APPENDIX IV.A Geotechnical Study

Transcription

1 City of Los Angeles February 2014 APPENDIX IV.A Geotechnical Study Technical Appendices Museum Square Office Building Draft Environmental Impact Report

2 February 8, 2013 File No Wilshire, LLC 5757 Wilshire Boulevard, PH-30 Los Angeles, California Attention: Kacy Keys Subject: Geotechnical Supplement to Environmental Impact Report Proposed Museum Square Office Building 5757 Wilshire Boulevard, Los Angeles, California Dear Ms. Keys: 1.0 INTRODUCTION This updated letter has been prepared to discuss potential soil and geological issues required by the California Environmental Quality Act, Section VI. The conclusions presented in this letter are based on review of available geotechnical references. No subsurface investigation has been performed on the site. 2.0 SITE DESCRIPTION AND PROJECT SCOPE The proposed project site is located at the northwest corner of Wilshire Boulevard and Curson Avenue in the City of Los Angeles. The site is shown relative to nearby topographic features on the attached Vicinity Map. Nearly square in shape, the site measures 7.6 acres in area. The site has a relatively level slope ranging in elevation from approximately 190 feet on the east to 180 feet on the west. Existing development on the site includes several office buildings from 1 to 10 stories in height and a 5 level parking structure. It is not known if the structures have basements. At grade parking and landscaped patios fill the open spaces. The proposed development consists of an at-grade 12 story office building with a penthouse. Column loads are estimated to be between 800 and 1,200 kips. Wall loads are estimated to be between 6 and12 kips per lineal foot. Grading will consist of removal and recompaction of existing unsuitable site soils and filling of basements, if any. The current site conditions are depicted on the attached Plot Plan. 3.0 SOIL AND GEOLOGY ISSUES 3.1 General Geology The site is located in the Los Angeles Basin which is at the northern end of the Peninsular Ranges Geomorphic Province. The basin is bounded by the east and southeast by the 439 Western Avenue, Glendale, California fax

3 February 8, 2013 File No Page2 3.2 Faults Santa Ana Mountains and San Joaquin Hills, 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 5 miles of marine and non-marine sedimentary rock as well as intrusive and extrusive igneous rocks have filled the basin. During the last 2 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 relatively recent subtle uplift have been eroded with gullies. According to the attached Local Geologic Map, the site is underlain by older surficial sediments (Alluvium) that consists of interlayered mixtures of clay, sand and gravel. The site is located across from the La Brea Tar Pits. The tar pits consist of active seeping pools of tar, nearby paleontological excavations and a museum. The pools are created by oil and tar from the nearby Salt Lake Oil Field seeping through fractures to the ground surface. Tar seepage has occurred for at least 40,000 years and continues to this day. No active tar seeps are known to occur on the site. However, oil-and tar-saturated soils are known to occur in the areas outside of the La Brea Pits park and may be present below the site. The subject site is not located within an Alquist-Priolo Earthquake Fault Zone, and no other known active surface fault traces cross the site (Hart and Bryant, 2007). Therefore, the likelihood of surface fault rupture affecting the subject site should be considered remote. A copy of the pertinent Earthquake Fault Zone Map is attached (CGS, 1979). A table summarizing the location of nearby faults, their distance from the site and pertinent data regarding the fault are presented in the attached Seismic Source Summary Table. The nearest fault to the site is the Santa Monica Fault located 2.22 miles to the northwest. The fault has not been designated with an Earthquake Fault Zone by the California Geological Survey. As with all of Southern California, the site is subject to potential strong ground motion should a moderate to strong earthquake occur on a local or regional fault. Design of the 439 Western Avenue, Glendale, California Tel: Fax:

4 February 8, 2013 File No Page3 proposed structures in accordance with the provisions of the 2010 California Building Code will mitigate the potential effects of strong ground shaking. 3.3 Oil Wells The site is located approximately 800 feet northeast of the Salt Lake Oil Field (Dibblee, 1991). According to the attached Oil Field Map, no oil wells have been drilled on the subject site (DOGGR, 2001). 3.4 Methane The site is located in a city of Los Angeles designated Methane Zone (City of Los Angeles, 2003). A copy of the Methane Zone Risk Map is attached. 3.5 Radon The subject site is not located in a Radon Potential Zone (CGS, 2005). A copy of this map is attached. 3.6 Unique Geologic Features The site is located across the Curson Avenue from the La Brea Tar Pits which is considered a unique geological feature. Therefore the proposed project would not result in the loss of any unique geologic feature. 3.7 Geologically Unstable Geologic Materials The project is not located on a geologically unstable material or material that would become unstable as a result of the project. Additionally, the site is not located in an earthquake-induced landslide area (CDMG, 1999). Therefore, the project would not result in any on- or off-site landslide or mudflow. 3.8 Seismic Related Ground Failure The proposed construction will not cause or increase the potential for any seismic related ground failure on the subject site or adjacent sites. The site is not located in an area that is mapped as a potentially liquefiable zone According to the attached Seismic Hazard Zone Map (CDMG, 1999). 3.9 Erosion The project would not result in the soil erosion or the loss of topsoil. 439 Western Avenue, Glendale, California Tel: Fax:

5 February 8, 2013 File No Page Inundation The site is located within the inundation area of the Hollywood Reservoir in the event of a seismically-induced breach (Leighton, 1990). The site may be affected in such an event Tsunami The site is not located within an area that could be impacted by a potential tsunami (Leighton, 1990). appreciates the opportunity to provide our services on this project. Should you have any questions please contact this office. Very truly yours, GEOTECHNOLOGIES, INC. REINARD T. KNUR G.E. 2755, C.E.G RTK:aa Enclosures: References Vicinity Map Plot Plan Local Geologic Map Seismic Source Summary Table Earthquake Fault Zone Map Oil Field Map Methane Zone Risk Map Radon Zone Map Seismic Hazard Zone Map [kacy.keys@jhsnyder.net], Attn: Kacy Keys Distribution: (4) Addressee 439 Western Avenue, Glendale, California Tel: Fax:

6 REFERENCES California Division of Mines and Geology, 1998, Seismic Hazard Evaluation Report for the Hollywood 7.5-Minute Quadrangle, Los Angeles County, California, Seismic Hazard Zone Report 026. California Division of Mines and Geology, 1997, Seismic Hazard Zone Map, map scale 1:24,000. California Geological Survey (CGS), 2005, Radon Potential Zone Map for Southern Los Angeles County, California. City of Los Angeles, Department of Public Works, 2003, Methane and Methane Buffer Zones Map, Map Number A Dibblee, T.W., 1991, Geologic Map of the Hollywood and Burbank (South ½) 7.5-Minute Quadrangles, Map No DF-30, map scale 1: 24,000. Division of Oil Gas and Geothermal Resources (DOGGR), 2001, Las Cienegas Salt Lake West Portion Los Angeles Oil Well Location Map, Northern Los Angeles Basin, map 118, map scale 1:7,200. Hart, E.W. and Bryant, W.A., 1999 (updated 2005), Fault Rupture Zones in California, Division of Mines and Geology, Special Publication 42, 25pp. Leighton and Associates, Inc. (1990), Technical Appendix to the Safety Element of the Los Angeles County General Plan: Hazard Reduction in Los Angeles County. National Flood Insurance Rate Program, 2008, Los Angeles County and Incorporated Areas, Map #06037C1605F. 439 Western Avenue, Glendale, California Tel: Fax:

7 SUBJECT SITE LAT: / LONG: N REFERENCE: U.S.G.S. TOPOGRAPHIC MAPS, 7.5 MINUTE SERIES, HOLLYWOOD, CA QUADRANGLE Consulting Geotechnical Engineers VICINITY MAP FILE NO

8 ADJACENT PROPERTY CURSON AVENUE 0 SCALE IN FEET PLOT PLAN REFERENCE: SITE PLAN PROVIDED BY JERDE DATED 12/20/12 Consulting Geotechnical Engineers FILE No DATE: January '13

9 SUBJECT SITE SCALE IN FEET LEGEND Qa: Surficial Sediments - Alluvium consisting of clay, sand and gravel Qae: Older Surficial Sediments - Elevated and Dissected Alluvium consisting of clay, sand and gravel N REFERENCE: DIBBLEE, T.W., (1991), GEOLOGIC MAP OF THE HOLLYWOOD AND BURBANK (SOUTH 1/2) QUADRANGLES, MAP #DF-30 LOCAL GEOLOGIC MAP Consulting Geotechnical Engineers FILE NO

10 Project: 5757 Wilshire, LLC File No.: Fault Name SEISMIC SOURCE SUMMARY TABLE Closest Distance* (km) Site Lies* Deterministic Magnitude* Relative Motion* Activity Reference SANTA MONICA 2.22 SE 7.4 Reverse PA 3 NEWPORT-INGLEWOOD 3.94 NE 7.2 Strike Slip A (EFZ) 2 PUENTE HILLS (LA) 4.29 NW 7.0 Reverse - 1 HOLLYWOOD 4.30 S 6.7 Strike Slip A 3 VERDUGO SW 6.9 Reverse A 1, 3 ELYSIAN PARK (Upper) 8.19 SW 6.7 Reverse - 1 RAYMOND SW 6.8 Reverse A (EFZ) 2 MALIBU COAST E 7.0 Strike Slip A (EFZ) 2 ANACAPA-DUME E 7.2 Reverse PA 3 MISSION HILLS (San Fernando) North 6.7 Reverse A (EFZ) 2 PALOS VERDES NE 7.3 Strike Slip A 2 SIERRA MADRE SW 7.2 Reverse A 3 NORTHRIDGE SE 6.9 Reverse A 3 SAN GABRIEL South 7.3 Strike Slip A (EFZ) 2 ELSINORE W 7.8 Strike Slip A (EFZ) 2 SANTA SUSANA SE 6.9 Reverse A 3 CLAMSHELL-SAWPIT SW 6.7 Reverse PA 3 HOLSER SE 6.8 Reverse - 1 SIMI-SANTA ROSA SE 6.9 Strike Slip A (EFZ) 2 SAN JOSE W 6.7 Strike Slip - 1 OAK RIDGE SE 7.4 Reverse - 1 CHINO W 6.7 Strike Slip PA 2 SAN CAYETANO SE 7.2 Reverse A (EFZ) 2 SAN JOAQUIN HILLS NW 7.1 Reverse - 1 CUCAMONGA W 6.7 Reverse A (EFZ) 2 SAN ANDREAS SW 7.6 Strike Slip A (EFZ) 2 NEWPORT-INGLEWOOD (Offshore) NW 7.0 Strike Slip A 3 SANTA YNEZ (East) SE 7.2 Strike Slip A 2 SAN JACINTO W 7.7 Strike Slip A (EFZ) 2 VENTURA - PITAS POINT SE 7.0 Reverse A (EFZ) 2 OAK RIDGE (Offshore) E 7.0 Reverse PA 2 SANTA CRUZ ISLAND E 7.2 Strike Slip A 2 CHANNEL ISLANDS THRUST E 7.3 Reverse - 1 MISSION RIDGE-ARROYO PARIDA SE 6.9 Reverse - 1 CLEGHORN W 6.8 Strike Slip - 1 RED MOUNTAIN E 7.4 Reverse A (EFZ) 2 CORONADO BANK NW 7.1 Strike Slip - 1 GARLOCK SE 7.7 Strike Slip A (EFZ) 2 PLEITO SE 7.1 Reverse A (EFZ) 2 Notes: 1 = United States Geological Survey A = Active 2 = California Geological Survey A (EFZ) = Active (Earthquake Fault Zone) 3 = County of Los Angeles, Dept. of Public Works, 1990 PA = Potentially Active *Based on USGS California 2008 database Fault Distances Calculated using EZ-Frisk (Version 7.62)

11 SUBJECT SITE Earthquake Fault Zones Alquist-Priolo Earthquake Fault Zone N REFERENCE: SPECIAL STUDIES ZONES, HOLLYWOOD QUADRANGLE, CALIFORNIA, DMG, EARTHQUAKE FAULT ZONE Consulting Geotechnical Engineers FILE NO

12 6TH STREET SUBJECT SITE LEGEND N PLUGGED AND ABANDONED OIL WELL REFERENCE: STATE OF CALIFORNIA, DEPARTMENT OF CONSERVATION. MAP 118, 2001 OIL FIELD MAP GEOTECHNOLOGIES, INC. CONSULTING GEOTECHNICAL ENGINEERS FILE NO

13 SUBJECT SITE LEGEND N REFERENCE: GIS Mapping, Bureau of Engineering, Department fo Public Works - 09/24/03 METHANE ZONE RISK MAP Consulting Geotechnical Engineers FILE NO

14 WML SUBJECT SITE N REFERENCE: RADON POTENTIAL ZONE MAP FOR SOUTHERN LOS ANGELES COUNTY, CALIFORNIA BY RON CHURCHILL CALIFORNIA GEOLOGICAL SURVEY, JANUARY 2005 RADON ZONE MAP Consulting Geotechnical Engineers FILE No

15 SUBJECT SITE N LIQUEFACTION AREA REFERENCE: SEISMIC HAZARD ZONES, HOLLYWOOD QUADRANGLE OFFICIAL MAP (CDMG, 1999) SEISMIC HAZARD ZONE MAP Consulting Geotechnical Engineers FILE NO