IV. Environmental Impact Analysis F. Geology and Soils

Transcription

1 IV. Environmental Impact Analysis F. Geology and Soils 1. Introduction This section addresses potential geologic and soils hazards attributable to the Proposed Project. This section is based, in part, upon the Report of Geotechnical Consultation for Proposed Development: 2025 Avenue of the Stars Century City District, Los Angeles, CA, Tract No , prepared by MACTEC, May 27, 2010 ( Geotechnical Report ) which is included in Appendix IV.F-1 to this Draft EIR, and the Supplemental Geotechnical Consultation Memorandum, Proposed Project, 2025 Avenue of the Stars, Century City District, Los Angeles, California, Tract No ( Geotechnical Report Supplement ), February 19, 2009, which is included in Appendix IV.F-2 to this Draft EIR. The Geotechnical Report includes a review of previous geologic and geotechnical reports prepared for the Project Site, site reconnaissance, and recommendations based on site conditions and local regulations for both Option A and Option B. The Geotechnical Report Supplement provides additional information on on-site soils. 2. Environmental Setting a. Existing Conditions The Project Site is approximately 5.74 acres and is generally rectangular in shape. It is located at the southwest corner of Avenue of the Stars and Constellation Boulevard. The Project Site is currently occupied by the 16-story Hyatt Regency Century Plaza Hotel ( Existing Hotel ), which includes a two-story subterranean parking garage. (1) Geologic Setting and Topography The Project Site is located in the Los Angeles Basin in the northernmost part of the Peninsular Ranges province near the boundary between the Transverse Ranges and Peninsular Ranges geomorphic provinces. The Transverse Ranges geomorphic province is characterized by east-west trending mountain ranges that include the Santa Monica Mountains. The southern boundary of the province is marked by the Santa Monica, Hollywood, Raymond, Sierra Madre, and Cucamonga faults. The Peninsular Ranges province is characterized by northwest-southeast trending alignments of mountains and hills and intervening basins, reflecting the influence of northwest trending major faults and Page IV.F-1

2 folds controlling the general geologic structural fabric of the region. This province extends northwesterly from Baja California into the Los Angeles Basin and westerly into the offshore area, including Santa Catalina, Santa Barbara, San Clemente, and San Nicolas islands. This province is bounded on the east by the San Jacinto fault zone. Locally, the Project Site is located on the relatively flat portion of an alluvial fan. The ground surface ranges from approximately 260 to 318 feet above mean sea level ( msl ). The relationship of the Project Site to the local geologic conditions is depicted in Figure IV.F-1, Regional Geologic Setting, on page IV.F-3. The locations of major faults and earthquake epicenters in Southern California are shown on Figure IV.F-2, Regional Faults and Seismicity Map, on page IV.F-4. (a) Faults The Project Site is located in the seismically active region of Southern California. The numerous faults in Southern California are classified as active, potentially active, and inactive faults. The criteria for these major groups are based on criteria developed by the California Geological Survey ( CGS ), previously the California Division of Mines and Geology, for the Alquist-Priolo Earthquake Fault Zoning Program. An active fault is defined as one that has had surface displacement within Holocene time (about the last 11,000 years). A potentially active fault is a fault that has demonstrated surface displacement of Quaternary age deposits (last 1.6 million years). Inactive faults have not moved in the last 1.6 million years. Numerous active and potentially active faults have been mapped within the Los Angeles metropolitan region; however, the Project Site itself is not located within an established State of California Alquist-Priolo Earthquake Fault Zone for surface fault rupture, and no active or potentially active faults are known to underlay the Project Site. Additionally, the Project Site is not included in a Fault Rupture Study Area. While the Project Site is not located within an identified fault zone, active faults in the Los Angeles metropolitan region could affect on-site development by resulting in significant ground shaking at the Project Site. The closest fault to the Project Site is the active Santa Monica fault, located approximately 0.7 mile north of the Project Site. Additional active faults in the Los Angeles metropolitan area that could affect the Project Site include the Hollywood, Newport-Inglewood, Puente Hills Blind Thrust, Malibu Coast, Raymond, Verdugo, and Palos Verde Faults. The Mojave segment of the active San Andreas Fault Zone is located approximately 38 miles northeast of the Project Site. This fault zone trends northwest for almost the entire length of the state. A discussion of Page IV.F-2

3 Source: MACTEC, 12/09/2008. Figure IV.F-1 Regional Geologic Setting Page IV.F-3

4 Source: MACTEC, 12/08/2008. Figure IV.F-2 Regional Faults and Seismicity Map Page IV.F-4

5 each of these active faults is below. For a detailed discussion of all faults within the Project vicinity, including potentially active and inactive faults, refer to the Geotechnical Report included as Appendix IV.F-1 to this Draft EIR. The faults in the vicinity of the Project Site are shown in Figure IV.F-2, Regional Faults and Seismicity Map. (i) Active Faults Santa Monica Fault The closest known active fault is the Santa Monica Fault, located approximately 0.7 mile north of the Project Site. The Santa Monica-Hollywood Fault Zone forms a portion of the Transverse Ranges Southern Boundary fault system, which includes the Malibu-Coast Fault to the west of the Santa Monica Fault and the Raymond and Cucamonga Faults to the east of the Hollywood Fault. The Santa Monica Fault Zone is the western segment of the Santa Monica-Hollywood Fault Zone. The Santa Monica-Hollywood fault zone trends east-west from the Santa Monica coastline on the west to the Hollywood area on the east. The surface expression of the Santa Monica Fault Zone includes fault-related geomorphic features, offset stratigraphy, and groundwater barriers within late Quaternary deposits. Research indicates that the Santa Monica Fault Zone is separated into an east segment and a west segment, divided by the West Beverly Hills Lineament. The Project Site is located within the eastern portion of the Santa Monica Fault Zone, which is not considered active. Although the west segment of the Santa Monica Fault Zone is considered active, it has not been included in a State of California Alquist-Priolo Earthquake Fault Zone. 1 Hollywood Fault The active Hollywood Fault is located about 1.7 miles north-northeast of the Project Site and trends east-west along the base of the Santa Monica Mountains from the West Beverly Hills Lineament in the West Hollywood-Beverly Hills area to the Los Feliz area of Los Angeles. The Hollywood Fault is the eastern segment of the Santa Monica-Hollywood Fault Zone. The fault is a groundwater barrier within Holocene sediments. Based on geomorphic evidence, stratigraphic correlation between exploratory borings, and fault trenching studies, this fault is classified as active. 1 California Division of Mines and Geology. State of California Special Studies Zones, Beverly Hills Quadrangle. Revised Official Map Page IV.F-5

6 Until recently, the approximately 9.5-mile long Hollywood Fault Zone was considered to be expressed as a series of linear ground-surface geomorphic expressions and southfacing ridges along the south margin of the eastern Santa Monica Mountains and the Hollywood Hills. Multiple recent fault rupture hazard investigations have shown that the Hollywood Fault Zone is located south of the ridges and bedrock outcroppings along Sunset Boulevard. The Hollywood Fault Zone has not produced any damaging earthquakes during the historical period and has had relatively minor micro-seismic activity. Newport-Inglewood Fault Zone The Newport-Inglewood Fault Zone is located about 3.7 miles southeast of the Project Site and is in an established State of California Special Studies Earthquake Fault Zone. The Newport-Inglewood Fault Zone is composed of a series of discontinuous northwest-trending en echelon faults (which are separate, parallel faults having a step-like pattern) extending from Ballona Gap southeastward to the area offshore from Newport Beach. The Newport-Inglewood Fault Zone is reflected at the surface by a line of hills and mesas formed by the folding and faulting of a thick sequence of Pleistocene age sediments and Tertiary age sedimentary rocks. Readings from seismographs for 39 small earthquakes (between 1977 and 1985) show mostly strike-slip faulting (a vertical fault where the two sides of the fault move horizontally past each other with little or no vertical movement) with some reverse faulting (a horizontal fault where the upper block is pushed upwards from the ground surface) along the north segment (north of Dominguez Hills) and some normal faulting (a horizontal fault where the upper block slips downwards from the ground surface) along the south segment (south of Dominguez Hills to Newport Beach). Malibu Coast Fault Zone The active Malibu Coast Fault Zone is located 7.4 miles west-southwest of the Project Site and is an east-west trending reverse fault extending westward from Santa Monica to offshore of Point Mugu. Fault trenching conducted in 1985 and 1986 on south Winter Mesa in the Malibu area of Los Angeles County exposed several faults, with one fault offsetting deposits estimated to be 6,000 years old. The observed faults, named the Winter Mesa Faults, are believed to be outward extensions of the Malibu Coast Fault; accordingly, the Holocene faulting on the Winter Mesa Faults is considered representative of active faulting along the Malibu Coast Fault Zone. Raymond Fault The Raymond Fault is located approximately 10 miles east-northeast of the Project Site. The Raymond Fault is primarily a strike-slip fault. The Raymond Fault has long been recognized as a ground-water barrier in the Pasadena/San Marino area and numerous geomorphic features along its entire length (such as visible ground-surface fault Page IV.F-6

7 expressions, ponds, springs, and ridges) attest to the fault s activity during the last 11,000 years. The most recent fault movement, based on radiocarbon ages from materials collected in an excavation exposing the fault, occurred sometime between 2,160 (± 105) and 1,630 (± 100) years before present. The CGS estimates an average slip rate of 1.5 millimeters per year ( mm/yr ) and a maximum magnitude of 6.5 for the Raymond Fault. 2 Verdugo Fault Zone The active Verdugo Fault Zone is composed of several faults including the Verdugo Fault, the San Rafael Fault, and the Eagle Rock Fault. The Verdugo Fault is located approximately 11 miles northeast of the Project Site. The most recent documented activity along this fault occurs in the Holocene age alluvial deposits along the western flank of the Verdugo Mountains in the Burbank area. 3 A State of California Alquist-Priolo Earthquake Fault Zone has not been established for the Verdugo Fault by the State; however, this portion of the fault is considered active by the State 4. Palos Verdes Fault Zone Studies indicate that there are several active on-shore extensions of the Palos Verdes Fault Zone, which is 12 miles southwest of the Project Site. Geophysical data also indicate the off-shore extensions of the fault are active, offsetting Holocene age deposits. No historic large magnitude earthquakes are associated with this fault; however, the fault is considered active by the CGS. San Andreas Fault Zone The Mojave segment of the active San Andreas Fault Zone is located about 38 miles northeast of the Project Site. This fault zone, California's most prominent geological feature, trends generally northwest for almost the entire length of the state. The 1857 Fort Tejon earthquake was the last major earthquake along the San Andreas Fault Zone in Southern California California Geological Survey. The Revised 2002 California Probabilistic Seismic Hazard Maps. Appendix A. June Los Angeles County. Los Angeles County General Plan. Technical Appendix California Geological Survey. The Revised 2002 California Probabilistic Seismic Hazard Maps. Appendix A. June Page IV.F-7

8 (ii) Blind Thrust Fault Zones Several buried thrust faults, commonly referred to as blind thrusts, underlie the Los Angeles Basin at depth. These faults are not exposed at the ground surface and are typically identified at depths greater than three kilometers. These faults do not present a potential surface fault rupture hazard. However, the following described blind thrust faults are considered active and potential sources for future earthquakes and may result in significant ground shaking at the Project Site. Puente Hills Blind Thrust The Puente Hills Blind Thrust is defined based on seismic reflection profiles, petroleum well data, and precisely located seismicity. This blind thrust fault system extends eastward from Downtown Los Angeles to Brea in northern Orange County. The Puente Hills Blind Thrust includes three north-dipping segments, named from east to west as the Coyote Hills segment, the Santa Fe Springs segment, and the Los Angeles segment. These segments are overlain by folds expressed at the surface as the Coyote Hills, Santa Fe Springs Anticline, and the Montebello Hills. The Santa Fe Springs segment of the Puente Hills Blind Thrust is believed to be the causative fault of the October 1, 1987, Whittier Narrows Earthquake. The vertical surface projection of the Puente Hills Blind Thrust is approximately 6.6 miles east of the Project Site at its closest point. Postulated earthquake scenarios for the Puente Hills Blind Thrust include single segment fault ruptures capable of producing an earthquake of 6.5 to 6.6 magnitudes and a multiple segment fault rupture capable of producing an earthquake of 7.1 magnitude. The Puente Hills Blind Thrust is not exposed at the ground surface and does not present a potential for surface fault rupture. However, based on deformation of late Quaternary age sediments above this fault system and the occurrence of the Whittier Narrows earthquake, the Puente Hills Blind Thrust is considered an active fault capable of generating future earthquakes beneath the Los Angeles Basin. An average slip rate of 0.7 mm/yr and a maximum moment magnitude of 7.1 are estimated by the CGS for the Puente Hills Blind Thrust. 5 Northridge Blind Thrust The Northridge Blind Thrust is located beneath the majority of the San Fernando Valley and is the causative fault of the January 17, 1994, Northridge earthquake. This thrust fault is not exposed at the surface and does not present a potential surface fault rupture hazard. However, the Northridge Blind Thrust is an active feature that can 5 Los Angeles County. Los Angeles County General Plan. Technical Appendix Page IV.F-8

9 generate future earthquakes. The vertical surface projection of the Northridge Blind Thrust is approximately 7.1 miles northwest of the Project Site at the closest point. The CGS estimates an average slip rate of 1.5 mm/yr. and a maximum moment magnitude of 7.0 for the Northridge Blind Thrust. 6 Upper Elysian Park Blind Thrust The Upper Elysian Park Blind Thrust is a blind thrust fault that overlies the Los Angeles and Santa Fe Springs segments of the Puente Hills Blind Thrust. The eastern edge of the Upper Elysian Park Blind Thrust is defined by the northwest-trending Whittier fault zone. The vertical surface projection of the Upper Elysian Park Blind Thrust is approximately 7.3 miles east of the Project Site at its closest point. Like other blind thrust faults in the Los Angeles area, the Upper Elysian Park Blind Thrust is not exposed at the surface and does not present a potential surface rupture hazard; however, the Upper Elysian Park Blind Thrust should be considered an active feature capable of generating future earthquakes. An average slip rate of 1.3 mm/yr and a maximum moment magnitude of 6.4 are estimated by the CGS for the Upper Elysian Park Blind Thrust. 7 (iii) Potentially Active Faults Overland Fault The potentially active Overland Fault is located approximately 1.7 miles eastsoutheast of the Project Site. The Overland Fault trends northwest between the Charnock Fault and the Newport-Inglewood Fault Zone. The fault extends from the northwest flank of the Baldwin Hills to Santa Monica Boulevard in the vicinity of Overland Avenue. Based on water level measurements, displacement along the fault is believed to be vertical, with an offset of about nine meters. The west side of the fault has apparently moved downward, relative to the east side, forming a graben (a depressed block of land bordered by parallel faults) between the Charnock and Overland Faults. However, there is no evidence that this fault has offset late Pleistocene of Holocene age alluvial deposits. A lack of displacement of Holocene age alluvium indicates that the fault is potentially active. 6 7 California Geological Survey. The Revised 2002 California Probabilistic Seismic Hazard Maps. Appendix A. June Los Angeles County. Los Angeles County General Plan. Technical Appendix Page IV.F-9

10 Charnock Fault The Charnock Fault is located approximately 3.2 miles south of the Project Site. The Charnock Fault trends northwest-southeast subparallel to the trend of the Newport- Inglewood Fault Zone and the Overland Fault. Differential water levels across the fault occur in the early Pleistocene age San Pedro Formation. However, there is no evidence that this fault has offset late Pleistocene or Holocene age alluvial deposits. A lack of displacement of Holocene age alluvium indicates that the fault is potentially active. MacArthur Park Fault The potentially active MacArthur Park Fault is located about 6.3 miles east of the Project Site. The fault, inferred west of Downtown Los Angeles, has been located based on south-facing scarps, truncated drainages and other geomorphic features. The fault is approximately eight kilometers long, extending northwest from the Pershing Square area in Downtown Los Angeles through MacArthur Park to the Paramount Studios areas in Hollywood. Current information suggests that the fault is potentially active. (b) Earthquake Catalog Data The seismicity of the region surrounding the Project Site was determined from research of an electronic database of seismic data. This database includes earthquake data compiled by the California Institute of Technology for 1932 through 2007 and data for 1812 to 1931 compiled by Richter and the U.S. National Oceanic Atmospheric Administration. The search for earthquakes that occurred within 100 kilometers of the Project Site indicates that 409 earthquakes of Richter magnitude 4.0 and greater occurred from 1932 through 2007; no earthquakes of magnitude 6.0 or greater occurred between 1906 and 1931; and one earthquake of magnitude 7.0 or greater occurred between 1812 and A number of earthquakes of moderate to major magnitude have occurred in the Southern California area within about the last 75 years. These include the 6.4 magnitude Big Bear Earthquake on June 28, 1992, the 6.7 magnitude Northridge earthquake on January 17, 1994, and the 7.1 magnitude Hector Mine Earthquake on October 16, (2) Site-Specific Characteristics (a) Soils and Fill Material Based on explorations of the Project Site conducted prior to the construction of the Existing Hotel, the Project Site previously contained fill soils up to 27 feet thick in some locations. In other locations, no fill soils were encountered. The fill soils consisted of clay, Page IV.F-10

11 silt, and silty sand and were not uniformly well compacted. However, during the construction of the Existing Hotel and other on-site development, the fill soils at the Project Site were removed and replaced with properly compacted (certified) soils. Thus, fill on the Project Site currently consists of properly compacted artificial fill soils, primarily as backfill. The Existing Hotel basement extends deeper than the depth of fill and is established in the natural soils. The natural soils underlying the fill on the Project Site consist of Late to Middle Pleistocene age alluvial fan deposits. These deposits consist of silty sand, sand, and clayey sand with layers of clay and silt and local gravel and cobbles. The upper natural soils are moderately firm to firm. The underlying silty sand and sand are dense to very dense throughout the depth explored. The soils become denser with an increase in depth to the maximum 151-foot depth explored. Firm to very firm highly cemented soils were encountered below depths of roughly 70 feet. The surface of the dense to very dense silty sand and sand soils in the prior borings ranges between 13 and 58 feet below the existing ground surface. The surface of the dense soils appears to be deeper on the western portion of the Project Site based on the depths of the foundations for the Existing Hotel. (b) Groundwater During geotechnical investigations conducted for the construction of the Existing Hotel, borings were drilled to determine underlying soil conditions, including groundwater. Water seepage was encountered at depths ranging from 40 feet to 74 feet within the six deeper borings previously drilled at the Project Site below the then-existing ground surface. Five of these borings are located in the western portion of the Project Site while one boring is located along the eastern perimeter of the Existing Hotel; the boring along the eastern perimeter of the Existing Hotel encountered the deepest groundwater at 74 feet, which is approximately 40 feet below the foundation of the existing eastern parking garage. These findings are consistent with Seismic Hazard Zone Report 023 published by the CGS, which indicates the historical high-water level was greater than 40 feet below the ground surface. Groundwater encountered beneath the Project Site is believed to be perched on impermeable layers and not part of a groundwater basin. There are no groundwater production wells or public water supply wells within one mile of the Project Site. 8 8 Los Angeles County Department of Public Works, Groundwater Wells Website, accessed July 13, Page IV.F-11

12 (c) Liquefaction and Seismic Settling Liquefaction involves a sudden loss in strength of a saturated, cohesionless soil, which is caused by ground shaking and results in a temporary transformation of the soil to a fluid mass. The surface effects of liquefaction typically take the form of sand boils, differential ground settlement, or lateral spreading. Liquefaction typically occurs in areas where the groundwater is less than 50 feet from the surface and where soils are composed of poorly consolidated, fine to medium-grained sand. In addition to the necessary soil conditions, the ground acceleration and duration of the earthquake must also be of a sufficient level to initiate liquefaction. Structures constructed on or above potentially liquefiable soils may experience bearing capacity failures due to the temporary loss of foundation support or vertical settlements (both total and differential), and may undergo lateral spreading. Seismic settlement is often caused by loose to medium-dense granular soils densified during ground shaking. Uniform settlement beneath a given structure would cause minimal damage. However, because of the variations in distribution, density, and conforming conditions of the soils, seismically-induced settlement is generally non-uniform and can result in serious structural damage. Dry and partially saturated soils, as well as granular soils, are subject to seismically-induced settlement. The Geotechnical Report prepared for the Proposed Project evaluated potential impacts for seismic-related ground failure, including liquefaction and differential seismic settlement. The Project Site is not located within an area identified as having the potential for liquefaction. 9 Additionally, the Project Site is not located within a State of California designated Liquefaction Hazard Zone. 10 The estimated depth to groundwater is relatively deep ranging from 40 to 74 feet below ground surface, based on previous borings, and the CGS Seismic Hazard Zone Report 023 indicated an historical high groundwater level greater than 40 feet below ground surface level. Further, the alluvial soils below the planned foundation are generally dense and very dense and are not subject to liquefaction or seismic settlement. 9 10, Department of City Planning, Los Angeles Citywide General Plan, Safety Element, November 26, 1996., Department of City Planning. Parcel Profile Report, 2025 S Avenue of the Stars. Generated January 7, Page IV.F-12

13 (d) Slope Stability According to the California Division of Mines and Geology, the Project Site is not located within an area identified as having a potential for seismic slope instability. The Project Site is included in an area designated Cluster of Small Shallow Surficial Landslides. 11 However, there are no known landslides at the Project Site, nor is the Project Site in the path of any known or potential landslides. (e) Tsunamis, Inundation, and Flood Zones The Project Site is at an elevation of 260 to 318 feet above msl and is over five miles from the coastline. Therefore, tsunamis (seismic sea waves) are not considered a significant hazard at the Project Site. The Project Site is not located downslope of any large bodies of water that could adversely affect the Project Site in the event of earthquake-induced dam failures or seiches (wave oscillations in an enclosed or semi-enclosed body of water). Further, the Project Site is not located in an identified 100-year flood hazard area as mapped on a Federal Emergency Management Agency ( FEMA ) Federal Hazard Boundary or Flood Insurance Rate Map. 12 Additionally, the Project Site is in an area outside the 0.2 percent annual chance floodplain, Zone X as defined by FEMA. 13 (f) Subsidence Subsidence occurs when fluids from the ground (such as petroleum or groundwater) are withdrawn. The Project Site is not within an area of known subsidence associated with fluid withdrawal (groundwater or petroleum), peat oxidation, or hydrocompaction. (g) Expansive Soils Expansive soils are those that, as a result of their composition, swell or expand when subjected to moisture. Expansive soils are typically those that contain clay materials that absorb water. When these soils expand, it places uneven pressure on building , Department of City Planning, Los Angeles Citywide General Plan, Safety Element, November 26, 1996., Department of City Planning. Parcel Profile Report, 2025 S Avenue of the Stars. Generated January 7, Ibid. Page IV.F-13

14 foundations. This uneven pressure can lead to movement in the foundation, which can result in damage ranging from small cracks to various degrees of structural failure. According to the Supplemental Geotechnical Consultation Memorandum (Appendix IV.F-2 to this Draft EIR) and as discussed above, the on-site natural soils consist of silty sand, sand, and clayey sand with layers of silt. The clay ranges from low to highly expansive, with Expansion Index values ranging from 31 to 138. The on-site expansive soils will therefore shrink and swell with changes in moisture content. b. Regulatory Framework (1) State Level The State of California adopted the 2007 California Building Code ( California Building Code ), which is based on the 2006 International Building Code, on January 1, The California Building Code includes provisions for site work, demolition, and construction, which include excavation and grading, as well as provisions for foundations, retaining walls, and expansive and compressible soils. The California Building Standards Commission is currently undergoing the 2009 annual code adoption cycle, which will conclude with the adoption of the 2010 California Building Code on January 1, The Alfred E. Alquist Seismic Safety Commission provides oversight, review, and recommendations to the Governor and State Legislature regarding seismic issues. The Commission has adopted several documents based on recorded earthquakes, such as the 1994 Northridge earthquake, 1933 Long Beach earthquake, and the 1971 Sylmar earthquake. Some of these documents relevant to the Proposed Project are: Research and Implementation Plan for Earthquake Risk Reduction in California 1995 to 2000, report dated December 1994; Commercial Property Owner s Guide to Earthquakes Safety, report dated October 2006; California Earthquake Loss Reduction Plan , report dated July The Alquist-Priolo Geologic Hazards Zone Act was enacted by the State of California in 1972 to address the hazard and damage caused by surface fault rupture during an earthquake. It was renamed the Alquist-Priolo Earthquake Fault Zoning Act ( Alquist-Priolo Act ), effective January 1, The Alquist-Priolo Act requires the State Geologist to establish earthquake fault zones along known active faults in the State. Page IV.F-14

15 Cities and counties that include earthquake fault zones are required to regulate development projects within these zones. The Seismic Hazard Mapping Act of 1990 was enacted, in part, to address seismic hazards not included in the Alquist-Priolo Act, including strong ground shaking, landslides, and liquefaction. The State Geologist is assigned the responsibility of identifying and mapping seismic hazards zones. The CGS has also adopted seismic design provisions in Special Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards in California, March 13, (2) City Level The City s primary seismic regulatory policy is the Safety Element of the City of Los Angeles General Plan, adopted November 26, The City s regulations incorporate the State s requirements. The objective of the Safety Element is to better protect occupants and equipment during various types and degrees of seismic events. In the City s Safety Element, specific guidelines are included for the evaluation of liquefaction, tsunamis, seiches, non-structural elements, fault rupture zones, and engineering investigation reports. The City s Emergency Operations Organization ( EOO ) helps to administer certain policies and provisions of the Safety Element. The EOO is a City department comprised of all City agencies. The Administrative Code, EOO Master Plan, and associated EOO plans establish the chain of command, protocols, and programs for integrating all of the City s emergency operations into one unified operation. Each City agency in turn has operational protocols, as well as plans and programs, to implement EOO protocols and programs. A particular emergency or mitigation triggers a particular set of protocols that are addressed by implementing plans and programs. The City s emergency operations program encompasses all of these protocols, plans, and programs. The Safety Element goals, objectives, and policies are broadly stated to reflect the comprehensive scope of the EOO. The adopted the 2007 California Building Code and a series of amendments, on January 1, 2008, collectively known as the City of Los Angeles Building Code ( LABC"), Volumes 1 and 2. Volume 2 of the LABC includes Seismic Design provisions for Foundations, Retaining Walls, and Expansive and Compressible Soils, provisions for Site Work, Demolition, and Construction, and provisions for Grading, Excavation, and Fills. Together, the provisions in Volumes 1 and 2 of the LABC address issues related to site grading, cut and fill slope design, soil expansion, geotechnical investigations before and during construction, slope stability, allowable bearing pressures and settlement below footings, effects of adjacent slopes on Page IV.F-15

16 foundations, retaining walls, basement walls, shoring of adjacent properties, and potential primary and secondary seismic effects. 14 The Department of Building and Safety ( LADBS ) Grading Division has also adopted Rules of General Application (RGA), a series of Geotechnical Standards that supplement the requirements of the LABC. These include specific requirements for seismic design, slope stability, grading, foundation design, geologic investigations and reports, soil and rock testing, and groundwater. The LADBS is responsible for implementing the provisions of the LABC and RGA. 3. Environmental Impacts a. Thresholds of Significance The L.A. CEQA Thresholds Guide (2006) requires the geology and soils analysis to address the following four areas of study: (1) geologic hazards; (2) sedimentation and erosion; (3) landform alteration; and (4) mineral resources. Based on the criteria set forth in the L.A. CEQA Thresholds Guide, a project would have a significant impact under the following criteria if: (1) Geologic Hazards 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. (2) Sedimentation and Erosion The project constitutes a geologic hazard to other properties by causing or accelerating instability from erosion; or The project accelerates the natural processes of wind and water erosion and sedimentation, resulting in sediment runoff or deposition which would not be contained or controlled on-site. 14 See LABC Sections , , , , , and Page IV.F-16

17 (3) Landform Alteration One or more distinct and prominent geologic or topographic features would be destroyed, permanently covered or materially and adversely modified. Such features may include, but are not limited to, hilltops, ridges, hillslopes, canyons, ravines, rock outcrops, water bodies, streambeds and wetlands. (4) Mineral Resources The project might result in the permanent loss of, or loss of access to a mineral resource that is located in a MRZ-2 or other known or potential mineral resource area (and the degree to which this would occur); and Whether the mineral resource is of regional or statewide significance, or is noted in the Conservation Element as being of local importance. b. Issues Scoped Out from Further Study Geologic Hazards, Sedimentation and Erosion, and Landform Alteration are addressed in this section. As discussed in Section IV.A (Impacts Found to be Less Than Significant) of this Draft EIR, the Proposed Project under both Option A and Option B would have no impact with respect to mineral resources. Therefore, further discussion of this issue is not required. c. Project Design Features In accordance with standard BMPs and LADBS review and permitting procedures, both Option A and Option B would implement the following Project Design Features (PDFs) which are considered in the analysis of potential Project impacts: Both Option A and Option B would be designed in accordance with the requirements of the latest edition of the LABC. A final site-specific geotechnical report would be prepared for the Proposed Project under both Option A and Option B, in accordance with LADBS standard design review and permitting procedures. In addition to the Mitigation Measures below, which are based on the findings of the preliminary Geotechnical Report prepared for this Draft EIR, the recommendations contained within the final sitespecific geotechnical report would become Conditions of Approval and, as such, required to be implemented during final design and construction of the Proposed Project. Page IV.F-17

18 d. Project Impacts As discussed in Section III (Project Description) of this Draft EIR, Option A would involve the construction of a mixed-use development that would include two 49-story buildings positioned on the north and south sides of an approximately two-acre publicly accessible plaza with ground level retail and restaurant uses. Option A would consist of residential, hotel and office uses, as well as retail and restaurant uses. Parking for Option A would be provided by expanding the existing two-level subterranean parking garage to a five-level subterranean parking garage, in addition to approximately 400 spaces that would be located off-site at the existing multi-level parking structure across MGM Drive to the southwest. The Existing Hotel and associated buildings, as well as all landscaping on the Project Site, would be removed. Option B would retain and rehabilitate the Existing Hotel into a mixed-use building containing hotel, residential, retail, and restaurant uses. Additional development would be provided surrounding the Rehabilitated Building. The proposed north and south buildings, both 46 stories, would be symmetrically positioned behind (west of) the Rehabilitated Building. At the ground level, Option B would include one-story retail buildings along Constellation Boulevard and at the base of both the north and south buildings within an approximately two-acre publicly accessible plaza. As part of the rehabilitation project in Option B, the sunken plaza would be filled in and developed with single-story retail/restaurant uses, outdoor seating areas, water features, landscaping, and hardscape areas. Under Option B, the existing two-level subterranean parking garage adjacent to and east of the Rehabilitated Building would remain with the existing parking stalls reused as is. An additional parking level would be created by infilling the existing sunken plaza and reconfiguring the circular ramps at both the north and south ends of the existing garage. Parking west of the Rehabilitated Building and beneath the new north and south buildings would be provided on two above-grade and five subterranean levels (three levels lower than the existing western portion of the parking garage). The existing west parking levels would be removed and replaced with the new expanded parking levels. Finally, parking would also be provided on the north and south sides of the Rehabilitated Building in order to connect the east with the west garage sections. In addition, approximately 400 spaces would be located off-site at the existing multi-level parking structure across MGM Drive to the southwest. It should be noted that due to the substantial similarities in the building layout, grading and excavation design, and building footprints between the Option B With Office Scenario and Without Office Scenario, the geology and soils analysis presented here for Option B is representative of both development Scenarios. Page IV.F-18

19 (1) Geologic Hazards (a) Fault Rupture Fault rupture occurs when the movement of a below-ground fault plane results in a surface expression of the fault plane, causing ground surface displacement on either side of the fault plane and resulting in visible evidence of the fault below. Fault rupture can result in ground surface displacement from one inch to as much as 20 feet. As noted above, the Project Site is not located within a currently established Alquist-Priolo Earthquake Fault Zone, or a Fault Rupture Study Area. The closest fault to the Project Site is the Santa Monica Fault, located approximately 0.7 mile north of the Project Site. No active or potentially active faults are known to underlay the Project Site. Therefore, the fault rupture potential on-site is considered very low. Thus, impacts related to fault rupture would be less than significant under Option A and Option B. No mitigation measures are required. (b) Strong Seismic Ground Shaking As noted above, the Project Site is located in the seismically-active Southern California region with the Santa Monica Fault and the Newport-Inglewood Fault zones located nearby. Thus, the location of the Project Site within a seismically active area could expose people or structures to strong seismic ground shaking. However, this is similar to conditions present throughout the region and the Project Site is not exposed to a greaterthan-normal seismic risk as compared to other areas of Southern California. The Geotechnical Report prepared for the Proposed Project found that both Option A and Option B are feasible from a geotechnical standpoint. The Geotechnical Report further outlined recommendations to ensure that both Option A and Option B would withstand significant ground shaking in accordance with all applicable California Building Code requirements listed above. Additionally, the LABC specifies that all proposed structures on the Project Site should be able to: (1) resist minor earthquakes without damage; (2) resist moderate earthquakes without structural damage but with some nonstructural damage; and (3) resist major earthquakes without collapse but with some structural as well as nonstructural damage. Pursuant to existing law and applicable regulations, design and construction of Option A and Option B would be required to incorporate measures to protect against strong seismic shaking. These measures, which are reflected in the PDFs above, include compliance with the LABC, the City s building permit requirements, and site-specific engineering recommendations based on a final geotechnical report prepared by a licensed geotechnical engineer and approved by the LADBS. These existing laws and regulations Page IV.F-19

20 would ensure that Option A and Option B would not result in a significant impact related to strong seismic ground shaking during operation. Because Option B would retain the Existing Hotel on-site, special precautions would be required during construction to maintain the structural integrity of the Existing Hotel and ensure that the Existing Hotel would not be exposed to a greater risk from potential seismic shaking during the construction phase. In accordance with Mitigation Measures F-11 and F-12 under the Mitigation Measures for Option B Only heading, bracing measures including underpinning of the existing foundations would be required to support the Existing Hotel during construction. By positively securing the soils, the foundation of the entire Existing Hotel is expected to retain its structural integrity as designed. In addition, as part of the rehabilitation work, the Existing Hotel would require structural work that conforms with Building Code seismic safety standards. Thus, with implementation of Mitigation Measures F-11 and F-12, Option B s impacts related to strong seismic ground shaking would be reduced to a less than significant level. (c) Liquefaction Based on the previously noted conditions of the Project Site, the potential for liquefaction to occur on the Project Site is low. As stated above, the Project Site is not located within an area identified as having the potential for liquefaction. 15 The estimated depth to groundwater is relatively deep ranging between 40 and 74 feet below ground surface based on previous borings. The CGS Seismic Hazard Zone Report 023 indicated an historical high groundwater greater than 40 feet below ground surface level. Further, the alluvial soils that underlie the artificial fill material on the Project Site are dense and very dense and are therefore not subject to liquefaction. Therefore, impacts related to liquefaction would be less than significant under both Option A and Option B. No mitigation measures are required. (d) Groundwater As noted above, incidental groundwater was encountered at depths of approximately 40 through 74 feet below ground surface in previous borings. Groundwater encountered beneath the Project Site is believed to be perched on impermeable layers and not part of a groundwater basin. Groundwater was encountered in six borings: five of these borings are located in the western portion of the Project Site while one boring is located 15, Department of City Planning, Los Angeles Citywide General Plan, Safety Element, November 26, Page IV.F-20

21 along the eastern perimeter of the Existing Hotel. The boring along the eastern perimeter of the Existing Hotel encountered the deepest groundwater at 74 feet, which is approximately 40 feet below the foundation of the existing eastern parking garage. During construction, excavation required for Option A would extend below the foundation of the existing parking garage to a maximum depth of up to approximately 60 feet below ground surface. Excavation under Option B would also extend below the foundation of the existing parking garage in the western portion of the Project Site to a depth of 60 feet below ground surface in most places, and up to approximately 70 feet below ground surface in limited areas next to the western edge of the Existing Hotel structure. Thus, during grading, temporary excavations and cut slopes in the natural soils may reveal unanticipated groundwater seepage, potentially requiring localized dewatering during construction under both Option A and Option B. This likelihood would be slightly higher for portions of the site under Option B due to the modest additional depth that would be excavated. Any localized dewatering activities associated with Proposed Project construction would occur in accordance with all applicable permit requirements, including all applicable National Pollutant Discharge Elimination System requirements. If contaminated groundwater is found during construction, treatment and discharge, as appropriate, would be conducted in compliance with applicable regulatory requirements including Los Angeles Regional Water Quality Control Board ( LARWQCB ) General Permit conditions and requirements. During operation, the Geotechnical Report identified that the exterior walls of the subterranean parking garage may encounter incidental groundwater during both Option A and Option B operations, due to the greater depth of excavation required under both Options as compared to existing conditions, and the estimated depth to groundwater. This likelihood would be slightly higher under Option B due to the additional modest depth that would be excavated at portions of the Project Site. Also, in the case of Option B, this potential would only exist in the western parking garage, where excavation beyond existing foundations is planned and groundwater was previously encountered in five borings within the additional planned depth. At the eastern parking garage, where groundwater was encountered in one boring at a depth approximately 40 feet deeper than the existing foundation, there is no existing or future potential for groundwater seepage in subterranean walls. Accordingly, the Geotechnical Report recommended for both Option A and Option B that walls below grade be drained to dissipate any hydrostatic pressure, and that drained water be directed to collection basins at the base of these walls, where a water disposal system would be provided. In the case of Option B this would be required in the western parking garage but would not be required in the eastern parking garage. The Geotechnical Report further indicated that because the natural soils beneath the Project Site are predominantly granular, water collected in the collection basins can be discharged into the natural soils without the use of a mechanical pumping system. Additionally, it was Page IV.F-21

22 determined that a sub-drain system would not be required beneath the lowest floor slab under either Option A or Option B (i.e., the subdrain system described above would only be required above the lowest floor slab). Thus, impacts associated with groundwater seepage would be potentially significant under both Option A and Option B, and Mitigation Measure F-1 is required. Compliance with Mitigation Measure F-1 would reduce groundwater impacts to a less than significant level under both Option A and Option B. As previously noted, groundwater encountered beneath the Project Site is believed to be perched and not part of a groundwater basin. If any groundwater is encountered, it would be incidental and in small amounts. Localized dewatering activities during construction and/or operation of the sub-drain system during project operation would not have the potential to significantly deplete a groundwater basin or affect the rate, change the direction, or expand the area of a known groundwater contamination plume. Thus, impacts related to groundwater depletion and groundwater contamination hazards would be less than significant under both Option A and Option B, and no mitigation is required. (e) Landslides and Slope Stability The Project Site is not within an area identified as having a potential for seismic slope instability. As noted above, the Project Site is included in an area of Cluster of Small Shallow Surficial Landslides in the General Plan Safety Element. 16 However, there are no known landslides at the Project Site, nor is the Project Site in the path of any known or potential landslides. Further, the Project Site is relatively level. Thus, impacts related to landslides would be less than significant, and no mitigation measures are required. Regarding slope stability, the planned five-level subterranean parking garage under Option A would be approximately 40 to 60 feet below ground surface, depending on the location within the Project Site. For Option B, which would extend up to three levels lower than the existing parking garage on the western portion of the site, excavation up to feet below ground surface would occur. As noted above, the eastern portion of the existing garage would be retained under Option B. The planned excavations for the subterranean parking garage would expose alluvial deposits that are horizontally stratified and generally lack well-developed planar features such as bedding or joints, which (if present) would act as planes of weakness. Therefore, the geologic conditions would not create an additional 16 Ibid. Page IV.F-22