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Federal Register / Vol. 86, No. 23 / Friday, February 5, 2021 / Notices 12 dB, and 15 dB were modeled to gauge the effects on the ranges to thresholds given these levels of attenuation. Although five attenuation levels and associated ranges are provided, South Fork Wind anticipates that the use of a noise mitigation system will produce field measurements of the isopleth distances to the Level A
harassment and Level B harassment thresholds that accord with those modeled assuming 10 dB of attenuation see Estimated Take, Proposed Mitigation, and Proposed Monitoring and Reporting sections.
The updated acoustic thresholds for impulsive sounds such as impact pile driving contained in the Technical Guidance NMFS, 2018 were presented as dual metric acoustic thresholds using
both SELcum and peak sound pressure level metrics Table 5. As dual metrics, NMFS considers onset of PTS Level A
harassment to have occurred when either one of the two metrics is exceeded i.e., metric resulting in the largest isopleth. The SELcum metric considers both level and duration of exposure, as well as auditory weighting functions by marine mammal hearing group.
Tables 7 and 8 shows the modeled acoustic ranges to the Level A
harassment thresholds, with 0, 6, 10, 12
and 15 dB sound attenuation incorporated. For the peak level, the greatest distances expected within a given hearing group are shown, typically occurring at the highest hammer energies Table 7. The SELcum
Level A harassment threshold is the only metric that is affected by the number of strikes within a 24 hr period;
therefore, it is only this acoustic threshold that is associated with differences in range estimates between the standard scenario and the difficultto drive pile scenario Table 8. The maximum distances for the other two metrics peak sound pressure level SPLpk and SPLrms are equal for both scenarios because these metrics are used to define characteristics of a single impulse and do not vary based on the number of strikes Denes et al., 2020a.
The radial distances shown in Tables 7
and 8 are the mean distances from the piles, averaged between the two modeled locations and between summer and winter sound velocity profiles.

TABLE 7MEAN ACOUSTIC RANGE R95% TO LEVEL A PEAK SOUND PRESSURE LEVEL SPLpk ACOUSTIC HARASSMENT
THRESHOLDS FOR MARINE MAMMALS DUE TO IMPACT PILE DRIVING
Mean distance m to threshold Threshold SPLpk dB re 1 Pa
Marine mammal hearing group
Low-frequency cetaceans
Mid-frequency cetaceans
High-frequency cetaceans
Phocid pinnipeds

0 dB
attenuation
219
230
202
218

6 dB
attenuation
87
8 1,545
101

10 dB
attenuation
22
2 541
26

12 dB
attenuation
9 1
243
12

15 dB
attenuation
7 1
183
8

2
1 108
2

dB re 1 Pa = decibel referenced to 1 micropascal.

TABLE 8MEAN ACOUSTIC RANGE R95% TO LEVEL A SOUND EXPOSURE LEVEL SELcum ACOUSTIC HARASSMENT
THRESHOLDS FOR MARINE MAMMALS DUE TO IMPACT PILE DRIVING OF A STANDARD PILE S; 4,500 STRIKES AND A
DIFFICULT TO DRIVE PILE D; 8,000 STRIKES
Threshold SELcum dB re 1
Pa2s
Marine mammal hearing group
Low-frequency cetaceans
Mid-frequency cetaceans
High-frequency cetaceans
Phocid pinnipeds

183
185
155
185

Mean distance m to threshold 0 dB attenuation S
16,416
107
9,290
3,224

6 dB attenuation
D

S

21,941
183
13,374
4,523

10 dB attenuation
D

8,888
43
4,012
1,375

11,702
59
6,064
2,084

12 dB attenuation
15 dB attenuation
S

D

S

D

S

D

6,085
27
2,174
673

7,846
32
3,314
1,080

5,015
27
2,006
437

6,520
26
2,315
769

3,676
26
814
230

4,870
26
1,388
415

dB re 1 Pa2 s = decibel referenced to 1 micropascal squared second;
Approximation.

Table 9 shows the acoustic ranges to the Level B harassment threshold with no attenuation, 6, 10, 12, and 15 dB
sound attenuation incorporated.
Acoustic propagation was modeled at two representative sites in the SFWF as
described above. The radial distances shown in Table 8 are the mean distance to the Level B harassment threshold from the piles, derived by averaging the R95percent to the Level B harassment thresholds for summer and winter see
Appendix P2 of the SFWF COP for more details. The range estimated assuming 10 dB attenuation 4,684 m was used to determine the extent of the Level B
harassment zone for impact pile driving.

TABLE 9MEAN ACOUSTIC RANGE R95% TO LEVEL B HARASSMENT ACOUSTIC THRESHOLD SPLrms DUE TO IMPACT
PILE DRIVING

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Mean distance m to threshold Threshold SPLrms dB re 1 Pa
0 dB
attenuation
160

6 dB
attenuation
11,382

10 dB
attenuation
6,884

4,684

dB re 1 Pa = decibel referenced to 1 micropascal.

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12 dB
attenuation 4,164

15 dB
attenuation 3,272