SITE INFORMATION AND CORRESPONDENCE

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GEOMATRIX cleaned up with silica gel to remove any soluble biogenic material (e.g., naturally occurring polar compounds or metabolites resulting from intrinsic bioremediation of petroleum). TPHd was not detected in these samples, indicating that July 1998 results were positively biased due to the presence of soluble biogenic material. Geomatrix also analyzed groundwater samples for PAHs using detection limits 100 times lower than those applied to samples collected by Radian; these analyses were done to confirm that PAHs are not present in groundwater above WQOs (e.g.,MCLs). PAHs were not detected in any of the.groundwater samples. These combined results indicate that the residual petroleum is not providing a source of dissolved petroleum constituents to groundwater. Groundwater analytical results are summarized on Figure 4 and in Table 5. 4.4 SEPARATE-PHASE PETROLEUM Monitoring well MW-1 contained approximately 6 inches of separate-phase petroleum on the water surface. Separate-phase petroleum is limited to the vicinity of well MVV-1; samples collected from borings advanced within approximately 44 feet of SB-8/MW-1 exhibited no separate-phase petroleum or significant amounts of petroleum hydrocarbon constituents. The estimated lateral extent of petroleum-affected soil in this area is shown on Figure 5. Geomatrix collected a sample of separate-phase petroleum from well MW-1 on October 23, 1998, and submitted the sample to Chevron Research and Technology Company(CRTC) for a chemical fingerprint evaluation. CRTC reported that the sample was composed of"evaporated crude oil...typical of may California San Joaquin Valley Crudes." The report also states that the sample contained no evidence of diesel fuel or lube oil, and that if these products were present they would be masked by the presence of the crude oil. A copy of the analytical report, along with the chromatogram, is presented in Appendix E. 4.5 SUMMARY OF RESULTS The sail underlying the site is composed primarily of silts and clays,with gravels present at 25 feet bgs; groundwater occurs between 30 and 32 feet bgs (Figure 6). As shown on Figures 5 and 6, residual petroleum(i.e.,highly weathered crude oil) is found beneath the site primarily at depths of approximately 15 to 50 feet bgs in the immediate vicinity of a section of the former pipeline adjacent to borings SB-8 and MW-1. Benzene and MTBE were not detected in any of the soil samples. Low concentrations of ethylbenzene,toluene, and xylenes, along with various PAHs, are collocated with the residual petroleum at depths of 15 feet bgs and greater. Approximately 6 inches of separate-phase petroleum was estimated to be in well MW-1; petroleum hydrocarbon constituents were not detected in groundwater samples collected from 11s131degtdata Doc_SaPe15�OQs1591 I1Sl HRA RpIAM 9