5 Tonkin & Taylor Ltd Assessment of mine vent air quality impacts to inform an assessment of ecological effects on Archey’s frog Oceana Gold (NZ) Limited June 2022 Job No: 1017908 3.4 Human health assessment criteria For completeness, the human health assessment criteria applied when considering the impacts of PM10 and NO2 emissions are summarised in Table 3.2. Comparison against these concentrations is only made in this report to provide some context as to the magnitude of measured and modelled concentrations. Table 3.2: Air quality assessment criteria Contaminant and averaging period Criteria Source PM10 24-hour average Annual average 50 µg/m³ 20 µg/m³ NESAQ AAQG NO2 1-hour average 24-hour average 200 µg/m³ 100 µg/m³ NESAQ NESAQ NESAQ = National Environmental Standards for Air Quality AAQG = Ambient Air Quality Guidelines 4 Model results 4.1 Particulate matter The predicted maximum 24-hour average PM10 concentrations are illustrated as a contour plot in Appendix B. This figure shows concentrations that are significantly influenced by impingement of the vent plumes against elevated terrain surrounding the vents. However, predicted concentrations are comparatively low, with the maximum off-site ground level concentration due to the vent discharges only of approximately 2 µg/m³ - this occurs at a location between the two vents. To put this concentration into context, it is less than the limit of detection of standard PM10 ambient monitoring instruments. A maximum cumulative 24-hour average PM10 concentration of 21 µg/m³ is predicted, given a background concentration of 19 µg/m³ (see Section 3.3). This is less than half of the National Environmental Standard for Air Quality (NESAQ) for PM10 (24-hour average concentration of 50 µg/m³). The predicted maximum annual average concentrations is 0.17 µg/m³. This concentration is considered negligible and consequently a contour plot and further analysis is not provided. 4.2 Nitrogen dioxide The model predicted maximum 1-hour and 24-hour average NOX concentrations are presented as contour plots in Appendix B. From this, predicted maximum 1-hour and 24-hour average concentrations are approximately 11 µg/m³ and 6 µg/m³ respectively. Nitrogen oxide (NO) can react with atmospheric background ozone and oxidise to form NO2. This atmospheric conversion can be accounted for in air quality assessments. However, in this instance we have conservatively assumed all NOX emitted is in the form of NO2 and have conservatively added those concentrations to background levels set out in Section 3.3. Given this, we predict cumulative 1-hour and 24-hour average NO2 concentrations of 48 µg/m³ and 29 µg/m³, noting that these are very conservative predictions. Notwithstanding their conservative nature, the cumulative concentrations are low when compared to the human health assessment criteria of 200 µg/m³ (1hour average) and 100 µg/m³ (24-hour average).
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