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7 <br />L <br />C <br />L' <br />u <br />n <br />C <br />G <br />L <br />n <br />u <br />0 <br />-1 <br />7 <br />Soil, geology, and ground -water data for the proposed site were compiled by <br />EMCON Associates in its Geologic and Hydrogeologic Report completed in <br />September 1987 and Ground -Water Monitoring Plan completed in March 1988. <br />[011i 0 • r 0 <br />The North County Sanitary Landfill is near the northeastern edge of the San <br />Joaquin Valley. The valley is a deep, asymmetric structural trough filled with <br />sediments derived from adjacent mountain ranges. The geology of the eastern <br />portion of the San Joaquin Valley is characterized by alluvial sediments de- <br />posited by rivers and streams emanating from source terrains in the Sierra <br />Nevada Mountains to the east. <br />The youngest geologic units underlying the site are semiconsolidated alluvial de- <br />posits of the Turlock Lake and Riverbank Formations. These two formations <br />consist of heterogeneous deposits of gravels, sands, silts, and clays. Because of <br />similar origins and common lithologies, differentiation of alluvial deposits into <br />formations is difficult. Regionally, lateral and vertical lithologic variations within a <br />formation can be pronounced. <br />The geologic units beneath the site were characterized by reviewing existing lo- <br />cal data and drilling six borings from 40.5 to 215 feet in depth (see Appendix A). <br />In addition to the borings drilled by EMCON, previous drilling has been conducted <br />on the site and on the half -section parcel immediately to the west. Data from <br />these earlier borings were also analyzed in studying the subsurface geology of <br />the site. <br />The exploratory drilling performed during this and the previous investigation con- <br />firm that subsurface conditions are consistent with the regional information de- <br />scribed above. Borings penetrated interlayered silts, clay, and fine sand to their <br />entire depths. Finer -grained materials (silt, clay, and silty sand) predominate. <br />Boring logs are contained in Appendix A. <br />r 9390219A.00W 36 Rev. 0 July • 989 <br />