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Federal Register / Vol. 86, No. 122 / Tuesday, June 29, 2021 / Notices
DTH pile installation involves drilling rock sockets into the bedrock to support installation of the 6 permanent piles and 12 temporary piles. Rock sockets consist of inserting the pile in a drilled hole into the underlying bedrock after the pile has been driven through the overlying softer sediments to refusal by vibratory or impact methods. The pile is advanced farther into this drilled hole to properly secure the bottom portion of the pile into the rock. The depth of the rock socket varies, but 1015 ft is commonly required. The diameter of the rock socket is slightly larger than the pile being driven. Rock sockets are constructed using a DTH device with both rotary and percussion-type actions.
Each device consists of a drill bit that drills through the bedrock using both rotary and pulse impact mechanisms.

This breaks up the rock to allow removal of the fragments and insertion of the pile. The pile is usually advanced at the same time that drilling occurs.
Drill cuttings are expelled from the top of the pile using compressed air. It is estimated that drilling rock sockets into the bedrock will take about 13 hours hrs per pile. Tension anchors will be installed in each of the six permanent piles. Tension anchors are installed within piles that are drilled into the bedrock below the elevation of the pile tip after the pile has been driven through the sediment layer to refusal. A
6- or 8-in diameter steel pipe casing will be inserted inside the larger diameter production pile. A rock drill will be inserted into the casing, and a 6- to 8in diameter hole will be drilled into bedrock with rotary and percussion
drilling methods. The drilling work is contained within the steel pile casing and the steel pipe pile. The typical depth of the drilled hole varies, but 20
30 ft is common. Rock fragments will be removed through the top of the casing with compressed air. A steel rod will then be grouted into the drilled hole and affixed to the top of the pile. The purpose of a tension anchor is to secure the pile to the bedrock to withstand uplift forces. It is estimated that tension anchor installation will take about 12
hrs per pile.
No concurrent pile driving is anticipated for this project.
Please see Table 1 below for the specific amount of time required to install and remove piles.

TABLE 1PILE DRIVING AND REMOVAL ACTIVITIES
Number of piles
Pile diameter and type
I

Rock sockets
Tension anchors
I

Impact strikes per pile duration in minutes
Vibratory duration per pile minutes
I

DTH pile installation rock socket duration per pile minutes
DTH pile installation tension anchor duration per pile minutes
I

Total duration of activity per pile hours
Piles per day range
I

Total days
I

Pile Installation 24-in Steel Plumb Piles Permanent
24-in Steel Batter Piles Permanent
24-in Steel Piles Temporary

I

4

4

4

20 15

15

180

120

5.5

0.5 01

8

2

2

2

20 15

15

90

120

4

0.5 01

4

60

N/A

N/A

N/A

N/A
N/A

N/A
N/A

12

I

12

I

0

I

20 15

I

15

I

I

1.5

I

2 13

I

6

Pile Removal 16-in Steel Piles
24-in Steel Piles Temporary
Totals

11

I

12
29

N/A

I

N/A
18

Note: DTH = down-the-hole; N/A = not applicable.

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Proposed mitigation, monitoring, and reporting measures are described in detail later in this document please see Proposed Mitigation and Proposed Monitoring and Reporting.
Description of Marine Mammals in the Area of Specified Activities Sections 3 and 4 of the application summarize available information regarding status and trends, distribution and habitat preferences, and behavior and life history, of the potentially affected species. Additional information regarding population trends and threats may be found in NMFS Stock Assessment Reports SARs; https
www.fisheries.noaa.gov/national/
marine-mammal-protection/marinemammal-stock-assessment-reports and more general information about these species e.g., physical and behavioral descriptions may be found on NMFSs website https www.fisheries.noaa.
gov/find-species.

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Table 2 lists all species or stocks for which take is expected and proposed to be authorized for this action, and summarizes information related to the population or stock, including regulatory status under the MMPA and Endangered Species Act ESA and potential biological removal PBR, where known. For taxonomy, we follow Committee on Taxonomy 2020. PBR is defined by the MMPA as the maximum number of animals, not including natural mortalities, that may be removed from a marine mammal stock while allowing that stock to reach or maintain its optimum sustainable population as described in NMFS SARs. While no mortality is anticipated or authorized here, PBR and annual serious injury and mortality from anthropogenic sources are included here as gross indicators of the status of the species and other threats.
Marine mammal abundance estimates presented in this document represent
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the total number of individuals that make up a given stock or the total number estimated within a particular study or survey area. NMFS stock abundance estimates for most species represent the total estimate of individuals within the geographic area, if known, that comprises that stock. For some species, this geographic area may extend beyond U.S. waters. All managed stocks in this region are assessed in NMFS U.S. Pacific and Alaska SARs Carretta et al., 2020; Muto et al., 2020.
All MMPA stock information presented in Table 2 is the most recent available at the time of publication and is available in the 2019 SARs Caretta et al., 2020; Muto et al., 2020 and draft 2020 SARs available online at:
www.fisheries.noaa.gov/national/
marine-mammal-protection/draftmarine-mammal-stock-assessmentreports.

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