GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-6 Dust suppression for the site is deducted from the dewatering flows prior to treatment in the WTP and this is specified by a fixed average rate for the life of the mine. Seepage (rock stacks and embankments) Seepage flows as described in Section 2.7.3 are each defined by a daily average value for the duration of the model. These flows gravitate to the WTP without the ability for intermediate storage. As there is no storage modelled; these flows are treated as Priority One and are treated immediately. E-3-3 Sinks Evaporation The WBM assumes that water will evaporate from the TSF ponds where decant water is available. Evaporation is calculated daily based on average monthly Penman open-water evaporation rates. These are taken from Cliflow Station B75381 records from 26/4/1971 to 30/7/2001. Retained Moisture When the tailings are placed in the TSF impoundment a small component of tailings liquor is retained as porewater (~24% depending upon slurry makeup) and the remainder is released to decant water or seepage. E-3-4 Processes Water Treatment Plant The central component of the WBM is the WTP which aims to treat all minewater and cyanide impacted water generated or captured across the site. The consented discharge of the WTP is governed by the operating regimes and the daily flow rate of the Ohinemuri River. The operating regime is determined by the ratio of minewater to cyanide water to be treated. The maximum discharge of the WTP is set to 90% of the daily permitted discharge. This reduction factor is applied to recognise that the WTP cannot consistently operate at an efficiency to achieve the maximum consented discharge each day. To make up the consented discharge, water is requested from each of the sources based on a set of priorities. These priorities reflect the ability to control or importance of controlling each water source: Priority 1 - Process area runoff, WUG minewater, seepage and collection ponds Priority 2 - Decant water from the TSF’s Priority 3 - Mine dewatering Priority One flows are those with little or no storage capacity and the model reports an error if these sources cannot be treated and/or contained. Priority Two flows are allocated to the active TSF ponds. The remaining capacity is allocated to Priority Three flows, which attempt to satisfy mine dewatering rates. Ore Processing and Stockpile Daily ore volumes are calculated from the mine plan production schedule. The volume of water required to process ore on a daily basis is calculated based on the average fraction of tails in the slurry mix. The required volume of processing water is requested from available sources based on the following order of preference. Elution flow - extracted at a fixed daily rate from the Ohinemuri River where flow conditions allow. Decant water - from the active tailings pond. Seepage flow.
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