This draft regulation references many ordinances laws and regulations in effect by many cities and counties in the U. S. and other countries. Also, referenced are technical papers, reports and nationally recognized standards relating to wind turbines. …
Wind Farm Noise Emissions
Noise emission from the site shall not be greater than the dB(A) slow and dB(C) slow, one-hour energy equivalent exceedance levels:
|Exceedance Value – %||Hourly Exceedance Level Turbine Noise|
|dB(A) Slow – Leq||dB(C) Slow – Leq|
Pure tones shall be defined using un-weighted one-third octave level as existing when the one-third octave band levels adjacent to the one-third octave band containing the tone are 5 dB or more less at frequencies greater than 500 Hz. Below 500 Hz, the differences must be 8 dB for center frequencies, 160, 200, 250. For center frequencies of 125 Hz and lower the differences must be 10 dB. If there are pure tones present as described in this section, then the audible noise standard shall be reduced by 5 dB.
Low Frequency Noise or Infrasound Noise
No low frequency noise or infrasound noise from wind turbine operations shall be created which causes the noise level at the project boundary or at a one-mile radius beyond the closest turbine, which ever is greater to exceed the following limits:
|1/3 Octave Band Center Frequency (Hz)||Sound Pressure Level (Leq)|
No impulsive noise from wind turbine operations shall be created which causes the noise level at the project boundary or at a one-mile radius beyond the project boundary or noise setback boundary that exceeds the following limits as measured by either of the two following methods.
- Method 1
A qualification of impulsivity can be obtained from the average of several measurements of the difference between the C-weighted “impulse hold” and maximum C-weighted “slow” sound pressure levels. The difference between the two shall be less than 20 dB.
- Method 2
The impulsive character can also be displayed as a time history of the acoustical signal which has been filtered through an octave band filter set at 31.5 Hz center frequency. The filtered octave band signal shall then be converted to a root-mean-square (RMS) value, slow response, and log converted to dB. The display can be either analogue or digital. The average difference between the maximum and minimum value shall be less than 20 dB when computed as the arithmetic average of 100 differences.
Clear Creek County Planning Department may require seismic (ground vibration) measurements at selected locations, when the site is in operation.
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