GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 71 7 CONCLUSIONS Based on the water balance analysis and the assumptions outlined, the Waihi North Project can be implemented using the existing and upgraded WTP functionality and within the currently consented discharge and receiving environment conditions subject to renewal of those consents for an appropriate term. The capacity of the current WTP facilities will require upgrading to cope with the expected volume of water requiring treatment. Based on the principles of the Waikato Regional Council Erosion and Sediment Control Guidelines being adopted for the design, construction, maintenance and decommissioning as outlined in Southern Skies (2022) and BECA (2022) and the collection and treatment of mine impacted water being directed to the WTP, the project is not expected to cause significant adverse flooding or erosion effects, have significant adverse effects on water quality and/or flow regimes at locations adjacent project infrastructure, at points of discharge to the receiving environment and/or downstream of the project areas. The estimated volume of water from the Wharekirauponga Underground Mine has a significant impact on the total volume of water requiring treatment at Waihi. Both high K and low K WUG estimates are modelled within the WBM. Given the peak flows would not occur until 2027, assumptions relating to groundwater inflow rates will be validated well in advance and, importantly, OGNZL will have time to adapt their water management approach in advance of the critical period. In addition, the assumed water chemistry for WUG water sources is considered conservative. As more information on the WUG inflow volumes and geochemistry becomes available, this will be incorporated into the assessment. There is a modelled risk of surplus of Priority One water sources during summer dry periods once WUG is fully developed. These flows can be managed operationally by one or more of the following measures: Excess flows sent to the operational TSF Dewatering of MUG/WUG temporarily suspended Mine scheduling amendments / changes Potential future alternative discharge options The storage available within the TSFs is shown to be adequate to contain predicted water gains without overflow based on 10-year 72 hour and/or 10-year 24 hour events. There is a modelled risk to the inundation of deeper stopes in MUG during LOM as WUG water treatment requirements increase. The majority of the stopes (apart from the very deepest ones) show a low risk of inundation. Dewatering in advance (before the critical period) could reduce the risk of this inundation. Water quality predictions for the LOM as outlined are compliant with existing discharge and receiving environment consent conditions. The current WTP operating regimes suit the expected changes in operation for the Waihi North Project. In the event that water quality parameters are encountered that are worse than those anticipated in this report, and as a consequence, discharge water quality approaches the compliance limits, there is opportunity to utilise the RO plant to mitigate the impact and ensure compliance is maintainted. Furthermore, most in-river concentrations are modelled as being one or more orders of magnitude less than the corresponding receiving water compliance criteria ensuring that higher than predicted discharge concentrations are unlikely to lead to non-compliance. Key differences to current operations that will need to be managed by OGNZL include: To meet dewatering targets, the WTP operation will need to focus on maximising the treatment and discharge of minewater to the Ohinemuri River flow. If dewatering targets are not met the impact will be on mine development.
RkJQdWJsaXNoZXIy MjE2NDg3