| Potential Effects of Project on Environment | WNP Wharekirauponga Underground Mine - Assessment of Effects of Discharges to Air | 4397169-66885702-23 | | 41 (i.e greater than 10 µm) with a smaller proportion of the finer particulates (PM10 and PM2.5) from vehicle emissions. Particles greater than 50 µm, which are expected to make up the majority of the particulate generated by the project, have the potential to create nuisance effects due to soiling of surfaces and irritation of eyes and nose. The distance a particle that is entrained in the wind will travel is dependent on the height of discharge above the ground, the particle size and the wind speed. For example, in a 5 m/s wind a 100 µm particle disturbed from ground level will settle back onto the ground within approximately 10 m from the source. However, a 10 µm particle may travel up to 1 km under the same conditions24. Because deposited particulate is relatively large, it usually falls out of the air within 100 - 200 m of the source25. Dust nuisance is therefore most likely to occur where sensitive receptors are located within such proximity (i.e up to 200 m) of a significant dust source if appropriate mitigation is not carried out. The finer particles (known as suspended particulate or TSP) are generally less than 20 µm in diameter and can travel large distances downwind. The portions of TSP that pose the greatest health risks are PM10 and PM2.5 as they are able to penetrate the respiratory tract. PM2.5 can penetrate into the lungs and is responsible for an increase in human morbidity and mortality in some circumstances. Local environmental conditions may influence the potential range of dust effects. High average wind speeds, a high frequency of strong winds, or complex topography may increase the potential range over which dust can travel. Discharges from elevated sources are able to travel proportionally further before reaching ground level. Discharges from below ground level (e.g within pits or low points) are likely to reach ground level closer to the source. The WRS and the outlets to the ventilation raises will be located on elevated terrain. Taking this into account, it is considered that areas within approximately 200 m of these elevated dust sources may be adversely affected under worst case weather conditions, if appropriate mitigation measures are not implemented. 7.4.2 Wind speed and direction Based on wind data at the nearby Barrys Road weather station, the wind speed and frequency of stronger winds (ie >5m/s) that blow generally in the direction of the closest dwellings is relatively high (ie from the west south westerly quarter through to the westerly quarter, winds exceed 5m/s approximately 19.8% of the time). However, very high winds (>10m/s) from these directions occur relatively infrequently ie approximately 0.8 and 0.6% of the time respectively. Strong winds from other directions are expected to be low. The stronger wind conditions from the southwest to west, as well as the hilly terrain may increase the range of downwind dust effects beyond the site boundary especially during the construction of surface infrastructure. 7.4.3 Results of OGNZL and WRC monitoring at Waihi The results of OGNZL and WRC ambient air monitoring programmes (as summarised in the Waihi North Project Air Discharge Assessment-Waihi Facilities Report (Beca, 2022) show the impact of emissions from the Martha Mine have only a relatively small impact on TSP concentrations at downwind distances of 150 – 210 m from mine operations. These results provide an indication for assessment purposes of the likely impacts of dust from the Willows Road operation. 24 Ministry for Environment (2016) Good Practice Guide for Assessing and Managing Dust 25 Institute of Air Quality Management (2016) Guidance on the Assessment of Mineral Dust Impacts for Planning
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