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Federal Register / Vol. 86, No. 167 / Wednesday, September 1, 2021 / Notices
Compendium NAVFAC SW, 2020. The only exception to this is the sound source data for the vibratory hammer, which was sourced from the City of Seattle Pier 62 project Greenbusch Group, 2018. The source levels for the pile clippers, single and simultaneous use, and underwater chainsaw for this project utilized the mean maximum RMS SPL rather than the median sound levels we typically use as this will provide a more conservative measure.
The diamond wire saw utilized the noise profile measurements associated with the removal of 66-inch and 84-inch caissons in the Navy Compendium NAVFAC SW, 2020. The Navy has noted, and we agree, that these values are likely much lower in reality as this project would remove 16-inch concrete piles instead of the much larger variants modeled in the Compendium. However, no recorded data currently exists for the wire saws cutting concrete; therefore,
we used the mean of the source level data from the Navy Compendium. The vibratory hammer used the highest average weighted RMS sound level per the Seattle Pier 62 project acoustic monitoring report Greenbusch Group, 2018.
During pile driving/removal activities, there may be times when two pile extraction methods i.e., pile clippers are used simultaneously. The likelihood of such an occurrence is anticipated to be infrequent, will depend on the specific methods chosen by the contractor, and will be for short durations on that day. In-water pile removal occurs intermittently, and it is common for removal to start and stop multiple times as each pile is adjusted and its progress is measured. Moreover, the Navy has multiple options for pile removal depending on the pile type and condition, sediment, and how stuck the pile is, etc. When two continuous noise
sources, such as pile clippers, have overlapping sound fields, there is potential for higher sound levels than for non-overlapping sources. When two or more pile removal methods pile clippers are used simultaneously, and the sound field of one source encompasses the sound field of another source, the sources are considered additive and combined using the following rules see Table 3. For addition of two simultaneous methods, the difference between the two sound source levels SSLs is calculated, and if that difference is between 0 and 1 dB, 3 dB are added to the higher SSL; if difference is between 2 or 3 dB, 2 dB are added to the highest SSL; if the difference is between 4 to 9 dB, 1 dB is added to the highest SSL; and with differences of 10 or more dB, there is no addition NMFS, 2018b; WSDOT, 2018.

TABLE 3RULES FOR COMBINING SOUND LEVELS GENERATED DURING PILE REMOVAL
Difference in SSL

Level A harassment isopleths
0 or 1 dB
2 or 3 dB
4 to 9 dB
10 dB or more

Add Add Add Add
3 2
1 0

dB
dB
dB
dB

to to to to
the the the the
higher higher higher higher
source source source source
level level level level

Level B harassment isopleths Add Add Add Add
3 2
1 0

dB
dB
dB
dB

to to to to
the the the the
higher higher higher higher
source source source source
level.
level.
level.
level.

Source: Modified from USDOT, 1995; WSDOT, 2018; and NMFS, 2018b.
Note: dB = decibel; SSL = sound source Level.

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Level A Harassment Zones When the NMFS Technical Guidance 2016 was published, in recognition of the fact that ensonified area/volume could be more technically challenging to predict because of the duration component in the new thresholds, we 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. We note that because of some of the assumptions included in the methods used for these tools, we anticipate 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
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where appropriate. For stationary sources, such as the localized pile removal activities discussed above, the NMFS User Spreadsheet predicts the distance at which, if a marine mammal remained at that distance the whole duration of the activity, it will incur PTS.
The Navy provided estimates to NMFS for the duration of sound exposure for each pile removal activity.
The durations used in this project for each pile removal method were noted as conservative estimates that are greater than durations observed in the San Diego Noise Compendium by the Navy.
In discussions with NMFS, the Navy has explained that the average durations found in the IHA application and Compendium were based around data collected in the from the old Fuel Pier demolition projects NAVFAC SW 2014, 2015a, 2016, 2017a, 2017b, 2018a, and 2018b. These values were adjusted to account for either the maximum amount of time the activity could occur i.e., pile
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clippers, a duration that is greater than the maximum i.e., underwater chainsaw and vibratory hammer, or an adjusted duration based on the removal of a smaller pile i.e., diamond wire saw in order to provide somewhat more conservative measurements using realworld data. These values were likely considered more realistic for past projects and could safely be assumed as conservative for this project as the Navy will be cutting smaller sized piles. The Navy also performed an ultraconservative hypothetical review by modeling a 1-hour duration for each pile being removed. Using a rate of five piles removed per day, the resulting Level A
harassment isopleths were still smaller than the 20 m shutdown zone the Navy plans to implement. Further information on durations can be found in the Compendium NAVFAC SW, 2020.
All inputs used in the User Spreadsheet are reported below in Table 4.

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