6 02. Contour drains and diversion drains/bunds will be used through the Stockpile 2 area to ensure that majority of runoff is directed to SRP-TSF3-02 and limiting catchment area to 2ha draining to SRP-TSF3-03. SRP-TSF3-03 will also be used to treat runoff during the construction of the permanent uphill clean water diversion drain. The stockpiles will be progressively stabilised (e.g. with grass seed and grassed). Paleo Gully Undercut To maximise the TSF3 site and provide for a structure of similar geotechnical integrity as the existing TSF1A and 2 embankments, some excavation of areas of weak and compressible soils and backfilling with a structural fill will be undertaken. An undercut to 20m depth is proposed in an area termed the Paleo Gully, which is the controlling geological feature limiting the downstream toe position. The Paleo Gully undercut specifically removes 140,000m3 of soft alluvium and 120,000m3 of sensitive reworked rhyolite tuff material. Alluvium suitable for reuse will be sent to the stockpiles to dry out and any unsuitable alluvium and sensitive tuff is proposed to be placed up the east gully. This work will require bulk excavation and dewatering. The undercut will need to start at the shallow northern end of the Paleo Gully and progressively work to the south. The excavated material will be NAF. Pumped water from the excavation will be discharged to SRP-TSF3-04 and then discharged to the Ruahorehore Stream. SRP-TSF3-04 will have minimal overland flow runoff as majority of water will be pumped from the excavation. Therefore, this SRP has been sized based on the predicted pumping rates provided by EGL. Dewatering rates of up to 2,500m3/day is predicted (refer to EGL Engineers Report for further details). If SRP-TSF3-04 cannot adequately cope with the volume of pumped water, then it will be pumped to nearby sediment ponds or the TSF1A existing storage ponds. Realign Ruahorehore Stream The Ecological Assessment prepared by Boffa Miskel states that the construction of TSF3 will result in the diversion of a tributary of the Ruahorehore Stream. Approximately 2.111km of stream length will be diverted to form a 2.95km permanent uphill diversion drain. The construction of the permanent uphill clean water diversion is discussed in Stage 5. Additionally, sections of the Ruahorehore stream are proposed to be realigned below the proposed Collection Ponds measuring approximately 311m. These sections of stream diversion will be undertaken within Stage 1 (refer to ESCP-TSF3-001-04). Initially, a silt fence will be installed below the footprint of SRP-TSF3-06. This SRP will be constructed at this stage to provide impoundment for dirty water during the stream realignment but will also be utilised during the construction of the Collection Ponds. The sections of stream realignment will be constructed offline (i.e., in the dry) with no effect on the existing stream channel. Any dirty water will be pumped to the SRP for treatment. Once the new offline stream sections are completed and stabilised as per the Ecologists recommendations, then the downstream tie in, followed by the upstream tie in with the Ruahorehore Stream will be completed. The tie ins will utilise a dam and over-pump methodology during day works. Each tie in will likely be completed within 1-2 days. 2.2. Stage 2 Refer to ESCP-TSF3-002-01, ESCP-TSF3-002-02, ESCP-TSF3-002-03 and ESCP-TSF3-002-04.
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