3 Tonkin & Taylor Ltd Waihi North Project - Technical Review of Air Quality Assessments Oceana Gold (New Zealand) Limited 22 June 2022 Job No: 1017908.0000 2.4 Section 6: Existing air quality effects Section 6 of the Waihi Facilities Report presents information relating to the operation of the existing mining activities, including summarising monitoring data and complaints and compliance history. This information is useful as it provides context for the assessment of the proposed development and indicates the likely effects and efficacy of control/mitigation measures. The monitoring primarily comprises the measurement of dust deposition and total suspended particulate (using HiVols and samples collected over a 7-day period). The dust deposition data that is presented in Section 6 highlights relatively low deposition rates when compared with the MfE guideline of 4 g/m²/30-days for all monitoring sites, albeit that the results are not presented as the deposition rate above background levels (as per the MfE guideline). Section 6 also provides a detailed statistical analysis of the deposition rate data using a ‘pairwise Wilcox Rank Sum test’, with the purpose of determining whether there is a significant difference between the measured dust deposition rates for the different sites. The statistical analysis concludes there is no statistical difference between the different monitoring sites, from which it is inferred that site discharges do not have a measurable effect on deposited dust levels. The above finding seems at odds with the subsequent analysis of annual average deposition rates and production capacity in Section 6.2.1, which clearly identifies deposition rates correlating with the annual tonnage of material handled (which in turn indicates a clear relationship between site activity and dust deposition). It is also at odds with a visual analysis of Figure 6.2 and reference to Table 6.1 which indicates sites close to and downwind of key sources experience higher dust deposition rates. T+T considers that the use of the pairwise Wilcox Rank Sum analysis in this instance may not be particularly useful given it most likely focuses on mean concentrations rather than the upper quartile and peak concentrations, the latter which are of most interest in terms of effects. Many of the comments provided above in relation to dust deposition data are applicable to the analysis of TSP data. In particular, the use of the pairwise Wilcox Rank Sum test. The summary discussion provided in Section 6.1 relating to TSP concentrations is helpful. In particular, where it notes TSP concentrations between 150 m and 250 m from the existing Martha Pit become less significant, and consistent with measured levels elsewhere in Waihi that are not impacted by the mine. Section 6.2 also discusses short duration monitoring campaigns for the measurement of PM10 and respirable crystalline silica (RCS). The discussion would benefit from a clear identification of the locations where the monitoring was undertaken and the proximity of the monitors to the mining activities. Regarding RCS monitoring, it is unclear what monitoring methods were used, the location where monitoring was undertaken, the distance of monitoring locations from discharge sources and periods over which monitoring occurred. Accordingly, the assessment would benefit from detailing these aspects of the monitoring programme. The review of the RCS data appropriately refers to the Californian Office of Environmental Health Hazard Assessment (OEHHA) Reference Exposure Levels (REL)2 annual average guideline of 3 µg/m³. However, the analysis seeks to derive a 24-hour average criterion for evaluating the results using a power law relationship described in the MfE ‘Good Practice Guide for Atmospheric Dispersion 2 OEHHA 2016. Acute, 8-hour and chronic reference exposure levels. Office of Environmental Health Hazard Assessment as of June 2016, California. .
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