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Frontier Transportation, Inc. B23502.01 <br /> October 16, 1996 Page 2 <br /> California. The Great Valley is a nearly flat northwest to southeast trending structural basin <br /> approximately 450 miles long by 50 miles wide. The Great Valley has been filled with a <br /> sequence of older to younger alluvium of Pliocene to Holocene age which overlie <br /> sedimentary rocks of Cretaceous to Tertiary age. These sedimentary units, in turn, overlie <br /> a crystalline basement of Paleozoic and Mesozoic metamorphic and igneous rocks. The <br /> shallow subsurface geology in the site vicinity is a heterogeneous mix of gravel, sand, silt, <br /> and clay (Hackel, 1966). <br /> 2.2.2 Hydrology±: Sediments containing fresh groundwater are largely unconsolidated silts <br /> and sands deposited as river channel, flood plain, and alluvial fan deposits of Pliocene to <br /> Recent age (Davis and others, 1959). During Twining's investigation, first encountered <br /> groundwater beneath the site occurs under unconfined (water table) conditions at a depth <br /> of approximately 10 feet below site grade (BSG). Local groundwater elevation and flow <br /> direction may be influenced by pumping of water wells and recharge from various sources. <br /> The effect of these influences on groundwater beneath the site is beyond the scope of this <br /> investigation. <br /> 2.3 Pro-ject History: On July 21, 1995 three gasoline and three diesel USTs were <br /> removed from the project site. Twining personnel were present during the removal of the <br /> gasoline USTs; however, the diesel USTs had been removed prior to the arrival of the <br /> Twining technician. The contents of the tanks and tank capacity are summarized in Table <br /> 1. <br /> TABLE <br /> 7.Summary of Underground Storage Tank (UST) Contents and Capacity <br /> UST UST Contents DtameteY Length': Vofutne Depth <br /> Number(1) feet;>. feet gallons(�) feet,(3) <br /> ' 39-2257-01 Gasoline 4 1S 1,413 6 <br /> 39-2257-02 Gasoline 4 7 659 6 <br /> 39-2257-03 Gasoline 4 7 659 6 <br /> 39-2257-04 Diesel Unknown Unknown 12,000 10 <br /> 39-2257-05 Diesel Unknown Unknown 12,000 10 <br /> 39-2257-06 Diesel Unknown Unknown 12,000 10 <br /> UST = Underground Storage Tank <br /> (1) SdCPHS tank identification number as stated in November 7, 1995 correspondence <br /> (2) = Approximate <br /> (3) = Depth of bottom of tank below site grade <br /> Note = Diesel USr data based on information provided by K.S. Dunbar and Associates personnel <br /> Following tank removal, four soil samples were collected from approximately 3 feet below <br /> the bottom of the gasoline USTs (S-1-W, S-1-E, S2, and S3) and twelve soil samples were <br />