GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 91 Boundary type Scenario/s applied to Adopted boundary conditions Justification Drains 3 and 4 Water rate – potential seepage face review set 0 m3/day. Applied to drains: sub soils, upstream cut off, initial and downstream toe) Removal of leachate and embankment rock infiltration through drains. Locations of drains adopted from EGL (2021b) TSF3 geotechnical report (DWGs 0620 and 0626 of EGL report Appendix A) Water total head – 1,108.5 m RL. Leachate collection sump drain Gravity outlet, as per EGL design. 5 Water rate – potential seepage face review set 0 m3/day Applied only to downstream toe drain. Assumes multiple drain failure for long-term scenario. Embankment rock infiltration 3 Water flux – potential seepage face review: 2 x 10-3 m/d (35% average annual rainfall) Upper catchment rainfall recharge value applied directly to the embankment rock (Zones B – D) 4 and 5 Water flux: 1 x 10-3 m/d 5-year average cap infiltration rate for Zones G & H, which is 370 mm/yr (17% of GHD’s adopted average rainfall value) (AECOM, 2020) Table I.9 Adopted material parameters for TSF3 model scenarios (where additional to Table I.2) Material (1) (2) Scenario/s applied to KH (m/s) KV (m/s) VWC and K function(3) Hydraulic conductivity justification Tailings: HDPE liner Material applied as a line: ___________ 3-5 2 x 10-15 2 x 10-15 Well graded clay Sufficiently low to enable liner leakage boundary condition in Table I.8 to provide the dominant leakage mechanism. Starter embankment tailings 3 1 x 10-7 2 x 10-8 Sandy silt (coarse tailings) Kv provided by EGL (2019b). Modelling outputs for estimated consolidation provided in Figure I.6. Note: The KV values indicated for closure in Figure I.6 remain applicable to the current proposed height of 1,155 m RL (pers. comm. EGL, email dated 12/07/2021). Operational – closure tailings 4 5 x 10-8 1 x 10-8 Sandy silt (coarse tailings) Long-term / Post closure tailings 5 1 x 10-8 5 x 10-9 Sandy silt (coarse tailings) Embankment rock NAF undercut structural backfill 3-5 1 x 10-6 1 x 10-6 Well graded #2 Based on embankment material information provided by EGL (2019c). Zone A 1-5 1 x 10-8 1 x 10-8 Clayey silt Zone B 3-5 1 x 10-8 1 x 10-8 Clayey silt Zone C1 3-5 1 x 10-6 1 x 10-6 Silty sand Zone C2 3-5 1 x 10-6 1 x 10-6 Silty sand Zone D2 3-5 1 x 10-5 1 x 10-6 Silty sand Zone D3 4-5 1 x 10-6 1 x 10-7 Silty sand Zone F 4-5 1 x 10-4 1 x 10-5 Uniform sand Zone G/H 4-5 1 x 10-8 1 x 10-8 Clayey silt 1. Geological units are colour coded as per the SEEP/W cross section (Figure 5.15 of the main report). 2. TSF construction materials are described in Table 5.1 (Section 5.1.2) of the main report. 3. VWC = Volumetric water content function (SEEP/W 2012 database), selected based on EGL descriptions of materials provided by email (EGL 2019b and 2019c).
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