| Summary and Recommendation | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 22 Sensitivity: General 7 Summary and Recommendation 7.1 Summary of Assessment The primary air quality concern for the Processing Plant is the emission of mercury - although other metals will also be emitted. Emissions of mercury from the Processing Plant are expected to increase when GOP and WUG ore is being processed and in response to the proposed increase in the ore processing rate. An assessment of the potential impact of mercury and other metal emissions from the Processing Plant has been undertaken using dispersion modelling methods. Modelled emission parameters have been based on the information provided by OGNZL. 7.1.1 Assessment of Mercury Emissions The potential health impact of mercury emissions has been assessed by comparing predicted concentrations against the relevant annual average guideline concentrations. The OEHHA annual average REL of 0.03 µg/m3 is the most conservative of the published guidelines and is protective of the most sensitive members of community. The results of the dispersion modelling show mercury emissions from the Processing Plant are not predicted to exceed the MfE, USEPA, and OEHHA annual average guideline limits when 2.25 MTPA of ore is being processed. The maximum annual average mercury concentration predicted at any of the nearby dwellings is 24.7% of the OEHHA REL once the retort oven is installed. The results also indicate that of emissions would not exceed the guidelines limits even if there was no change to the plant’s existing configuration. 7.1.2 Assessment of other (non-mercury) metal emissions The results of the modelling indicate that emissions of other (non-mercury) metals do not exceed any of the relevant ambient guideline concentrations for the proposed ore processing of 2.25 MTPA. The results show even if plant emissions were to be more than 120 to 22,500 times higher than those assumed in the model, ambient air metal concentrations would still not exceed the relevant health-based guideline concentrations. 7.2 Recommendations It is recommended that an annual mercury emission testing programme is implemented when GOP and WUG ore is being processed to confirm expected mercury discharges. The testing programme should include the electrowinning, retort oven, furnace, and carbon regeneration stacks. Other metals (including cadmium, chromium and nickel) should also be included in the testing programme to confirm the emission rates of these contaminants.
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