IV. Environmental Impact Analysis E. Geology and Soils
1. Introduction
This section of the Draft EIR analyzes the Project’s potential impacts with regard to geology and soils. The analysis includes an evaluation of the potential geologic hazards associated with potential rupture of a known earthquake fault, seismic ground shaking, seismic-related ground failure, landslides, erosion, geologic unit and soil stability, and expansive soils. The analysis is based on review of California regulatory requirements, City of Los Angeles requirements, and the Geology and Soils Technical Report (Geotechnical Report) prepared for the Project Site by Geotechnologies, Inc. (February 2015), included as Appendix F of this Draft EIR.
2. Environmental Setting a. Regulatory Framework
(1) State of California
(a) Alquist-Priolo Earthquake Fault Zoning Act
The Alquist-Priolo Earthquake Fault Zoning Act (Public Resources Code Section 2621) was enacted by the State of California in 1972 to address the hazard of surface faulting to structures for human occupancy.1 The Alquist-Priolo Earthquake Fault Zoning Act was enacted in response to the 1971 San Fernando Earthquake, which was associated with extensive surface fault ruptures that damaged homes, commercial buildings, and other structures. The primary purpose of the Alquist-Priolo Earthquake Fault Zoning Act is to prevent the construction of buildings intended for human occupancy on the surface traces of active faults. The Alquist-Priolo Earthquake Fault Zoning Act is also intended to provide citizens with increased safety and to minimize the loss of life during and immediately following earthquakes by facilitating seismic retrofitting to strengthen buildings against ground shaking.
1 The Act was originally entitled the Alquist-Priolo Geologic Hazards Zone Act.
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The Alquist-Priolo Earthquake Fault Zoning Act requires the State Geologist to establish regulatory zones, known as “Earthquake Fault Zones,” around the surface traces of active faults and to issue appropriate maps to assist cities and counties in planning, zoning, and building regulation functions. Maps are distributed to all affected cities and counties for the controlling of new or renewed construction and are required to sufficiently define potential surface rupture or fault creep. The State Geologist is charged with continually reviewing new geologic and seismic data, and revising existing zones and delineating additional earthquake fault zones when warranted by new information. Local agencies must enforce the Alquist-Priolo Earthquake Fault Zoning Act in the development permit process, where applicable, and may be more restrictive than State law requires. According to the Alquist-Priolo Earthquake Fault Zoning Act, before a project can be permitted, cities and counties shall require a geologic investigation, prepared by a licensed geologist, to demonstrate that buildings will not be constructed across active faults. If an active fault is found, a structure for human occupancy cannot be placed over the trace of the fault and must be set back. Although setback distances may vary, a minimum 50-foot setback is required. The Alquist-Priolo Earthquake Fault Zoning Act and its regulations are presented in California Department of Conservation, California Geological Survey, Special Publication 42, Fault-Rupture Hazard Zones in California.
(b) Seismic Safety Act
The California Seismic Safety Commission was established by the Seismic Safety Act in 1975 with the intent of providing oversight, review, and recommendations to the Governor and State Legislature regarding seismic issues. The Commission’s name was changed to Alfred E. Alquist Seismic Safety Commission in 2006. Since then, the Commission has adopted several documents based on recorded earthquakes, including:2
Research and Implementation Plan for Earthquake Risk Reduction in California 1995 to 2000, report dated December 1994;
Seismic Safety in California’s Schools, “Findings and Recommendations on Seismic Safety Policies and Requirements for Public, Private, and Charter Schools,” report dated December 2004;
Findings and Recommendations on Hospital Seismic Safety, report dated November 2001; and
Commercial Property Owner’s Guide to Earthquakes Safety, report dated October 2006.
2 Alfred E. Alquist Seismic Safety Commission. Publications, www.seismic.ca.gov/pub.html, accessed October 14, 2014.
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(c) Seismic Hazards Mapping Act
In order to address the effects of strong ground shaking, liquefaction, landslides, and other ground failures due to seismic events, the State of California passed the Seismic Hazards Mapping Act of 1990 (Public Resources Code Section 2690-2699). Under the Seismic Hazards Mapping Act, the State Geologist is required to delineate “seismic hazard zones.” Cities and counties must regulate certain development projects within these zones until the geologic and soil conditions of the project site are investigated and appropriate mitigation measures, if any, are incorporated into development plans. The State Mining and Geology Board provides additional regulations and policies to assist municipalities in preparing the Safety Element of their General Plan and encourage land use management policies and regulations to reduce and mitigate those hazards to protect public health and safety. Under Public Resources Code Section 2697, cities and counties shall require, prior to the approval of a project located in a seismic hazard zone, a geotechnical report defining and delineating any seismic hazard. Each city or county shall submit one copy of each geotechnical report, including mitigation measures, to the State Geologist within 30 days of its approval. Public Resources Code Section 2698 does not prevent cities and counties from establishing policies and criteria which are stricter than those established by the Mining and Geology Board.
State publications supporting the requirements of the Seismic Hazards Mapping Act include the California Geological Survey Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California and California Geological Survey Special Publication 118, Recommended Criteria for Delineating Seismic Hazard Zones in California. The objectives of Special Publication 117 are to assist in the evaluation and mitigation of earthquake-related hazards for projects within designated zones of required investigations and to promote uniform and effective statewide implementation of the evaluation and mitigation elements of the Seismic Hazards Mapping Act. Special Publication 118 implements the requirements of the Seismic Hazards Mapping Act in the production of Probabilistic Seismic Hazard Maps for the State.
(d) California Building Code
The California Building Code (California Code of Regulations, Title 24, or CBC) is a compilation of building standards, including seismic safety standards for new buildings. California Building Code standards are based on building standards that have been adopted by state agencies without change from a national model code; building standards based on a national model code that have been changed to address particular California conditions; and building standards authorized by the California legislature but not covered by the national model code. Given the State’s susceptibility to seismic events, the seismic standards within the California Building Code are among the strictest in the world. The California Building Code includes provisions for demolition and construction as well as
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IV.E Geology and Soils regulations regarding building foundations and soil types. The California Building Code applies to all occupancies in California, except where stricter standards have been adopted by local agencies. The California Building Code is published on a triennial basis, and supplements and errata can be issued throughout the cycle. The 2013 edition of the California Building Code became effective on January 1, 2014, and incorporates by adoption the 2012 edition of the International Building Code of the International Code Council, with California amendments.3 The 2013 California Building Code incorporates the latest seismic design standards for structural loads and materials as well as provisions from the National Earthquake Hazards Reduction Program to mitigate losses from an earthquake and provide for the latest in earthquake safety. Specific California Building Code building and seismic safety regulations have been incorporated by reference in the Los Angeles Building Code with local amendments. As such, the California Building Code forms the basis of the Los Angeles Building Code.
(2) City of Los Angeles
(a) Los Angeles General Plan Safety Element
The City of Los Angeles General Plan Safety Element, which was adopted in 1996, addresses public safety risks due to natural disasters including seismic events and geologic conditions, and sets forth guidance for emergency response during such disasters. The Safety Element also provides generalized maps of designated areas within the City that are considered susceptible to earthquake-induced hazards such as fault rupture and liquefaction.
Regarding assessment of seismic hazards, the Safety Element states that the State Public Resources Code Section 2699 requires that a safety element take into account available seismic hazard maps prepared by the State Geologist pursuant to the Alquist- Priolo Earthquake Fault Zoning Act. The Public Resources Code also requires that the State Geologist map active faults throughout the State. The Safety Element states that those maps which are applicable to the City of Los Angeles are incorporated into Exhibit A of the Safety Element. It also states that local jurisdictions are required by the Seismic Hazards Mapping Act to require additional studies and appropriate mitigation measures for development projects in the areas identified as potential hazard areas by the maps. In addition, the Safety Element states that as maps are released for Los Angeles, they will be utilized by the Building and Safety Department in helping to identify areas where additional soils and geology studies are needed for evaluation of hazards and imposition of appropriate mitigation measures prior to the issuance of building permits. The Safety
3 California Building Standards Commission. 2013 California Building Standards Code, www.bsc.ca.gov/, accessed October 12, 2014.
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Element was approved in 1996 during an ongoing mapping effort by the State. Thus, it contemplated that, once the entire set of maps for Los Angeles was complete, it would be used to revise the soils and geology exhibits of the Safety Element. The 1996 Safety Element acknowledged that it was based on available official maps at the time, and that exhibits in the Safety Element would be revised following receipt of reliable new information. It is important to note that the State of California released the official and final Earthquake Zones of Required Investigation Map for the Hollywood Quadrangle on November 6, 2014.4 This map is the State of California’s official earthquake fault zone map for the Hollywood area. It is the most current and accurate map available to delineate the boundaries of earthquake fault zones in the Hollywood area.5 The State of California map is the type of information that the Safety Element contemplated using (once available) to revise and update the seismic hazard zone exhibits therein. Accordingly, the seismic hazards analysis in this Draft EIR relies primarily on the official State of California map to determine the location of the Project Site in relation to the nearest officially mapped earthquake fault zone and other seismic hazard zones.
(b) Los Angeles Building Code
Earthwork activities, including grading, are governed by the Los Angeles Building Code, which is contained in Los Angeles Municipal Code (LAMC), Chapter IX, Article 1. Specifically, Section 91.7006.7 includes requirements regarding import and export of material; Section 91.7010 includes regulations pertaining to excavations; Section 91.7011 includes requirements for fill materials; Section 91.7013 includes regulations pertaining to erosion control and drainage devices; Section 91.7014 includes general construction requirements as well as requirements regarding flood and mudflow protection; and Section 91.7016 includes regulations for areas that are subject to slides and unstable soils. Additionally, Section 91.1803 of the Los Angeles Building Code includes specific requirements addressing seismic design, grading, foundation design, geologic investigations and reports, soil and rock testing, and groundwater. The Los Angeles Building Code incorporates by reference the California Building Code, with City amendments for additional requirements. The City Department of Building and Safety is responsible for implementing the provisions of the Los Angeles Building Code.
4 State of California, California Geologic Survey, Hollywood Quadrangle, Earthquake Fault Zones (November 6, 2014) and Seismic Hazard Zones (March 25, 1999) Map. 5 Id. at Note 2.
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b. Existing Conditions
(1) Regional Geology
The Project Site is located along the northern portion of the Los Angeles Basin, a coastal plain south of the Santa Monica Mountains, west of the Puente Hills and Whittier faults, east of the Palos Verdes Peninsula and Pacific Ocean, and north of the Santa Ana Mountains and San Joaquin Hills. The Los Angeles Basin is located in the northern portion of the Peninsular Ranges geomorphic province and is a northwest-trending alluviated lowland plain, sometimes called the Coastal Plain of Los Angeles. The Peninsular Ranges are characterized by northwest-trending blocks of mountain ridges and sediment-floored valleys. The dominant geologic structural features are northwest trending fault zones that either die out to the northwest or terminate at east-trending reverse faults that form the southern margin of the Transverse Ranges.
The Los Angeles Basin is located at the northern end of the Peninsular Ranges Geomorphic Province. The basin is bounded by the east and southeast by the Santa Ana Mountains and San Joaquin Hills, and to the northwest by the Santa Monica Mountains. Over 22 million years ago the Los Angeles basin was a deep marine basin formed by tectonic forces between the North American and Pacific plates. Since that time, over five miles of marine and non-marine sedimentary rock as well as intrusive and extrusive igneous rocks have filled the basin. During the last two million years, defined by the Pleistocene and Holocene epochs, the Los Angeles basin and surrounding mountain ranges have been uplifted to form the present day landscape. Erosion of the surrounding mountains has resulted in deposition of unconsolidated sediments in low-lying areas by rivers such as the Los Angeles River. Areas that have experienced subtle uplift have been eroded with gullies.
(2) Regional Faulting and Seismicity
The numerous faults in Southern California include active, potentially active, and inactive faults. Based on criteria established by the California Geological Survey (CGS), active faults are those that have shown evidence of surface displacement within the past 11,000 years (i.e., Holocene-age). Potentially active faults are those that have shown evidence of surface displacement within the last 1.6 million years (i.e., Quaternary-age). Inactive faults are those that have not shown evidence of surface displacement within the last 1.6 million years. The Southern California region also includes blind thrust faults, which are faults without a surface expression. Due to the buried nature of these thrust faults, their existence is usually not known until they produce an earthquake. Since the seismic risk of these buried thrust faults in terms of recurrence and maximum potential magnitude is not well established, the potential for earthquakes with magnitude higher than 6.0 occurring on buried thrust faults cannot be precluded. The faults in the vicinity of the
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Project Site (within approximately 10 kilometers or six miles) are discussed below and shown in Figure IV.E-1 on page IV.E-8.
The Alquist-Priolo Special Studies Zones Act (now known as the Alquist-Priolo Earthquake Fault Zoning Act) defines “active” and “potentially active” faults utilizing the same aging criteria as that used by CGS described above. Therefore, the Alquist-Priolo Earthquake Fault Zoning Act identifies zones that include faults which have direct evidence of movement within the last 11,000 years. The CGS considers fault movement within this period a characteristic of faults that have a relatively high potential for ground rupture in the future. As discussed in the Regulatory Framework above, the Alquist-Priolo Earthquake Fault Zoning Act requires the State Geologist to establish earthquake fault zones around the surface traces of active faults and to issue appropriate maps to assist cities and counties in planning, zoning, and building regulation functions. These zones, which generally extend from 200 to 500 feet on each side of a known active fault, based on the location precision, complexity, or regional significance of the fault, identify areas where potential surface fault rupture along an active fault could prove hazardous and identify where special studies are required to characterize hazards to habitable structures. If a site lies within an Earthquake Fault Zone on an official CGS map, then a geologic fault rupture investigation must be performed before issuance of permits to demonstrate that the proposed development is not threatened by surface displacement from the fault.
As discussed above, the State of California released the official Earthquake Zones of Required Investigation Map for the Hollywood Quadrangle on November 6, 2014 (Earthquake Fault Zones Map). This map is State of California’s CGS official earthquake fault zone map for the Hollywood area. It is the most current and accurate map available to delineate the boundaries of earthquake fault zones in the Hollywood area. As illustrated in Figure IV.E-2 on page IV.E-9, the Project Site is not located within an earthquake fault zone according to the Earthquake Fault Zones Map. The Project Site is approximately 0.45 kilometer (0.28 mile) south of the closest fault zone as officially mapped by CGS. However, the Project Site is located in the seismically active Southern California region, and could be subjected to moderate to strong ground shaking in the event of an earthquake on one of the many active Southern California faults.
(a) Active Faults
(i) Hollywood Fault
Fault investigations on the Hollywood Fault indicate geomorphic evidence of recent activity exists in the form of groundwater barriers in the Hollywood area and faceted ridges. To the east, the Hollywood fault forms a tenuous junction with the Raymond fault. Based upon offset alluvial sediments and geomorphic evidence, the Malibu Coast–Hollywood– Raymond fault system is judged to have been active during very late Quaternary time.
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PROJECT SITE
1 Alamo thrust 21 Helendale fault 41 Redondo Canyon fault 2 Arrowhead fault 22 Hollywood fault 42 San Andreas Fault 3 Bailey fault 23 Holser fault 43 San Antonio fault 4 Big Mountain fault 24 Lion Canyon fault 44 San Cayetano fault 5 Big Pine fault 25 Llano fault 45 San Fernando fault zone 6 Blake Ranch fault 26 Los Alamitos fault 46 San Gabriel fault zone 7 Cabrillo fault 27 Malibu Coast fault 47 San Jacinto fault 8 Chatsworth fault 28 Mint Canyon fault 48 San Jose fault 9 Chino fault 29 Mirage Valley fault zone 49 Santa Cruz-Santa Catalina Ridge f.z. 10 Clamshell-Sawpit fault 30 Mission Hills fault 50 Santa Monica fault 11 Clearwater fault 31 Newport Inglewood fault zone 51 Santa Ynez fault 12 Cleghorn fault 32 North Frontal fault zone 52 Santa Susana fault zone 13 Crafton Hills fault zone 33 Northridge Hills fault 53 Sierra Madre fault zone 14 Cucamonga fault zone 34 Oak Ridge fault 54 Simi fault 15 Dry Creek fault 35 Palos Verdes fault zone 55 Soledad Canyon fault 16 Eagle Rock fault 36 Pelona fault 56 Stoddard Canyon fault 17 El Modeno fault 37 Peralta Hills fault 57 Tunnel Ridge fault 18 Frazier Mountain thrust 38 Pine Mountain fault 58 Verdugo fault 19 Garlock fault zone 39 Raymond fault 59 Waterman Canyon fault 20 Grass Valley fault 40 Red Hill (Etiwanda Ave) fault 60 Whittier fault REFERENCE: http://pasadena.wr.usgs.gov/info/images/LA%20Faults.pdf SOUTHERN CALIFORNIA FAULT MAP Geotechnologies, Inc. SUNSET STUDIOS HOLDING, LLC Consulting Geotechnical Engineers FILE No. 20618 EXHIBIT E Figure IV.E-1 Regional Fault Map
Source: Geotechnologies, Inc., 2015. SUBJECT SITE
LEGEND
? Fault Location Zone Boundary REFERENCE: CGS, NOVEMBER 6, 2014, HOLLYWOOD QUADRANGLE, EARTHQUAKE FAULT ZONE MAP (OFFICIAL MAP) EARTHQUAKE FAULT ZONE MAP
SUNSET STUDIOS HOLDINGS Geotechnologies, Inc. Consulting Geotechnical Engineers FILE NO. 20618 EXHIBITFigure C IV.E-2 Hollywood Quadrangle Earthquake Fault Zone Map
Source: Geotechnologies, Inc., 2015. IV.E Geology and Soils
Dolan and others (1997) have performed a study along the eastern portion of the Hollywood Fault. Dolan maps the east portion of the Hollywood Fault and its splays in approximately the same location as Dibblee. Dolan’s work includes original subsurface exploration, review of subsurface work by others, seismic trenching, storm drain excavation logging and Metro Rail excavation logs by others. Based on charcoal samples from recent trenching, Dolan concludes that the most recent rupture along the Hollywood Fault occurred between a maximum of 20,000 years ago and as recently as 4,000 years ago. It is believed that the Hollywood fault is capable of producing a 6.7 magnitude earthquake. The CGS published the Earthquake Fault Zones Map of the Hollywood Quadrangle on November, 2014. This map is the official Earthquake Fault Zones Map from CGS for the Hollywood area. According to this map, the Hollywood Fault is located approximately 0.45 kilometer (0.28 mile) north of the Project Site.
(ii) Santa Monica Fault
The Santa Monica Fault Zone is part of the west trending Transverse Ranges Southern Boundary fault system. The Santa Monica fault forms the onshore concealed extension of the Malibu Coast fault. The Santa Monica Fault extends east from the coastline in Pacific Palisades through the City of Santa Monica and West Los Angeles and merges with the Hollywood Fault, along the southern foothills of the Santa Monica Mountains. Based on geomorphic evidence and fault trenching studies, the Santa Monica Fault is considered active by CGS, but has not been assigned as an Alquist-Priolo earthquake fault zone. It is estimated that the Santa Monica Fault is capable of producing a maximum magnitude 7.4 earthquake. According to CGS, the Santa Monica fault is located approximately 0.81 kilometer (0.5 mile) north of the Project Site.
(iii) Newport-Inglewood Fault System
The Newport-Inglewood fault zone is a broad zone of discontinuous north to northwest on echelon faults and northwest to west trending folds. The fault zone extends southeastward from West Los Angeles, across the Los Angeles Basin, to Newport Beach and possibly offshore beyond San Diego (Barrows, 1974; Weber, 1982; Ziony, 1985). The onshore segment of the Newport-Inglewood fault zone extends for about 37 miles from the Santa Ana River to the Santa Monica Mountains. Here it is overridden by, or merges with, the east-west trending Santa Monica zone of reverse faults. The surface expression of the Newport-Inglewood fault zone is made up of a strikingly linear alignment of domal hills and mesas that rise on the order of 400 feet above the surrounding plains. From the northern end to its southernmost onshore expression, the Newport-Inglewood fault zone is made up of: Cheviot Hills, Baldwin Hills, Rosecrans Hills, Dominguez Hills, Signal Hill-Reservoir Hill, Alamitos Heights, Landing Hill, Bolsa Chica Mesa, Huntington Beach Mesa, and Newport Mesa. Several single and multiple fault strands, arranged in a roughly left stepping en echelon arrangement, make up the fault zone and account for the uplifted mesas. The
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IV.E Geology and Soils most significant earthquake associated with the Newport-Inglewood fault system was the Long Beach earthquake of 1933 with a magnitude of 6.3 on the Richter scale. It is believed that the Newport-Inglewood fault zone is capable of producing a 7.5 magnitude earthquake. According to CGS, the Newport-Inglewood fault system is located 9 kilometers (5.6 miles) southwest of the Project Site.
(iv) Raymond Fault
The Raymond fault is an effective groundwater barrier which divides the San Gabriel Valley into groundwater sub-basins. Much of the geomorphic evidence for the Raymond fault has been obliterated by urbanization of the San Gabriel Valley. However, a discontinuous escarpment can be traced from Monrovia to the Arroyo Seco in South Pasadena. The very bold, “knife edge” escarpment in Monrovia parallel to Scenic Drive is believed to be a fault scarp of the Raymond fault. Trenching of the Raymond fault is reported to have revealed Holocene movement (Weaver and Dolan, 1997). The recurrence interval for the Raymond fault is probably slightly less than 3,000 years, with the most recent documented event occurring approximately 1,600 years ago (Crook, et al, 1978). However, historical accounts of an earthquake that occurred in July 1855 as reported by Toppozada and others, 1981, place the epicenter of a Richter Magnitude 6 earthquake within the Raymond fault. It is believed that the Raymond fault is capable of producing a 6.8 magnitude earthquake. The probability of an earthquake occurring on this fault during the expected lifetime of the Project is considered remote. According to CGS, the Raymond fault is located approximately 9.11 kilometers (5.7 miles) east of the Project Site.
(v) Verdugo Fault
The Verdugo Fault runs along the southwest edge of the Verdugo Mountains. The fault displays a reverse motion. According to Weber, et. al., (1980) 2- to 3-meter-high scarps were identified in alluvial fan deposits in the Burbank and Glendale areas. Further northeast, in Sun Valley, faults were reportedly identified at a depth of 40 feet in a sand and gravel pit. Although considered active by the USGS, the fault is not designated with an Earthquake Fault Zone by the CGS. The Verdugo Fault is located approximately 10 kilometers (6.2 miles) northeast of the Project Site.
(b) Blind Thrust Faults
Blind or buried thrust faults are faults without a surface expression but are a significant source of seismic activity. They are typically broadly defined based on the analysis of seismic wave recordings of hundreds of small and large earthquakes in the Southern California area. Due to the buried nature of these thrust faults, their existence is sometimes not known until they produce an earthquake. Two blind thrust faults in the Los
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Angeles metropolitan area are the Puente Hills blind thrust located just east of downtown Los Angeles and the Elysian Park blind thrust just north of downtown Los Angeles. Another blind thrust fault of note is the Northridge fault located in the northwestern portion of the San Fernando Valley.
The Puente Hills blind thrust is reported to have produced at least four large earthquakes in the last 11,000 years (Dolan, 2003). The magnitude 5.9 Whittier Earthquake of 1987 has been attributed to the Puente Hills blind thrust in recent studies by many researchers. The Elysian Park anticline is thought to overlie the Elysian Park blind thrust. This fault has been estimated to cause an earthquake every 500 to 1,300 years in the magnitude range of 6.2 to 7.0. According to the USGS database, the Elysian Park Thrust Fault is located approximately 3.91 kilometers (2.4 miles) northeast of the Project Site and the Puente Hills Thrust Fault is located approximately 5.74 kilometers (3.6 miles) south of the Project Site. Therefore, surface rupture from these blind thrust faults is considered low.
The 1994 Magnitude 6.7 Northridge earthquake was caused by the sudden rupture of a previously unknown, blind thrust fault. This fault has since been named the Northridge Thrust. However, it is also known in some of the literature as the Pico Thrust. It has been assigned a maximum magnitude of 6.9 and a 1,500 to 1,800 year recurrence interval. The Northridge thrust is located approximately 22.67 kilometers (14 miles) northwest of the Project Site.
(3) Local Geology
(a) Soil Conditions
Based on the Geotechnical Report included in Appendix F of this Draft EIR, the Project Site is underlain by earth fill and alluvial deposits. Fill materials range from one to seven feet in depth. Fill materials on the Project Site consist primarily of silty sands and sandy to silty clays. The native soils underlying the Project Site consist of silty and clayey sands to sands, and silty to sandy clays. The native earth materials consist predominantly of detrital sediments deposited by river and stream action typical to this area of Los Angeles County.
(b) Liquefaction
Liquefaction is a phenomenon in which saturated silty to cohesionless soils below the groundwater table are subject to a temporary loss of strength due to the buildup of excess pore pressure during cyclic loading conditions such as those induced by an earthquake. Liquefaction-related effects include loss of bearing strength, amplified ground oscillations, lateral spreading, and flow failures. Liquefaction occurs primarily in saturated,
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IV.E Geology and Soils loose, fine to medium-grained soils in area where the groundwater table is 50 feet or less below the ground surface.
The Safety Element of the City of Los Angeles General Plan classifies the Project Site as part of an area that is susceptible to liquefaction.6 However, the California Geological Survey Seismic Hazards Map for the Hollywood Quadrangle does not classify the Project Site as part of a liquefiable area.7 This determination by the California Geological Survey is based on groundwater depth records, soil type, and distance to a fault capable of producing a substantial earthquake. Furthermore, the historic high groundwater in the Project area is greater than 50 feet beneath the ground surface. In addition, liquefaction analysis of the soils underlying the site was performed by assuming a magnitude 7.1 earthquake and a peak horizontal acceleration of 0.66g. For conservative purposes, a historic high groundwater level of 50 feet below grade was assumed. This semi-empirical method is based on a correlation between measured values of Standard Penetration Test resistance and field performance data. The liquefaction analysis, contained in the Geotechnical Report indicates that site soils would not be prone to liquefaction during the ground motion expected during the design based earthquake. Therefore, the potential for liquefaction to occur beneath the Project Site is negligible.
(c) Landslides
The California Geological Survey Seismic Hazards Map for the Hollywood Quadrangle does not classify the Project Site as part of a landslide area.8 In addition, the Project Site is not located in a landslide area as mapped by the City of Los Angeles, or within an area identified as having a potential for slope instability.9 Further, the Project Site is characterized by a relatively flat topography with minimally sloping terrain. Based on these considerations, the Geotechnical Report concluded that the potential for earthquake- induced landslides to occur at the Project Site is negligible.
(d) Seismically Induced Settlement
Seismically-induced settlement or the compaction of dry or moist, cohesionless soils may also occur during a major earthquake. Based on the uniform nature of the underlying
6 Los Angeles General Plan Safety Element, Exhibit B, Areas Susceptible to Liquefaction, page 49 (November 1996). 7 California Division of Mines and Geology, 1999, Seismic Hazard Zone Hollywood 7.5-Minute Quadrangle, Los Angeles County, California. 8 Ibid. 9 Los Angeles General Plan Safety Element, Exhibit C, Landslide Inventory & Hillside Areas, page 51 (November 1996).
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IV.E Geology and Soils older alluvial soils, the Geotechnical Report concluded that the potential for seismically induced settlements is negligible.
(e) Subsidence
Subsidence occurs when a large portion of land is displaced vertically, usually due to the withdrawal of groundwater, oil, or natural gas. Soils that are particularly subject to subsidence include those with high silt or clay content. The Project Site is not located within an area of known ground subsidence. No large-scale extraction of groundwater, gas, oil, or geothermal energy is occurring or is planned at the Project Site. Therefore, the Geotechnical Report concluded that there is little to no potential for ground subsidence due to withdrawal of fluid or gas at the Project Site.
(f) Expansive Soils
Expansive soils are soils that swell when subjected to moisture and shrink when dried. Expansive soils are typically associated with clayey soils. The soils underlying the Project Site consist of interlayered mixtures of sand, silt, and clay. Based on the Geotechnical Report, the soils beneath the Project Site are in the low to moderate expansion range.
(g) Other Geologic Conditions
According to the Geotechnical Report, the Project Site is not located within a City of Los Angeles Methane Zone or Methane Buffer Zone. Additionally, according to the Division of Oil, Gas, and Geothermal Resources Regional Wildcat Map, the Project Site is not located within the limits of an oil field, and no oil wells have been drilled on the Project Site. Lastly, no distinct or prominent geologic or topographic features such as hilltops, ridges, hillslopes, canyons, ravines, rock outcrops, water bodies, streambeds, or wetlands are located at the Project Site.
3. Environmental Impacts a. Methodology
To evaluate potential impacts relative to geology and soils, the Geotechnical Report was prepared for the Project Site. The Geotechnical Report included a review of published geologic data relevant to the Project Site, a site reconnaissance, field exploration, and laboratory testing. Preliminary recommendations regarding the design and construction of the Project are based on these results. A final design-level geotechnical report would be prepared, reviewed, and approved by the City of Los Angeles Department of Building and
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Safety prior to issuance of building permits to construct the Project. The Geotechnical Report is provided in Appendix F of this Draft EIR.
b. Thresholds of Significance
Appendix G of the CEQA Guidelines provides a set of sample questions that address impacts with regard to geology and soils. These questions are as follows:
Would the project:
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?
– 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?
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?
In the context of these questions from the CEQA Guidelines, the City of Los Angeles CEQA Thresholds Guide states that a project would normally have a significant geology and soils impact if the project would:
Cause or accelerate geologic hazards, which would result in substantial damage to structures or infrastructure, or expose people to substantial risk of injury.
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Constitute a geologic hazard to other properties by causing or accelerating instability from erosion.
Accelerate natural processes of wind and water erosion and sedimentation, resulting in sediment runoff or deposition which would not be contained or controlled on-site.
One or more distinct and prominent geologic or topographic features would be destroyed, permanently covered, or materially and adversely modified as a result of the project. Such features may include, but are not limited to, hilltops, ridges, hillslopes, canyons, ravines, rock outcrops, water bodies, streambeds, and wetlands.
With regard to the above questions from Appendix G of the CEQA Guidelines, as discussed in the Initial Study prepared for the Project, which is included as Appendix A of this Draft EIR, and described above, the Project Site is not located in a landslide area or within an area identified as having a potential for slope instability. In addition, the Project does not propose a substantial alteration to the existing topography. Therefore, no impacts with regard to landslides would occur. As further discussed in the Initial Study, construction activities would occur in accordance with erosion control requirements, including grading and dust control measures, imposed by the City pursuant to grading permit regulations. The Project would also be required to have an erosion control plan approved by the Los Angeles Department of Building and Safety, as well as a Storm Water Pollution Prevention Plan pursuant to the National Pollutant Discharge Elimination System permit requirements. With compliance with regulatory requirements, impacts regarding soil erosion would be less than significant. Lastly, the Project Site is located within a community served by existing sewage infrastructure and the Project’s wastewater demand would be accommodated via connections to the existing wastewater infrastructure. As such, the Project would not require the use of septic tanks or alternative wastewater disposal systems and the Project would not result in impacts related to the ability of soils to support septic tanks or alternative wastewater disposal systems. Therefore, no further analysis regarding the significance thresholds related to landslides, soil erosion, and the ability of soils to support septic tanks or alternative wastewater disposal systems is provided below.
c. Regulatory Compliance Measures and Project Design Features
(1) Regulatory Compliance Measures
Regulatory Compliance Measure E-1: All Project construction shall conform to the requirements of the Los Angeles Municipal Code, which incorporates the requirements of the California Building Code, including all provisions related to seismic safety.
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Regulatory Compliance Measure E-2: A final design-level geotechnical, geologic, and seismic hazard investigation report that complies with all applicable State and local code requirements shall be prepared for the Project by a qualified geotechnical engineer and certified engineering geologist and shall be submitted to the Los Angeles Department of Building and Safety, consistent with City of Los Angeles Building Code requirements. The site-specific geotechnical report shall be prepared to the written satisfaction of the City of Los Angeles Department of Building and Safety and shall include recommendations for the specific building location and design, including those pertaining to site preparation, fills and compaction, building foundations, and all other performance standards required by the California Building Code and the City of Los Angeles Building Code.
(2) Project Design Features
Project Design Feature E-1: A shoring plan shall be implemented during construction to provide stable excavations and prevent settlement due to the removal of adjacent soil. Project Design Feature E-2: If existing fill material is to be re-used as engineered fill, any oversize material and any deleterious debris and/or organic matter encountered in the fill material shall be removed.
d. Analysis of Project Impacts
(1) Seismic Hazards
(a) Surface Rupture
Ground rupture is defined as surface displacement which occurs along the surface trace of the causative fault during an earthquake. Based on research of available literature and the findings of the Geotechnical Report, no known active or potentially active faults underlie the Project Site. The Project Site is also not located within an Alquist-Priolo Earthquake Fault Zone corresponding to the Hollywood Fault. As discussed above, the State of California released the official Earthquake Fault Zones Map for the Hollywood Quadrangle on November 6, 2014. This map is State of California’s official earthquake fault zone map for the Hollywood area. The Project Site is not located within an earthquake fault zone. The projected Hollywood Fault trace is located approximately 0.45 kilometer (0.28 mile) north of the Project Site, and the southern boundary of the Hollywood Earthquake Fault Zone delineated by CGS is located approximately 0.29 kilometer (0.18 mile) north of the Project Site. The possibility of surface ground rupture from a fault this distance from the Project Site is remote. As such, the Project
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IV.E Geology and Soils would not cause or accelerate geologic hazards related to fault rupture, which would result in substantial damage to structures or infrastructure, or expose people to substantial risk of injury. Impacts associated with surface rupture from a known earthquake fault would be less than significant and no mitigation measures are required.
(b) Strong Seismic Ground Shaking
As described above, the Project Site is located within the seismically active region of Southern California and would potentially be subject to strong ground motion if a moderate to strong earthquake occurs on a local or regional fault. These potentially significant impacts at the Project Site can be overcome through engineering design solutions that would reduce the substantial risk of exposing people or structures to loss or injury. State and local code requirements ensure that buildings are designed and constructed in a manner that, although the buildings may sustain damage during a major earthquake, would reduce the substantial risk that buildings would collapse. The potentially significant impacts related to seismic ground shaking at the Project Site can be reduced to less than significant through conformance with existing state laws, City ordinances, and the application of accepted and proven construction engineering practices. The Geotechnical Report contains preliminary recommendations for the type of engineering practices that would be used to minimize the risks associated with seismic shaking. Those recommendations are included below as mitigation measures. In addition, per Mitigation Measure E-6 below, a final design-level geotechnical report would be prepared by the Applicant and reviewed to the satisfaction of the Department of Building and Safety before the issuance of grading permits. The final recommendations from that report would be enforced before construction of the Project.
In addition, as discussed above, the state and City mandate compliance with numerous rules related to seismic safety, including the Alquist-Priolo Earthquake Fault Zoning Act, Seismic Safety Act, Seismic Hazards Mapping Act, the California Building Code, the General Plan Safety Element, and the Los Angeles Building Code. Pursuant to those laws, and the mitigation measures proposed in this Draft EIR, the Project must demonstrate compliance with the applicable provisions of these safety requirements before permits can be issued for the Project.
Based on the Geotechnical Report, the Project Site is suitable for development and the Project may be constructed using standard, accepted, and proven engineering practices considering the seismic shaking potential and geologic conditions at the Project Site. As with other development projects in the Southern California region, the Project would comply with the current seismic design provisions of the California Building Code to minimize seismic impacts, as reflected in Regulatory Compliance Measure E-1, above. The California Building Code incorporates the latest seismic design standards for structural loads and materials as well as provisions from the National Earthquake Hazards Reduction City of Los Angeles 5901 Sunset SCH No. 2014021009 March 2015
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Program to mitigate losses from an earthquake and provide for the latest in earthquake safety. Additionally, construction of the Project would be required to adhere to the seismic safety requirements contained in the Los Angeles Building Code (LAMC, Chapter IX, Article 1). The Los Angeles Building Code incorporates by reference the California Building Code, with City amendments for additional requirements. The Los Angeles Department of Building and Safety is responsible for implementing the provisions of the Los Angeles Building Code. The Project would also be required to comply with the site plan review and permitting requirements of the Los Angeles Department of Building and Safety including the recommendations provided in a final, site-specific geotechnical report subject to review and approval by the Los Angeles Department of Building and Safety, as provided in Regulatory Compliance Measure E-2, above. Through compliance with regulatory requirements, site-specific geotechnical recommendations contained in a final design-level geotechnical engineering report, and adherence to the mitigation measures herein, the Project would not cause or accelerate geologic hazards related to strong seismic ground shaking, which would result in substantial damage to structures or infrastructure, or expose people to substantial risk of injury and impacts related to strong seismic ground shaking would be less than significant.
(c) Liquefaction
The Safety Element of the City of Los Angeles General Plan classifies the Project Site as part of an area that is susceptible to liquefaction. However, the Seismic Hazard Map for the Hollywood Quadrangle, approved by the CGS, classifies the Project Site as not being part of a liquefiable area. This determination by the California Geological Survey is based on groundwater depth records, soil type, and distance to a fault capable of producing a substantial earthquake. Groundwater was encountered during exploration at a depth of 51½ feet below the existing grade. Furthermore, the historic high groundwater level in the Project area is on the order of 50 feet below the existing grade.
Field explorations and laboratory testing of extracted soils were performed to confirm the liquefaction potential at the Project Site. The liquefaction potential evaluation was performed by assuming a magnitude 7.1 earthquake and a peak horizontal acceleration of 0.66g. For conservative purposes, a historic high groundwater level of 50 feet below grade was assumed. This semi-empirical method is based on a correlation between measured values of Standard Penetration Test resistance and field performance data. The liquefaction analysis indicates that site soils would not be prone to liquefaction during the ground motion expected during the design-based earthquake.
Due to the depth of the historical highest groundwater level, the type of soils underlying the Project Site, and the liquefaction mapping by the CGS, the Project Site would not be capable of liquefaction during the design-based earthquake. Therefore, the Project would not cause or accelerate geologic hazards related to liquefaction, which would City of Los Angeles 5901 Sunset SCH No. 2014021009 March 2015
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IV.E Geology and Soils result in substantial damage to structures or infrastructure, or expose people to substantial risk of injury. As such, impacts associated with liquefaction would be less than significant and no mitigation measures are required.
(d) Seismically Induced Settlement
Seismically-induced settlement or compaction of dry or moist, cohesionless soils can be an effect related to earthquake ground motion. Such settlements are typically most damaging when the settlements are differential in nature across the length of structures. Some seismically-induced settlement of the proposed structures should be expected as a result of strong ground-shaking. However, based on the uniform nature of the underlying older alluvial soils, differential settlement within the Project Site may be considered negligible. The Project would also be required to comply with the site plan review and permitting requirements of the Los Angeles Department of Building and Safety including the recommendations provided in a final, site-specific geotechnical report subject to review and approval by the Los Angeles Department of Building and Safety, as provided in Regulatory Compliance Measure E-2, above. Through compliance with regulatory requirements and site-specific geotechnical recommendations, the Project would not cause or accelerate geologic hazards related to seismically induced settlement, which would result in substantial damage to structures or infrastructure, or expose people to substantial risk of injury. Impacts related to seismically induced settlement would be less than significant and no mitigation measures are required.
(2) Soil Stability
As discussed above, the Project Site is underlain by earth fill and alluvial deposits. Based on on-site investigations, the depth of fill materials encountered on the Project Site range from one to seven feet below existing grade. The anticipated maximum depth of excavation for Project development is approximately 35 feet below ground surface. As discussed in the Geotechnical Report, all required excavations would be sloped, or properly shored, in accordance with the provisions of the California Building Code and additional Los Angeles Building Code requirements, as applicable. In addition, as set forth in the Geotechnical Report, existing on-site fill materials would be removed during excavation of the subterranean parking levels and would be recompacted in accordance with Los Angeles Department of Building and Safety standards prior to reuse on-site, provided any debris and/or organic matter is removed. Further, as previously described, the Project Site is not located within an area of known ground subsidence and the Project would not involve large-scale extraction of groundwater, gas, oil, or geothermal energy which would result in ground subsidence. Pursuant to Regulatory Compliance Measures E-1 and E-2 and Project Design Features E-1 and E-2 above, the Project Applicant would be required to prepare and implement a final, site-specific geotechnical report that incorporates the recommendations of the final, site-specific geotechnical report.
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Therefore, through compliance with regulatory requirements and site-specific geotechnical recommendations, impacts related to soil stability would be less than significant, and no mitigation measures are required.
(3) Expansive Soils
The older alluvium underlying the Project Site consists of interlayered mixtures of silty sand, sand, silt and clay. According to the Geotechnical Report, the earth materials underlying the Project Site have yielded test results in the low to moderate expansion range. Specifically, the expansion index for onsite soils was between 20 and 60 for bulk samples remolded to 90 percent of the laboratory maximum density. Based on the expansion range of the earth materials underlying the Project Site, reinforcing these materials beyond the minimum required by the City of Los Angeles Department of Building and Safety is not required. Therefore, through compliance with regulatory requirements and site-specific geotechnical recommendations, potential impacts related to expansive soils would be less than significant and no mitigation measures are required.
(4) Landform Alteration
As described above, there are no distinct and prominent geologic or topographic features (i.e., hilltops, ridges, hillslopes, canyons, ravines, rock outcrops, water bodies, streambeds, or wetlands) on the Project Site or vicinity. Therefore, the Project would not destroy, permanently cover, or materially and adversely modify any distinct and prominent geologic or topographic features. Impacts associated with landform alteration would not occur and no mitigation measures are required.
4. Cumulative Impacts
Due to the site-specific nature of geological conditions (i.e., soils, geological features, subsurface features, seismic features, etc), geology impacts are typically assessed on a project-by-project basis, rather than on a cumulative basis. Nonetheless, cumulative growth through 2017 (inclusive of the 71 related projects identified in Section III, Environmental Setting, of this Draft EIR) would expose a greater number of people to seismic hazards. However, as with the Project, related projects and other future development projects would be subject to established guidelines and regulations pertaining to building design and seismic safety, including those set forth in the California Building Code and the Los Angeles Building Code. In addition, construction activities, including any necessary excavation, associated with the adjacent Sunset and Gordon Mixed-Use Project (Related Project No. 6) have been completed. Therefore, with adherence to applicable regulations, Project impacts with regard to geology and soils would not be cumulatively
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IV.E Geology and Soils considerable and cumulative impacts with regard to geology and soils would be less than significant.
5. Mitigation Measures
The following mitigation measures would ensure that impacts associated with strong seismic ground shaking would be reduced to less than significant levels:
Mitigation Measure E-1: All vegetation, existing fill, and soft or disturbed earth materials shall be removed from the areas to receive controlled fill. The excavated areas shall be carefully observed by the geotechnical engineer prior to placing compacted fill. Mitigation Measure E-2: Any vegetation or associated root system located within the footprint of the proposed structures shall be removed during grading. Any existing or abandoned utilities located within the footprint of the proposed structures shall be removed or relocated as appropriate. All existing fill materials and any disturbed earth materials resulting from grading operations shall be removed and properly recompacted prior to foundation excavation. Subsequent to the indicated removals, the exposed grade shall be scarified to a depth of six inches, moistened to optimum moisture content, and recompacted in excess of the minimum required comparative density. Mitigation Measure E-3: All fill shall be mechanically compacted in layers not more than eight inches thick. All fill shall be compacted to at least 95 percent of the maximum laboratory density for the materials used. The maximum density shall be determined by laboratory testing using the most recent revision of ASTM D 1557. Mitigation Measure E-4: Field observation and testing shall be performed by a geotechnical engineer during grading to assist the contractor in obtaining the required degree of compaction and the proper moisture content. Where compaction is less than required, additional compactive effort shall be made with adjustment of the moisture content, as necessary, until a minimum of 95 percent compaction is obtained. Mitigation Measure E-5: The excavated onsite materials are considered satisfactory for reuse in the controlled fills as long as any debris and/or organic matter is removed. Any imported materials shall be observed and tested by a geotechnical engineer prior to use in fill areas. Imported materials shall contain sufficient fines so as to be relatively impermeable and result in a stable subgrade when compacted. Any required import materials shall consist of relatively non-expansive soils with an expansion index of less than 20. The
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water-soluble sulfate content of the import materials should be less than 0.1 percent by weight. Mitigation Measure E-6: Prior to issuance of grading permits, the Project Applicant shall submit final design plans and a geotechnical engineering report to the Los Angeles Department of Building and Safety for review and approval. The design-level geotechnical engineering report shall be used for final design of the foundation system for the structures and will take into consideration the engineering properties beneath the proposed structures and the projected loads. The final report shall specify exact design coefficients that are needed by structural engineers to determine the type and sizing of structural building materials. The final report shall be subject to the specific performance criteria imposed by all applicable state and local codes and standards. The final geotechnical report shall be prepared by a registered civil engineer or certified engineering geologist and include appropriate measures to minimize seismic hazards and ensure structural safety of the proposed structure. The proposed structure shall be designed and constructed in accordance with all applicable provisions of the applicable California Building Code and the Los Angeles Building Code.
6. Level of Significance After Mitigation
Considering the rigorous investigation process required under the engineering standard of care, compliance with state laws and City regulatory requirements, technical review and approval by the regulatory agency of a design-level geotechnical engineering report, and adherence to the mitigation measures proposed above, Project-level impacts related to geology and soils would be less than significant. In addition, cumulative impacts with regard to geology and soils would be less than significant.
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