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B. SITE GEOLOGY The geologic units beneath the Landfill Development Site were charac- terized by reviewing existing local data and drilling six borings (P-1 through P-3 and G-1 through G-3) ranging from 40-1/2 to 215 feet in depth (see Drawing 1 and Appendix A) . In addition to the borings drilled under the supervision of ECON, previous drilling was conduct- ed by J.H. Kleinfelder and Associates both on the same property and on the half-section parcel immediately to the west (Kleinfelder, 1980a and 1986) . Data from these earlier borings was also analyzed in studying the subsurface geology underlying the site. Additionally, a seismic refraction survey was conducted by Portola Geophysics to evaluate the rippability of subsurface materials. The locations of seismic lines S-1 through S-6 are shown on Drawing 1, with survey results contained in Appendix B. The site is situated within an area of gently rolling topography. Surficial soils consisting of silts and clays extend from the ground surface to a depth of 2 to 3 feet, commonly underlain by a 1/2-foot layer of cemented soil referred to as hardpan. Extensive soil depos- its cover and inhibit surface observations or mapping of the underly- ing alluvial deposits of the Turlock Lake and Riverbank Formations. The exploratory drilling performed during this and previous investiga- tions confirmed subsurface site conditions to be consistent with the regional setting discussed above. Beneath surficial soils, all bor- ings penetrated interlayered silts, clays, and sands to their entire depth (see Drawing 2) . Logs of the borings are attached in Appen- dix A, along with monitoring well construction details. As the cross-sections on Drawing 2 indicate, lithologies within the upper 100 feet vary widely across the site. Two shallow borings, P-1 and P-2, were drilled to supplement existing data on sediments within and immediately below potential soil excavations. The borings were PJ9 9390206.00D 6