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' Gaa�Oguarr�lrr Page 5 -
<br /> Site Conceptual Model Report
<br />' Project No 724 2
<br /> 0 May 2,2005
<br />' oxygenated fuel compounds These COC have been identified at the site and are included in
<br /> the monitoring and analytical protocols
<br /> ' GTI has compiled fact sheets available on government and commercial internet sites for the
<br /> COC and has included the sheets in Appendix D The fact sheets include physical and
<br /> chemical properties of the COC in a pure form, not necessarily that which occurs upon
<br /> ' release to the environment Although the solubility of the COC in water vanes from
<br /> chemical to chemical, each of the COC has the potential to migrate off site with groundwater
<br /> movement
<br /> ' 2.4 Geological/Hydrogeologic Site Characteristics
<br /> '
<br /> Geology
<br /> The site is in southern portion the City of Stockton, California, which is located in the San
<br /> Joaquin Valley The Valley is underlain by a series of Quaternary and Tertiary marine and
<br /> ' non-marine sediments The sediments investigated in the project are Pleistocene and
<br /> Holocene non-marine sediments consisting of basin deposits major stream flood-deposits in
<br /> basins lying between natural levees and alluvial fans (source Geologic Map of California,
<br /> San Jose Sheet, Division of Mines and Geology, 1966) The following section discusses the
<br /> subjective field observations and geology documented during this investigation based on the
<br /> interpretations of various field geologists
<br /> Borings TH-1 through TH-7, MW-1, MW-2 and MW-3 (1992) p
<br /> ESE described the subsurface as low to moderate permeability, loose, light brown, very
<br /> ' silty, very fine to medium grained, sandy soils to a depth of 13 feet bgs From 13 to 27 SCJ
<br /> feet the soils were characterized as moderate to highly permeable, loose, dark brown, 27,
<br /> silty, fine to medium grained sand Below this depth the soils were logged as
<br /> consolidated, slight to moderate plasticity, medium dense, low permeability, gray brown,
<br /> silty, organic clay extending to 53 feet bgs The clays are underlain by soils described as y ,
<br /> consolidated, slight to moderate plasticity, medium dense, low permeability, light brown, 53V
<br /> ' trace very fine sand, minor silt, clays to a depth of 57 feet bgs These clays are underlain
<br /> by consolidated, slightly dense, moderate to low permeability, wet silt with minor fine
<br /> sand to 61 feet bgs Beneath this silt/sand layer is consolidated, slight to moderate
<br /> ' plasticity, medium dense, low permeability, light brown, trace very fine sand, minor silt, 3"
<br /> clays to a depth of 65 feet bgs (From Earth Systems Environmental, Inc 's "Preliminary
<br /> Site Characterization", May 6, 1992 and "Preliminary Groundwater Assessment",
<br /> ' November 6, 1992 )
<br /> GTI logged the remainder of the borings-
<br /> MW-4 and MW-5 1999
<br /> These boreholes were described as primarily clayey by GTI The clay is typically tan to
<br /> brown and shows the presence of small amounts of sand The color changes to a gray or
<br /> blue color once groundwater is encountered The clay ranges from plastic and soft to
<br /> hard depending on moisture content
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