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Report: Groundwater-quality Monitoring—October 27, 2003: 7500 West Eleventh Street, Tracy, CA. Page 10 ..• Note: In the case of the analyses for Diesel, the sub-aliquot of the sample from each .., monitoring well was hItered before injection into the gas chromatograph. 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 i.. also includes the results of analyses of groundwater samples recovered from the previous sampling rounds. ,. Figures 2 through 5 were developed from the results of the groundwater-quality sampling program to provide an interpretation of the lateral and vertical extent to which the subsurface was affected by components of fuel hydrocarbons on October 27, 2003. 2.4.1 Groundwater Qualfty in the Near-Surface Unconfined Aquifer The results of analyses of samples of groundwater recovered on October 27, 2003 from wells screened in the near surface unconfined aquifer beneath the 7500 West Eleventh Street site arc evaluated below. 2.4.I.1 Analytes of Concern in Groundwater Along Principal Plume Axis ...`�' The groundwater sample recovered from Monitoring Well MW-3, which is close to the location where the fuel hydrocarbons were released on the 7500 West Eleventh Street site, but where the groundwater quality has benefited from the remediation work performed when the underground storage tanks and piping were removed from the site, contained 360 gg/L of TPH quantified as gasoline and 65 gg/L of diesel. Of the BTEX compounds, benzene was present 65 pg/L, toluene at 1.1 gg/L ethyl benzene at 3.2 gg/L '- and total xylene isomers at 12 gg/L. The fuel oxygenate MTBE was present in the sample recovered from that well at a concentration of 280 gg/L and TBA was detected at a concentration of 66 gg/L, but no other fuel oxygenates were detected. s. In the case of Monitoring Well MW-4, the sample recovered contained gasoline at a concentration of 130 gg/L but no diesel was detected. The only other analyte of concern detected in that sample was MTBE at 180 gg/L. The concentrations of analytes of concern in samples recovered from Monitoring Wells MW-3 and MW-4, with the exception of a less than significant increase in the concentration of toluene in the sample recovered from Monitoring Well MW-3, are significantly lower than the concentrations detected in the samples recovered in those wells on July 30, 2003. These results are consistent with the previously-recorded pattern in which increases and decreases have occurred around a steadily declining trend that has been ongoing since groundwater affected by floating product was pumped from the large excavations opened on the 7500 West Eleventh Street site at the time the underground storage tanks were removed. Within that general pattern, the proximate cause of the sic