GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 51 Baseline WRS Gladstone Pit* NRS TSF3 Cu <0.01 <0.01 - <0.01 <0.01 Fe <0.01 <0.01 - 29 0.6 Hg <0.01 <0.01 - <0.01 <0.01 K <0.01 <0.01 - 1.4 0.6 Mg <0.01 <0.01 - 11 0.3 Mn 0.8 0.4 - 1.6 0.09 Na <0.01 <0.01 - 10 11 Ni <0.01 <0.01 - 0.08 <0.01 Pb <0.01 <0.01 - <0.01 <0.01 SO4 2000 18 - 140 20 Sb <0.01 <0.01 - <0.01 <0.01 Zn <0.01 <0.01 - 0.1 <0.01 *All Gladstone seepage is assumed captured and treated The assessment undertaken is considered conservative as mass loads are calculated on fully built facilities and do not take into account attenuation which will likely result in co-precipitation of trace elements. 6.2 WUG WBM Outputs 6.2.1 WRS and Groundwater Inflow Water Based on the operational capacities outlined in Section 5, the WRScollection pond is modelled to determine the return flows to the WTP. The modelled volume of water from the collection pond (via pipe to the Waihi WTP) is provided in Figure 33 and shows the seasonal fluctuation and impact of increasing the active area of the WRS. During initial development, WUG groundwater inflow water may be discharged to the WRS collection pond before transfer to the WTP via pipe. However it is generally assumed that WUG water is piped and pumped through the tunnels directly to the WTP without surfacing at the WSFA during peak development. The combined calculated median water volumes requiring treatment (WUG groundwater inflow and collection pond water (containing WRS seepage and runoff)) are provided in Figure 34 (high K scenario) and Figure 35 (low K scenario). Treatment requirements increase largely in line with the progression of the WUG Access Tunnel and extent of underground development and are largely driven by the volume of groundwater entering the access tunnels based on the estimated inflow. Currently it is assumed that the groundwater inflow is constant and as it is the dominant water source requiring treatment, there is little difference between estimated minimum and maximum flows – the minimum flow simply being the maximum flow less the collection pond decant rate. The flows presented assume decreasing collection pond water requiring treatment in line with the reduced footprint of the WRS but no reduction in groundwater inflow due to backfilling. The post WUG mining predictions (last ore is scheduled as 2037) are therefore not considered an accurate reflection of water treatment requirements as the installation of bulkheads will result in a large reduction in groundwater inflow.
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