GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 46 6 SITE WATER BALANCE 6.1 Model Overview A WBM was used to assess how water gains change over the life of the mine to check that proposed infrastructure for conveyance, storage and treatment will be adequate and to inform the design of the proposed infrastructure. This is carried out using the GoldSim (refer www.goldsim.com) software package which is designed to run Monte Carlo simulations for probabilistic analysis of dynamic systems. The WBM was first developed in 2012 for the Waihi mines as an initiative of the site environmental team. The objective of building the model was to have a tool to forecast storage requirements in the TSFs and as an ongoing check that the site water management infrastructure as a whole had capacity for ongoing mine development. The model was also used to predict water treatment requirements post closure as a component of annual bond calculations. The WBM was further developed to represent Project Martha and now also includes the components of the Waihi North Project. The model aims to capture all significant water movements across the site affected by mine operations. The model is run as a probabilistic analysis based on 100 years of measured rainfall data, corresponding combined Ohinemuri River and Ruahorehore Stream flow rates, and the projected mine plan for the Waihi North Project. A full description of how the Waihi North Project is represented in the WBM is given in Appendix E. A calibration of the WBM was completed with measured river flow data and recorded operational data from the WTP and existing mine site. This calibration is summarised in Appendix E. Given the model has been calibrated against the site water balance and in use for some time there is confidence that it does represent well the quantities of water generated from the different water sources that require treatment. Overall, the model is considered to provide a good representation of site conditions and, based on the calibration, is conservative. 6.1.1 Wharekirauponga Operations A standalone element within the WBM aims to assess the infrastructure required to manage water gains resulting from the proposed WUG Access tunnel, WUG Mine and WRS runoff and seepage (denoted as WUG in Figure 32). The model has also been used to generate a synthetic flow record for Mataura Stream. A diagram of the WUG model showing the key elements and controls is provided in Figure 28. The WTP depicted is the WTP element within the main Waihi WBM.
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