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: v <br /> W(:0 <br /> A S S O C I A T E S I N C <br /> Soil in bonngs SB7, SB 8, SB9, SB 10, SB 11, and SB 12 consisted of poor to well graded sand and <br /> silty sand from the surface to between 20 and 25 feet bgs Some sandy silt was encountered in <br /> borings SB7, SB 11, and SB 12 Soil in boring SB9 from 24 feet bgs to 26 feet bgs consisted of <br /> silty clays <br /> tThe lithology encountered in the boreholes of MW 1, MW2, and MW3 was similar and generally <br /> consisted of interbedded silty sands, clayey sands, sand, sandy clay, and lean clay Lean clay was <br /> encountered in the bottom of each borehole at depths ranging from approximately 38 to 41 feet <br /> bgs <br /> Soil bonng/well construction logs from previous reports are contained in Appendix B <br /> 4 1 2 Petroleum Hydrocarbons in Soil <br /> ' A review of historical soil analytical data and field measurements indicate TPHg and BTEX <br /> constituents were generally present in soil samples collected from the former tank excavation pit <br /> and in soil samples collected from borings located hydrologically upgradient to the southeast and <br /> southwest of the former tank excavation pit Petroleum hydrocarbons were generally present at <br /> the highest concentrations in soil bonngs advanced on the southern portion of the site, near the <br /> former UST locations where TPHg and benzene were detected at concentrations up to 330 and <br /> 0 024 mg/kg, respectively, in soil samples collected at depths ranging from 25 to 30 5 feet bgs <br /> Laboratory analytical data indicate that petroleum hydrocarbons were not detected at or above <br /> ' laboratory detection limits in soil samples collected from off-site soil borings The lateral extent <br /> of shallow TPHg and BTEX impacted soils appears to be limited to the vicinity of the former <br /> UST locations Figure 4 shows a TPHg isocontour map of the estimated lateral extent of TPHg <br /> ' concentrations in soil from 25 to 30 5 feet bgs <br /> 4 13 Mass Balance Calculations - Soil <br /> ' ATCusin erformed mass balance calculations soil data from 1997 to 1999 Residual soil <br /> p g <br /> ' contamination is present from approximately 25 to 30 feet bgs The laboratory analytical data <br /> indicate the area of impacted soil from 20 to 25 feet bgs consists of very low concentrations <br /> limited to the SBI and SB2 soil boring locations Mass balance calculations for residual <br /> ' petroleum hydrocarbons in impacted soil were performed using soil analytical data from soil <br /> borings at depths of approximately 25 feet bgs to 31 feet bgs <br /> ' ATC calculated that there is approximately 21,375 cubic feet of hydrocarbon impacted soil <br /> beneath the site The calculated mass of total petroleum hydrocarbons remaining in soil is <br /> approximately 64 8 kilograms or 143 pounds The calculated mass of benzene remaining in soil is <br /> ' approximately 0 07 kilograms or 0 16 pounds Mass balance calculations and figures showing the <br /> estimated lateral extent of impacted soil are contained in Appendix C <br /> w 1149SIVepodkiosum doo 4 <br />