GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 66 Table 14 Modelled Discharge Water Quality Range of Concentration Operational Consented Water Quality Chemical Parameter Modelled 97%ile of Daily Mean Modelled Maximum Normal Compliance Maximum Compliance pH1 Not modelled Not modelled 6.5 – 9.5 Total Suspended Solids (g/m3)1 Not modelled Not modelled 8 40 Cyanide, WAD (g/m3) 0.014 0.056 0.09 – 0.36 0.25 – 1.02 Iron (g/m3) 0.60 0.65 0.1 – 1.0 0.3 – 6.7 Manganese (g/m3) 0.010 0.018 0.1 – 1.0 0.4 – 1.3 Copper (g/m3)2 0.002 0.009 0.07 – 0.055 0.05 – 0.13 Nickel (g/m3) 2 0.0034 0.009 0.42 – 1.2 Zinc (g/m3) 2 0.009 0.010 0.27 – 0.8 Silver (g/m3) 2 <0.0001 <0.0001 0.007 – 0.02 0.011 – 0.03 Antimony (g/m3) 0.0087 0.026 0.05 – 0.1 0.08 – 0.33 Arsenic (g/m3) 0.0076 0.011 0.02 – 1.45 Selenium (g/m3) 0.003 0.007 0.05 – 0.22 0.09 – 0.38 Mercury (g/m3) 0.00008 0.0003 0.0005 Cadmium (g/m3) 2 0.0011 0.0012 0.003 – 0.008 Chromium VI (g/m3) <0.01 <0.01 0.03 – 0.08 Lead (g/m3) 2 0.00024 0.00060 0.0006 – 0.02 Ammoniacal N (g/m3)3 3.07 6.23 0.50 – 33.00 2.21 – 384.97 1. Refer to previous note regarding expected pH and TSS 2. Based on a minimum required discharge hardness of between 243 and 670 g/m3 CaCO3 (dependent of operating regime) to achieve in river hardness of 100 g/m3. Actual compliance concentrations for these elements vary depending on the recorded hardness in the discharge. 3. Based on discharge pH and temperature. Consent refers to Total Ammonia. 6.3.6 Ohinemuri River Water Quality Compliance The modelled maximum daily mean and modelled maximum concentrations of the consented trace elements within the Ohinemuri River are provided in Table 15. OH6 results included within the GoldSim cumulative assessment are representative of downstream water quality and assume full mixing of the WTP discharge and the Ohinemuri River. OH5 further upstream of OH6 also has to adhere to the same consent conditions as OH6 however there is an assumption that large volume discharges and discharges under low flow conditions will maximise use of location E2 (located between OH5 and OH6). The results show that water quality within the Ohinemuri River is predicted to be within the consented limits for all elements throughout the LOM. Most elements model a mean and maximum concentration at least one order of magnitude below the consented limits ensuring there is significant buffer available to account for the underestimation of discharge concentrations. Based on the results presented it is considered that the receiving environment will be compliant with the consented water quality conditions.
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