3.6 Geology, Soils, and Seismicity

Transcription

1 3.6 Geology, Soils, and Seismicity ENVIRONMENTAL SETTING PHYSICAL SETTING Geology The city of Emeryville is situated within the Coast Ranges geomorphic province of California. The Coast Ranges is the largest of the state s geomorphic provinces extending approximately 400 miles from the Klamath Mountains (near northern Humboldt County) to the Santa Ynez River in Santa Barbara County. The province lies between the Pacific Ocean and the Great Valley (Sacramento and San Joaquin valleys) provinces and is characterized by a series of northwest trending mountain ridges and valleys, running generally parallel to the San Andreas Fault zone. These mountain ridges and valleys have been formed by tectonic forces that compressed ancient sedimentary deposits over the course of millions of years. The San Francisco Bay is located in a broad depression in the Franciscan bedrock resulting from an east-west expansion between the San Andreas and the Hayward fault systems. The bedrock surface can be found at elevations of 200 to 2,000 feet below mean sea level across the Bay Area. Sedimentary deposits that overlie the Franciscan bedrock originated from millions of years of erosion, deposition, and changes in sea level. Geologists categorize these sedimentary deposits into geologic formations based on the period of deposition and material type, as described below for the San Francisco Bay region. The Alameda Formation is the deepest and oldest of these sedimentary deposits and consists of a mixture of clay, silt, sand, gravel, and some shells with predominantly silt and clay sediments surrounding discontinuous layers of sand and gravel. Members of this formation include Yerba Buena Mud (also named Old Bay Mud), and the San Antonio/Merrit/Posey Member, and Young Bay Mud (RWQCB, 2008). Younger alluvial deposits once referred to as the Alameda Formation are deposited on top of the San Antonio and consist of sandy clays, clayey sands, sands and gravels. The source material for these alluvial deposits comes from the Berkeley Hills. Emeryville lies at the eastern edge of San Francisco Bay as part of the flatlands which are also referred to as the East Bay Plain. The East Bay Plain consists of alluvial deposits that originated from the Berkeley Hills. The western side of the city contains former tidal sloughs and marshlands that were progressively filled in dating back to the 1900s. Before it was filled and developed, the topography of the city was probably at or slightly above mean sea level (msl), and is currently between 10 to 25 feet or more above msl. The city is essentially flat with many areas located on fill; in areas not covered by fill, the city s surface soils consist predominantly of fine-grained alluvium, including silts and clays, and towards the western portion of the city the alluvium is underlain by Bay Mud, as depicted in Figure Bay Mud is a natural marine deposit that consists of soft saturated clays that can contain lenses of sand and shell fragments. Development on artificial fill placed over Bay mud often presents unique 3.6-1

2 40TH ST YERBA BUENA AVE INTERSTATE 580 HOLDEN ST HUBBARD ST 55TH ST VALLEJO ST BEAUDRY ST 67TH ST 66TH ST San Francisco Bay FEET BERKELEY EMERYVILLE EMERYVILLE OAKLAND POWELL ST INTERSTATE 80 FRONTAGE ROAD LACOSTE ST EASTSHORE FREEWAY CHRISTIE AVE WAY SHELLMOUND CHRISTIE AVE 65TH ST ASHBY AVE SHELLMOUND ST SHELLMOUND ST OVERLAND AVE BAY ST 63RD ST BEACH ST HORTON ST MANDELA PKWY HALLECK ST STANFORD POWELL ST HARUFF ST HOLLIS ST OCEAN AVE 64TH ST 65TH ST SHERWIN AVE HORTON ST 53RD ST 59TH ST 61ST ST CHIRON WAY AVE DOYLE ST 62ND ST HOLLIS ST VALLEJO ST PEABODY LN HAVEN ST PARK AVE 45TH ST SAN PABLO AVE 36TH ST WATTS PERALTA 37TH ST 38TH ST W. MACARTHUR BLVD APGAR ST 39TH ST. EMERY ST HARLAN ST WATTS ST YERBA BUENA AVE 43RD ST 41ST ST ESSEX ST SALEM ST 47TH ST 45TH ST 46TH ST 45TH ST 44TH ST 43RD ST 42ND ST 41ST ST 40TH ST. ADELINE ST 47TH ST SALEM ST SAN PABLO AVE 48TH ST 54TH ST Figure GEOLOGY AND EARTHQUAKE SHAKING POTENTIAL Undifferentiated surficial deposits (Quaternary) (Potential very strong shaking) Artificial fill over marine and marsh deposits (Quaternary)(Potential violent shaking) Source: USGS Geologic Map and Map Database of parts of Marin, San Francisco, Alameda, Contra Costa, and Sonoma Counties, California by M.C. Blake Jr., R.W. Graymer, and D.L. James; This map is a derivative of the Probabilistic Seismic Hazard Map that was produced by the California Seismic Safety Commission, California Geological Survey, California Office of Emergency Services and US Geological Survey, Note: This map is intended for planning use only and is not intended to be site specific. Rather, it depicts the general risk within neighborhoods and the relative risk from community to community.

3 Chapter 3: Settings, Impacts, and Mitigation Measures geotechnical engineering challenges because, unless the fill is properly engineered, structures can be damaged by differential settlement and subsidence. Under the bearing load of a new structure, Bay Mud tends to go through a cycle of consolidation that can lead to settlement. Erosion is the wearing away of exposed soil and rock by processes such as mechanical or chemical weathering, mass wasting, and the action of waves, wind and underground water. Excessive soil erosion can eventually lead to damage of building foundations, roadways, and loss of topsoil. Throughout Emeryville, areas that are most susceptible to erosion are those that would be exposed during construction phase and along the shoreline where soil is subjected to wave action. Seismic Hazards Seismic hazards include those hazards that could reasonably be expected to occur in the area during a major earthquake on any of the active faults in the region. Some hazards can be more severe than others, depending on the location, underlying materials, and level of ground shaking. Emeryville lies within an area that contains many active and potentially active faults and is considered to be an area of high seismic activity. The U. S. Geological Survey (USGS) Working Group on California Earthquake Probabilities evaluated the probability of one or more earthquakes of Richter magnitude 6.7 or higher occurring in the San Francisco Bay Area within the next 30 years (USGS, 2008). The result of the evaluation indicated a 63-percent likelihood that such an earthquake event will occur in the Bay Area between 2007 and 2037 (USGS, 2008). Regional Faults Hayward-Rodgers Creek Fault The Hayward fault trends to the northwest within the East Bay, extending from San Pablo Bay in Richmond, 60 miles south to east San José. The Hayward fault in San José converges with the Calaveras fault, a similar type fault that extends further south towards Hollister. The Hayward fault is designated by the Alquist-Priolo Earthquake Fault Zoning Act as an active fault which is defined as having displacement within the last 11,000 years. The Rodgers Creek fault located north of San Pablo Bay is considered to be an extension of the Hayward fault and the two are often combined in modeling studies. A characteristic feature of the Hayward fault is its well-expressed and relatively consistent fault creep. Although large earthquakes on the Hayward fault have been rare since 1868, slow fault creep has continued to occur and has caused measurable offset. Fault creep on the East Bay segment of the Hayward fault is estimated at 9 millimeters per year (Peterson, 1996). However, a large earthquake could occur on the Hayward fault with an estimated moment magnitude (Mw) of about Mw 7.3. The USGS Working Group on California Earthquake Probabilities includes the Hayward-Rodgers Creek Fault Systems in the list of those faults that have the highest probability of generating earthquakes of magnitude (M) 6.7 or greater in the Bay Area (USGS, 2008). San Andreas Fault The San Andreas Fault Zone is a major structural feature that forms at the boundary between the North American and Pacific tectonic plates, extending from the Salton Sea in Southern California near the border with Mexico to north of Point Arena, where the fault trace extends out into the 3.6-3

4 Emeryville General Plan Draft Environmental Impact Report Pacific Ocean. The main trace of the San Andreas fault runs through the Bay Area and trends northwest through the Santa Cruz Mountains along the eastern side of the San Francisco Peninsula. As the principal strike-slip boundary between the Pacific plate to the west and the North American plate to the east, the San Andreas is often a highly visible topographic feature, such as between Pacifica and San Mateo, where Crystal Springs Reservoir and San Andreas Lake clearly mark the rupture zone. Calaveras Fault The Calaveras fault is a major right-lateral strike-slip fault that has been active during the last 11,000 years. The Calaveras fault is located in the eastern San Francisco Bay region and generally trends along the eastern side of the East Bay Hills, west of San Ramon Valley, and extends into the western Diablo Range, and eventually joins the San Andreas Fault Zone south of Hollister. The northern extent of the fault zone is somewhat conjectural and could be linked with the Concord fault. The Calaveras fault has been the source of numerous moderate magnitude earthquakes, and the probability of a large earthquake (greater than M6.7) is much lower than on the San Andreas or Hayward faults (USGS, 2008). Concord-Green Valley The Concord and Green Valley faults are part of the larger San Andreas Fault system. The Concord fault extends from the northwestern slope of Mt. Diablo north to Suisun Bay, where the Green Valley fault is generally thought to be connected to the Concord fault and continues north to Wooden Valley in Napa County. Several site-specific studies on these faults have been conducted in compliance with the Alquist-Priolo Earthquake Fault Zoning Act, and they report the most recent displacement on these faults between 2,600 and 2,700 years ago in the late Holocene. Marsh Creek-Greenville Fault The Marsh Creek-Greenville fault extends along the base of the Altamont Hills, which form the eastern margin of the Livermore Valley. The fault is recognized as a major structural feature and has demonstrated activity in the last 11,000 years. The Marsh Creek-Greenville fault is located approximately 23 miles northwest of Emeryville. Ground Shaking Ground movement during an earthquake can vary depending on the overall magnitude, distance to the fault, focus of earthquake energy, and type of geologic material. The composition of underlying soils, even those relatively distant from faults, can intensify ground shaking. For this reason, earthquake intensities are also measured in terms of their observed effects at a given location. The Modified Mercalli (MM) intensity scale (Table 9.4-1) is commonly used to measure earthquake damage due to ground shaking. The MM values for intensity range from I (earthquake not felt) to XII (damage nearly total), and intensities ranging from IV to X can cause moderate to significant structural damage. The intensities of an earthquake vary over the region of a fault and generally decrease with distance from the epicenter of the earthquake

5 Chapter 3: Settings, Impacts, and Mitigation Measures Historic earthquakes have caused strong ground shaking and damage in the San Francisco Bay Area, the most recent being the Loma Prieta earthquake (moment magnitude 6.9) in October The epicenter was approximately 50 miles south of Emeryville, and the earthquake caused very strong ground shaking for about 20 seconds and resulted in varying degrees of structural damage as far as 50 miles away. This event produced strong (Modified Mercalli VII) to very strong (Modified Mercalli VIII) shaking intensities in the project area (ABAG, 2008a). The 1906 San Francisco earthquake, with an estimated moment magnitude of 7.9, produced very strong (Modified Mercalli VIII) to violent (Modified Mercalli IX) shaking intensities in the City of Emeryville (ABAG, 2008a). Emeryville does not lie in an Alquist-Priolo Earthquake Fault Zone, and no known active fault exists within the boundaries of the city. The Hayward-Rodgers Creek fault is located approximately one mile east of the eastern boundary of the city limits. Similar to the entire Bay Area, Emeryville is subject to ground shaking in the event of an earthquake on the regional faults. The common way to describe ground motion during an earthquake is the duration of the shaking. However, a common measure of ground motion is also the peak ground acceleration; which for a given component of motion is the largest value of horizontal acceleration obtained from a seismograph. 1 Peak ground acceleration is expressed as the percentage of the equivalent acceleration of gravity (g), which is approximately 980 centimeters per second squared. For comparison purposes, the maximum peak acceleration value recorded during the Loma Prieta earthquake was in the vicinity of the epicenter, near Santa Cruz, at 0.64 g. The lowest values recorded were 0.06 g in the bedrock on Yerba Buena Island. An earthquake on the Hayward-Rodgers Creek fault could produce more severe ground shaking than was observed during the Loma Prieta earthquake, as the epicenter of the earthquake would be in close vicinity of Emeryville. Probabilistic seismic hazard maps indicate that peak ground acceleration in the project region could reach or exceed 0.7 g (CGS, 2003). 1 In terms of automobile acceleration, one g of acceleration is a rate of increase in speed equivalent to a car accelerating from a standstill to 60 mph in less than 3 seconds

6 Emeryville General Plan Draft Environmental Impact Report Table Modified Mercalli Intensity Scale Intensity Value Intensity Description Average Peak Acceleration (% g 1 ) I Not felt except by a very few persons under especially favorable < circumstances. II Felt only by a few persons at rest, especially on upper floors on buildings. Delicately suspended objects may swing. III Felt noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake. Standing motor cars may rock slightly, vibration similar to a passing truck. Duration estimated. IV During the day felt indoors by many, outdoors by few. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. V Felt by nearly everyone, many awakened. Some dishes and windows broken; a few instances of cracked plaster; unstable objects overturned. Disturbances of trees, poles may be noticed. Pendulum clocks may stop. VI Felt by all, many frightened and run outdoors. Some heavy furniture moved; and fallen plaster or damaged chimneys. Damage slight. VII Everybody runs outdoors. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving motor cars. VIII Damage slight in specially designed structures; considerable in ordinary substantial buildings, with partial collapse; great in poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed. IX Damage considerable in specially designed structures; well-designed frame structures thrown out of plumb; great in substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes broken. X Some well-built wooden structures destroyed; most masonry and > 124 frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from riverbanks and steep slopes. Shifted sand and mud. Water splashed (slopped) over banks. XI Few, if any, (masonry) structures remain standing. Bridges destroyed. > 1.24 Broad fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. XII Damage total. Practically all works of construction are damaged greatly or destroyed. Waves seen on ground surface. Lines of sight and level are distorted. Objects are thrown upward into the air. > g (gravity) = 980 centimeters per second squared. 1.0 g of acceleration is a rate of increase in speed equivalent to a car traveling 328 feet from rest in 4.5 seconds. Source: ABAG, 2008b

7 Chapter 3: Settings, Impacts, and Mitigation Measures Surface Fault Rupture Seismically-induced ground rupture is defined as the physical displacement of surface deposits in response to an earthquake s seismic waves. The magnitude, sense, and nature of fault rupture can vary for different faults or even along different strands of the same fault. The city of Emeryville does not lie within an Alquist-Priolo Fault Rupture Hazard Zone, as designated through the Alquist-Priolo Earthquake Fault Zoning Act (see regulatory setting below), and no mapped active faults are known to pass through the immediate area. Therefore, the risk of ground rupture in the project area is low. Liquefaction Liquefaction is a transformation of soil from a solid to a liquefied state during which saturated soil temporarily loses strength resulting from the buildup of excess pore water pressure, especially during earthquake-induced cyclic loading. Soils susceptible to liquefaction include saturated loose to medium dense sands and gravels, low-plasticity silts, and some low-plasticity clay deposits. Liquefaction and associated failures could damage foundations, disrupt utility service, and can cause damage to roadways. Hazard maps available through ABAG and produced by the USGS depict liquefaction and lateral spreading hazards for the entire Bay Area in the event of a significant seismic event. 2 Within the city of Emeryville, liquefaction susceptibility ranges from moderate to very high (Knudsen et al., 2000). The California Geological Survey (CGS) has mapped the entire City of Emeryville within a Seismic Hazard Zone for liquefaction according to the requirements of the Seismic Hazards Mapping Act, discussed below (CGS, 2008). Landslides Slope failures, commonly referred to as landslides, include phenomena that involve the downslope displacement and movement of material, either triggered by static (i.e., gravity) or dynamic (i.e., earthquake) forces. A slope failure is a mass of rock, soil, and debris displaced downslope by sliding, flowing, or falling. Exposed rock slopes undergo rockfalls, rockslides, or rock avalanches, while soil slopes experience shallow soil slides, rapid debris flows, and deepseated rotational slides. Landslides may occur on slopes of 15 percent or less; however, the probability is greater on steeper slopes that exhibit old landslide features such as scarps, slanted vegetation, and transverse ridges. Areas susceptible to landslides are characterized by steep slopes and downslope creep of surface materials. Debris flows consist of a loose mass of rocks and other granular material that, if saturated and present on a steep slope, can move downslope. The rate of rock and soil movement can vary from a slow creep over many years to a sudden mass movement. Landslides occur throughout the state of California, however, the density of incidents increases in zones of active faults. Emeryville is not located in an area where earthquake-induced landslides are likely to occur because of the relatively flat topography of the city. As noted in the Seismic Hazard Zone Report for the Oakland West Quadrangle (CGS, 2002), landslides are abundant in the hillside areas of Oakland and Berkeley, although none have been mapped in the small hillside areas within the 2 Lateral spreading is a type of ground failure associated with liquefaction and generally results from predominantly horizontal displacement of materials toward relatively unsupported free slope faces

8 Emeryville General Plan Draft Environmental Impact Report Oakland West Quadrangle. Therefore, the risk of landslide at the site is low and is not discussed further in this analysis. Geologic Hazards Considering the geologic context of the project area and nature of the project, other typical geologic hazards could include soil erosion and expansive soil. These hazards are discussed briefly below. Expansive Soils Expansive soils possess a shrink-swell behavior. Shrink-swell is the cyclic change in volume (expansion and contraction) that occurs in fine-grained clay sediments from the process of wetting and drying. Structural damage to buildings can occur over a long period of time, usually as a result of inadequate soil and foundation engineering or the placement of structures directly on expansive soils. Expansive soils are prevalent in the East Bay Plain area. Soil Erosion Erosion is the wearing away of soil and rock by processes such as mechanical or chemical weathering, mass wasting, the action of waves, wind and underground water. Excessive soil erosion can eventually lead to damage of building foundations and roadways. REGULATORY FRAMEWORK FEDERAL Alquist-Priolo Earthquake Fault Zoning Act The Alquist-Priolo Earthquake Fault Zoning Act (formerly the Alquist-Priolo Special Studies Zone Act), signed into law December 1972, requires the delineation of zones along active faults in California. The Alquist-Priolo Act regulates development on or near active fault traces to reduce the hazard of fault rupture and to prohibit the location of most structures for human occupancy across these traces3. Cities and counties must regulate certain development projects within the delineated zones, and regulations include withholding permits until geologic investigations demonstrate that development sites are not threatened by future surface displacement (Hart, 1997). Surface fault rupture, however, is not necessarily restricted to the area within an Alquist- Priolo Zone. Emeryville does not lie within an Alquist-Priolo Zone. Seismic Hazards Mapping Act The Seismic Hazards Mapping Act of 1990 addresses non-surface fault rupture earthquake hazards, including liquefaction and seismically-induced landslides. The purpose of the Act is to protect public safety from the effects of strong ground shaking, liquefaction, landslides, and other ground failure, and other hazards caused by earthquakes. The Act requires the State Geologist to delineate various seismic hazard zones and requires cities, counties, and other local permitting 3 A structure for human occupancy is defined by the Alquist-Priolo Act as any structure used or intended for supporting or sheltering any use or occupancy that has an occupancy rate of more than 2,000 person-hours per year

9 Chapter 3: Settings, Impacts, and Mitigation Measures agencies to regulate certain development projects within these zones. Before a development permit is granted for a site within a seismic hazard zone, a geotechnical investigation of the site must be conducted and appropriate mitigation measures incorporated into the project design. The entire city of Emeryville lies within a seismic hazard zone for liquefaction (CGS, 2008). STATE California Building Code The California Building Code (CBC) has been codified in the California Code of Regulations (CCR) as Title 24, Part 2. Title 24 is administered by the California Building Standards Commission, which, by law, is responsible for coordinating all building standards. Under state law, all building standards must be centralized in Title 24 or they are not enforceable. The purpose of the CBC is to establish minimum standards to safeguard the public health, safety and general welfare through structural strength, means of egress facilities, and general stability by regulating and controlling the design, construction, quality of materials, use and occupancy, location, and maintenance of all building and structures within its jurisdiction. In addition, the CBC contains necessary California amendments which are based on the American Society of Civil Engineers Minimum Design Standards 7-05, which provide requirements for general structural design and include means for determining earthquake loads as well as other loads (flood, snow, wind, etc.) for inclusion into building codes. The provisions of the CBC apply to the construction, alteration, movement, replacement, and demolition of every building or structure or any appurtenances connected or attached to such buildings or structures throughout California. The earthquake design requirements take into account the occupancy category of the structure, site class, soil classifications, and various seismic coefficients which are used to determine a Seismic Design Category (SDC) for a project. The SDC is a classification system that combines the occupancy categories with the level of expected ground motions at the site and ranges from SDC A (very small seismic vulnerability) to SDC E/F (very high seismic vulnerability and near a major fault). Design specifications are then determined according to the SDC. LOCAL The City of Emeryville Municipal Code includes regulatory requirements that would apply to geology and soils for new development under the General Plan. Title 9 includes requirements for subdivisions and commercial developments that would occur under the General Plan. Chapter 3 of Title 9 requires preparation of a soils report for subdivisions, when specifically requested by the Planning Commission. In the case a soils report is required, and such report discloses an unstable condition, the City shall require appropriate steps to be taken to correct such condition, or, if such unstable condition cannot be eliminated, the subdivision, parcel map, or other division of land shall be disapproved. New development may also require a preliminary geological study of the property and surrounding area

10 Emeryville General Plan Draft Environmental Impact Report IMPACT ANALYSIS SIGNIFICANCE CRITERIA Implementation of the proposed Emeryville General Plan could have a significant geology and soils impact if it would: Expose people or structures to potential substantial risk of loss, injury, or death involving a) Rupture of a known earthquake fault, as delineated on the most recent Alquist- Priolo Earthquake Fault Zoning Map or Seismic Hazards Map issued by the State Geologist for the area or based on other substantial evidence of a known fault (refer to Division of Mines and Geology Special Publication 42) b) Strong seismic ground shaking; c) Seismic-related ground failure, including liquefaction; d) Landslides Result in substantial soil erosion or the loss of topsoil; Be located on geologic unit or soil that is unstable, or that would become unstable as a result of the project, and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse; Be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994, as it may be revised), creating substantial risks to life or property; Have soils incapable of adequately supporting the use of septic tanks or alternative wastewater disposal systems where sewers are not available for the disposal of wastewater. METHODOLOGY AND ASSUMPTIONS The impact analysis takes into account the proposed General Plan policies and goals, geologic and seismic conditions within Emeryville, and applicable regulations and guidelines. The proposed General Plan would facilitate development and growth within Emeryville. Consideration is given to erosion associated with future development, related construction activities, as well as potential geologic hazards posed by liquefaction, ground shaking, and underlying geologic materials. The potential for seismic activity to affect people and structures in Emeryville and the protection from seismic hazards provided by proposed General Plan policies are assessed. SUMMARY OF IMPACTS Impacts related to erosion, surface fault rupture, ground shaking, liquefaction, and differential settlement are all found in this analysis to be less than significant assuming proper enforcement of existing state and local building code requirements, as well as implementation of the policies in the proposed General Plan. The new development proposed under the General Plan would be connected to the existing sewer system (Section 3.10: Public Services and Utilities states there will be no alternative disposal systems), therefore alternative wastewater disposal systems would not be required. This impact is not discussed further. The relatively flat topography of the project area

11 Chapter 3: Settings, Impacts, and Mitigation Measures also indicates that the likelihood of potential impacts from landslides is very low and also not discussed further. IMPACTS AND MITIGATION MEASURES Impact New development under the proposed General Plan could generate loose and erodible soils during construction activities that, if not properly managed, could result in substantial erosion. (Less than Significant) Emeryville predominantly lies on flat topography and has a developed landscape with office, regional retail, and high-density residential land uses, as well as mixed-use developments. Under the General Plan, new residential and nonresidential development would replace existing development. Construction of the new development would involve activities such as site clearing, grading, and excavation. Some earthwork activities associated with construction activities would disturb subsurface soils, causing erosion. To minimize wind or water erosion on the site during construction, developments would adhere to standard engineering practices and prepare stormwater pollution prevention plan (refer to Section 9.3, Hydrology and Water Quality, for additional information) and implement measures to control any erosion that may occur on construction sites. The common practice of implementing best management practices reduces the potential for erosion during construction. Typically, the soil erosion potential is reduced once the soil is graded and covered with concrete, structures, asphalt, slope protection, or vegetation. Long-term erosion potential shall be addressed through installation of project landscaping and storm drainage facilities, both of which would be designed to meet applicable regulations. See Section 3.5, Hydrology and Flooding, for additional information. Proposed General Plan Policy that Reduces the Impact CSN-P-31 The City will continue to require soil erosion control measures during construction. Adherence to established regulations, as well as the proposed General Plan policy listed above, ensure the potential impact is less than significant. Mitigation Measures No mitigation measures are required. Impact New development under the proposed General Plan could be subject to fault rupture, severe ground shaking, or liquefaction capable of causing injury and/or structural damage. (Less than Significant)

12 Emeryville General Plan Draft Environmental Impact Report Emeryville is not located within a Fault-Rupture Hazard Zone as designated by the Alquist-Priolo Earthquake Fault Zoning Act of 1972, and no known active faults have been mapped on or in the immediate vicinity. As the site is not located on an active or potentially active fault, potential for surface fault rupture is low. Emeryville is located within a Seismic Hazard Zone for liquefaction as designated by the California Geological Survey (CGS), indicating a moderate to high liquefaction potential. Liquefaction could result in potentially damaging effects to the proposed structures and related improvements. Development under the proposed General Plan would be required to perform a geotechnical investigation, which will specifically address the potential for liquefaction and provide measures such as specific foundation types and pile specifications, to mitigate potential damage to the proposed residential and commercial units in accordance with CGS Special Publication 117. Although some structural damage is typically not completely avoidable during a major earthquake, building codes and current foundation design standards have been established to protect against the adverse effects of ground failure such as liquefaction and lateral spreading. For example, deep foundations extending below any liquefiable layers can be designed to support the structures and reduce the potential effects of liquefaction. In accordance with standard City practices, complying with the Uniform Building Code (UBC) standards, and incorporating a foundation design intended to minimize effects of ground shaking and seismicity-related ground failures, the developers would be required to submit an engineering analysis along with detailed engineering drawings to the Emeryville Planning and Building Department prior to excavation, grading, or construction activities on the site. The City maintains a seismic safety and retrofit ordinance and program to upgrade structures, particularly unreinforced masonry structures that are susceptible to damage from seismic activity (Title 8, Chapter 15). The project sponsors would be required to submit an engineering analysis report along with detailed engineering drawings and relevant grading or construction activities on the project site to address constraints and incorporate recommendations identified in the geotechnical investigations. In addition, the required submittals would ensure that the buildings are designed and constructed in conformance with the requirements of all applicable building code regulations, pursuant to standard City procedures. Because all development is required to be constructed in conformance with the CBC and UBC, the risks of injury and structural damage from a known earthquake fault, ground shaking, or seismic-related ground failure would be reduced to a less than significant level. Proposed General Plan Policies that Reduce the Impact CSN-P-28 The City will continue to regulate development, including remodeling or structural rehabilitation, to ensure adequate mitigation of safety hazards on sites having a history or threat of seismic dangers, erosion, subsidence, or flooding. CSN-P-29 The City will require geotechnical investigation of all sites proposed for development in areas where geologic conditions or soil types are susceptible

13 Chapter 3: Settings, Impacts, and Mitigation Measures to liquefaction (see very high and high level areas on Figure 6-4). The City also requires submission of geotechnical investigation and demonstration that project conforms to all recommended mitigation measures prior to city approval (as required by State law). CSN-P-31 The City will enforce regulation of potentially hazardous structures to be retrofitted and made safe and encourage property owners to abate or remove structural hazards that create unaccepted levels of risk. Adherence to established regulations, as well as the proposed General Plan policies listed above, ensure the potential impact is less than significant. Mitigation Measures None required. Impact New development under the proposed General Plan could be subject to settlement due to compressive soils or settlement/uplift as a result of expansive soils. (Less than Significant) Bay Mud is typically made up of soft compressible layers of saturated clays that are susceptible to consolidation and settlement. The amount and rate of consolidation can depend on the weight of any new fill or structural loads (i.e., footings), the thickness of the existing fill, the thickness of the Bay Mud deposit, the degree to which consolidation has already occurred from former and existing structures, and the presence of sand layers within the Bay Mud. Constructing new shallow foundations and/or placement of new fill at the site could begin a new or secondary cycle of consolidation settlement in the Bay Mud. Where primary consolidation is complete, ground surface settlement is still expected to occur under the existing loads due to secondary compression of the Bay Mud layer. The underlying soils at the proposed project site may also have the potential for expansion. The shrink-swell capacity of expansive soils can cause damage to foundations and pipelines. Due to the fact that settlement would likely occur, the final structural design for any proposed development would be required to address the potential for expansive soils to cause structural damage, and foundation support may have to be obtained from the competent soil of the deeper geologic units. Adherence to established regulations ensure the potential impact is less than significant. Mitigation Measures None required

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