GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project E-11 Figure 2 Ohinemuri water discharge and Sampling locations Based on the calculated contaminant mass load at OH6, the proportion of load attributable to the WTP discharge and natural background has been calculated. Where the WTP discharge and natural background load do not account for the full contaminant load observed at OH6, the additional load is assumed to be from a combination of uncaptured seepage / runoff from current site operations and other potential non-mining sources. These loads have been calculated where flow data and water quality align at the various monitoring locations throughout the 2019 period with data points covering a range of different flow conditions. Figure 3Figure shows plots of the calculated additional mass loads versus flow at OH6. For most trace elements (ie. Sb, Ni, Zn and Se) the calculated difference (between known load inputs and load at OH6) is negligible (< 0.2 kg/day) and the difference observed are more likely a result of inconsistent sampling between sampling locations (ie. sampling carried out throughout the day and not simultaneously) and use of recorded concentrations at the method detection limit. However for manganese and sulphate there is a distinct pattern of additional calculated loadings at most flow levels suggesting that another source apart from the known sources is possible. Measurements of other trace elements of concern were recorded as being largely below the method detection limit at OH6 and therefore no additional loading was assumed or could be calculated.
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