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Federal Register / Vol. 86, No. 108 / Tuesday, June 8, 2021 / Notices
maximum ensonified area for blasting is smaller 0.335 km2 because, prior to the removal of bedrock, a portion of the west closure wall will be installed, providing an additional boundary between noise produced within the super flood basin and the surrounding environment.
Level A Harassment Zones When the original NMFS Technical Guidance 2016 was published, in recognition of the fact that the 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 predict a simple isopleth that can be used in conjunction with marine mammal density or occurrence to help predict takes. NMFS notes that because of some of the assumptions included in the methods used for these tools, NMFS
anticipates that isopleths produced are typically going to be overestimates of some degree, which may result in some degree of overestimate 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 in-water vibratory and impact pile driving, NMFS User Spreadsheet predicts the closest distance at which, if a marine mammal remained at that distance the entire duration of the activity, it would not
incur PTS. Inputs used in the User Spreadsheet i.e., pile driving duration or number of strikes per pile, and the number of piles installed or removed per day used to calculate distances to the Level A harassment isopleths for pile driving and drilling are shown in Table 8.
For blasting, the calculated distances to Level A harassment thresholds are based on a single blast event per day.
The Navy plans to conduct 150 blast events over 130 days, so on the majority of construction days 110 only one blast event will occur. NMFS recognizes that if two blasts do occur on a single day, the cumulative SEL for the 24-hour timeframe over which blasting occurs would be higher than that analyzed here. However, the distances to the Level A harassment thresholds in Table 9 do not reflect the attenuating influence of the double bubble curtain that will be in place across any openings between the super flood basin and the surrounding environment during blasting events. If multiple blast events occur within a 24-hour period, they will be separated by 4 to 5 hours. It is likely that if marine mammals are present in the vicinity of the construction area outside of the shutdown zone during the first blast event they will avoid the area for at least the remainder of day.
Blasting will occur at multiple locations within the super flood basin.
The minimum and maximum distances from the blasting locations to the center of the entrance to the super flood basin are 37.5 and 160 m, respectively.
Acoustic modeling is based on the location closest to the entrance to the
basin; the resulting distances to Level B
harassment and Level A harassment isopleths are, therefore, a conservative estimate of the maximum extent of potential acoustic impact outside of the basin. The distance to the Level A
harassment isopleth for blasting for harbor porpoises 1,007 m is larger than that for phocids 110 m, but the density of harbor porpoises near the construction area is very low see Marine Mammal Occurrence section.
Harbor seals and gray seals are more common, but the distance to the Level A harassment isopleth for phocids is fully encompassed by the shutdown zone.
The Level A harassment zones are calculated using the same Equation 2.
For all pile driving/drilling activities, ensonified areas are based on distances to the cumulative SEL Level A
harassment thresholds using the NMFS
acoustic guidance NMFS 2018 because they were larger than the values calculated against the SPLpeak criteria.
Following the approach used for estimating Level B harassment zones, if the calculated value is larger than the maximum potential ensonified zone, Level A harassment zones are corrected to 0.418 km2 for pile driving activity and 0.335 km2 for blasting activity.
The calculated distances to Level A
harassment and non-auditory injury to the gastrointestinal tract isopleths, estimated distances to Level B
harassment isopleths, and associated ensonified areas for the marine mammal species likely to be affected by the construction activities are provided in Tables 8 and 9.

TABLE 8DISTANCES AND AREAS OF HARASSMENT ZONES FOR PILE DRIVING AND DRILLING
Level A harassment Activity
Pile size, type, and rate
Number of strikes/pile or duration
Number of days
HF cetacean Dist.
m
Level B harassment Phocid
Area km2

Dist.
m
Dist.
m
Area km2

Area km2

Impulsive Construct west closure wall.
Entrance structure closure walls.

18-inch flat-webbed sheet pile 12 pile/
day.
28-inch Z-shaped sheet pile 12 pile/day.

300

13

516

0.258

232

0.068

341

0.126

300

4

2,056

0.418

923

0.395

2,512

0.418

I

I

I

I

I

I

I

Non-impulsive
jbell on DSKJLSW7X2PROD with NOTICES

Construct west closure wall.
Install west closure wall template.
Remove west closure wall template.
Remove temporary dolphins.
Entrance structure closure walls.

VerDate Sep<11>2014

18-inch flat-webbed sheet pile 12 pile/
day.
30-inch steel pipe pile 3 pile/day.
30-inch steel pipe pile 3 pile/day.
30-inch steel pipe pile 8 pile/day.
28-inch Z-shaped sheet pile 12 pile/day.

16:36 Jun 07, 2021

Jkt 253001

5 min/pile 60 min/day

13

13.7

0.000556

5.6

0.00098

7,356

0.418

5 min/pile 15 min/day

5

10.1

0.000319

4.1

0.000053

13,594

0.418

5 min/pile 15 min/day

5

10.1

0.000319

4.1

0.000053

13,594

0.418

5 min/pile 40 min/day

2

19.4

0.01068

8.0

0.001996

13,594

0.418

5 min/pile 60 min/day

4

25.4

0.00174675

10.4

0.000338

13,594

0.418

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