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r - <br /> • NO FURTHER ACTION REQUEST <br /> COLBERG BOAT WORKS <br /> JUNE 2002 <br /> Sediments encountered in the Stockton area consist of recent fill material,which vanes according <br /> to construction activities, older Pleistocene, Holocene and Recent Quaternary sediments which <br /> are approximately 200 feet thick in this area, and deeper continental deposits of Pliocene and <br /> Pleistocene age <br /> Locally,the site is underlain by the Riverbank Formation,which consists of a brown to red-gray <br /> locally pebbly sand with minor silt and clay Overlying the Riverbank Formation is a thin layer <br /> of recent alluvial deposits chiefly composed of tan to brown silty sand with local zones of gravel <br /> and clay. <br /> Subsurface Soil Conditions <br /> Soil samples were collected in the boreholes shown on Figure 2 Two cross-section locations are <br /> shown on Figure 3 and the respective cross-sections are shown on Figure 4 Geologic logs for <br /> the subject site are contained in Appendix C. <br /> The cross-sections show soil types across the eastern portion of the site in the vicinity of the <br /> • former gasoline UST Section A-A' has an east-west trend south of the former UST excavation <br /> Section B-B'has a northwest southeast trend north and east of the former UST excavation Silt <br /> and clay are the most abundant soil types Sand is present only in the lower 2 feet of monitoring <br /> well MW-3 and soil boring SB-24 <br /> Groundwater Conditions <br /> Six monitoring wells (MW-1 through MW-6)were installed and monitored during the <br /> investigation of the subject site Those wells, soil bongs and geoprobes constructed during the <br /> investigation are shown on Figure 2 Groundwater elevations on the subject site averaged 8.83 <br /> feet below ground surface(bgs)and vaned from 5 89 to 1102 bgs Historical groundwater <br /> gradients are to the east(Figure 5)and appear to be influenced by seepage from the Stockton <br /> Deep Water Channel,which is a man-made structure Historical groundwater elevation data are <br /> contained in Table 1 and a groundwater contour map for October 21, 1999 is shown on Figure 6 <br /> 3 <br />