EGL Ref: 9215 23 June 2022 Page 37 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. construction TSFs are designed, constructed, and operated in a safe manner. However, if the design does not include the appropriate drainage to limit the extent of saturation of the tailings, construction occurs without the appropriate management of tailings deposition and drainage within the tailings is not properly constructed, those tailings can be subject to liquefaction when saturated and failures can occur even under normal static conditions. OceanaGold Corporation, the parent company of OGNZL, has chosen to completely avoid risks associated with TSFs constructed by the upstream construction method by not constructing any new upstream constructed TSFs. The existing TSFs at the Waihi Operation benefit from the source of earth and rock fill from the Martha Open Pit which is used to construct the TSF embankments using the downstream construction method. The materials used to construct the downstream and centreline embankments are compacted to specified standards with specific fill zoning to contain tailings and seepage which results in a robust embankment which the tailings are impounded behind. These embankments will not liquefy and have good resistance to earthquake loadings. Other failure modes, like shear planes within the foundation and internal erosion of the embankment, are also possible at any dam or TSF, including Waihi, and are managed through proper design, construction, operation, monitoring and surveillance. This is no different to the safe design, construction, and operation of a water storage dam. 6.0 INPUTS FOR TECHNICAL DESIGN OF TAILINGS STORAGE AND ROCK DISPOSAL The chosen options for tailings storage and rock disposal take into consideration a wide range of information about the characteristics of each option being evaluated, and relevant to the planning needs. This includes technical, environmental, and socio-economic considerations and project economics. This section of the report discusses technical inputs to the design that need to be considered to provide long term security for the containment of tailings and rock, minimise impacts on groundwater and surface water, and create a rehabilitated landform that will provide a netgain in terms of biodiversity. To achieve these objectives requires a collaborative approach with input from a wide range of technical experts (geologists, hydrogeologists, hydrologists, geochemists, engineers), scientific experts (ecologists, biologists, dust and noise consultants), landscape architects and consultation with iwi. The aim is to meet obligations under the Resource Management Act, meet community and iwi expectations and to design and construct structures that meet structural stability and durability requirements under the Building Act. The following sections of this report summarise storage requirements for tailings and rock, stakeholders, and factors that need to be considered to meet acceptable performance objectives. 6.1. Future Sources of Ore Future sources of ore for the Waihi Operation includes existing Life of Mine resources (Martha Open Pit (MOP) and Martha Underground Mine (MUG)) and the proposed future Gladstone Open Pit (GOP) and Wharekirauponga Underground Mine (WUG). The existing TSFs (Storage 2 and Storage 1A) have capacity to store
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