EGL Ref: 9018 22 June 2022 Page 21 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. 9.11. Closure Plan The closure plan concepts for the NRS are shown in Drawings 0780, 0781 and 0782. The current plan comprises a capping layer of Zone G and H NAF material and establishment of pasture or vegetation. The final maximum closure height of RL148 is lower than the maximum operational height of RL173. The closure profile is less than the operational profile as stockpile material is eventually used in TSF construction or underground backfill. The closure profile indicated is a maximum and may be less for the WNP. The NRS Collection Pond will be converted to wetlands and will be rehabilitated. The Northern Uphill Diversion Drain is to be retained permanently as it will provide the outlet channel for Storage 2 in closure. Closure details will be advanced, and possibly revised, in the site’s Annual Rehabilitation and Closure Plan. 10.0 DESIGN ASSESSMENT 10.1. Stability Slope stability analyses for the proposed NRS have been carried out using limit equilibrium methods outlined in Appendix B. The stability design criteria are outlined in Section 8.1. The analyses have been undertaken for operation and closure groundwater levels for the final profile. Two critical cross sections were analysed. These were Section 1 and Section 2 shown in plan view in Drawing 0715 and in cross section in Drawings 0716 and 0717. Section 1 runs from the southeast corner to the northwest. It includes the west slope of the NRS. The foundations include rhyolite over dacite and ignimbrite materials. Section 2 runs from the south to the north and includes the north slope of the NRS. The foundations include fill placed for the Workshop Ramp (haul road) at the south end, with rhyolite overlying weathered dacite materials. On Section 2 there is some minor ignimbrite materials at the surface, which are stronger than the weathered dacite surface and therefore a weathered dacite profile has been preferentially applied in the analyses. Geotechnical stability is dependent on the management of materials of different strengths within stockpile. Weaker material strengths were applied in the analyses in the centre of the stockpile with stronger material applied at the outer extents. The analyses indicate that with the key cut to rock at the toe of the outer slope and preferential placement of the stronger stockpile material at the toe, there is the ability to manage any weaker materials in stockpile while meeting design criteria proposed. The assessed factor of safety (FOS) values for each loading condition are summarised in Table 6 below. Refer to Appendix B for the calculations and analysis outputs.
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