GHD | Oceana Gold NZ Ltd | 12552081 | Geochemical Assessment Wharekirauponga Underground Mine (WAI985-000-REP-LC-0013) 25 All WRS runoff and collected seepage will be collected in collection ponds and pumped to Waihi for treatment at the existing WTP. As the available dataset is expanded, consideration will be given to the segregation of non-acid forming (NAF) material should it be present. 6.1 General Management Philosophy To ensure appropriate geochemical management of PAF spoil and to reduce potential effects on water quality, the implementation of an appropriate spoil management strategy is required. Commonly used methods for the management of mine spoil that have the potential to mitigate adverse effects to water quality include: Oxidation control – Control of oxygen flux to reactive sulphides, such as by deposition under water or through the application of low permeability layers; Geochemical control - Blending rock types or addition of neutralising materials to control pH and oxidation rates; and Hydrological control - Placement of low permeability layers, evapotranspiration layers and spoil management structures to control the potential leaching rate from the disposal facility. OceanaGold has utilised a combination of these methods to effectively manage spoil at its Waihi operations to date and it is envisaged that management of rock sourced from the Willows Access tunnel and WUG Mine will employ similar methods. The means of minimising acid generation of the spoil from the WUG development is likely to include: Limiting exposure time of spoil between excavation and disposal to the WRS; Blending and/or layering the spoil with limestone, in order to prevent the onset of acidification where the specific acid forming characteristics of the material being excavated suggest that the material is at risk of producing ARD; Compaction of placed spoil material in the WRS to reduce permeability, limiting oxygen and water ingress; and Covering PAF spoil with NAF material to sufficient thickness to limit oxygen ingress to the encapsulated PAF material. The design of the WRS is outlined in WSP, 2022 and will be constructed with the above principles in mind. These principals are implemented at OGNZL current Waihi operations and have proven to be successful throughout the mine’s operations.
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