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TECHNICAL MEMORANDUM Page 6 June 3, 1992 SAC31583.AC.ZZ resultant ground motions expected at the site. Assuming stiff soils site conditions, a maximum peak bedrock acceleration of 0.18g also corresponds to a ground surface acceleration of approximately 0.18g (Seed and Idriss, 1982). This maximum ground surface acceleration, which corresponds to a Magnitude 7 MCF, was used in evaluating the potential for permanent slope displacement that may result from earthquake -induced ground motions. Site Conditions The information presented in this section is based on a review of existing data, the results of the soil borings and laboratory testing, and observations during site visits. The subsection on subsurface conditions presents our interpretation of the conditions based on this information. Subsurface Conditions The soil encountered during the field exploration generally consists of interbedded layers of sand, silt, and lean clay. The cohesive materials are generally of very stiff to hard consistency. The cohesionless materials can be characterized as dense to very dense. The soil deposits at the site were found to be heterogeneous and laterally and vertically discontinuous. Based on the four soil borings performed for this geotechnical exploration, the subsurface soils at the site can be generally divided into six layers of interest. It should- be houldbe noted that the generalized subsurface profile described below has been greatly simplified for purpose of settlement and stability analyses. A generalized subsurface profile is shown in Appendix III. Beginning at the existing ground surface (approximately elevation 39 feet), these six layers are as follows: • A 10- to 15 -foot layer of light brown material ranging from lean clay to silt and silty clay. This layer is dry and very stiff to hard in consistency, with moisture contents typically at or below the plastic limit. A UU triaxial compression test performed on a sample at a depth of 15 feet in Boring BH -4, indicated an undrained shear strength of 5,145 pounds per square foot (psf). SPT blow - counts in this layer are typically greater than 50. • A 16- to 20 -foot layer of material ranging from silty sand to clayey sand. This layer is dry to moist and typically dense to very dense. Within this layer, a 5 - foot zone of very stiff lean clay (UU shear strength of 2,262 psf) was