NORTH TH PI PILE LE AND D WATER TER MANA NAGE GEMENT MENT - - PowerPoint PPT Presentation

MVLWB Technical Session Snap Lake Mine Final Closure, and Water Licence and Land Permit Renewal July 16 to 18, 2019

NORTH TH PI PILE LE AND D WATER TER MANA NAGE GEMENT MENT

PUBLIC LIC PRESEN ENTATION ION

1

• Overview of System
• North Pile
• Material Balance Covers
• Geotechnical Monitoring
• Geochemistry
• Water Management
• Climate Change
• Wetlands

OUTL TLINE

2

SNAP LAKE NORTH TH PILE AND WATER ER MANAGE GEMENT ENT - CURRENT RRENT

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITH WETLANDS

4

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITH WETLANDS

Not to scale

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITHOUT WETLANDS

NO NORTH TH PI PILE E

7

NORTH TH PILE - CURRENT RRENT

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DETAIL ILED ED DESIGN IGN NORTH TH PILE ENGINEERE EERED D COVER ER

Grading 3H:1V west perimeter embankment regrade Nominal 2% top surface gradient Landfill Waste Capacity 114,000 m3 Starter Cell deposited PK movement:

• Excavate Cell 2
• Place in Cell 3

Starter Cell waste placement:

• Cell 1 (existing landfill)
• Cell 2

Flow Conveyance West Cell 1 outlet, toward west influent storage pond East Cell 5 outlet, toward east influent storage pond

9

AVAILABL ABLE E BORR RROW AREAS

ID ID Borrow Area ea Locati ation

• n

Primar ary Use Availa vailable le Quanti tity ty Estimate e (m3) 1 Crusher stockpile west of North Pile erosion protection cover material 11,200(a) 2 Explosive management bunker west of East Cell erosion protection cover material 1,700 3 Laydown area southeast of North Pile erosion protection cover material and/or transition material 256,000(b) 4 Organic stockpile former AN storage facility riprap 29,400(c) 5 SP5 quarry north of East Cell, Cell 1 erosion protection cover material and/or transition material 68,200 6 West Cell divider dyke North Pile West Cell erosion protection cover material 81,000(d)

(a) Quantity provided by De Beers (b) Quantity assumes 80% of total available volume will be suitable (c) Quantity assumes 20% of total available volume will be suitable (d) Quantity assumes 100% of total available volume will be suitable 2 5 6 1 3 4

Source:

• FCRP, Table 5.5

10 10

MATERI ERIAL AL BALANCE – FINAL AL CLOSURE SURE (ALL REQU QUIREMEN REMENTS) TS)

Earthwork rks - Materi erial Balance e with Wet etland (Limited ed Scavenge) ge) Excava vation

• n

Place Cell 5 Outlet Channel 21,000 Cell 5 Outlet Channel 100 South Perimeter Ditch 102,600 South Perimeter Ditch 45,400 North Perimeter Ditch

• North Perimeter Ditch

75,300 West Cell Initial Divider Dyke Channel 5,500 East Cell 127,000 West ISP 290,700 Starter Cell 139,300 West CW 150,100 West Perimeter 5,800 East ISP 96,500 West ISP 133100 East CW 437,600 West CW 32450 Starter Cell 29,000 East ISP 23500 Culverts 11,700 East CW 37850 Total 1,144,700 Access Roads (temp) 3750 Portal Fill 39500 Cut to fill Cover (infrastructure areas) 138,556 East Cell 118,300 Total 801,606 Starter Cell 119,700 West Perimeter 14,000 Rip Rap Total 252,000 East Cell 2,100 Starter Cell 4,300 Total Excavation 1,396,700 West Perimeter 800 Total Place 1,063,146 Culverts 2,340 Remaining 333,555 Total 9,540 24% 24% Excludi ding g Wetlands s - Full Borr rrow

• w Sourc

rces Borr rrow Sou

• urc

rces (Availabl ble) e) Crusher 11200 Explosive Management Bunker 1700 laydown area (1 only) 256000 Organic Stockpile 29400 SP5 quarry 68200 West Cell Divider Dyke 81000 Total 447,500 Excavation

• n

Cell 5 Outlet Channel 21,000 South Perimeter Ditch 102,600 West ISP 290,700 East ISP 96,500 Starter Cell 29,000 Culverts 11,700 Total 551,500 Cut to Fill East Cell 118,300 Starter Cell 119,700 West Perimeter 14,000 Total 252,000 Total without additional roadway or laydown scavenge 1,251,000 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)

11 11

• 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.

GEOTECHN TECHNICA CAL L MONI NITORING ORING RESPON PONSE FRAMEW MEWORK ORK – CLOSURE URE AND POST T CLOSUR SURE

Reviewe wer Concer erns ns

• GNWT-ENR-95, 101, 103, 104: visual monitoring for physical stability

12 12

• Response framework for extended care and maintenance, Table 1 of 5.

GEOTECHNICAL MONITORING RESPONSE FRAMEWORK – CLOSURE AND POST CLOSURE

Source: North Pile management plan Version 2.

11June2018

13 13

• 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.

GEOTECH TECHNICAL CAL MONITORING ORING METHOD OD

Revie iewe wer Concern erns

• GNWT-ENR-155: monitoring plan to describe the instruments used for monitoring performance of North Pile

14 14

GEOTECHNICAL MONITORING METHOD

Source: De Beers 2019e - North Pile management plan Ver. 3. March 2019

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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

16 16

CLOSUR SURE AND POST T CLOSUR SURE PERFORM ORMANC ANCE E MONITORING RING

Source: De Beers 2019e - North Pile management plan Ver. 3. March 2019

GEO EOCHE CHEMIS MISTR TRY

18 18

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)

19 19

• De Beers confirms that PAG rock will not be used

for closure construction

• Geochemical testing has been undertaken
• 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 Revi viewer er Concer ern:

• PAG material should not be used for construction.

Some metavolcanic rock is located in the perimeter embankments and should be monitored.

NORTH TH PILE GEOCHE CHEMISTR TRY

Reviewe wer comment nts:

• ECCC-#10, 11, GNWT # 114, 116, 119, 130, 131: Metavolcanic and PAG rock in North Pile

20 20

• The active layer within the North Pile will be

confined to the thickness of the cover material

• 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 Revi viewer er Concer ern :

• Cover thickness on North Pile must be adequate to

isolate PAG rock

NORTH TH PILE GEOCHE CHEMISTR TRY

Reviewe wer comment nts:

• ECCC#12, GNWT#114, 115, 192

21 21

• Review of geochemistry data was undertaken
• Processed kimberlite and granite are non-acid generating

with excess neutralization potential

• Metavolcanic rock is mainly non-acid generating (68%) to

uncertain (17%), to potentially acid generating (15%)

• Metavolcanic rock will be fully blended in the pile and the
• verall the material is expected to be non-acid

generating.

• Additional information :
• Blending of materials was observed during placement
• Runoff water quality (15 years data) is non-acidic with low

metal concentrations

Revi viewer er Concer ern :

• Provide rationale for geochemical classification of

metavolcanic as non-acid generating

NORTH TH PILE GEOCHE CHEMISTR TRY

Reviewe wer comment nts:

• GNWT #176, 177: Justification of Metavolcanic Geochemistry
• ECCC #10, 11, GNWT#176, 177: Metavolcanic and PAG rock in North Pile

22 22

KIMBERLIT BERLITE E AND METAVOL OLCANI CANIC ABA CHARA RACTERI CTERISTICS TICS

2010 samples intentionally contained visible sulphide minerals to determine mineralogy and are not representative of the overall rock – this rock was not used in the north pile construction (De Beers 2011 – 2010 Annual Geochemistry report) 2005 – two of five samples selected were selected to determine oxidation properties in samples that had elevated sulphide and are not representative of the overall rock (De Beers 2006 – 2005 annual report)

Reviewe wer comment nts:

• GNWT #117,176,177: Metavolcanic and PAG rock in North Pile

23 23

• PK will supply additional buffering

capacity (FCRP Appendix K)

• The potential for metal release was

assessed under various conditions (EAR 2002) documents, and metal release is included in the existing water quality model

• Erosion protection layer will be

placed over the PK in the toe berm to limit solids release and erosion (similar to other areas of the pile). Revi viewer er Concer ern:

• use of Processed Kimberlite use in the toe berm

NORTH TH PILE GEOCHE CHEMISTR TRY

Reviewe wer comment nts:

• GNWT#116, 119

WATER TER MA MANA NAGEMENT GEMENT

25 25

Design ign Objectiv jectives

• Collect North Pile drainage (surface runoff and seepage) and convey it to the passive treatment systems
• Provide gravity conveyance
• To be physically stable over the long-term
• To not pose a risk to wildlife land use and meet closure criteria and objectives proposed for the closure of

the mine

• To preserve access to various locations at the site
• To use existing water management infrastructure to the extent practical

Desig ign Crit iter eria ia

• 3H:1V slopes to be used where commensurate with engineering
• Convey the peak flow from the 200-year, 24-hour event plus snowmelt (Environmental Design Flood event) to

the passive treatment facilities, while providing 0.3 m of freeboard

• Safely pass the probable maximum precipitation 24-hour event plus snowmelt (Inflow Design Flood event),

without compromising the water management structures

DESIGN IGN OBJECTI ECTIVE AND CRIT RITERIA ERIA NORTH TH PILE WATER ER MANAGEMEN GEMENT

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITH WETLANDS

27 27

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITH WETLANDS

Not to scale

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITHOUT WETLANDS

WE WETLANDS TLANDS

TOTAL AL IMAGE GE POST-CLOSURE SITE CONDITION – NORTH PILE AND WATER SYSTEMS – WITH WETLANDS

31 31

• Current plan is to not conduct field/pilot testing of constructed wetland systems
• Wetlands are used for reduction of nitrate throughout the North in cold climates
• Reference Documents:
• Public Works and Government Services Canada Constructed Wetland Fact Sheet (http://gost.tpsgc-

pwgsc.gc.ca/tfs.aspx?ID=32&lang=eng)

• Government of Nunavut Guidance Document: “Guidelines for the Design and Assessment of Tundra Wetland Treatment Areas in

Nunavut (http://centreforwaterresourcesstudies.dal.ca/files/documents/Report%20CWRS%20wetland%20design%20guidelines.pdf)

• During construction De Beers will optimize the constructed wetland design using best practices to enhance microbial activity
• Primary uncertainty with respect to the use of wetlands for nitrate removal at this site is the length of time for vegetation maturation
• Water will not be discharged from the wetland systems until the effectiveness of the treatment is proven through testing consistent with

the Water Licence

• Until the wetland is able to reliably meet discharge criteria, effluent from the wetland systems will be sent to the current reverse osmosis

water treatment plant prior to discharge to the environment

FIELD/ D/PI PILOT T TESTING

Reviewe wer conc ncerns ns:

• ECCC 4 – describe any planned field testing or demonstration scale testing
• MVLWB 22 – is a test site/demonstration wetland planned?
• MVLWB 54 – questions around timing and water quality from sumps to wetland

32 32

• Organic soils will be sourced from on site as available, and

supplemented/augmented with solid state carbon amendments as required

• Established vegetation will be sourced from on-site as available, and

transplanted to the constructed wetlands

• The order of preference for establishing vegetation in the constructed

wetlands is: 1) transplant established vegetation, 2) nursery plants, and 3) native seed mixture

• The length of time to fully establish vegetation is unknown at this time,

depending on the type of vegetation planted (i.e., the more transplanted plants used, the shorter the likely period of establishment/time to maturation vs. the more seed mixes used the longer the likely period of establishment/time to maturation)

Photo: Gary Austin, 2012. University of Idaho

CONSTR TRUCTED CTED WETLANDS ANDS ORGANI ANIC C SOIL AND VEGET ETATI TION ON MATUR URATI TION ON

Reviewe wer conc ncerns ns:

• MVLWB 24 – how will you adapt if wetlands do take 15 years to develop with respect to regulatory, EQC compliance monitored etc.
• MVLWB 97 – impact of vegetation maturation on the timeframe of Post-closure
• MVLWB 170 – questions around length of time for wetland vegetation of mature

33 33

• Wetland Vegetation (Appendix L):
• Wetland species are selected based on habitat and moisture, native species (sedges, willows, mosses)
• Wetlands are not a ‘priority area’ for revegetation.
• Wetland vegetation will be monitored annually (%cover) however the criteria will be EQC, not % cover of vegetation

WETLAND AND VEGET ETATI TION

Reviewe wer comment nts:

• MVLWB 28 – how will species be selected for the wetlands?
• MVLWB 29 – how will wetland plants be monitored?

34 34

CONSTR TRUCTION CTION SEQUENC UENCING G / SCHEDULI EDULING G OF WETLANDS ANDS AND WATER ER DISCH SCHAR ARGE GE

2019 2019 2020 2020 2021 2021 2022 2022 2023 2023 2024 2024 2025 2025 2026 2026 2027 2027 2028 2028 2029 2029 2030 2030 2031 2031 2032 2032 2033 2033 2034 2034

2035 2035-2045 2045

Demolition Winter Road Water Management System and North Pile Cover Construction (Influent Storage Ponds, Wetlands and spillways) Active Demolition Activity Revegetation, Landforming and Site Stabilization Final Winter Road Owners Team Fully Activated Extended Care and Maintenance Winter Road 1 Post Closure Water Licence Process Monitoring of System Biota Growth and Denitrification

35 35

• Consistent with Anglo American requirements for climate risk our systems utilize an inflow design flood (IDF) based on the

Probable Maximum Flood (PMF) as a design criteria. This is a more conservative approach than using the Canadian Dam Association (CDA) criteria for IDF at closed facilities

• The v-notch overflow provides a back-up that sends water in excess of the maximum treatment flow rates to the wetlands in

the event that the normal conveyance piping is temporarily compromised.

• Emergency spillways on the ISPs provide contingency release in case of higher than anticipated volume that exceed the

design storm event, or the wetland influent pipe system and v-notch weir being temporarily compromised at the same time.

• Site water quality is expected to meet Effluent Quality Criteria (EQC) without treatment approximately 20 years into the Post-

Closure phase, and therefore wetland flow at the design flow rate is not required in perpetuity.

IMPACT CT OF EXTRE REME E PRECI CIPI PITATI TION ON ON THE WETLANDS ANDS (WET) T)

Reviewe wer conc ncerns ns:

• ECCC-2, MVLWB-45 – Was the water management system designed for extreme weather (including wet and dry years)
• MVLWB-45 – how was uncertainty addressed in the design
• GNWT-ENR-29 – Were the wetlands designed for extreme weather (including wet and dry years)
• GNWT-ENR-140 – how was variable precipitation accounted for in the design

36 36

• During low water years, no flow through the wetland is necessary

to maintain vegetation, only enough flow to allow the plants to stay submerged.

• All flows from the North Pile are directed to the wetlands, and the

wetlands stay submerged at all times, so the likelihood of no flow feeding them and/or the wetland drying out is low.

• In the medium term, the warming temperatures and increased

precipitation rates generally expected for the region of the Snap Lake mine are anticipated to be beneficial for on-going wetland and revegetated area development, such that closure criteria may be attained sooner than expected.

IMPACT CT OF EXTRE REME E PRECI CIPI PITATI TION ON ON THE WETLANDS ANDS (DRY)

Revie iewe wer conce cerns:

• ECCC-2 – Was the water management system designed for extreme weather (including wet and dry years)
• MVLWB-45 – how was uncertainty addressed in the design
• GNWT-ENR-29 – Were the wetlands designed for extreme weather (including wet and dry years)
• GNWT-ENR-139 – Impacts of climate change on hydrological model outputs
• GNWT-ENR-140 – how was variable precipitation accounted for in the design

37 37

Predicted nitrate in Sump 3 of the North Pile (Site WQ Model Report; Golder 2019)

WATER ER MANAGEMEN GEMENT T – NORTH RTH PILE AND PERMAFR FROS OST

Reviewe wer comment nts:

• GNWT-ENR-20: Is permafrost required to reach steady-state
• GNWT-ENR-134: Is freezing required for long-term stability of the North Pile

50 100 150 200 250 2018 2020 2022 2024 2026 2028 2030 2032 2034 2036 2038 2040 2042 2044 2046 2048 Nitrate, as N (mg/L) Year

Sump 3

ECM Closure Post-closure

The system is designed very conservatively: West Passiv ive e Treatm tmen ent t System em

• 95th Percentile Flow weighted average influent NO3=

68.3 mg/L as N East Passiv ive e Treatm tment ent System

• 95th Percentile Flow weighted average Influent NO3=

72.8 mg/L as N

• Convey the peak flow from the 200-year, 24-hour event plus

snowmelt (Environmental Design Flood event) to the passive treatment facilities, while providing 0.3 m of freeboard.

• Prior to construction the most current data will be evaluated

prior to finalizing designs (if necessary)

CLIMA IMATE TE CHANGE ANGE

39 39

• Site structures desig

signed ed to rema main stable ble under er bot

• th

h perma mafr frost st and unfroze

• zen conditio

ditions - not sensitive to climate change.

• Water containing structures utilize an inflow desig

sign flood

• od (IDF)

) based sed on the Proba

• bable

le Maximu imum m Flood

• od (PMF)

)

• more conservative than the CDA requirement.
• Post-Closure water quality model included groundw

dwater er flow w and d drain aindo down in an unfroz

• zen North

th Pile. With higher precipitation, water quality would be diluted

• Revegetation programs use loc
• cal

al nativ ive specie ies

CLIMATE TE CHANGE GE CONSIDERA SIDERATION TIONS

Revie iewe wer Concern erns

• ECCC 2 – how well will the influent storage ponds manage extreme weather given climate change?
• GNWT ENR 20 – is permafrost required to reach steady state conditions in the North Pile?
• GNWT ENR 140 – assess trends related to precipitation over time
• MVLWB 45 – how is worst case scenario in terms of wet and dry year addressed? How is uncertainty regarding climate change addressed?
• GNWT ENR 134 – clarification about whether freezing is required for long term physical and chemical stability of NP

40 40

SNAP LAKE DESIGN GN IS CONSER ERVATIV TIVE

Notes: Precipitation rate predictions generated by CanRCM4 (CCCma 2017) RCP4.5/RCP8.5 = Representative Concentration Pathway4.5/8.5 (greenhouse gas emissions scenario; IPCC 2014) Approximate location of Snap Lake mine is marked with a black ring Precipitation rate scale is in units of mm /day

• The largest changes in

precipitation were projected to

• ccur in winter, with increases in

precipitation ranging from 5.3% to 22.4%.

• Our Syst

stems s are desi signe ned d to remain n stable under er bot

• th

permafr afrost st and unfr froze zen n condi diti tions ns

DEM EMOLITION OLITION

42 42

• Appendix G.1, Tables G.1-5 and G.1-6 include lists of the ancillary buildings, and other equipment/debris to

be decommissioned as part of the work.

• Common tasks that will be required for the decommissioning of buildings on site include:
• removal of utilities from the building;
• removal of hazardous materials for offsite transport;
• removal of all equipment, piping, and other items to facilitate the demolition of the structure (load,

haul, and placement of the material in the on-site landfill);

• demolishing and hauling to the on-site landfill the building structure and any remaining items that

were not removed as part of stripping work;

• removal of concrete above the slab-on-grade (SOG) elevation and creating holes in the SOG to

promote drainage of precipitation into the subsurface;

• placement of a 0.5 m thick layer of fill material over all building foundations/SOGs and grading to

match adjacent ground surface (fill material will be borrowed from site infrastructure features that are no longer required, such as a portion of the airstrip and laydown areas with considerable fill materials); and

• post-demolition evaluation and reporting

DEMOLIT OLITION

43 43

DEMOLIT OLITION SEQUENC UENCING

Major Demolition will

• Process Building, Utilities Building, Services Complex, Utilidor
• Once Utilidor is dropped, other structures can proceed at

Contractor’s discretion Removals continue with AST’s and minor structures:

• Structural Steel (Process Transfer Tower, FAR1, etc.)
• Fold-Away portable buildings (17 different shops and storage

buildings)

• ATCO trailers (over 60 trailers)
• Sprung structures (4 separate steel/fabric style structures)
• Seacans (there were approximately 28 seacans of various sizes)
• Simple Frame Construction (wood frame buildings which

included structures ranging from the large Permanent Accommodation Camp structure to a smaller building like the Gazebo or the Logistics Warehouse Office)

• Several pipelines to remove, 26 surface debris piles inventoried
• Demolition and disposal of all buildings and equipment will be

completed by a Demolition Contractor in accordance with the Waste Management Plan.

44 44

Culverts/conduits will be removed and the materials disposed as per the approved waste disposal method.

• Culverts/conduits located along major

right-of-way – the final reclamation condition of the roadway includes a grade that should not be less than 3H:1V with a base width that permits vehicle traffic. A typical drawing of the condition after reclamation is presented in Appendix G.3.

• Culverts located where water

conveyance is necessary – a typical drawing of the condition after reclamation is presented in Appendix G.3, and generally includes a 3H:1V side slope and minimum 2 m base

• width. The side slopes and base are to

be covered with a non-erodible (minimum 150 mm down) material of a 0.3 m thickness.

CULVER ERTS TS AND CONDU DUITS TS