GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 48 Table G.5 Gladstone Pit west – east model section parameters and boundary conditions Parameter / boundary Adopted condition Justification Model scenario Rainfall recharge Gladstone Hill, Winner Hill and south of pit: Water flux (potential seepage face review) – 9 x 10-10 m/s Calibrated to 1.3 % rainfall. Considered appropriate given low permeability materials and gradient of hillside. All model scenarios East and west of pit: Water flux (potential seepage face review) – 3 x 10-8 m/s Calibrated to 45% rainfall. Considered appropriate given higher permeability materials and lower slope gradients. Ohinemuri River (OH3) Water total head – 1,092.85 mRL Surveyed elevation close to OH3 sample point (08/08/2017) Ohinemuri River (OH6) Water total head – 1,084.65 mRL Surveyed elevation close to OH6 sample point (21/02/2019) Andesite underdrainage Base of Model: Water rate – potential seepage face review Shallow system is underdrained due to existing below ground workings Current conditions, GOP excavation and operational TSF Pit dewatering Interface between pit and adjacent shallow units: Water rate – potential seepage face review Shallow groundwater discharge into the pit will be removed through pit dewatering GOP excavation Rock backfill Kx 1 x 10-5 m/s Kx/Ky 0.1 VWC – Sandy loam Considered appropriate for rock backfill after placement, amendment with limestone and compaction. Operational TSF, TSF closure and long-term TSF Liner subgrade Kx 1 x 10-5 m/s Kx/Ky 1.0 VWC - sand Sub-20 mm crushed and screened high quality rock from mining operations Geosynthetic liner Kx 1 x 10-10 m/s Kx/Ky 1.0 VWC – clayey silt Expected seepage rate approximately 5x10-9 – 3.5x10-8 m/s depending on hydraulic gradient across the liner TSF drainage Water rate – potential seepage face review TSF drainage system beneath the geosynthetic liner at the base of the tailings Operational TSF and TSF closure Tailings Kx 1 x 10-7 m/s Kx/Ky 0.2 VWC – sandy silt (coarse tailings) Hydraulic conductivity and VWC based on EGL unconsolidated tailings description (email communication 28/02/2019 EGL 2019b) Operational TSF Operational tailings pond Water total head at top of tailings – 1,103 mRL Max. tailings emplacement height Tailings Kx 1 x 10-8 m/s Kx/Ky 0.5 VWC – sandy silt (coarse tailings) Hydraulic conductivity and VWC based on EGL consolidated tailings description (email communication 28/02/2019; EGL 2019b) TSF closure Tailings cap infiltration Water flux – 1 x 10-8 m/s 5-year average cap infiltration rate (AECOM, 2020) TSF closure and long-term TSF Tailings cover (rockfill) Kx 1 x 10-5 m/s Kx/Ky 0.1 VWC – Sandy loam Considered appropriate for rock after placement, amendment with limestone and compaction. Martha pit lake water pressure water pressure Water total head – 1,106 mRL Proposed water level of Martha Pit Lake (1,104 mRL) after rewatering of the deep groundwater system Kx = horizontal hydraulic conductivity. Ky = vertical hydraulic conductivity. VWC = Volumetric water content function (SEEP/W 2012 database)
RkJQdWJsaXNoZXIy MjE2NDg3