WAI-985-000-REP-LC-0056 Revision 0 Page 11 of 21 Waihi North Project – Tailings and Rock Storage – Functional Need Assessment 3 TAILINGS STORAGE FACILITY 3 TSF3 is proposed as part of the Waihi North Project to provide storage for tailings from the processing of ore from the proposed Wharekirauponga Underground Mine. The tailings will be pumped as a slurry mixed with water from the Processing Plant to the facility via a pipeline. TSF3 incorporates a downstream embankment design that will be constructed to the east of the existing TSF1A that will provide 6.8M tonnes of tailings storage (combining with 2.1M tonnes of storage in GOP TSF to meet the 8.66M tonnes of tailings storage required for WNP). Downstream construction involves the progressive raising of the embankment in the downstream direction, using compacted earth and rock fill to create the tailings impoundment. A report undertaken by Engineering Geology (EGL) titled; Waihi North Project Tailings Storage and Rock Disposal Volume 1 Natural Hazards and Options Assessment Technical Report OGNZL Document Reference:WAI-985-000-REP-LC-0002, was produced to present the range of options considered for tailings storage and rock disposal for the Waihi North Project. The individual storage options were developed and investigated with input from OGNZL. In assessing the options, the EGL report considers natural hazards which can affect the site and choice of technologies, best available tailings storage technologies, potential locations for tailings storage and rock disposal facilities, and a combination of storage and disposal options for the Waihi North Project. As per the Global Industry Standard on Tailings Management requirement clause 3.2, each potential tailings storage option was assessed using a Multi Criteria Assessment (MCA). The categories considered for each option included the following: • Technical (e.g., geotechnical, geochemical/hydrogeological, mine operations, constructability, materials balance, operability, project schedule). • Environmental (e.g., potential impacts on terrestrial and aquatic ecosystems, groundwater, surface water). • Socio-economic and permitting (potential social and economic impacts and benefits on communities, Mana Whenua, recreation, archaeological/heritage, and landscape/visual effects). • Project economics (land ownership, short-term and long-term capital and operating expenses) Each option was scored against each of the respective categories using weightings. TSF3 in combination with GOP as a TSF scored the highest in the MCA, based on its higher scoring for socio economic & permitting, and project economics criteria compared with other options. Potential tailings and rock storage alternative options are summarised by EGL (2022). Options considered that would avoid the need for the TSF3 and impact on tributaries of the Ruahorehore Stream are summarised below. These options have scheduling and project economic issues that make them unfeasible for the Waihi North Project: Downstream raise of TSF2 to RL176 This option requires the downstream toe of TSF2 to be extended beyond its current footprint by approximately 50m. This is required for geotechnical stability. This relocation of the downstream toe of the embankment closer to the Ohinemuri River reduces the potential to mitigate any adverse groundwater quality effect if they were to occur. The space to mitigate any unforeseen groundwater effects was one of the reasons why TSF2 was set back from the Ohinemuri River in its original design. Relocation of the embankment toe out from its existing position requires new collection ponds, realignment of the perimeter road and perimeter drainage, new key cut to rock, extension of all the existing underdrainage, relocation of the core shed and placement of a new Zone A pad, before PAF rock can be received from GOP. The vegetation, embankment capping layers to prevent acid
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