2 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 Waihi Facilities The Waihi Facilities Report assesses the potential effects of discharges to air from the proposed activities associated with the WNP that are based in and around Waihi with the exception of discharges to air from the Processing Plant, which were assessed separately and are discussed in Section 3 below. The following summarises our review of Waihi Facilities report where we consider commenting is appropriate. Overall, we agree with the assessment conclusions. 2.1 Section 3: Discharges to air and associated mitigation measures Section 3.2 of the Waihi Facilities Report describes the main discharge from the activities as being ‘dust’, describing the likely sources and composition of that dust, and factors that influence dust generation. It also discusses general mitigation measures for minimising dust emissions, which we consider are consistent with industry practice. Notwithstanding this latter point, we have not been provided any air quality management plan to review that sets out the detail of the implementation of the mitigation measures. Section 3.2 also discusses exposed surfaces as being potential sources of dust during strong wind conditions. This includes the pit walls, which in our opinion are unlikely to be an appreciable sources of dust due to the mine being hard rock. We agree with the commentary that to effects beyond the mine boundary from combustion emissions are minimal. 2.2 Section 4: Air quality standards and guidelines Section 4 of the Waihi Facilities Report discusses the applicable air quality standards and guidelines. It appropriately canvases the range of contaminants expected for a mining activity of this nature, albeit that it includes guideline values applicable to metal emissions associated with the Processing Plant that are assessed separately from this report. The corresponding guideline/standard sources that have been used are appropriate and follows Ministry for the Environment (MfE) guidance1 for selecting suitable air quality assessment criteria. Section 4.3 discusses the existing resource consent trigger values as they relate to dust monitoring. These include values relating to 7-day average total suspended particulate and for dust deposition monitoring. As part of ongoing dust monitoring associated with the WNP, T+T considers it good practice to adopt 1-hour average dust trigger values, enabling a proactive response to dust events as they occur. As such we recommend that 1-hour average dust trigger values be proposed in the application or be required in a dust management plan. 2.3 Section 5: Environmental setting Our review of this section of the Waihi Facilities Report describing the environmental setting for the Waihi Facilities does not raise any issues of note, with the exception of Section 5.25, which defines a ‘rain day’ as being when “at least 1 mm of rain is recorded”. This is likely to overstate the number of ‘wet days’ and by inference under-estimate the dry days each month when dust emissions from mining activities might occur. It is our experience that the potential for surfaces to remain moist is only likely to occur where rainfall exceeds evaporation by more than 1 mm per day. This is because during summer, evaporation rates typically exceed 1 mm/day meaning that surfaces would likely rapidly dry under such conditions. 1 MfE 2016. Good Practice Guide for Assessing Discharges to Air from Industry. Ministry for the Environment. Publication number: ME 1276.
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