U:\2021\BM210482_IBo_Waihi_North_Project\Documents\WNP_Freshwater_Report_May_2022\FINAL_Freshwater_Report_FOR DELIVERY_June 2022\FINAL DELIVERED 17 JUNE 2022\WAI-985-000-REP-LC-0007_Rev0_Freshwater_20220621_FINAL.docx Table 33: WTP discharge volumes, rates and estimated percentage of Ohinemuri River flow under various operating regimes (from GHD 2022A). Criteria Operating Regime A Operating Regime B Operating Regime C Operating Regime D Operating Regime E Daily Discharge 20,000 m3/d 26,000 m3/d 5,200 m3/d 26,000 m3/d 52,000 m3/d Discharge Rate 235 l/sec 301 l/sec 60 l/sec 301 l/sec 602 l/sec Percentage of river flow 15% 20% 10% 40% 60% 19.4 Proposed Water Management for WNP GHD (2022A) concluded that, based on their water balance analysis, the WNP can be implemented using the existing and upgraded WTP functionality and within the current consented discharge and receiving environment conditions. The estimated volume of water from WUG has a significant impact on the total volume of water requiring treatment at OGNZL’s Baxter Road facilities, and the capacity of the current WTP facilities will require upgrading throughout the project’s lifetime to cope with the expected volume of water requiring treatment. Due to discharge restrictions during low river flow periods, GHD (2022A) also notes that there will be excess water requiring treatment during summer dry periods once WUG is developed. GHD (2022A) outlines how these flows can be managed and OGNZL is investigating a range of water reuse options that could be implemented to reduce the amount of water ultimately needing to be discharged to the river. . We also note that GHD (2022A) states that the utilisation of the reverse osmosis (RO) plant to further reduce concentrations of elevated trace elements is a contingency that could be utilised in the event that predicted discharge concentrations are higher than predicted. 20.0 Water Quality Criteria for the Ohinemuri River 20.1.1 Introduction Resource consents 971285, 971311, 971312, 971303-971306 and 971323 document the receiving water quality standards that are to be met by the discharge of treated water to the Ohinemuri RiverOceana Gold Waihi. These receiving standards were originally derived from USEPA (1986), the applicable standard at the time these consents were granted. The results outlined below and the lengthy history of monitoring of ecological values within the Ohinemuri River, show that there has been no adverse effect on in river ecological values from the operation’s treated water discharge. In fact, throughout the reach of the Ohinemuri River in the vicinity of the Oceana Gold WaihiOceana Gold Waihi operations, the ecological characteristics of the river have remained consistent over the period of monitoring.
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