Federal Register - February 8, 2021
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Source: Federal Register
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Federal Register / Vol. 86, No. 24 / Monday, February 8, 2021 / Notices
Caltrans compendium 2015
measurements of 24-inch steel sheetpiles supported by acoustic data from another project in Seattle,
Washington that used 48-inch steel sheetpiles Greenbusch Group, 2015, while the source data for H piles comes from the Caltrans 2015 compendium.
Needle guns can produce sounds up to 112 dbA OSHA, 2020 and we use that as the source level for that activity.
TABLE 3PROJECT SOUND SOURCE LEVELS
Method
Pile type
Estimated noise level
Vibratory Driving/Removal
Vibratory Driving/Removal
48-inch sheet
12-inch H pile
165 dBRMS
150 dBRMS
Source CALTRANS 2015, Greenbusch Group 2015.
CALTRANS 2015.
Note: SEL = single strike sound exposure level; dB peak = peak sound level; rms = root mean square.
spreading equals 15
R1 = the distance of the modeled SPL from the driven pile, and R2 = the distance from the driven pile of the initial measurement.
Level B Harassment Zones Transmission loss TL is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography.
The general formula for underwater TL
is:
TL = B Log10 R1/R2
where, TL = transmission loss in dB
B = transmission loss coefficient; for practical
The recommended TL coefficient for most nearshore environments is the practical spreading value of 15. This value results in an expected propagation environment that would lie between spherical and cylindrical spreading loss conditions, which is the most appropriate assumption for WADOTs proposed activity in the absence of specific modelling.
Using the equation above, underwater noise is predicted to fall below the behavioral effects threshold of 120 dB
rms for marine mammals at distances of 1,000 or 10,000 m depending on the pile types and methods Table 4. It should be noted that based on the geography of Henderson Bay, sound will not reach the full distance of the Level B
harassment isopleths in most directions.
In-air needle gun noise is predicted to reach the phocid harbor seal threshold 90 dB at 192 meters 629 feet, and the otariid threshold 100 dB at 60 meters 200 feet.
TABLE 4LEVEL A AND LEVEL B HARASSMENT ISOPLETHS m FOR EACH PILE TYPE AND HEARING GROUP
Level A harassment Pile type
Low frequency
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Sheet
H pile
31.8
3.2
Level A Harassment Zones When the NMFS Technical Guidance 2016 was published, in recognition of the fact that ensonified area/volume could be more technically challenging to predict because of the duration component in the new thresholds, we developed a User Spreadsheet that includes tools to help predict a simple isopleth that can be used in conjunction with marine mammal density or occurrence to help predict takes. We note that because of some of the assumptions included in the methods used for these tools, we anticipate that isopleths produced are typically going to be overestimates of some degree, which may result in some degree of overestimate of take by Level A
harassment. However, these tools offer the best way to predict appropriate
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Mid frequency
High frequency
2.8
0.3
47
4.7
isopleths when more sophisticated 3D
modeling methods are not available, and NMFS continues to develop ways to quantitatively refine these tools, and will qualitatively address the output where appropriate. For stationary sources such as vibratory pile driving or removal using any of the methods discussed above, NMFS User Spreadsheet predicts the closest distance at which, if a marine mammal remained at that distance the whole duration of the activity, it would not incur PTS. Inputs used in the User Spreadsheet are reported in Table 5 and the resulting isopleths are reported in Table 4 for each of the work scenarios.
Note that while the inputs for driving and removal of each type of pile are different, the resulting isopleths are the same because the total time per day
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Otariid 19.3
1.9
Level B
harassment
Phocid 1.4
0.1
10,000
1,000
number of piles per day times minutes per pile of pile driving is identical.
Therefore Table 4 includes only a single row for each pile type. The above input scenarios lead to PTS isopleth distances Level A thresholds of less than 1 m to 47 m.
The Level A harassment zones identified in Table 4 are based upon an animal exposed to pile driving multiple piles per day. Considering duration of driving or removing each pile up to 30
minutes and breaks between pile installations to reset equipment and move pile into place, this means an animal would have to remain within the small area estimated to be ensonified above the Level A harassment threshold for multiple hours. This is highly unlikely given marine mammal movement throughout the area.
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