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08 September 2009 AGE -NC Project No. 03-1055 Page l I of 19 Adams Street (B 13 through B 14) and from within the sidewalk of the westside of Adams Street (B 10 and B11) for the collection of soil samples; a total of 24 soil samples were analyzed from the borings. TPH-g were reported in all borings, except B10 (located immediately east of the former Chevron's 5,000 -gallon UST area), at concentrations ranging between 2.0 mg/kg (BI t-15) and 160 mg/kg (BI1-10); TPH-g were only reported within the saturated zone (between 10 feet and 15 feet bsg). The highest concentrations of TPH-g reported during this investigation were from boring B 11, located immediately down -gradient of the former Chevron UST areas, and equi-gradient to the former Tracy Diner UST areas. In April and May 2008, 14 soil samples were analyzed from pilot soil borings MW 11, MW 13, and MW 14. Constituents were only reported in the samples collected from MW 11; TPH-g and TPR -d were reported at maximum concentrations of 71 mg/kg (MW 11-22) and 400 mg/kg (MW 1140), respectively. Pilot boring MW 11 was located immediately down -gradient of the former Chevron UST areas. Historical analytical results of soil samples are summarized in Tables 1. �%W 3.1. DISTRIBUTION OF PETROLEUM HYDROCARBON -IMPACTED SOIL Laboratory analyses of soil samples indicate the source of petroleum hydrocarbon -impacts to soil on-site are the former 500 -gallon UST and northernmost dispenser. Once released to the subsurface, contaminants migrated through fine grained clay and silt mixes, to a vertical depth of approximately 15 feet bsg, at which point contaminants encountered a more porous sandy unit and began to migrate laterally. The direction of lateral migration was predominantly toward the northeast, the preferred ground water flow direction (Appendix G). The vertical migration of soil contamination appeared to be slowed by the silty and clayey layers encountered below the sand unit. Geologic cross sections are depicted on Figures 4, 5 and 6. Boring MW I 1 exhibited the only `deep' (beyond 15 feet bsg) soil contamination throughout all subsurface investigations; contamination encountered in this boring is likely from the former Chevron site. Additionally, the impacted area of Adams Street in the vicinity of borings B 13, B 14 and BIS is likely the result of the former Chevron release as evidenced by the following: 1) the borings are located down -gradient of the former Chevron UST areas and significantly impacted boring SB2; 2) the borings are located in an upgradient location to the Tracy Diner former UST areas; and 3) the non -detection of constituents in boring MW14-15, located between the former Tracy Diner UST areas and borings B 13 through B 15. Former Tracy Diner and former Chevron soil sample locations and the estimated extent of TPH-g impacted soil beneath the site and the former Chevron site are depicted in cross sectional view in Advanced GeoEnviromnental, Inc.