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Report:Groundwater-quality Monitoring—October 20-21,2005, 7500 West Eleventh Street, Tracy, CA. Page 13 Analyte Method of Analysis Total Petroleum Hydrocarbons EPA Method 8015M (quantified as Diesel) with silica gel cleanup Total Petroleum Hydrocarbons EPA Method 8260B (quantified as Gasoline) Benzene EPA Method 8260B Toluene EPA Method 8260B Ethyl benzene EPA Method 826013 Total Xylene Isomers EPA Method 8260B tertiary-Butyl alcohol EPA Method 8260B Methyl-tertiary butyl ether EPA Method 8260B f Di-isopropyl ether EPA Method 8260B Ethyl tertiary-butyl ether EPA Method 8260B 4-- Tertiary-amyl methyl ether EPA Method 8260B STL is certified to perform the specified analyses by the California Department of Health Services (DHS). The results of the analyses of samples of groundwater are presented in Table 2, which also includes the results of analyses of groundwater samples recovered from all previous sampling rounds. Copies of the laboratory Certificates of Analysis generated from the October 2005 monitoring round are included in Appendix B of this report. = 2.5 Groundwater Quality in the Near-Surface Unconfined Aquifer The results of analyses of samples of groundwater recovered in October 2005 are evaluated below. 2.5.1 Anal es of Concern in Groundwater Along Principal Plume Axis � i Monitoring Wells MW-3, MW-13, MW-7, MWFP-4, MW-16 and MW-18, are, as is shown on Figure 3, arrayed along the approximate long axis of the primary plume of affected groundwater. As can be seen by inspection of Table 2, compared to the concentrations of analytes of concern that were found in the groundwater samples recovered from those wells in June 2005, the concentrations in the samples recovered in October 2005 were generally lower than those measured in samples recovered from the sic t;