4.5 Geology and Soils

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1 Environmental Impact Analysis Geology and Soils 4.5 Geology and Soils This section assesses potential impacts related to geologic and soil hazards Setting a. Topography and Geology San Leandro is located on the East Bay Plain (the Plain), a flat area that extends 50 miles from Richmond in the north to San Jose in the south. The Plain is about three miles wide in the San Leandro area. At its eastern edge, the plain transitions into low hills, rising to 526 feet at the highest point in the City s Bay-O-Vista neighborhood. On its western edge, the Plain slopes down to San Francisco Bay, the largest estuary on the California Coast (City of San Leandro 2016i). San Leandro s rich alluvial soils and temperate climate support a wide variety of plants and animals. Wetlands in the southwest part of San Leandro provide habitat for the salt marsh harvest mouse and other special status species. San Leandro Creek remains one of the few waterways in the urbanized East Bay that retains its natural character along most of its course (City of San Leandro 2016i). San Leandro is located within the United States Geological Survey s (USGS) San Leandro and Hayward Quadrangle 7.5-minute topographic map areas. The area is typified by low topographic relief, with gentle slopes to the southwest in the direction of San Francisco Bay. By contrast, the San Leandro Hills that lie directly northeast of San Leandro have more pronounced topographic relief, with elevations that locally approach 1,000 feet above mean sea level (City of San Leandro 2016i). The geology in the vicinity of San Leandro has been mapped by a variety of organizations, including the USGS. In its 2000 geologic map and map database for the Oakland, California area, the shallow geology underlying much of San Leandro consists of Holocene alluvium with fluvial deposits frequently composed of medium dense to dense, gravelly sand or sandy gravel that often grade upward to sandy or silty clay. Close to the bay shoreline along the west edge of San Leandro, the shallow geology is dominated by artificial fill, and in places, Bay Mud. The bedrock geology beneath San Leandro is best expressed in the hills that flank the east side of San Leandro (i.e. the area between Interstate Highway 580 and Lake Chabot), that are directly underlain by highly altered Jurassic metamorphic and plutonic rocks. Some of these rocks include pillow basalts and keratophyres (a type of silica-rich volcanic rock) that have been mapped as members of the Coast Range Ophiolite complex, a rock assemblage that is widely believed to represent oceanic crustal material that was tectonically emplaced along the west margin of the North American (tectonic) Plate (City of San Leandro 2016i). Additionally, the Specific Plan Area is located in proximity to the San Andreas and Hayward fault zones, one of the most seismically active regions in the United States, however it is not located within the Alquist-Priolo fault zone. Specific Plan Area faults are discussed in greater detail below under part (d), Geologic Hazards, Figure 16, and Figure 17 show faults within the proximity of the Specific Plan Area to the Hayward Fault and the Alquist-Priolo fault zone, respectively. Draft Environmental Impact Report 149

2 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan Figure 16 Regional Fault Map 150

3 Environmental Impact Analysis Geology and Soils Figure 17 Alquist-Priolo Fault Zone Map Draft Environmental Impact Report 151

4 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan b. Soils The properties of soils city-wide are variable, ranging from poorly drained, plastic soils of the Clear Lake clay to the more permeable, well-drained soils of the Yolo silt loam. According to published test data, several soil types, notably the Clear Lake clay, are characterized by high shrink-swell potential, where alternating heavy and cracking in overlying foundations, utility lines, and/or flatwork (City of San Leandro 2016i). As mapped by the Natural Resource Conservation Service (NRCS), three soil types are located in the Specific Plan Area (USDA 2017). The Specific Plan Area is comprised primarily of drained Clear Lake clay 0 to 2 percent slopes, MLRA 14 (84.1 acres). The remainder of the Specific Plan Area is comprised of Botella loam 0 to 2 percent slopes, MLRA 14 (54.9 acres) and Danville silty clay loam 0 to 2 percent (15.8 acres). Specific Plan Area soils are shown in Figure 18 and soil characteristics for the Specific Plan Area soils related to water holding capacity, permeability, shrink-swell potential, rate of surface runoff, and erosion hazard are listed below in Table 9. Table 9 Map Unit # Specific Plan Area Soil Parameters Name 106 Botella loam, 0 to 2 percent slopes 107 Clear Lake clay, 0 to 2 percent slopes, drained 111 Danville silty clay loam, 0 to 2 percent slopes Water Holding Capacity (in.) Permeability (in/hr) 9-11 Moderately slow Shrink-Swell Potential Rate of Surface Runoff Erosion Hazard Moderate Slow Slight Slow High Slow None Slow Moderate to High Sources: U.S. Department of Agriculture (USDA), Natural Resources Conservation Service (NRCS), Web Soil Survey of Alameda County, California, April 11, 2017; U.S. Department of Agriculture (USDA), Soil Conservation Service, Soil Survey of Alameda County, California, Western Part, March, c. Geologic Hazards Similar to much of California, the Specific Plan Area is located within a seismically active region. The seismic hazards relevant to the Specific Plan Area are described below. Faulting and Seismically Induced Ground Shaking The U.S. Geological Survey (USGS) defines active faults as those that have had surface displacement within Holocene time (about the last 11,000 years). Surface displacement can be recognized by the existence of cliffs in alluvium, terraces, offset stream courses, fault troughs and saddles, the alignment of depressions, sag ponds, and the existence of steep mountain fronts. Potentially active faults are faults that have had surface displacement during the last 1.6 million years. Inactive faults have not had surface displacement within the last 1.6 million years. Several faults are located in the vicinity of the Specific Plan Area (refer to Figure 17). These major faults and fault zones are described in the paragraphs below: San Andreas Fault The San Andreas Fault, which is the most likely source of a major earthquake in California, is located approximately 15 miles west of San Leandro. The San Andreas Fault is the primary surface boundary between the Pacific and the North American plates. There have been numerous historic Slow None 152

5 Environmental Impact Analysis Geology and Soils Figure 18 Specific Plan Area Soils Map Draft Environmental Impact Report 153

6 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan earthquakes along the San Andreas Fault, and it generally poses the greatest earthquake risk to California. In general, the San Andreas Fault is likely capable of producing a Maximum Credible Earthquake (MCE) of 8.0. Hayward Fault The Hayward Fault, one of ten major faults that comprise the San Andreas Fault Zone, runs northeast of the Specific Plan Area and links with the Rodgers Creek Fault to the north. Although the last major earthquake generated by the Hayward Fault was in 1868, pressure is slowly building again and will begin to overcome the friction and other forces that are causing the fault zone to stick. According to a 2008 study of earthquake probabilities by the U.S. Geological Survey and other partners, the fault system that includes the Hayward and Rodgers Creek faults has a 31 percent probability of generating an earthquake with a magnitude greater than or equal to 6.7 on the Mercalli Richter Scale in the next 30 years (City of San Leandro 2016f). The Hayward Fault would likely cause extensive damage throughout the Specific Plan Area due to its close proximity to urban communities and infrastructure. The Hayward Fault and surrounding area is a designated Alquist- Priolo Zone, which lies just northeast of the Specific Plan Area (see Figure 17). Other active faults within the Specific Plan Area vicinity include the Chabot, Calaveras, Greenville, and Las Positas faults, as well as several potentially active faults and unnamed secondary faults adjacent to these faults. There are few or no studies pertaining to these additional secondary faults; therefore it is unknown if these faults may or may not experience secondary ground rupture during a large earthquake. In addition to the primary hazard of surface rupture, earthquakes often result in secondary hazards that may cause widespread damage. The three most likely secondary earthquake hazards in the Specific Plan Area are ground shaking, liquefaction and ground failure (City of San Leandro 2016f). Surface Rupture Faults generally produce damage in two ways: ground shaking and surface rupture. Surface rupture is limited to very near the fault. As discussed above, the Hayward Fault runs northeast of the Specific Plan Area. Since the fault zone is outside the Specific Plan Area, surface rupture in the Specific Plan Area is not expected to occur (see Figure 17). Ground Shaking Seismically induced ground shaking covers a wide area and is greatly influenced by the distance of the site to the seismic source, soil conditions, and depth to groundwater. The USGS and ABAG have worked together to map the likely intensity of ground-shaking throughout the Bay Area under various earthquake scenarios. The most intense ground-shaking scenario mapped in the Specific Plan Area assumes a 6.9 magnitude earthquake on the Hayward Fault system. The predicted ground-shaking from such an earthquake would be very violent or violent throughout the Specific Plan Area (ABAG 2016a). Hazards associated with seismically induced ground shaking include liquefaction, seismically induced settlement, and earthquake-triggered landslides. Movement along any of the faults shown in Figure 17 could potentially generate substantial ground shaking in the Specific Plan Area leading to these secondary hazards, as discussed below. 154

7 Liquefaction and Seismically-Induced Settlement Environmental Impact Analysis Geology and Soils Liquefaction is defined as the sudden loss of soil strength due to a rapid increase in soil pore water pressure resulting from seismic ground shaking. Liquefaction potential is dependent on such factors as soil type, depth to ground water, degree of seismic shaking, and the relative density of the soil. When liquefaction of the soil occurs, buildings and other objects on the ground surface may tilt or sink, and lightweight buried structures (such as pipelines) may float toward the ground surface. Liquefied soil may be unable to support its own weight or that of structures, which could result in loss of foundation bearing or differential settlement. Liquefaction may also result in cracks in the ground surface followed by the emergence of a sand-water mixture. Seismically induced settlement occurs in loose to medium dense unconsolidated soil above groundwater. These soils compress (settle) when subject to seismic shaking. The settlement can be exacerbated by increased loading, such as from the construction of buildings. Settlement can also result solely from human activities including improperly placed artificial fill, and structures built on soils or bedrock materials with differential settlement rates. Earthquake hazard maps produced by ABAG indicate that a large Hayward Fault quake would trigger very strong shaking throughout San Leandro and a high risk of liquefaction in the Washington Manor and Bonaire neighborhoods, each neighborhood located less than a mile southwest of the Specific Plan Area (City of San Leandro 2016f). The Specific Plan Area is located within an area identified by the California Geologic Survey, California Department of Conservation (2003), as having moderate susceptibility and therefore is in a Zone of Required Investigation for liquefaction potential (refer to Figure 19). The identified seismic hazard zone is due to the area having historical occurrence of liquefaction, or where local geological geotechnical and ground-water conditions indicate a potential for permanent ground displacements such that mitigation as defined in Public Resources Code Section 2693(c). However, seismic hazard zones identified by the California Geologic Survey may include developed land where delineated hazards have already been mitigated to city or county standards. Slope Stability and Landslides Landslides result when the driving forces that act on a slope (i.e., the weight of the slope material, and the weight of objects placed on it) are greater than the slope s natural resisting forces (i.e., the shear strength of the slope material). Slope instability may result from natural processes, such as the erosion of the toe of a slope by a stream, or by ground shaking caused by an earthquake. Slopes can also be modified artificially by grading, or by the addition of water or structures to a slope. Development that occurs on a slope can substantially increase the frequency and extent of potential slope stability hazards. Areas susceptible to landslides are typically characterized by steep, unstable slopes in weak soil/bedrock units which have a record of previous slope failure. There are numerous factors that affect the stability of the slope, including: slope height and steepness, type of materials, material strength, structural geologic relationships, ground water level, and level of seismic shaking. According to the Environmental Hazards Element of the 2035 General Plan (2016), landslide risk is low throughout the majority of San Leandro. However, localized areas of instability exist throughout the San Leandro Hills (see Figure 20). The Specific Plan Area is generally flat and not located in the San Leandro hills. Therefore, landslides within the Specific Plan Area are unlikely. Draft Environmental Impact Report 155

8 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan Figure 19 Liquefaction Susceptibility Map 156

9 Environmental Impact Analysis Geology and Soils Figure 20 Landslide Hazard Map Draft Environmental Impact Report 157

10 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan Expansive Soils Expansive soils can change dramatically in volume depending on moisture content. When wet, these soils can expand; conversely, when dry, they can contract or shrink. Sources of moistures that can trigger this shrink-swell phenomenon include seasonal rainfall, landscape irrigation, utility leakage, and/or perched groundwater. Expansive soil can develop wide cracks in the dry season, and changes in soil volume have the potential to damage concrete slabs, foundations, and pavement. Special building/structure design or soil treatment are often needed in areas with expansive soils. Expansive soils are typically very fine-grained with a high to very high percentage of clay. The clay minerals present typically include montmorillonite, smectite, and/or bentonite. As shown in Table 9, the U.S. Geological Survey has mapped soils in the Specific Plan Area as having moderate potential for shrink-swell. Areas characterized by moderate shrink-swell potential may pose a geologic hazard in the Specific Plan Area. Erosion Erosion is the wearing away of the soil mantle by running water, wind or geologic forces. It is a naturally occurring phenomenon and ordinarily is not hazardous. However, excessive erosion can contribute to landslides, siltation of streams, undermining of foundations, and ultimately the loss of structures. Removal of vegetation tends to heighten erosion hazards. The City enforces grading and erosion control ordinances to reduce these hazards. Maintenance programs along San Leandro Creek also reduce the threat of erosion (City of San Leandro 2016f). The Specific Plan Area lies in a generally flat area, sitting at approximately 29 feet above mean sea level and the Specific Plan Area is characterized by having none or a slight potential for erosionrelated hazards. Additionally, the majority of on-site soils have none or a slight potential for erosion-related hazards. d. Regulatory Setting Federal Clean Water Act Congress enacted the Clean Water Act (CWA), formerly the Federal Water Pollution Control Act of 1972, with the intent of restoring and maintaining the chemical, physical, and biological integrity of the waters of the United States. The CWA requires states to set standards to protect, maintain, and restore water quality through the regulation of point source and non-point source discharges to surface water. Those discharges are regulated by the National Pollutant Discharge Elimination System (NPDES) permit process (CWA Section 402). NPDES permitting authority is administered by the California State Water Resources Control Board (SWRCB) and its nine Regional Water Quality Control Boards (RWQCBs). San Leandro is within a watershed administered by the Bay Area RWQCB. Individual projects within the City that disturb more than one acre would be required to obtain NPDES coverage under the California General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities (Construction General Permit). The Construction General Permit requires the development and implementation of a Storm Water Pollution Prevention Plan (SWPPP) describing Best Management Practices (BMPs) the discharger would use to prevent and retain stormwater runoff and to prevent soil erosion. 158

11 State Environmental Impact Analysis Geology and Soils State geotechnical regulations applicable to the Specific Plan Area include the Seismic Hazards Mapping Act and the California Building Code (CBC). The Seismic Hazards Mapping Act addresses geo-seismic hazards, other than surface faulting, and applies to public buildings and most private buildings intended for human occupancy. The Seismic Hazards Mapping Act identifies and maps seismic hazard zones to assist cities and counties in preparing the safety elements of their general plans and encourages land use management policies and regulations that reduce seismic hazards. The Act mandated the preparation of maps delineating Liquefaction and Earthquake-Induced Landslide Zones of Required Investigation. The Specific Plan Area contains land designated as liquefaction risk areas according to the California Geologic Survey (2003). The CBC requires, among other things, seismically resistant construction and foundation and soil investigations prior to construction. The CBC also establishes grading requirements that apply to excavation and fill activities, and requires the implementation of erosion control measures. The City is responsible for enforcing the 2016 CBC, or most current CBC version, within the Specific Plan Area. Local San Leandro Municipal Code Chapter 7, Section 12, Grading, Excavations, and Fills, of the San Leandro Municipal Code (SLMC) maintains a grading ordinance to mitigate hazards associated with erosion and land stability. The ordinance establishes criteria for permits and identifies grading plan submittal and construction requirements. San Leandro 2035 General Plan The following goal, policies, and actions in the City s 2035 General Plan relate to geology and soils: Goal EH-1. Reduce the potential for injury, property damage, and loss of life resulting from earthquakes, landslides, and other natural disasters. Policy EH-1.1 Risk Management. Minimize risks from geologic, seismic, flood, and climate change-related hazards by ensuring the appropriate location, site planning, and design of new development. The City s development review process, and its engineering and building standards, should ensure that new construction is designed to minimize the potential for damage. Action EH-1.1.A: Soils and Geologic Reports. Require soils and/or geologic reports for development in areas where potentially serious geologic risks exist. These reports should address the degree of hazard, design parameters for the project based on the hazard, and appropriate mitigation measures. Policy EH-1.2. Earthquake Retrofits. Strongly encourage the retrofitting of existing structures to withstand earthquake ground shaking, and require retrofitting when such structures are substantially rehabilitated or remodeled. Action EH-1.2.A. Residential Retrofit Program. Undertake programs to assist homeowners with earthquake retrofitting. As funding allows, such programs could include home inspections, do-it-yourself classes, tool lending libraries, the Brace and Bolt Program, and other measures that reduce the risk of damage and injury in an earthquake. Draft Environmental Impact Report 159

12 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan Action EH-1.2.B: Change of Occupancy Upgrades. Continue requirements that structures at high risk of earthquake damage be retrofitted when there is a change of occupancy or major building remodel. Action EH-1.2.C. Soft-Story Buildings. Develop an implementation strategy to reduce the hazards posed by soft-story buildings (multi-story structures with little or no first floor bracing). Policy EH-1.4 Code Revisions. Revise and update construction codes and regulations to incorporate the latest available information and technology related to earthquake hazards Impact Analysis a. Methodology and Significance Thresholds Assessment of impacts is based on review of site information and conditions and County information regarding geologic issues. In accordance with Appendix G of the CEQA Guidelines, a project would result in a significant impact if it would: 1. Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: i. ii. iii. iv. Rupture of a known earthquake fault, as delineated on the most recent Alquist-Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault, Strong seismic ground shaking, Seismic-related ground failure, including liquefaction, or Landslides Result in substantial soil erosion or the 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 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), creating substantial risks to life or property; and/or Have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for the disposal of waste water. 160

13 Environmental Impact Analysis Geology and Soils b. Project Impacts and Mitigation Measures Threshold: Threshold: Would the Specific Plan expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: i. Rupture of a known earthquake fault, as delineated on the most recent Alquist- Priolo Earthquake Fault Zoning Map issued by the State Geologist for the area or based on other substantial evidence of a known fault, ii. Strong seismic ground shaking, iii. Seismic-related ground failure, including liquefaction, or iv. Landslides? Would the Specific Plan 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? IMPACT GEO-1 THE SPECIFIC PLAN AREA IS NEAR THE HAYWARD FAULT ZONE. THEREFORE, THE SPECIFIC PLAN AREA IS SUBJECT TO SEISMICALLY-INDUCED GROUND SHAKING AND OTHER SEISMIC HAZARDS, INCLUDING LIQUEFACTION, WHICH COULD DAMAGE STRUCTURES IN THE SPECIFIC PLAN AREA AND RESULT IN LOSS OF PROPERTY AND RISK TO HUMAN HEALTH AND SAFETY. HOWEVER, INCORPORATION OF STATE- MANDATED BUILDING STANDARDS AND COMPLIANCE WITH 2035 GENERAL PLAN POLICIES WOULD ENSURE IMPACTS WOULD BE LESS THAN SIGNIFICANT. Ground Rupture The Specific Plan Area is located in a seismically active region of California, and is subject to potential ground shaking associated with seismic activities. Specifically, the Hayward Fault runs less than 2 miles northeast of the Specific Plan Area (see Figure 1) and links with the Rodgers Creek Fault to the north. However, the Specific Plan Area is not located within an Alquist-Priolo Earthquake Fault Zone, as delineated by the State Geologist (see Figure 2). Therefore, implementation of the Specific Plan would not directly expose persons or structures to substantial risk of surface rupturing in the event of an earthquake. Impacts related to ground rupture would be less than significant. Seismic Shaking As previously mentioned, the Hayward fault system near the Specific Plan Area has been assessed to have a 31 percent probability of generating an earthquake with a magnitude greater than or equal to 6.7 on the Mercalli Richter Scale in the next 30 years (Alameda County 2013). A seismic event with magnitude 6.7 or greater would be substantial, and would have potential to damage structures and result in loss of property and risk to human health and safety. These risks exist throughout the Specific Plan Area, regardless of development proposed under the Specific Plan. The area is currently developed and populated. Full implementation of the proposed Specific Plan would increase population of the area, structural development, and infrastructure that would be exposed to these hazards. New development that would occur within the Specific Plan Area would conform to the CBC (as amended at the time of permit approval) as required by law. With the exception of certain enforcement provisions, the City of San Leandro adopted the CBC by reference pursuant to Title 7, Chapter 7-5, Article 1, Section of the SLMC. Chapter 16 of the CBC contains specific requirements for structural design, including seismic loads and Chapter 18 of the CBC includes Draft Environmental Impact Report 161

14 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan requirements for soil testing, excavation and grading, and foundation design (City of San Leandro 2016i). As discussed above under Regulatory Environment, the CBC requires that structures be designed and constructed to resist seismic hazards, including through foundation design and the completion of soil investigations prior to construction. The City would ensure that any development occurring under the proposed Specific Plan will be consistent with the current CBC, thereby ensuring that appropriate investigations and design measures have been employed to effectively minimize or avoid potential hazards associated with redevelopment and/or new building construction. Proper engineering, including compliance with the CBC, would minimize the risk to life and property associated with potential seismic activity in the area. Impacts related to seismic shaking would be less than significant with no mitigation required. Unstable Soils and Liquefaction The entire Specific Plan Area is in an area of moderate liquefaction potential (see Figure 19). As such, the Specific Plan Area has been identified as an area where historical liquefaction has occurred, or local geological, geotechnical and ground-water conditions indicate a potential for permanent ground displacement. Unstable soils in the Specific Plan Area also introduce potential risks to existing or proposed infrastructure, and/or to human health and safety. Unstable soils may include any materials not capable of supporting a selected land use. As required by the Public Resources Code (PRC) Section , Seismic Hazards Mapping Act and CBC requirements as adopted in the SLMC, site-specific geotechnical evaluations would be conducted for individual development projects with the Specific Plan Area to identify the degree of potential hazards, design parameters for the project based on the hazard, and describe appropriate mitigation measures. These geotechnical studies customarily include recommendations for foundation design, as well as soil improvement techniques, both of which help mitigate these unstable soils and liquefaction hazards. In addition, Action EH-1.1.A: Soils and Geologic Reports, Action EH-1.2.A: Residential Retrofit Program and Action EH-1.2.B: Change of Occupancy Upgrades of the City s 2035 General Plan Environmental Hazards Element would provide extra measures to identify and mitigate potential risks of seismic hazards for new development and renovation within the Specific Plan Area. Future development included under the proposed Specific Plan would be consistent with these policies, meaning that development located in areas with identified hazards such as those associated with liquefaction potential would appropriately address and be designed to withstand associated hazards to the maximum extent feasible. Compliance with the CBC, PRC Section , 2035 General Plan policies, and the City s Municipal Code would ensure that potential impacts associated with unstable soils and liquefaction are less than significant. Mitigation Measures No mitigation measures are required. Threshold: Would the Specific Plan result in substantial soil erosion or loss of topsoil? IMPACT GEO-2 WITH ADHERENCE TO APPLICABLE LAWS AND REGULATIONS, THE PROPOSED SPECIFIC PLAN WOULD NOT RESULT IN SUBSTANTIAL SOIL EROSION OR THE LOSS OF TOPSOIL. THEREFORE, IMPACTS WOULD BE LESS THAN SIGNIFICANT. As mapped by the NRCS, three soil types are located in the Specific Plan Area (USDA 2017). The Specific Plan Area is comprised primarily of drained Clear Lake clay 0 to 2 percent slopes, MLRA

15 Environmental Impact Analysis Geology and Soils (84.1 acres). The remainder of the Specific Plan Area is comprised of Botella loam 0 to 2 percent slopes, MLRA 14 (54.9 acres) and Danville silty clay loam 0 to 2 percent (15.8 acres). Specific Plan Area soils are shown in Figure 18 and soil characteristics for the Specific Plan Area soils related to water holding capacity, permeability, shrink-swell potential, rate of surface runoff, and erosion hazard are listed in Table 9. The Specific Plan Area lies in a generally flat area, sitting at approximately 29 feet above mean sea level, and the Specific Plan Area soils are characterized by having none or a slight potential for erosion-related hazards, which limits the potential for substantial soil erosion (refer to Section 4.8, Hydrology and Water Quality). In addition, construction activities that disturb one or more acres of land surface are subject to the National Pollutant Discharge Elimination System (NPDES) General Permit for Storm Water Discharges Associated with Construction and Land Disturbance Activities (Order No DWQ) adopted by the State Water Resources Control Board (SWRCB). Compliance with the NPDES permit requires each qualifying development project to file a Notice of Intent with the SWRCB. Permit conditions require the development of a stormwater pollution prevention plan (SWPPP), which must describe the site, the facility, erosion and sediment controls, runoff water quality monitoring, means of waste disposal, implementation of approved local plans, control of construction sediment and erosion control measures, maintenance responsibilities, and nonstormwater management controls. Inspection of construction sites before and after storms is also required to identify stormwater discharge from the construction activity and to identify and implement erosion controls, where necessary. Compliance with the Construction General Permit is reinforced through the City s Municipal Code in Chapter 7-12, which requires erosion and sedimentation control plans that must be submitted with a grading permit application. Furthermore, adherence to Action EH-1.1.A of the 2035 General Plan Environmental Hazards Element, Soils and Geologic Report, would ensure the identification of the soil composition on a specific project site. These reports shall address the degree of hazard, design parameters for the project based on the hazard, and appropriate mitigation measures, as needed. The existing soil composition of the overall Specific Plan Area, along with required compliance with aforementioned policies, NPDES permit and regulations, ensures that impacts associated with substantial soil erosion or loss of topsoil would be less than significant. Mitigation Measures No mitigation measures are required. Threshold: Would the Specific Plan be located on expansive soil, as defined in Table 18-1-B of the Uniform Building Code (1994), creating substantial risks to life or property? IMPACT GEO-3 THE SPECIFIC PLAN AREA IS LOCATED ON EXPANSIVE SOILS. PROPER SOILS ENGINEERING PRACTICES WOULD BE REQUIRED TO ENSURE THAT SOIL CONDITIONS WOULD NOT RESULT IN SIGNIFICANT ADVERSE IMPACTS. WITH REQUIRED IMPLEMENTATION OF STANDARD ENGINEERING PRACTICES, IMPACTS ASSOCIATED WITH UNSTABLE OR EXPANSIVE SOILS WOULD BE LESS THAN SIGNIFICANT. Expansive soils are characterized by high clay content which expands when saturated with water and shrinks when dry, potentially threatening the integrity of buildings and infrastructure foundations. Figure 18 shows that soil types in the proposed Specific Plan Area include the following: Botella loam (0 to 2 percent slope), Clear Lake clay (0 to 2 percent slopes), and Danville silty clay loam (0 to 2 percent slope); as indicated in Table 9, all of these soil types are identified as having Medium, High, or Medium-High potential for shrink-swell behavior, or expansiveness. The Draft Environmental Impact Report 163

16 City of San Leandro Bay Fair Transit Oriented Development (TOD) Specific Plan presence of expansive soils throughout the proposed Specific Plan Area would make it necessary to conduct geologic investigations for all future development projects and ensure that soils for foundation support are sound. Building on unsuitable soils would have the potential to create future subsidence or collapse issues that could result in the settlement of Specific Plan infrastructure, and/or the disruption of utility lines and other services. Compliance with existing State and local laws and regulations, such as the CBC and 2035 General Plan Action EH-1.1-A would ensure that the impacts from development associated with implementation of the Specific Plan on expansive soil are minimized by requiring the submittal and review of detailed soils and/or geologic reports prior to construction. Such evaluation must contain recommendations for ground preparation and earthwork specific to the site, which become an integral part of the construction design. The City s Municipal Code Chapter also restricts grading permits from being issues for any site which is underlain by expansive soils unless the grading plan includes mitigation measures to prevent structural damages which may be caused by conditions due to expansive soils. With adherence to CBC requirements and the City s requirements, potential impacts associated with expansive soils that could occur with implementation of future development under the proposed Specific Plan would be minimized or avoided because specified studies and design considerations would be employed as relevant and feasible at the individual project level. Impacts associated with expansive soils at the program level would be less than significant. Mitigation Measures No mitigation measures are required. Threshold: Would the Specific Plan have soils incapable of adequately supporting the use of septic tanks or alternative waste water disposal systems where sewers are not available for waste water disposal? IMPACT GEO-4 THE PROPOSED SPECIFIC PLAN WOULD NOT INCLUDE SEPTIC TANKS OR ALTERNATIVE WASTEWATER DISPOSAL SYSTEMS. NO IMPACT WOULD OCCUR. Future development in the Specific Plan Area would be served by the Oro Loma Sanitary District, which is responsible for the regulation, collection, treatment and disposal of wastewater from all residential and commercial sources within its sewer service area. The proposed Specific Plan would not include septic tanks or alternative wastewater disposal systems; therefore, there is no potential for adverse effects due to soil incompatibility. No impact would occur. Mitigation Measures No mitigation measures are required. 164

17 Environmental Impact Analysis Geology and Soils c. Cumulative Impacts Cumulative development in Specific Plan Area would gradually increase population and therefore gradually increase the number of people exposed to potential geological hazards, including effects associated with seismic events such as ground rupture and strong shaking. However, conformance with the current CBC and City s 2035 General Plan policies, as well as other laws and regulations mentioned above, would ensure that project-specific impacts associated with geology and soils would be less than significant. Potential impacts associated with geology and soils would not be cumulatively considerable, and cumulative impacts related to geologic hazards would be less than significant. Draft Environmental Impact Report 165

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