A. Average Sound Level: The average sound level for wind facilities shall not exceed fifty (50) dBA during the daytime and forty (40) dBA during the nighttime at any point within neighboring, residentially zoned or used property. The average sound level from wind facilities shall not exceed sixty five (65) dBA on neighboring industrial properties and sixty (60) dBA on other neighboring nonresidential properties at any time of day. Measurements can be taken at any location on nonparticipating properties and must account for ambient sound contributions.
B. Operation Of WES With Average Sound Level More Than Five dBA Above Level: No WES shall operate with an average sound level more than five (5) dBA above the nonoperational ambient level, as measured within one hundred feet (100') of any neighboring residential dwelling.
C. Limitation Of Low Frequency Sound: To limit the level of low frequency sound, the average C-weighted sound level during facility operation shall not exceed the A-weighted ambient sound level by more than twenty (20) dB.
D. Sound Level Measurement:
1. Sound Measurement Worksheet: The wind energy facilities sound measurement worksheet is intended to determine the average sound level (i.e., source sound level) from operating wind energy facilities by correcting for the ambient sound levels. This measurement will determine whether the sound exceeds the limits indicated in this section.
2. Sound Level Meters: Sound level meters (SLM) must meet the type 2 grade or better per the latest revision of ANSI S1.4 "American National Standard Specification For Sound Level Meters" and must have an integrating feature that meets ANSI S1.43 "American National Standard Specifications For Integration Averaging Sound Level Meters".
3. Basis Of Procedures: The procedures outlined herein are based in essences on applicable portions of ANSI S12.9 "American National Standard Quantities And Procedures For Description And Measurement Of Environmental Sound" and part 910 of title 35: environmental protection, subtitle H: noise, chapter 1: Illinois pollution control board.
4. Frequency Measurement:
a. The A-weighted scale is most often utilized for the measurement of tonal or audible sound levels. These are sounds that range from twenty (20) to twenty thousand (20,000) Hz and that the human ear can typically hear.
b. The C-weighted scale is utilized especially for measurement of low frequency sound, i.e., more bass tones or infrasound, which may or may not be audible to the human ear. Low frequency sounds can travel farther and may be enhanced in different locations such as in buildings.
5. Instrumentation Setup:
a. Ensure the battery is in good condition.
b. Measurements may be taken at any position on a nonparticipating property, provided the location is not within:
(1) Five feet (5') of small surfaces (e.g., trees, posts, etc.);
(2) Twenty five feet (25') of a large reflective surface (e.g., shed, building, etc.); or
(3) Fifty feet (50') of a large reflective surface if the sound is tonal in nature.
c. A tripod for the microphone or SLM is required if the sound is high pitched. If the sound is low frequency in nature, a handheld meter is acceptable as long as the arm is extended.
d. The microphone on the SLM must be aimed toward the noise source and oriented at an angle recommended by the manufacturer (usually 45 to 70 degrees off the ground). (Ord. 2010-816, 5-18-2010)