E-3: VAN BEVEREN & BUTELO, INC., TECHNICAL MEMORANDUM GEOTECHNICAL INPUT TO ENVIRONMENTAL DOCUMENTATION

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1 E-3: VAN BEVEREN & BUTELO, INC., TECHNICAL MEMORANDUM GEOTECHNICAL INPUT TO ENVIRONMENTAL DOCUMENTATION PROPOSED MIDDLE SCHOOL PROJECT, MAY 8, 2003

4 SCOPE This technical memorandum provides geotechnical input to the environmental documentation being prepared for the proposed Middle School Project. The information in this memorandum is based upon the results of our geotechnical investigation currently in process. A list of the prior reports is included in the References section at the end of this document. We are performing our professional services using that degree of care and skill ordinarily exercised, under similar circumstances, by reputable geotechnical consultants practicing in this or similar localities. No other warranty, expressed or implied, is made as to the professional advice included in this memorandum. This memorandum has been prepared for Stephen S. Wise Temple and their planning and design consultants to be used solely in the design of the proposed Middle School Project. The memorandum has not been prepared for use by other parties, and may not contain sufficient information for the purposes of other parties or other uses. PROJECT DESCRIPTION The proposed Middle School Project will include a single story classroom and administration buildings constructed to the north and west of the existing Milken Community High School. Because of restrictions imposed on the school by the Mulholland Scenic Corridor, the building pads will be graded about 20 to 30 feet below the elevation of Mulholland Drive. The Middle School Project will be constructed near the top of a 50- to 75-foot high slope above Sepulveda Boulevard. The slope is as steep as ½:1 (horizontal to vertical). A playfield is planned north of the proposed buildings. The playfield will be developed by placing additional fill, derived from excavation in the classroom area, over an existing playfield and into a shallow canyon. The fill will extend near the existing Sepulveda Tunnel, however, the limits of the filling will be restricted to avoid surcharging the tunnel.

5 GEOLOGIC SETTING GENERAL The site is located near the crest of the northern flank of the central Santa Monica Mountains. This mountain range trends east-west along the southern margin of the San Fernando Valley and was formed during broad, regional uplift. The site is situated on the northern limb of the east-west trending Santa Monica anticline, which is best developed in Jurassic age rocks known as the Santa Monica Slate, that comprise the core of the range. TOPOGRAPHY The proposed Middle School campus location comprises a near level pad between Mulholland Drive on the north and east and Sepulveda Boulevard on the west. Elevations vary across the pad from about 1250 to 1265 feet above sea level. The Middle School Project will be constructed near the top of a 50- to 75-foot high, west-facing slope above Sepulveda Boulevard. This slope is a combination of natural, cut and fill slopes inclined at about ¾:1 to 2:1 (horizontal to vertical) in the natural portions and as steep as ½:1 in the cut portions of the slope; fill slopes were built at 1¾:1 to 2:1. The fill slopes occupy two pre-existing canyons that were backfilled during prior construction phases. A third canyon located to the south of the lower athletic field has been graded with nonengineered fill placed over colluvium, according to a prior Law/Crandall investigation. This canyon topography has not been modified, except at the top, and has slope angles between ¾:1 to 1½:1. An 80-foot high cut-slope offsite to the east of Mulholland Drive, was graded at approximately 1:1 for roadway construction. This slope exposes northerly dipping units of the Modelo Formation similar to those units encountered beneath the proposed classroom site. 2

6 GEOLOGIC MATERIALS The site is mantled by man-placed fill material ranging from about 1 foot to 16½ feet as encountered in our explorations. This fill is composed of fine silty sand and sandy silt with some sand and clay and with siltstone and sandstone fragments. The fill soils are underlain by marine sedimentary rock units of the late Miocene age Modelo Formation. The Modelo Formation at the site is characterized by laminated to thickly bedded, cemented, siltstone/shale with some thinly bedded sandstone units. The bedrock beneath the site is fine-grained and there is the potential for expansive soils beneath the site. The fill materials may also be expansive. Laboratory testing of soil samples from the field investigation is currently being evaluated to address this potential condition. Bedrock in this portion of the Santa Monica Mountains includes sulfide minerals in some of the unweathered bedrock units, particularly black shale deposits. Sulfide minerals can undergo a chemical reaction when exposed to oxygen to become sulfates. This reaction can create expansion-related problems due to crystal growth. The black shale deposits encountered and sampled during the field investigation were chemically analyzed for levels of sulfide-sulfate minerals. Results of chemical testing on the samples will be evaluated for their potential to expand. Mitigation of this potential condition may include deepened foundations, or overexcavation and recompaction of the black shale units. GROUNDWATER The site is located near the crest of the Santa Monica Mountains well beyond the regional groundwater basins. Some minor groundwater seepage was encountered in the exploratory borings drilled at the site during our field investigation. The proposed development is not expected to affect the groundwater resources of the area and groundwater is not expected to effect the proposed development. 3

7 MINERAL RESOURCES There are no known economically extractable deposits of mineral resources such as building stone, clay or light-weight aggregate beneath the site. Therefore, the proposed Middle School Project is not anticipated to have an impact on mineral resources in the area. GEOLOGIC SEISMIC HAZARDS SLOPE STABILITY Available geologic maps of the project area do not indicate landslides on the site. A previous sitespecific geotechnical investigation report (Law/Crandall, 1996) did not indicate potentially unstable deep seated slope conditions at the site. The site is not located within an area identified to have the potential for seismically induced landsliding on the State of California Seismic Hazard Zones map (CDMG, Seismic Hazard Zone, Van Nuys Quadrangle, 1998) and is not located within a City or County of Los Angeles Landslide Inventory Area (County of Los Angeles, 1990) (City of Los Angeles, 1996). Evidence of large-scale landslides was not observed during our field investigation at the site. A small surficial failure was observed on the slope located to the south of the lower field, beyond the limits of the proposed construction. Locally, the colluvial-covered and oversteepened portions of the slope below the proposed buildings are surficially unstable and are undergoing downhill creep and spalling. This condition is occurring where the slope is steeper then generally 1½:1. The proposed school pad will be excavated up to approximately 25 feet and much of the upper existing slope will be removed. Recommendations to mitigate surficially unstable slopes will be included in our investigation report. The proposed building pad will be relatively level and will be bounded by the remaining westfacing slope to the west. Most of the excavation will expose bedrock deposits of siltstone and shale. Bedding within the Modelo Formation here is generally neutral to the slope face or dips slightly into the slope. Additionally, joint planes generally dip approximately 70 degrees to 4

8 vertical, which is steeper than the existing cut slope. These conditions are considered favorable for deep seated stability from a geotechnical standpoint. Excavation for any north-facing cut slopes or retaining walls on the south side of the site may expose bedding dipping out of slope. This condition will be evaluated during our engineering analyses and will be discussed in our investigation report. Locally abundant rodent burrows are present in the natural portion of the slope and erosion has resulted in some burrow enlargement. Recommendations to mitigate this condition can include a rodent control program and will be addressed in the forthcoming geotechnical report. The steep slope along Sepulveda Boulevard is generating loose debris, particularly during and following rainstorms. This slope will continue to spall and deposit soil and rocks on or near Sepulveda Boulevard and will regress uphill into the building pad and measures will need to be implemented to stabilize the slope. These methods could include construction of a slough wall along Sepulveda Boulevard and the installation of rock mesh over the slope. This condition will be addressed in the geotechnical report along with recommendations to mitigate adverse slope conditions. We did not observe evidence of distress from lateral spreading (movements in a fractured mass of rock, soil, or fill, which result from liquefaction or plastic flow) during our field investigation. FAULTING The numerous faults in southern California are categorized as active, potentially active, and inactive. Active faults are those faults that in general have displaced rock units during the Holocene Epoch (i.e. the last 11,000 years). Potentially active faults have demonstrated displacement within the Pleistocene Epoch (i.e. the last 1.6 million years) but do not displace Holocene Strata. Inactive faults do not exhibit displacement younger than 1.6 million years before the present. 5

9 Active faults have not been identified on, or are known to trend through or toward the site. The closest active fault to the site is the Northridge Thrust fault, located about 0.1 mile to the west. Other nearby active faults to the site are the Hollywood fault located about 4.2 miles southeast, the Malibu Coast fault located about 7 miles south-southwest, and the Newport-Inglewood fault zone located about 7.9 miles southeast. The closest potentially active faults are the Overland fault 7.9 miles south-southeast, and the Charnock fault 8.6 miles south-southeast. The regionally extensive Benedict Canyon fault is located approximately 2.6 miles southeast of the site. This fault is considered inactive but significantly offsets various geologic units and influences geologic structure along the fault trace. The Northridge Thrust was responsible for the January 17, 1994, magnitude 6.7 Northridge earthquake. This earthquake was the largest earthquake to strike below an urban area in the United States since the 1933 Long Beach earthquake. The active Hollywood fault trace trends generally east-west along the southerly 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 the City of Los Angeles. The Hollywood fault is reported to be a north-dipping, thrust fault with a left lateral, oblique slip component. The active Malibu Coast fault zone is a series of east-west trending, north-dipping reverse faults extending westward from Santa Monica to offshore of Point Mugu. Although some seismologists and geologists attribute movement of the fault to the February 21, 1973 Point Mugu earthquake, Holocene age activity on the fault had not been positively established until 1980 s. The active Newport-Inglewood fault zone is composed of a series of discontinuous northwesttrending en echelon faults extending from the southern edge of the Santa Monica Mountains southeastward to the area offshore of Newport Beach. Fault-plane solutions for 39 small earthquakes (1977 to 1985) show mostly strike-slip faulting with some reverse faulting along the north segment (north of Dominguez Hills) and some normal faulting along the south segment (south of Dominguez Hills to Newport Beach) (Hauksson, 1987). 6

10 The subject site is not located within an Alquist-Priolo Earthquake Fault Rupture Hazard Zone or a Seismic Hazard Zone established by the California Geological Survey (CDMG Special Publication 42, 1997). The classroom site is located within the seismically active southern California Region and will likely experience the affects of strong ground motion from earthquakes occurring on neighboring active faults. However, the subject site is at no greater risk than other sites in the region with respect to strong ground motion and the proposed school buildings should perform satisfactorily if designed and constructed in accordance with current building codes. In addition, while the site is subject to similar seismic risks due to ground shaking as other sites in southern California, the potential for ground rupture at the subject site due to faulting is considered remote. We did not observe evidence of distress from lurching (earth movement at right angles to a fill slope, cliff or steep slope resulting from strong ground motion) during our site reconnaissance and geologic mapping. LIQUEFACTION AND SEISMICALLY-INDUCED SETTLEMENT The site is not located within an area designated by the State of California or by the City of Los Angeles for potential liquefaction. The materials beneath the site are primarily bedrock units consisting of siltstone and shale with some sandstone. The site is not located within a regional groundwater basin and the risk of liquefaction is therefore remote. Seismic settlement is caused by loose to medium-dense granular soils densifying during ground shaking. The site is underlain by dense, cemented bedrock materials, and the potential for seismically-induced settlement is remote. TSUNAMIS, INUNDATION, SEICHES, AND FLOODING The site is approximately 7 miles from the Pacific Ocean at an elevation of about 1,250 feet above mean sea level. Therefore, tsunamis (seismic sea waves) are not considered a significant hazard at the site. 7

11 According to the Los Angeles County Seismic Safety Element (1990), the site is not located downslope of a large body of water that could adversely affect the site in the event of earthquakeinduced failures or seiches (wave oscillations in an enclosed or semi-enclosed body of water). The site is located near the crest of the Santa Monica Mountains, well above low lying flood prone areas. Curbs and drainages along Mulholland Drive that direct surface water to storm drains, control runoff. Paved areas within the classroom areas and playfield will be graded to direct surface water runoff to drainage devices that discharge to Sepulveda Boulevard. Therefore, the proposed Middle School Project will not result in the potential for site flooding. SUBSIDENCE The site is not within an area of known subsidence associated with fluid withdrawal (groundwater or petroleum), peat oxidation, or hydrocompaction. SITE RUNOFF AND EROSION Runoff generated within the areas of the proposed classroom, administrative buildings, roadway and surface parking will be drained away from the top of the slopes and will be collected in a storm drain system. The runoff will be controlled and will not result in an increase in erosion. The site is located near the top of a 75-foot high slope above Sepulveda Boulevard. Runoff from the pad will be directed away from the top of the slope to storm drains. Existing fill slopes and any new fill slope construction will contain non-erosive terrace and downdrains that direct surface water into storm drain catch basins at the toe of slope. An 18-inch corrugated metal pipe daylights at the head of the canyon at the south end of the proposed project. The pipe collects runoff from Mulholland Drive and discharges it into the unprotected canyon drainage. A slough or diversion wall is present near the bottom of the canyon. Captured water from this pipe should discharge into a nonerosive drainage device to reduce the 8

12 potential for erosion and drainage regression up the slope. The geotechnical investigation report will address this condition and determine appropriate measures to be implemented. FOUNDATIONS The excavation for the classrooms will expose Modelo Formation bedrock throughout most of the area. Foundations for new construction could be established in the bedrock using conventional spread footings. The expansive bedrock may require the use of deep foundations and a structurally supported floor to mitigate the expansion potential. Deep foundations will be required near the top of the slope to provide the necessary setback. The use of deep foundations consisting of drilled cast-in-place concrete piles could mitigate the expansive bedrock and provide the needed setback. SEPULVEDA BOULEVARD TUNNEL The existing Sepulveda Boulevard Tunnel is adjacent to the western property line and about 70 feet below the grade of the existing playfield. The placing of new fill in this area could place surcharge loads on the tunnel. However, the grading will be restricted in the vicinity of the tunnel to avoid surcharge loads on the tunnel. Retaining walls extending below a 1:1 plane projecting upward from the tunnel bottom are being considered as part of the mitigation measures. 9

13 REFERENCES Association of Engineering Geologists, 1982, Southern California Section, Geologic Maps of the Santa Monica Mountains, Sheet 105, Los Angeles, California for the City of Los Angeles, dated 1982, at a scale of 1 inch to 400 feet. Barrows, A.G., 1974, A Review of the Geology and Earthquake History of the Newport-Inglewood Structural Zone, Southern California, California Division of Mines and Geology Special Report 114. California Department of Conservation Division of Mines and Geology, 1998, Seismic Hazard Zones Van Nuys Quadrangle, dated February 1, Fall, E.W., Rzonga, G.F., and Spellman, H.A., 1987, Quaternary Faulting, Malibu Coast Fault Zone, Malibu, California (abstract), Association of Engineering Geologists Annual Meeting, October 8-1, 1987, Atlanta, Georgia, Abstracts and Program p. 83. Hart, Earl W. and Bryant, William A., 1997, Fault-Rupture Hazard Zones in California, California Department of Conservation, Division of Mines and Geology Special Publication 42, Revised 1997, Supplements 1 & 2 added Hauksson, E., 1987, Seismotectonics of the Newport-Inglewood Fault zone in the Los Angeles Basin, Southern California, Bulletin of the Seismological Society of America, Vol. 77, pp Hecker, Suzanne, et. al., 1995, Ground Deformation in Granada Hills and Mission Hills Resulting from the January 17, 1994, Northridge, California, Earthquake, United States Geological Survey Open-File Report Hoots, H.W., 1931, Geologic Map of the Eastern Part of the Santa Monica Mountains, Los Angeles County, California, USGS Professional Paper 165, dated Law/Crandall, Inc., 1996, Report of Geotechnical Investigation, Proposed Community High School, Mulholland Drive, Los Angeles, California, report dated February 20, Law/Crandall, Inc., 1998, Final Report, Geotechnical Inspection Services, Buildings 1, 2, and 3, Community High School, Mulholland Drive, Los Angeles, California, report dated March 6, Los Angeles, County of, 1975, Draft revision 1990, Seismic Safety Element. Los Angeles, County of, 1990, Technical Appendix to the Safety Element of the Los Angeles County General Plan, Draft Report by Leighton and Associates with Sedway Cooke Associates. Los Angeles, City of, 1996, Safety Element of the Los Angeles City General Plan. 10

14 Shakal, A., et. al., 1994, CSMIP Strong-Motion Records from the Northridge, California Earthquake of January 17, 1994, California Division of Mines and Geology Report OSMS 94-07, dated February 18, Thomas W. Dibblee, Jr., 1991, Geologic Map of the Beverly Hills-Van Nuys (south ½) Quadrangles, Los Angeles County, dated 1991, at a scale of 1:24,000, #DF-31. Wissler, S.G., 1943, Stratigraphic Formations of the Producing Zone of the Los Angeles Basin Oil Fields, California Division of Mines and Geology, Bulletin 118, pt. 2, p Ziony and Jones, 1989, Map Showing Late Quaternary Faults and Seismicity of the Los Angeles Region, California. 11

IV. ENVIRONMENTAL IMPACT ANALYSIS E. GEOLOGY/SEISMIC HAZARDS

IV. ENVIRONMENTAL IMPACT ANALYSIS E. GEOLOGY/SEISMIC HAZARDS 1. ENVIRONMENTAL SETTING The following analysis of geology and seismic hazards for the Middle School Project is based on the Report of Geotechnical