Final Mitigated Negative Declaration and Response to Comments

XII. NOISE.
ENVIRONMENTAL SETTING
The project area is located in Emerald Bay State Park (SP) in the Lake Tahoe Basin. Activities
would be conducted from a boat or barge and work would occur in the underwater portion of
the park. This area is characterized by a natural setting which is often free of loud noise;
however, boat traffic can be very heavy at times in this area and noise can travel great
distances over the flat lake surface.
Sound is any detectable fluctuation in air pressure and generally is measured on a logarithmic
scale in decibels (dB). When unwanted sound (i.e., noise) is measured, an electronic filter is
used to de-emphasize extreme high and low frequencies to which human hearing has
decreased sensitivity. Resulting noise measurements are expressed in weighting frequencies
called A-weighted decibels (dBA). While zero dBA is the low threshold of human hearing, a
sustained noise equal or greater than 90 dBA is painful and can cause hearing loss (Table XI-
1, Bearden 2000).
Table XI-1: Sound Levels Generated by Various Sources of Noise
Sound Level
dBA
Quiet library, soft whispers 30
Living room, refrigerator 40
Light traffic, normal conversation, quiet office 50
Air conditioner at 20 feet, sewing machine 60
Vacuum cleaner, hair dryer, noisy restaurant 70
Average city traffic, garbage disposals, alarm clock at 2 feet 80
Constant exposure to the following sound levels can lead to hearing loss
Subway, motorcycle, truck traffic, lawn mower 90
Garbage truck, chain saw, pneumatic drill 100
Rock band concert in front of speakers, thunderclap 120
Gunshot blast, jet plane 140
Rocket launching pad 180
(Bearden 2000)
Noise is further described according to how it varies over time and whether the source of noise
is moving or stationary. Background noise in a particular location gradually varies over the
course of a 24-hour period with the addition and elimination of individual sounds. Several
terms are used to describe noise and its effects. The equivalent sound level (L eq ) describes
the average noise exposure level for a specific location during a specific time period, typically
over the course of one hour. The Community Noise Equivalent Level (CNEL) is a twenty-four
hour average of L eq with an additional 5 dBA penalty for noise generated between the hours of
7:00 p.m. and 10:00 p.m. and a 10 dBA penalty during the hours of 10:00 p.m. and 7:00 a.m.
The penalties account for how much more pronounced a noise is at night when other sounds
have diminished. Federal, state, and local governments have defined noise and established
Asian Clam Control Project IS/MND
Emerald Bay State Park
California Department of Parks and Recreation
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