Water Quality Objective for the protection of aquatic life of 0.02 mg/L, up to 20-fold dilution is required in Pinchi Lake.  Given the annual average flow rate through Pinchi Lake is over 7000 L/s @ 0.0003 mg/L Sb, this is readily achieved. ? Total mercury (Hg) concentrations averaged 350 ng/L (0.00035 mg/L) with a high of 1,440 ng/L between 1993 and 2010. Mercury concentrations were frequently high and variable, consistently exceeding 200 ng/L until 2005. Since 2006 concentrations have tended to diminish, usually hovering around 100 ng/L. Total mercury concentration averaged 107 ng/L (74 ? 201 ng/L) over the course of the remediation. The average mercury concentration in the four monitoring episodes leading up to remediation was 98 ng/L and it was 99 ng/L in the final four episodes post- remediation. Figure 5 illustrates the stability in mercury concentration over time, with no change upwards or downwards. All of these values are well below the Pinchi mine discharge permit limit of 5,000 ng/L (5 ?g/L), and close to the limit at which Environment Canada does not require on-going monitoring (0.1 ?g/L or 100 ng/L (vs. recent measured values averaging 99 ng/L)) under MMER.  ? Methyl mercury (MeHg) concentrations showed similar pattern to total mercury (Figure 6). Between 1993 and 1999 methyl mercury ranged between 12 and 20 ng/L indicating that some methylation of the inorganic mercury was occurring within the mine. In 2000 concentrations diminished and ranged between 5 and 10 ng/L until 2009 with lower concentrations over time. Methyl mercury concentration averaged 2.4 ng/L (1.7 ? 3.7 ng/L) over the course of WZP remediation, which is much less than the long term monitoring average of 11 ng/L prior to 2010. Comparing the four months prior to the four months after remediation, mean methyl mercury concentration has diminished from 5.7 ng/L to 2.5 ng/L. These data suggest that methyl mercury concentration in adit water has been reduced. Whether this is due to capping or not, is uncertain.   The discharge permit ? including long term monitoring requirements and discharge limits ? is currently under review.  The expected plan is to continue to monitor the portal discharge water on a decreasing frequency, with newly established limits for Hg, As and Sb.  Trigger levels will also be adopted such that adverse trends in water quality will prompt more frequent monitoring.  Figure 2  Sulphate Concentration  Figure 3  Total Antimony Concentration    Figure 4  Total Arsenic Concentration    Figure 5   Total Mercury Concentration   Figure 6  Methyl Mercury Concentration     0 50 100 150 200 250 300 350 400 450 500 Jan-2000 Jan-2001 Jan-2002 Jan-2003 Jan-2004 Jan-2005 Jan-2006 Jan-2007 Jan-2008 Jan-2009 Jan-2010 Jan-2011 Jan-2012 Jan-2013 Total Sulphate (mg/L) 750 Level Portal Effluent SO4 Tailings Pond Effluent SO4  Proposed Discharge Limit = 500 mg/L  0.0 0.5 1.0 1.5 2.0 2.5 Jan-2000 Jan-2001 Jan-2002 Jan-2003 Jan-2004 Jan-2005 Jan-2006 Jan-2007 Jan-2008 Jan-2009 Jan-2010 Jan-2011 Jan-2012 Jan-2013 Total Antimony (mg/L) 750 Level Adit Effluent Sb Tailings Pond Effluent Sb  Proposed Discharge Limit = 0.8 mg/L  0.00 0.05 0.10 0.15 0.20 0.25 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Total Arsenic (mg/L) 750 Level Portal Effluent As Tailings Pond Effluent As  Proposed Discharge Limit = 0.2 mg/L  0 200 400 600 800 1000 1200 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Total Mercury ng/L 750 Level Portal Effluent T-Hg Tailings Pond Effluent T-Hg  Proposed Discharge Limit = 1000 ng/L  0 5 10 15 20 25 30 35 Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08 Jan-09 Jan-10 Jan-11 Jan-12 Jan-13 Methyl Mercury ng/L 750 Level Portal Effluent Me-Hg Tailings Pond Effluent Me-Hg  Proposed Discharge Limit = 30 ng/L  CONCLUSIONS  By bringing the local First Nations in to the remediation options selection process through the TWG it was possible to develop a mutually agreeable plan.  The selected option, minimizing risk and liability by keeping the potentially contaminated building materials on site in a stable, long term disposal facility, struck a good balance in terms of objectives for site-related risks, responsible materials stewardship and safety aspects of the remediation actions.  The landfill was operated under a temporary discharge approval from MoE from October 2010 to November 2011.  In total, nearly 2000 tonnes of demolition debris were landfilled, and nearly 114,000 m3 of waste rock was returned to the pit as fill.  The facility was capped with 1 m of till to shed runoff.  The monitoring to the end of 2012 has not shown any effect on water quality.   REFERENCES  Azimuth, 2012. Technical Memorandum ? 750-Level Adit Water Quality Monitoring, prepared for Teck Metals Ltd by Azimuth Consulting Group, October 16, 2012.  Lee, 2004. Mercury Assessment 130 Liberty Street Property, Technical Memorandum H3:  Remediation of Steel.  Prepared for Deutsche Bank.  Prepared by RJ Lee Group Inc., May 2004.  MEA, 2009. Pinchi Lake Mercury Mine Decommissioning and Reclamation Plan. Prepared for Teck Cominco Metals Ltd. Prepared by Marsland Environmental Associates Ltd., April 2009.   MEA, 2010. Pinchi Lake Mercury Mine Demolition Debris Landfill Technical Assessment Report. Prepared for Teck Metals Ltd. Prepared by Marsland Environmental Associates Ltd., June 2010.   Teck, 2012.  Pinchi Mine ? West Zone Pit Summary Report ? AR-104969, Submitted to Ministry of Environment, February 21, 2012.  


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