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Federal Register / Vol. 86, No. 23 / Friday, February 5, 2021 / Notices
Impact Pile Driving: Exposure-Based Ranges Modeled acoustic ranges to threshold levels may overestimate the actual distances at which animals receive exposures meeting the Level A SELcum harassment threshold criterion. In addition, modeled acoustic ranges to thresholds assume that receivers i.e., animals are stationary. Therefore, such ranges are not realistic, particularly for accumulating metrics like SELcum.
Applying animal movement and behavior Denes et al. 2020c within the propagated noise fields provides the exposure range, which results in a more
realistic indication of the distances at which acoustic thresholds are met. For modeled animals that have received enough acoustic energy to exceed a given threshold, the exposure range for each animal is defined as the closest point of approach CPA to the source made by that animal while it moved throughout the modeled sound field, accumulating received acoustic energy.
The resulting exposure range for each species is the 95th percentile of the CPA
distances for all animals that exceeded threshold levels for that species termed the 95 percent exposure range ER95percent. Notably, the ER95percent are species-specific rather than categorized
only by hearing group which affords more biologically-relevant data e.g., dive durations, swim speeds, etc. to be considered when assessing impact ranges. The ER95percent for SELcum are provided in Table 10 and are smaller than the acoustic ranges calculated using propagation modeling alone Table 7 and 8. Please see the Estimated Take section below and Appendix P1 of the SFWF COP for further detail on the acoustic modeling methodology. The ER95percent ranges assuming 10 dB
attenuation for a difficult-to-drive pile were used to determine the Level A
harassment zones for impact pile driving.

TABLE 10EXPOSURE-BASED RANGES ER95% TO LEVEL A SOUND EXPOSURE LEVEL SELcum HARASSMENT ACOUSTIC THRESHOLDS DUE TO IMPACT PILE DRIVING OF A STANDARD PILE S; 4,500 STRIKES AND A DIFFICULT TO
DRIVE PILE D; 8,000 STRIKES
ER95% to SELcum thresholds m 0 dB
attenuation
Species
S

6 dB
attenuation
D

S

10 dB
attenuation
D

12 dB
attenuation
15 dB
attenuation
S

D

S

D

S

D

1,451
1,488
1,346
3,034
1,481
1,451

1,769
1,571
1,756
3,642
1,621
1,769

959
887
1,023
2,450
918
959

1,381
964
1,518
2,693
1,070
1,381

552
524
396
1,593
427
552

621
628
591
1,813
725
621

0
0 0
0 0
0 0

0
0 0
0 0
0 0

0
0 0
0 0
0 0

0
0 0
0 0
0 0

0
0 0
0 0
0 0

0
0 0
0 0
0 0

79

365

26

39

21

26

46
22

117
85

0
22

21
0

0
21

21
0

Low-Frequency Cetaceans Fin whale
Minke whale
Sei whale
Humpback whale
North Atlantic right whale
Blue whale 1

5,386
5,196
5,287
9,333
4,931
5,386

6,741
6,033
6,488
11,287
5,857
6,741

2,655
2,845
2,648
5,195
2,514
2,655

2,982
2,882
3,144
5,947
3,295
2,982

Mid-Frequency Cetaceans Sperm whale
Atlantic spotted dolphin
Atlantic white-sided dolphin
Common dolphin
Rissos dolphin
Bottlenose dolphin
Long-finned pilot whale

0
0 20
0 24
13
0

0
0 6
0 13
13
0

0
0 20
0 24
0 0

0
0 6
0 0
0 0

High-Frequency Cetaceans Harbor porpoise

2,845

3,934

683

996

Pinnipeds in Water Gray seal
Harbor seal

1,559
1,421

1,986
2,284

276
362

552
513

dB re 1 Pa2 s = decibel referenced to 1 micropascal squared second.
Approximation.
1 There were no Level A SEL
cum exposures as a result of animal movement modeling for the blue whale which resulted in a 0 exposure range; however, an expected exposure range for mitigation purposes must be applied to each species. Therefore, the fin whale exposure range was used as a proxy for the blue whale given similarity of species and activity.

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Cofferdam Installation and Removal For vibratory pile driving nonimpulsive sounds, sound source characteristics were generated by JASCO
using GRLWEAP 2010 wave equation model Pile Dynamics, Inc., 2010.
Installation and removal of the cofferdam were modeled from a single location. The radiated sound waves were modeled as discrete point sources over the full length of the pile in the water and sediment 9.1 m 30 ft water depth, 9.1 m 30 ft penetration with a
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vertical separation of 0.1 m 0.32 ft.
Removal of the cofferdam using a vibratory extractor is expected to be acoustically comparable to installation activities. No noise mitigation system will be used during vibratory piling.
Summaries of the maximum ranges to Level A harassment thresholds and Level B harassment thresholds resulting from propagation modeling of vibratory pile driving are provided in Table 11.
Peak thresholds were not reached for any marine mammal hearing group.

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The large Level B harassment isopleths resulting from vibratory piling installation and removal are a reflection of the threshold set for behavioral disturbance from a continuous noise i.e., 120 dBrms. Level B harassment thresholds are highly contextual for species and the isopleth distance does not represent a definitive impact zone or a suggested mitigation zone; rather, the information serves as the basis for assessing potential impacts within the context of the project and potentially exposed species.

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