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Geologtcal7ecknlcsln� Page 3 <br /> Site Conceptual Model Report <br /> Marci Property <br /> Protect No 7012 <br /> August 23,2004 <br /> 0 Total Petroleum Hydrocarbons as Gasoline (TPH-G)by EPA method 5030/8015(M) <br /> ' + Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) by EPA method 602 <br /> • Oxygenated Fuel Compounds (MTBE, DIPE, ETBE, TAME &TBA)by EPA method <br /> 8260 <br /> ' a 1,2 DCA &EDB by EPA method 8260 <br /> • Methanol & Ethanol by GC-FID <br /> • bead by EPA method E200 7 �I <br /> ' The above analyses were conducted primarily to define the nature and extent of the <br /> contarrunatron <br /> ' The groundwater analytical data compiled by Wm J Hunter&Associates (WJH) and GTI are <br /> included in Tables 3 and 4 in Appendix A, respectively <br /> 2.3 Chemicals of Concern <br /> ' The investigation of the release documented in Sections 2 1 and 2 2 above has identified <br /> diesel range petroleum hydrocarbons as the chermcals of concern (COC) at the site The <br /> analysis of diesel/gasoline components is usually limited to benzene, toluene, xylene and <br /> ethyl benzene (BTXE), total petroleum hydrocarbons as diesel (TPH-D), total petroleum <br /> hydrocarbons as gasoline (TPH-G), and oxygenated fuel compounds because (1) they are <br /> readily adaptable to gas chromatographic detection, (2) they pose a serious threat to human <br /> m health (benzene is carcinogen), (3) they have the potential to move through soil and <br /> contaminate groundwater, (4) their vapors are highly flammable and explosive (Leaking <br /> Underground Fuel Tank Field Manual, State of California Leaking Underground Fuel Tank <br /> Task Force, October 1989), (5) a high percent of gasoline is composed of these compounds, <br /> and (6) because of the highly soluble nature of the oxygenated fuel compounds These COC <br /> have been identified at the site and are included in 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 C 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 chenucal,-each of the COC has the potential to migrate off site with-groundwater <br /> movement <br /> 2.4 Geological/Hydrogeologic Site Characteristics <br /> Geoloav <br /> The site is 1n southeast 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-mann sediments The sediments investigated in the project are Pleistocene and <br /> Holocene non-marine sediments consisting of basin deposits mayor stream flood-deposits in <br /> basins lying between natural levees and alluvial fans (source Geologic Map of California, <br /> r <br />