2 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 Table 2.1: Summary of emission testing Parameter Average value Comment Exhaust temperature 21 °C TSP concentration 1 mg/Nm³ Note concentration is well below WES-TWA for respirable and inhalable particulate matter Nitrogen dioxide (NO2) Oxides of nitrogen (NOX)* 2.1 mg/Nm³ 3.1 mg/Nm³ *NOx expressed as NO2 The workplace exposure standards (WES)2 can also be used to estimate maximum possible emission rates, given that the ventilation air needs to achieve these standards. Table 2.3 lists the current WES values. Two values are given for particulate matter (respirable and inhalable particulate matter). Inhalable particulate matter is the portion of airborne dust that is taken in through the mouth and nose during breathing – it relates to particles where more than 50% are smaller than 30 µm in diameter. Respirable particulate matter relates to the fraction of inhalable particulate matter that can penetrate and deposit in the lower bronchioles and alveolar region of the lungs – it relates to particles where more than 50% are less than 4 µm in diameter. Comparing the results of the source emission testing (Table 2.1) with the WES values (Table 2.2) is not straightforward given the different averaging periods that the concentrations apply to. Source emission testing samples are typically made over an hour, whereas WES concentration values are expressed as an 8-hour average. Notwithstanding this, we note the following: • Measured TSP concentrations levels are well below the both the inhalable and respirable particulate matter WES concentrations. • The measured NO2 concentration is slightly higher than the current WES concentration. However, the measure NO2 concentration relates to peak conditions associated with underground blasting. Given this, an 8-hour average concentration that includes period when blasting is not occurring is expected to be lower and within the WES concentration. Table 2.2: Applicable workplace exposure standards Contaminant WES-TWA (8-hour average) Respirable particulate matter (PM4) 3 mg/m³ Inhalable particulate matter 10 mg/m³ Nitrogen dioxide (NO2) 1.9 mg/m³ From discussions with OGNZL, it is understood that current mine vent emissions are expected to be lower than in 2007. This is because more stringent workplace exposure requirements are now inplace, including greater controls on dust and higher exhaust emission standards for diesel-fired mining equipment and trucks. On balance, we consider using the WES to derive model emission rates would produce unrealistically high emission rates. By contrast, the measured concentration values are expected by T+T to provide a more realistic basis for deriving emission rates, albeit a conservative one given the improved emission controls implemented since the testing was undertaken. 2 Worksafe 2020. Workplace exposure standards and biological exposure indices. Edition 12-1.
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