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M1 ! 1 29 December 1999 AGE-NC Project No 97-0312 r " ' Page 8 of 9 L - f / I 45 EXTENT OF IMPACTED SOIL ; ' B6' Petroleum hydrocarbons were not detected in soil samples collected from borings B3, B4, B5, , B 12,B 16,B23,B25, B28, B29,UST-2 and UST-3, limiting the lateral extent of Impacted soil Only 3 ' low concentrations of BTEX were detected in borings B8,B 13,B22,B27 and UST4 Borings UST-1 through UST-5,B 14 through B 1/9 and B21 through B29 were`advanced to depths below the vertical ' extent of impacted soil, defining the vertical extent of Impacted soil at these location's The greatest concentrations of hydrocarbons were detected beneath the former UST locations Higher concentrations were also detected in the shallow piping samples and In borings UST-1 and UST-5 ' The approximate lateral and vertical extent of impacted soil are Illustrated in Figures 5 through 11 Iw ' 46 MASS CALCULATIONS _ Approximately 416 gallons of gasolineand2495 gallons of diesel'are estimated to have Impacted ' a total of 3167 and 7495 cubic yards of soil, respectively Nearly all the gasoline-impacted soil is also Impacted with diesel Approximately 73 percent of the gasoline and 90 percent of the diesel hydrocarbons contained within approximately 1230 cubic yards of soil are located within 25 feet of surface grade z Data collected as early as 1990 was Included in the calculations of the mass of hydrocarbons at the ' site Some reduction of hydrocarbon concentrations by natural attenuation may have occurred in these areas, which would reduce the total mass of hydrocarbons remaining beneath the former UST and dispenser area AGE notes that the hydrocarbon masses calculated are not intended to be precise, but are only, estimates,'based on the assumptions s listed above and In Appendix E The mass calculations and,forniulas are presented in Appendix E i 5.0. r DISCUSSION AND CONCLUSIONS Based upon data collectedfrom the site, AGE'concludes the following 1 1 , ' iGround water elevation decreased nearly 7 feet at the site between the June and September 1999 monitonng events Ground water was approximately 6 to 7 feet above the screened interval in UST-2,UST-3 and-UST-4,4 feet above the screened Interval In UST-6 and within ' the screened Interval of UST-5 1 • } Petroleum'hydrocarbons were detected in the water sample collected from UST-5 t Hydrocarbons were not detected In the water samples collected from UST-2, UST-3, UST-4 or UST-6 r , + , 1 r Advanced GeoEnvironmental,Inc 1 , }