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1 ' 12 December 2006 AGE-NC Project No 01-0827 Page 6 of 14 ' 4.0. PETROLEUM HYDROCARBON DISTRIBUTION IN SOIL Between the first UST removal of April 1987 and February 2005, eighteen soil borings(B 1 through ' B 17 and OZ 1) and seven soil excavation samples were analyzed as part of an ongoing subsurface petroleum hydrocarbon investigation Analytical results of soil samples are summarized in Table 1 ' • To date, a total of 43 soil samples at depths ranging from 2 feet to 46 5 feet bsg have been submitted for laboratory analysis of petroleum hydrocarbons, TPH-g, TPH-d and BTEX compounds were detected in 20 of the soil samples analyzed,analysis for fuel additives were ' not generally included when the soil samples were analyzed (Table 1) The greatest concentrations of petroleum hydrocarbon-impacted soil were encountered at soil borings BI 0 and B 16 which were completed as soil vapor extraction wells, with TPH-g concentrations as high as 5,100 mg/kg(B 16 at 15 feet),and BTEX compounds at concentrations as high as 11 mg/kg benzene, 40 mg/kg toluene, 18 mg/kg ethylbenzene and 110 mg/kg xylenes (B 1 at 25 and 35 fest) The boring B10 trace was established through the former UST excavation ' area • Soil boring B9 (VW-1) had low detections of TPH-g and BTEX compounds, however, soil ' • sample collected from bonng B16 (VW-4), Iocated further east from the UST excavation than B9, had more significant detections of hydrocarbons TPH-g and BTEX compounds were also detected in soil samples collected from boring B 13 and B 15 ' • The most significant concentrations were detected above a depth of 25 feet bsg, indicating that ground water was likely at 25 feet to 30 feet bsg during the release period and/or the ' sand to silt contact at 30 feet bsg mitigated the vertical migration of the hydrocarbon release • From the former UST area, the lateral extent of TPH-g-impacted soil appears to extend approximately 20 feet towards the west, less than 10 feet towards the east which is the ' down-gradient ground water flow direction, also less than 10 feet towards the south and up to a distance of 30 feet towards the north,under the building at the site The lateral extent of petroleum-impacted soil appears to be moderately defined in all directions by boring/11, ' 3F�5 Oand boring B 15 • The vertical extent of TPH-g-impacted soil is defined towards the west (B7), east (B 11), south(B5)and north(B 13 and B 15),where TPH-g-impacted soil appears to extend to at least 40 feet bsg (Figures 3 and 4 depict selected soil sample locations and the estimated extent of TPH-g concentrations adsorbed in soil in cross sectional view) • The majority of the UST removal samples collected in 1993 were non-detect for petroleum hydrocarbons, however, the initial soil sample collected in April 1987 indicating that the source of the release was the decommissioned/removed UST#1 at the northern edge of the common UST excavation, near vapor well VW2d Advanced GeoEnvironrnentai,Inc