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Mohr-Fry Ranches 950 Industrial Drive, Stockton, California August 6, 1996 Site Closure Report Page• S ' S.0 Groundwater Conditions All historical groundwater sampling data is included as Appendix B The groundwater ' laboratory analytical data has been tabulated All gradient maps are included as Appendix C ' Groundwater monitoring has not detected appreciable contamination during the last four quarterly sampling events (one year) Therefore, application was made for and approved ' by San Joaquin County PHS/EHD to destroy the three (3) monitoring wells 6.0 Geology ' This site, at 950 Industrial Drive, Stockton, California, is located in the northern end of California's San Joaquin Valley This area is monotonous geologically, representing primarily the alluvial flood and delta plains of the major rivers and tributaries of the region The region persisted as a lowland or shallow marine embayment during the entire Cenozoic period The surface of the Valley is composed of unconsolidated Quaternary sediments ' The hthologic units encountered were interbedded inorganic micaceous clayey silts and silty clays with numerous sands and silty, clayey sands of varying thicknesses This is typical of the valley fill deposits in the region ' Stockton lies in thentr 1 Ce al Valley Physiographic Province of California The Valley is I about 40 miles wide in this area It is bounded to the west by the foothills of the Coast Ranges, and to the east by the foothills of the Sierra Nevada Range The Stockton area is nearly devoid of structural geologic features The Valley is floored by unconsolidated Quaternary sediments to depths of at least 400 or more feet in the Stockton area All of these units can be considered soils in the I engineering sense, because they are unconsolidated Quaternary sediments in the Central Valley were deposited as a series of coalescing alluvial fans The fans originated where valleys of the major streams which drained the Sierra Nevada Range emptied into the broad expanses of the valley The coarser sediments which comprise the fans are mainly arkosic in composition and were derived from erosion associated with glacial stages in the mountains The finer grained sediments are predominantly composed of rock flour washed out of the former extensive glaciers in the Sierras, (Arkley, 1964) The axis of the Central Valley Trough was a marshy, wet area throughout much of the Pleistocene Epoch Lacustrine, flood plain and marshy depositional environments