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TECHNICAL MEMORANDUM Page 7 June 3, 1992 SAC31583.AC.ZZ encountered in Boring BH -2 at an approximate depth of 19 feet. This layer was not encountered in'other borings and is believed to be discontinuous. A 5- to 10 -foot layer of very stiff yellowish -brown lean clay. This material is moist, with moisture contents between the plastic and liquid limit. A consolidation test indicates that this material is consolidated to approximately three times the effective overburden stress (OCR of 3). The overconsolidation ratio (OCR) is the ratio of the maximum effective stress the soil has been subjected to in the past (preconsolidation pressure) to the existing effective stress in the soil. A UU tri 'al compression test at an approximate depth of 34 feet in Boring BH -1 indicated a shear strength of 2,286 psf. A 30- to 36 -foot layer of very dense sandy material. This material ranged from silty and clayey sand to poorly graded and well graded sand. Within this layer, zones of very stiff lean clay (UU shear strength of 3,302 psf) were encountered in Borings BH -1 and B-2 at approximate depths of 50 feet and 64 feet. This material has an approximate OCR of 1.4. A 30 -foot layer of material consisting of very stiff to hard silt and lean clay. This material is moist to wet, with moisture contents between the plastic and liquid limit. This material has an approximate OCR of 1.7 (Boring BH -1, approximate depth 78 feet). Very dense poorly graded sand was observed near the bottom of Boring 1314-1, starting approximately at a depth of 100 feet. Sand was also observed in Emcon's Boring No. 17 to the maximum depth drilled of 178 feet (EMCON, 1972). Soil type and properties of the materials encountered in the geotechnical explorations performed by EMCON and Insitu-Tech were generally consistent with the conditions described above. In EMCON's subsurface exploration, a Modified California Sampler (with a 140 -pound hammer with a 30 -inch drop) was used to collect samples. Blow -counts recorded with the Modified California Sampler typically ranged from 20 to 60 blows per foot. Unconfined compression strength tests performed on silty clay samples between depths of 3 to 10 feet ranged from 1,310 psf to 5,100 psf (3,000 psf average shear strength) (EMCON, 1972). The shear strength is defined as one half of the deviator stress at failure. Shear strength based on Insitu-Tech's CPT data (performed to a maximum depth of 50 feet)