| Discharges to Air and Associated Mitigation Methods | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 19 Indicative particulate size distributions are provided by the USEPA AP-42 emission factors10111213. The estimated proportion of the TSP emitted as PM10 and PM2.5 is summarised in Table 3-1. The emission factor indicates that the proportion of TSP emitted as PM10 and PM2.5 would be expected to 30 - 50% and 3 - 7.5% respectively. The proportion of PM10 emitted as PM2.5 would be expected to be approximately 10 -15%. Table 3-1. Proportion of TSP emitted as PM10 and PM2.5 (US EPA AP-42 Emission factors) Operation Percentage TSP as PM10 (%) Percentage TSP as PM2.5 (%) Material handling and crushing operations 40% 5.3% Unpaved haul roads 30% 3.0% Wind erosion of open aggregate storage piles and exposed areas 50% 7.5% The material mined at Waihi contains crystalline silica, and consequently the dust created during mechanical operations such as crushing processes will also contain a proportion of crystalline silica. Fine particles of crystalline silica (less than 10 µm) that are able to be inhaled deep into the lungs, known as respirable silica, can cause significant adverse human health effects (silicosis) if people are exposed to concentrations above recommended guideline levels over extended periods of time. 3.2.2 Factors which influence dust generation The major factors that influence dust emissions from surfaces are: ● Wind speed across the surface – the critical wind speed for pick-up of dust from surfaces without disturbances such as traffic is 5 m/s: above 10 m/s the pickup increases rapidly14 ● The percentage of fine particles in the material on the surface (e.g. the silt content of the material) ● Moisture content of the material on the surface ● The area of exposed surface ● Disturbances such as traffic, excavation, loading and unloading of materials. Vehicles travelling over exposed surfaces tend to pulverise surface particles. Particles are lifted and dropped from rolling wheels and the road surface is exposed to strong air currents due to turbulence between the wheels and surface. Dust is also sucked into the turbulent wake created behind moving vehicles. The smaller the particle size of the material on the surface of a road or an exposed surface, the more easily the particles are able to be picked up and entrained in the wind. Moisture binds particles together preventing them from being disturbed and mobilised by wind or vehicle movements. Hence, one of the most effective means of minimising dust emissions is the use of water to keep surfaces and materials damp. 10 United States Environmental Protection Agency (USEPA) AP42 Emission Factor Database Chapter 11.24 Metallic Minerals Processing 11 United States Environmental Protection Agency (USEPA) AP42 Emission Factor Database Chapter 13.2.2 Unpaved Roads (assuming a silt content of 10%) 12 United States Environmental Protection Agency (USEPA) AP42 Emission Factor Database Chapter 13.2.4 Aggregate Handling And Storage Piles 13 United States Environmental Protection Agency (USEPA) AP42 Emission Factor Database Chapter 13.2.5 Industrial Wind Erosion 14 Air and Waste Management Association “Air Pollution Engineering Manual” 2nd edition edited by Wayne T Davis, 2000.
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