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Appendix IS-3 Soils and Geology Report Appendix IS-3 Soils and Geology Report August 7, 2017 Revised February 22, 2019 File No. 21439 Bishop A. Elias Zaidan, Successor Trustee Our Lady of Mt. Lebanon – St. Peter Maronite Catholic Cathedral Los Angeles Real Estate Trust 333 San Vicente Boulevard Los Angeles, California 90048 Attention: Construction Committee Subject: Environmental Impact Report, Soils and Geology Issues Proposed Church Addition and Residential Tower 333 South San Vicente Boulevard, Los Angeles, California Ladies and Gentlemen: 1.0 INTRODUCTION This document is intended to discuss potential soil and geological issues for the proposed development, as required by Appendix G of the California Environmental Quality Act (CEQA) Guidelines. This report included one exploratory excavation, collection of representative samples, laboratory testing, engineering analysis, review of published geologic data, review of available geotechnical engineering information and the preparation of this report. 2.0 SITE CONDITIONS The site is located at 333 South San Vicente Boulevard, in the City of Los Angeles, California. The site is triangular in shape, and just under one acre in area. The site is bounded by a city alley to the north, San Vicente Boulevard to the east, Burton Way to the south, and Holt Avenue to the west. The site is shown relative to nearby topographic features in the enclosed Vicinity Map. The site is currently developed with a catholic church complex, and a paved parking lot. The structures which currently occupy the site range between one and three stories in height. The site’s grade is relatively level, with no pronounced highs or lows. Vegetation at the site consists of abundant mature trees, grass lawns, bushes and shrubs, contained in manicured landscaped areas. Drainage across the site appears to be by sheetflow to the city streets to the south. www.geoteq.com August 7, 2017 Revised February 22, 2019 File No. 21439 Page 2 3.0 PROJECT SCOPE Information concerning the proposed development was obtained by review of the architectural plans prepared by Nadel Architecture and Planning, dated January 20, 2019. The proposed development consists of the construction of a new 19-story residential tower, a new 3-story podium structure, and an addition to the existing church structure. The entire development, including the existing structure, will be underlain by a new parking garage consisting of five subterranean parking levels. The finished floor elevation of the proposed subterranean parking garage is expected to extend to a depth of 64 feet below the existing grade. Excavations up to 72½ feet in depth are anticipated for construction of the proposed subterranean garage, elevator pit and foundation elements. The proposed structure will be designed in accordance with the provisions of the applicable City of Los Angeles Building Code. 4.0 FIELD EXPLORATION The site was explored by this firm on June 12, 2017. The exploration consisted of drilling one boring to a depth of 100 feet below the existing grade. The boring was drilled with the aid of a truck-mounted drilling machine using 8-inch diameter hollowstem augers. The location of the boring is shown on the enclosed Plot Plan, and the geologic materials encountered are logged on the enclosed Plate A-1. 5.0 GEOLOGIC MATERIALS Fill: Fill materials were encountered in the exploratory boring to a depth of 3 feet below the existing grade. The fill consists of silty clay, which is gray in color, moist and stiff. Alluvium: The fill materials were observed to be underlain by native alluvial soils, consisting of interlayered mixtures of sand, silt and clay. The native alluvial soils range from light gray to grayish brown to dark gray in color, and are moist to wet, medium dense to very dense, or stiff, and fine grained, with occasional gravel. More detailed descriptions of the earth materials encountered may be obtained from the enclosed log of the subsurface excavation. 6.0 GROUNDWATER Groundwater was encountered during drilling of Boring 1 at an approximate depth of 18 feet below the existing grade. The historically highest groundwater level was established by review of the Beverly Hills 7½ Minute Quadrangle Seismic Hazard Evaluation Report, Plate 1.2, Geotechnologies, Inc. 439 Western Avenue, Glendale, California 91201-2837 Tel: 818.240.9600 Fax: 818.240.9675 www.geoteq.com August 7, 2017 Revised February 22, 2019 File No. 21439 Page 3 Historically Highest Ground Water Contours (CDMG, 2006). Review of this plate indicates that the historically highest groundwater level for the site was on the order of 10 feet below the existing grade. A copy of the historically highest groundwater map is enclosed herein. 7.0 LOCAL GEOLOGY The subject site is located in the Los Angeles Basin. 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, to the northwest by the Santa Monica Mountains. The distribution of nearby geologic materials is shown on the Local Geologic Map enclosed in the Appendix of this report. 8.0 REGIONAL GEOLOGIC SETTINGS The subject site is located within the Peninsular Ranges Geomorphic Province. 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-west trending reverse faults that form the southern margin of the Transverse Ranges (Yerkes, 1965). The regional distribution of geologic materials is shown on the Regional Geologic Map enclosed in the Appendix of this report. 9.0 PRELIMINARY RECOMMENDATIONS Based upon the exploration, laboratory testing, and research, it is the preliminary finding of Geotechnologies, Inc. that construction of the proposed structure is considered feasible from a geotechnical engineering standpoint. These recommendations are preliminary in nature due to the limited subsurface exploration conducted, and because the proposed project is not well defined at this point. Supplemental subsurface exploration and laboratory testing will be required to meet the standards of a final geotechnical investigation required prior to issuance of building permits. It is anticipated that the finished floor elevation of the lowest subterranean level would extend to a depth of 64 feet below grade. Based on the depth of the proposed structure, relative to the depth of the existing and historically highest groundwater levels, it is the recommendation of this firm that the subterranean portion of the proposed structure be designed to resist hydrostatic forces. It is anticipated that a mat foundation would be suitable for support of the proposed structure. The mat foundation may bear in the undisturbed native soils expected at the subterranean subgrade. Under the hydrostatic design approach, mat foundations shall be designed to resist hydrostatic uplift based on the historically highest groundwater level (depth = 10 feet). The proposed subterranean retaining walls should be designed to resist hydrostatic pressures based on the surrounding grade elevation. Geotechnologies, Inc. 439 Western Avenue, Glendale, California 91201-2837 Tel: 818.240.9600 Fax: 818.240.9675 www.geoteq.com August 7, 2017 Revised February 22, 2019 File No. 21439 Page 4 Excavation of the proposed subterranean levels will require shoring and temporary dewatering in order to achieve a dry and stable excavation. It is expected that a formal pre-construction temporary dewatering program consisting of wells or well-points will be required to lower the groundwater table prior to excavation of the subterranean levels. The expected number and depths of well-points, expected flow rates, and expected pre-pumping time frames should be determined during a dewatering test program conducted by a qualified dewatering consultant. Once the temporary construction dewatering is discontinued, the water table will likely return to its current elevation. 10.0 SOIL AND GEOLOGY ISSUES a) Regional Faulting Based on criteria established by the California Division of Mines and Geology (CDMG) now called California Geologic Survey (CGS), faults may be categorized as active, potentially active, or inactive. Active faults are those which show evidence of surface displacement within the last 11,000 years (Holocene-age). Potentially-active faults are those that show evidence of most recent surface displacement within the last 1.6 million years (Quaternary-age). Faults showing no evidence of surface displacement within the last 1.6 million years are considered inactive for most purposes, with the exception of design of some critical structures. 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 usually not known until they produce an earthquake. The risk for surface rupture potential of these buried thrust faults is inferred to be low (Leighton, 1990). However, the seismic risk of these buried structures in terms of recurrence and maximum potential magnitude is not well established. Therefore, the potential for surface rupture on these surface-verging splays at magnitudes higher than 6.0 cannot be precluded. A list of faults located within
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