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4 <br />Analytical data from soil and groundwater samples indicate the subsurface beneath the Site has <br />0. been impacted by the presence of petroleum hydrocarbons. TPH-g; TPH-d,'fPH-mo, BTEX, <br />TBA, and EDB have been detected in soil samples collected at the Site. However, the primary <br />compounds and chemicals of concern in soil are TPH-g and BTEX. <br />Outside the former gasoline UST excavation area, the maximum concentration of TPH-g in soil <br />was 4,900 mg/kg detected north of the former gasoline UST excavation (H3 at 25 feet BGS). i <br />L Soil samples collected from borings drilled in the former UST excavation also contained TPH-g <br />\ r at concentrations up to 4,800 mg//kg. The residual TPH-g impact in soil has been identified at <br />o , <br />a� 40 depths of 15 feet BGS or more, with some elevated concentrations generally detected where <br />impacted groundwater is present (approximately 35 feet BGS or more As illustrated on <br />Figure 5, the lateral extent of TPH-g in soil to the nc`rthland squth of the former gasoline UST <br />excavation is undefined. Wt/ ' c \ <br />V v'' <br />I I / A101, <br />to I, �ID �� <br />TPH-g, TPH-d, BTEX, MTBE, TBA, D1PE, T$E,.4&E, and 1,2 -DCA have been detected <br />�. in groundwater samples. However, the primary compounds in groundwater are TPH-g, BTEX, <br />DIPE, and 1,2 -DCA. Grab groundwater samples collected in the vty of the former UST <br />excavation contained TPH-g at concentrations up to 82,000 gg/L. Groundwater monitoring <br />r well samples collected during the second quarter 2007 groundwater monitoring event <br />immediately downgradient of the former gasoline UST excavation contained TPH-g at <br />concentrations up to 20,000 gg/L (PZ -2) and benzene at concentrations up to 960 gg/L (PZ-1).- <br />�^ TPH-g was generally not detected in samples collected from groundwater monitoring wells <br />_,located upgradient of the former UST excavation. Data obtained from CPT borings indicate <br />6&+1 that impacts in groundwater extend approximately 90 feet BGS the vicinity of the former <br />gasoline USTs. ea,IcAear*of' US 71 <br />Due to the volatility of petroleum hydrocarbon compounds, soil vapor beneath the Site may also <br />be impacted. Assessment of this transport mechanism and potential exposure pathway will be <br />addressed through future investigation following remediation. <br />3.2 ESTIMATED MASS OF TPH-G <br />L.. Due to data gaps in vertical and lateral delineation of petroleum hydrocarbons in the subsurface <br />at the Site, additional subsurface investigation is proposed in this work plan. The residual <br />TPH-g mass in soil and groundwater will be calculated after receiving the analytical data from <br />the investigation proposed in this work plan. <br />4— <br />3.3 SOURCES OF CONTAMINATION <br />Analytical data indicate that the two 6,000 -gallon gasoline UST systems were the source of <br />petroleum hydrocarbons detected in the subsurface. 11 <br />SL AIR SCM and RI WP 10 <br />