4.4 GEOLOGY, SOILS AND SEISMICITY

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1 4.4 GEOLOGY, SOILS AND SEISMICITY This section of the EIR describes the regional geology, regional seismicity, topography and soil and subsurface conditions of the project area, which includes Coaches Field and Blair Park. This section assesses potential impacts from seismically-induced fault rupture, strong ground shaking, liquefaction, seismic-induced landslides, soil erosion and loss of topsoil, slope stability, differential settlement, and unstable or expansive soils. Mitigation measures for the identified significant impacts are provided, as appropriate Existing Setting The following section describes the existing conditions pertinent to geology and soils at the project sites and in the vicinity. The setting description is based on published and unpublished geologic reports and maps from the United States Geological Survey (USGS), the California Geological Survey (CGS), Association of Bay Area Governments (ABAG), site-specific geotechnical investigations conducted for Blair Park, and other sources. Geologic Conditions. The geology, topography, and soil and subsurface conditions of the project sites and surrounding area are described below. Geology. The project sites are located in the Oakland Hills, in the northern portion of the Coast Range geomorphic province of California. The Coast Range province is bound on the east by the Great Valley and on the west by the Pacific Ocean. The region is characterized by northwest-trending mountain ranges and valleys that generally parallel the major geologic structures, such as the San Andreas and Hayward faults. 48 The oldest widespread rocks in the region are highly deformed sedimentary and volcanic rocks of the Mesozoic-age (the period from 225 million to 65 million years before present) Franciscan Assemblage. 49 These rocks are in fault contact with similar-age sedimentary rocks of the Mesozoicage Great Valley Sequence. The Mesozoic rocks are, in turn, overlain by a diverse sequence of Tertiary-age (the period from 65 million to 1.8 million years before present) sedimentary and volcanic rocks. Since their deposition, the Mesozoic and Tertiary rocks have been extensively deformed by repeated episodes of folding and faulting. 50 Within the region, many valleys have been partially filled with unconsolidated sedimentary deposits of Quaternary age (the last 1.8 million years). These deposits, which include alluvium and colluvium, underlie the gently sloping valley bottoms and hillside swales and consist of clay, silt, sand, and gravel Joyce Associates, Geologic Feasibility Investigation, Blair Park Project, Piedmont, California. Prepared for LSA Associates, Inc. 3 October. 49 Graymer, R.W, Geologic map and map database of the Oakland metropolitan area, Alameda, Contra Costa, and San Francisco counties, California: U. S. Geological Survey, Miscellaneous Field Studies Map MF-2342, 1 sheet, scale 1:50, Joyce Associates, op. cit. 51 Ibid. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 173

2 Topography. The project sites are located in Moraga Canyon, which extends west from near SR 13 toward the Mountain View Cemetery located west of Coaches Field. Blair Park is located on the south side of Moraga Avenue at the toe of a north-facing hillside. Along Moraga Avenue, the existing ground surface elevation of the park increases toward the east, from about 397 feet to 490 feet. Areas of the park adjacent to Moraga Avenue are relatively level. Along the southern boundary of the park, the hillside rises to a maximum elevation of approximately 508 feet. 52 Coaches Field is located on the north side of Moraga Avenue at approximately 300 feet above mean sea level. The existing field is relatively level, but the canyon slopes steeply downward to the west and upward to the north and east of the site. Soils and Subsurface Conditions. Soil is generally defined as the unconsolidated mixture of mineral grains and organic material that mantles the land surface. Soils can develop on unconsolidated sediments and weathered bedrock. The characteristics of soil reflect the five major influences on their development: topography, climate, biological activity, parent (source) material, and time. According to the U.C. Davis Soil Resources Lab, natural slopes on the Blair Park site contain soils in the Maymen-Los Gatos Complex. 53 The Maymen series consists of shallow, somewhat excessively drained soils that formed in residuum weathered from shale, schist, greenstone, sandstone and conglomerate. This series occurs on slopes of 5 to 100 percent. Typically, Los Gatos soils have brown, light clay loam, granular, slightly acidic surface soils, and brown and yellowish red, slightly and medium acid clay loam and gravelly clay loam subsurface soils over sandstone bedrock at a depth of 36 inches. 54 The results of the Treadwell & Rollo geotechnical investigation (2009) conducted for Blair Park, which included four subsurface soil borings, indicate that the portions of the Blair Park site adjacent to Moraga Avenue are generally blanketed by artificial fill ranging in thickness from about 13 to 23 feet. 55 Bedrock, consisting of weak sandstone, was encountered about 1.5 feet below the existing ground surface (bgs) in the northeastern portion of the site. According to the geologic feasibility investigation prepared for the site by Joyce Associates (2008), the fill at Blair Park is likely the result of grading to widen Moraga Avenue prior to The fill generally consists of a heterogeneous mix of sand, clay, sandy clay, and clayey sand, with varying amounts of gravel and debris that includes brick and charcoal. The clayey fill encountered in the borings conducted by Treadwell & Rollo was generally moist and medium stiff to very stiff. The sandy and gravelly fill was generally moist and loose to medium dense. 57 At the north side of Moraga Avenue at the entrance to Coaches Field, bedrock was encountered at depths ranging from 25 feet bgs to 30 feet bgs. The Blair Park geologic investigation conducted by Joyce Associates, which included 14 excavated test pits at the rear of the site along the north-facing slope, indicates that this area is generally covered 52 Treadwell & Rollo Environmental and Geotechnical Consultants, Geotechnical Investigation and Geologic Hazard Evaluation, Blair Park Playing Fields, Piedmont, California. Prepared for the City of Piedmont. 27 August. 53 U.C. Davis Soil Resource Laboratory, Online Soil Survey (B.E. Beaudette and A.T. O Geen), California Soil Resource Laboratory. Available online at: Accessed March 18, Ibid. 55 Treadwell & Rollo, op. cit. 56 Joyce Associates, op. cit. 57 Treadwell & Rollo, op. cit. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 174

3 by up to about four feet of surficial soil consisting of sandy silt with clay. 58 The surficial soil is underlain by bedrock that consists of moderately to deeply weathered sandstone and claystone. The surface of the bedrock is occasionally exposed at the ground surface. Groundwater seepage was not observed during the Blair Park site investigation performed by Joyce Associates, 59 and groundwater was not encountered in the borings drilled during the Treadwell & Rollo investigation. 60 Groundwater levels are expected to fluctuate considerably at the Blair Park site based on seasonal variations in rainfall. Additionally, groundwater generally flows through fractures in the upper rock strata and along the soil/rock interface. 61 The facilities at Coaches Field were constructed on top of artificial fill. The soils at the Coaches Field site are mapped as a loam in the Maymen Series. 62 The Maymen series consists of shallow, somewhat excessively drained soils that formed in residuum weathered from shale, schist, greenstone, sandstone and conglomerate. This series occurs on slopes of 5 to 100 percent. Seismic Conditions. The entire San Francisco Bay Area is located in a region of active seismicity. The seismicity of the region is primarily related to the San Andreas Fault Zone (SAFZ), a complex of active faults forming the boundary between the North American and the Pacific plates. Historically, numerous moderate to strong earthquakes have been generated in northern California by several major faults and fault zones in the SAFZ system. The level of active seismicity results in classification of the San Francisco Bay Area as seismic risk Zone 4 (the highest risk category) in the California Building Code. The SAFZ includes numerous faults found by the CGS under the Alquist- Priolo Earthquake Fault Zoning Act (A-PEFZA) to be active (i.e., to have evidence of fault rupture in the past 11,000 years). Some of the major active faults within the SAFZ include the San Andreas, Mayacama, Hayward-Rodgers Creek, San Gregorio-Seal Cove, Concord-Green Valley, Greenville, and Calaveras faults. The principal active faults in the project area include the Hayward Fault, located approximately 2,700 feet east of Blair Park; the San Andreas Fault, located 8.5 miles to the southwest; and the Calaveras Fault, located approximately 10.7 miles to the east of the project area Regional active faults are shown on Figure Figure also shows the earthquake epicenters for events with a Moment Magnitude (M W ) 65 greater than 5.0 from January 1800 through January Joyce Associates, op. cit. 59 Ibid. 60 Treadwell & Rollo, op. cit. 61 Ibid. 62 U.C. Davis Soil Resource Laboratory, op. cit. 63 Jennings, Charles W., Fault Activity Map of California and Adjacent Areas, with Locations and Ages of Recent Volcanic Eruptions: California Division of Mines and Geology Geologic Data Map No. 6, 1:750, Wagner, D. L., E. J. Bortugno, and R. D. McJunkin, Geologic Map of the San Francisco-San Jose Quadrangle, California: California Division of Mines and Geology Regional Geologic Map Series Map No. 5A (Geology), 1:250, Moment Magnitude is an energy-based scale and provides a physically-meaningful measure of the size of a faulting event. Moment Magnitude is directly related to the average slip and fault rupture area. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 175

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5 PROJECT FIGURE NOTES: Digitized data for fault coordinates and earthquake catalog was developed by the California Department of Conservation Division of Mines and Geology. The historic earthquake catalog includes events from January 1800 to December SOURCE: TREADWELL & ROLLO (2009) P:\CPI0901\g\EIR\Figure 4.4.1_SFBayAreaMajorFaults&EarthquakeEpicenters.ai (05/11/10) Moraga Canyon Sports Fields Project Major Faults and Earthquake Epicenters in the San Francisco Bay Area

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7 The U.S. Geological Survey s Working Group on California Earthquake Probabilities estimated that there is a 63 percent probability that between 2008 and 2038, a 6.7 or greater magnitude earthquake will occur in the San Francisco Bay Region. 66 The probability of a 6.7 magnitude or greater earthquake occurring along individual faults was estimated to be 21 percent along the San Andreas Fault, 31 percent along the Hayward-Rodgers Creek Fault, and 7 percent along the Calaveras Fault. In addition, there is a cumulative 14 percent chance of a background (other earthquake source, either mapped or undiscovered) event occurring. When predictions are expanded to 100 years, it is estimated that about three M W 6.7 or greater events could occur during that time. Thus, the probability of at least one M W 6.7 or greater earthquake rises to approximately 96 percent when calculated for a 100-year span. 67 Seismic and Geologic Hazards. Seismic and geologic hazards specific to the project sites are discussed below. Surface Rupture. Surface rupture occurs when the ground surface is broken due to fault movement during an earthquake. The location of surface rupture generally can be assumed to be along an active or potentially active major fault trace. There are no A-PEFZA active or potentially active 68 faults mapped that intersect the project area. 69 The project area does not intersect an Alquist-Priolo Earthquake Fault Zone, and the nearest A-PEFZA fault zone is located approximately 2,700 feet east of Blair Park along the Hayward Fault. A thrust fault mapped just east of the Blair Park site by Graymer 70 and through the site by Dibblee 71 is not considered active. 72 The next nearest active fault is the San Andreas Fault located 8.5 miles to the southwest of the project area. Both the San Andreas and Hayward-Rodgers Creek faults are right lateral strike-slip faults with a northwest-southeast axis, 73 and, as noted above, have a 21 percent and 31 percent chance, respectively, of an M w 6.7 earthquake occurring between 2008 and Ground Shaking. Ground shaking is a general term referring to all aspects of motion of the earth s surface resulting from an earthquake, which is normally the major cause of damage in seismic events. The extent of ground shaking is controlled by the magnitude and intensity of the earthquake, distance from the epicenter, and local geologic conditions. A related concept is acceleration, which is measured as a fraction or percentage of the acceleration gravity (g); it measures the acceleration of the ground as it moves during an earthquake. The Modified Mercalli Intensity Scale (MMI) is the Working Group on California Earthquake Probabilities, 2008, The Uniform California Earthquake Rupture Forecast, Version 2 (UCERF 2): U.S. Geological Survey Open-File Report and California Geological Survey Special Report 203 [ 67 Ibid. 68 Originally defined as those faults showing Quaternary displacement, since 1975 limited to those with a relatively high potential for ground rupture, sufficiently active (Holocene displacement somewhere on the fault), and well defined. 69 Bryant, William A., Hart, Earl W., Interim Revision Special Publication 42: Fault-Rupture Hazard Zones in California, Alquist-Priolo Earthquake Fault Zoning Act with Index to Earthquake Fault Zones Maps. California Department of Conservation, California Geological Survey. 70 Graymer, R.W, op. cit. 71 Dibblee, Thomas W., Jr., Geologic Map of the Oakland East Quadrangle, Contra Costa and Alameda and Counties, California: Dibblee Geology Center Map #DF :24, Joyce Associates, op. cit. 73 Right-lateral: If the trace of the fault were viewed while standing on one side during an event, it would appear that the ground on the other side of the fault moved to the right. Strike-slip: The sides of a fault are moving laterally relative to each other with little or no vertical movement. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 179

8 most commonly used scale for measurement of the subjective effects of earthquake intensity (Table 4.4.A). The closest active fault to the project area is the South Hayward Segment of the Hayward- Rodgers Creek Fault, located approximately 2,700 feet to the east of Blair Park. The ABAG earthquake hazard mapping, which is based on research by the USGS, indicates that a Magnitude 6.7 event on the South Hayward Fault would result in very strong (VIII) shaking in the project area. 74 Other potentially damaging seismic sources located in the vicinity of the project area include the San Andreas Fault, approximately 8.5 miles to the southwest. According to the ABAG mapping, a Magnitude 7.9 event on the San Andreas Fault (similar to the 1906 earthquake) would result in moderate (VI) shaking in the project area. 75 Estimates of the peak ground acceleration have been made for the Bay Area based on probabilistic models that account for multiple seismic sources. Under these models, consideration of the probability of expected seismic events is incorporated into the determination of the level of ground shaking at a particular location. The CGS estimates the expected peak horizontal acceleration generated by any of the seismic sources potentially affecting the project area as approximately This level of ground acceleration at the project area is a potentially significant hazard; and park facilities would need to be constructed to withstand the expected acceleration of the ground. Liquefaction and Lateral Spreading. Liquefaction is the temporary transformation of loose, saturated granular sediments from a solid state to a liquefied state as a result of seismic ground shaking. In the process, the soil undergoes transient loss of strength, which commonly causes ground displacement or ground failure to occur. This can result in either incremental or catastrophic structural failure. Liquefaction potential varies according to the thickness of the alluvial deposits, the distribution of clay-free granular materials within those deposits, and the abundance of groundwater shallower than 50 feet. Since saturated soils are a necessary condition for liquefaction, soil layers in areas where the groundwater table is near the surface have higher liquefaction potential than those in which the water table is located at greater depths. 77 Because groundwater was not encountered during any of the subsurface investigations on the Blair Park site and the subsurface generally consists of shallow bedrock, the potential for liquefaction is low The ABAG liquefaction susceptibility map confirms that the risk is very low for both the Coaches Field and Blair Park sites ABAG, Earthquake Shaking Scenario, South Hayward Segment of the Hayward-Rodgers Creek Fault System: Magnitude 6.7 event. Available online at: Accessed March 18, ABAG, Earthquake Shaking Scenario, Entire San Andreas Fault System: Magnitude 7.9 event. Available online at: Accessed March 18, California Geological Survey (CGS), 2007 revised 2008, Probabilistic Seismic Hazards Mapping Ground Motion Website, Available online at: Accessed March 18, Perkins, Jeanne B., The Real Dirt on Liquefaction, A Guide to the Liquefaction Hazard in Future Earthquakes Affecting the San Francisco Bay Area. ABAG Publication Number: P01001EQK, February. 78 Treadwell & Rollo, op. cit. 79 Joyce Associates, op. cit. 80 ABAG, Liquefaction Susceptibility Map. Available online at: Accessed March 19, P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 180

9 Table 4.4.A: Modified Mercalli Intensity Scale I II III IV V VI VII VIII IX X XI Not felt except by a very few under especially favorable circumstances. Felt only by a few persons at rest, especially on upper floors of buildings. Delicately suspended objects may swing. Felt quite 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 like passing of truck. Duration estimated. 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. Felt by nearly everyone, many awakened. Some dishes, windows, etc., broken; a few instances of cracked plaster; unstable objects overturned. Disturbances of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop. Felt by all, many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged chimneys. Damage slight. Everybody runs outdoors. Damage negligible in building 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. 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, and walls. Heavy furniture overturned. Sand and mud ejected in small amounts. Changes in well water. Persons driving motor cars disturbed. 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. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed (slopped) over banks. Few, if any, (masonry) structures remain standing. Bridges destroyed. Board fissures in ground. Underground pipelines completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly. Damage total. Practically all works of construction are damaged greatly or destroyed. Waves seen XII on ground surface. Lines of sight and level are distorted. Source: California Geological Survey, How Earthquakes and Their Effects are Measured: Note 32. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 181

10 Lateral spreading is a form of horizontal displacement of soil toward an open creek channel or other free face, such as an excavation boundary. Lateral spreading can result from either the slump of low-cohesion unconsolidated material or more commonly by liquefaction of either the soil layer or a subsurface layer underlying soil material on a slope. 81 The lateral spreading hazard tends to mirror the liquefaction hazard for a site. Therefore, the potential for lateral spreading at both project sites is low because the potential for liquefaction at both project sites is low. 82 Expansive Soils. Expansion and contraction of volume can occur when expansive soils undergo alternating cycles of wetting (swelling) and drying (shrinking). During these cycles, the volume of the soil changes markedly. As a consequence of such volume changes, structural damage to building and infrastructure may occur if the potentially expansive soils were not considered in project design and during construction. Expansive soils generally consist of clay soils that may shrink and swell in accordance with water content. Some of the soils at the Blair Park site are clay soils and thus are potentially expansive. The geologic feasibility investigation prepared by Joyce Associates concludes, based on the subsurface testing, that the existing fill on the site is composed largely of relatively non-expansive materials. 83 The soils underlying the Coaches Field site consist of sandy loam that generally drains adequately and was placed as fill over sandstone, shale, and fill during the construction of the field. These soils are not generally expansive. Slope Stability and Landslides. Slope failure can occur as either rapid movement of large masses of soil ( landslide ) or slow, continuous movement ( creep ). The primary factors influencing the stability of a slope are: 1) the nature of the underlying soil or bedrock, 2) the geometry of the slope (height and steepness), 3) rainfall, and 4) the presence of previous landslide deposits. According to CGS mapping prepared in accordance with the Seismic Hazards Mapping Act of 1990, the slope along the southern boundary of the Blair Park site is within the designated seismic hazard zone for earthquake-induced landslides. 84 A review of maps published between the years of 1969 and 2005 by the USGS, CGS, and other organizations as part of the geologic feasibility investigation for Blair Park indicated that no landslides were mapped within or near the site. 85 The review of aerial photographs conducted as part of this same study also revealed no indications of landslides within or above Blair Park; however, three soil slips that resulted in the movement of debris into the site were observed on aerial photographs from These soil slips originated in the undeveloped portions of the private property above the site. Soil slips typically occur during periods of unusually intense rainfall. The resulting soil slip is typically relatively small amounting to a few cubic yards or tens of cubic yards of material. This material moves down slope coming to rest at the toe of the slope. Aerial photographs indicate that soil slips have occurred only once during the last 60 years at the Blair Park site. Soil slips of this type are unlikely to present a public safety hazard because they are relatively 81 Rauch, Alan F., EPOLLS: An Empirical Method for Predicting Surface Displacements due to Liquefaction-Induced Lateral Spreading in Earthquakes, Ph. D. Dissertation, Virginia Tech, Blacksburg, VA. 82 Treadwell & Rollo, op. cit. 83 Joyce Associates, op. cit. 84 California Geological Survey, 2003b. State of California Seismic Hazards Zones, Oakland East and Part of Las Trampas Ridge Quadrangles. Prepared by James F. Davis, State Geologist. Delineated in Compliance with Chapter 7.8, Division 2 of the California Public Resources Code (Siesmic Hazards Mapping Act). Official Map Released 14 February, Joyce Associates, op. cit. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 182

11 small, and occur infrequently. 86 The Joyce Associates geologic feasibility report concluded the risk of earthquake-induced landsliding is very low for the Blair Park site under existing conditions. 87 The Coaches Field site is relatively flat. However, CGS mapping indicates that the slopes surrounding the site have been designated as being in the seismic hazard zone for earthquake-induced landslides. 88 Settlement and Differential Settlement. Settlement or differential settlement of development could occur if they were built on low-strength foundation materials (including imported non-engineered fill) or if constructed features straddle the boundary between different types of subsurface materials (e.g., a boundary between native material and fill). Although settlement generally occurs slowly enough that its effects are not dangerous to users, it can cause significant structural damage over time. According to the Treadwell & Rollo geotechnical report prepared for Blair Park, up to 23 feet of heterogeneous fill is present on the site, and placement of several feet of new engineered (compacted) fill is planned. 89 Elastic settlement of the existing fill and planned engineered fill may occur. The geotechnical investigation concluded that near-surface Blair Park site modifications supported on fill, in its current condition, may experience erratic settlements of up to two percent of the total existing fill thickness and up to one-half percent of the total proposed fill thickness. 90 Elastic compression of the existing fill would result in immediate settlements up to about 5.5 inches. These settlements would occur during construction as the new fill is being placed and no significant post-construction settlement is anticipated. 91 Treadwell & Rollo estimate that settlements associated with the compression of proposed engineered fill placed at the Blair Park site would be up to 0.5 inch. Cyclic densification 92 of non-saturated sand (sand above the groundwater table) caused by earthquake vibrations may also result in differential settlement on the site. Calculated settlements resulting from cyclic densification range from less than 0.5 inch to approximately 2.8 inches. 93 On the Coaches Field site, soils were compacted during the construction of the existing field to minimize differential settlement. No additional fill would be placed on the Coaches Field site as part of the proposed project Regulatory Framework The following section describes the regulatory framework related to the geology and soils of the project area. California Geological Survey. The Alquist-Priolo Earthquake Fault Zoning Act of 1972 (prior to January 1, 1994 known as the Alquist-Priolo Special Studies Zones Act CCR, Title 14, Section 3600) sets forth the policies and criteria of the State of California in regard to building within active 86 Ibid. 87 Ibid. 88 California Geological Survey, 2003b. op. cit. 89 Treadwell & Rollo, op. cit. 90 Ibid. 91 Ibid. 92 Cyclic densification is a phenomenon in which non-saturated, cohesionless soil is densified by earthquake vibrations, causing settlement. 93 Ibid. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 183

12 fault zones. The Alquist-Priolo Earthquake Fault Zoning Act outlines the responsibilities of cities and counties to prohibit the location of developments and structures for human occupancy across the trace of active faults. The policies and criteria are limited to potential hazards resulting from surface faulting or fault creep within Earthquake Fault Zones delineated on maps officially issued by the State Geologist. No active faults have been mapped crossing the project area; it is therefore not subject to the restrictions of the Alquist-Priolo Act. Uniform Building Code and California Building Code. The Uniform Building Code (UBC) was first enacted in 1927 and has been revised approximately every three years since then. The function of the UBC is to promote the development of improved building construction and greater safety to the public by uniformity in building laws. The UBC is founded on broad-based principles that make possible the use of new materials and new construction systems. It is designed to be compatible with related publications to provide a complete set of documents for regulatory use. The UBC recognizes that nearly all of western California is seismically active, and that within this broad region there are areas underlain by deeper unconsolidated deposits that are subject to higher amplitude, longer duration shaking motions. Thus, while these shaking impacts are potentially more damaging, implementation of UBC criteria tend to reduce these effects. From the standpoint of earthworks construction and seismic criteria, the UBC and the California Building Code (CBC) are nearly identical. The UBC includes a seismic zone map to determine applicable seismic standards for proposed structures. Seismic zones range from 0 to 4, with Zone 0 being the least active and Zone 4 the most active. The City of Piedmont is located in Seismic Zone 4. All structures built in the City must comply with requirements for this zone, which include provisions for buildings to structurally survive an earthquake without collapsing and include such measures as anchoring to the foundation and structural frame design. Structures within the project area must be constructed in accordance with UBC Seismic Zone 4 criteria. Seismic Hazards and Mapping Act. The Seismic Hazards Mapping Act of 1990 (Public Resources Code, Chapter 7.8, Section ) directs the Department of Conservation, California Geological Survey to identify and map areas prone to earthquake hazards of liquefaction, earthquakeinduced landslides, and amplified ground shaking. The purpose of the act is to reduce the threat to public safety and to minimize the loss of life and property by identifying and mitigating these seismic hazards. The act was passed by the state Legislature following the 1989 Loma Prieta earthquake. This pertains to seismic hazards other than the fault surface rupture hazard regulated by the Alquist-Priolo Earthquake Fault Zoning Act of The maps produced per the Seismic Hazards Mapping Act are the Seismic Hazard Zone Maps, prepared by California Geological Survey geologists in the Seismic Hazard Mapping Program (Program). The Program will ultimately map all of California s principal urban and major growth areas. Each map covers an area of approximately 60 square miles and uses a scale of 1 inch = 2,000 feet (1:24,000 scale). The Seismic Hazard Zone maps include designated Zones of Required Investigation for areas prone to liquefaction and earthquake-induced landslides. Once a map becomes available for a certain area, cities and counties within that area are required to withhold development permits for projects proposed within a Zone of Required Investigation until geologic and soil conditions are investigated and appropriate mitigations, if any, are incorporated into development plans. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 184

13 The project sites are mapped in the Oakland East Quadrangle. 94 The Blair Park site and a portion of the Coaches Field site are mapped as Zones of Required Investigation for earthquake induced landslides, and are subject to the requirements of the Seismic Hazards Mapping Act. City of Piedmont General Plan (2009). The Environmental Hazards Element of the City of Piedmont General Plan (2009) contains policies pertaining to geologic hazards, seismic design standards, and geotechnical studies required for proposed developments. Policies relevant to the proposed project include: Policy 13.1: Respecting Natural Terrain. Maintain the natural topography of Piedmont by avoiding lot splits and subdivisions that would lead to large-scale grading and alteration of hillsides. Planning and building regulations should ensure that any construction on steep slopes is sensitively designed and includes measures to stabilize slopes, reduce view blockage, and mitigate adverse environmental impacts. Policy 18.1: Restricting Development on Unstable Sites. Permit development only in those areas where potential danger to the health, safety, and welfare of Piedmont residents can be adequately mitigated. Policy 18.2: Seismic Design Standards. Maintain and enforce seismic design and construction standards which meet or exceed the standards established by the Building Code. Piedmont s Municipal Code should be periodically reviewed, updated, and amended to incorporate the most current knowledge and highest standards of seismic safety. Policy 18.4: Soil and Geologic Reports. Require site-specific soils reports and geologic studies in instances where development may be exposed to substantial geologic or seismic hazards, including ground shaking and landslides. Ensure that any identified hazards are appropriately mitigated. City of Piedmont Municipal Code. The City of Piedmont Municipal Code contains various ordinances relevant to the conditions of the geology and soils of the proposed project. Outlined below are City of Piedmont Code excerpts pertaining to building design and soil investigations, excavations, and erosion control/stormwater management which relate to the proposed project. City Code Chapter 5: Building Code. Section 5.1 of the City Code adopts the 2007 California Building Code (CBC). Section 5.2 contains City-adopted amendments to the CBC. The amendment in Section requires a soils report prepared by a State licensed engineer for sites with slopes of 20 percent or greater. City Code Chapter 7: Excavations Generally. Chapter 7 of the City Code requires a permit for excavation, including the removal of any soil, rock, sand or other material for purposes of sale, fill, building or other construction usage off the premises from which removed. The chapter details permit application procedures and conditions. 94 California Geological Survey, 2003b. op. cit. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 185

14 4.4.3 Significance Criteria The proposed project would result in a significant geologic, soils or seismic impact if it would have any of the following effects: Expose people or structures to potential substantial adverse effects, including the risk of loss, injury, or death involving: - 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. (Refer to Division of Mines and Geology Special Publication 42); - Strong seismic ground shaking; - Seismic-related ground failure (including liquefaction); and/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, creating substantial risks to life or property; or Be subject to or cause differential settlement, creating risks to life or property Impacts and Mitigation Measures This section describes the potential impacts to geology and soils of the project. The section presents the impacts associated with the proposed project and identifies mitigation measures, if appropriate. Less than significant impacts are discussed first, followed by significant impacts. Less Than Significant Geology and Soil Impacts. The following describes the less than significant geology and soils impacts associated with the project. (1) Fault Rupture. No active or potentially active faults have been mapped at, or directly adjacent to, the project sites, and no portion of the project area is located within an Alquist-Priolo Earthquake Fault Zone. The closest active fault is the Hayward Fault, which is located approximately 2,700 feet east of Blair Park. Therefore, the potential for fault rupture at either site is very low. (2) Liquefaction and Lateral Spreading. As described above, the risk of liquefaction and lateral spreading is low for both project sites based on the findings of the geotechnical reports prepared for Blair Park and ABAG hazards mapping for both Blair Park and Coaches Field. Therefore, this impact is less than significant. (3) Subsidence or Collapse. Subsidence is the sinking of the earth s surface in response to geologic or man-induced causes. Primary causes of subsidence include the collapse of subsurface limestone, mining, extraction of water or petroleum by means of wells, and irrigation of virgin areas P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 186

15 of alluvial deposits. The project sites do not contain limestone, and mining and water extraction have not occurred on the project sites. Therefore, the risk of subsidence or collapse on the project sites is low. Potentially Significant Geology and Soils Impacts. Implementation of the proposed project could result in the following significant geology and soils impacts, as described below. (1) Strong Seismic Groundshaking. The entire San Francisco Bay Area, including the project area, is in a seismically-active region subject to varying degrees of seismic groundshaking. Considering the proximity of the project sites to the Hayward, San Andreas, and other major active faults in the San Francisco Bay Area, there is a high potential for the project sites to experience moderate to very strong ground shaking during a major earthquake. 95 Impact GEO-1: Strong seismic groundshaking at the project sites could result in risks to humans and damage to property. (S) The proposed project would be constructed in compliance with the latest and most stringent seismic guidelines in accordance with the 2007 California Building Code, Alameda County Code, and the City of Piedmont Municipal Code. In addition, use of the proposed project would occur primarily outdoors, which would reduce the risk of injury or death. Structural collapse is responsible for 75 percent of earthquake-related fatalities. 96 Nevertheless, injuries, death, or damage to structures could still occur during a seismic event. The closest active fault to the project area is the South Hayward Segment of the Hayward-Rodgers Creek Fault, located approximately 2,700 feet to the east of Blair Park. A Magnitude 6.7 event on the South Hayward Fault would result in very strong (VIII) shaking in the project area. 97 The Treadwell and Rollo geotechnical investigation prepared for Blair Park contains specific design criteria for construction of project features (e.g, retaining walls, concession building, and pedestrian bridge) in response to expected seismic events. Seismic hazards cannot be completely eliminated, even with site-specific geotechnical methods and advanced building practices. However, exposure to seismic hazards is a generally accepted part of living in the seismically active areas of California, and therefore the mitigation measure described below would reduce the potential hazards associated with seismic activity to a less than significant level. Mitigation Measure GEO-1: Design and construction of the proposed project shall be in conformance with current best standards for earthquake resistant construction in accordance with the California Building Code (Seismic Zone 4), applicable local codes, and in accordance with the generally accepted standard of geotechnical practice for seismic design in Northern California. In addition, project design for the Blair Park site shall follow the recommendations of the site-specific geotechnical investigation reports prepared for the proposed project by Joyce Associates (2008) and Treadwell & Rollo (2009). The City Engineer shall approve all final design and engineering plans prior to 95 Treadwell & Rollo, op. cit. 96 Colburn, A.W., Spence, R.J.S., and Pomonis, A., Factors determining human casualty levels in earthquakes: Mortality prediction in building collapse: Proceedings of the Tenth World Conference on Earthquake Engineering, pp ABAG, op. cit. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 187

16 issuance of a grading permit. Prior to construction, a qualified engineering geologist shall review the project plans and specifications for Blair Park to verify that they conform to the intent of the recommendations included in their 2009 geotechnical report. During construction, a qualified engineering geologist shall provide on-site observation and testing. (LTS) (2) Soil Erosion or Loss of Topsoil. Implementation of the proposed project would include vegetation removal, excavation, grading and placement of fill that could result in short-term soil erosion or loss of topsoil during the construction period. Exposed soils are considered erodible when subjected to concentrated surface flow or wind. Impact GEO-2: Construction activities of the proposed project could result in soil erosion and loss of topsoil. (S) As authorized by the Clean Water Act, the National Pollutant Discharge Elimination System (NPDES) permit program controls water pollution by regulating point sources that discharge pollutants into waters of the United States. The NPDES permit program requires the preparation of a storm water pollution prevention plan (SWPPP) for projects that result in at least one acre of ground disturbance. The SWPPP prepared for the proposed project would incorporate best management practices (BMPs) for erosion control that are recognized by the Regional Water Quality Control Board. BMPs would include, but would not be limited to, utilization of hay bales for reducing siltation from runoff; timely covering of Coaches Field with the new synthetic turf after the existing grass turf is stripped; restricting grading, excavation, placement of fill, and vegetation removal to the dry season; and street sweeping (See Section 4.6, Hydrology and Water Quality). Soil erosion and loss of topsoil would also be minimized through implementation of the BAAQMD fugitive dust control measures (See Section 4.9, Air Quality). In addition, the Treadwell & Rollo geotechnical report 98 contains recommendations for surface drainage on the Blair Park project site that would help to prevent soil erosion. Implementation of Mitigation Measure GEO-2, described below, would ensure adherence to these recommendations and would reduce impacts related to soil erosion and loss of topsoil to a less than significant level. Mitigation Measure GEO-2: Prior to issuance of a grading permit for construction at Coaches Field or Blair Park, a site-specific erosion control plan shall be prepared by a licensed professional and submitted to the Public Works Department for review and approval. Consistent with the geotechnical report prepared by Treadwell & Rollo, the proposed Blair Park project shall also incorporate the following additional recommendations related to surface drainage and the minimization of erosion. These recommendations shall be incorporated, by reference, into the Erosion Control Plan. Surface drainage shall be provided to collect surface runoff, prevent surface erosion, contain slough, and prevent saturation of the engineered fill. All surfaces shall be sloped to drain and all water shall be directed to lined v-ditches to collect and transport runoff water to a suitable outlet or retention basin. Lined v-ditches shall be constructed at the crest of all engineered slopes, at the back of all terraced benches in 98 Ibid. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 188

17 cut areas, and at the toe of all slopes greater than five feet in height, including slopes above retaining walls. The v-ditches shall be cleaned and maintained on a regular basis. The final engineered slopes shall be re-vegetated by seeding or hydro-mulching with deeply-rooted, fast-growing vegetation as soon as possible after grading. If the vegetation will not be established prior to the rainy season, slopes shall be protected using measures such as netting, hay bales, and/or silt fences. Slopes shall not be irrigated except for an initial period if necessary to establish vegetation. (LTS) (3) Landslides and Slope Instability. The existing Coaches Field site is relatively flat. The potential for landslides was previously addressed as part of the original field development, which included a geotechnical investigation followed by the construction of a retaining wall, placement of drains, and the planting of landscaping to stabilize the toe and slope above the northern perimeter of the site. 99 Any risks associated with landslides would be similar to existing conditions at the Coaches Field site after project completion. Therefore, the potential for landslide impacts at the Coaches Field site is less than significant. However, the slope along the southern boundary of the Blair Park site is within the designated seismic hazard zone for earthquake-induced landslides. 100 A review of maps published between the years of 1969 and 2005 by the USGS, CGS, and other organizations as part of the geologic feasibility investigation for Blair Park indicated that no landslides were mapped within or near the site. 101 However, three rainfall-induced soil slips have occurred over the last 60 years at the Blair Park site, based on a review of aerial photography. 102 The proposed project includes slope-cuts and retaining walls that could potentially increase the instability of the existing hillsides on the project site. Retaining walls would be constructed along the north-facing slope behind both sports fields to create a level playing surface. Along Moraga Avenue, a landscaped berm would be constructed with a retaining wall at the northeast corner of the large field. The proposed project would also include three underground water storage tanks on the Blair Park site. Excavation for the installation of the onsite underground water storage tanks could increase slope instability. Impact GEO-3: Slope excavation and installation of retaining walls and onsite underground water storage tanks could cause slope instability potentially resulting in landslides at Blair Park. (S) The reports by Joyce Associates and Treadwell & Rollo conclude that the proposed Blair Park project is feasible from a geologic and geotechnical standpoint based on the results of the subsurface investigation and review of available information, assuming that the geotechnical recommendations included in the reports are implemented The Treadwell & Rollo report states that the principal 99 Larry Seeman Associates, Environmental Impact Report, Moraga Sports Field Corporation Yard Relocation. Prepared for the City of Piedmont. 31 January. 100 California Geological Survey, 2003b. op. cit. 101 Joyce Associates, op. cit. 102 Ibid. 103 Joyce Associates, op. cit. 104 Treadwell & Rollo, op. cit. P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 189

18 geologic concerns for the proposed project include the feasibility of constructing the required retaining walls in relation to the future stability of the slope and the potential for future soil slips on the slope to deposit debris within the site. The Joyce Associates geologic feasibility report states that if the retaining walls are designed to meet accepted safety standards for both static and earthquake forces, in accordance with the current California Building Code, the risk of slope instability in the retaining wall area would be very low. 105 The Treadwell & Rollo geotechnical report contains recommendations on the method of slope excavation and the design of the retaining wall to ensure that the proposed project would meet safety standards and adhere to relevant building codes. 106 Implementation of Mitigation Measures GEO-3 and GEO-4, described below, would ensure adherence to the recommendations contained in the Treadwell & Rollo geotechnical report and would reduce impacts related to landslides and slope instability on the Blair Park site to a less than significant level. Mitigation Measure GEO-3: Project design of the retaining walls at Blair Park shall be in accordance with the recommendations contained in the site-specific geotechnical investigation prepared by Treadwell & Rollo (e.g., specifications related to slope grade, resistance to static pressure, backdrainage, backfill materials, permanent tiebacks, etc.). The design and construction of the retaining walls shall be in conformance with current best standards for earthquake resistant construction in accordance with the California Building Code (Seismic Zone 4), applicable local codes, and in accordance with the generally-accepted standard of geotechnical practice for seismic design in Northern California. Prior to issuance of a grading permit, detailed retaining wall design drawings and a site-specific grading plan for the project site shall be prepared by a licensed professional and submitted to the City Engineer for review and approval. The retaining wall design drawings shall be reviewed by a qualified engineering geologist and show the heights of the walls, the backfill material type, drainage details, and the earth pressure used in design. The grading plan shall include reference to the site-specific recommendations included in the Treadwell & Rollo geotechnical report. All cut slopes shall be observed by a qualified engineering geologist at the time of grading to assess the applicability of the recommendations and make supplemental recommendations, if necessary. Supplemental recommendations may include slope flattening, installation of drainage, slope reconstruction in areas where weak rock, adverse bedding, or other local anomalies are encountered, or construction of retaining walls. Retaining wall tieback installation and testing shall be observed by a qualified engineering geologist. (LTS) Mitigation Measure GEO-4: The following measures, provided by Treadwell & Rollo subsequent to the preparation of the final geotechnical report 107, shall be implemented to reduce slope stability impacts related to the installation of underground water storage tanks. The excavations for underground water tank installation shall be sloped or shored depending on their depth and the contractor s preference. 105 Joyce Associates, op. cit. 106 Treadwell & Rollo, op. cit. 107 Rodgers, Richard Geotechnical Engineer for Treadwell & Rollo. Personal Communication ( ) with Clarence Mamuyac of ELS Architecture and Urban Design and LSA Associates, April 12, P:\CPI0901\EIR\Public Review Draft\MoragaSportsDEIR_Public Review.doc (06/18/10) 190