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C,tologlcalTicknlrslxG Page 4 Revised Site Conceptual Model Report Project No.507.2 April 3,2008 �.f 2.2.2 Groundwater `+ Wm. J. Hunter & Associates commenced groundwater monitoring in July 1995. Quarterly monitoring has been consistently performed from April 1999 and continues to the present. Specific analyses that have been utilized in the investigation include: • Total Petroleum Hydrocarbons as Gasoline (TPH-G), MTBE by EPA method 5030/8015(M). • Benzene, Toluene,Ethyl Benzene and Xylene (BTEX)by EPA method 602, 8020. • Oxygenated Fuel Compounds (MTBE, DIPE,ETBE,TAME & TBA)by EPA method 8260. �. • 1,2 DCA &EDB by EPA method 8260. • Methanol &Ethanol by GC-FID. • Standard Minerals (various methods) The above analyses were conducted primarily to define the nature and extent of the contamination. The groundwater analytical data are included in Table 3 in Appendix A. �- The 2004 pilot test data laboratory data are included in Table 4, Appendix A. 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 chemicals of concern (COC) at the site. The analysis of gasoline components is usually limited to benzene, toluene, ethyl benzene and xylene (BTEX), total petroleum hydrocarbons as gasoline (TPH-G) fuel compounds 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), and (5) a high percent of gasoline is composed of these compounds. These COC have been identified at the site and are included in the monitoring and analytical protocols. GTI has compiled fact sheets available on government and commercial internet sites for the COC and has included the sheets in Appendix D. The fact sheets include physical and chemical properties of the COC in a pure form, not necessarily that which occurs upon release to the environment. Although the solubility of the COC in water varies from chemical to chemical, each of the COC has the potential to migrate off site with groundwater movement.