Federal Register - February 3, 2021
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Source: Federal Register
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Federal Register / Vol. 86, No. 21 / Wednesday, February 3, 2021 / Notices
decided which of the various pile removal methods it will use, we only calculate a worst-case scenario of
simultaneous operation of two of the loudest sound producing methods large pile clippers to consider the largest
possible harassment zones for simultaneous pile removal.
TABLE 5LEVEL A AND LEVEL B ISOPLETHS FOR EACH PILE DRIVING TYPE AND METHOD
Pile driving activity
Radial distance or maximum modeled length width m
Method
Pile type
Vibratory Extraction
12-inch timber/plastic
20 and 24-inch concrete
16-inch steel
20-inch concrete
12 to 24-inch concrete
12-inch timber/plastic
20 to 24-inch concrete
20 to 24-inch concrete
20 and 24-inch concrete
16-inch fiberglass
Water Jetting
Underwater Chainsaw
Small Pile Clipper
Large Pile Clipper
Two Large Pile Clippers
Impact Hammer
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 take by Level A
harassment. 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 impact/vibratory pile driving or removal using any of the methods discussed above, NMFS User Spreadsheet predicts the closest distance at which, if a marine mammal
Level A
< 10
< 10
< 10
< 10
< 10
< 10
< 10
< 10
< 10
< 10
Level B
2167 1065
6,990 1,173
7,140 1,595
1359
398
736
2154
3415
192
< 10
remained at that distance the whole duration of the activity, it would not incur PTS.
As discussed above, the Navy modelled sound propagation for impact and vibratory hammering of piles DallOsto and Dahl 2019 and used those models to calculate Level A
harassment isopleths. For all other pile removal methods we used the User Spreadsheet to determine the Level A
harassment isopleths. Inputs used in the User Spreadsheet or models are reported in Table 6 and the resulting isopleths are reported in Table 6 for each of construction methods.
TABLE 6NMFS TECHNICAL GUIDANCE USER SPREADSHEET INPUT TO CALCULATE LEVEL A ISOPLETHS FOR A
COMBINATION OF PILE DRIVING
Pile driving activity Method
Pile type
Vibratory Extraction
12-inch timber/plastic
20 and 24-inch concrete
16-inch steel
20-inch concrete
12 to 24-inch concrete
12-inch timber/plastic
20-inch concrete
20 and 24-inch concrete
16-inch fiberglass
Water Jetting
Underwater Chainsaw
Small Pile Clipper
Large Pile Clipper
Impact Hammer
The above input scenarios lead to PTS
isopleth distances Level A thresholds of less than 10 m for all methods and piles Table 5.
jbell on DSKJLSW7X2PROD with NOTICES
Radial distance or maximum modeled length width m
Marine Mammal Occurrence and Take Calculation and Estimation In this section we provide the information about the presence, density, or group dynamics of marine mammals that will inform the take calculations.
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17:21 Feb 02, 2021
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Piles per day
Here we describe how the information provided above is brought together to produce a quantitative take estimate.
No California sea lion density information is available for south San Diego Bay. Potential exposures to impact and vibratory pile driving noise for each threshold for California sea lions were estimated using data collected during a 2010 survey as reported in Sorensen and Swope 2010.
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Strikes per pile/duration to drive a single pile 10 min 10 min 10 min 20 min 10 min 10 min 10 min 600 strikes 600 strikes
During this survey two separate sea lions were observed in the project area.
The available survey data from Sorenson and Swope 2010 and other unpublished monitoring data from recent nearby projects on Naval Base San Diego suggests two California sea lions could be present each day in the project area. However given the limited data available and the more northerly location of this project relative to the
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