APPENDIX 6.3-A Noise Modelling Year 2

Transcription

1 ENVIRONMENTAL ASSESSMENT APPENDICES APPENDIX 6.3-A Noise Modelling Year 2 VE51988 Appendices

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3 1.0 THE NOISE MAPPING MODEL The predicted changes to environmental sound levels from the proposed Project during its operation were determined using the SPM9613 noise prediction model developed by Power Acoustics, Inc. (2010), Orlando, Florida. The model includes two subroutines: ISO specifically addressing atmospheric attenuation and ISO which specifies an engineering method for calculating environmental noise from a variety of noise sources. This is by prescribing methods to determine the various attenuation effects observed during outdoor sound propagation. The model incorporates the following parameters: geometric spreading; barrier effects; atmospheric absorption; ground attenuation; specific wind speed/direction; source size and location; and acceptance of sound power level and sound pressure level spectrum data. 1.1 Modelling Assumptions and Inputs The operation noise modelling incorporated the following assumptions: the model included noise sources listed in Section Operations Noise Table ; primary gyratory crusher, pebble crusher and conveyers will be enclosed resulting in noise suppression; the maximum environmental noise generated during mining will occur during operation in Year 2, with sources located across the pit area and beyond but within the proposed Project fence line; the facility will operate continuously and steadily over the modelled year on a 24/7 basis; the mill building noise is presented as a computed cumulative source; octave bands spectrum provided for similar equipment is used for each type of noise source; model input acoustical specification of noise sources are given in sound power level spectrum (PWL, db Linear); the terrain is complex with surrounding hills acting as major noise barriers; atmospheric conditions that would minimize sound attenuations (rain or snow) are not taken into account; the grid size was selected to include both the local and regional study areas to predict near-by and distant noise levels; and the lowest noise level is equal to the baseline value of 40 dba. Page 1

4 The intensity of noise emission quantified by the sound power level (PWL) over the 1/1 octave frequency spectrum for equipment scheduled to operate at the Project site in Year 2 is shown in Table Equipment powered by quiet electric motors is not included in the table. The PWL is required as input data for the computer model in order to predict ambient noise levels in the surrounding area. The model input data includes location of noise sources, 3D dimensions of each source, meteorological parameters, the pit geometry, ground elevation and ground attenuation defined by hardness on a scale from 0 (very hard) to 1 (very soft). A total of 22 noise sources presented in Table were modelled, including eight sources in the pit (below the grade). When the processing plant commences operation, the major noise sources will be located in the mill building which accommodates high-level noise sources comprised of the SAG mill, ball mill, grinding circuit, and vibration screens. Noise generated by each unit will be added to the overall indoor noise. This combined noise will be transmitted through the building walls made of corrugated steel panels. During transmission some sound energy will be lost. The magnitude of the transmission loss (TL) depends on the thickness of the wall panels and their structural properties. The TL is computed for the mill building walls over the octave band sound power levels using engineering noise control design software (ENC 2004). Calculation results and associated parameters for individual sources are summarized in Section Operations Noise Table Results The sound level modelling results are shown in Figures and as noise level contour plots for the project area. The colour scale corresponds to sound levels in 5 dba intervals. Arbitrarily selected X-Y axes of the model have the 0-0 central point located at the primary crusher with the UTM Zone 9 NAD 83 at me, mn. Replacing the UTM with the project-referred coordinates improved spatial transparency of the model s graphical presentation of distances in the local and regional study areas. Page 2

5 Figure 1.2-1: Noise Level Contours (in dba) in the Proposed Project Study Area. The 40 dba Refers to the Annual Average 24-hour Baseline Noise Level (L 90 24h ) Page 3

6 Figure 1.2-2: Noise Isopleths Within the Local Study Area As shown in Figure , the highest sound pressure levels (SPL) may exceed the 70 dba level within the pit. However, due to the mitigation effect of the pit walls, the noise levels on the surface near the pit will be much lower, in the range of 50 to 60 dba, descending outwards. At the proposed Project fence line the maximum SPL will be approximately 45 dba which is the suggested permissible sound level for nighttime. Compliance with daytime objective of 55 dba is highly certain as this isopleth is located well within the proposed Project local study area. Furthermore, proposed Project noise will not Page 4

7 reach the Kitsault Townsite and Alice Arm. A background noise of 40 dba will be maintained throughout this area. 1.3 Camp Noise As this is a relatively remote site, a camp will be provided for all personnel on site. The noise levels in dormitory rooms will need to be at or below 30 dba to meet the Health Canada (2005) and WHO (1999) guideline to assure comfortable sleeping conditions. The modelling results presented in Figure show ambient noise levels at the camp location to be approximately 48 dba. The camp walls will be constructed as a prefabricated modules made of metal clad walls with thick thermal insulation. The walls are effective noise barriers. Their octave band noise reduction (NR) and transmission loss (TL) is estimated with the engineering acoustics program (ENC 2004) which gives an overall transmission loss of 21 dba. Therefore, an outdoor sound level of 48 dba will be reduced to an indoor sound level of 27 dba which is lower than the 30 dba guideline. Page 5

8 References ENC Engineering Noise Control Software Version 2.0. Causal Systems, Rundle Mall, SA, Australia. Health Canada National Guidelines for Environmental Assessment: Health Impacts of Noise. Draft Version. Prepared by the Acoustic Unit, Consumer and Clinical Radiation Protection Division Product Safety Programme, Healthy Environments and Consumer Safety Branch. Ottawa, ON, May. Power Acoustics Power Acoustics, Inc - Acoustical Consultants. Accessed December 2nd, 2010 from WHO Guidelines for Community Noise, Edited by Birgitta Berglund, World Health Organization, Thomas Lindvall, and Dietrich Schwela, Geneva, April. Page 6