3.1    introduction

This EIR Addendum focuses on aspects of the proposed HVDC PLUS converter station technology/design that have the potential to result in new or different significant environmental impacts relative to the previously proposed HVDC "conventional" design as evaluated in the Draft and Final EIRs. As discussed in Sections 1.0 and 2.0 of this EIR Addendum, the HVDC PLUS technology/converter station design allows the converter stations to be smaller in size (both footprint and height) in both San Francisco and Pittsburg. The proposed San Francisco HWC (Mitigated) Converter Station site is now a subset of what was evaluated in Section 4.A and Table 6-1 of the Final EIR. The proposed Pittsburg West Tenth Street Converter Station site consists of a modified Pittsburg West Tenth Street Alternative 1 as evaluated in the Draft and Final EIRs, extending approximately 50 feet south of the original configuration. As discussed in Section 1.2.1 of this EIR Addendum, the adoption of the Siemens HVDC "PLUS" technology/converter station design has multiple advantages compared to the HVDC "conventional" design evaluated in the Draft and Final EIRs. The HVDC PLUS design requires less equipment and materials, equipment deliveries, and earthwork to construct (estimated reduction of approximately 20 to 25 percent) relative to the HVDC "conventional" design evaluated in the Draft and Final EIRs. In addition, the HVDC PLUS converter stations are smaller (i.e., less visibly apparent) and would generate less noise during Project operations than the HVDC "conventional" design. The proposed HVDC PLUS technology/converter station design would result in less impacts than those identified in the Final EIR as discussed herein and in Table 1-1 of this EIR Addendum.

The impact findings and mitigation measures requirements presented in the Final EIR, as certified by the City of Pittsburg, are generally the same for the refined Trans Bay Cable Project utilizing HVDC PLUS technology/design (refer to Table 1-1 of this EIR Addendum) except as itemized in the following subsections.

Brief environmental assessments that focus on the differences between the proposed HVDC PLUS design and site modifications in San Francisco and Pittsburg relative to HVDC conventional design and sites evaluated in the Final EIR follow for these environmental resource topics:

• Air Quality


• Geologic Resources and Soils


• Water Resources and Quality


• Terrestrial Biological Resources


• Marine Biological Resources


• Cultural Resources


• Land Use and Recreation


• Marine Transportation and Commercial Fishing


• Traffic and Transportation


• Noise and Vibration


• Public Services and Utilities


• Visual Resources/Aesthetics


• Hazardous Materials and Waste Management


• Paleontological Resources

All identified impacts are less than significant with mitigation and are equal to or typically less than those identified in the Draft and Final EIRs for the HVDC conventional design.

3.2    AIR QUALITY

With implementation of Mitigation Measures AIR-1, AIR-2, AIR-3, and AIR-4 (refer to Table 1-1 of this EIR Addendum), Impacts AIR-1, AIR-2, AIR-3, and AIR-4 would all be reduced to a less than significant level. With adoption of the HVDC PLUS converter station design/layout, construction emissions would be reduced by an estimated 20 to 25 percent relative to "conventional" HVDC at the converter station sites in San Francisco and Pittsburg due to the smaller footprint, the need for less equipment and materials (including truck deliveries), the need for less grading and subsurface excavation, and the shorter duration and/or intensity of the onshore construction phase. In addition, with the proposed HVDC PLUS converter station design there is no longer a need for an emergency backup generator during the operational phase. The operational emission estimates associated with required periodic testing of the diesel-fueled emergency generator (refer to Table 4.2-11 of the Draft EIR) are no longer applicable in San Francisco or Pittsburg. The operational emissions associated with the Project would now be limited to the two diesel fire pumps, and the emission estimates presented in Table 4.2-11 of the Draft EIR would be reduced by approximately 66 percent (i.e., estimates based on combined 1,350 kilowatts [kW] of output; the elimination of the emergency generator would reduce the output by 900 kW, or about 66 percent).

3.3    GEOLOGIC RESOURCES AND SOILS

With implementation of Mitigation Measures GEO-1, GEO-2, GEO-3, GEO-4, and GEO-5, Impacts GEO-1 through GEO-5 (refer to Table 1-1 of this EIR Addendum) would all be reduced to a less than significant level. As discussed previously, with the adoption of the HVDC PLUS design the amount of grading and excavation at the San Francisco and Pittsburg converter station sites would be reduced, thereby reducing soil disturbance and erosion relative to the HVDC conventional design converter stations evaluated in the Draft and Final EIRs. In addition, the smaller HVDC PLUS converter station design (i.e., smaller footprint, less equipment, shorter structure heights) would reduce the facility's potential susceptibility to damage associated with strong ground shaking. The HVDC PLUS converter stations in San Francisco and Pittsburg would still be designed to conform with the Uniform Building Code requirements for Seismic Zone 4 as well as the provisions of the 2001 California Building Code.

3.4    WATER RESOURCES AND QUALITY

With implementation of Mitigation Measures WATER-1 through WATER-7, Impacts WATER-1 through WATER-7 would be reduced to a less than significant level (refer to Table 1-1 of this EIR Addendum). Impact WATER-8 (Flooding) applied to the northwest corner of the Pittsburg West Tenth Street Alternative 1 site as evaluated in the Draft and Final EIRs. With the adoption of the HVDC PLUS converter station design/layout, the location of the Pittsburg HVDC PLUS converter station on the eastern portion of the previously evaluated converter station site would avoid the Federal Emergency Management Agency (FEMA) designated 100-year floodplain, thus Impact WATER-8 (Flooding) no longer applies to the converter station. However, Impact WATER-8 does apply to a portion of the proposed temporary access road on the northerly portion of the property which connects the converter station site to the Mirant Power Plant access road. With implementation of Mitigation Measure WATER-8 (Flood Mitigation), this potentially significant impact would be reduced to a less-than-significant level.

3.5    TERRESTRIAL BIOLOGY

Construction of the proposed HVDC PLUS converter station at the San Francisco HWC (Mitigated) site would not potentially impact any terrestrial biological resources. Construction of the proposed HVDC PLUS converter station at the Pittsburg West Tenth Street Alternative 1 site, as modified, would also not potentially impact any terrestrial biological resources. However, construction of the proposed onshore AC/DC cable routes for the Pittsburg West Tenth Street site has the potential to impact sensitive biological resources (wetland, and potential Giant Garter Snake and Western Pond Turtle habitat associated with the wetland to the north of the Pittsburg West Tenth Street Converter Station site). With the adoption of HDD or Comparable Technology for AC/DC cable installation into the proposed Project in this area, impacts would be avoided.

3.6    MARINE BIOLOGICAL RESOURCES

No potentially significant impacts to marine biological resources are associated with the proposed HVDC PLUS Project, including consideration of the modified submarine cable design (refer to Section 2.4 for more information).

3.7    CULTURAL RESOURCES

3.7.1    Introduction

Construction of the proposed Project at the Pittsburg West Tenth Street Alternative 1 Converter Station site, as modified, would not potentially impact any cultural resources (archeological or historic resources). With implementation of Mitigation Measures CUL-3a through -3c, potentially significant impacts to archaeological resources (e.g., shipwrecks) associated with installation of the proposed HVDC submarine cable (Impact CUL-3) would be reduced to a less than significant level.

3.7.2    San Francisco HWC (Mitigated) Converter Station Site

Implementation of the proposed San Francisco converter station at the HWC (Mitigated) site has the potential to significantly impact buried archaeological resources (Impact CUL-1) as did the formerly proposed HWC (Mitigated) site. With implementation of Mitigation Measure CUL-1a through -1c, this potentially significant impact would be reduced to a less than significant level.

3.8    LAND USE AND RECREATION

3.8.1    San Francisco Converter Station

Section 4.A.8 (Land Use and Recreation) of the Final EIR addresses the environmental setting and environmental impacts of the San Francisco HWC (Mitigated) Converter Station site. No potentially significant impacts were identified in the Final EIR relative to Land Use and Recreation. The proposed refined proposed Project utilizing HVDC PLUS technology/design would increase the distances between the HWC (Mitigated) converter station facilities and potentially sensitive land uses (refer to Table 4.A.8-1 of the Final EIR) by approximately 90 feet. The HVDC PLUS design (i.e., versus conventional design evaluated in the Draft and Final EIRs) would allow the maximum converter station building height to be reduced from 64 to 35 feet, and the overall station footprint would be substantially reduced. Additionally, the approximate 90-foot buffer between the converter station boundary and the east side of Illinois Street associated with the HVDC PLUS design at this site would be landscaped, thereby increasing land use compatibility with the potential future mixed-used residential contemplated in the Draft Central Waterfront Neighborhood Plan.

In summary, the proposed Project refinements associated with utilization of the HVDC PLUS technology/design would be positive from a land use compatibility standpoint, and no potentially significant impacts relative to land use and recreation have been identified.

3.8.2    Pittsburg Converter Station

Section 5.4.8 (Land Use and Recreation) of the Draft EIR describes the environmental setting, environmental impacts, and mitigation measures for the Pittsburg West Tenth Street Alternative 1 site, which is identified as the proposed Pittsburg converter station site (as modified) in the Final EIR. Utilization of the HVDC PLUS converter station technology/design as assessed in this EIR Addendum allows for a smaller converter station footprint. The converter station site now encompasses only the eastern portion of the previously assessed Alternative 1 site plus a small portion (approximately 50 feet southward from the southern boundary of the previous Alternative 1 site) into what was the Pittsburg West Tenth Street Alternative 2 site as evaluated in the Draft and Final EIRs. The approximately 255-foot buffer area between the southern HVDC PLUS converter station boundary (modified Alternative 1 site) and the north side of West Tenth Street would potentially be landscaped following construction. An operational phase access road between the converter station and West Tenth Street would be constructed on the westernmost portion of Parcel 25 (refer to Figure 2.6-2 of this Addendum).

From a land use perspective, the key differences between the HVDC PLUS converter station layout on the Pittsburg West Tenth Street Alternative 1 site (modified) as assessed in this EIR Addendum and the West Tenth Street Alternative 1 site addressed in the Draft and Final EIRs are as follows:

• The Pittsburg West Tenth Street Alternative 1 facility location (modified) is approximately 400 feet north of the closest residential area (i.e., potentially sensitive land uses), which is south of West Tenth Street off Enterprise Street; the West Tenth Street Alternative 1 and 2 sites as assessed in the Draft and Final EIRs were 450 and 150 feet away from these residences, respectively (refer to Table 5.4.8-1 in the Draft EIR).


• The Pittsburg West Tenth Street Alternative 1 site (modified) includes an approximate 255-foot buffer between the southern converter station fence line and West Tenth Street; this area would potentially be landscaped to City of Pittsburg standards although final determinations regarding the future land use of this area have not been determined at this time.


• The westernmost portion of the Pittsburg West Tenth Street buffer area would be used for an operational access road.


• The proposed HVDC PLUS converter station design conforms with the conditions (e.g., 65-foot maximum building structure height and 250-foot setback from West Tenth Street) of the Pittsburg West Tenth Street zoning overlay amendment that was approved and adopted by the Pittsburg City Council on November 20, 2006.

In summary, the utilization of the HVDC PLUS technology/converter station design at the West Tenth Street site would not result in any identified potentially significant land use- or recreation-related impacts.

3.9    MARINE TRANSPORTATION AND COMMERCIAL FISHING

The adoption of the HVDC PLUS design for the converter stations in San Francisco and Pittsburg, including consideration of the modified HVDC submarine cable design as well as moving the San Francisco converter station from the HWC (Mitigated) site to the Mirant site would have no effect on the impact findings presented in the Draft and Final EIRs relative to marine transportation and commercial fishing (refer to Table 1-1 of this EIR Addendum).

3.10  TRAFFIC AND TRANSPORTATION

As discussed in Section 1.2.1 of this EIR Addendum, adoption of the HVDC PLUS converter station design requires an estimated 20 to 25 percent less materials and equipment deliveries relative to the HVDC conventional design evaluated in the Draft and Final EIRs. In addition, the overall intensity and/or duration of the construction phase would be reduced due to the smaller, less complex design associated with the HVDC PLUS technology.

The aforementioned aspects of the proposed HVDC PLUS design/layouts all contribute to reduced traffic and transportation related impacts from the Project relative to the HVDC conventional design evaluated in the Draft and Final EIRs.

Site access for the San Francisco HWC (Mitigated) HVDC PLUS Converter Station would be via 23^rd Street and via Illinois Street (refer to Figure 2.5-2 of this Addendum) near the intersection with 24^th Street, as was evaluated in the Final EIR (Section 4.A.10).

Site access during the operational phase for the Pittsburg West Tenth Street Alternative 1 site, as modified, would be via West Tenth Street (refer to Figures 2.6-1 and 2.6-2 of this Addendum) similar to the previously considered site except that the road would be situated further to the east for the HVDC PLUS site. Construction access to the Pittsburg West Tenth Street Alternative 1 site as evaluated in the Draft and Final EIRs involved use of the Mirant Pittsburg Power Plant access road as does this EIR Addendum although an extension would need to be constructed to the east to the modified site. None of these Project modifications would result in any new potentially significant traffic related impacts.

With implementation of Mitigation Measures TRAFFIC-1 through TRAFFIC-4, Impacts TRAFFIC-1 through TRAFFIC-4 would all be reduced to less than significant levels.

3.11  NOISE AND VIBRATION

3.11.1  San Francisco Converter Station

Section 4.A.11 (Noise and Vibration) of the Final EIR addresses the environmental setting and environmental impacts of the San Francisco HWC (Mitigated) Converter Station site. No potentially significant impacts were identified in the Final EIR relative to noise and vibration at this site. In addition, no potentially significant impacts related to noise and vibration are identified in this EIR Addendum for the HVDC PLUS design/layout.

The proposed Project utilizing HVDC PLUS technology/design would increase the distances between the HWC (Mitigated) Converter Station facilities and potentially sensitive receptors (refer to Table 4.A.11-1 of the Final EIR) by approximately 90 feet for the short-term pile driving portion of the construction phase as well as the operational phase due to the added 90-foot setback east of Illinois Street. The non-pile driving construction activities associated with demolition of existing buildings would still occur on the east side of Illinois Street in the area that would become an approximate 90-foot, landscaped buffer zone between Illinois Street and the converter station.

Section 4.A.11 of the Final EIR concluded that there were no potentially significant noise or vibration impacts associated with the HWC (Mitigated) site. With adoption of the HVDC PLUS technology/design, including the added 90-foot buffer from Illinois Street and the inherent lower operational noise levels associated with the HVDC PLUS converter station design, Project-related noise and vibration impacts would be reduced beyond those identified in the Final EIR. The following sections address construction and operational noise and vibration impacts for the HVDC PLUS design versus the conventional HVDC design evaluated in the final EIR.

3.11.1.1  Construction-related Impacts

Ambient noise measurement locations utilized to assess the HWC (Mitigated) site utilizing HVDC PLUS technology/design are the same as those presented in Section 4.11 of the Draft EIR for the previously proposed HWC site. The results of the ambient noise measurements are summarized in Table 4.11-2 of the Draft EIR. The measurement locations are shown on Figure 4.11-1 of the Draft EIR.

Sensitive receptors in the HWC (Mitigated) site Project area are the same as those identified for the previously proposed HWC site in Section 4.11 of the Draft EIR. They consist of multi-family residences approximately 480 feet west of the eastern side of Illinois Street at 2638 3^rd Street in between 22^nd and 23^rd streets and multi-family residences approximately 1,150 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 site. In addition, both residences are within 500 feet of Interstate 280 to the west.

Scheduled construction hours at the San Francisco HWC (Mitigated) Converter Station would be the same as those given for the previously proposed HWC Project site in Section 4.11 of the Draft EIR. The anticipated noise sources would be the same as those outlined in Section 4.11 of the Draft EIR.

Acoustical calculations were performed to estimate noise from construction activities at the closest residences with the same methodology as described for the previously proposed HWC site in Section 4.11 of the Draft EIR. The closest offsite residential uses to the San Francisco (Mitigated) Converter Station site consist of multi-family residences approximately 480 feet west and 1,150 feet to the west. Average construction sound levels at the closest residences to the San Francisco HWC (Mitigated) Converter Station construction site would be 69 and 62 dBA (A-weighted sound level), respectively, as summarized in Table 3.11-1. Because of the intermittent nature of construction work and he intervening buildings, it is unlikely that noise from construction 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 result in a less-than-significant impact.

3.11.1.1.1  Pile Driving. Calculations were performed to estimate sound levels from pile driving at the receptors. As shown in Table 3.11.1-1, the distance from pile driving activities to the closest receptors is approximately 90 feet greater than the distance for general construction since the HVDC PLUS design includes a 90-foot buffer between Illinois Street and the converter station. Direct line-of-sight sound levels at the residences were calculated to be 84 dBA maximum sound level (L_max) (79 dBA equivalent sound level [L_eq]) at the residences 570 feet west and 77 dBA L_max (72 dBA L_eq) at the residences 1,240 feet west. 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. Section 4.11.3.1.1 of the Draft EIR details pile driving restrictions to be followed in San Francisco. 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 of the Draft EIR. Vibration from pile driving was

TABLE 3.11.1-1
CALCULATED SOUND LEVELS FROM THE CONSTRUCTION OF THE
SAN FRANCISCO HWC (MITIGATED) CONVERTER STATION
UTILIZING HVDC PLUS DESIGN

¹        Applies to both HWC (Mitigated) sites evaluated in Final EIR and this EIR Addendum.

²        Applies to HWC (Mitigated) site as evaluated in this EIR Addendum; the comparable numbers presented in the Final EIR are all higher by approximately 1 dBA (i.e., pile driving impacts for HVDC PLUS design are lower in all cases).

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 the closest residences 570 feet from the pile driving would be 0.007 in/sec, which is well below the FTA threshold of 0.20 in/sec; resulting in a less-than-significant impact.

3.11.1.2  Operations-related Impacts

Calculations were performed by Siemens for the HVDC PLUS converter station design (refer to Appendix A of this EIR Addendum) using linear octave band sound power levels as inputs from each noise source. As shown on Figures 2.5-2 and 2.5-3 of this EIR Addendum, the proposed Project design for the San Francisco HWC (Mitigated) Converter Station includes an approximately 15-foot-tall sound wall along the western boundary and a 10-foot-tall sound wall along the southern and northern boundaries. A noise analysis was conducted for the HWC (Mitigated) site, and the results are summarized here and provided in Appendix A of this EIR Addendum.

As summarized in Table 3.3-2, hourly average sound levels from the San Francisco HWC (Mitigated) Converter Station utilizing the HVDC PLUS design and layout would range from 48 dBA L_eq on the western property line to 60 dBA L_eq at the eastern property line. Because sound levels are below the San Francisco 75 dBA L_eq requirement, there would not be a significant impact.

TABLE 3.11.1-2
CALCULATED SOUND LEVELS FROM OPERATION OF THE
SAN FRANCISCO HWC (MITIGATED) CONVERTER STATION
UTILIZING THE HVDC PLUS DESIGN

The L_dn are used by the State of California to define acceptable land use compatibility with respect to noise. Because of the time-of-day penalties 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_eq will be 6 dB lower than the L_dn value. Thus, the San Francisco noise ordinance requirement of 75 dBA L_eq (1 hr) at the property lines would be equivalent to 81 dBA L_dn. Comparing the calculated sound levels presented in Table 3.11.1-2 of this EIR Addendum (for HVDC PLUS design) with those presented in Table 4.A.11-2 of the Final EIR indicates that operational noise levels at the property site boundaries would all be substantially less for the HVDC PLUS design/layout.

3.11.1.3  Cumulative Impacts

The proposed San Francisco HWC (Mitigated) Converter Station site is located approximately 90 feet east of Illinois Street between 23^rd and 24^th streets. As discussed in Section 7.2.3.4 (Central Waterfront Neighborhood Plan [Plan]) of the Draft EIR, the City and County of San Francisco is considering rezoning the location of the overall HWC site to PDR (Production, Distribution, & Repair). In addition, the draft Plan envisions rezoning the west side of Illinois Street to mixed use residential. An assessment of the potential operational noise impacts of the proposed HWC (Mitigated) layout utilizing the HVDC PLUS design/layout, including the approximate 90-foot setback from Illinois Street, with the possible future mixed use residential development across Illinois Street follows. The calculated operational noise level on the west side of Illinois Street (approximately 170 feet west of converter station) is 44 dBA L_eq (50 dBA L_dn). This noise level is well below the current noise ordinance requirement as well as the currently applicable noise requirements for R1 and R2 residential zoning in San Francisco of 50 dBA from 10:00 p.m. to 7:00 a.m. In summary, no significant possible future cumulative noise impacts would be expected to occur.

3.11.2  Pittsburg Converter Station

3.11.2.1  Introduction

Sections 5.4.11 and 5.5.11 (Noise and Vibration) of the Draft EIR address the environmental setting and environmental impacts of the Pittsburg West Tenth Street Alternative 1 and Alternative 2 converter station sites, respectively. One potentially significant impact was identified in the Draft and Final EIRs relative to noise and vibration at the Alternative 1 site (Impact NOISE-1, Converter Station Operations Sound Levels). With implementation of Mitigation Measure NOISE-1 (Noise Barrier Installation for Converter Station), this impact would be reduced to a less than significant level. In addition, the noise and vibration assessments performed in this EIR Addendum for the HVDC PLUS design/layout at the Alternative 1 converter station site, as modified, indicate that no potentially significant noise or vibration impacts would occur during the construction or operational phases of the Project.

The proposed Project utilizing the HVDC PLUS design/layout at this site now encompasses only the eastern portion of the previously assessed Alternative 1 site plus a small portion (approximately 50 feet southward from the southern boundary of the previous Alternative 1 site) into what was the previous Alternative 2 site as assessed in Section 5.5.11 of the Draft EIR. The approximately 255-foot buffer area between the southern HVDC PLUS converter station layout boundary (modified Alternative 1 site) and the north side of West Tenth Street would potentially be landscaped following construction. To provide operational access to the site, a new access road would be constructed along the western portion of the overall site. This would require the removal of the existing structures (i.e., via demolition) on what was the southern portion of the Pittsburg West Tenth Street Alternative 2 site as evaluated in the Draft EIR (Section 5.5.11). The Alternative 1 and Alternative 2 sites as evaluated in the Draft EIR shared a common eastern boundary which is applicable to the HVDC PLUS layout/site as well. Therefore, the general construction noise assessment (excluding pile driving) presented in Section 5.5.11 of the Draft EIR for the Pittsburg West Tenth Street Alternative 2 site relative to the closest potentially sensitive receptors (i.e., single family residences south of West Tenth Street at 182 Builders Court [150 feet south of southernmost extent of general construction activities] and the single family residences at 900 Beacon Street [600 feet east of eastern converter station/property boundary]) are essentially the same for the HVDC plus design/layout with 255-foot buffer to the south. Examples of short-term, general construction activities that could occur in portions of the buffer area include demolition of existing buildings and construction of the permanent access road along the western border.

Short-term pile driving activities would only occur north of the 255-foot buffer above West Tenth Street and west of the eastern converter station boundary which is essentially the same for HVDC PLUS design/layout and the Pittsburg West Tenth Street Alternative 1 site evaluated in Section 5.4.11 of the Draft EIR. Due to the smaller footprint of the HVDC PLUS converter station layout and the reduction in the amount of equipment on the site, it is expected that the duration of pile driving activities would be reduced relative to that estimated in the Draft EIR.

For the HVDC PLUS design/layout operational phase noise and vibration impact assessment, the closest sensitive receptors (i.e., aforementioned residences to the south and east) are located approximately 405 feet to the south and 600 feet to the east.

The following sections address construction and operational noise and vibration impacts for the HVDC PLUS design/layout for the Pittsburg West Tenth Street Alternative 1 site, as modified, versus the HVDC conventional design/layout as evaluated in the Draft and Final EIRs.

3.11.2.2  Construction-related Impacts

As discussed in Section 5.4.11 of the Draft EIR, a series of sound level measurements was conducted on September 13 through 14, 2005, to quantify the existing acoustical environment for the Pittsburg West Tenth Street Converter Station site as well as at sensitive receptors near the site. The results of the measurements are summarized in Table 4.11-3, and the measurement locations are shown on Figure 4.11-2 of the Draft EIR.

Sensitive receptors in the vicinity of the Pittsburg Alternative 1 converter station site, as modified, are discussed in Section 3.11.2.1 of this EIR Addendum.

Scheduled construction hours at the Pittsburg West Tenth Street Converter Station site are consistent with those given in Section 4.11 of the Draft EIR (7:00 a.m. to 7:00 p.m.). Criteria are not set forth by the Pittsburg Noise Element or Noise Ordinance related to construction noise levels and times of operations. The anticipated noise sources would be the same as those outlined for the proposed Project site in Section 4.11 of the Draft EIR.

Acoustical calculations were performed to estimate noise from general construction activities at the closest residences with the same methodology as described for the Pittsburg Standard Oil Converter Station site in Section 4.11 of the Draft EIR. The closest offsite residential uses to the proposed West Tenth Street Converter Station Alternative 1 site, as modified to accommodate the HVDC PLUS design/layout, consist of residences approximately 150 feet south and 600 feet to the east. Average general construction sound levels at the closest residences to this alternative site would be 79 dBA 150 feet south and 67 dBA 600 feet east, as summarized in Table 3.11.2-1. Construction of the converter station facility (versus demolition and permanent access road construction in the buffer area to the south) would occur at least 405 feet north of the closest residences.

TABLE 3.11.2-1
CALCULATED SOUND LEVELS FROM CONSTRUCTION OF THE PITTSBURG WEST TENTH STREET ALTERNATIVE 1 CONVERTER STATION SITE
(AS MODIFIED) UTILIZING HVDC PLUS DESIGN

Construction noise would be audible at the residential receptors south of West Tenth Street. Once the initial demolition activities were completed in the southern buffer/setback area, general construction noise levels would drop at the receptors south of West Tenth Street. Construction noise would be intermittent and limited to the hours of 7:00 a.m. to 7:00 p.m. Monday through Friday; thus, there would be no significant impact.

3.11.2.2.1  Pile Driving. Calculations were performed to estimate sound levels from pile driving at the receptors. Direct line-of-sight sound levels at the closest residences from the West Tenth Street Converter Station Alternative 1 site, as modified, were calculated to be 87 dBA L_max (82 dBA L_eq). Pile driving is not subject to sound level restrictions in Pittsburg, but it is limited to the hours of 7:00 a.m. to 10:00 p.m. For this Project, the City of Pittsburg will further limit the permissible hours for pile driving to 7:00 a.m. to 5:00 p.m. This alternative could result in received noise levels as high as 82 dBA (L_eq) at the closest receptors. This noise level is less than the 90 dBA L_eq threshold of significance (FTA, 1995), and, therefore, would be less than significant.

Calculations were performed to estimate vibrations from pile driving activities at the closest residences. 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 405 feet from the pile driving under Alternative 1, as modified, would be less than 0.04 in/sec, which is well below the FTA threshold, resulting in a less than significant impact.

3.11.2.3  Operations-related Impacts

Calculations were performed using linear octave band sound power levels as inputs from each noise source. Siemens conducted the noise analysis, the results of which are summarized here and provided in Appendix A of this EIR Addendum. As summarized in Table 3.11.2-2, sound levels at the Pittsburg West Tenth Street Converter Station Alternative 1 site, as modified, utilizing the HVDC PLUS design/layout would not exceed the City of Pittsburg 75 L_dn requirement, and impacts would be less than significant. Therefore, Impact NOISE-1 (Converter Station Operations Sound Levels) and corresponding Mitigation Measure NOISE-1 (Noise Barrier Installation for Alternative Converter Station) as identified in the Draft and Final EIRs are no longer applicable and/or required. However, the Applicant has committed to implement Mitigation Measure NOISE-1 at this site by constructing a 10-foot-tall sound wall around the southern, western, and eastern site boundaries.

TABLE 3.11.2-2
CALCULATED SOUND LEVELS FROM OPERATION OF THE
PITTSBURG WEST TENTH STREET ALTERNATIVE 1 CONVERTER
STATION SITE (AS MODIFIED) UTILIZING HVDC PLUS DESIGN

¹ These calculated sound levels are all below the calculated sound levels at the closest receptors identified in the Draft EIR for both the Pittsburg West Tenth Street Alternative 1 and Alternative 2 sites.

In summary, implementation of the HVDC PLUS design converter station at the Pittsburg West Tenth Street Alternative 1 site, as modified, would not result in any potentially significant noise or vibration impacts.

3.12  PUBLIC SERVICES AND UTILITIES

The potentially significant public services and utilities related impacts of the proposed San Francisco HWC (Mitigated) and Pittsburg West Tenth Street Converter Station sites are the same as presented in Sections 5.2.12 and 5.4.12 of the Draft EIR, respectively with implementation of Mitigation Measures PS-1 (Construction Fire Prevention), PS-2 (Utility Survey), and PS-3 (Operations Fire Prevention), Impacts PS-1 (Construction Fire Hazard), PS-2 (Existing Onshore Underground Utilities), and PS-3 (Operations Fire Hazards) would all be reduced to less than significant levels.

3.13  VISUAL RESOURCES/AESTHETICS

3.13.1  Introduction

This section addresses the potential visual resource impacts of the converter stations in San Francisco and Pittsburg considering utilization of the HVDC PLUS design and layout instead of the HVDC conventional design evaluated in the Draft and Final EIRs. Key differences in the HVDC PLUS design addressed in this EIR Addendum relative to the HVDC conventional design evaluated in the Draft and Final EIRs from a visual perspective include:

• Smaller footprint required (i.e., approximately 3 to 4 acres needed for the converter station facilities versus the 5 to 6 acres needed for the conventional design evaluated in the Draft and Final EIRs).


• The converter building is only 35 feet tall versus the 64-foot tall structures associated with the conventional design.


• The HVDC PLUS design involves lightning arrestor poles that are 65 feet tall versus the 80-foot tall poles associated with the HVDC conventional design, and they would be fewer in number.


• The HVDC PLUS design avoids the need for outdoor filters and switch gear associated with the HVDC conventional design.


• The smaller footprint requirements provide the opportunity to establish greater setbacks/visual buffers on the given sites and thereby provide space for landscaping to provide visual screening and/or buffering for the San Francisco and Pittsburg converter station sites.

The visual analysis presented in this EIR Addendum addresses the San Francisco HWC (Mitigated) Converter Station site (subset of San Francisco HWC Mitigated site as evaluated in Section 4.A.13 of the Final EIR) and the Pittsburg West Tenth Street Alternative 1 site, as modified.

The concepts, terminology, and impact assessment methodology as well as the locations and descriptions of the key observation points (KOPs) used in the visual analysis are as described in Sections 4.13 (Draft EIR)/4.A.13 (Final EIR) for the San Francisco Converter Station site and Sections 5.4.13/5.5.13 for the Pittsburg West Tenth Street Converter Station site.

Site specific visual resource impact assessments follow for the San Francisco and Pittsburg converter stations utilizing the HVDC PLUS design/layouts and sites.

3.13.2  San Francisco Converter Station

The San Francisco HWC (Mitigated) Converter Station site is visible from Illinois Street and when viewing down both 23^rd and 24^th streets. All views are within the context of the existing Mirant Power Plant, the adjacent PG&E substation, or the Sheedy construction site. This is an existing industrial area both in terms of the visual context and the type of traffic traversing the area. The converter station site is also visible from the Potrero housing projects approximately 0.5 mile to the west. While the facility would be visible from a more birds-eye view, again it would be seen in the context of the larger industrial activity of the area, and the primary focus of any viewer would be toward San Francisco Bay in the background. The third viewing area is from Warm Water Cove Park which is located more than 200 feet east of the San Francisco HWC (Mitigated) Converter Station site. Existing views from this area are toward the Bay to the east and the existing industrial structures to the north, west, and south. In this context, the existing buildings to the west would be demolished and replaced by the proposed San Francisco HWC (Mitigated) Converter Station utilizing the smaller HVDC PLUS layout. The HVDC PLUS layout would be set back from Illinois Street by approximately 90 feet and would include a landscaped buffer area.

Operations-related impacts are defined as those impacts that would be visible while the converter station is in operation and visible over the lifetime of the structure. The potential for impacts is discussed on a key observation point (KOP)-by-KOP basis. Refer to Map 4.13-1 in the Draft EIR for KOP locations.

The proposed San Francisco HWC (Mitigated) Converter Station HVDC PLUS site is located on an approximately 3- to 4-acre site on the east of Illinois Street between 23^rd and 24^th streets. Use of this site as proposed would require removal of the existing Airgas/DHL warehouse and office structures. The most visible component would be the converter building structure, which has a ridgeline of approximately 35 feet in height. The electric switchyard includes a series of metal poles approximately 65 feet in height, which would be most visible from Illinois Street. An articulated 12- to 14-foot high screening wall with vines (similar to those utilized by the California Department of Transportation [Caltrans] in the San Francisco Bay area) is included as visual screening along the fence line. In addition, the 90-foot wide setback area between the converter station fence line and Illinois Street would be landscaped to provide screening and a visual buffer.

KOP SF-1: 23^rd Street at Illinois Street. From this location (see Photo A, Figure 3.13.2-1), the visual changes include the replacement of the large white masonry warehouse (Airgas/DHL) by the HVDC PLUS converter station (see Photo B, Figure 3.13.2-1). The
65-foot high metal poles and portions of the control building are visible above the screening wall (Photo B, Figure 3.13.2-1). From this KOP, while the visual character is more cluttered than the existing condition, the Project structures would be neither out of scale with the adjacent buildings nor would they unfavorably contrast with surrounding context; no scenic vista would be obscured. The landscape buffer area along Illinois Street is considered an improvement to the existing condition as well as an improvement to the HVDC conventional design evaluated in the Final EIR. The Impact Severity is classified as Low.

Since the Impact Susceptibility for the area is also Low, the resulting impact per the guidance provided in Table 4.13-2 of the Draft EIR would be less-than-significant for this KOP.

KOP SF-2: Potrero Hill. There are glimpsed views of the Project site for residents of the housing projects on Potrero Hill (see Photo A, Figure 3.13.2-2). However, as can be seen (Photo B, Figure 3.13.2-2), the view is relatively distant, and the converter station would replace structures of a similar size and character. The new structures would not project to a height that would significantly obscure views of San Francisco Bay. They are neither out of scale nor unfavorably contrasting. The Impact Severity is classified as Low. Since the Impact Susceptibility for the area is Low to Moderate, the resulting impact would be less than significant.

KOP SF-3: Warm Water Cove Park. The replacement of the existing warehouse structures (see Photo A, Figure 3.13.2-3) by the Project structures, generally of the same scale, would result in less visual clutter (Photo B, Figure 3.13.2-3). While a small portion of the view west towards Potrero Hill would be blocked, this is not considered a significant scenic vista. The increased visual impact of the building mass is considered somewhat offset by the reduced clutter and removal of the existing structures and related storage yards. The Impact Severity is considered Moderate. The Impact Susceptibility for the area is also Moderate given that the views from Warm Water Cove, a public place. The resulting impact would be considered adverse but less than significant.

KOP SF-5: 24^th Street at Illinois Street. From this location, the visual change would be the replacement of the large white Airgas/DHL warehouse office structure (see Photo A, Figure 3.13.2-4) with the converter building structure (Photo B, Figure 3.13.2-4). The 65-foot high metal poles are also visible above the screen wall (Photo B, Figure 3.13.2-4). The existing PG&E Potrero Substation is visible north of 23^rd Street on the left portion of the photo. From this KOP, the Project structure would be neither out of scale with the adjacent buildings nor would it unfavorably contrast with the existing surrounding context; no scenic vista would be obscured. The Impact Severity is classified as Low. The landscaped frontage along Illinois Street and along 24^th Street to Warm Water Cove Park is classified as an improvement on the existing condition, as well as an improvement to the HVDC conventional design evaluated in Section 4.A.13 of the Final EIR for the HWC (Mitigated) site. Since the Impact Susceptibility for the area is also Low, the resulting impact per Table 4.13-2 of the Draft EIR would be less than significant for this KOP. For comparison purposes, the photosimulation of the HWC (Mitigated) site utilizing the HVDC conventional design (Figure 4.A.13-4 of the Final EIR) is also presented herein.

Impact VIS-1A: HWC (Mitigated) Converter Station Domination of View. Since the architectural design character of the building and the general character of proposed landscaping have not been identified in detail, there is the possibility of generating potentially significant visual impacts based upon the potential of the Project to dominate the scene or become obtrusive on views from Warm Water Cove Park. This condition may also be true of the landscape screening wall proposed along Illinois, 23^rd, and 24^th streets.

While this impact has been classified as less than significant without design controls, it may still be adverse. This adversity can be lessened through the application of Mitigation Measures VIS-1a and VIS-1b. These measures are the same as those specified in the Final EIR, as certified.

Impact VIS-2: Converter Station Will Create Substantial Light and Glare. There is potential for the Project to cast more ambient light into the immediate area than the existing conditions. There is also the possibility that the luminaries of some of the lighting fixtures may be seen directly by either residents of Potrero Hill or visitors to Warm Water Cove Park, which through the abrupt contrast of the fixtures' light with the surrounding general darkness, may create the effect of glare. While this impact has been classified as less than significant, without design controls it may still be adverse. This adversity can be lessened through the application of Mitigation Measure VIS-2. This mitigation measure is the same as that specified in the Final EIR, as certified.

With implementation of the following mitigation measures, potential visual impacts associated with the HVDC PLUS converter stations at this site would be reduced further:

• Mitigation measures VIS-1a (Plan Submittal Requirements for Building Materials and Colors) and VIS-1b (Plan submittal Requirements for Landscaping) for Impact VIS-1 (Converter Station Domination of View


• Mitigation Measure VIS-2 (Plan Submittal Requirements for Lighting) for Impact VIS-2 (Converter Station will Create Substantial Light and Glare)

In conclusion, adoption of the HVDC PLUS design/layout, including the landscaped buffer along Illinois Street, versus the HVDC conventional design evaluated in the Draft and Final EIRs, would not result in any new potentially significant visual impacts and would actually reduce visual impacts compared to the previously proposed HVDC conventional design. This conclusion also applies to the possible mixed used residential development that may occur in the future on the west side of Illinois Street.

3.13.3  Pittsburg Converter Station

The Pittsburg West Tenth Street Alternative 1 Converter Station site, as modified, is located in a service-commercial area of Pittsburg, south of the existing Mirant Pittsburg Power Plant property and the existing PG&E Pittsburg substation. The site is located in the north-central portion of the overall West Tenth Street property. The Pittsburg West Tenth Street Alternative 1 site as modified to accommodate the HVDC PLUS design also includes a 255-foot buffer on the south to West Tenth Street. This area was previously part of the West Tenth Street Alternative 2 site. The existing buildings in this area would be removed. Once construction was completed, the area would potentially be landscaped to provide a visual buffer. The proposed converter station site is set north of the existing commercial frontage along West Tenth Street. It is located approximately 400 feet north of a residential community that was recently developed. The existing character in the area is one of wholesale and service commercial business of a relatively modest scale. To the north are a series of larger scale fuel tanks and the Mirant Pittsburg Power Plant with its substantial stack. There is relatively low-density commercial clutter on the north frontage of West Tenth Street with a backdrop of heavy industrial as indicated by the tanks and stacks. There are no scenic vistas or natural features. The visual quality is lacking in harmony and coherence. Visual quality is classified as Low. Traffic on West Tenth Street used to be predominantly commercial, but, recently, with the development of new housing tracts to the west of Pittsburg, there is an increasing amount of residential traffic as well.

Operations related impacts are assessed as follows by key observation point (KOP) (refer to Map 5.4-1 in the Draft EIR for locations).

KOP P-3 (West Tenth Street). Visual impacts of constructing the Project at this location (see Photo A, Figure 3.13.3-1) would be relatively minimal with consideration of utilization of the HVDC PLUS design/layout on the modified site with a 255-foot landscaped buffer area to the south (see Photo B, Figure 3.13.3-1). Photo B on Figure 3.13.3-2 provides a simulation of what the facility would look like if the 255-foot buffer was not landscaped. No scenic vistas would be blocked and the project character, seen in the context of the background fuel tanks and Mirant Pittsburg Power Plant would be in character. The 35-foot high control building would be co-dominant with other major features in this scene but would not be a prominent feature along West Tenth Street. The Impact Severity is classified Low. For comparison purposes, the photosimulation of the West Tenth Street Alternative 1 site utilizing the HVDC conventional design (Figure 5.4-2 of the Draft EIR) is also presented herein.

Light and glare would be a concern with the recent residential development south of West Tenth Street. However, given the distance from the converter station and the intervening screening by adjacent structures this would not be a significant issue if lighting design were controlled.

The Impact Susceptibility for the area is classified as Moderate, and the resulting impact would be less than significant. With implementation of the following mitigation measures, potential visual impacts associated with the HVDC PLUS converter stations at this site would be reduced further:

• Mitigation Measures VIS-1a (Plan Submittal Requirements for Building Materials and Colors) and VIS-1b (Plan Submittal Requirements for Landscaping) for Impact VIS-1 (Converter Station Domination of View)


• Mitigation Measure VIS-2 (Plan Submittal Requirements for Lighting) for Impact VIS-2 (Converter Station will Create Substantial Light and Glare)

These impacts and mitigation measures are the same as those presented in the Draft and Final EIRs for the Pittsburg West Tenth Street Alternative 1 site. No new potentially significant visual impacts have been identified for the HVDC PLUS design at the West Tenth Street Alternative 1 site, as modified, and the identified impacts are less than significant with implementation of the specified mitigation measures.

3.14  HAZARDOUS MATERIALS AND WASTE MANAGEMENT

3.14.1  San Francisco Converter Station

The hazardous material and waste management assessment for the San Francisco HWC (Mitigated) Converter Station site is as presented in Section 4.A.14 of the Final EIR. Soil and groundwater contamination are known to occur at the site, and the existing structures are known to have asbestos-containing materials and lead-based paint. The proposed HVDC PLUS converter station design/layout at the HWC (Mitigated) site would require less area and less earthwork/excavation than was previously associated with the HVDC conventional design evaluated in the Draft and Final EIRs. With implementation of Mitigation Measures HAZ-1 through HAZ-12, Impacts HAZ-1 through HAZ-12 would all be reduced to less than significant levels.

3.14.2  Pittsburg Converter Station Site

The hazardous material and waste management assessment for the proposed Pittsburg West Tenth Street site utilizing HVDC PLUS design/layout is as presented in Sections 5.4.14 (Alternative 1) and 5.5.14 (Alternative 2) of the Draft EIR. Since the HVDC PLUS layout is located on the eastern portion of the previously assessed Alternative 1 site (Draft and Final EIRs) and this area generally coincides with the northern portion of the previously assessed Alternative 2 site, the assessment presented in Section 5.5.14 of the Draft EIR is most applicable herein.

The proposed Pittsburg West Tenth Street Alternative 1 site, as modified, is known to have contaminated soil, asbestos containing building materials, and lead-based paint. With implementation of Mitigation Measures HAZ-1 through HAZ-12, potentially significant impacts HAZ-1 through HAZ-12 would all be reduced to less than significant levels.

3.15  PALEONTOLOGICAL RESOURCES

No fossil localities have been identified at the San Francisco HWC (Mitigated) (see Draft EIR Section 4.A.15) or Pittsburg West Tenth Street (see Draft EIR Section 5.4.15) converter station sites. However, construction excavations have the potential to penetrate into undisturbed Qal sediments which could contain significant fossil resources and thereby result in potentially significant impacts (Impact PALEO-1). With implementation of Mitigation Measure PALEO-1 (Potential Fossil Resources Protection), Impact PALEO-1 (Disturbance of Fossil Resources) would be reduced to a less than significant level.

3.16  SUMMARY AND CONCLUSION

While many impacts associated with implementation of the proposed Project are considered to be potentially significant, with implementation of the proposed mitigation measures no impacts would remain significant. The refinements and improvements that have been made to the proposed Project (i.e., utilization of the HVDC PLUS design) reduce the impacts of the Project as presented in the Final EIR and present no new potentially significant impacts.

3.16.1  Unavoidable Adverse Significant Impacts

This section of the EIR Addendum discusses unavoidable significant adverse impacts that would be expected to occur if the proposed Project as now proposed with the HVDC PLUS technology/design at the San Francisco HWC (Mitigated) and Pittsburg West Tenth Street converter station sites (as modified) was implemented. Unavoidable significant adverse impacts are those which cannot be reduced to a less-than-significant level. Approval and implementation of a project that involves unmitigable significant impacts typically requires a Statement of Overriding Considerations by the Lead Agency for CEQA compliance (i.e., City of Pittsburg for this Project) and/or other regulatory agencies with discretionary approvals (e.g., City and County of San Francisco).

No unavoidable adverse significant impacts have been identified for the refined proposed Project utilizing HVDC PLUS technology/design, including the San Francisco HWC (Mitigated) site, the modified Pittsburg West Tenth Street Alternative 1 (E/W) site, and the submarine cable.

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