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r <br /> Report:Groundwater-quality Monitoring—January 26,2004: 7500 West Eleventh Street, Tracy, CA. Page 9 <br /> Anal3je Method of Analysis <br /> tertiary-Butyl alcohol EPA Method 8260B~ <br /> Methyl-tertiary butyl ether EPA Method 8260B <br /> Di-isopropyl ether EPA Method 8260B <br /> y Ethyl tertiary-butyl ether EPA Method 8260B <br /> Tertiary-amyl methyl ether EPA Method 8260B <br /> STL is certified to perform the specified analyses by the California Department of Health <br /> Services (DHS). <br /> The results of the analyses of samples of groundwater are presented in Table 2, which <br /> " also includes the results of analyses of groundwater samples recovered from the previous <br /> sampling rounds. <br /> Figures 2 through 5 were developed from the results of the groundwater-quality sampling <br /> program to provide an interpretation of the lateral and vertical extent to which the <br /> subsurface was affected by components of fuel hydrocarbons on January 26, 2004. <br /> 2.4.1 Groundwater Quality in the Near-Surface Unconfined Aquifer <br /> The results of analyses of samples of groundwater recovered on January 26, 2004 from <br /> wells screened in the near surface unconfined aquifer beneath the 7500 West Eleventh <br /> Street site are evaluated below. <br /> 2.4.1.1 Analytes of Concern in Groundwater Along Principal Plume Axis <br /> The groundwater sample recovered from Monitoring Well MW-3, which is close to the <br /> location where the fuel hydrocarbons were released on the 7500 West Eleventh Street <br /> site, but where the groundwater quality has benefited from the remediation work <br /> performed when the underground storage tanks and piping were removed from the site, <br /> contained 250 gg/L of TPHg and no detectable concentrations of TPHd. Both of those <br /> results show a reduction from concentrations detected in the October 2003 monitoring <br /> round. Of the BTEX compounds, benzene was present at 13 gg/L (compared to 65 gg/L <br /> in October 2003), toluene was not detected (compared to 1.1 gg/L detected in October <br /> 2003), ethyl benzene was detected at 3.2 gg/L (the same concentration found in October <br /> 2003), and total xylene isomers were detected at 9.1 gg/L (compared to 12 µg/L in <br /> October 2003). The only fuel oxygenate present in the sample recovered from Monitoring <br /> Well MW-3 was MTBE, at a concentration of 130 gg/L, a significant reduction from the <br /> - 280 gg/L detected in that well in October 2003. <br /> sic <br />