GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 109 Table J.2 WRS model set-up Boundary type Adopted boundary condition Justification Model scenario Groundwater boundary (base of model) Constant head – 1,160 mRL Based on the conceptual understanding provided in Section 6.2.3 of the report. Base model and WRS operation Rainfall recharge Water flux – 4 x 104 m/d (7% average annual rainfall) Recharge to the rock stack Two recharge rates applied to the rock stack: Water flux – – Scenario 1: 2 x 10-3 m/d – Scenario 2: 3 x 10-3 m/d 30 & 50 % of average rainfall at the site (2,110 mm/year; NIWA 2019) WRS operation Leachate drains Water rate – 0 m3/day with potential seepage face review Removal of leachate through rock drain WRS operation Table J.3 WRS model adopted hydrogeological material parameters Material unit Hydraulic conductivity (m/s) Anisotropy (KV/KH) VWC and K function* Hydraulic conductivity justification Residual soil 1 x 10-8 0.5 Sandy silty clay From site-specific testing (refer to Section 6.2.4 of the main report) Weathered tuff 1 x 10-8 0.1 Sandy clayey silt Andesite rock 3 x 10-8 1.0 Sandy silt Rock drain 1 x 10-2 1.0 Uniform sand Nominal values considered appropriate for rock drain Rock stack 1 x 10-5 0.5 Silty sand Considered appropriate for emplaced rock materials (as applied for NRS). ** VWC = Volumetric water content function (SEEP/W 2012 materials database) J.2.1 SEEP/W outputs The proportion of predicted rock stack leachate captured by the seepage rock drain versus to groundwater is presented in Table J.4. The predicted leachate to groundwater in Table J.4 is also the predicted volume to enter the Ohinemuri River catchment via the Mataura Steam. Table J.4 Total infiltration volume through the rock stack Infiltration conditions Leachate captured by rock drain (m3/day) Leachate seepage to groundwater and surface water (m3/day) Total infiltration through WRS (m3/day) WRS operation 30% rainfall 30 7 37 50% rainfall 53 8 61
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