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f <br /> 1 <br /> 15 June 2009 <br /> AGE-NC Project No.05-1306 <br /> Page 8 of 33 <br /> I - <br /> 3 <br /> fi* Neither benzene nor methyl tertiary butyl ether(MTBE)has been detected in soil samples collected <br /> at the site. Toluene, etbylbenzene, and xylenes have only been detected in the two soil samples <br /> collected from the boring for monitoring well MW-2 at maximum concentrations of 1.3 mg/kg, <br /> 0.11mg/kg and 4.2 mg/kg, respectively. Again, this area has been removed, therefore, no BTEX <br /> constituents have been detected on the site after remediation. <br /> f Soil boring locations are illustrated on Figure 2. Analytical results of soil samples are summarized <br /> in Tables I and 2. <br /> Figures 6 and 7 depict selected soil sample locations and the estimated extent of TPH-d <br /> concentrations adsorbed in soil in cross sectional view;Figure 8 depicts the estimated lateral extent <br /> of TPH-d impacted soil in a plan view. <br /> Based on the estimated lateral and vertical extent of adsorbed TPH-d,which has impacted soil and <br /> a review of the analytical results (Figures 6 through 8; Table 1), an-updated mass of TPH-d was <br /> prepared for the primary source area. Based on soil sample analysis performed prior to site soil <br /> t remediation, AGE estimates TPH-d in the source area of approximately 11,301 pounds in an area <br /> of approximately 4,237 cubic yards. This includes all areas where the TPH-d concentration was <br /> greater than 100 mg/kg. <br /> It was estimated that approximately 75 percent of the mass was located in an area approximately <br /> 60 feet in diameter around the location of the former tank excavation and at depths of 10 feet to <br /> 30 feet bgs. <br /> 4.0. ASSESSMENT OF TPH-D-IMPACTED GROUND WATER <br /> Between August 1998 and March 2009 quarterly ground water monitoring events have been <br /> $u � q Y i�' g <br /> performed on-site,to monitor the dissolved petroleum hydrocarbon concentrations in ground water <br /> and to characterize ground water flow direction and gradient. <br /> 4.1. GROUND WATER DEPTHS <br /> Generally, ground water levels between 1998 and 2008 were recorded at the site to be between <br /> 4.05 feet below casing grade and 14.01 feet below casing grade. Ground water elevations at the site <br /> generally fluctuated between 2 feet above mean sea level (msl) and 6 feet below msl. <br /> Advanced GeoEnvironmental,Inc. <br />