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Federal Register / Vol. 86, No. 108 / Tuesday, June 8, 2021 / Notices TABLE 6SUMMARY OF IN-WATER PILE DRIVING SOURCE LEVELS
at 10 m from source Pile diameter inch
Pile type
Installation/extraction method
Z-shaped steel sheet 1 3

Vibratory 2
Impact 3
Vibratory
Impact
Vibratory
Drilling

Flat-webbed steel sheet 1 4
Steel pipe 2
Blast holes 5

SPLpk, dB
re 1 Pa
28
28
18
18
30
4.5

NA
211
NA
201
NA
NA

SPLrms, dB
re 1 Pa 167
196
163
183
167
166.2

SEL, dB
re 1 Pa2-s 167
181
163
172
167
166.2

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Key: dB = decibels; NA = Not applicable; dB re 1 Pa = dB referenced to a pressure of 1 micropascal, measures underwater SPL. dB re 1
Pa2-s = dB referenced to a pressure of 1 micropascal squared per second, measures underwater SEL.
1 = A proxy value for 28-inch sheet piles could not be found for impact and vibratory driving so the proxy for a 30-inch steel pipe pile has been used NAVFAC SW 2020. A proxy value for 18-inch flat-webbed sheet piles could not be found for impact and vibratory driving so the proxy for a 24-inch Z-shaped sheet pile has been used CALTRANS 2015.
Sources: DoN 2015 2; NAVFAC SW 2020 3 CALTRANS 2015 4; Denes et al., 2016.5

The proxy source level for drilling of blast-charge holes is derived from Denes et al. 2016, which reports sound pressure levels measured during rock socket drilling at Kodiak Ferry Terminal in Alaska. The size of the blast-charge holes considered here 4.5-inch is much smaller than the size of the drilled holes 24-inch in Denes et al. 2016, making the use of 166.2 dB re 1mPa conservative.
There are no data on sound source levels from explosives used under circumstances identical to the blasting activity described here e.g., charge composition and weight, bathymetry, substrate composition, and the dimensions of holes for stemmed charge placement. Therefore, the Navy made approximations by reference to mathematical models that have been empirically validated, under roughly comparable circumstances, to estimate source levels both in terms of absolute peak sound pressure level SPL in units of dB re 1mPa and sound exposure level SEL in units of dB re 1mPa2-s Table 7.
The peak source level calculation of a confined blast follows Coles 1948
equation and a regression curve from the Miami Harbor Deepening Project Hempen et al. 2007, using a distance of 2.4 m and a weight of 120 pounds lbs for a single charge. Based on this approach, the peak source level for the project is estimated to be 257 dB re 1
mPa for a 120 lb charge. Following Urick 1983, the Navy estimated the SEL for 30, 120 lb charges at 1 m by first calculating the instantaneous pressure following the onset of a shock wave, as a relationship between peak pressure and time. Blasting operations will involve detonating 120 lb up to 30 times in rapid succession, with a split second delay between each detonation. Without specific information regarding the layout of the charges, the modeling assumes a grid of 2.4 m by 2.4 m charges for the majority of the super flood basin,
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and 1.5 m by 1.8 m for the rows closest to Berth 11. Due to time and spatial separation of each single charge by a distance of 2.4 m, the accumulation of acoustic energy is added sequentially, assuming the transmission loss follows cylindrical spreading within the matrix of charges. Using this approach for multiple confined charges, the modeled source SEL for 30, 120 lb charges at 1
m is estimated to be 227 dB re 1mPa2s. Please see the Navys IHA application for more details regarding these calculations.

TABLE 7BLASTING SOURCE LEVELS
Explosive charge
SPLpk, dB re 1
Pa
SEL
dB re 1
Pa2-s
30 x 120 lb charge
257

227

These source levels for pile driving, drilling, and blasting are used to estimate the Level B harassment zones and calculate the Level A harassment zones.
Level B Harassment Zones Transmission loss TL is the decrease in acoustic intensity as an acoustic pressure wave propagates out from a source. TL parameters vary with frequency, temperature, sea conditions, current, source and receiver depth, water depth, water chemistry, and bottom composition and topography.
The general formula for underwater TL
is:
1 TL = B log10R1/R2
Where, R1 = the distance of the modeled SPL from the driven pile, and R2 = the distance from the driven pile of the initial measurement.

The degree to which underwater sound propagates away from a sound source is dependent on a variety of factors, most notably the water
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bathymetry and presence or absence of reflective or absorptive conditions including in-water structures and sediments. Spherical spreading occurs in a perfectly unobstructed free-field environment not limited by depth or water surface, resulting in a 6 dB
reduction in sound level for each doubling of distance from the source 20logrange. Cylindrical spreading occurs in an environment in which sound propagation is bounded by the water surface and sea bottom, resulting in a reduction of 3 dB in sound level for each doubling of distance from the source 10logrange. A practical spreading value of 15 is often used under conditions, such as at the Shipyard dock, where water increases with depth as the receiver moves away from the shoreline, resulting in an expected propagation environment that would lie between spherical and cylindrical spreading loss conditions.
The Level B harassment distances for construction activities are calculated using practical spreading impact and vibratory pile driving, drilling and spherical spreading with absorption blasting, which includes an additional term in the equation that accounts for frequency-specific transmission loss to the environment due to absorption, using the source levels provided in Tables 6 and 7, respectively.
Ensonified areas A are calculated using the following equation.
2 A = pR2
Where, R is the harassment distance.

However, the maximum distance from the source is capped due to landmass interception in the surrounding area.
For this reason, the maximum area that could be ensonified by noise from pile driving and drilling is an estimated 0.418 km2. Therefore, all harassment zones that are larger than 0.418 km2 are corrected to this maximum value. The
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