GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 127 6. Willows Rock Stack 6.1 Site overview 6.1.1 General site setting The location of the Wharekirauponga Portal (next to WRS) is presented in Figure 2.2. Existing land use comprises dry stock and dairy farmland on the slopes of the Mataura and Walmsley Streams, both tributaries of the Ohinemuri River. The proposed WRS is located within the Mataura Stream catchment, which is approximately 6.6 km2, with steep slopes and the upper catchment covered in native vegetation. The grade of the slopes reduces at the location of the proposed Wharekirauponga infrastructure across the terrace deposits. There are several unnamed tributaries of the Mataura Stream, some of which intermittently flow with others appearing to be spring fed (Mitchell Daysh, 2022). There is a small existing area of wetland adjacent to the Mataura Stream, with the infrastructure proposed to be placed to avoid impact on the more identified wetland areas. 6.1.2 Summary of proposed activity WUG will comprise surface infrastructure, tunnel portals, a tunnelling system and the mine itself. PAF rock (PAF) from the WUG Access tunnels will be stored at the WRS. The WRS is proposed to be located within a steeplysided gully (up to 56º slopes; the WRS gully) which forms a tributary of the Mataura Stream. (Figure 6.1) (referred to as “Tributary 2”, as explained in Section 6.2.2). In summary, the development of the WRS is understood to require: – Removal of up to 1.1 m weak material (weathered ash) and 0.3 m topsoil in the lower norther-eastern valley slopes. Stockpile storage will have a maximum 3 m face height. – Establishment of a main collection pond to collect runoff from the rock stack, which will have capacity for a 1 in 10-year storm event. – Installation of a toe seepage collection pond at the base of the proposed WRS (approx 1,180 m RL). – Placement of rock starting at ~1,180 mRL, moving up the WRS gully to a maximum stack height at 1,265 m RL over a 4 year period. The stack will be constructed in 10 m lifts, to a maximum height of 20 m above natural ground. – Lime will be introduced progressively to assist in neutralising PAF contact waters. – A seepage drain system will be constructed up the WRS gully as the WRS construction progresses up the slope. Contact water will be directed through this drain to the toe seepage collection pond and ultimately to the WTP. – Catchment water will be partially directed back to the Mataura Stream through an existing wetland area. The water collected in the main collection pond will be directed to the WTP for treatment. WRS is intended to be a temporary rock stack, with the rock returned to the WUG as backfill shortly after commencement of mining. Final rock will be removed from the stockpile area approximately eight years after WRS construction commences. On exhaustion of the rock from this stack, the site will be rehabilitated and returned largely to its original configuration, with improved riparian areas and stock exclusion fencing to protect waterways. There is no groundwater dewatering or diversion activity proposed for this WNP area.
RkJQdWJsaXNoZXIy MjE2NDg3