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or SB9 The estimated areal extent of gasoline hydrocarbons in soil at depths of 4 5 and 8 0 feet <br /> below grade are shown on Figures 4 and 5, respectively. <br /> Based upon analytical results of soil samples collected to date, it appears that soil contamination <br /> ' exists within a relatively thin zone beginning at approximately 4 to 5 feet below grade to a depth <br /> of approximately 10 to 11 feet below grade over an area of approximately 4,330 square feet <br /> ' Based upon this configuration, the volume of soil requiring excavation is estimated to be 1,604 <br /> to 1,765 cubic yards Of this total, the volume of impacted soil requiring treatment or disposal <br /> Iis approximately 802 to 1,123 cubic yards The volume of clean overburden requiring removal <br /> is estimated to be 642 to 802 cubic yards Calculations for estimated volumes are included in <br /> Appendix III <br /> ' 5.2 Groundwater <br /> Laboratory analyses of groundwater samples collected from monitoring wells T1, T2, and T3 <br /> have historically been free of contaminants (Table 2) However, the recent analytical results of <br /> groundwater samples collected from soil borings on May 13, 1994 indicate that groundwater in <br /> the vicinity of the former gasoline storage tank and fuel dispenser has been impacted by <br /> petroleum hydrocarbons <br /> ' Dissolved hydrocarbons were detected in SB3 (230,000 ppb TPHg), SB5 (92,000 ppb TPHg), <br /> SB7 (8,200 ppb TPHg, and SB9 (200 ppb TPHg) These results are thought to represent worst <br /> ' case concentrations based on the collection technique which is subject to contamination from soil <br /> disturbed during drilling No dissolved hydrocarbons were detected above the method detection <br /> limit in SB2 The groundwater sample from SB7 (collected at approximately 20 feet below <br /> grade) contained TPHg at significantly lower levels than those from crossgradient boring SB3 <br /> and downgradient boring SB5 (collected at approximately 10 feet below grade), suggesting that <br /> groundwater contamination is reduced as the depth increases The estimated lateral extent of <br /> groundwater contamination is shown on Figure 6 The figure indicates that the full lateral extent <br /> of groundwater contamination at the site has not yet been defined <br /> 1500871R 053194 FNL 6 <br />