Noise Study / Memo by Ryan Russell 4/28/11Bionomics Environmental, Inc.
1045 East Winding Creek
Eagle, ID 83616
Phone: 208-939-1022
FAX: 208-368-0001
Memo
To: Ryan Russell
Idaho Sand & Gravel
From: Kris Horton
Date: 4/28/11
Re: Noise Study Southridge Gravel Mining Site
Introduction
Bionomics Environmental, Inc. was retained by Idaho Sand & Gravel of Nampa, Idaho to
perform and analyze a series of field noise measurements in the vicinity of the Southridge
Gravel Mining site at Overland Road, Meridian, Idaho. The purpose of this study is to assess
whether noise generated at the site by the gravel crusher impacts surrounding properties.
Background
Sound is created by a "source" that through vibration causes the air to vibrate at a frequency
that can be heard by the human ear. This sound propagates through the air and is affected by
environmental factors such as distance, barriers, atmospherics and other influences. It is then
picked up as sound by the receiver and can also be impacted by the sensitivity of that receiver
(e.g. human ear, microphone).
The human ear can hear sounds from 20 micro Pascals (.00002 Pascals, a measure of air
pressure) to as much as 6,500,000 micro Pascals. Because of this wide range, the decibel was
developed as a logarithmic measure of sound specifically heard by the human ear. Using this
scale a doubling of sound will only add 3 decibels so; for example, doubling the amount of
traffic on a road would only increase the sound from 50 to 53 decibels. An actual perception
of sound being twice as loud would be 10 decibels and would beaten-fold increase in the
sound energy.
Frequency is another component of sound that can be distinguished by the human ear. The
frequency range of hearing for the human ear is approximately 20 Hertz (cycles per second) to
20,000 Hertz. A piano ranges from 32 Hertz on the base to 4,000 Hertz on the high end with
"Middle C" being 256 Hertz.
Because the human ear is less sensitive to higher and lower frequencies, the A-weighted scale
was developed and the unit of measurement is known as the dBA (decibel A-weighted). In the
A-weighted scale the lower and higher frequency decibel levels are reduced while the middle
decibel levels that the human ear is more sensitive to are increased. All noise levels in this
report are stated as hourly Leq (energy-averaged equivalent sound pressure level) in terms of
dBA. An example of different noise levels is illustrated in Table 1.
Table 1. (:~mm~n indoor and outdoor noises
------ -- - -
Common Outdoor Noises
Sound Pressure Level (dBA)
Common Indoor Noises
Jet Flyover at 300 meters 110 Rock Band at 5 meters
Gas Lawn Mower at 1 meter 100 Inside Subway Train (New York)
Diesel Truck at 15 meters 90 Food Blender at 1 meter
Noisy Urban Daytime 80 Garbage Disposal at 1 meter or
Shouting at 1 meter
Gas Lawn Mower at 30 meters 70 Vacuum Cleaner at 3 meters
Commercial Area 60 Large Business Office and Normal
Speech at 1 meter
Quiet Urban Daytime 50 Dishwasher in next room
Quiet Urban Nighttime
Quiet Suburban Nighttime 40 Large Conference Room (background)
Quiet Rural Nighttime 30 Bedroom at Night
20 Recording Studio
0 Threshold of Hearing
Source: FHWA Highway Noise Fundamentals
As noise spreads out from a source, the sound intensity will drop at a rate of 3 decibels per
doubling of distance for a line source such as a road and at 6 decibels per doubling of distance
for a point source such as a race car track or piece of heavy equipment. The gravel crusher
operation would represent a point source. The type of ground (hard or soft) can affect this rate
of drop in the sound level as well as natural barriers.
Field Results
Field-testing for this noise study was performed on Apri126, 2011 at eight locations during
operation of the crusher. An additional two readings were taken during non operational hours
to determine the ambient background noise levels. The noise level readings were taken using
a CEL-593.C 1 precision impulse integrating sound level meter S 1.4 Type 1. The meter was
calibrated using a CEL 284/2 calibrator before use and meteorological measurements were
taken. Each location consisted of three five minute readings.
Table 2. Results of field testing at eight locations at and in the vicinity of the
Southridge Gravel Mining site.
Location Time dBA Average dBA
Gravel Crusher Site Point 1 8:05 am 73 77
8:10 am 78
8:15 am 81
792 Feet from Site Point 2 8:27 am 65 66
8:33 am 66
8:38 am 67
906 Feet from Site Point 3 8:49 am 60 60
8:54 am 60
8:59 am 61
Entrance at Overland Rd Point 4 9:18 am 58 56
9:23 am 55
9:28 am 56
2050 As en Cove Dr Point 5 9:44 am 57 57
9:49 am 57
Idaho Sand & Gravel Noise Memo
Location Time dBA Average dBA
9:55 am 57
2143 As en Cove Dr Point 6 10:04 am 55 55
10:09 am 58
10:14 am 52
2150 As en Cove Dr Point 7 10:28 am 56 57
10:33 am 58
10:38 am 57
2307 As en Cove Dr Point 8 10:48 am 56 56
10:53 am 55
10:59 am 56
2050 As en Cove Dr Point 5 5:00 m 49 47
5:05 m 45
5:10 m 48
2307 As en Cove Dr Point 8 5:19 m 43 44
5:24 m 45
5:29 m 45
Results
During Operation:
Noise levels at the gravel crusher site had an initial reading of 73; however, the decibel level
increased during the second and third readings to 78 and 81, respectively, due to the start of
the conveyer belt and two bulldozers. The primary source of noise at the Overland Street
entrance was passing traffic and construction noise from a site to the north of Overland Road,
therefore it was intermittent. There was some variance at 2143 Aspen Cove Drive due to an
overhead jet flyover and geese landing on a pond at the property during the second reading.
The average for the readings at all four private homes was 56 dBA.
Post Operation:
Readings were taken again at points 5 and 8 to get a representative sample of ambient
background noise while the gravel crusher operation was idle. Average of the readings at
Point 5 was 47 dBA with an average of 44 dBA at Point 8. This represents an average
increase of 10 dBA from the average of 46 dBA to 56 dBA during gravel crushing operation.
Conclusions
Noise dBA levels decreased from an average of 77 dBA at the gravel crusher site to 66 dBA
at a distance of 792 feet from the site and 60 dBA at a distance of 906 feet from the site. This
is consistent with the decrease of noise levels as it propagates from a point source. It
decreased an additional average of 4 dBA to the private homes which would also be
consistent with noise propagation. When measuring noise from a point source several factors
can impact noise levels. The actual design of the point source (quiet side versus loud side)
can impact noise levels as they propagate out from the source. Also, landform contours or
elevational differences can impact noise levels and in some instances creating a situation
where the noise level is the same at a location further away. This could have resulted in
similar noise levels at Point 4 (Entrance at Overland Road) in relation to the residences
located at Aspen Cove Drive further away due to the landform contours and funnel effect of
the narrow canyon leading to the private homes. The 10 decibel increase at the private homes
during operation of the crusher would be perceived as twice as loud and represent a
substantial increase in noise levels.
Idaho Sand & Gravel Noise Memo
Photographs
Photograph 1. Point 1. at site.
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Photograph 3. Point 3, 906 feet from site.
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Photograph 5. Point 5, 2050 Aspen Cove Ur.
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Photograph 4. Point 4, at entrance to site.
Photograph 6. Point 6, 2143 Aspen Cove Dr.
/daho Sand & Gravel Noise A~emo `~
Photograph 2. Point 2. 792 feet from site.
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Photograph 7. Point 7, 2150 Aspen Cove Dr.
Photograph 9. Point 5, 20150 Aspen Cove Dr
after operations shutdown.
Photograph 8. Point 8, 2307 Aspen Cove Ur.
Idaho Srnac~ & Gravel Norse Memo 5
Photograph 10. Point 8, 2307 Aspen Cove Ur
after operations shutdown..
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