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i, 3.0 SITE BACKGROUND ' 3�1 Tank Removal and Excavation "1'k-A In-May"1988,men-underground storage tanks (USTs) were removed and properly disposed of During the tank removals, soil staining was observed and the nine soil samples collected from the tank excavation contained elevated concentrations of petroleum hydrocarbons Laboratory results are ' summarized in Tables I and 2 The locations of the former tanks are shown on Figure 2 Due to the elevated concentrations of petroleum hydrocarbons in the soils, further investigation was required ' 312 Assessment of Soil Contamination In December 1988, Dames and Moore performed an initial site investigation to determine the extent of hydrocarbon contamination The investigation included the advancement of four soil bonngs, MW-1 through MW4, to a depth of approximately 30 feet below ground surface (bgs) Soil samples were collected at five foot intervals and selected samples were analyzed for total petroleum hydrocarbons as ' gasoline (TPHg), benzene, toluene, ethylbenzene, and xylenes (BTEX) Soil samples collected from boring MW-1 contained elevated concentrations of TPHg and BTEX Based on these results, additional soil investigation activities were necessary In September 1989, Dames and Moore performed a Phase II Site Investigation to further investigate g g the extent of hydrocarbon contamination in the soil and groundwater beneath the site The investigation included the advancement of five soil bonngs, SB-1 through SB-5, to a depth of approximately 25 feet bgs and the advancement of two soil bonngs, MW-5 and MW-6, to a depth of approximately 45 feet bgs Soil samples were collected at five foot intervals and selected samples were ' analyzed for TPHg, BTEX, total petroleum hydrocarbons as diesel (TPHd), chlorinated solvents (HVOCs), tetraethyl lead, and ethyl dibromnde(EDB) ' The results of these investigations were used to estimate the extent of soil contamination as shown on Figure 4 Using this estimated extent and analytical results, the original mass of contamination in soil was calculated to be 119 3 pounds of benzene and 7,793 pounds of TPHg Soil boring locations are shown on Figure 3 and analytical results are summanzed in Table 3 Soil boring logs are included in Appendix A Calculation of the mass of contamination in soil are included in Appendix B ' L33 Assessment of Groundwater Contamination In December 1988, Dames and Moore completed four soil borings, MW-1 through MW4, as groundwater monitoring wells at the locations shown on Figure 3 The wells were constructed with 4- inch diameter PVC casing and completed as shown on the well logs contained in Appendix A The wells were installed to depths ranging from 28 5 feet to 34 feet bgs with 10-foot screen intervals Depth to water was measured, the wells were developed, and samples were collected The samples w\94331klosure dw 2 r SWrH