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1 Page 8 January 30, 1992 Job No 400511-SA Figure 5, Groundwater Gradient Map, is a water table contour map for the site based on the October 15, 1991 measurements The groundwater gradient is very slight towards the southwest at a 1 magnitude of approximately 0 0004 foot per foot 53 Occurrence and Extent of Hydrocarbons m the Soil Soil samples from each borehole were retained and submitted to the State of Callforn>ia-licensed laboratory, Trace Analysis Laboratory, Inc (Hayward), for analysis Soil samples were collected for possible laboratory analysis at 5-foot intervals from the boreholes A total. of 160 soil samples were , collected On-site field screening, utilizing an organic vapor meter (OVM), helped to determine which samples were sent to the'laboratory for analysis Approximately every other sample was submitted for , laboratory analysis as per the work plan The samples were analyzed for TPHg by the DHS method and BTXE by modified EPA Method 8020 A total of 86 soil samples were analyzed The laboratory reports are summarized in Table C and are presented in Appendix E Methods followed for on-site screening are contained Appendix A The OVM readings are presented on the well logs in Appendix B Hydrocarbon concentrations in sods were generally enerally greatest in the permeable sands that occur between 40 to 65 feet below grade Vapor extraction well VW-35 had the highest hydrocarbon concentration in sample 35-10 recovered from a depth of 51 to 515 feet This sample had the highest TPHg concentration at 1,000 mg/kg Soil samples recovered from the exploratory borings contained variable concentrations of toluene which ranged, for example, from less than 0 005 mg/kg to 170 mg/kg ' Benzene occurred at 0 058 mg/kg in sample 30-16 recovered from a depth of 80 5 to 81 feet from MW- 30 The soil analytical results are summarized in Table C detected at low levels in almost Toluene was every soil sample, even where TPHg, benzene, ethylbenzene, and xylenes were all non detect The toluene detected at low levels is likely to be a laboratory contaminant A letter from the analytical laboratory stating this probability is included in Appendix E -Hydrocarbon odor was detected in many soil samples recovered during exploratory drilling though only a few of these samples had detectable concentrations of TPHg reported by the laboratory ' This generally occurs with degraded gasoline in soil The odors detected may be from compounds such as methane which is not generally found in gasoline Concentrations of TPHg expressed as parts per million (ppm) in the soil are contoured on Cross Sections A-A' and B-B' in Figures 6 and 7, respectively These figures graphically illustrate the distribution of petroleum hydrocarbons currently within the soil at the site On Figure 6, TPHg concentrations are highest in the area of VW-35 at a depth of 50 - 60 feet, and extend laterally to 4005111_Rev 1 Du Pant Environmental Remediation Services_ Printed on Recycled Paper '