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 23 of 79 5.0 NOISE CALCULATION METHODOLOGY This section of the report sets out the noise calculation methodology and Sections 6 to 9 deal with discrete sections of WNP individually. These sections of the report present the noise levels from each of the four key areas of the WNP. Cumulative results for all parts of the WNP are given in Section 10.0 for each year over the duration of the project. We have undertaken a significant amount of 3D computer noise modelling to account for the spatial and temporal extent of works. For each of the discrete activity areas, different scenarios were modelled for each year or activity phase. Combining these ultimately allows us to illustrate how the project’s noise envelope will vary over its lifespan. Cumulative noise from the areas of the project east of the township (i.e. excluding WUG) also requires consideration given the proximity of these activities. Table 7 below demonstrates how the components of the activity, excluding WUG, combine within each year, based on the input data provided by OGNZL. Cumulative noise effects have been calculated on this basis. Dark red shading indicates a unique activity scenario for that year and light red shading indicates a previous year’s activity is assumed to continue. The cumulative noise calculations are therefore a conservative representation because they assume that worst-case noise emissions from each portion of the project will occur concurrently, which is unlikely to be the case in practice. Table 7: Summary of modelled operational scenarios for each year Year* Modelled Operational Activity Scenarios GOP NRS TSF3 2023 2024 WWTP upgrades; Process Plant upgrades 2025 2026 2027 2028 2029 GOP TSF 2030 GOP TSF 2031 GOP TSF 2034 Legend: NEW ACTIVITY PREVIOUS YEAR NO ACTIVITY Because noise from the WUG portion of the project will not overlap with the portions closer to the town, we have presented the analysis of these noise levels separately in this report – refer to Section 9.0. 5.1 Noise Modelling Software Computer noise modelling was undertaken using the SoundPLAN suite of noise modelling software (version 8.2). This software implements calculation procedures described in International Standard ISO 9613-2:1996 “Acoustics – Attenuation of sound during propagation outdoors – Part 2: General method of calculation”, with adaptions as appropriate from ISO/TR 17534-3:2015 “Acoustics – Software for the calculation of sound outdoors – Part 3: Recommendations for quality assured implementation of ISO 9613-2 in software according to ISO 17534-1”. This method accounts for a range of factors affecting sound propagation including: • The magnitude of the noise source in terms of sound power; • The distance between source and receiver; • The presence of obstacles such as screens or barriers in the propagation path; • The presence of reflecting surfaces; • The hardness of the ground between the source and receiver; • Attenuation due to atmospheric absorption; and • Meteorological effects such as wind gradient, temperature gradient and humidity. The effect of meteorological conditions is simplified in ISO 9613 by calculating the average downwind sound pressure level. The Standard adopts the conservative approach of assuming “supportive” propagation conditions, assuming that wind is always blowing from the noise sources to the receiver locations (i.e. in all directions simultaneously). 5.1.1 Assessment Considerations Noise levels have been predicted to enable an assessment in accordance with NZS 6802:2008. The method described in this Standard requires the derivation of a “rating level” (LR) that is compared with a given noise limit. This rating level accounts for: • Adjustments for any special audible characteristics (e.g. tonality or impulsiveness); and • Adjustments for duration (except for activities occurring at night). NZS 6802 also recommends the use of a “reference time interval” of 15 minutes. This is the time interval over which each individual time-averaged sound pressure level is measured. All noise levels presented in this report are rating levels (LR) in dB calculated by averaging the LAeq (15 min) over the daytime period allowing for the above adjustments. No averaging has been allowed for in calculations of night-time noise scenarios. 5.1.2 Selected Receivers We have selected representative receivers for each aspect of this project and have reported discrete noise levels at each of these in our report (section 10). This is complimented by area wide noise contour calculations that show the spatial noise emission extent. The selected receivers were chosen because of their likelihood to be most adversely affected by noise generated from different parts of the project. This includes consideration of how close they are to the project, and the presence of, or lack of existing screening. They therefore represent the reasonable worst case locations and thus if noise levels are compliant at these representative receivers, they would be compliant everywhere else. However, as detailed in section 6.3 with respect to Gladstone, it became clear that noise levels at that particular location were just exceeding the criteria in some localised and specific locations and therefore additional receivers have been reported in that section.
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