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0 • 1 City of Stockton Redevelopment Agency B34604.01a ' February 16, 2001 Page 2 2.2 Geologic and Hydrologic Char cteristics: The following subsections summarize the geology and hydrology of the Stockton area. 2.2.1 Geolo¢v: The SITES are in the central portion of the San Joaquin Valley within the southern ' portion of the Great Valley geomorphic province of California. The Great Valley is a nearly flat northwest to southeast trending structural basin spanning approximately 450 miles from the Cascade Mountains in the north to the Tehachapi Mountains in the south and 50 miles wide form the Coast ' Ranges in the west to the Sierra Nevada in the east. The Great Valley has been filled with a sequence of alluvium of Pliocene to Holocene age which overlie sedimentary rocks of Cretaceous to Tertiary age. These sedimentary units, in turn, overlie a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks. The shallow subsurface geology in the area is a heterogeneous mix of gravel, sand, silt, I d clay(Hackel, 1966). ' 2.2.2 Hydrology: Sediments containing fresh groundwater in the San Joaquin Valley are largely unconsolidated silts and sands derived from river channel, flood plain, and alluvial fan deposits of Pliocene to Recent age(Davis and others, 1959). The depth to first encountered groundwater in the vicinity of the SITES was reported to be approximately 45 feet below site grade(BSG)and flowed to the north during the installation of thremonitoring wells as part of a groundwater investigation at Skips Service Station at 300 California Street in March of 1995. Local groundwater flow and water table elevation may be influenced by pumping ofwater wells and ' recharge from various sources. The effec of these influences on groundwater is beyond the scope of this investigation. 2.3 Project History The project history was compiled from the PHASE I investigations conducted by Twining during April, 2000. Review of historical site uses indicate the following former activities and facilities on or near the SITES that may have impacted the environmental ' conditions at the SITES. Ski 's Auto Re air 300 Califoniia Street ' The areas of concern exist associated with: 1.01 The on-going soil and groundwater investigation at Skips Service Station; and 1.02 The areas of concern that have not been previously investigated. These areas include a clarifier in the auto repair bays, and some stained soil observed along the eastern edge of the concrete apron of the building. American Body Shop (323 American Street) The areas of concern exist associated with: • The clarifier and an unde Iground hydraulic hoist located in the service bay at the SITE. California Radiator Works(328 California Street) The areas of concern exist associated with: • The former carpet cleaning/awning repair and storage facility which occupied the SITE for an unknown period of time until 1960; ' The two dip tanks located on a wooden flooring within the existing structure;