Boffa Miskell Ltd | Waihi North Project | Terrestrial Ecology Values and Effects of the WUG | 22 June 2022 63 6.4.5 Water and Air Discharges from Ventilation Raise Effects on Fauna An Assessment of Mine Vent Air Quality was undertaken by Tonkin & Taylor specifically to inform potential effects on native frogs (Tonkin & Taylor 2022). The nature of emissions from the tunnel are expected to be similar to those from the existing Martha and underground mines. The main discharges to air from the vents will be particulate matter and products of combustion (i.e. oxides of nitrogen (NOx)) 40 from exhaust of mining equipment and trucks, as well as blasting events (Tonkin & Taylor 2021) 41. The ventilation air will meet or exceed workplace exposure standards for these air quality parameters. We note that vehicle emissions will be effectively continuous, but particulate matter associated with blasting will be of very short duration. Underground emissions will be discharged to air via the ventilation shafts as a point source discharge rather than a diffuse source. The vent stack will be 8 m tall and have a diameter of 5.5 m and exhaust temperature is expected to be between 20 - 21⁰C. Emissions from the ventilation raises will be visible as a plume of water vapour in cool, calm conditions. Dispersion modelling was undertaken to predict ambient contaminant concentrations around likely vent locations (Figure 11). These concentrations were then compared to measured contaminant concentrations on metalled public roads to infer conditions that native frogs (Hochstetter’s frogs) may experience (and persist with) at sites elsewhere in the Coromandel where they are recorded near unpaved roads42. This method allows for an assessment of native frogs’ potential tolerance to particulates and nitrogen oxide (acknowledging the paucity of data for this assessment, particularly the tolerance of forest-dwelling frogs to elevated contaminant concentrations). Dispersion modelling methodology and parameters used, and results are described in Tonkin & Taylor (2021). The maximum ground level concentration of particulate matter (PM10) due to the vent charges was modelled as 2 µg/m3 in the area between two vents. Predicted maximum 1hour and 24-hour average NOx concentrations are approximately 11 μg/m³ and 6 μg/m³ respectively. The findings of the Assessment of Mine Vent Air Quality with respect to native frogs includes: • Predicted cumulative concentrations of PM10 in the vicinity of the vent raises will be lower than measured concentrations adjacent to an unpaved road in Northland (based on weekend traffic volumes). • Based on similarity in traffic levels, PM10 concentrations are likely to be similar in areas adjacent to an unpaved public road in the Coromandel (north of the WUG) where baseline ecological assessments of Hochstetter’s frog habitat have been undertaken. Therefore, it can be inferred that Hochstetter’s frogs at this Coromandel location are exposed to greater levels of PM10 than anticipated in the vicinity of the proposed vents. The potential effect of air discharges to fauna habitats within Coromandel Forest Park includes particulates settling on vegetation (habitats) and animals themselves. Native frogs are 40 Such as particulate matter (PM10, PM2.5,), nitrogen oxides (NOx) and carbon monoxide (CO) 41 Blasting generates emissions of particulates (CO, NOx and small quantities of SO2), as well as dust from the shattering of rock. Blasting will occur using ammonium nitrate explosives (at any time in accordance with all relevant safety procedures). 42 A total of eight Archey’s frogs were recorded during a survey along Tapu-Coroglen Road in April 2022. The road is unpaved and vegetation was observed as dusty, despite rain during the day. Frogs were recorded between 1.60 and 2.65 m from the road edge. This finding suggests that Archey’s frogs can persist with some level of dust deposition on habitat surfaces.
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