GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 90 Figure I.5 TSF3 Cross-section 1 SEEP/W model set-up with close up of undercut and key monitoring locations Table I.7 Summary of transient model scenarios for Cross-section 1 (construction dewatering) Scenario Stage of work Days Description 2A (Parent for 2B) Partial excavation 0 - 30 Removal of surficial alluvium down to sensitive tuff, and includes excavations for the cut off and toe drains, and shear key. 2B (Parent for 2C) Full excavation 30 - 75 Removal of sensitive tuff to maximum depth present in model (15 m). Assumes no inflow mitigation (such as piling). Scenario 2C (75-120 d) Partial backfilled 75 - 120 Backfill to original sensitive tuff surface, using NAF structural backfill (to be subsequently overlain by the Zone A soil liner). * As discussed in the Rationale (Section 5.4.2) of the main report, additional analyses were run to provide a range of potential effects. Refer to appendix sections I.2.2 and I.2.3. Table I.8 Boundary conditions for TSF3 model scenarios (where different from Table I.1) Boundary type Scenario/s applied to Adopted boundary conditions Justification Construction dewatering 2 (steady state) 2a-c (transient) Water rate – potential seepage face review set 0 m3/day Removal of water from model where dewatering required. Applied to excavations: sensitive tuff, cut off drain, toe drain, shear key. Recharge to tailings 3-5 Water flux – potential seepage face review: 3 x 10-3 m/day Sufficiently large value (70% of rainfall) applied to achieve saturation at tailings surface. HDPE liner leakage 3-5 Water flux - 1.7 x 10-5 m/d Upper limit as provided by EGL (2019b). Refer to Section 5.5.2 of the main report.
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