9 First American Way - Soils Report

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Lut:ky Associates Development. LP - Geotechnical Investigation MACTEC Project 4953-03-263] September 18.2003 The relationship of the site to local geologic features is depicted in Figure 3, Local Geology, and the faults in the vicinity of the site are shown in Figure 4, Regional Faults. Figure 5, Regional Seismicity, shows the locations of major faults and earthquake epicenters in Southern California. 5.2 GEOLOGIC MATERIALS The site is underlain by Holocene age alluvia] deposits. Based on published geologic maps, the Holocene age sediments consist primarily of silt and clay that are estimated to be approximately 15 to 25 feet thick. The Holocene age materials are underlain by Pleistocene age sediments estimated to be approximately 835 feet thick. The upper Pleistocene age materials beneath the site are typically sandier in nature, consisting of interlayered sand and silt. About 3 to 8 feet of fill was encountered in our borings at the site of the proposed Data Center. The fills soils consist of sandy silty clay with gravel, silty sand and silty clay. Deeper fill could be present in other locations. The natural soils encountered beneath the proposed Data Center consist of medium stiff to very stiff silty clay and sandy silt, medium dense to dense poorly graded sand, poorly graded sand with silt, and silty sand. 5.3 GROUND WATER The site is located in Section 30 of Township 5 South, Range 9 West, within the East Coastal Plain Hydrologic Subarea in the Santa Ana River Hydrologic Unit. According to the California Division of Mines and Geology (2001), the-bistodcltighwaterieveUUbg.,Rite,itinitxj#.aL#.dgglb.less.thall-11), Iss!.hlow-the-existing.groundjurface. According to Sprotte et al. (1980), the depth to the free water in the vicinity of the site inÂ¢tlen042 derind.suESÂ·. Ground water was encountered in our borings at the site at depths of 14 to 16 feet beneath the existing ground surface. 4