| Potential Effects on the Environment of WNP | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 64 No emission testing has been conducted for the carbon regeneration stack from which reliable emission estimate can be derived. Therefore, the emissions of the non-mercury metals emissions from the carbon regeneration stack were not included in the dispersion model. A summary of the predicted maximum contaminant concentrations is shown in Table 7-2. The results show that emissions from the Processing Plant are not predicted to exceed any relevant air quality guideline limits. The maximum annual average mercury concentration predicted at any residential property is 24.7% of the OEHHA REL of 0.03 µg/m3 and 2.2% of the MfE AAQG of 0.33 µg/m3. The maximum concentration predicted for other non-mercury metal is predicted to be less than 0.82% of guideline levels. Emissions of non-mercury metals from the carbon regeneration stack are expected to be comparable or lower than emissions from the electrowinning and furnace stack. The results of the modelling indicate that, even if discharges of non-mercury metal from the carbon regeneration stack were incorporated into the model, the predicted concentrations are still highly unlikely to exceed any of the relevant air quality guideline concentrations. However, it is recommended that emissions testing confirm the metal emission rate from the carbon regeneration stack. Overall, the modelling indicates that emissions from Processing Plant would not be expected to have adverse health effects outside the site boundary. Table 7-2. Predicted maximum non-mercury metal concentrations predicted at the most impacted nearby dwellings Contaminant Averaging period Predicted maximum concentration (µg/m3) Guideline concentration (µg/m3) Guideline concentration (%) Mercury Annual 0.0074 0.03 24.7% Arsenic 1-hour 0.000056 0.2 0.03% 8-hour 0.000016 0.015 0.11% annual 0.0000005 0.0055 0.01% Cadmium annual 0.000046 0.0056 0.82% Chromium (VI) annual 0.0000014 0.0011 0.12% Manganese 8-hour 0.00024 0.17 0.14% annual 0.0000040 0.09 0.004% Nickel 1-hour 0.00083 0.2 0.42% 8-hour 0.00024 0.06 0.40% annual 0.0000072 0.014 0.05% Lead 3-month 0.000089 0.2 0.04% Selenium annual 0.00023 20 0.00% 7.8 Summary of Potential Effects The assessment of potential effects has identified that there is a risk of sensitive receptors located within 200 m of the mine being exposed to a small increase in deposited dust and TSP concentrations as a result of the WNP, although concentrations are not expected to exceed standard and guideline values. In order to mitigate the risk of dust events causing adverse effects on sensitive locations in close proximity to the proposed works, it is recommended that some additional mitigation and monitoring is carried out when works are being undertaken in close proximity to sensitive receptors. The additional monitoring and mitigation methods are described in Section 8.
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