Je veux savoir à propos de…

30424

Federal Register / Vol. 86, No. 108 / Tuesday, June 8, 2021 / Notices
the activity. A single detonation is not likely to disrupt behavioral patterns beyond a brief startle response, therefore, the 160 dB re 1 mPa rms threshold for behavioral harassment from impulsive acoustic sources is not applicable. However, TTS, which as mentioned previously is a form of Level B harassment take, may occur. The behavioral threshold used in analyses for multiple explosive events is determined relative to 5 dB less than the TTS onset threshold DoN 2017.
The threshold associated with the onset of effect for non-auditory injury to the gastrointestinal tract 237 dB re 1 mPa peak is used to determine the distances at which there is a one percent likelihood of injury occurring, informing mitigation measures rather than take estimates DoN 2017. Take estimates are based on the 243 dB re 1
mPa peak threshold, the criterion used to predict the distances at which there is a 50 percent probability of gastrointestinal injury resulting from underwater explosions DoN 2017.
During the public comment period, the Marine Mammal Commission noted that the thresholds for slight lung injury and mortality were incorrectly specified in
the notice of the proposed IHA.
However, the distances to isopleths associated with the onset of and 50
percent probability of gastrointestinal injury were correctly modeled, resulting in very small zone sizes, and the zone sizes for slight lung injury and mortality although not presented here are expected to be commensurate with those modeled for the City of Juneaus Statter Harbor project 84 FR 11066;
March 25, 2019, given that both projects 1 analyze acoustic impacts of confined blasting in drill shafts in underwater bedrock within a harbor/
basin, 2 utilize the same sound exposure level for blasting events, and 3 estimate transmission loss by combining spherical spreading with frequency-specific absorption loss to the environment. The size of the shutdown zone for blasting, relative to these small zones, is sufficiently large to discount the potential for this type of injury. The shutdown zone for blasting equates to the Level A harassment zone for harbor porpoises, which is a 0.335 square kilometers km2 arc-shaped area that encompasses the super flood basin and extends into the Piscataqua River show in Figure 65 of the IHA application.

This shutdown zone fully encompasses the Level A harassment zone for phocids 0.01978 km2, and onset of 0.000254 km2 and 50 percent probability of 0.0008 km2
gastrointestinal injury zone, Further, the Navy will not begin blasting activities until one sheet pile face of the west closure wall is installed, thus providing an additional barrier to sound propagating into the environment beyond the super flood basin reducing the maximum ensonified zone from 0.418 km2 to 0.335 km2. In addition, the Navy will install a double bubble curtain at the entrance to the super flood basin during blasting and drilling activities within the basin, the attenuation from which although not incorporated into the acoustic analyses presented here will further reduce the impact of sound produced during these activities. The references, analysis, and methodology used in the development of the thresholds are described in NMFS
2018 Technical Guidance, which may be accessed at: http
www.nmfs.noaa.gov/pr/acoustics/
guidelines.htm.

TABLE 5EXPLOSIVE ACOUSTIC AND PRESSURE THRESHOLDS FOR MARINE MAMMALS
Level B harassment Group
High-Frequency HF
Cetaceans.
Phocid Pinnipeds PW
Underwater.

TTS

PTS

Gastro-intestinal tract onset of effect
Gastro-intestinal tract injury
135 dB SEL

140 dB SEL or 196 dB SPLpk
155 dB SEL or 202 dB SPLpk
237 dB SPLpk

243 dB SPLpk
165 dB SEL

170 dB SEL or 212 dB SPLpk
185 dB SEL or 218 dB SPLpk.

Source Levels The project includes impact pile driving, vibratory pile driving and pile removal, drilling, and blasting. Of these, only drilling and vibratory pile driving will occur concurrently. When two continuous noise sources have overlapping sound fields, there is a potential for higher sound levels and a jbell on DSKJLSW7X2PROD with NOTICES

Non-auditory
Behavioral multiple detonations
Ensonified Area The operational and environmental parameters of the activity that fed into identifying the area ensonified above the acoustic thresholds, which include source levels and transmission loss, are described below.

VerDate Sep<11>2014

Level A harassment
16:36 Jun 07, 2021

Jkt 253001

larger associated ensonified zone than for non-overlapping sources. When drilling and vibratory pile driving cooccur, the larger of the two shutdown zones will trigger mitigation measures.
Source levels of pile driving activities are based on reviews of measurements of the same or similar types and dimensions of piles available in the literature. Source levels for impact pile driving of a 30-inch steel pipe pile are used as a proxy for impact driving of 28inch Z-shaped steel sheet piles NAVFAC, 2020. Similarly, source levels for impact pile driving of an 18inch flat-webbed sheet pile were unavailable, so proxy values for
PO 00000

Frm 00024

Fmt 4703

Sfmt 4703

installation of a 24-inch Z-shaped sheet pile are used. In the notice of the proposed IHA, the proxy source levels were incorrectly specified. As a result of NMFS review of public comment, the approach to estimating the source levels for this pile type was modified by taking the mean of the maximum values for each type of sound level in Table 1.6
5 of CALTRANS 2015, resulting in the decreased source levels shown in Table 6.
The source levels in Table 6 are assumed for pile driving and drilling underwater noise produced by construction activities.

E:FRFM08JNN1.SGM

08JNN1