COMFREY WIND PROJECT. NOISE STUDY In Brown and Cottonwood Counties, Minnesota. For WESCO Wind 04/16/12

Transcription

1 COMFREY WIND PROJECT NOISE STUDY In Brown and Cottonwood Counties, Minnesota For WESCO Wind 04/16/12 April 16, 2012

2 This report was undertaken to determine the noise impact on the area surrounding the installation of seventeen Sinovel SL1500/89/80HH Wind Energy Conversion Systems (WECS) in Brown and Cottonwood Counties, Minnesota. The project is located on agricultural land that is very lightly populated. The closest occupied structure to a WECS is approximately 1,000 feet. The noise impact is based on a decibel rating (db). Following is information on Decibel Rating for those that are not familiar with these terms and calculations: DECIBEL RATING Decibel rating is the calculation of the noise emission level at various noise- sensitive areas (NSA). In this case the wind turbine generator is the source of the emission (release point of the noise energy into the environment) and surrounding structures are the immission point (target for receiving the energy). There are many factors that affect the travel of the noise such as wind speed, ground attenuation, meteorological coefficient, pure tones and height of immission point above ground level. There are acceptable levels for sound rating at given types of noise-sensitive areas (NSA) mandated in Minnesota. The basis for this study is the General ISO requirements and is used in these calculations. ISO is the International Organization for Standards and ISO covers: Acoustics - Attenuation of sound during propagation outdoors - Part 2: General method of calculation. It describes a method for calculating the attenuation of sound during propagation outdoors in order to predict the levels of environmental noise at a distance from a variety of sources. The method predicts the equivalent continuous A-weighted sound pressure level (as described in ISO 1996) under meteorological conditions. In the State of Minnesota, the Minnesota Pollution Control Agency (MPCA) regulates noise pollution. MPCA Noise Area Classification classifies Noise Area #1 as Household units (including Farm Houses) and then in Noise Standards shows Noise Area #1 with a maximum allowable L 50 rating of 50db during the night time. RESULTS The Decibel calculations clearly indicated that the noise created at an occupied living structure closest to a WECS unit is well below the sound thresholds that are established by the MPCA. The requirement is for the db rating created by the WECS to be less than 50db. The results for all homes (26) in close proximity to the WECS range from 24.1db to 40.5db. To provide a perspective on noise levels, 45 decibels would compare to a quiet office; while 55 decibels is comparable to a car 100 meters (328 feet) away traveling at 40 mph. Therefore, the layout of the Comfrey Wind Project meets and exceeds the requirements by the MPCA for Noise Requirements. The complete results for the Decibel calculations including the assumptions are attached. Prepared by: John J. Wiltzer, P.E., LLC 2

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