GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 74 H.2 NRS assessment results H.2.1 Groundwater flow assessment results Shallow groundwater flow upgradient of the NRS site is predicted to be approximately 722 m3/day. Additional recharge across the alluvial flats under existing conditions is estimated at approximately 449 m3/day, with a predicted total groundwater discharge to the Ohinemuri River of approximately 1,171 m3/day. H.2.2 Construction dewatering assessment results Construction of uphill stormwater diversion drains will involve excavation of rhyolite rock at the south-eastern extent of the NRS. Interception of groundwater is anticipated, with estimated initial groundwater inflow rates and distance of influence of groundwater drawdown presented in Table H.4. The inflow rates determined assume that the full length of excavation required will be undertaken at the same time, however it is considered likely that the excavation will be progressively advanced. Groundwater inflow rates are also predicted to reduce over time as groundwater levels and gradients towards the uphill diversion drains reduce as the system equilibrates to the change in conditions. Table H.4 NRS groundwater inflow rates and distance of influence of dewatering for uphill diversion drain construction Uphill Diversion Drain Groundwater Assessment Result range Initial groundwater inflow rate (m3/day) 7 - 70 Distance of influence of dewatering (m) 1 – 11 H.2.3 NRS assessment results The predicted rock stack leachate captured by leachate collection drains seepage through the Zone A liner are presented in Table H.5. The predicted leachate and groundwater captured in the sub-soil drains is presented in Table H.6. The predicted groundwater and leachate flow within the groundwater system to the Ohinemuri River is presented in Table H.7. Table H.5 Predicted leachate capture and leachate seepage through zone A liner Infiltration conditions Leachate captured by leachate collection drains (m3/day) Leachate seepage through Zone A liner (m3/day) NRS operation 30% rainfall 29 413 50% rainfall 109 605 NRS closure 5-year average cap infiltration (369 mm/year) 2 262 Table H.6 Predicted groundwater and leachate captured in sub-soil drains Infiltration conditions Groundwater captured by sub-soil drains (m3/day Leachate captured by subsoil drains (m3/day) Total sub-soil drains capture (m3/day) NRS operation 30% rainfall 744 342 1087 50% rainfall 736 508 1244 NRS closure 5-year average cap infiltration (369 mm/year)2 751 212 963
RkJQdWJsaXNoZXIy MjE2NDg3