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' Geologual Teckxus lnr Page 4 Site Conceptual Model Report Project No 724 2 May 2,2006 ' The soil laboratory data generated during the investigation are summarized in Tables 1 and 3 in Appendix B It should be noted that the waste oil tank data are omitted as not relevant to the investigation - no further action required by SJC PHS/EHD The data is on file at SJC ' PHS/EHD in ESE and/or Wm J Hunter & Associates reports Figure 2 contains the locations of the boreholes advanced in the current investigation Appendix C includes the borehole drilling/CPT logs generated in the site investigation ' 2.2.2 Groundwater Earth System Environmental Inc commenced groundwater monitoring in October 1992 and ' Wm J Hunter & Associates performed intermittent/semi-annual monitoring through 1999 Quarterly monitoring has been performed from November 1999 and continues to the present The majority of the groundwater analyses were performed for gasoline range petroleum ' hydrocarbons because the former USTs contained gasoline fuel and this comprised the residual contamination detected in soil Specific analyses for groundwater samples that have been utilized in the investigation include ' • Total Petroleum Hydrocarbons as Diesel (TPH-D) by EPA method SW3500/M8100 • Total Petroleum Hydrocarbons as Gasoline (TPH-G) by EPA method 5030/8015(M) • Benzene, Toluene, Ethyl Benzene and Xylene (BTEX) by EPA method 602. ' • Oxygenated Fuel Compounds (MTBE, D1PE, ETBE, TAME & TBA) by EPA method 8260 • 1,2 DCA &EDB by EPA method 8260 o Methanol &Ethanol by GC-FID o Lead by EPA method E200 7 ' The above analyses were conducted primarily to define the nature and extent of the contamination The groundwater analytical data are included in Tables 2A, 2B and 2C ' The January 2006 CPT boring's groundwater and soil data are included in Table 3 in Appendix B ' 2.3 Chemicals of Concern The investigation of the release documented in Sections 2 1 and 2 2 above has identified gasoline range petroleum hydrocarbons as the compounds of concern (COC) at the site The analysis of gasoline components is usually limited to benzene, toluene, xylene and ethyl benzene (BTXE), total petroleum hydrocarbons as gasoline (TPH-G), and the oxygenated ' fuel compound MTBE because (1) they are readily adaptable to gas chromatographic detection, (2) they pose a serious threat to human health (benzene is carcinogen), (3) they have the potential to move through soil and contaminate groundwater, (4) their vapors are highly flammable and explosive (Leaking Underground Fuel Tank Field Manual, State of California Leaking Underground Fuel Tank Task Force, October 1989), (5) a high percent of gasoline is composed of these compounds, and (6) of the highly soluble nature of the 1