EGL Ref: 8983 23 June 2022 Page 10 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. Trig Road North is the closest road to Storage 3 and is located 500m to the southeast of the facility. The haul road (Eastern Haul Road and Northern Haul Road) from the existing conveyor loadout behind Storage 2 and Storage 1A will be extended down the East Stockpile to the Storage 3 site. The conveyor delivers material from the MOP and it is proposed that this will be modified to deliver material from GOP. The main function of the TSF embankment is to provide secure containment of the tailings. A secondary function is the disposal of PAF mine overburden material from the MOP and GOP. This is necessary as PAF mine overburden material, if exposed to oxygen for a period of time, can oxidise and generate low pH runoff. This can result in the release of heavy metals and poor water quality. Special measures will be incorporated into the design of Storage 3 embankment, as for Storage 1A and 2, to prevent this from happening and ensure that there are no detrimental long-term effects to the environment associated with the disposal of PAF materials. Limitations on where PAF mine overburden material can be used are set. PAF materials are encapsulated in low permeability, Non-Acid Forming (NAF) mine overburden material in specific zones to restrict both oxygen and water entry. To achieve the design objectives, the embankment will be designed as a zoned structure. The primary functions of the different zones are summarized below: Zone A - Low permeability zone (earth liner) that restricts seepage from mine overburden material into underlying ground Zone B - Low permeability upstream zone that restricts seepage from the tailings Zones C1 and C2 - Structural fill zones that provide support to Zone B and provide a transition between the finer grained material in Zone B and the coarser material in Zones D2 and D3 Zones D2 and D3 - Bulk fill zones with less restrictive requirements than other zones. Zone D2 has a higher strength specification than Zone D3. Zone E - Specified zones for the weakest material Zone F - Structural fill zone on outside shoulder that also provides a transition between the coarser material in Zone D and finer material in Zone G. Also provides a drainage path for leachate. Zone G - Outer sealing layer of the embankment that restricts entry of oxygen and water Zone H - Plant growth layer Zone I - Structural fill forming downstream section of the Perimeter road where it is in fill. PAF mine overburden material and high mercury (>3.5 mg/kg) is not permitted for use in Zones A, G, H and I. Typical profiles illustrating these zones are discussed in Section 11.
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