ir-t04 decision report template · western areas limited (wsa) operates the cosmic boy nickel...

Works Approval: W6372/2020/1

IR-T0X Decision Report Template (short) v0.1 (August 2018) i

Application for works approval

Division 3, Part V Environmental Protection Act 1986

Works approval number

W6372/2020/1

Applicant Western Areas Limited

File number DER2020/000061

Premises Cosmic Boy Tailings Storage Facility

Forrestania-Southern Cross Road

FORRESTANIA WA 6359

Legal description –

Mining tenements M77/335 and M77/399

Date of report 24 April 2020

Status of report Final

Decision Report


IR-T0X Decision Report Template (short) v0.1 (August 2018) 1

Overview of premises

Background and classification of premises

Western Areas Limited (WSA) operates the Cosmic Boy nickel concentrator under licence L8041/1990/5 as part of its Forrestania Nickel Operations (FNO), an active nickel mining and processing operation located on the Forrestania greenstone belt, around 400 km east of Perth.

The concentrator treats ore mined from the Flying Fox and Spotted Quoll ore bodies to produce a nickel concentrate product, with tailings deposited in an adjacent tailings storage facility (TSF). The scope of this application relates to an expansion of the existing TSF.

The original TSF at the site, which was a rectangular two cell facility established by Outokumpu Mining Australia Pty Ltd as part of the initial mining and processing operation at the site, was operated from 1992 until closure in 1999. It was decommissioned and rehabilitated in 2001, with the top surface covered with a topsoil/waste rock cap.

The existing TSF at the site was then constructed on top of the original TSF site in late 2008/early 2009 under the ownership of WSA. This TSF is a circular paddock facility around 33 ha in footprint area, and has previously been raised on four occasions to a crest level of RL419 m using the upstream construction method.

The most recent perimeter raise was completed in August 2019 under works approval W5859/2015/1. This approval originally included construction of a new cell to the south of the existing TSF (the ‘southern extension’), however this part of the approval was subsequently withdrawn after becoming aware that WSA had not yet submitted an application for approval under the Mining Act 1978 – this application is seeking approval for an updated proposal for the southern extension.

The works relate to the following prescribed premises category:

Description of application

WSA is proposing to construct a new cell as an extension to the existing TSF and raise it once, to provide tailings storage capacity commensurate with the remaining life-of-mine (around 5 years). To support the extension and ongoing operations, WSA are also proposing to undertake the following ancillary work:

establishing a tailings reclamation storage area within the northern apron of the existing cell to the north, for the temporary storage of materials reclaimed from the legacy footprint of the original TSF, prior to transport for use within paste-fill operations;

constructing a new access ramp and batters along the eastern side of the existing TSF, to allow haulage truck access to tailings for future reclamation; and

establishing an area for contingency monitoring infrastructure to the southeast of the proposed extension.

Classification of Premises

Description Premises design capacity

Category 5 Processing or beneficiation or metallic or non-metallic ore: premises on which –

(a) metallic or non-metallic ore is crushed, ground, milled or otherwise processed;

(b) tailings from metallic or non-metallic ore are reprocessed; or

(c) tailings or residue from metallic or non-metallic ore are discharged into a containment cell or dam.

680,000 tonnes per annual period



▲ TSF expansion – site layout.



Cell design

The starter perimeter embankment, which will be raised once by 2.5 m (Stage 1), will be constructed using the upstream construction method, with construction undertaken on both the existing crest and over the existing tailings beach, using compacted tailings sourced from within the existing TSF.

The downstream batters will be protected by an outer zone of mine waste capping, sourced from an existing stockpile on the Premises. The embankments will have the following final geometry (see below figure):

downstream batter 1:4 (v:h); upstream batter 1:1.5 (v:h);

crest width 7.0 m; crest crossfall of 2% (sloped inwards into the TSF).

The TSF has been assigned a hazard rating of Medium and is classified as Category 2, based on classification criteria outlined in the ANCOLD Guidelines on Tailings Dams 2012 (ANCOLD guidelines) and the DMIRS Code of Practice for Tailings Storage Facilities in Western Australia (2015). The design criteria adopted are in accordance with ANCOLD guidelines.

Storage capacity

A summary of the estimated storage characteristics of the TSF for recent and future embankment raises is shown below. The volume and storage life have been estimated based on a deposited tailings dry density of 1.5 t/m3 obtained from laboratory testing, an average tailings beach slope of 1.43% (1:70) and total tailings production over the next 10 years of 3.6 Mt.

Crest RL

(mAHD)

Tailings Storage Capacity Storage life

(years) Volume (m3) Tonnage (t)

Stage 2 (RL 415 m) 540,000 810,000 1.9

Stage 3 (RL 417 m) 520,000 780,000 1.8

Stage 4 (RL 419 m) 495,000 742,000 1.8

Southern Extension – starter (RL 413.5 m)

580,000 870,000 1.9

Southern Extension – Stage 1 (RL 416 m)

404,500 606,750 End of mine life

Decant structures

The starter (RL 413.5 m) and Stage 1 (RL 416 m) decant structures will be constructed using standard pre-cast slotted concrete pipes and select coarse waste rock, to allow filtration of water liberated from tailings. Only clean select filter rock material with low fines content will be placed around the decant structures.

Placed rock will be clean, fines-free (<3 % passing 75 µm), competent rock mine waste with a well-graded particle size distribution between 50 and 150 mm. All rock will be carefully placed to ensure the concrete pipes are not dislodged or damaged. Surface water liberated from the tailings slurry will be recovered via decant pumps deployed within the decant structures and pumped back to the process plant for reuse.

Operation

As currently occurs at the existing TSF, tailings will continue to be deposited sub-aerially and spirally around the tailings storage perimeter via multi-point spigot discharge. This spigotting process is undertaken to ensure the water pond is maintained away from the embankment and around the decant structure, and allows the deposited tailings to form a concave valley sloping toward the decant structure at a 1.43 % gradient (1:70). This cycling of spigots is also important in maintaining relevant freeboard.



▲ TSF southern extension – proposed starter embankment and raise (Stage 1)



Monitoring instrumentation

Groundwater is monitored quarterly in eleven bores around the existing TSF for water level and quality.

A total of eight Vibrating Wire Piezometers (VWPs) were installed in the TSF in 2013 – four in the perimeter embankment (north and south) and four on top of the tailings beach (two north and two south). At least 4 new VWPs will be installed in the perimeter embankment of the proposed southern extension.

Seepage

Seepage modelling presented by Coffey (2015) indicates that groundwater levels will rise in the order of 4 – 6 metres following the most recent embankment raise to Stage 4 crest height. Future groundwater levels will likely exceed 4 mbgl at bores MB06 and potentially MB03 on the northern corridor, with the predicted depth to groundwater being less than 1 mbgl. It is also predicted that seepage may occur at the embankment toe along the northern embankment.

The predicted groundwater level rise is not expected to exceed 4 mbgl for the southern bores MB10 and MB11, providing the operational supernatant pond area is managed to be less than 30% of the total TSF surface area.

In order to address the predicted rise in groundwater levels, two existing groundwater recovery bores (RB03 & RB04) were commissioned in December 2019.

Surface water management

The 4-hour PMP (Probable Maximum Precipitation) rainfall event equates to around 590 mm of rainfall. The total surface area of the TSF (existing cell and proposed southern extension) is around 442,175 m2 (including perimeter embankment crest), therefore up to 260,883 m3 of water can be expected to accumulate with a runoff coefficient of 1.0. With around 620,000 m3 of storage capacity available in the TSF basin, the ponded water would be at least 50 m from the closest embankment crest, and the likelihood of overtopping is therefore considered to be negligible at closure.

The TSF has been sized to accommodate tailings storage and design rainfall, incorporating an operational freeboard of 300 mm. For this reason, WSA has not designed the TSF with a spillway.

Surface water falling on the downstream slope of the TSF will infiltrate into the topsoil and waste rock cover, with the remainder flowing downslope as runoff. A perimeter drain will direct flow towards an existing surface water management pond located at the western side of the facility, in order to protect the embankment from damage from surface water flow. Runoff from a 1:100 year, 72 hour storm event (~150 mm) reporting to the surface water management pond will be around 15,000 m3, which is less than 50% of the capacity of the pond.

Proposed controls

Effective management of the TSF decant pond will ensure excess water is continually removed and with the pond being maintained around the decant tower, this will minimise the risk of a perimeter breach and release of saturated tailings.

Based on seepage modelling (see below), seepage is expected to increase up to 130 m3/d, of which additional seepage can be minimised by increasing the dewatering bore network to four recovery bores yielding around 100 m3/d within the northern corridor and downgradient of the TSF. Thus WSA proposes to use at least two additional recovery bores (RB05 and RB06) to suppress the rise of water levels at the northern corridor of the TSF, with two other recovery bores (RB07 and RB08) proposed for contingency purposes.



Construction works

A detailed construction and earthworks specification is included at Attachment 2, providing a description of construction requirements and procedures for the starter embankment and decant accessway. The above sections include a general description of the works.

Tailings reclamation storage area

Consistent with mining proposal 31895, WSA are currently undertaking reclamation of tailings from the footprint of the original TSF in the area of the proposed southern extension cell. This tailings material is combined with sand and binder at the paste plants to fill voids left by underground mining. It is proposed that a temporary tailings storage area is established within the northern apron of the existing northern cell, prior to transport to the existing paste plants at the Spotted Quoll and Flying Fox sites.

Access ramp and batters

In order to transport tailings material to the Spotted Quoll site and to provide access to haulage trucks, a ramp and associated batters are proposed to be constructed along the eastern side of the existing TSF. The proposed ramp has a gradient of 1:40, will be 10 m wide and contain a 2.5 m wide window with a 15 degree batter angle.

Infrastructure

Prescribed Activity Category 5

Existing infrastructure

1 Cosmic Boy TSF – current embankment level Stage 4 (RL 419 m)

2 Stage 4 decant access causeway – current level RL 419 m

Proposed works to infrastructure

1 Construction of starter embankment for southern extension cell (RL 413.5 m)

2 Construction of decant accessway for southern extension cell (RL 413.5 m)

3 Establish tailings reclamation area

4 Construction of access ramp and batters along eastern side of existing TSF

Environmental siting

The Cosmic Boy TSF is located on vacant Crown land with its footprint contained entirely within the existing mining tenements M77/399 and M77/335. It is situated centrally to the greater Forrestania Nickel Operations, and is about 80 km from Hyden, the nearest populated centre.

The TSF is surrounded by remnant vegetation that is largely undisturbed, with only the concentrator and processing plant, workers accommodation village and an airstrip located adjacent to the west. Vegetation in the vicinity of the TSF is comprised of rehabilitated areas often dominated by juvenile Eucalyptus salubris and E. annulata and natural Eucalyptus woodlands typically dominated by Eucalyptus salmonophloia, E. longicornis and E. urna in the upper stratum with Eucalyptus mallee species such as E. calycogona and E. flocktonaiae subsp. Flocktoniae dominating the mid stratum.

The Lake Cronin Nature Reserve is located about 14 km north-east of the Cosmic Boy TSF. This lake is listed on the ‘Directory of Important Wetlands in Australia’ as the best example of a Melaleuca dominated wetland in this bio-region. No other specified ecosystems or areas of high conservation value have been identified in proximity that may be directly impacted from the proposed activities. There are no permanent surface water bodies or seasonal wetlands in the immediate area.

Geology

The geology of the Forrestania area largely consists of a greenstone belt running on an axis from Mt Holland in the north to Hatters Hill in the south and includes many types of ancient



metamorphic rocks. The Forrestania greenstone belt is constrained by granitoid rocks that developed during the late Archaean / Proterozoic and form the western and eastern boundaries to the greenstone belt. During the period of granite emplacement significant alteration, folding and faulting occurred within the greenstone belt. The most significant alteration to the greenstone ‘stack’ of mafics, ultramafics and sediments was the formation of a major synclinal structure – this feature dominates the structural geology of the region.

Hydrogeology

Groundwater in the Forrestania area occurs in weathered and fractured bedrock aquifers. Groundwater salinity ranges from generally saline to hypersaline and is on average around 40,000 mg/L TDS (Total Dissolved Solids) and pH ranges from 3.9 to 7.1. Groundwater movement is generally from higher parts of the landscape, often where greenstone belts occur, to discharge at salt lakes, which may indicate the presence of palaeochannel systems. Recharge is mostly by widespread infiltration of rainfall, probably at low rates as indicated by the prevailing high groundwater salinities.

Golder Associates (2005) state that groundwater is scarce and there are no local supplies of potable water in the site area. In addition, hypersaline groundwater was located in deep sterilization holes which were drilled between 80 m and 100 m vertical depth.

Legislative context and other approvals

Relevant approvals

Legislation Details

Part V of the EP Act (WA)

The Applicant holds Licence L8041/1990/5 for operation of the Forrestania Nickel Operations, which includes the processing of mine ore into nickel concentrate at the Cosmic Boy Concentrator, and the discharge of mine dewatering water to a network of aquifer re-injection borefields, mine voids and evaporation ponds.

Mining Act 1978 (WA) The Department of Mines, Industry Regulation and Safety (DMIRS) is currently assessing a Mining Proposal (Registration ID: 85133) for the southern expansion cell proposal.

Part V of the EP Act

The overarching legislative framework of this assessment is the EP Act and EP Regulations.

The guidance statements which inform this assessment are listed in Appendix 1.

Works approval and licence history

Note: Licence L8041 was originally issued for the Forrestania Nickel Operations (FNO), initially for dewatering operations at the Flying Fox site. Following the commencement of mining, separate licences were issued once additional operations at the FNO came online, including ore processing at the Cosmic Boy site (L8331) and dewatering at the Digger Rocks South site (L8233). In 2013, the Department determined to amalgamate all prescribed activities associated with the FNO into one licence (L8041). The pre-existing licences (and registrations) were then relinquished by the Applicant and are now inactive.

Instrument Issued Nature and extent of works approval, licence or amendment

W4019/1990/1 17/11/2004 Works Approval for construction of dewatering operational and monitoring infrastructure at Flying Fox, to enable commencement of mining and subsequent disposal of mine dewater into the abandoned Flying Fox underground mine (stage 1), and the abandoned McMahon and Lounge Lizard open mine pits (stages 2 & 3).

L8041/1990/1 17/10/2005 New licence issued to authorise commencement of dewatering



operations (2,000,000 tpa) at Flying Fox.

W4244/1990/1 09/10/2006 Works Approval for expansion of dewatering operations at Flying Fox to allow mining of the T5 zone (2,900,000 tpa). This included constructing a 22 km transfer pipeline from Flying Fox to Cosmic Boy, re-establishment of the Seagull and Liquid Acrobat reinjection borefields, and development of a new reinjection borefield (Sibelius).

L8041/1990/2 16/10/2006 Licence reissued for the Flying Fox mine.

W4243/1990/1 09/11/2006 Works Approval for construction of the Cosmic Boy Concentrator (350,000 tpa capacity) and TSF.

L8041/1990/2 31/08/2007 Amendment to Flying Fox licence to authorise discharge of dewatering effluent to the 3 reinjection borefields and to formalise commitments regarding groundwater and native vegetation monitoring.


W4465/2008/1 19/12/2008 Works Approval for construction of the Mossco Farm evaporation ponds, including 32 km of dewatering pipeline from the Cosmic Boy site.

L8233/2008/1 01/01/2009 New licence issued for dewatering operations at Digger Rocks (Diggers Rock South – stage 1).

W4465/2008/1 19/02/2009 Amendment to works approval for construction of the Mossco Farm evaporation ponds, to include an additional tenement that was omitted from the original approval.

L8331/2009/1 26/02/2009 New licence issued for the Cosmic Boy Concentrator & TSF.

L8041/1990/3 27/08/2009 Amendment to Flying Fox licence following complete review of operations and issue in new format. Conditions added requiring groundwater monitoring, groundwater discharge criteria (limits and targets) and exceedance reporting, native vegetation monitoring and annual audit compliance reporting (AACR). Additional tenements added to the premises description.

W4558/2009/1 03/09/2009 Works Approval for stage 2 upgrade of the Cosmic Boy concentrator to 600,000 tpa capacity.

W4499/2008/1 28/09/2009 Works Approval for construction of the Spotted Quoll mine and associated dewatering infrastructure.

W4499/2008/1 19/10/2009 Amendment to Spotted Quoll works approval for a temporary mobile screening operation.

L8041/1990/3 05/11/2009 Amendment to Flying Fox licence to include category 12 for a temporary mobile screening operation.

L8041/1990/3 04/02/2010 Amendment to Flying Fox licence to authorise dewatering at the new Spotted Quoll mine.

W4604/2009/1 11/02/2010 Works Approval for the McMahon clearwater pond expansion, to separate dewatering effluent from Flying Fox and the new Spotted Quoll mine, the latter of which contains higher salinity.


L8331/2009/1 15/10/2010 Amendment to Cosmic Boy TSF licence to increase licensed capacity to 600,000 tpa.

W4771/2010/1 11/11/2010 Works Approval for construction of a paste fill plant at the Spotted Quoll mine.

L8041/1990/4 02/12/2010 Licence amendment to the Flying Fox licence following a compliance inspection in November 2010.



L8041/1990/4 03/11/2011 Licence amendment to the Flying Fox licence to add the Mossco Farm evaporation ponds as an authorised discharge point for mine dewater.

L8233/2008/2 01/01/2012 Licence renewed for the Digger Rocks dewatering operation.

L8331/2009/2 25/01/2012 Licence renewed for the Cosmic Boy Concentrator & TSF.

L8041/1990/5 04/10/2013 Licence renewed for the Flying Fox mine, including amalgamation of all other instruments issued to Western Areas Ltd for the Forrestania Nickel Operations, being the Cosmic Boy Concentrator and TSF (L8331), Diggers Rock South mine (L8233), Cosmic Boy sewage facility (R1996) and Flying Fox landfill (R2311).

W5665/2014/1 21/08/2014 Works Approval for construction of a septic tank sludge drying lagoons in an old gravel pit east of the Spotted Quoll site.

W5750/2014/1 15/01/2015 Works Approval for construction of a paste fill plant at the Flying Fox mine site.

W5767/2014/1 26/02/2015 Works Approval for construction of an additional septage evaporation pond for the workers accommodation village.

W5839/2015/1 20/08/2015 Works Approval for construction of a bioleach plant at the Cosmic Boy site, to improve nickel recovery from processing.

W5859/2015/1 08/10/2015 Works Approval for the Cosmic Boy TSF embankment raise and southern extension.

L8041/1990/5 14/04/2016 Licence amendment following full review. Category 12 added to authorise various on-site crushing and screening operations. Category 5 design capacity increased to 680,000 tpa. Expiry extended to 2027 to align with tenement expiry.

L8041/1990/5 14/12/2017 Amendment Notice 1 – update conditions relating to dewatering discharge to Mossco Farm evaporation pond and associated groundwater management.

L8041/1990/5 26/01/2019 Amendment Notice 2 – authorise discharge of mine dewater from Spotted Quoll underground operations, including construction of new dewatering pipeline.

L8041/1990/5 14/05/2019 Amendment Notice 3 – authorise operation of septic tank sludge drying lagoons constructed under W5665/2014/1.

W6273/2019/1 02/09/2019 Replacement works approval for the expired W5859.

W6372/2020/1 24/04/2020 Works approval for the southern extension cell (this approval).

Modelling and monitoring data

Tailings geochemistry

The tailings slurry is discharged at a pH of around 8.5; however the slurry contains significant amounts of sulfide minerals (pyrrhotite and pyrite) and is therefore classified as ‘acid-forming’. The supernatant water is near neutral and saline, with low concentrations of minor elements, although nickel concentrations may be within the mg/L range.

Monitoring of seepage impacts to groundwater

Groundwater beneath the TSF is hypersaline (35,000 – 80,000 mg/L TDS), low pH and with elevated levels of lead, zinc and boron; therefore the key impact from tailings deposition relates to the mounding of groundwater that can potentially bring groundwater and salts into the root zone of nearby vegetation, causing waterlogging and salt toxicity, leading to deterioration of vegetation health and potentially vegetation death.



Groundwater monitoring data

In 1992 (i.e. prior to any mining operations) the groundwater table was not intersected in investigative boreholes at the TSF site. The pre-mining groundwater table is reported to have an elevation of RL371 m and sloped towards the west to a drainage depression some 9 km away.

Monitoring bores MB1 – MB3 were installed in 1993. During the period of Outokompu operations (1992 – 1999), groundwater levels rose up to 18 m at bore MB1, to intersect natural ground at a topographic low point on the western boundary of the TSF. MB2 is reported to have risen up to 13 m over the same period. This was the result of seepage occurring at the external toe of the north face of the original TSF.

Monitoring bores MB04 – MB11 were installed in 1999 to monitor the extent of the seepage mound. From 1999 through to January 2009 (i.e. the period of no mining), the groundwater mound slowly retreated and spread primarily west (downgradient), to the point where pre-2009 water levels were close to steady-state (with the exception of MB08).

In 2009, WSA re-commissioned the TSF and mounding has rebuilt on the previously dissipating mound. The volume of water infiltrating since re-commissioning of the TSF appears to have been significantly less than the volume of water that infiltrated during the previous operations, which may be attributed to the shorter period of operations and lower plant throughput, the smaller TSF footprint, refinements to the size of the pond, or a lower permeability of the TSF base (being situated over previous tailings).

Prior to the preparation of the TSF groundwater recovery plan (Coffey, 2012), which was a requirement of L8331 following a rise of groundwater levels to within 4 m of ground surface at MB1, four recovery bores (RB01 – RB04) were installed in late 2011 in the vicinity of MB1. Only two of these bores (RB01 & RB02) have been commissioned to date, and have had the desired effect of lowering the water level in bore MB1 via intermittent pumping.

Water levels in MB06 appear to be unaffected by pumping of both RB01 and RB02, which suggests the seepage pathways from the TSF towards MB06 are not subject to the drawdown or radius of influence from the current pumping strategy. However, water levels may increase over time in tandem with rising tailings levels and associated supernatant water in the TSF.

Seepage modelling

Seepage modelling presented by Coffey (2015), using a three-dimensional groundwater model (Modflow), indicates that a rise of groundwater levels can be expected to be between 4 m (MB10) and 6 m (MB06) with the existing TSF embankment being raised to the Stage 4 crest height and construction of the southern extension. This implies that future water levels will likely rise to within 4 m of ground surface at MB06 (and potentially MB03, on the northern corridor), with the predicted depth to groundwater being less than 1 m. Seepage is also predicted to occur at the embankment toe along the northern embankment.

For the southern monitoring bores, MB10 and MB11, the predicted groundwater level rise due to the embankment raises is not expected to exceed 4 mbgl, provided the operational supernatant pond area is maintained less than 30% of the total TSF surface area. The predicted depth to water at MB10 is approximately 14.3 mbgl.

Based on the predicted rise in groundwater levels, the WSA has recently commissioned the existing recovery bores RB03 and RB04, which were installed in 2011. The Modflow model Coffey (2015) also indicates that at least two additional recovery bores (RB05 and RB06) will be needed to suppress the rise of water levels along the northern corridor of the TSF. Two other recovery bores (RB07 and RB08) are proposed for contingency purposes, with their final locations subject to field conditions, noting the anticipated low success rate based on experience in construction of the original RB01 – RB04 bores at this site.



Risk assessment

Risk event

Consequence rating

Likelihood rating

Risk Reasoning

Regulatory controls

(Refer to conditions of the granted works approval) Source/Activities

Potential emissions

Potential receptors Potential pathway & receptor (impact)

Category 5

TSF southern extension - cell embankment construction

Civil excavation / vehicle movements on unsealed roads

Southern extension starter embankment construction works

Stage 1 crest raise

Noise and dust associated with construction activities

No residences or other sensitive receptors in proximity.

Closest receptor is >25 km away

Air / wind dispersion, causing amenity impacts/ health impacts

Not applicable Not applicable Not applicable Based on the separation to off-site receptors (at least 25 km), the delegated officer considers that a pathway does not exist for noise and dust generated during construction works to impact on off-site human receptors.

None specified.

Risk event

Consequence rating

Likelihood rating

Risk Reasoning

Regulatory controls

(Refer to conditions of the granted works approval) Source/Activities

Potential emissions

Potential receptors Potential pathway & receptor (impact)

Category 5

TSF cell Stage 4 operation

Tailings deposition into TSF southern extension to starter crest height of RL413.5 m

Tailings deposition into TSF southern extension to Stage 1 crest height of RL416 m

Dust lift-off from TSF surface

Noise from operation of the TSF

No residences or other sensitive receptors in proximity.

Closest receptor is >25 km away

Air / wind dispersion, causing amenity impacts/ health impacts

Not applicable Not applicable Not applicable Based on the separation to off-site receptors (at least 25 km), the delegated officer considers that a pathway does not exist for noise and dust generated during operation of the TSF to impact on off-site human receptors.

None specified.

Seepage of deposited tailings through base of TSF

Native vegetation in proximity to TSF

Mounding causing rising hypersaline groundwater inundating root zone of vegetation

High-level impact at local scale

Major

Could occur if not adequately managed

Possible

High

Acceptable, subject to works approval holder controls and additional regulatory controls conditioned

Rising groundwater levels may inundate adjacent vegetation root zones with hypersaline water with potentially elevated metal(loids), causing vegetation death. Seepage modelling indicates groundwater levels will exceed 4 mbgl, particularly on the northern corridor. The Applicant proposes to commission the 2 existing groundwater recovery bores in the vicinity in order to address this. Seepage modelling (Coffey, 2015) also indicates an additional 4 recovery bores are required, in order to lower groundwater to acceptable levels. Recovered seepage water will be returned to the process water circuit.

Seepage modelling also indicates that groundwater levels should not rise to within 4 metres of ground surface if the operational supernatant pond area is maintained less than 30% of the total TSF surface area.

As these controls are existing requirements on W6273 for the previous Stage 4 embankment raise, they will not be duplicated in this works approval.

None specified on this works approval– controls to address this risk event are existing requirements on W6273 and L8041:

W6273 controls:

- groundwater recovery bores RB03 and RB04 to be commissioned;

- additional recovery bores RB05 to RB08 to be installed along the northern corridor

L8041 controls:

- groundwater mounding limit of 4 mbgl to be reinstated, as per L8331

- groundwater mounding target of 6 mbgl to be reinstated, including management response requirements

- must maintain an operational supernatant pond area ≤30% of the total TSF surface area

Groundwater Direct discharge, causing groundwater contamination

Low level on-site impacts

Minor

May occur in exceptional circumstances only

Rare

Low

Acceptable, not subject to controls

Based on the quality of groundwater being hypersaline (35,000 – 80,000 mg/L TDS) the delegated officer considers there to be no beneficial uses except for mining purposes.

None specified

Overtopping of the TSF, causing tailings discharge to land

Soil, remnant vegetation adjacent to TSF

Embankment failure, leading to contamination of surrounding land with metals and metalloids, dissolved solids

High level on-site impacts, minimal off-site impacts, on local scale

Major

May occur in exceptional circumstances only

Rare

Medium

Acceptable, subject to Licence Holder controls conditioned

TSF design remains unchanged from the design as per Coffey (2014). TSF previously assessed and approved with capacity for a 1:100 year, 72 hour rainfall event in addition to 500 mm operational freeboard via the existing licence L8041/1990/5.

Existing licence controls:

- operational freeboard of 500 mm (existing condition 1.2.3)

- routine inspections to be conducted (existing condition 1.2.4)



Consultation

The application was publicly advertised on DWER’s website in March 2020. No submissions were received within the specified timeframe.

DMIRS (Environmental Compliance Branch) advises the application is consistent with the mining proposal, however further clarification is being sought on the store and release cover specifications for the TSF, the selection of NAF waste rock material to cover the TSF walls, flooding risk, groundwater flow direction and placement of monitoring bores, and seepage controls. A site mine closure plan (Reg ID 82944) was submitted on 28 September 2019 and is currently being assessed. Amongst other requests, further information has been required regarding TSF closure design for management of acid and metalliferous drainage.

The applicant was provided with drafts of this report and the works approval on 22 April 2020 and made no additional comments.

Conclusion

This assessment of the risks of activities on the Premises has been undertaken with due consideration of a number of factors, including the documents and policies specified in this decision report (listed in Appendix 1).

Based on this assessment, it has been determined that a works approval will be granted subject to conditions commensurate with the determined controls and necessary for administration and reporting requirements.

DWER notes that it may review the appropriateness and adequacy of controls at any time and that, following a review, DWER may initiate amendments to the approval under the EP Act.

Tim Gentle MANAGER, RESOURCE INDUSTRIES REGULATORY SERVICES Delegated Officer Under section 20 of the Environmental Protection Act 1986



Appendix 1: Key documents

Document title In text ref Availability

Forrestania Nickel Operations – Works Approval application: Cosmic Boy Tailings Storage Facility – TSF Southern Extension and ancillary works (February 2020).

Application DWER records (A1864290)

Coffey, 2012. Cosmic Boy Project - TSF Groundwater Recovery Plan. Prepared for Western Areas Ltd by Coffey Mining Pty Ltd.

Coffey, 2012 DWER records (A482056)

Coffey, October 2015. DER Draft Works Approval W5839/2015/1: Seepage. Unpublished report prepared by Western Areas Ltd by Coffey Mining Pty Ltd.


Coffey, February 2016. Cosmic Boy TSF Embankment Raise – Revised Design Report. Prepared for Western Areas Ltd by Coffey Mining Pty Ltd.


DER, July 2015. Guidance Statement: Regulatory principles. Department of Environment Regulation, Perth.

DER, 2015a accessed at www.der.wa.gov.au

DER, October 2015. Guidance Statement: Setting Conditions. Department of Environment Regulation, Perth.

DER, 2015b

DER, February 2017. Guidance Statement: Risk Assessments. Department of Environment Regulation, Perth.

DER, 2017a

DER, February 2017. Guidance Statement: Decision Making. Department of Environment Regulation, Perth.

DER, 2017b

Licence L8041/1990/5 – Forrestania Nickel Operations.

Existing Licence

accessed at www.der.wa.gov.au

Golder Associates, 2005. Technical Documentation in support of Notice of Intent for Cosmic Boy Tailing Storage Facility. Report prepared for Western Areas NL by Coffey Mining Pty Ltd.

Golder Associates, 2005

DWER records (A1813676)

Licence L8331/2009/2 – Cosmic Boy Concentrator & TSF.

L8331 DWER records (A469487)

Clark Lindbeck, 2016. Forrestania Nickel Operations – Cosmic Boy TSF Expansion – Revised Mining Proposal M77/399. Prepared for Western Areas Ltd by Clark Lindbeck & Associates Pty Ltd

Mining Proposal

accessed at minedexext.dmp.wa.gov.au

Works Approval W5859/2015/1 – Cosmic Boy TSF embankment raise and southern extension.

W5859 DWER records (A986279)

http://www.der.wa.gov.au/

http://www.der.wa.gov.au/

http://www.dmp.wa.gov.au/



Attachment 1: Works Approval W6372/2020/1



Attachment 2: Construction and earthworks specifications

ir-t04 decision report template · western areas limited (wsa) operates the cosmic boy nickel...

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