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Federal Register / Vol. 86, No. 195 / Wednesday, October 13, 2021 / Proposed Rules expected propagation environment that would lie between spherical and cylindrical spreading loss conditions.
Practical spreading was used to determine sound propagation for this project.

Sound source levels
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similar environments from other Navy pile driving projects that were evaluated and used as proxy sound source levels to determine reasonable sound source levels likely to result from the pile driving and removal activities Table 6.
Some of the proxy source levels are expected to be conservative, as the values are from larger pile sizes.

The intensity of pile driving sounds is greatly influenced by factors such as the type of piles, hammers, and the physical environment in which the activity takes place. There are sound source level SSL measurements available for certain pile types and sizes from the
TABLE 6UNDERWATER NOISE SOUND SOURCE LEVELS MODELED FOR IMPACT AND VIBRATORY PILE DRIVING
Pile size, type
Sound pressure levels SPL or sound exposure level SEL at 10 m distance
Method
Peak SPL
42-in Diameter Steel Pipe 1
30-in Diameter Steel Pipe 2
14-in Steel H-pile 3
31.5-in Z-shaped Steel Sheet 4
31.5-in Z-shaped Steel Sheet 5
22.5-in Z-shaped Steel Sheet 3
22.5-in Z-shaped Steel Sheet 5

Impact
Impact
Vibratory
Impact
Vibratory
Impact
Vibratory

211
211
NA
211
NA
205
NA

RMS SPL
196
196
158
196
163
190
163

SELL
181
181
158
181
163
180
163

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Legend: All sound pressure levels SPLs are unattenuated; dB = decibels; rms = root mean square, SEL = sound exposure level; NA = Not applicable; NR = Not reported.
Notes:
1 = Navy pers comm. 2021.
2 = Navy San Diego Bay Acoustic Compendium NAVFAC SW 2020.
3 = Caltrans 2015.
4 = A proxy value for 31-in sheet piles could not be found for impact driving so the proxy for a 30-in steel pipe pile has been used from NAVFAC SW 2020. This value was also used for Z-shaped steel sheets for the Navys Dry Dock 1 Modification and Expansion, Portsmouth Naval Shipyard, Kittery, Maine 2021 IHA 86 FR 14598; March 17, 2021.
5 = For vibratory driving of 31-in sheet piles and 22.5-in Z-shaped steel sheet piles, 163 dB SPL was used based on measurements conducted by the Naval Facilities Engineering Command Mid-Atlantic NAVFAC Mid-Atlantic in the Technical Memorandum Nearshore Marine Mammal Surveys, Portsmouth Naval Shipyard 2018.

For 42-in steel piles, a SSL of 181 db SEL was used for impact driving and is similar to SSL of 180 dB SEL for 36-in piles in CALTRANS 2015. There are no SSL values for 42-in piles in CALTRANS, the nearest values are for 36-in and 60-in steel pipe piles. For 30in steel pipe piles, a SSL of 181 dB SEL
was used for impact pile driving as a proxy from the Navys San Diego Bay Acoustic Compendium NAVFAC SW
2020 the median value from the greatest sound levels recorded for 30-in steel piles. The SSL used for 30-in steel piles during impact pile driving is also more conservative than the SSL of 177
dB SEL for 30-in steel piles in CALTRANS 2015. For 31.5-in sheet piles, a SSL of 181 dB SEL was used for impact pile driving as a proxy from 30in steel pipe piles NAVFAC SW 2020, which is also slightly more conservative than a SSL of 180 dB SEL for 24-in piles in CALTRANS 2015 no larger sheet piles are described in CALTRANS
2015. During vibratory pile driving of 31.5-in sheet piles, the Navy used a SSL
of 163 dB SPL, which is also more
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conservative than a SSL of 160 dB SPL
for 24-in sheet piles in CALTRANS
2015 no large sheet piles are described in CALTRANS 2015. For 22.5-in Z-shaped steel sheet piles, a SSL
of 180 dB SEL was used for impact pile driving and is also equivalent to 24-in sheet piles in CALTRANS 2015.
During vibratory pile driving, a SSL of 163 dB SPL is a proxy from NAVFAC
Mid-Atlantic 2018 and is also more conservative than 24-in sheet piles in CALTRANS 2015 where the SSL is 160
dB SPL for 24-in sheet piles no larger sheet piles are described in CALTRANS
2015. For 14-in steel H-piles, a SSL of 158 dB SPL was used from CALTRANS
2015.
Level A Harassment In conjunction with the NMFS
Technical Guidance 2018, 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, NMFS developed a User Spreadsheet that includes tools to help
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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 overestimation of Level A
harassment take. However, these tools offer the best way to predict appropriate 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 from impact and vibratory pile driving, the NMFS User Spreadsheet 2020 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 Tables 7 and 8, and the resulting isopleths are reported below Table 9.

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