Je veux savoir à propos de…

7996

Federal Register / Vol. 86, No. 21 / Wednesday, February 3, 2021 / Notices
Acoustic Thresholds NMFS recommends the use of acoustic thresholds that identify the received level of underwater sound above which exposed marine mammals would be reasonably expected to be behaviorally harassed equated to Level B harassment or to incur Permanent Threshold Shift PTS of some degree equated to Level A harassment.
Level B Harassment for non-explosive sourcesThough significantly driven by received level, the onset of behavioral disturbance from anthropogenic noise exposure is also informed to varying degrees by other factors related to the source e.g., frequency, predictability, duty cycle, the environment e.g., bathymetry, and the receiving animals hearing, motivation, experience, demography, behavioral context and can be difficult to predict Southall et al., 2007, Ellison et al., 2012. Based on what the available science indicates and the practical need to use a threshold based on a factor that is both predictable and measurable for most activities, NMFS uses a generalized acoustic
threshold based on received level to estimate the onset of behavioral harassment. NMFS predicts that marine mammals are likely to be behaviorally harassed in a manner we consider Level B harassment when exposed to underwater anthropogenic noise above received levels of 120 decibel dB re 1
microPascal mPa root mean square rms for continuous e.g., vibratory pile-driving and above 160 dB re 1 mPa rms for non-explosive impulsive e.g., impact pile driving or intermittent e.g., scientific sonar sources.
The Navys proposed activity includes the use of continuous vibratory piledriving, water jetting, chainsaw and pile clippers and impulsive impact piledriving sources, and therefore the 120
and 160 dB re 1 mPa rms thresholds are applicable. However, as discussed above, the Navy has established that the ambient noise in the project area is 126
dB re 1 mPa rms. Since this is louder than the 120 dB threshold for continuous sources, 126 dB becomes the effective threshold for Level B
harassment for continuous sources.

Level A harassment for non-explosive sourcesNMFS Technical Guidance for Assessing the Effects of Anthropogenic Sound on Marine Mammal Hearing Version 2.0
Technical Guidance, 2018 identifies dual criteria to assess auditory injury Level A harassment to five different marine mammal groups based on hearing sensitivity as a result of exposure to noise from two different types of sources impulsive or nonimpulsive. The Navys activity includes the use of impulsive impact piledriving and non-impulsive vibratory pile driving/removal and other removal methods sources.
These thresholds are provided in Table 2. The references, analysis, and methodology used in the development of the thresholds are described in NMFS
2018 Technical Guidance, which may be accessed at https
www.fisheries.noaa.gov/national/
marine-mammal-protection/marinemammal-acoustic-technical-guidance.

TABLE 2THRESHOLDS IDENTIFYING THE ONSET OF PERMANENT THRESHOLD SHIFT
PTS onset acoustic thresholds
received level
Hearing group
Impulsive Low-Frequency LF Cetaceans
Mid-Frequency MF Cetaceans
High-Frequency HF Cetaceans
Phocid Pinnipeds PW Underwater Otariid Pinnipeds OW Underwater
Cell Cell Cell Cell Cell
1 3
5 7
9

Lpk,flat:
Lpk,flat:
Lpk,flat:
Lpk,flat:
Lpk,flat:

219
230
202
218
232

dB
dB
dB
dB
dB

Non-impulsive
LE,LF,24h: 183 dB
LE,MF,24h: 185 dB
LE,HF,24h: 155 dB
LE,PW,24h: 185 dB
LE,OW,24h: 203 dB

Cell Cell Cell Cell Cell
2 LE,LF,24h: 199 dB.
4 LE,MF,24h: 198 dB.
6 LE,HF,24h: 173 dB.
8 LE,PW,24h: 201 dB.
10 LE,OW,24h: 219 dB.

jbell on DSKJLSW7X2PROD with NOTICES

Dual metric acoustic thresholds for impulsive sounds: Use whichever results in the largest isopleth for calculating PTS onset. If a non-impulsive sound has the potential of exceeding the peak sound pressure level thresholds associated with impulsive sounds, these thresholds should also be considered.
Note: Peak sound pressure Lpk has a reference value of 1 Pa, and cumulative sound exposure level LE has a reference value of 1Pa2s.
In this Table, thresholds are abbreviated to reflect American National Standards Institute standards ANSI 2013. However, peak sound pressure is defined by ANSI as incorporating frequency weighting, which is not the intent for this Technical Guidance. Hence, the subscript flat is being included to indicate peak sound pressure should be flat weighted or unweighted within the generalized hearing range. The subscript associated with cumulative sound exposure level thresholds indicates the designated marine mammal auditory weighting function LF, MF, and HF
cetaceans, and PW and OW pinnipeds and that the recommended accumulation period is 24 hours. The cumulative sound exposure level thresholds could be exceeded in a multitude of ways i.e., varying exposure levels and durations, duty cycle. When possible, it is valuable for action proponents to indicate the conditions under which these acoustic thresholds will be exceeded.

Ensonified Area Here, we describe operational and environmental parameters of the activity that will feed into identifying the area ensonified above the acoustic thresholds, which include source levels and transmission loss coefficient.
The sound field in the project area is the existing background noise plus additional construction noise from the proposed project. Marine mammals are expected to be affected via sound generated by the primary components of the project i.e., impact pile driving, vibratory pile removal, water jetting, pile clippers and underwater chainsaws.

VerDate Sep<11>2014

17:21 Feb 02, 2021

Jkt 253001

Vibratory hammers produce constant sound when operating, and produce vibrations that liquefy the sediment surrounding the pile, allowing it to penetrate to the required seating depth or be withdrawn more easily. An impact hammer is a steel device that works like a piston, producing a series of independent strikes to drive the pile.
Impact hammering typically generates the loudest noise associated with pile installation. The actual durations of each installation method vary depending on the type and size of the pile.
In order to calculate distances to the Level A harassment and Level B

PO 00000

Frm 00008

Fmt 4703

Sfmt 4703

harassment sound thresholds for piles of various sizes being used in this project, NMFS used acoustic monitoring data from other locations to develop source levels for the various pile types, sizes and methods see Table 3. Data for the removal methods including water jetting, pile clippers and underwater chainsaws come from data gathered at other nearby Navy projects in San Diego Bay NAVFAC SW, 2020, the source levels used are from the averages of the maximum source levels measured, a somewhat more conservative measure than the median sound levels we typically use.

E:FRFM03FEN1.SGM

03FEN1