GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-10 some groundwater volumes that are captured in the underdrainage assessment. Captured GOP TSF seepage is estimated to be 1,252 m3/d; this volume is only realised post LOM and after groundwater recharge. WUG Groundwater Inflow Inflow volumes of groundwater into the Willows access tunnel and Plant access tunnel are detailed in GWS, 2022 and are calculated at up to 22,260 m3/d. MUG Dewatering Rates To achieve the target water table drawdown rates annual average extraction rates between 10,000 m3/d and 17,000 m3/d are expected (GWS Ltd 2018). To represent the practicalities of achieving this rate under variable WTP discharge conditions and fluctuating flows from other sources, a variable pump rate is applied. Operational Water Dust suppression is taken at a constant daily rate that is assumed to be 500 m3/d. Production Rates Production rates and ore sources for the LOM were provided by OGNZL and are reproduced in Appendix F for reference. E-6 Ohinemuri Cumulative Assessment Existing Uncaptured Seepage The existing uncaptured seepage is defined as seepage from existing facilities (predominantly TSF1A and TSF2) that is currently not intercepted by drains but seepage that leaks through the facility liners, mixes with groundwater and ultimately ends up in the Ohinemuri River. The existing uncaptured seepage also potentially includes non-mine related sources. This existing seepage has been calculated as a mass contaminant load utilising water quality and flow data from 2019. Utilising days in which monitoring data aligned, it has been possible to calculate background mass loads at the following locations: • OH3. Representative of water quality upstream of the mine. • E1 & E2. Representative of water quality discharged from the WTP to the Ohinemuri River • RU1. Representative of water quality from Ruahorehore before discharge into Ohinemuri River • OH6. Representative of downstream mixing / consent compliance location These locations are presented on Figure 2.
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