GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 110 Theis was used as a “first principles” check from the deepest point of the excavation to assist with defining the ZOI at distance (see Section 5.5.1). It is noted that the cross section alignments only allowed for up to 15 m thickness of sensitive for removal. Theis was applied to a full 20 m excavation depth. The approaches adopted are considered to provide an appropriately conservative assessment. The predicted effects (Section 5.6) are provided in the context of effects also identified to have resulted from operation of the existing TSF1A and TSF2 facilities. Figure 5.12 TSF3 cross-section locations 5.5 TSF3 analysis results The below sections provide summarised assessment results, with additional detail provided in Appendix I. 5.5.1 Construction dewatering Inflows Given the large nature of the proposed excavation and variable geology, there is some degree of uncertainty around the actual volume of water to be dewatered. A range of predicted inflows is provided in Table 5.6. The actual inflows are expected to: – Occur at the lower end of the ranges presented. The results for Cross-section 2 provide the upper limit of inflows presented for the reasons provided in Section 5.4.2. – Be greatest at the initial period of each stage, reducing as groundwater levels (and water held in aquifer storage) reduces over time. – Be greatest at the deepest and widest section of the undercut (20 m bgl), where higher permeability materials and upward gradients are expected to be encountered. – The undercut will be backfilled with structural fill before the construction of the embankment and drainage systems. This structural fill material will be NAF.
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