SECTION 4.0

ENVIRONMENTAL SETTING, IMPACTS, AND MITIGATION

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PROPOSED PROJECT

4.3    Geologic Resources and Soils

This section addresses regional and site-specific geologic and seismic conditions, and discusses potential geologic and seismic hazards, as they might pertain to implementation of the proposed Project. San Francisco Bay sediments are addressed in Section 4.4, Water Resources and Quality. Paleontological Resources are discussed in Section 4.15, Paleontological Resources.

4.3.1    Environmental Setting

The study area for geology and seismic hazards for the proposed Project is the broad geographic area of northern San Francisco Bay, San Pablo Bay, and Suisun Bay. The following sections present the regional geologic and seismic settings, as well as geologic hazards, and local geology.

4.3.1.1    Regional Geology

General regional geology of the Project area is shown on Figure 4.3-1. The topography of the Bay Area consists of north- to northwest-trending mountain ranges and intervening valleys that are characteristic of the Coast Range geomorphic province. The Coast Ranges consist of the Mendocino Range to the north of San Francisco Bay, the Santa Cruz Mountains west of the Bay, and the Diablo Range to the east of the Bay. The San Andreas Fault Zone lies to the west, and represents a major boundary that separates Franciscan Complex rocks on the North American Plate from Salinian basement rocks of the Pacific Plate.

The geology of the San Francisco Bay Area is made up primarily of three different geologic provinces: the Salinian block, the Franciscan complex, and the Great Valley sequence. The Salinian block is located west of the San Andreas fault (see Figure 4.3-2) and is composed primarily of granitic plutonic rocks.

The Mesozoic Franciscan complex is bounded on the east side by the Hayward fault and on the west side by the San Andreas fault. The Franciscan rocks represent pieces of former oceanic crust that have been accreted to North America by subduction and collision. These rocks are primarily deep marine sandstone and shale. However, chert and limestone are also found within the assemblage. The rocks of the Franciscan complex are prone to landslides.

To the east of the Hayward fault is the Great Valley sequence. This is composed primarily of Cretaceous and Tertiary marine sedimentary rocks in the Bay Area. These rocks are also prone to landsliding.

The Coast Ranges represent northwest-southeast trending structural blocks comprised of a variety of basement lithologies that are juxtaposed by major geologic structures. The Coast Ranges-Sierran Block boundary zone lies to the east of the site. To the west, the major boundary is the San Andreas Fault Zone, which separates Franciscan Complex rocks of the North American plate from the Salinian basement rocks on the Pacific plate. The Coast Ranges ophiolites within the Franciscan Complex have been deformed by a series of thrust faults, most of which appear to be inactive.

The Diablo Range extends from the Sacramento River Delta, south along the western side of the San Joaquin Valley. Rocks of the Mesozoic Great Valley are thrust upon Franciscan basement along the San Joaquin Valley margin, and are covered locally by younger sediments of Paleocene to Pleistocene age.

Faults of the San Andreas system separate the Diablo Range from the remainder of the Coast Ranges. Mount Diablo is separated from the western East Bay hills by the Calaveras fault and from the southern extension of the Diablo Range by the Livermore Valley, an east-west-trending Cenozoic basin. The Diablo Range is bounded to the east by the Coast Range-Sierran Block boundary zone, which typically is represented by a series of blind and partially concealed thrust faults (Wong et al., 1988; Unruh and Moores, 1992). The eastern side of Mount Diablo is bounded by the San Joaquin fault (Sowers et al., 1992).

The Diablo Range comprises a series of large asymmetrical anticlines, with intervening synclines. The anticlines are composed of Franciscan Complex rocks, while the synclines contain younger rocks. The folds are frequently cut by east‑ and west-verging thrust faults. These thrust faults are displaced or truncated by strike-slip movement on the northwest-striking, right-lateral faults of the San Andreas fault system.

4.3.1.2    Regional Seismic Setting

The San Francisco Bay region is located on the boundary between the North American and Pacific tectonic plates. The Pacific plate is moving northwest relative to North America across a plate boundary oriented in a north-northwest direction that is approximately 100 kilometers wide. This zone encompasses all the major faults in Northern California (Figure 4.3-2). The relative motion across this plate boundary amounts to 35 to 38 millimeters per year, with the majority of this motion occurring during large earthquakes (Working Group on Northern California Earthquake Potential [WGNCEP], 1999). Seismically, this region is one of the most active in the world, highlighted by the number of large, damaging earthquakes that have occurred in the past. Major earthquakes have occurred along the margins of the Bay on the San Andreas and Hayward faults in 1836, 1838, 1868, and 1906 (Bakun, 1999). Some slip also occurs as aseismic fault creep (i.e., fault movement that does not generate earthquakes) on the Hayward, Concord, and Calaveras faults (Galehouse, 1992).

Faults of the San Andreas system form the major structural features in the vicinity of the study area. The San Andreas fault is the major tectonic boundary between the Pacific and North American plates. This portion of the San Andreas fault also marks the boundary with the less active San Francisco Bay block described by Olsen et al. (1994). The San Francisco Bay block is an area of low to moderate rates of seismicity and structural deformation, with no Holocene active tectonic features. The Hayward fault located approximately 10 miles to the east of the Bay block is another major active tectonic feature in the Bay Area and separates the Bay block from the East Bay hills. As described in the following sections, both the San Andreas and Hayward faults have generated major historical earthquakes and are considered to have a moderate probability of producing another major earthquake within the next 30 years.

Historical seismicity for the region is primarily associated with the strike-slip faults of the San Andreas system. Fourteen earthquakes of magnitude (M) 6.0 or greater have occurred in the Bay Area in historical times. Earthquakes of this magnitude pose significant ground-shaking hazard to the study area.

The most significant Quaternary faults in the region of the proposed Project, as well as estimates of the maximum earthquake for each fault, are listed in Table 4.3-1; their locations are shown on Figure 4.3-2. Maximum earthquake magnitude estimates are based on data from WGNCEP (1996). The table also indicates the closest distance from each fault to the Project sites. The proposed offshore cable alignment potentially crosses traces of both the Pittsburg-Kirby Hills Fault Zone and the Hayward-Rodgers Creek fault. Descriptions of the significant faults in the study area are described below.

4.3.1.2.1    San Gregorio Fault. The San Gregorio fault is a major Holocene active fault that lies west of the San Andreas fault. It extends from Big Sur northward to the area offshore of Bolinas Bay. Most of the fault lies offshore; however, in several areas the fault lies onshore and has been actively investigated (Simpson et al., 1992). The fault has an estimated Quaternary slip rate of 5 millimeters per year (mm/yr). Paleoseismic estimates of earthquake recurrence intervals on the fault range from 350 to 680 years based on offset archaeological remains at Seal Cove (Simpson et al., 1992). The maximum earthquake magnitude for the San Gregorio fault is estimated to be approximately Moment Magnitude (M_W) 7.3. M_W refers to measurement of earthquake size based on the energy released. The amount of energy released during an earthquake is a function of the surface area of the fault that has slipped, the amount of slip, and the rigidity of the rock through which the fault passes.

4.3.1.2.2    San Andreas Fault. The San Andreas fault is the largest active fault in California, and extends from the Gulf of California to Cape Mendocino. It was the source of the 1906 M_W 7.9 San Francisco earthquake (Wallace, 1990). In the Bay Area, various segments of the fault include the southern Santa Cruz Mountains, possible source of

TABLE 4.3-1
MAXIMUM EARTHQUAKE POTENTIALS FOR FAULTS
PROXIMAL TO THE PROPOSED SAN FRANCISCO AND PITTSBURG PROJECT SITES

the 1989 M_W 7.0 Loma Prieta earthquake; the Peninsula segment; and the North Coast segment. These segments have been assigned maximum earthquakes of M_W 7, M_W 7.1, and M_W 7.9, respectively, by WGNCEP (1996).

4.3.1.2.3    Hayward Fault. The Hayward fault is approximately 62 miles long and has been divided into two fault segments: a longer southern segment and a shorter northern segment. This structure is considered to be the most likely source of the next major earthquake in the San Francisco Bay Area (WGNCEP, 1996). The WGNCEP (1996) has assigned maximum earthquakes of M_W 6.9 for both the northern and southern segments of the Hayward fault. The proposed submarine cable route traverses the Hayward-Rodgers Creek fault north of Point Pinole in San Pablo Bay.

4.3.1.2.4    Rodgers Creek Fault. The Rodgers Creek fault is a 38-mile-long, northwest-striking, right-lateral strike-slip fault that extends northward from the projection of the Hayward fault on the south side of San Pablo Bay. Paleoseismic investigations by Schwartz et al. (1992) identified evidence for three earthquakes in the last 925 to 1,000 years, yielding a predicted earthquake recurrence interval of 230 years for an earthquake of M_W 7.0.

4.3.1.2.5    Calaveras Fault. The 75-mile-long Calaveras fault represents a significant seismic source in the southern and eastern San Francisco Bay region. It extends from an intersection with the Paicines fault south of Hollister, through the Diablo Range east of San Jose, and along the Pleasanton-Dublin-San Ramon urban corridor. The fault consists of three major sections: the southern Calaveras fault (from the Paicines fault to San Felipe Lake), the central Calaveras fault (from San Felipe Lake to Calaveras Reservoir), and the northern Calaveras fault (from Calaveras Reservoir to Danville). The level of contemporary seismicity along the southern section is low to moderate, whereas the central section has generated numerous moderate earthquakes in historic time. The northern section has a relatively low level of seismicity and may be locked. Paleoseismologic studies suggest a recurrence interval for large ruptures of between 250 and 850 years on the northern fault section. The timing of the most recent rupture on the northern Calaveras fault is unknown, but it may have occurred several hundred years ago (Kelson, 1999). Seismologic evidence suggests that the southern and central sections may produce earthquakes as large as M_W 6.2. Geologic and seismologic data suggest that the northern section may produce earthquakes as large as M_W 7.0.

4.3.1.2.6    Concord-Green Valley Fault Zone. The Concord-Green Valley fault is a northwest-striking, right-lateral strike-slip fault zone that extends from the Walnut Creek area across Suisun Bay and continues to the north. The Concord fault extends approximately 12 miles, from the northern slopes of Mt. Diablo to Suisun Bay. North of Suisun Bay, the Green Valley fault continues to the north about 28 miles. The Concord fault is an actively creeping structure that has a long-term creep rate of approximately 5 mm/yr. It is estimated that rupture of both faults would produce a maximum earthquake of about M_W 6.9 with a recurrence interval of approximately 180 years (WGNCEP, 1996).

4.3.1.2.7    Greenville-Marsh Creek Fault. The Greenville-Marsh Creek fault is a northwest-striking strike-slip fault of the San Andreas system in the northern Diablo Range, extending from Bear Valley to the east side of Mount Diablo. This fault has a lower slip rate than other structures within the San Andreas system with a long-term rate of approximately 1 to 3 mm/yr. This fault produced a moderate magnitude earthquake in 1980. Research is currently being conducted on the fault zone to better constrain its slip rate and its history of past earthquakes. WGNCEP (1996) assigned a maximum earthquake of M_W 6.9 to the Greenville fault; the recurrence interval is estimated to be about 550 years.

4.3.1.2.8    West Napa Fault. The West Napa fault consists of a north-northwest-striking zone of short right-lateral strike-slip fault segments in the hills to the west of the city of Napa (Bryant, 1982). The fault extends about 19 miles from Napa to Yountville. It is characterized by well-defined active fault features such as tonal lineations, scarps in late Pleistocene and Holocene alluvium, closed depressions, and right-laterally deflected drainages. WGNCEP (1996) has assigned a maximum earthquake of M_W 6.5 for the West Napa fault based on fault length and continuity.

4.3.1.2.9    Coast Range-Sierran Block Boundary Zone. The Coast Range-Sierran Block (CRSB) boundary zone consists of a complex zone of thrust faulting marking the boundary between the Coast Ranges block and the Sierran basement rocks concealed beneath the Great Valley sedimentary sequence of the Sacramento and San Joaquin valleys. The basal detachment within the CRSB is a low-angle, west-dipping thrust accommodating eastward thrusting of the Coast Range block over the Sierran block. Above this detachment is a complex array of west-dipping thrusts and east-dipping back-thrusts. The CRSB extends from near Red Bluff in the northern Sacramento Valley to Wheeler Ridge in the southern San Joaquin Valley (Wong et al., 1988; Wakabayashi and Smith, 1994).

The CRSB was the probable source of the two M_W 6.25 to 6.75 earthquakes recorded in 1892 near Winters, and the 1983 M_W 6.5 Coalinga earthquake in the western San Joaquin Valley (Wong et al., 1988). Although the faults themselves do not have surface expression, the CRSB is marked by an alignment of fault-propagation folds such as the Rumsey Hills along much of its length (Unruh and Moores, 1992). Empirical relationships between fault length and earthquake magnitude suggest that these segments of the CRSB are capable of generating maximum earthquakes of M_W 6.5 to 6.75, with an average recurrence interval of 360 to 440 years (Wakabayashi and Smith, 1994).

4.3.1.2.10  Pittsburg-Kirby Hills Fault. The Pittsburg-Kirby Hills fault extends a distance of approximately 26 miles from the Kirby Hills north of the Sacramento River, to the eastern flank of Mount Diablo, south of Pittsburg (refer to Figure 4.3-2). Unruh and Sawyer (1997) suggest that the structure is a right-lateral tear fault bounding the eastern margin of a series of thrusts and folds in the Grizzly Bay-Van Sickle Island area. The fault is defined by a linear alignment of microseismicity, which is unusual in that it occurs at depths of 20 to 25 kilometers (Wong et al., 1988). Focal mechanisms indicate that the movement on the fault is almost pure right-lateral strike-slip. Empirical relationships among various fault parameters and earthquake magnitude indicate that the maximum earthquake for the fault is M_W 6.75 (Wells and Coppersmith, 1994). The Pittsburg thrust has been considered to be a potentially active trace (Williams, 1998). In the vicinity of Pittsburg, the fault is defined as the Pittsburgh-Kirby Hills Fault Zone (refer to Figure 4.3-5) and is located approximately 1.1 miles to the west of the Standard Oil site. However, a recent fault rupture hazard investigation for the proposed Mariner Walk housing development at Herb White Way and 8^th Avenue in Pittsburg (Terrasearch, 2005) found no evidence that the fault is active in the Project vicinity. The investigation included a series of trenches across the fault zone as well as review of previous boring data.

4.3.1.2.11  Mount Diablo Thrust Fault. The Mount Diablo thrust fault is a northeast-dipping structure located beneath the Mount Diablo anticline. Unruh and Sawyer (1997) estimated long-term average Quaternary shortening rates across the Mount Diablo region, from balanced cross sections, to be 3.4 ± 0.9 mm/yr. Taking into consideration the presumed fault geometry, an average slip rate for the Mount Diablo thrust is calculated to be approximately 4.1 ± 1.4 mm/yr. This blind thrust fault is judged capable of generating a maximum earthquake of M_W 6.25.

4.3.1.2.12  Antioch Fault. The Antioch fault was previously considered active and was zoned under the Alquist-Priolo Act as potentially capable of surface rupture. A recent study by Wills (1992) indicates that the Antioch fault is not active and does not pose a surface-faulting hazard. The fault is no longer zoned by the State of California as an earthquake fault zone under the Alquist-Priolo Act.

The majority of contemporary seismicity in the San Francisco Bay Area is associated with the major faults, namely, the Hayward, Rodgers Creek, San Gregorio, Calaveras, and San Andreas faults, or related secondary structures located within about 5 kilometers (km) of the major faults (Zoback et al., 1999).

4.3.1.3    Geologic Hazards

4.3.1.3.1    Surface Fault Rupture. Surface fault rupture is defined as slip on a fault plane that has propagated upward to, and offsetting or disturbing, the earth's surface. Offset on a fault intersecting the ground surface can create a discrete step or fault scarp if fault slip occurs on a single fault plane or within a narrow fault zone. If fault slip is accommodated over a broader area, then the deformation may manifest as a zone of fracturing and ground cracking, with minor amounts of offset on individual fractures. However, the cumulative offset across the entire zone may be significant. Surface faulting may also arise as a secondary effect from other geologic processes. Secondary surface faulting can be triggered by aquifer compaction and subsidence or by the effects of strong ground shaking triggering slip on neighboring faults. Surface fault rupture has occurred on a number of faults within the study region during the last 10,000 years. The San Andreas, Hayward, Calaveras, and Greenville faults have all experienced surface rupture associated with large, damaging earthquakes during historical time (Figure 4.3-2).

4.3.1.3.2    Earthquake Ground Shaking. Strong earthquake ground shaking is probably the most important seismic hazard that can be expected anywhere in the San Francisco Bay Area. The amount of earthquake shaking at a site is a function of earthquake magnitude; the type of earthquake source (i.e., type of fault); distance between the site and the earthquake source; the geology of the site; and how the earthquake waves attenuate (decrease) or amplify (increase) as they travel from their source to the site in question. The larger the earthquake and the shorter the distance between the earthquake source and the site, the greater the amount of shaking. The geologic materials through which the earthquake energy travels toward the site act to attenuate the amount of shaking. Conversely, softer soils and topographic ridges can amplify seismic ground motions.

Liquefaction. Liquefaction is a phenomenon in which the strength and stiffness of a saturated granular soil is reduced by earthquake shaking. Liquefaction and related phenomena have been responsible for tremendous amounts of damage by historical earthquakes around the world.

Liquefaction is the transformation of a granular material from a solid state into a liquefied state as a consequence of increased pore pressure and decreased effective stress. Observed types of ground failure resulting from liquefaction can include sand boils, lateral spreads, ground settlement, ground cracking, and ground warping. Liquefaction occurs in saturated soils of low density.

Lateral spread is the lateral displacement of surficial blocks of sediment as the result of liquefaction in the subsurface. Once liquefaction transforms the subsurface layer into a fluidized mass, gravity may cause the mass to move downslope toward a cut slope or free face (such as a river channel or a canal). Lateral spreads most commonly occur on gentle slopes that range between 0.3 degrees and 3 degrees. When liquefaction occurs, the strength of the soil decreases and the ability of a soil deposit to support foundations for buildings or other structures is reduced. Liquefied soil also exerts higher pressure on retaining walls, which can cause them to tilt or slide. This movement can cause settlement of the retained soil and destruction of structures on the ground surface. Extensive liquefaction was triggered by the 1906 M_W 7.9 San Francisco earthquake, resulting in widespread damage in areas of loose, saturated soils. Liquefaction also resulted locally in major damage during the 1989 M_W 6.9 Loma Prieta earthquake.

4.3.1.3.3    Subsidence. Land surface subsidence can result from both natural and man-made phenomena. Natural phenomena include subsidence resulting from tectonic deformations and seismically induced settlements (see liquefaction); soil subsidence due to consolidation; subsidence due to oxidation or dewatering of organic-rich soils: and subsidence related to subsurface cavities. Subsidence or settlement related to human activities includes subsidence caused by decreased pore pressure due to the withdrawal of subsurface fluids, including water and hydrocarbons.

4.3.1.3.4    Expansive Soils. Expansive soils contain mixed-layer clay minerals that increase and decrease in volume upon wetting and drying, respectively. Expansive soils are common throughout California and can cause damage to foundations and slabs unless properly treated during construction. Most fine-grained deposits along the margins of San Francisco Bay contain clay layers and exhibit expansive or potentially expansive behavior. However, the hazard for expansive behavior is considered a low risk for coastal locations in and around the Bay Area because these areas are permanently saturated.

4.3.1.3.5    Asbestos-containing Serpentine Excavation. Asbestos is a term used for several types of naturally occurring fibrous minerals that are a human health hazard when airborne. Serpentinite may contain chrysotile asbestos, especially near fault zones. Ultramafic rock, a rock closely related to serpentinite, may also contain asbestos minerals. Asbestos is classified as a known human carcinogen by state, federal, and international agencies and was identified as a toxic air contaminant by the California Air Resources Board (CARB) in 1986.

Asbestos can be released from serpentine and ultramafic rocks when the rock is broken or crushed. At the point of release, the asbestos fibers may become airborne, causing human health hazards. Asbestos may be released to the atmosphere due to vehicular traffic on unpaved roads, during grading for development projects, and at quarry operations. All of these activities may have the effect of releasing potentially harmful asbestos into the air. Natural weathering and erosion processes can also act on asbestos-bearing rock and make it easier for asbestos fibers to become airborne if such rock is disturbed.

CEQA provides an opportunity for lead agencies to identify whether serpentinite or ultramafic rocks would be disturbed by the proposed Project, to investigate ways to avoid, control, or otherwise mitigate the impacts and gives lead agencies the authority to require mitigation measures as a condition of the approval of a proposed Project. CARB has developed a list of mitigation measures that can reduce asbestos emissions during the design, construction, and operation phases of projects. These have been incorporated into Mitigation GEO-2 in Section 4.3.3.2.1.

4.3.1.4    Local Geologic Setting

4.3.1.4.1    San Francisco HWC Converter Station. The San Francisco HWC Converter Station discussion includes the onshore AC and DC cable routes and the proposed and alternative construction laydown areas as shown on Figure 4.3-3.

Site Geology. The majority of the San Francisco peninsula near the proposed Project is comprised of Franciscan complex serpentinites (Schlocker, 1974), which are locally overlain by Holocene Bay Mud, late Pleistocene alluvial deposits, and eolian deposits of the Colma formation. Along the western portion of the peninsula, and within the Colma Valley to the south of the site, Neogene rocks of the Merced and Colma formations unconformably overlie rocks of the Franciscan complex.

The geology of the San Francisco area is shown on Figure 4.3-3. Soil types are shown on Figure 4.3-4. The proposed San Francisco HWC Converter Station site is underlain by Pleistocene and Holocene alluvial deposits and by artificial fill over reclaimed tidal flats featuring Bay Mud and estuarine deposits. The northwestern portion of the site is underlain by Franciscan serpentine bedrock at depth. The artificial fill consist of gravels, sands, and clays.

The proposed laydown area of up to 7 acres (located at the Western Pacific site) (Figure 4.3-3) would be devoted to equipment and materials laydown, storage, parking of construction equipment, small fabrication areas, and office trailers for the San Francisco HWC Converter Station site. The proposed laydown area as well as the alternative laydown area (at Pier 94/96) are located on Quaternary alluvial deposits locally overlain by fill.

Geologic Resources. The converter station site does not have any identified unique geologic features or resources.

Faults. The closest known active faults are the San Andreas fault (9.5 miles to the west of the site) and the Hayward fault (12 miles to the east of the site). Figure 4.3-2 illustrates the location of the site with respect to the major Quaternary faults in the site region. Table 4.3-1 presents maximum earthquake magnitude estimates based on WGNCEP (1996) and indicates the closest distance from each fault to the site. Each fault zone is described in detail in Section 4.3.1.2.

4.3.1.4.2    Pittsburg Standard Oil Converter Station. The discussion for the proposed Standard Oil site includes the onshore AC/DC cable, as well as proposed and alternative laydown areas and access roads. The converter station site is a 7.5-acre parcel within an industrial area in Pittsburg. The converter station location is shown on Figure 4.3-5. The site contains two abandoned concrete wastewater storage tanks and a small dilapidated building. The remainder of the site has been intermittently occupied by an automobile storage yard. There is very little vegetation on the relatively flat potion of the site where the converter station would be located. The southernmost edge of the site is bordered by Kirker Creek, just north of the Pittsburg/Antioch Highway. The proposed access road crosses over a channelized portion of Kirker Creek.

Site Geology. The Pittsburg Standard Oil Converter Station site is located approximately 3,600 feet southwest of New York Slough. The geology of the Pittsburg area is shown on Figure 4.3-5. Soil types are shown on Figure 4.3-6. The soils in the area are flatland soils (soils with slopes between 0 and 20 percent) (City of Pittsburg, 2001). They are mostly clays and loams of Pleistocene alluvial and fluvial deposits. The proposed and alternative access roads and laydown areas are underlain by the same Pleistocene alluvial and fluvial deposits as the proposed converter station site.

Geologic Resources. The converter station site does not have any identified unique geologic features or resources.

Faults. Figure 4.3-2 illustrates the location of the site with respect to the major Quaternary faults in the site region. Table 4.3-1 presents maximum earthquake magnitude estimates based on WGNCEP (1996) and indicates the closest distance from each fault to the site. The Pittsburg-Kirby Hills Fault Zone is approximately 1.1 miles west of the site and the Greenville Fault is approximately 8 miles southwest of the site. The Pittsburg-Kirby Hills Fault Zone, the Greenville Fault, and other regional fault zones are described in detail in Section 4.3.1.2.

4.3.1.4.3    Offshore DC Cable Route. San Francisco Bay is California's largest estuarine system, and its configuration and the surrounding landscape have been shaped by a combination of tectonic activity, recent sea level changes, and human activities. Along the centerline of the Bay, the majority of the bottom consists of thick sequences of Younger Bay Mud (very fine soft silty clays), underlain by Older Bay Mud (more cohesive silty clays). Nearer the margins, sediments tend to be coarser, with interbedded layers of Bay Mud and layers of fine to coarse sand, shell deposits, and occasional layers of peat.

The proposed cable system would be buried underwater and routed from the Pittsburg Converter Station into the water at Suisun Bay and New York Slough, through Carquinez Strait, San Pablo Bay, and San Francisco Bay to a landing point near the San Francisco Converter Station. The cable system route has been selected to avoid shipping channels, anchorages, dredge disposal areas, and all other known obstacles to the greatest extent possible.

The proposed cable route traverses the Pittsburg-Kirby Hills Fault Zone (refer to Figure 4.3-5) and the Hayward-Rodgers Creek fault north of Point Pinole in San Pablo Bay.

Before cable laying commenced, a detailed survey of the Bay floor would be conducted over a study corridor centered on the HVDC cable. Sonar devices would be used to detect both natural and man-made obstructions. Electromagnetic devices would be used to detect and precisely locate existing cables and pipelines that cross the cable path.

4.3.2    Regulatory Setting

4.3.2.1    Federal

No federal regulations related to geologic hazards and conditions have been identified for the proposed Project.

4.3.2.2    State

4.3.2.2.1    California Building Code. The California Building Code (CBC) contains the minimum standards for design and construction of structures in California. Local standards other than the CBC may be adopted if those standards are stricter. Design considerations associated with seismic hazards would need to address the appropriate building codes for each converter station facility location. The CBC includes the standards associated with seismic engineering detailed in the Uniform Building Code (UBC) of 1997.

4.3.2.2.2    California Public Resources Code Section 25523(a); 20 CCR 1752(b) and (c); 1972 Alquist-Priolo Earthquake Fault Zoning Act (Amended 1994). The Alquist-Priolo (AP) Earthquake Fault Zoning Act was passed in 1972 to mitigate the hazard of surface faulting to structures for human occupancy. Its main purpose is to prevent the construction of buildings used for human occupancy on the surface trace of active faults.

Before a project can be permitted in an Alquist-Priolo Earthquake Fault Zone, cities and counties must require a geologic investigation to demonstrate that potential buildings will not be constructed across active faults. An evaluation and written report of a specific site must be prepared by a licensed geologist. If an active fault is found, a structure for human occupancy cannot be placed over the trace of the fault and must be set back from the fault (generally 50 feet).

Fault rupture hazard is generally assessed for specific sites and ranked as follows: High (located within an AP Earthquake Fault Zone), Moderate (located adjacent to an AP Zone), and Low (located away from known AP Zones).

4.3.2.2.3    California Public Resources Code Chapter 7.8, 1990 Seismic Hazards Mapping Act. The Seismic Hazards Mapping Act of 1990 allows the lead agency to withhold permits until geologic investigations are conducted and mitigation measures are incorporated into plans. The Seismic Hazards Mapping Act addresses not only seismically induced hazards but also expansive soils, settlement, and slope stability.

4.3.2.3    Local

4.3.2.3.1    City of Pittsburg General Plan. The Health and Safety Element of the General Plan identifies various hazards that may occur in the City of Pittsburg. It gives basic policies that consider geologic conditions in the selection of land for development and the design of developments in order to preserve life and protect property in the event of a disaster.

The Resource Conservation Element of the General Plan identifies the City's basic policies pertaining to natural resources, including soil and water resources.

4.3.2.3.2    Public Health Code. Article 22A of the City and County of San Francisco Public Health Code governs development of properties located in the filled land adjacent to San Francisco Bay with respect to hazardous materials that would be encountered during construction. Formerly known as the Maher Ordinance, it stipulates testing and reporting protocols for proposed developments in its area of jurisdiction.

4.3.2.3.3    Local Building Code. Acceptable design criteria for excavations and structures for static and dynamic loading conditions are specified by the Uniform Building Code (UBC) of 1997. The City of Pittsburg has adopted the UBC per Section 15.08.010 of the Municipal Code. The San Francisco Building Code (SFBC) adopts the UBC and CBC, including Chapter 70, which establishes excavation, grading, and erosion control standards.

4.3.3    Environmental Impacts

The following section discusses potential impacts to and from the geologic environment for the proposed Project. Geologic hazards considered include surface fault rupture, earthquake ground shaking, liquefaction, expansive soils, subsidence, and soil erosion. Mitigation measures to reduce the various geologic hazards are presented, as applicable.

4.3.3.1      Thresholds of Significance

Based on CEQA Guidelines (Appendix G), impacts would be considered significant if they would:

• Expose people or structures to potential substantial adverse effects, including the risk of loss, injury or death involving rupture of a known earthquake fault, strong seismic ground shaking, seismic-related ground failure, including liquefaction, or landslides

• Result in substantial soil erosion or loss of topsoil

• Be located on a geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on or offsite landslide, lateral spreading, subsidence, liquefaction or collapse

• Be located on expansive soil as defined in Table 18-1-B of the Uniform Building Code (1997), creating substantial risks to life or property

4.3.3.2    San Francisco HWC Converter Station

4.3.3.2.1    Construction-related Impacts.

Soil Erosion. Construction, including demolition, excavation and grading of the site, could lead to soil erosion. Soil erosion causes the loss of topsoil and can increase the sediment load in surface receiving waters downstream of the construction site. Surface erosion resulting from construction of the proposed Project could also have a local impact on water quality, which is discussed in Section 4.4, Water Resources and Quality.

Construction of the proposed Project would also result in soil compaction due to the erection of foundations and paving. In addition, soil compaction would result from vehicular traffic along temporary access roads and in construction laydown areas (if not paved). Compaction densifies the soil, reducing pore space, and impeding water and gas movement through this medium. This can result in increased runoff, erosion, and sedimentation.

Impact GEO-1: Soil Erosion and Compaction. Construction activities would lead to soil compaction and could lead to soil erosion. This impact is considered to be potentially significant.

Mitigation Measure GEO-1: Design Project for Erosion Control. Standard Best Management Practices (BMPs) shall be incorporated into the Storm Water Pollution Prevention Plans (SWPPPs) for construction and operation, and shall minimize onsite soil erosion and offsite sedimentation. Temporary erosion control measures shall be required during the construction period to help maintain water quality, protect property from erosion damage, and prevent accelerated soil erosion or dust generation. These measures shall be installed before construction begins and shall be removed after completion and shall include the following:

• Temporary erosion control measures include slope stabilizers, dust suppression, construction of berms and ditches, and sediment barriers.

• During construction of the proposed Project, dust erosion control measures shall be employed to minimize wind erosion and loss of soil. Clean water shall be sprayed on the soil in construction areas to minimize wind erosion.

• Sediment barriers, such as straw bales or silt fences, slow runoff and trap sediment. These are generally placed below disturbed areas, at the base of exposed slopes. Sediment barriers are often placed around sensitive areas, such as wetlands or creeks, to prevent contamination by sediment-laden water. Barriers shall be placed around the proposed Project site, including ancillary facilities, to prevent sediment from leaving the site. Because the sites are relatively level, standard surface erosion control techniques should be effective. The need for runoff retention basins, drainage diversions, and other large‑scale sediment traps shall be evaluated and incorporated into the construction SWPPP, as appropriate. Soil stockpiles generated during construction shall be covered and protected from rainfall if left onsite for long periods of time.

• Temporary erosion control devices shall be installed in accordance with the required Construction SWPPP before initial site clearing and shall be visually inspected during the regular site environmental compliance inspections.

Implementation Responsibility:  Project proponent/construction contractor

Requirements and Timing:         Notice of Intent (NOI) submitted to RWQCB prior to construction

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance with SWPPP over course of construction

Resulting Level of Significance. Implementation of Mitigation Measure GEO-1 would reduce Impact GEO-1 to a less-than-significant level.

Asbestos-containing Serpentine Excavation. The HWC site may be underlain by serpentinite within the footprint of the proposed Project. Excavation of serpentine could expose asbestos, which is a human health hazard when airborne. Ultramafic rock, a rock closely related to serpentinite, may also contain asbestos minerals. Asbestos is classified as a known human carcinogen by state, federal, and international agencies and was identified as a toxic air contaminant by CARB in 1986. Asbestos could be released from serpentine and ultramafic rocks when the rock is broken or crushed. It can become airborne from wind, due to vehicular traffic on unpaved roads, during grading for development projects, and at quarry operations.

Impact GEO-2: Asbestos-containing Serpentine. The San Francisco site is potentially underlain with asbestos-containing soils and rocks. Asbestos could be released during construction phases at the San Francisco sites. Asbestos is a human health hazard when airborne. This is considered a potentially significant impact.

Mitigation Measure GEO-2: Controls for Excavation of Serpentine. Prior to Project construction, previously-prepared geotechnical reports and boring and trenching logs from the site would be reviewed to identify areas of serpentinite bedrock that would be disturbed during excavation and Project construction. An Asbestos Dust Mitigation Plan would be submitted to the Bay Area Air Quality Management District (BAAQMD) for approval in accordance with the Final Regulation Order Asbestos Airborne Toxic Control Measure for Construction, Grading, Quarrying, and Surface Mining Operations. The Asbestos Dust Mitigation Plan would address the following:

• Prevention of dust emissions offsite

• Control of dust for disturbed areas and storage piles

• Traffic control for on-site unpaved areas; Control for earthmoving activities

• Track-out prevention

• Control for off-site transport

• Post-construction stabilization of disturbed areas

• Air monitoring for asbestos (if required by the district Air Pollution Control Officer [APCO])

The Asbestos Dust Mitigation Plan would include BMPs to minimize dust during grading and other earthmoving operations. BMPs could include, but not be limited to:

• Limiting vehicle speed to fifteen mph or less on the site

• Applying water to the site prior to and during ground disturbance to prevent visible emissions from crossing the property line

• Keeping storage piles adequately wetted or covered

• Washing down vehicles before leaving the site

• Cleaning visible track-out on paved public roads using wet sweeping or a HEPA filter-equipped vacuum within 24 hours

The BAAQMD would also be notified at least fourteen days prior to construction activities at the site.

Implementation Responsibility:  Project proponent/construction contractor

Requirements and Timing:         Implementation of Asbestos Dust Mitigation Plan during all excavation activities in areas underlain with serpentinite

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Levels of Significance. Mitigation Measure GEO-2 would reduce Impact GEO-2 to a less-than-significant level.

4.3.3.2.2    Operations-related Impacts. Converter station operation would not result in impacts to the soil from erosion. Routine vehicle traffic during Project operation would be limited to existing roads, all of which are or would be paved, and standard operational activities would not involve the disruption of soil.

Earthquake-related Impacts. Ground fault rupture occurs during seismic events along active faults. Since there are no active faults onsite, the potential for ground rupture on the site is considered less than significant.

Due to the relatively flat topography of the Project site, landslide potential is considered less than significant. Because the proposed HWC Converter Station site is within 9.5 and 12 miles of the San Andreas and Hayward faults, respectively, there is a potentially high risk of strong ground shaking in the event of a large earthquake in the area.

Impact GEO-3: Strong Ground Shaking. There is a high risk of strong ground shaking in the event of a large earthquake in the area. This impact is considered potentially significant.

Mitigation Measure GEO-3: Design to Seismic Design Requirements. Due to the site's proximity to earthquake faults and the characteristics of the soil profile, a site-specific study shall be conducted to develop seismic design criteria. Project facilities shall be designed and constructed at a minimum to the seismic design requirements for ground shaking specified in the Uniform Building Code for Seismic Zone 4. Additionally, to satisfy the provisions of the 1998 California Building Code, these facilities shall be designed to withstand ground motions equating to approximately a 500-year return period (10 percent probability of exceedance in 50 years). For design purposes, site-specific ground motions shall be calculated for all project sites.

Implementation Responsibility:  Project proponent

Requirements and Timing:         Prior to final design

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Levels of Significance. Implementation of Mitigation Measure GEO-3 would reduce Impact GEO-3 to a less-than-significant level.

Liquefaction. The Project site is within the potential Liquefaction Zone (CDMG, 2000), which is defined as "areas where historical occurrence of liquefaction or local geological, geotechnical, and groundwater conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693c would be required."

Impact GEO-4: Liquefaction. There is a potential for liquefaction at the Project site. This impact is considered potentially significant.

Mitigation Measure GEO-4: Design Project for Liquefiable Deposits. A site-specific program of exploratory borings and accompanying laboratory testing shall be required in order to delineate potentially liquefiable materials beneath the construction area. Geotechnical investigations shall be required for consideration prior to foundation design and development of site-specific design criteria.

Implementation Responsibility:  Project proponent

Requirements and Timing:         Investigation to be conducted prior to final design and appropriate design completed prior to issuance of building permit.

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Levels of Significance. Mitigation Measure GEO-4 would reduce Impact GEO-4 to a less-than-significant level.

Impact GEO-5: Shrink-Swell/Subsidence. The proposed San Francisco HWC Converter Station site is potentially underlain with expansive soils, which requires specific attention during grading to avoid future heaving and cracking of overlying materials. The potential for damage due to shrink-swell/subsidence to site facilities is potentially significant.

Mitigation Measure GEO-5: Design Project for Shrink-Swell/Subsidence. A program of site-specific exploratory borings and accompanying laboratory testing shall be required to delineate any potentially expansive materials underneath the proposed Project facility sites and to evaluate the potential for site subsidence and identify and implement appropriate design measures (e.g. pile supports or replacement of undesirable materials) in accordance with applicable codes.

Implementation Responsibility:  Project proponent

Requirements and Timing:         Investigation and appropriate design completed prior to issuance of building permit

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Level of Significance. Mitigation Measure GEO-5 would reduce Impact GEO-5 to a less-than-significant level.

4.3.3.3    Pittsburg Standard Oil Converter Station

4.3.3.3.1    Construction-related Impacts. Use of the site would require demolition and removal of two abandoned concrete wastewater storage tanks, a dilapidated building, and debris. Before construction of the proposed converter station, the site would be cleared of all structures and stored materials and graded.

An area of up to approximately 7 acres located on vacant property adjacent to and north of the site would be devoted to equipment and materials laydown, storage, parking of construction equipment, small fabrication areas and office trailers for the Pittsburg Converter Station site. The laydown site location and proposed access road to the Pittsburg-Antioch Highway are shown on Figure 4.3-5.

Construction, including excavation and grading of the site, including ancillary facilities, could lead to soil erosion. Soil loss estimates have not been calculated for the Project site or for the onshore cable routes.

Construction of the proposed Project would also result in soil compaction due to the erection of foundations and paving. In addition, soil compaction would result from vehicle traffic along temporary access roads and in equipment staging areas.

Impact GEO-1: Soil Erosion and Compaction. The soil erosion and compaction impact (Impact GEO-1) described in Section 4.3.3.2.1 applies to the Pittsburg Standard Oil Converter Station site.

Mitigation Measure GEO-1: Design Project for Erosion Control. Mitigation Measure GEO-1 described in Section 4.3.3.2.1 shall be applied at the Pittsburg Standard Oil Converter Station site.

Implementation Responsibility: Project proponent/construction contractor

Requirements and Timing:         Approval of SWPPP by RWQCB prior to construction

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance with SWPPP over course of construction

Resulting Level of Significance. Mitigation Measure GEO-1 would reduce Impact GEO-1 to a less-than-significant level.

4.3.3.3.2    Operations-related Impacts.

Earthquake-related Impacts. Ground fault rupture occurs during seismic events along active faults. Since there are no active faults on site, the potential for ground rupture on the site is considered less than significant.

Due to the relatively flat topography of the Project site, landslide potential is considered less than significant.

Because the Pittsburg-Kirby Hills Fault Zone is approximately 1.1 miles from the site, there is potentially a high risk of strong ground shaking in the event of a large earthquake in the area.

Impact GEO-3: Strong Ground Shaking. The strong ground shaking impact (Impact GEO‑2) described in Section 4.3.3.2.2 applies at the Pittsburg Standard Oil Converter Station site.

Mitigation Measure GEO-3: Design to Seismic Design Requirements. Mitigation Measure GEO-3 described in Section 4.3.3.2.2 shall be applied at the Pittsburg Standard Oil Converter Station site.

Implementation Responsibility:  Project proponent

Requirements and Timing:         Prior to final design, construction, and operations

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Level of Significance. Mitigation Measure GEO-3 would reduce Impact GEO-3 to a less-than-significant level.

Liquefaction. As with the HWC site, the nature of the alluvial and fluvial deposits on which the facility would be sited and the presence of potentially liquefiable materials indicates that liquefaction and lateral spreading could occur.

Impact GEO-4: Liquefaction. The liquefaction impact (Impact GEO-4) described in Section 4.3.3.2.2 applies to the Pittsburg Standard Oil Converter Station site.

Mitigation Measure GEO-4: Design Project for Liquefiable Deposits. Mitigation Measure GEO-4 described in Section 4.3.3.2.2 shall be applied to the Pittsburg Standard Oil Converter Station site.

Implementation Responsibility: Project proponent

Requirements and Timing:         Investigation to be conducted prior to final design and appropriate design competed prior to the issuance of building permit

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Level of Significance. Mitigation Measure GEO-4 would reduce Impact GEO-4 to a less-than-significant level.

Shrink-Swell/Subsidence. Expansive soils shrink and swell as a result of moisture changes. This can cause heaving and cracking of slabs-on-grade, pavements, and structures founded on shallow foundations. Successful construction on expansive soils requires special attention during grading. The site soils have moderate to high shrink-swell/subsidence potential (City of Pittsburg, 2001).

Impact GEO-5: Shrink-Swell/Subsidence. The proposed Pittsburg Standard Oil Converter Station site is potentially underlain with expansive soils, which requires specific attention during grading to avoid future heaving and cracking of overlying materials. The potential for damage due to shrink-swell/subsidence to site facilities is potentially significant.

Mitigation Measure GEO-5: Design Project for Shrink-Swell/Subsidence. A program of site-specific exploratory borings and accompanying laboratory testing shall be required to delineate any potentially expansive materials underneath the proposed Project facility sites and to evaluate the potential for site subsidence and identify and implement appropriate design measures (e.g. pile supports or replacement of undesirable materials) in accordance with applicable codes.

Implementation Responsibility:  Project proponent

Requirements and Timing:         Investigation and appropriate design completed prior to issuance of building permit

Monitoring Requirements:          City of Pittsburg to monitor and ensure compliance

Resulting Level of Significance. Mitigation Measure GEO-5 would reduce Impact GEO-5 to a less-than-significant level.

4.3.3.4    Offshore DC Cable Route

4.3.3.4.1    Construction-related Impacts. Installation of the proposed offshore DC (and AC for the Pittsburg Standard Oil Converter Station) would disturb and temporarily suspend Bay sediments. This impact is addressed in Section 4.4, Water Resources and Quality.

4.3.3.4.2    Operations-related Impacts.

Surface Rupture. The proposed offshore cable alignment crosses both the Pittsburg-Kirby Hills Fault Zone and the Hayward-Rodgers Creek Fault Zone. A strong earthquake along either of these faults could potentially cause surface rupture along the cable alignment. This potential impact is considered to be adverse, but less than significant. In the event of cable damage during the operational phase, the line would shut down automatically and be repaired as described in Section A.5.2.2 in Appendix A of this EIR.

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