7 Tonkin & Taylor Ltd Waihi North Project - Technical Review of Air Quality Assessments Oceana Gold (New Zealand) Limited 22 June 2022 Job No: 1017908.0000 3 Wharekirauponga Underground Mine The air quality assessment covering the Wharekirauponga Underground Mine (WUG) assesses the potential effects of dust and fine particulate matter emissions associated with the surface infrastructure to be established at Willows Road site, approximately 4 to 5 km north of Waihi. The footprint of the surface infrastructure is expected to cover approximately 18 ha. Some of the content of the WUG report is the same as that presented in the Waihi Facilities report and consequently the review comments that we have made in relation to the Waihi Facilities report are also applicable to the WUG report. The WUG report refers to, and appends, a report prepared by T+T that separately assesses mine vent discharges to inform an ecological assessment of Archey’s Frog. This technical review does not consider the T+T report. The following summarises our technical review of relevant sections of the WUG report where we consider commenting is appropriate. 3.1 Section 3: Environmental setting Section 3.2.1 of the WUG report describes the ‘Human receptors (dwellings)’ surrounding the Willows Road site. It describes that “several privately owned dwellings are located on Willows Road relatively close to the topsoil storage area and noise bunds”, listing the closest separation distances as being 109, 234 m and 145 m respectively. This section would significantly benefit from the inclusion of a map clearly illustrating the location of the sensitive receptors relative to the location of the surface infrastructure. Section 3.4 considers background air quality in the vicinity of the Willows Road site, noting that TSP concentrations are expected be low. We agree with this given the rural nature of the site. Section 3.5 addresses meteorology, relying on data from Oceana Gold’s monitoring station in Waihi. While there may be some differences between the two locations, we consider the data are likely to be broadly representative of conditions at the site. Discussion is also provided regarding the frequency of wet days – this is essentially the same text as discussed in the Waihi Facilities report and the matters that we identified above in relation to that report are applicable here. 3.2 Section 4: Air quality standards and guidelines Section 4 of the WUG report covers the various air quality standards and guidelines. Overall, we agree with the criteria used and note that the choice of those criteria is consistent with MfE guidelines. Notwithstanding this, Beca describes the annual average respirable silica guideline of 3 µg/m³ as being “approximately equivalent to a 24-hour average guidelines of 9 µg/m³. As discussed in Section 2.4 of this report, we do not consider the approach to derive a 24-hour value from an annual average criterion to be appropriate. Instead, we consider a more valid approach would is to simply compare the long-term average of measured RCS concentrations against the OEHHA annual average guideline of 3 µg/m³. In this regard, we note that the long-term average of the 24-hour average results from monitoring in Waihi are below the OEHHA of 3 µg/m³. 3.3 Section 5: Air discharges and associated mitigation methods Section 5 of the WUG report describes the various factors that influence the generation of dust and outlines methods to minimise emissions. Section 5.2 describes the generation of dust from surface sources associated with the Willows Road site. We generally agree with the information provided describing the sources and factors associated with those sources that result in the propagation of dust emissions.
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