This document may not be reproduced in full or in part without the written consent of Marshall Day Acoustics Limited Rp 001 R0 20210601 SJP (Waihi North Noise Assessment) ISSUE 42 of 79 9.3.2 Vent Raise Fan Noise Emissions Surface ventilation raise sound power levels have been calculated from fan noise from the fans located at the base of the vent raise. The calculated sound power levels are based on measurements of sound pressure levels at 5, 10 and 15 m from the existing Union Hill vent located close to Martha mine in Waihi. This is of equivalent duty, but the calculations of sound power levels have been adjusted where necessary to account for slight changes in duty, and vent raise geometry. Predictions of fan noise in the conservation area from typical vent raises are shown in Figure 27 below. This shows that noise levels are generally only above ambient noise levels (around 40 – 45 dB LAeq) within 100200m of the ventilation raise at the orebody, and would be barely audible at the other raises, and likely only if receivers are at the raise site itself. It is unlikely that noise from the ventilation raise would be audible on the Wharekirauponga walking track. Therefore, these noise levels are at a level low enough to be considered not significant. Figure 27: WUG Forest, operational noise from ventilation fans 9.3.3 Willows Road Portal Ventilation Fans The noise from the containerized ventilation plantroom has been based on fan sound power levels calculated frommeasurements within the tunnel at Martha for fans of a similar duty. The predicted noise levels would exceed the relevant night-time criteria without attenuation being included in the design of the container system. The temporary containerised fan therefore requires mitigation for the first 12 months of works/whilst on the surface to achieve acceptable noise levels. The operational noise level calculations for early phases of tunnelling include this attenuated noise source in the cumulative noise emissions to the nearby receivers. Allowance had been made for an 1800 mm long 50% open area attenuator at each side of the fan in addition to the standard 2D cylindrical attenuators. Transitions between the cylindrical attenuators and the attenuator should be of solid sheet metal construction a minimum of 1 mm thick with flexible connectors constructed frommass loaded vinyl minimum 4 kg/m2, no greater than 100 mm wide. The fans should be mounted on vibration isolation mounts and the ends of the container housing the fans should be sealed with a solid material with a surface weight of at least 8 kg/m2, such as 15 mm plywood, 9 mm fibre cement or 8 kg/m2 mass loaded vinyl.
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