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09 March 1998 ��`�� i AGE-NC Project No 95-0173 ' Page 4 of 5 i TBA was detected for the first time In water samples collected from wells MW-3, MW-4, MW-6 and VW-I V DIPE was detected for the first time In water samples collected from well MW-3 • Laboratory data continues to indicate that the greatest concentrations of TPH-g impacted ground water is located near VW-1 The approximate extent of dissolved TPH-g is depicted ' in Figure 4 Laboratory data suggest that the impacted ground water beneath the site appears to have taken a relatively elongated oval shape The dissolved plume is undefined to the east, southeast and northwest • Concentrations of benzene detected in samples collected from wells MW-1 through MW-4, MW-6, MW-9, VW-1, AW-1B and AW-2B were above the State of California Maximum ' Contaminant Level (MCL) for drinking water of 1 0 ppb The greatest concentrations of dissolved benzene is located near MW-4 The approximate extent of dissolved benzene Is depicted in Figure 5 • Concentrations of toluene were above the MCL of 150 ppb In wells MW-1 through MW-4 VW-1,AW-IB and AW-2B, concentrations ofethylbenzene were above its MCL of 700 ppb �. in wells MW-2, MW-3, VW-1 and AW-IB, concentrations of xylenes were above the MCL of 1,750 ppb in wells MW-2, MW-3, VW-1 and AW-1B • Utilizing EPA methods 8020 and 8260, concentrations of MTBE were detected above the laboratory reporting limits in samples from wells MW-1 through MW-4, VW-1 and AW-2B • Six quarterly ground water events have been performed in wells MWI through MW4, however, an overall trend of increasing/decreasing concentrations cannot be established from the analytical data The plots do indicate a trend of increasing ground water elevation in wells MWI through MW4 since April 1997 (Appendix C) ' The diesel-range chromatograms for the soil and ground water samples are not consistent with typical diesel fuel chromatograms,the detected hydrocarbons may be of gasoline origin ,. ' During ground water monitoring activities, the lowest concentrations of dissolved oxygen were measured from MW2,MW3,MW-4,MW-6,AW-1B and AW-2B (dissolved petroleum hydrocarbon core-area), which could be suggestive of aerobic biodegradation of hydrocarbons occurring in the core-area (Table 2) • Significant concentrations of dissolved petroleum hydrocarbons were detected from AW 1 ' with a screened interval of 50 to 60 feet bsg, and from AW2 with a screened interval of 60 to 70 feet bsg Advateced GcoEn%ironmental,Inc