IV.D GEOLOGY 1. INTRODUCTION This section identifies and evaluates geologic and soils conditions at the project site that could affect, or be affected by, implementation of the proposed project and recommends mitigation measures to avoid or lessen potential impacts. This section incorporates and summarizes information contained in a geotechnical investigation report prepared by R. T. Frankian & Associates Geotechnical Engineering and Engineering Geology, dated May 5, 2006. A copy of the report is provided in Appendix IV.D. 2. ENVIRONMENTAL SETTING a. Geology and Topography The project site is located on the southeastern corner of Wilshire Boulevard and La Brea Avenue in the City of Los Angeles. Specifically, the approximately 3.4-acre project site comprises an entire city block and is bound by Wilshire Boulevard to the north, Sycamore Avenue to the east, 8th Street on the south, and La Brea Avenue to the west. Existing development on the site includes a three-story church (including a basement), a commercial strip center, a private alley, and paved parking areas. The project site is located in a relatively flat area of the Los Angeles Basin. The terrain at the site slopes gently downward from north to south with a maximum difference in existing ground surface elevation of about 8 feet. No distinctive natural landforms are located around the project site. The Santa Monica Mountain range and Santa Monica fault zone are located northwest of the project site. The Cucamonga fault zone is located 55 kilometers (34.18 miles) east of the project site. The La Brea Tar Pits are located to the west of the project site. b. Soils According to the geotechnical investigation report prepared for the proposed project, five test borings were drilled on the site with a wash-boring drill rig. The borings were 5 inches in diameter and were carried to depth between 51 and 61 feet below present grade. Structures and asphalt pavement covers nearly the entire site. No appreciable amounts of filled soils were found beneath the pavement. The naturally deposited soils consist of, for the most part, silty clay with variable amounts of silt. The soil is generally classified as stiff, although at some locations it is classified as firm or very firm. Each boring encountered layers of silty sand and clayey sand, which are generally Los Angeles Department of City Planning IV.D-1 Wilshire and La Brea Project Draft EIR Impact Sciences, Inc. (906-01) August 2008 IV.D Geology dense and occasionally very dense. These sand layers were at depths ranging from near surface to the bottom of some borings. c. Groundwater Groundwater was found in each of the five borings. The groundwater levels ranged from approximately 16 feet to 21 feet in depth.Recent readings in the monitoring wells were of similar levels. According to the State of California Division of Mines and Geology, the historic high groundwater level is at a depth of about 12 feet. d. Tectonics The project site, as with all of Southern California, is located within a seismically active region. However, the project site is not within a currently designated Fault Rupture Hazard Zone. The closest fault to the project site is the Santa Monica fault and is located approximately 4.5 kilometers (km) (2.8 miles) northwest of the site. The anticipated peak horizontal ground acceleration for the maximum probable earthquake presented in the Seismic Evaluation Report for the project area, California Division of Mines and Geology (CDMG) Open-File Report 98-17, is 0.46 g (acceleration due to gravity). The maximum probable earthquake as defined in the Los Angeles Uniform Building Code (LAUBC) is the maximum seismic event anticipated with a 10 percent probability of exceedance in 50 years. e. Liquefaction Liquefaction is a form of earthquake-induced ground failure that occurs primarily in relatively shallow, loose, granular, water-saturated soils. Liquefaction is the sudden decrease in the cohesiveness of soils, which, in turn, creates a liquefaction of soils. Liquefaction potential has been found to be the greatest where the groundwater level and loose sands occur within a depth of about 50 feet or less. The potential for liquefaction decreases with increasing soil and sand grain size and clay and gravel content, but increases as the ground acceleration and duration of shaking increase. The project site is not in a liquefaction area as designated by the State of California Seismic Hazard Zones Map, Hollywood Quadrangle, dated March 25, 1999. The site is not in an earthquake fault zone, as shown on the State of California Special Studies Zones Map, Hollywood Quadrangle, Revised Official Map, dated July 1, 1986. Although the historic high groundwater level is at a depth of only about 12 feet (Open-File Report 98-17, Division of Mines and Geology), the firm to stiff clay soils and the dense to very dense sands create a low Los Angeles Department of City Planning IV.D-2 Wilshire and La Brea Project Draft EIR Impact Sciences, Inc. (906-01) August 2008 IV.D Geology to very low potential for soil liquefaction at the site. The soils generally contain silt and occasionally contain gravel. They have high blow counts for the obtained soil samples. The project site is not listed near or on a liquefaction zone based on the California Geologic Survey (CGS) hazards maps.1 3. REGULATORY FRAMEWORK a. Federal Regulations Flood Insurance Rate Maps are prepared by the Federal Insurance Administration of the Department of Housing and Urban Development (HUD) after a risk study for a community has been completed and the risk premium rates have been established. The maps indicate the risk premium zones applicable in the community and when those rates are effective. They are used in making flood plain determinations and to determine if a proposed action is located in the base or critical action flood plain, as appropriate. Because, collectively, the project is over 1 acre in size, a General Permit for Discharges of Storm Water Associated with Construction Activity is required by the Los Angeles Regional Water Quality Control Board (LARWQCB), as part of the National Pollution Discharge Elimination System (NPDES), to control erosion and pollution during construction of the project. The permit requires the project applicant to prepare and submit a Storm Water Pollution Prevention Plan (SWPPP) to be administered throughout project construction. The SWPPP must list Best Management Practices (BMPs) that the discharger (project applicant) will use to protect stormwater runoff. b. State and Regional Regulations Under the Seismic Hazards Mapping Act, the CGS provides maps of seismic hazard zones to local governments for planning purposes. These maps are intended to protect the public from the risks involved with strong ground shaking, liquefaction, landslides and other hazards related to earthquakes. CGS also provides guidelines to evaluate and mitigate hazards for projects within seismic hazard zones. The Alquist-Priolo Earthquake Fault Zoning Act (PRC Section 2621.5) provides policies and criteria to assist cities, counties, and state agencies in the development of structures for human occupancy across the trace of active faults. Maps associated with this act show the seismic hazard zones throughout California. 1 Seismic Hazards Zonation Program, “California Geological Survey”, http://gmw.consrv.ca.gov/shmp/ (2007). Los Angeles Department of City Planning IV.D-3 Wilshire and La Brea Project Draft EIR Impact Sciences, Inc. (906-01) August 2008 IV.D Geology The South Coast Air Quality Management District’s Rule 403 – Fugitive Dust requires projects to comply with specific actions to prevent, reduce, or mitigate fugitive dust emissions during excavation, demolition, and other construction activities. The project applicant must comply with the California Building Code (CBC) (CCR Title 24, Part 2), which provides guidelines for building design to protect occupants from seismic hazards. c. Local Regulations The City of Los Angeles also regulates building design through the LAUBC. The LAUBC provides requirements for construction, grading, excavations, use of fill and foundation work, including type of materials, design and procedures, which are intended to limit the probability of occurrence and the severity of consequences from geological hazards. 4. ENVIRONMENTAL IMPACT ANALYSIS a. Significance Criteria The following thresholds for determining the significance of impacts related to geologic hazard conditions are contained in the L.A. California Environmental Quality Act (CEQA) Thresholds Guide, which was adopted by the City Council in 2006. Impacts related to geologic hazards are considered significant if the proposed 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. Impacts related to sedimentation and erosion are considered significant if the proposed project would Constitute a geologic hazard to other properties by causing or accelerating instability from erosion; or Accelerate natural processes of wind and water erosion and sedimentation, resulting in sediment runoff or deposition that would not be contained or controlled on site. Impacts related to landform alteration are considered significant if the proposed project would Have one or more distinct and prominent geologic or topographic features destroyed, permanently covered, or materially and adversely modified. Such features may include, but are not limited to, hilltops, ridges, hill slopes, canyons, ravines, rock outcrops, water bodies, streambeds, and wetlands. Los Angeles Department of City Planning IV.D-4 Wilshire and La Brea Project Draft EIR Impact Sciences, Inc. (906-01) August 2008 IV.D Geology b. Project Impacts The Wilshire and La Brea Project would provide a total of 562 new residential units and approximately 45,000 square feet of retail. The residential mix would include 138 studio units, 315 one-bedroom units, and 109 two-bedroom units. The retail component would include 37,000 square feet of general retail and 8,000 square feet of restaurant space.