ARCHIVED REPORTS_REPORT OF ADDITIONAL SOIL AND GROUNDWATER INVESTIGATION

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1 GEOMATP;X . µg/1 in the aliquot that was filtered prior to extraction and analysis. These collective results indicate ' that much of the original TPHd quantification(620µg/1)is due to polar biogenic byproducts resulting from intrinsic bioremediation and non-dissolved constituents adhered to particulates in these samples. ' Grab groundwater analytical results are summarized in Table 2 and are presented on Figure 2. The analytical laboratory report for the soil and grab groundwater samples is presented in Appendix C. 6.0 CONCLUSIONS ' Based on the results of this and previous investigations, Geomatrix has developed the following conclusions about site conditions. ' One area of petroleum hydrocarbon affected soil has been identified at the site. Based on review of chromatograms and the results of a forensic evaluation(Geomatrix,2000),the petroleum hydrocarbons are likely degraded crude oil. The affected soil has been encountered at depths ranging between 5.5 and 14 feet bgs. The lateral extent of affected soil has been delineated. • Groundwater quality downgradient of the affected soil is characterized by grab groundwater samples from borings GMX-23 and GMX-24. TPHg,BTEX, and PAHs were not detected in these samples. Constituents quantified as TPHd(without a silica gel preparation procedure)were not detected in the sample from GMX-23 and were detected at 86 µg/1 in the sample from GMX-24;this concentration is below the diesel taste and odor criteria that is used as a water quality objective(WQO)by the Regional Water Quality Control Board—Central Valley Region(RWQCB). It should be noted that TPHd detections following a silica gel preparation procedure were due to laboratory contamination. ' Groundwater within the area of affected soil is characterized by grab groundwater samples from borings GMX-12 and GMX-28. TPHg,benzene,ethylbenzene and MTBE ' were not detected in these samples. Toluene and xylenes were detected at concentrations well below their respective WQOs(e.g.,the drinking water maximum contaminant levels are 150 and 1750µg/1,respectively). Very low concentrations(less than 1 µg/1)of three PAHs(fluorene,phenanthrene and acenaphthene)were detected. Constituents quantified as TPHd(without a silica gel preparation procedure)were detected at a concentration of 620µg/1,which is above the diesel taste and odor criteria that is used as a WQO by RWQCB (100µg/1). Results from sample aliquots that were filtered prior to extraction and analysis(3 80µg/1)and treated with a silica gel preparation procedure(100µg/1) indicate that much of the original"TPHd"quantification is due to non-dissolved constituents adhered to particulates in the sample and soluble polar biogenic byproducts resulting from intrinsic bioremediation of residual petroleum hydrocarbons in soil. ' A human health screening evaluation was previously performed by Geomatrix • (Geomatrix,2000)based on the methodology presented in the PEA. In the evaluation, the maximum detected concentration for each constituent detected in soil and \\SF3\DEPTDATA\DOC_SAFE\6000S\6115.007\DEC2000REPORT\BURNS SO[LGW RPTN0V00_1.D0C 6