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1 *AW SUMMARY McClelland Consultants conducted a geotechnical study for PSE, Inc., at the proposed San Joaquin Limited cogeneration site (site 3058) in Lathrop, Califor- nia. The purpose of our study was to develop criteria to guide the design and construction of foundations and earthwork for the planned facility. The planned 2-acre facility is to the southwest of the Libbey Owens Ford (LOF) plant, about one-half mile southeast of the Interstate 5 and Louise Avenue interchange. Soil conditions at the site were investigated in December 1988 by eight soil borings, which were drilled to 13- and 62-ft depths, and three field electrical resistivity measurements. Previously, in March 1988, the excavations formed by five backhoe trenches were observed. Subsequent laboratory tests were performed on recovered samples. The site is in the Great Valley of California, which is a nearly flat, alluvial plain underlain by hundreds of feet of sediments. The flat natural topography and underlying subsurface in the project area has been significantly altered by glass disposal activities associated with the adjacent LOF plant. Subsurface materials appear to have been altered over much, if not all, of the site. The presence of glass ranges from a matrix of glass cullet that includes little soil to intermixed soil and glass to soil with some glass fragments. Glass was encountered to a maximum depth of 16 ft. Even where glass was not observed to be present, the surface sands are likely to be uncontrolled fill. Beneath the depth of alteration, the soils consist principally of alterna- ting deposits of clay and sand. A ±20-ft-thick stratigraphic sequence composed primarily of stiff to very stiff, lean, sandy clay extends from down about 14- to 16-ft depth. Dense to very dense, silty fine to medium sand was encountered below the lean clay. Groundwater was encountered at 7- to 11-ft depth in our borings. Construction of the cogeneration facilities will require raising the rela- tively flat, 2-acre plant area about 2 to 5 ft. The presence of substantial volumes of glass and glass by-products complicates the foundation design and earthwork considerations for the equipment and structures associated with this facility. Several approaches can be considered for supporting the cogeneration facilities' equipment and structures. Selection of appropriate foundation options will depend on: (a) flexibility in the layout of cogeneration facility 1144A/H-1 :7 McClelland