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 64 of 79 APPENDIX C GLADSTONE STRUCTURAL NOISE MITIGATION ANALYSIS This section describes the noise mitigation packages we have investigated and analysed in a noise mitigation design workshop with OGNZL staff and representatives. Most of the mitigation is focussed on reducing noise towards Barry Road to the north, an aim that is made difficult by the surrounding topography. Our intent with this analysis was to establish, at least at a concept level, what mitigation would be required to achieve a firm limit of 50 dB LAeq at all properties. Once we had a suite of mitigation options, these were presented to and discussed with the Project team. At this time several issues were raised that render some of the options undesirable for practical or logistical reasons. C1 Intention Develop noise mitigation to ensure a reasonable level of amenity is maintained at all properties not owned by OGNZL or subject to an agreement with OGNZL C2 Reasons This was initially required because our preliminary modelling indicated that noise levels up to 57 dB LAeq were predicted at some dwellings. The elevated levels were significantly influenced by noise from the new GOP crusher and associated loading activity, with this cluster of sources alone contributing over 50 dB LAeq at the closest dwellings. C3 Structural Mitigation Options We investigated a combination of structural mitigation (i.e. barriers and bunds) and source noise management (e.g. the selection of quieter equipment or similar restrictions). The following noise barrier concepts were developed through this process: • A standard timber fence on OGNZL land along the boundary with 56-88 Barry Road (‘Barrier A’); • A bund along Moore Street, halfway between the pit and Barry Road (‘Barrier B’); • A wall north of the GOP crusher slot and loading area (‘Barrier C’); • A wall along the south-western rim of the Gladstone pit, to block noise to the south (‘Barrier D’). These options are labelled accordingly in Figure 34. C4 Discussion and Workshop We discussed the potential effectiveness and practicalities of such measures with the project team. Northern Crusher Loading Initially, a main focus was on the northern crusher slot wall (Barrier C). This was required in part to control noise from a large 100t wheeled loader that was modelled at the new GOP crusher load point. Because this large piece of machinery would sit outside of the pit (effectively at normal ground level), noise from this area, combined with that from the CAT777 haul trucks, could relatively easily propagate up the valley to the north-west. To address this, the northern wall was initially modelled as 6 metres high. While such a structure is unlikely to be feasible from an engineering perspective, it was investigated to ascertain its noise reduction effectiveness. In practice, we expected that an equivalent degree of noise control could be achieved by dropping the ROM crusher tipping point and vehicle paths so that they are on a bench between the crusher slot and surrounding ground. A more conventionally sized noise barrier or bund could be formed on the top edge of this in order to create a significant ‘path difference’, i.e. a long noise path for noise to escape the pit. Barriers A and B had a further influence in reducing noise from these sources. Figure 34: Indicative noise barrier options in mitigation workshop Additional Mitigation A barrier has also been considered on the south-western edge of the pit to reduce noise emissions towards receivers in the Heath Road and Clarke Street areas. This is intended to reduce the noise from large mining equipment operating on the western portion of the pit before it is established to a reasonable depth, as described in Section 6.3. Further mitigation is considered in the form of equipment management, particularly during the early years of the project when the pit is not sufficiently deep. During this time – approximately years 2024 to 2026, inclusive – we investigated the impact of reducing the use of extra-large mining equipment such as the Hitachi 180t excavator and replacing them with multiple smaller plant items used instead (e.g. 2x 50t CAT excavators). Similarly, we proposed that use of the selected CAT 992 front end loader at the ROM processing plant could be limited to a smaller model such as a CAT 960 whenever possible. Subsequent Refinement Following discussion with OGNZL, the proposal and mitigation options have been refined to achieve a more practical balance. The CAT 992 loader was over specified for the task and has been scaled down to a maximum size of 51 tonnes, e.g. a CAT 988k. With noise suppression fitted, we have based our calculations on a sound power level of 110 dB LwA, which is a notable reduction over that used for the initial modelling. As a result, the barriers have also been refined, with a maximum proposed height of 3 metres for the northern wall now proposed.
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