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Report: Groundwater-quality Monitoring—April 15,2003: 7500 West Eleventh Street, Tracy, CA. Page 10 STL is certified to perform the specified analyses by the California Department of Health r- 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 the previous sampling rounds. Figures 2 through 5 were developed from the results of the groundwater-quality sampling conducted to provide an interpretation of the lateral and vertical extent to which the subsurface beneath the site was affected by components of fuel hydrocarbons on April 15, 2003. 2.4.1 Groundwater Ouality in the Near-Surface Unconfined Aquifer The results of analyses of samples of groundwater recovered on April 15, 2003 show that only the samples recovered from Monitoring Wells 2, 3, 4, 5, 6, 7, 10, 11 and 12 were affected by components of fuel hydrocarbons. No analytes of concern were detected in samples recovered from Monitoring Wells 1, 3A, 3B, 8, 9 and 12A. 2.4.1.1 Analytes of Concern in Groundwater Along Principal Plume Axis The groundwater sample recovered from Monitoring Well MW-3, which is close to the location on the 7500 West Eleventh Street site where the fuel hydrocarbons were released, 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 960 µg/L of TPH quantified as gasoline, but no detectable concentration of diesel. Of the BTEX compounds, only Benzene, at 140 µg/L, and ethyl benzene, at 12 µg/L, were present in that sample, together with the fuel oxygenates TBA and MTBE, at concentrations 200 p,g/L and 950 µg/L, respectively. In the case of Monitoring Well MW-4, the sample recovered contained no detectable concentrations of any analyte of ._ concern except MTBE at 1,200 µg/L. Those concentrations of analytes of concern in samples recovered from Monitoring Wells MW-3 and MW-4 are consistent with the previously-recorded pattern in which increases `=`1 and decreases in concentrations 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 from that location. ! When groundwater in Well MW-7 was first analyzed in May 2000, it was affected by ' l{ relatively moderate concentrations of diesel- and gasoline-range petroleum hydrocarbons (at concentrations of 1,300 gg/L and 1,400 µg/L, respectively), and MTBE (at 22 µg/L). However, over the next two years, the concentrations of both diesel and gasoline in . samples recovered from that well exhibited a significant upward trend. As the y concentration of those analytes increased, MTBE was no longer detected. That is almost sic