GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-7 Mine dewatering flow - to satisfy the remaining demand. Tailings are distributed to the active TSF and split into two components; tails solids with retained moisture, and decant water. Tailings Storage Facility The WBM accounts for the two existing TSF’s plus TSF3 and Gladstone TSF and makes provision for changes in their active status. Through the model run, tailings are deposited into the TSF defined as the “active” pond. Once the calculated tailings capacity of for each facility is reached, the active pond definition is updated to inactive. Based on previous experience with TSF2, a period of 2.5 years is applied to each TSF from when it was last active to when it can be considered “clean” and direct discharge is allowed. CN treatment is ceased after 1.5 years. The daily decant water gain is calculated as the sum of rainfall and decant water added less evaporation. Decant water is withdrawn from the TSF’s to satisfy a demand from the WTP based on the available treatment capacity. The WTP allocates a demand to each TSF that aims to remove the previous day’s rainfall, up to the smallest of the Priority Two flow capacity and defined decant pump capacity. A minimum of 20% of the Priority Two flow capacity is allocated to the active pond in order to remove any accumulated volume. The remaining flow capacity is allocated to the non-active TSF (if treatment is required) based on proportional catchment area. This distribution of demands prioritises withdrawal from the non-active TSF ponds for treatment. Further withdrawals from the active TSF pond are requested to satisfy slurry makeup requirements in the ore processing area. The demands from the WTP and ore processing area for each TSF are only fulfilled if there is a suitable volume of water available to satisfy the flow. The accumulation of tailings and decant water within each TSF is monitored against a stage-volume relationship for each TSF. This allows the remaining capacity and freeboard of each pond to be determined throughout each of the modelled scenarios. E-4 Model Calibration A calibration of the WBM was completed with measured river flow data and recorded operation data from the WTP and mine site. For the given calibration period the WBM is shown to provide a reasonable representation of the water balance and treatment requirements across the mine site. A degree of conservativeness is represented as the model has over predicted the minewater and cyanide water treatment requirements. Further to this, the collection pond overflow predicted is higher than measured. Overall, the model is considered to provide a good representation of site conditions and based on the calibration is conservative. E-5 Representation of Waihi North Project in the WBM The WBM was modified to represent the Waihi North Project as summarised below. TSF Operation and Capacity It is assumed for the purpose of this assessment that TSF1A will be constructed to a proposed height of 182.00 mRL resulting in an additional 4.07 Mm3 of tails storage; TSF2 will be constructed to a proposed height of 160.7 mRL resulting in an additional 1.65 Mm3 of tails storage; TSF3 will be constructed to a proposed height of 155.00 mRL resulting in an additional 5.67 Mm3 of tails storage; and Gladstone Pit
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