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_ r 16 August 2001 AGE-NC Project No 97-0312 - z Page 6 of 20 ' � 3 l ' framework and to assess potential migration pathways In general, the soil prof le beneath the site is fairly homogeneous vertically, consisting primarily of silt, clayey silt, sandy silt and silty clay However,interbedded coarse-grained soil consisting of silty sand and fine-grained sand with silt was observed in soil samples recovered from several of the soil borings at varying depths Figure-s 5 ' through 11 illustrate subsurface geologic profiles at the site Boring logs are included in Appendix B ' 5.0. ASSESSMENT OF HYDROCARBON-IMPACTED SOIL ' Between May 1990 and September 1999, soil sampling was performed at forty-two soil borings (B1 through B29, P-1 through P-13), six shallow tank excavation samples ( T-1 through T-6) and ,'six ground water monitoring well pilot borings (UST-1 through UST-6) as part of a subsurface - ' petroleum hydrocarbon investigation r Petroleum hydrocarbons were not detected in soil samples collected from borings B3, B4, B5, B6, ' B12,B 16,B23,B25,B28,B29,UST-2 and UST-3,delineating the maximum potential lateral extent of impacted soil Low concentrations of 13TEX were detected iri borings B8, B13, B22, B27 and UST4 Borings UST-1 through UST-5, B 14 through B 19 and B21 through B29 were advanced to ' depths below the vertical extent of impacted soil, defining the vertical extent of impacted soil at these locations 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 plume of impacted soil at the site has an estimated northeast-southwest diameter of approximately 180 feet, an northwest-southeast diameter of approximately 70 feet and appears to extend downward more than 80 feet bsg The calculated volume ofhydrocarbon-impacted ' soil is approximately 10,000 cubic yards (Appendix C) The approximate lateral and vertical extent of impacted,soil is illustrated in Figures 12 through 18 ` I 6.0 ASSESSMENT OF HYDROCARBON-IMPACTED GROUND WATER Between 25 July 1990 and 28 March 2001, twenty-six ground water monitoring events were conducted on Cherokee Truck Stop wells UST-1, UST-2, UST-3, UST-4, UST`5, and UST-6 to ' monitor shallow and deeper dissolved fuel component concentrations and to characterize ground water flow direction and gradient on the site In addition, grab ground water samples were collected from soil borings B-14,B-15 and B-17 Each grab groundwater sample was collected from a depth n I of 65 feet bsg Laboratory analysis of water samples from the wells and soil borings indicated that ground water at the site locally has been impacted by TPH-g,'TPH=d,BTEX compounds and MTBE (Tables 6 and 7) • The highest dissolved petroleum h drocarrbon concentrations detected in ground water monitoring well samples were detected in the samples collected from co-located monitoring wells UST-1 and Advanced GeoEnvironmental,Inc 1 I