| Air Quality Criteria | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 10 Sensitivity: General uncertainty factor of 3000. The OEHHA guideline is therefore highly conservative. Furthermore, the 1-hour average guideline is also not based on a short term acute Given the above context the 1-hour OEHHA guideline is most appropriately applied at locations where repeated exposures to pregnant women may occur, such as at residential dwellings. However, no other regulatory agency other than OEHHA have published acute 1-hour guideline levels for mercury. It is noted that ATSDR (2016) reviewed the same animal study used by OEHHA to develop the 1hour REL, but ATSDR only published a chronic exposure MRL based on the toxicological evidence. Additionally, the OEHHA 1-hour acute guideline is of the same magnitude as the annual average guideline published by the regulatory agencies. Therefore, given the limited animal test data on which the guideline has 1-hour average OEHHA guideline been based and the conservatism and applicability of the derived guideline, discharges from the processing plant have not been assessed against the OEHHA 1-hour REL. Table 3-1.Summary of Air Quality Criteria for Mercury Contaminant Criteria Concentration (μg/m3) Averaging Period Source Mercury (inorganic) 1.0 Annual WHO 0.33 Annual NZAAQG 0.30 Annual US EPA RfC 0.20 Annual ATSDR MRL 0.03 Annual OEHHA 3.3 Assessment Criteria for Other Metals The relevant assessment criteria for other non-mercury metals emitted from the Processing Plant are shown in Table 3-2. The concentration of copper in the emitted electrowinning and furnace exhaust gases (i.e. 4.97 µg/Nm3 and 6.18 µg/Nm3 – refer Table 2-7) measured during the 2021 emission testing programme was lower than the 1hour average guideline limit of guideline concentration of 100 µg/m3. The concentration of copper will be several magnitudes lower before the emission plume reaches the site boundary. The results of emission testing indicate that the discharge of copper would not have any adverse effects on air quality. Therefore, the discharge of copper from the Processing Plant has not been considered further in this report.
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