NORTH TH PI PILE LE AND D WATER TER MANA NAGE GEMENT MENT MVLWB Technical Session Snap Lake Mine Final Closure, and Water Licence and Land Permit Renewal July 16 to 18, 2019 PUBLIC LIC PRESEN ENTATION ION
OUTL TLINE • Overview of System • North Pile - Material Balance Covers - Geotechnical Monitoring • Geochemistry • Water Management - Climate Change • Wetlands 1
SNAP LAKE NORTH TH PILE AND WATER ER MANAGE GEMENT ENT - CURRENT RRENT 2
POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER TOTAL AL IMAGE GE SYSTEMS – WITH WETLANDS
POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER TOTAL AL IMAGE GE SYSTEMS – WITH WETLANDS Not to scale 4
POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER TOTAL AL IMAGE GE SYSTEMS – WITHOUT WETLANDS
NO NORTH TH PI PILE E
NORTH TH PILE - CURRENT RRENT 7
DETAIL ILED ED DESIGN IGN NORTH TH PILE ENGINEERE EERED D COVER ER 3H:1V west perimeter embankment regrade Grading Nominal 2% top surface gradient 114,000 m 3 Starter Cell deposited PK movement: - Excavate Cell 2 Landfill Waste - Place in Cell 3 Capacity Starter Cell waste placement: - Cell 1 (existing landfill) - Cell 2 West Cell 1 outlet, toward west influent storage pond Flow Conveyance East Cell 5 outlet, toward east influent storage pond 8
AVAILABL ABLE E BORR RROW AREAS Availa vailable le Quanti tity ty ID ID Borrow Area ea Locati ation on Primar ary Use Estimate e (m 3 ) Crusher stockpile west of North Pile erosion protection cover material 11,200 (a) 1 Explosive management west of East Cell erosion protection cover material 1,700 2 bunker Laydown area southeast of North Pile erosion protection cover material 256,000 (b) 3 and/or transition material 4 Organic stockpile former AN storage facility riprap 29,400 (c) SP5 quarry north of East Cell, Cell 1 erosion protection cover material 68,200 5 and/or transition material 6 West Cell divider dyke North Pile West Cell erosion protection cover material 81,000 (d) 5 Source: • FCRP, Table 5.5 6 (a) Quantity provided by De Beers (b) Quantity assumes 80% of total available volume will be suitable 2 (c) Quantity assumes 20% of total available volume will be suitable 4 1 (d) Quantity assumes 100% of total available volume will be suitable 9 3
MATERI ERIAL AL BALANCE – FINAL AL CLOSURE SURE (ALL REQU QUIREMEN REMENTS) TS) Excludi ding g Wetlands s - Full Borr rrow ow Sourc rces Earthwork rks - Materi erial Balance e with Wet etland (Limited ed Scavenge) ge) Excava vation on Place Borr rrow Sou ourc rces (Availabl ble) e) Cell 5 Outlet Channel 21,000 Cell 5 Outlet Channel 100 Crusher 11200 South Perimeter Ditch 102,600 South Perimeter Ditch 45,400 Explosive Management Bunker 1700 North Perimeter Ditch -North Perimeter Ditch 75,300 laydown area (1 only) 256000 West Cell Initial Divider Dyke Channel 5,500 East Cell 127,000 Organic Stockpile 29400 West ISP 290,700 Starter Cell 139,300 SP5 quarry 68200 West CW 150,100 West Perimeter 5,800 West Cell Divider Dyke 81000 East ISP 96,500 West ISP 133100 Total 447,500 East CW 437,600 West CW 32450 Excavation on Starter Cell 29,000 East ISP 23500 Cell 5 Outlet Channel 21,000 Culverts 11,700 East CW 37850 South Perimeter Ditch 102,600 Total 1,144,700 Access Roads (temp) 3750 West ISP 290,700 Portal Fill 39500 East ISP 96,500 Starter Cell 29,000 Cut to fill Cover (infrastructure areas) 138,556 Culverts 11,700 East Cell 118,300 Total 801,606 Total 551,500 Starter Cell 119,700 Cut to Fill West Perimeter 14,000 Rip Rap East Cell 118,300 Total 252,000 East Cell 2,100 Starter Cell 119,700 Starter Cell 4,300 West Perimeter 14,000 Total Excavation 1,396,700 West Perimeter 800 Total 252,000 Total Place 1,063,146 Culverts 2,340 1,251,000 Remaining 333,555 Total 9,540 Total without additional roadway or laydown scavenge 24% 24% Total without CW 1,063,146 Remaining 187,855 15% 15% Source: • Response to GNWT-ENR-129 (submitted as Attachment 7 on 3 June 2019) 10 10
GEOTECHN TECHNICA CAL L MONI NITORING ORING RESPON PONSE FRAMEW MEWORK ORK – CLOSURE URE AND POST T CLOSUR SURE • Closure response framework will be similar to the framework for extended care and maintenance (ECM) • Post closure response framework to be updated similar to the response framework for closure – after closure trends have been developed (visual and instrumentation monitoring) Engineering criteria and performance indicator trigger levels to be updated to include: • 1. Displacement prisms for the cover, landfill areas, wetland system berms, and sump berms - after cover placement and prism installation for the structures. 2. Surface cracks and erosion – after field cover trials completion ~Q4 2019 3. Sump and ISP water levels – after the structure construction record and instrumentation installation 4. Seepage monitoring – unchanged from ECM 5. Thermal monitoring – to include the new additional thermistor to monitoring the deposited material freeze-back – after cover placement and instrumentation are stabilized 6. Piezometer levels – after new additional piezometer instrumentation installed. Reviewe wer Concer erns ns • GNWT-ENR-95, 101, 103, 104: visual monitoring for physical stability 11 11
GEOTECHNICAL MONITORING RESPONSE FRAMEWORK – CLOSURE AND POST CLOSURE • Response framework for extended care and maintenance, Table 1 of 5. Source: North Pile management plan Version 2. 11June2018 12 12
GEOTECH TECHNICAL CAL MONITORING ORING METHOD OD • Closure and post closure monitoring method identified in the North Pile management plan V3, document entitled “Closure and Post closure geotechnical monitoring plan for the North Pile and Passive water treatment systems”, which describes the visual and instrumentation monitoring requirements and frequency. • Closure phase – visual and instrumentation monitoring, inspections by a geotechnical and water treatment engineer to verify the North Pile and wetland performance as expected in the design. • Post closure phase – monitoring reduced, once closure monitoring demonstrate no further intervention by De Beers is required for regular surveillance or operational personnel on site or remotely. Effective demonstration that the North Pile and wetland berms are permanently stable landforms where likelihood of release of solids or water is negligible. Revie iewe wer Concern erns • GNWT-ENR-155: monitoring plan to describe the instruments used for monitoring performance of North Pile 13 13
GEOTECHNICAL MONITORING METHOD Source: De Beers 2019e - North Pile management plan Ver. 3. March 2019 14 14
NORTH TH PILE LE CLOSURE URE AND POST CLOSUR URE BASELIN INE E AND FREEZ EZE-BACK CK MONITORI RING Source: De Beers 2019e - North Pile management plan Ver. 3. March 2019 15 15
CLOSUR SURE AND POST T CLOSUR SURE PERFORM ORMANC ANCE E MONITORING RING Source: 16 16 De Beers 2019e - North Pile management plan Ver. 3. March 2019
GEO EOCHE CHEMIS MISTR TRY
GEOC OCHEMI EMISTR TRY AT SNAP LAKE • Geochemistry is a key element for understanding chemical stability, and has been the focus of initial evaluation, annual updates and long term monitoring/evaluation. - Geochemical evaluation followed standard geochemistry practices and guidance - A full geochemical evaluation of available data from 2002 through 2018 was undertaken during development of the FCRP (summary report provided as Appendix K of the FCRP) Data sources related to geochemistry include: • Environmental Assessment and Permitting Reports (De Beers 2002) • Annual geochemistry reporting from 2002 through 2018 • Special geochemical investigations as included in the annual geochemistry reports (site chemistry, bog chemistry, nitrate and ammonia) 18 18
NORTH TH PILE GEOCHE CHEMISTR TRY Revi viewer er Concer ern: • De Beers confirms that PAG rock will not be used • PAG material should not be used for construction. for closure construction Some metavolcanic rock is located in the perimeter • Geochemical testing has been undertaken embankments and should be monitored. - Processed kimberlite is non-acid generating and has excess neutralization potential - Granite is non-acid generating - Metavolcanic is non-acid generating with excess buffering capacity when blended • Although not expected to be required, placement of covered processed kimberlite toe berm will provide additional buffering capacity Reviewe wer comment nts: • ECCC-#10, 11, GNWT # 114, 116, 119, 130, 131: Metavolcanic and PAG rock in North Pile 19 19
NORTH TH PILE GEOCHE CHEMISTR TRY Revi viewer er Concer ern : • The active layer within the North Pile will be confined to the thickness of the cover material • Cover thickness on North Pile must be adequate to isolate PAG rock • PAG material was placed in the internal divider dykes • The assessment conservatively considered fully thawed conditions to account for PAG material that may be in the active zone • Although not expected to be required, placement of covered processed kimberlite toe berm will provide additional buffering capacity Reviewe wer comment nts: • ECCC#12, GNWT#114, 115, 192 20 20
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