GHD | Oceana Gold (New Zealand) Limited | 12537997 | Gladstone Pit TSF 47 9. Conclusions and recommendations This report summarises the design of the GOP TSF, an in-pit tailings storage facility at Waihi Gold Mine. The following conclusions and recommendations are made based on this design: – The proposed GOP TSF design has been completed in accordance with NZSOLD Dam Safety Guidelines and ANCOLD (2019) Guidelines on Tailings Dams. – The design has included a geomembrane liner and underdrainage system to limit groundwater discharge to the surrounding environment. – The underdrainage is important to maintain liner stability and minimise potential bulging of the liner prior to tailings being deposited. – No tailings deposition is recommended until the completion of any underground workings connected to GOP due to the potential in-rush risk. – Backfill of the pit to provide a flatter, engineered surface for lining is recommended. The backfill shall consist of ROM overburden with a processed (crushed and screened) select rock used as a liner sub-grade. – PAF rockfill is proposed to be used for a majority of the backfill material and is recommended to be lime dosed in accordance with the rates recommended by AECOM (2021). – The tailings rate of rise should be slowed where possible to minimise post-closure settlement and the GOP TSF should be used as a supplementary storage for a fraction of the total tailings stream, with the remaining tailings going to the other TSFs on site. – Tailings density reconciliation through bathymetric surveys should be completed on a regular basis to confirm design assumptions related to settled dry density, rate of rise and post-deposition settlement. – Consider inclusion of a light vehicle road in the backfill surface to provide access for remediating potential erosion damage and providing safe access for tailings pipeline installation. The access road could also be used to run the tailings and/or water return pipelines to the base of the pit. – An OMS manual should be prepared for the GOP TSF. The emergency response plan for GOP TSF shall be incorporated into the OMS manual. The Waihi Operation Emergency Management Plan (EMP), which covers the entire site, should be updated to reflect the emergency requirements for GOP TSF.
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