SECTION 4.0

ENVIRONMENTAL SETTING, IMPACTS, AND MITIGATION

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PROPOSED PROJECT

4.11  Noise and vibration

This section describes the existing noise environment for the proposed Project. Potential noise impacts associated with the Project are assessed and noise-sensitive receptors are identified, as well as the laws, ordinances, regulations, and standards that regulate noise levels at those receptors. The following discussion describes the fundamentals of acoustics, the results of a detailed site reconnaissance, sound level measurements, and acoustical calculations.

4.11.1  Environmental Setting

4.11.1.1  Fundamentals of Acoustics

Noise is generally defined as loud, unpleasant, unexpected, or undesired sound that disrupts or interferes with normal human activities. Although exposure to high noise levels over an extended period has been demonstrated to cause hearing loss, the principal human response to environmental noise is annoyance. The response of individuals to similar noise events is diverse and influenced by the type of noise, the perceived importance of the noise, and its appropriateness in the setting, the time of day, the type of activity during which the noise occurs, and the sensitivity of the individual.

Sound is a physical phenomenon consisting of minute vibrations which travel through a medium, such as air, and are sensed by the human ear. Sound is generally characterized by a number of variables including frequency and intensity. Frequency describes the sound's pitch and is measured in Hertz (Hz), while intensity (or sound level) describes the sound's loudness and is measured in decibels (dB). Decibels are measured using a logarithmic scale. A sound level of 0 dB is approximately the threshold of human hearing and is barely audible under extremely quiet listening conditions. Normal speech has a sound level of approximately 60 dB. Sound levels above about 120 dB begin to be felt inside the human ear as discomfort and eventually pain at still higher levels. The minimum change in the sound level of individual events that an average human ear can detect is about 3 dB. An increase (or decrease) in sound level of about 10 dB is usually perceived by the average person as a doubling (or halving) of the sound's loudness, and this relationship holds true for loud sounds and for quieter sounds.

Sound level is usually expressed referenced to a known standard. This report refers to three acoustical quantities: 1) sound pressure level in air, 2) sound pressure level in water, 3) and sound power level. Although the units of each quantity are decibels, these terms are different and should not be confused. In expressing sound pressure on a logarithmic scale, the sound pressure is compared to a reference pressure value (discussed further below). In expressing sound power level, the standard reference sound power is 1 pico Watt. Sound pressure level depends not only on the power of the source, but also on the distance from the source and on the acoustical characteristics of the space surrounding the source; while sound power level is a measure of the acoustic power radiated by the source.

Because of the logarithmic nature of the decibel unit, sound levels cannot be added or subtracted directly and are somewhat cumbersome to handle mathematically. However, some simple rules are useful in dealing with sound levels. First, if a sound's intensity is doubled, the sound level increases by 3 dB, regardless of the initial sound level. Thus, for example: 60 dB + 60 dB = 63 dB, and 80 dB + 80 dB = 83 dB. Sound intensity in air uses a standard of 20 micropascals (µPa), while sound intensity measured in water uses a standard level of 1 µPa. The distinction between in-air and in-water reference levels is important since sound intensity in water would appear extremely high compared to values in air. In other words, 120 dB in the air is not the same as 120 dB in the water. There is a difference of 26 dB when converting air to water sound pressure levels. For example, if a jet engine has a sound pressure level of 140 dB in air, the equivalent underwater sound pressure level would be 166 dB; or a supertanker that emits 164 dB in air would sound more like 190 dB in water.

Hz is a measure of how many times each second the crest of a sound pressure wave passes a fixed point. For example, when a drummer beats a drum, the skin of the drum vibrates a number of times per second. A particular tone which makes the drum vibrate 100 times per second generates a sound pressure wave that is oscillating at 100 Hz; this pressure oscillation is perceived as a tonal pitch of 100 Hz. Sound frequencies between 20 Hz and 20,000 Hz are within the range of sensitivity of the best human ear.

Sound from a tuning fork (a pure tone) contains a single frequency. In contrast, most sounds one hears in the environment do not consist of a single frequency, but rather a broad band of frequencies differing in sound level. The method commonly used to quantify environmental sounds consists of evaluating all of the frequencies of a sound according to a weighting system that reflects that human hearing is less sensitive at low frequencies and extremely high frequencies than at the mid-range frequencies. This is called "A" weighting, and the decibel level measured is called the A-weighted sound level (dBA). In practice, the level of a noise source is conveniently measured using a sound level meter that includes a filter corresponding to the dBA curve. Underwater noise measurements typically do not have frequency weighting applied. In addition, underwater noise levels are reported only for limited frequency bands, while airborne noise is reported as an integrated value over a very wide range of frequencies.

Although the A-weighted sound level may adequately indicate the level of environmental noise at any instant in time, community noise levels vary continuously. Most environmental noise includes a conglomeration of noise from distant sources that creates a relatively steady background noise in which no particular source is identifiable. A single descriptor called the equivalent sound level (L_eq) is used. L_eq is the mean A-weighted sound level during a measured time interval. It is the "equivalent" constant sound level that would have to be produced by a given source to equal the fluctuating level measured. In addition, it is often desirable to know the acoustic range of the noise source being measured. This is accomplished through the L_max and L_min indicators. They represent the Root mean-square (RMS) maximum and minimum obtainable noise levels during the monitoring interval. The L_min value obtained for a particular monitoring location is often called the acoustic floor for that location.

To describe time-varying character of environmental noise, the statistical noise descriptors L₅, L₁₀, L₅₀, and L₉₀ are commonly used. They are the noise levels equaled or exceeded during 5 percent, 10 percent, 50 percent, and 90 percent of a stated time. Sound levels associated with the L₁₀ typically describe transient or short-term events, while levels associated with the L₉₀ describe the steady-state (or most prevalent) noise conditions.

Another sound measure known as the Day-Night Average Noise Level (L_dn) is defined as the A-weighted average sound level for a 24-hour day. It is calculated by adding a 10 dBA penalty to sound levels in the night (10:00 p.m. to 7:00 a.m.) to compensate for the increased sensitivity to noise during the quieter evening and nighttime hours. The L_dn is used by agencies such as the U.S. Environmental Protection Agency (EPA), the U.S. Department of Housing and Urban Development (HUD), and the Federal Aviation, Railroad, and Transit Administrations (FAA, FRA, FTA) to define acceptable land use compatibility with respect to noise. The L_dn is recommended by the State of California to be used by local agencies to define acceptable land use compatibility with respect to noise. Due to the time-of-day penalty associated with the L_dn descriptor, the L_eq for a continuously operating sound source during a 24-hour period will be numerically less. Thus, for a noise source operating continuously for periods of 24 hours, the L_dn level produced will be 6 dBA higher than the L_eq value. Sound levels of typical noise sources and environments are listed in Table 4.11-1 to provide a frame of reference.

4.11.1.2  Fundamentals of Vibration

Vibration consists of waves transmitted through solid material (Beranek and Ver, 1992). Unlike in air, there are several types of wave motion in solids including compressional, shear, torsional, and bending. The solid medium can be excited by forces, moments or pressure fields. This leads to the terminology "air-borne" (pressure fields) or "structureborne/
groundborne" (forces and moments) vibration.

Ground-borne vibration propagates from the source through the ground to adjacent buildings by surface waves. Vibration may be comprised of a single pulse, a series of pulses, or a continuous oscillatory motion. The frequency of a vibrating object describes how rapidly it is

TABLE 4.11-1
SOUND LEVELS OF TYPICAL NOISE SOURCES AND NOISE ENVIRONMENTS
(A-WEIGHTED SOUND LEVELS)

oscillating, measured in Hz. Most environmental vibrations consist of a composite, or "spectrum" of many frequencies, and are generally classified as broadband or random vibrations. The normal frequency range of most ground-borne vibration which can be felt generally starts from a low frequency of less than 1 Hz to a high of about 200 Hz.

Vibration energy spreads out as it travels through the ground, causing the vibration amplitude to decrease with distance away from the source. High frequency vibrations reduce much more rapidly than low frequencies, so that in the far-field from a source the low frequencies tend to dominate. Soil properties also affect the propagation of vibration. When ground-borne vibration interacts with a building there is usually a ground-to-foundation coupling loss but the vibration can also be amplified by the structural resonances of the walls and floors. Vibration in buildings is typically perceived as rattling of windows or items on shelves or the motion of building surfaces. The vibration of building surfaces can also be radiated as sound and heard as a low-frequency rumbling noise, known as ground-borne noise.

Perceptible ground-borne vibration is generally limited to areas within a few hundred feet of railway systems, certain types of industrial operations, and construction activities, especially pile driving. Road vehicles rarely create enough ground-borne vibration to be perceptible to humans unless the road surface is poorly maintained and there are potholes or bumps. If traffic, typically heavy trucks, does induce perceptible vibration in buildings such as window rattling or shaking of small loose items, then it is most likely an effect of low-frequency air-borne noise or ground characteristics.

Building structural components can also be excited by high levels of low-frequency noise (typically less than 100 Hz). The many structural components of a building, excited by low-frequency noise, can be coupled together to create complex vibrating systems. The low frequency vibration of the structural components can cause smaller items such as ornaments, pictures, and shelves to rattle which can cause annoyance to building occupants. Human sensitivity to vibration varies by frequency and by person, but generally people are more sensitive to low-frequency vibration. Human annoyance is also related to the number and duration of events. The more events or the greater the duration, the more annoying it will be to humans.

Construction activities can also produce varying degrees of ground vibration, depending on the equipment and methods employed. Ground vibrations from construction activities very rarely reach levels high enough to cause damage to structures, although special consideration must be made in cases where fragile historical buildings are near the construction site. The construction activities that typically generate the highest levels of vibration are blasting and impact pile driving.

Vibration from construction can be evaluated for potential impacts at sensitive receptors. Typical activities evaluated for potential building damage due to construction vibration include demolition, pile driving, and drilling or excavation in close proximity to structures. The ground-borne vibration can also be evaluated for perception to eliminate annoyance. Vibration propagates according to the following expression, based on point sources with normal propagation conditions:

where:

PPV_equip = the peak particle velocity in in/sec of the equipment adjusted for distance

PPV_ref = the reference vibration level in in/sec at 25 feet

D_ref = the reference distance (typically 25 feet)

D = the distance from the equipment to the receiver

The peak particle velocity (PPV) is defined as the maximum instantaneous positive or negative peak of the vibration and is often used in monitoring of blasting vibration because it is related to the stresses experienced by structures. Although PPV is appropriate for evaluating the potential of building damage, it is not suitable for evaluating human response. The human body responds to an average vibration amplitude. Because the net average of a vibration signal is zero, the root mean square (rms) amplitude is used to describe the "smoothed" signal. The root mean square of a signal is the average of the squared amplitude of the signal typically calculated over a 1 second period. Decibel notation acts to compress the range of numbers used to describe vibration, defined as VdB. The background vibration velocity level in residential areas is usually 50 VdB or lower, well below the threshold of perception for humans which is approximately 65 VdB. Human response to vibration is usually not significant until it exceeds 70 VdB.

4.11.1.3  Local Noise Setting

4.11.1.3.1  San Francisco HWC Converter Station. A series of sound level measurements was conducted on September 12 through 13, 2005 to quantify the existing acoustical environment at the proposed Project location in San Francisco as well as at sensitive receptors near the proposed Project. Table 4.11-2 summarizes the results of the measurements. The measurement locations are shown on Figure 4.11-1.

The sound level data were gathered using a Larson Davis Model 820 ANSI (American National Standards Institute) Type 1 Integrating Sound Level Meter (Serial Number 1323).

TABLE 4.11-2
SOUND LEVEL MEASUREMENTS OF EXISTING CONDITIONS
IN SAN FRANCISCO (dBA)

The meter was field-calibrated before and after each measurement period with a Larson Davis Model CAL150B acoustic calibrator (Serial Number 2233). The meter was mounted on a tripod 5 feet above the ground to simulate the average height of the human ear. All instruments were set to the slow time response and A-weighted decibel scale for all of the measurements in accordance with International Standards Organization (ISO) 1996a, b, and c. Details of the four measurement locations are provided below.

ST1     Thirty-minute measurements were conducted during the daytime and nighttime near the south property line of the proposed San Francisco HWC Converter Station. The actual property line was inaccessible at the time of the measurements; therefore, the measurement was taken at the eastern entrance to Warm Water Cove Park at the western termination of 24^th Street and is considered to be acoustically equivalent. The daytime measurement was taken between 12:30 p.m. and 1:00 p.m. on September 12 and the nighttime measurement was taken between 1:20 a.m. and 1:50 a.m. on September 13. The Mirant Potrero power plant was audible during both the daytime and nighttime, becoming more pronounced at night when other noise sources were reduced. Daytime noise sources included heavy-truck traffic from the Sheedy property to the south, general industrial noise, and occasional aircraft overflights. During the night, heavy-truck traffic from the Sheedy property was no longer present. Back-up beepers and intermittent vehicular traffic to the park also contributed to the ambient noise environment. The daytime one-hour L_eq was 56.0 dBA and the nighttime one-hour L_eq was 49.5 dBA.

ST2     Thirty-minute measurements were conducted during the daytime and nighttime on 23^rd Street near the north property line of the proposed San Francisco HWC Converter Station adjacent to the HMR Group Building parking lot. The daytime measurement was taken between 1:12 p.m. and 1:42 p.m. on September 12 and the nighttime measurement was taken between 12:42 a.m. and 1:12 a.m. on September 13. The Mirant Potrero power plant was audible during both the daytime and nighttime measurements, becoming more pronounced at night when other noise sources were reduced. Noise sources during the daytime included general industrial operation, background drilling or jackhammer use, highway and surface street vehicular traffic, and occasional aircraft overflights. The nighttime noise source was predominantly the Mirant Potrero power plant, with some distant vehicular traffic. The daytime one-hour L_eq was 63.8 dBA and the nighttime one-hour L_eq was 52.9 dBA.

Some land uses are considered sensitive to noise. Noise-sensitive receptors are land uses associated with indoor and outdoor activities that may be subject to stress or significant interference from noise. They often include residential dwellings, mobile homes, hotels, motels, hospitals, nursing homes, educational facilities, churches, and libraries.

Sensitive receptors in the Project area consist of multi-family residences approximately 900 feet west at 2638 Third Street and multi-family residences approximately 1,400 feet west at 1423 Indiana Street. No residences have a direct line-of-sight to the Project due to intervening three- and four-story commercial buildings in between the residences and the Project site. In addition, both residences are within 500 feet of Interstate 280 (I-280) to the east. The following summarizes the measurements that were conducted at the two receptors nearest to the proposed Project site.

ST3     Thirty-minute measurements were conducted during the daytime, evening, and nighttime at the intersection of 25^th Street and Minnesota Street. This location represents the noise environment at the multi-family residences on Minnesota Street. The residential units and measurement site are elevated approximately 30 feet above the Mirant Potrero power plant. Surrounding land uses were a mix of commercial and residential to the south and north and commercial to the east and west. The daytime measurement was taken between 1:54 p.m. and 2:24 p.m. on September 12, the evening measurement between 9:15 p.m. and 9:45 p.m. on September 12, and the nighttime measurement between 1:57 a.m. and 2:27 a.m. on September 13. The noise sources during the measurements were surface street vehicular traffic along 25^th Street, with a high number of buses traveling this route during the evening and nighttime measurements, and vehicular traffic on I-280. The visible portion of the highway from the measurement location was approximately 30 feet above the measurement height and was approximately 400 feet east of the measurement site. The daytime one-hour L_eq was 66.6 dBA, the evening one-hour L_eq was 61.7 dBA, and the nighttime one-hour L_eq was 58.9 dBA. The calculated L_dn was 67.6 dBA.

ST4     Thirty-minute measurements were conducted during the daytime, evening, and nighttime in front of residential units at 2638 Third Street approximately 900 feet west of the proposed Project. These receptors are the closest to the proposed San Francisco HWC Converter Station. Surrounding land uses were a mix of commercial and residential. The daytime measurement was taken between 2:34 p.m. and 3:04 p.m. on September 12, the evening measurement between 8:37 p.m. and 9:07 p.m. on September 12, and the nighttime measurement between 2:34 a.m. and 3:04 a.m. on September 13. The dominant noise sources for all three measurements were vehicular traffic along Third Street and I-280. Similar to ST3, a high number of buses were noted for the evening and nighttime measurements. Other sources of noise included aircraft overflights and rustling leaves. The daytime one-hour L_eq was 68.1 dBA, the evening one-hour L_eq was 62.8 dBA, and the nighttime one-hour L_eq was 57.9 dBA. The calculated L_dn was 68.0 dBA.

The proposed route for the HVDC cable entry into San Francisco Bay parallels the southern fence line of the proposed San Francisco HWC Converter Station for approximately 1,070 feet from the bore pit. The proposed AC cable interconnection between the HWC site and the PG&E Potrero substation to the northwest would be located almost entirely on the Mirant Potrero Power Plant property. The existing noise environment and sensitive receptors for the proposed DC and AC cable routes would be the same as that identified for the proposed San Francisco HWC Converter Station.

The proposed construction laydown area (Western Pacific site) would be devoted to equipment and materials laydown, storage, parking of construction equipment, and office trailers. The site has no standing buildings or structures. The existing noise environment and sensitive receptors would be the same as those identified for the proposed HWC Converter Station (ST1 through ST4).

An alternative construction laydown area at Pier 94/96 is also under consideration. This site is paved and not occupied by any buildings. There are no sensitive noise receptors in proximity to this alternative laydown area.

4.11.1.3.2  Pittsburg Standard Oil Converter Station. A series of sound level measurements was conducted on September 13 through 14, 2005 to quantify the existing acoustical environment at the proposed Project location as well as at sensitive receptors near the proposed Project. The same methodology identified for the San Francisco sound level measurements was used. The results of the measurements are summarized in Table 4.11-3.

TABLE 4.11-3
SOUND LEVEL MEASUREMENTS OF EXISTING CONDITIONS
IN PITTSBURG (dBA)

The measurement locations are shown on Figure 4.11-2. The following summarizes the property line measurements.

ST5     Thirty-minute measurements were conducted during the daytime and nighttime at the west property line of the proposed Standard Oil Converter Station. The site is bounded by a steel plant and auto auction yard, a Dow Chemical plant to the north, and Delta Energy Center power plant to the east. The daytime measurement was taken between 2:51 p.m. and 3:21 p.m. on September 13 and the nighttime measurement was taken between 10:20 p.m. and 10:50 p.m. on September 13. The daytime measurement noise source was predominantly vehicular traffic from the Pittsburg-Antioch Highway and State Route 4 (SR 4). Other noise sources include aircraft overflights, railroads, excavators, birds vocalizing, leaves rustling, an unidentified industrial hum, backup beepers, and metal grinding. Nighttime noise sources consisted of industrial noise, leaves rustling, crickets, and vehicular traffic. The daytime one-hour L_eq was 53.8 dBA and the nighttime one-hour L_eq was 51.8 dBA.

Sensitive receptors in the Project area consist of single-family residences approximately 3,050 feet southwest on the south side of SR 4 and single-family residences approximately 3,200 feet south on the south side of SR 4. These residences do not have a direct line-of-sight to the Project due to intervening buildings, as well as SR 4 and the Pittsburg-Antioch Highway in between the residences and the Project site. Therefore, ambient noise measurements were not necessary at these residences.

The proposed DC/AC onshore cable routings from the Pittsburg Standard Oil Converter Station site begin at the proposed converter station, traverse northeast and stay south of the BNSF Railroad right-of-way (ROW) for approximately 0.55 mile, then turn north for approximately 0.5 mile along the Delta Diablo outflow access road, ending at a splice box 200 feet south of New York Slough on Dow Chemical property. The existing noise environment and sensitive receptors would be the same as those identified for the proposed Standard Oil Converter Station (ST5).

The proposed laydown area is located adjacent to and north of the proposed Pittsburg Standard Oil Converter Station site on vacant property. The laydown area would be devoted to equipment and materials laydown, storage, parking of construction equipment, and office trailers. The existing noise environment and sensitive receptors would be the same as those identified for the proposed Standard Oil Converter Station (ST5).

An alternative construction laydown area is also under consideration on the Delta Energy Center property to the east of the proposed Pittsburg Standard Oil Converter Station site. This alternate laydown area is located on vacant land adjacent to an existing power plant. There are no sensitive receptors in proximity to this site.

The proposed access road would be constructed between the proposed Pittsburg Standard Oil Converter Station site and the Pittsburg-Antioch Highway with a bridge crossing over Kirker Creek. The alternative access road would involve minor upgrading of the existing access road between the site and Loveridge Road. The existing noise environment and sensitive receptors for the proposed and alternative access roads would be the same as that identified for the proposed Pittsburg Standard Oil Converter Station site.

4.11.1.3.3  Offshore DC Cable Route. The proposed offshore DC cable route would run from San Francisco to Pittsburg with a length of approximately 56 miles. The cable route, beginning in San Francisco, traverses San Francisco Bay, San Pablo Bay, the Carquinez Strait, Suisun Bay, and New York Slough. The existing noise environment consists of vessel traffic on the Bay, as well as other industrial noise sources along the route. Sensitive receptors located along the cable route consist of scattered residences located near the shoreline.

4.11.2  Regulatory Setting

4.11.2.1  Federal

There are no federal laws, ordinances, or regulations that directly affect this Project with respect to noise. However, there are guidelines at the federal level that direct the consideration of a broad range of noise and vibration issues as listed below:

• National Environmental Policy Act (42 USC 4321, et. seq.) (PL-91-190) (40 CFR §1506.5)

• Noise Control Act of 1972 (42 USC 4910)

4.11.2.1.1  HUD. HUD Noise Regulations, 24 CFR Part 51, Subpart B, Noise Assessment Guidelines identify sound levels that are compatible with residential land use. Sound not exceeding 65 dBA L_dn is considered acceptable. Sound levels between 65 dBA L_dn and 75 dBA L_dn are normally unacceptable unless noise reduction measures are included to limit noise levels within residences (45 dBA L_dn or below). Sound levels exceeding 75 dBA L_dn are unacceptable.

4.11.2.1.2  EPA. The EPA has not promulgated standards or regulations for environmental noise generated by electrical substations/converter stations or transmission lines. However, USEPA has published a guideline that specifically addresses issues of community noise. This guideline, commonly referred to as the "EPA Levels Document" (Report No. 556/9-74-664), contains goals for noise levels affecting residential land use of L_dn ≤ 55 dBA for outdoors and Ldn ≤ 45 dBA for indoors. The agency is careful to stress that the recommendations contain a factor of safety and do not consider technical or economic feasibility issues and, therefore, should not be construed as standards or regulations.

4.11.2.1.3  FTA. The Federal Transit Administration (FTA) has not promulgated standards or regulations for environmental noise by construction. However, they have published a guideline that specifically addresses issues of community noise. This guideline recommends that hourly sound levels of 90 dBA at residential uses from construction noise, including pile driving, would be considered a significant impact (FTA, 1995).

The FTA has published guidelines for assessing the impacts of ground-borne vibration associated with construction of rail projects, which have been applied by other jurisdictions to other types of projects (FTA, 1995). The FTA measure of the threshold of architectural damage for conventional sensitive structures is 0.2 in/sec PPV. The threshold of perception of vibration is 0.01 in/sec PPV.

4.11.2.2  State

• The following potentially relevant state noise regulations have been identified. California State Building Code (CCR Title 24) requires that indoor noise levels in habitable spaces of multi-family dwellings be less than 45 dBA L_dn when exposed to exterior noise sources

• California Department of Industrial Relations, Cal/OSHA (8 CCR, General Industrial Safety Orders, Article 105, Control of Noise Exposure, §5095) requires that all facility noise levels be limited to 85 dBA at 3 feet from equipment sources to protect worker safety. If workers frequent areas of the facility that exceed 85 dBA then all aspects of a hearing conservation program must be implemented by the employer

• California statutes (CCR 65302(f)) require local jurisdictions to prepare General Plans that include Land Use and Noise Elements

• State CEQA Guidelines (CCR §§15000-15387) and Appendix G (Environmental Checklist)

4.11.2.3  Local

4.11.2.3.1  San Francisco General Plan Noise Element. The City of San Francisco Noise Element of the General Plan establishes standards for land use compatibility with traffic noise levels. The maximum acceptable exterior noise level is 60 dBA L_dn for all residential and transient lodging uses; 65 dBA L_dn for school classrooms, libraries, churches, hospitals, and nursing homes; 70 dBA L_dn for playgrounds and parks, office buildings, commercial buildings; and 75 dBA L_dn for other uses. These standards are based upon accepted thresholds of significance and apply to traffic noise.

4.11.2.3.2  San Francisco Noise Ordinance. The City of San Francisco noise ordinance (San Francisco Police Code, Article 29, §2909) has established maximum noise levels for fixed sources at the boundary of various land use zones as shown in Table 4.11-4. The proposed San Francisco HWC Converter Station and adjacent properties are zoned M-2 (Heavy Industrial).

The noise ordinance limits interior noise levels inside residential units to 45 dBA between 10:00 p.m. and 7:00 a.m. or 55 dBA between the hours of 7:00 a.m. and 10:00 p.m.

TABLE 4.11-4
CITY OF SAN FRANCISCO SOUND LEVEL LIMITS
FROM FIXED SOURCES¹

¹   Note: If the measurement location is on a boundary between two zoning districts, the lower sound level shall apply.

The noise ordinance requires that standby equipment operated only in emergency situations shall not emit noise at a level in excess of 75 dBA when measured at the property line.

The noise ordinance also establishes limits related to construction noise (Article 29, §2907). The ordinance states:

(b)  It shall be unlawful to operate any powered construction equipment, regardless of age or date of acquisition, if the operation of such equipment emits noise at a level in excess of 80 dBA when measured at a distance of 100 feet from such equipment, or any equivalent sound level at some other convenient distance.

(c)  The provisions of Subsection (b) shall not be applicable to impact tools and equipment provided that such impact tools and equipment shall have intake and exhaust mufflers by the manufacturers thereof and approved by the Director of Public Works as best accomplishing maximum noise attenuation, and that pavement breakers and jackhammers shall also be equipped with acoustically attenuation shields or shrouds recommended by the manufacturers thereof and approved by the Director of Public Works as best accomplishing maximum noise attenuation as he deems to be in the public interest.

The noise ordinance establishes restrictions on construction noise (Article 20, §2908). The ordinance states:

      It shall be unlawful for any person, between the hours of 8:00 p.m. of any day and 7:00 a.m. of the following day to erect, construct, demolish, excavate for, alter or repair any building or structure if the noise level created thereby is in excess of the ambient noise level by 5 dBA at the nearest property line, unless a special permit therefore has been applied for and granted by the Director of Public Works.

4.11.2.3.3  Pittsburg General Plan Noise Element. The City of Pittsburg Noise Element of the General Plan establishes standards for land use compatibility with various noise levels, as shown in Table 4.11-5. The maximum acceptable exterior noise level is 60 dBA L_dn for single-family residential uses; 65 dBA L_dn for multiple-family residential uses and hotels and motels; 70 dBA L_dn for schools, libraries, churches, hospitals, parks, playgrounds, and office buildings; and 75 dBA L_dn for other uses. These standards are based upon accepted thresholds of significance and apply to noise (typically long term) from any source.

The Noise Element requires that interior noise levels in noise-sensitive uses (schools, hospitals, churches, or residences) do not exceed 45 dBA L_dn.

The Noise Element requires that noise on construction sites adjacent to noise-sensitive uses is limited to normal business hours between 8:00 a.m. and 5:00 p.m. but does not establish sound level limits.

4.11.2.3.4  Pittsburg Noise Ordinance. The City of Pittsburg noise ordinance does not establish noise level limits related to fixed noise sources or construction noise (Title 9 Public Peace, Safety and Morals, Chapter 9.44 Noise, §9.44.010).

The noise ordinance prohibits the use of a pile driver, steam shovel, pneumatic hammer, derrick, steam or electric hoist, or other appliance between the hours of 10:00 p.m. and 7:00 a.m.

4.11.2.3.5  Contra Costa County General Plan Noise Element. The County of Contra Costa Noise Element of the General Plan establishes standards for land use compatibility with various noise levels, as shown in Table 4.11-6. The limits are the same as those identified for the City of Pittsburg Noise Element.

The Noise Element requires that interior noise levels in noise-sensitive uses do not exceed 45 dBA L_dn.

TABLE 4.11-5

CITY OF PITTSBURG LAND USE COMPATIBILITY

TABLE 4.11-6
COUNTY OF CONTRA COSTA LAND USE COMPATIBILITY

The Noise Element requires that:

"Construction activities should be concentrated during the hours of the day that are not noise-sensitive for adjacent land uses and should be commissioned to occur during normal work hours of the day to provide relative quiet during the more sensitive evening and early morning periods."

4.11.2.3.6  Contra Costa County Noise Ordinance. The County of Contra Costa does not have a noise ordinance.

4.11.3  Environmental Impacts

The proposed Project would result in noise from construction of the Project components as well as operation of the converter stations. The following sections assess potential noise impacts from construction and operation of the proposed Project, as well as alternatives, at the property lines and offsite sensitive receptors.

4.11.3.1  Thresholds of Significance

Thresholds used to evaluate potential noise and/or vibration impacts are based on applicable criteria in the State CEQA Guidelines (CCR §§15000-15387), Appendix G; and the applicable noise ordinances and elements. Noise from construction of the Project would be considered significant if:

• Noise from construction equipment would exceed 80 dBA at a distance of 100 feet, occurred between 8:00 p.m. and 7:00 a.m., or increased ambient conditions by 5 dBA at the property lines in San Francisco

• Construction occurred between 5:00 p.m. and 8:00 a.m. in Pittsburg

• Vibration from construction would exceed 0.2 inches/second peak particle velocity (PPV) at residential structures

• Noise from construction traffic exceeded 60 dBA L_dn at residential receptors

• Noise from construction exceeds 90 dBA Leq (hourly) at residential uses

Noise from operation of the Project would be considered significant if:

• Noise levels exceeded an hourly average of 75 dBA at any time at the property lines in San Francisco

• Maximum exterior noise levels at single-family residences exceeded 60 dBA L_dn, 65 dBA L_dn at multi-family residences, or 75 dBA L_dn for industrial uses in Pittsburg or Contra Costa County

4.11.3.2  San Francisco HWC Converter Station

4.11.3.2.1  Construction-related Impacts. The Project is scheduled to take approximately 27 to 30 months to construct, including demolition activities and site preparation. The construction phase is scheduled to take approximately 20 months, including approximately 4 to 5 months to install the cable systems in the floor of San Francisco Bay and onshore, followed by 5 to 6 months of startup and commissioning activities. The construction phase would be preceded by approximately 3 to 6 months of demolition of existing structures, site preparation, and remediation (as applicable). The maximum time period where construction noise impacts could be expected to occur is anticipated to be less than 30 months.

The Pittsburg and San Francisco converter stations would be constructed concurrently. Construction activities would include building the converter stations, installation and connection of the HVAC and HVDC transmission lines, switchyard, and substations. Sequential construction activities would include demolition of existing facilities, grading and site preparation, foundation construction, erection of major equipment and structures, installation of electrical systems and control systems, and startup/testing. Construction at the converter station sites would include earthwork, pile driving, building structures, trenching and pipe laying, paving, and landscaping. Construction-related activities involving generation of noise would also occur at the proposed construction laydown area, along the onshore cable routes, and local roadways due to truck traffic. Work at the sites would be restricted in accordance with the requirements of the local noise ordinances unless an exception is granted.

The demolition and remediation phases would be performed in months 1 through 6 after the notice to proceed. Equipment that would be associated with these phases is listed in Table A.4-3 in Appendix A.

The excavation, grading, and construction phase would be performed from month 6 to month 27 after the notice to proceed. The anticipated number of and type of construction equipment that would be needed is presented in Table A.4-3 in Appendix A.

Construction activities at the proposed San Francisco HWC Converter Station site, laydown area, and onshore cable route would result in temporary increases in the ambient noise levels. Noise would result from the operation of construction equipment and truck traffic. The increase in noise levels would be primarily experienced close to the noise source. The magnitude of the impact would depend on the type of construction activity, noise level generated by various pieces of construction equipment, duration of the construction phase, and distance between the noise source and receiver. Figure 4.11-3 shows maximum noise levels generated by typical construction equipment. Sound levels of typical construction equipment range from approximately 65 dBA to 95 dBA at 50 feet from the source (EPA, 1971), with an average sound level of 89 dBA at 50 feet. This analysis uses 89 dBA at 50 feet as the reference noise level for conventional construction noise.

Acoustical calculations were performed to estimate noise from construction activities at the closest residences. Noise from construction activities was assumed to have point source acoustical characteristics. Strictly speaking, a point source sound decays at a rate of 6 dB per doubling of distance from the source. This is a logarithmic relationship describing the acoustical spreading of a pure, undisturbed spherical wave in air. The rule applies to the propagation of sound waves with no ground interaction. The calculations are based on the formula below (Harris, 1998):

    where:

SPL₁       =    known sound level,
SPL₂       =    desired sound level,
d₁            =    known distance, and
d₂            =    desired distance.

The residential uses closest to the proposed San Francisco HWC Converter Station site consist of multi-family residences approximately 900 feet northwest and 1,400 feet to the west. The loudest conventional construction activities will produce an average sound level at the closest residences of 64 and 59 dBA, respectively, as summarized in Table 4.11-7. Because of the intermittent nature of construction work and the intervening buildings, it is likely that noise from construction of the proposed HWC Converter Station would be inaudible to slightly audible at the residences, much less increase the existing noise levels by 5 dBA; therefore, there would be no potentially significant impacts. During this time period, construction activity would be required to comply with the City's noise ordinance criteria (80 dBA at 100 feet) and would not result in a potentially significant impact.

Pile Driving. Portions of the project would require driven piles. Noise from pile driving activity is different in character from typical conventional "construction phase" noise and thus this potential noise impact is analyzed separately. Maximum noise levels at 50 feet from a pile driver range from 89 to 114 dBA L_max, depending on many factors (e.g., driver power, driver type, pile size, soil characteristics, etc.). The typical L_eq produced during pile driving ranges from 101 to 105 dBA at 50 feet. The higher typical noise level values of 100 dBA L_eq and 105 dBA L_max at 50 feet from the pile driver noise source were selected for calculation purposes. Calculations were performed to estimate sound levels from pile driving at the

TABLE 4.11-7
CALCULATED SOUND LEVELS FROM CONSTRUCTION
AT PROPOSED CONVERTER STATIONS (dBA)

Converter Station Site		Receptor Description		Distance to Receptors (Ft)		Calculated Sound Level From Construction (dBA)		Calculated Sound Level from Pile Driving Noise (dBA)
								Lmax	Leq
San Francisco HWC		Multi-family residences (2638 3rd Street)		890		64		76	71
		Multi-family residences (1423 Indiana Street)		1,400		59		80	75
Pittsburg Standard Oil		Single-family residences (2200 Lakeview Court)		3,050		50		66	61

receptors. Worst-case direct line-of-sight sound levels at the residences were calculated to be 76 to 80 dBA L_max (71 to 75 dBA L_eq) at the closest receptors. Due to the intervening buildings, received sound levels at the receptors would be substantially less than predicted; although it is likely that noise from the pile driving would still be audible at the receptors. The use of impact tools, such as pile drivers, is not subject to sound level restrictions in San Francisco, but such tools are required to be equipped with acoustical attenuation shields or shrouds recommended by the manufacturer and approved by the San Francisco Director of Public Works. In addition, pile driving is limited to the hours of 7:00 a.m. to 8:00 p.m. Pile driving would be required to comply with these requirements and would result in a less-than-significant impact.

Calculations were performed to estimate vibration from pile driving activities at the closest residences, as detailed in Section 4.11.1.2. Vibration from pile driving was assumed to have point source propagation characteristics. Vibration levels for impact pile drivers are typically 0.644 inches/second peak particle velocity (PPV) at 25 feet (FTA, 1995). Under normal propagation conditions, vibration levels at residences 900 feet from the pile driving would be 0.003 in/sec, which is well below the FTA threshold of 0.20 in/sec; resulting in a less-than-significant impact.

Construction Traffic. The Project assumes that project-related container shipments from overseas would arrive at the Port of Oakland and would be shipped by truck to the converter station site or laydown area in San Francisco. Trucks would travel from the Port north on I-880, west across the Bay Bridge on I-80, and south along U.S. 101 to the Cesar Chavez Street exit. Trucks would continue on local streets, traveling eastbound on Cesar Chavez Street and turning left onto Illinois Street to reach the proposed converter station site (Figure 4.10-4A). To access the proposed construction laydown area (Western Pacific site), trucks would turn left from Cesar Chavez onto Illinois Street and then right onto 25th Street. To access the alternate laydown area (Pier 94/96), trucks would turn right onto Illinois Street, cross the new Islais Creek bridge, and turn left onto Cargo Way. At a later time, the equipment or material would be reloaded on trucks to travel the short distance between the laydown area and the converter station site, using the same streets to reach Illinois Street and the converter station site. Local truck shipments for the project (not originating at the Port of Oakland) would follow the same routing in the study area. For hauling demolition debris, the most probable truck route to landfills would be over Cesar Chavez Street to nearby I-280 via Pennsylvania Street and then south along I-280 and U.S. 101.

The total number of truck round trips to the San Francisco HWC Converter Station site would approximate 3,579, including demolition hauling, remediation and site preparation, and materials deliveries. In addition, local suppliers' shipments would be dispersed over an estimated 27- to 30-month period during the Project's construction phase. This number includes truck trips for hauling demolition debris and equipment from the HWC site. The number of truck round trips to the San Francisco HWC Converter Station site would be expected to peak between the 10^th and 12^th months of construction, with a maximum of 22 deliveries per day (based on an average of 22 work days per month) and decline thereafter.

Between the 12^th and 19^th months of the construction period, an estimated maximum of 45 daily employee auto round trips is expected at the construction site, for a possible maximum of 67 truck and commute round trips during the workday.

Average daily traffic volumes are approximately 5,000, 8,000 and 11,000 on Illinois Street, Cargo Way and Cesar Chavez Street, respectively. Because the maximum number of 67 daily round trips to and from the Project site would contribute less than 1 percent to the existing daily traffic volume, there would be no change (less than 0.0005 dBA) to existing noise levels on these roadways or at sensitive receptors. As a result, there would be a less-than-significant noise or vibration impact to local roads in the study area.

4.11.3.2.2  Operations-related Impacts. Noise would be produced during the operation of the proposed converter stations. The primary noise sources at the proposed converter stations include transformers, filters, heating and air conditioning units, circuit breakers, and an emergency generator. A list of noise-producing equipment and noise parameters is included in Table 4.11-8.

The Cadna A Noise Prediction Model was used to estimate the sound level that would be generated by the proposed Project at the property lines and noise-sensitive receptors. The Cadna A model predicts and assesses noise levels near industrial noise sources. The model uses industry-accepted propagation algorithms and accepts sound power levels (in decibels

TABLE 4.11-8
SUMMARY OF NOISE SOURCES FROM CONVERTER STATIONS¹

¹   Source: Siemens, 2005.
LW = sound power level (referenced to 1 pico Watt); SPL = sound pressure level (referenced to 20 цPa).
²   These pieces of equipment are expected to cause this noise only momentarily each day.

re 1 pico Watt) provided by the equipment manufacturer and other sources based on International Organization for Standardization (ISO) standards. The calculations account for classical sound wave divergence, plus attenuation factors resulting from air absorption, basic ground effects, and barrier/shielding. Air absorption was input to the model assuming "standard day" conditions of 59° Fahrenheit and 70 percent relative humidity.

The San Francisco HWC site and surrounding areas were assumed to be flat, therefore, no intervening topographical barrier effects were considered. However, major buildings, tanks, and large equipment were included as barriers.

Calculations were performed using linear octave band sound power levels as inputs from each noise source. The model outputs are in terms of octave band and overall A-weighted sound pressure levels. The modeled noise sources and source sound levels are summarized in Table 4.11-9. Results of the calculations and all source sound levels were provided by Siemens (see Appendix H). The Project site configuration was imported into Cadna A from the Project CAD files. The converter station was assumed to operate 24 hours per day, so the noise output would be constant regardless of time of day. Noise sources that would operate intermittently depending on need, such as the heating and air conditioning units, generator, or circuit breakers were assumed to operate continuously; therefore, the analysis is considered a worst-case.

TABLE 4.11-9
CALCULATED SOUND LEVELS FROM OPERATION
OF PROPOSED CONVERTER STATIONS (dBA)¹

¹  Not including consideration of pile driving.

As summarized in Table 4.11-9, hourly average sound levels from the proposed San Francisco HWC Converter Station would range from 62 to 73 dBA L_eq at the property lines. Therefore, Project generated sound levels would be below the City/County San Francisco noise impact threshold of 75 dBA L_eq at the property lines and would not result in a significant impact.

Construction of the onshore AC and DC cable routes would result in sound levels similar to those identified for construction of the proposed converter station. Because of the intermittent nature of construction work and the intervening buildings, it is unlikely that noise from construction of the onshore AC and DC cable routes would be audible at the residences, much less increase the existing noise levels by 5 dBA; therefore, there would be no significant impact. During this time period, construction activity would be required to comply with the City's noise ordinance criteria (80 dBA at 100 feet) and would not result in a significant impact.

No noise would be associated with operation of the proposed buried onshore cable routes.

4.11.3.3  Pittsburg Standard Oil Converter Station

4.11.3.3.1  Construction-related Impacts. Scheduled construction hours at the Standard Oil site are generally consistent with those given for the San Francisco HWC Converter Station site. Criteria are not set forth by the Pittsburg Noise Element or Noise Ordinance related to construction noise levels and times of operation. The anticipated noise sources would be identical to those outlined for the HWC site, with the exception of the following:

• Demolition of abandoned wastewater storage tanks and a small dilapidated building (duration: 3-4 months)

• Portable Generator used at Pittsburg initially for power demands

Acoustical calculations were performed to estimate noise from construction activities at the closest residences with the same methodology as described for the San Francisco HWC Converter Station site. The offsite residential uses closest to the proposed Pittsburg Standard Oil Converter Station consist of single-family residences approximately 3,050 feet to the south. Average sound levels at the residences closest to the proposed converter station site would be 50 dBA, as summarized in Table 4.11-7. Because of the intermittent nature of construction work and intervening structures and roads/highways, typical construction noise would not be expected to be audible at the receptors and would not result in a potentially significant impact.

Pile Driving. Calculations were performed to estimate sound levels from pile driving at the receptors. Direct line-of-sight sound levels at the residences were calculated to be 66 dBA L_max (61 dBA L_eq) at the closest receptors. Due to the intervening buildings, topography, and noise sources (highways), received sound levels at the receptors would be substantially less than predicted, although it is likely that noise from the pile driving would still be audible at the receptors. Pile driving is not subject to sound level restrictions in Pittsburg, but is limited to the hours of 7:00 a.m. to 10:00 p.m. Pile driving would be required to comply with these requirements. The calculated pile driving noise levels at the closest sensitive receptors to the Pittsburg Standard Oil site are well below the FTA threshold of 90 dBA and would result in a less-than-significant impact.

Calculations were performed to estimate vibration from pile driving activities at the residences closest to the proposed Standard Oil site, as detailed in Section 4.11.1.2. Vibration from pile driving was assumed to have point source propagation characteristics. Vibration levels for impact pile drivers are typically 0.644 inches/second peak particle velocity (PPV) at 25 feet (FTA, 1995). Under normal propagation conditions, vibration levels at residences 3,050 feet from the pile driving would be 0.0005 in/sec, which is well below the FTA threshold of 0.20 in/sec; resulting in a less-than-significant impact.

The proposed new access road to the proposed Pittsburg Standard Oil Converter Station site would run south from the converter station site to the Pittsburg-Antioch Highway. The new road would be approximately 30 feet wide with an asphalt concrete surface. The new road would require construction of a new bridge over Kirker Creek just north of the Pittsburg-Antioch Highway (refer to Figures A.4-1 and A.4-2). Average construction-related noise levels at the closest residences to the proposed bridge construction over Kirker Creek would be 54 dBA. Pile driving would be required for construction of the bridge over an estimated period of 5 days. The closest receptors to this site are approximately 2,300 feet to the south, on the other side of SR 4. Direct-line-of-sight sound levels at the receptors were calculated to be 70 dBA L_max (65 dBA L_eq). Due to the intervening buildings, topography, and noise sources (highways), received sound levels at the receptors would be substantially less than predicted, although it is likely that noise from the pile driving would still be audible at the receptors. Pile driving is not subject to sound level restrictions in Pittsburg, but is limited to the hours of 7:00 a.m. to 10:00 p.m. Pile driving would be required to comply with these requirements. The calculated noise levels associated with pile driving are well below the FTA threshold of 90 dBA and would result in a less-than-significant impact.

Calculations were performed to estimate vibration from pile driving activities at the residences closest to the proposed Kirker Creek bridge location, as detailed in Section 4.11.1.2. Vibration from pile driving was assumed to have point source propagation characteristics. Vibration levels for impact pile drivers are typically 0.644 inches/second peak particle velocity (PPV) at 25 feet (FTA, 1995). Under normal propagation conditions, vibration levels at residences 2,300 feet from the pile driving would be 0.0007 in/sec, which is well below the FTA threshold of 0.20 in/sec; resulting in a less-than-significant impact.

Construction Traffic. From the Port of Oakland, truck shipments would travel from I-880 northbound to I-80 (Eastshore Freeway), diverting eastward onto SR 4 in Hercules (Figure 4.10-1). Trucks would exit SR 4 in Pittsburg, traveling north on Loveridge Road (City of Pittsburg Ordinance 05-1238, Section 3, 2005, identifies specific arterials as truck routes). The Pittsburg Standard Oil Converter Station site would have access from the Pittsburg-Antioch Highway east of Loveridge Road. A new two-lane road would be constructed off the Pittsburg-Antioch Highway north across Kirker Creek into the project site. However, heavy loads such as the 196-ton transformers would access the site via the alternative access road off Loveridge Road since they would exceed the capacity of the proposed bridge over Kirker Creek associated with the proposed access road. Alternatively, trucks could continue north on Loveridge Road across the Pittsburg-Antioch Highway to a narrow unpaved road that parallels the south side of the BNSF railroad tracks and enters the Project site from the north. This is the existing access to the Project site.

Local shipments that do not originate from the Port of Oakland would most likely use SR 4 and the local street network to access the site as described above.

The number of daily truck deliveries to the Standard Oil Converter Station site would vary according to the phase of the construction work. The total number of truck round trips to the site would be approximately 2,522, including demolition hauling, remediation and site preparation, and materials deliveries. In addition, local suppliers' shipments would be dispersed over a 27-month period during the project's construction phase. The number of deliveries would increase over the first year of construction, peaking in the 11^th and 12^th months, and then would decline over the remaining months of construction. An estimated total of 364 truck round trips, or a maximum of 17 deliveries per day, would occur in the 11^th month of construction.

Between the 12^th and 19^th months of the construction period, an estimated maximum of 45 daily employee auto round trips is expected at the construction site, for a maximum total of 63 truck and commute round trips during the workday. Existing average daily traffic volumes on the Pittsburg-Antioch Highway is 9,500 vehicles, 17,000 vehicles on Loveridge Road, 30,000 vehicles on Railroad Avenue, and 12,500 vehicles on West Tenth Street. Because the maximum number of 63 daily round trips to and from the Project site would contribute less than 1 percent to the existing daily traffic volume on these roadways, there would be no change (less than 0.0005 dBA) to existing noise. As a result, there would be a less-than-significant noise or vibration impact to local roads in the study area.

4.11.3.3.2  Operations-related Impacts. Calculations were performed using linear octave band sound power levels as inputs from each noise source with the same equipment as the proposed San Francisco HWC Converter Station. Siemens conducted the noise analysis, the results of which are summarized here and provided in Appendix H.

There are no sensitive receptors near the onshore cable routes and no standards related to noise levels associated with operations; therefore, there would be no significant impact. In addition, there are no sensitive receptors near the proposed (or alternative) access road; therefore, there would be no potentially significant impacts during the operational phase.

As summarized in Table 4.11-9, unmitigated sound levels from the proposed Standard Oil Converter Station would range from 77 to 79 dBA L_dn at the property lines and would be 46 L_dn at the closest sensitive receptor. Sound levels would not exceed the 60 dBA L_dn standard at the closest sensitive receptors. Therefore, sound levels would exceed the Pittsburg 75 dBA L_dn requirement at the property lines and would result in a potentially significant impact.

Impact NOISE-1: Converter Station Operations Sound Levels. Sound levels from the operation of the Standard Oil Converter Station would range from 77 to 79 dBA L_dn at the property lines, which exceeds the Pittsburg 75 dBA L_dn requirement. This is considered a potentially significant impact.

Mitigation Measure NOISE-1: Noise Barrier Installation for Converter Station. An acoustical barrier approximately 10 feet high would be erected around a portion of the converter station and an acoustical barrier approximately 13 feet high would be erected around a portion of the emergency generator. If final design determined that an acoustical barrier were unnecessary, it shall not be required.

Implementation Responsibility:  Project proponent

Requirements and Timing:             Submit plans and obtain approval from City of Pittsburg Planning Department during Design Review; complete barrier installation prior to facility startup Project proponent shall perform post-startup noise monitoring at property line to confirm compliance with 75 dBA L_dn requirement

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance.

Resulting Level of Significance. With installation of barriers outlined in Mitigation Measure NOISE-1, sound levels would range from 71 to 74 dBA L_dn at the property lines and 42 dBA L_dn at sensitive receptors. Therefore, sound levels would be reduced to below the 75 dBA L_dn standard at the property lines and 60 dBA L_dn at the receptors. Mitigation Measure NOISE-1 would reduce Impact NOISE-1 to a less-than-significant level.

4.11.3.4  Offshore DC Cable Route

4.11.3.4.1  Construction-related Impacts. Submarine installation of the proposed offshore DC cable system would result in airborne and underwater noise. The primary noise sources associated with construction along the proposed cable route would consist primarily of underwater and airborne noise from vessel traffic including the cable laying ships (Giulio Verne and barges, as applicable), tugboats, supply barges, and support vessels.

Airborne noise would result from the use of various construction equipment and limited dredging activities in New York Slough in Pittsburg. The average of 89 dBA at 50 feet from typical construction equipment was used in this analysis. Acoustical calculations were performed to estimate noise from construction activities at the closest residences with the same methodology as described for the San Francisco HWC Converter Station site. The closest sensitive receptors are approximately 200 feet from the proposed construction activities. Average sound levels at the residences closest to the proposed cable laying would be expected to be less than 77 dBA. Because of the intermittent nature of the cable laying activities, intervening structures, and existing noise sources in the Bay, construction noise would not be expected to be audible at the receptors and would not result in a significant impact.

Potential impacts from underwater noise would be limited to those affecting marine life. With regard to noise, the National Marine Fisheries Service (NMFS) currently considers, as a guideline, received underwater peak sound pressure levels at or above 160 decibels referenced to 1 micropascal (160 dB re 1 µPa) as constituting harassment of marine mammals. NMFS has suggested that sound pressure levels above 180 dB re 1 µPa could cause temporary hearing impairment in marine mammals.

The marine mammals known to frequent the area include California sea lions (Zalophus californianus) and harbor seals (Phoca vitulina richardii). Sea lions in the water tolerate close and frequent vessel approaches and sometimes congregate around fishing vessels. Hauled out on land, sea lions are more responsive, but rarely react unless a boat approaches within 100 to 200 meters (Bowles and Stewart, 1980). Small boats that approach within 100 meters often displace harbor seals from haul-out sites and less severe disturbances can cause alert reactions without displacement (Bowles and Stewart, 1980; Allen et al., 1984). In general, evidence about reactions of seals to vessels is limited, but data suggest that seals often show substantial tolerance of vessels (Richardson et al., 1995).

Calculations were performed to determine the distance from cable laying construction activities in which a marine mammal would encounter underwater sound levels of 160 dB. Typical broadband received underwater source sound levels for vessels range from 145 to 190 dB re 1 µPa (Richardson et al., 1995). As discussed in Section 4.11.1.1, the distinction between in-air and in-water reference levels is important since sound intensity in water would appear extremely high compared to values in air. In other words, 120 dB in the air is not the same as 120 dB in the water. There is a difference of 26 dB when converting air to water sound pressure levels. For example, if a jet engine has a sound pressure level of 140 dB in air, the equivalent underwater sound pressure level would be 166 dB; or a supertanker that emits 164 dB in air would sound more like 190 dB in water. Noise from the activity was assumed to have cylindrical spreading characteristics. Cylindrical spreading occurs when the medium is non-homogeneous and the sound is reflected from the surface and bottom, such as shallow water within the Bay. With cylindrical spreading, sound levels diminish by 3 dB when distance doubles. The distance to the 160 dB contour was estimated to be approximately 800 feet from the location of cable laying. Marine mammals may experience sound levels that could be considered harassment if they came within 800 feet of the proposed construction area. However, the seals and sea lions will typically avoid coming into this zone of potential harassment due to the physical disturbance of the activities (i.e., presence of vessels) and would likely not be exposed to noise levels that would have a significant impact on their behavior. In addition, as discussed above, seals and sea lions inhabiting the area near the cable-laying activities are tolerant to vessel traffic and have become habituated to the existing high amounts of vessel traffic. . Furthermore, the area already has high amounts of vessel traffic; therefore, the increase to the existing noise environment would be minimal. Therefore, there would be no adverse impact from the short-term underwater activities on marine mammals.

4.11.3.4.2  Operations-related Impacts. No potential operations-related noise impacts have been identified for the proposed offshore cable portion of the Project.

4.11.4  References

Allen, S.G., D.G. Ainley, G.W. Page, and C.A. Ribic. 1984. The effect of disturbance on harbor seal haul-out patterns at Bolinas Lagoon, California. Fishery Bulletin 82:493-500.

Beranek, L.L. and I.L. Ver, eds. 1992. Noise and Vibration Control Engineering. John Wiley & Sons, Inc. New York, NY.

Bowles, A.E. and B.S. Stewart. 1980. Disturbances to the Pinnipeds and Birds of San Miguel Island, 1979-1980. Technical Report submitted by Hubbs-Sea World Research Institute and San Diego State University to U.S. Air Force. 246 pgs.

EPA (U.S. Environmental Protection Agency). 1971. Noise from Construction Equipment and Operations, Building Equipment and Home Appliances. (Prepared under contract by Bolt, et al., Bolt, Beranek & Newman, Boston, Massachusetts.) Washington, D.C.

FTA (Federal Transit Administration). 1995. Transit Noise and Vibration Impact Assessment. April.

Gill, H.S. 1983. Control of Impact Pile Driving Noise and Study of Alternative Techniques. Institute of Noise Control Engineering Journal. March-April, pp. 76-83.

Greene, R., Greene, M., Pirie, R. August 2002. Comparison of Pile-Driver Noise and Vibration from Various Pile-Driving Methods and Pile Types. Proceedings of the 2002 International Congress and Exposition on Noise Control Engineering, Dearborn, MI, USA.

Harris, Cyril M., ed. 1998. Handbook of Acoustical Measurements and Noise Control. Third Edition. McGraw-Hill, Inc. New York, NY.

ISO (International Organization For Standardization). 1996a. Description and Measurement of Environmental Noise, Basic Quantities and Procedures Part 1, ISO 1996/1.

     1996b. Description and Measurement of Environmental Noise, Basic Quantities and Procedures, Acquisition of Data Pertinent to Land Use, Part 2, ISO 1996/2.

     1996c. Description and Measurement of Environmental Noise, Basic Quantities and Procedures, Application to Noise Limits, Part 3, ISO 1996/3.

Richardson, W.J., C.R. Greene, C.I. Malme, and D.H. Thomson. 1995. Marine Mammals and Noise. Academic Press, Inc., San Diego, CA. 576 pp.