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31 January 2013 <br />AGE-NC Project No. 02-0926 <br />Page 5 of 21 <br />of discontinuous lenses of sandy material. <br />HU6 - Extending from approximately 90 feet bsg to the total depth of the borings, HU6 <br />consists of interbedded silty, clayey, and stiff, fine-grained material. This unit is <br />characterized by low to moderately high pore pressures. <br />Generalized cross-sectional models of the geology encountered at the site are included as <br />Figures 3 and 4. Boring logs and CPT logs are included in Appendix B. <br />4.0. MAXIMUM PETROLEUM HYDROCARBON DISTRIBUTION IN SOIL <br />Based on soil samples collected to date, the site appears to be primarily impacted by <br />TPH-g, TPH-d, and BTEX constituents. Hydrocarbon impact appears to be primarily <br />located surrounding the former underground storage tank location in the areas of MW-5 <br />and VW-1, and extends north towards MW-6, west towards VW-2, and south-southwest <br />towards boring B4. Hydrocarbon impact encountered at boring B4 appears to be <br />associated with a historic groundwater flow direction (Figures 5 and 9). <br />Vertically, the extent of petroleum hydrocarbon-impacted soil appears to be limited to a <br />depth of approximately 60 feet bsg. Hydrocarbon impact to soil is vertically defined by <br />samples collected in borings MW-6 and CPT-3 at depths of 65, 70 and 75 feet bsg <br />respectively (Table 1 and Figures 5 and 6). <br />When the data collected at the site is plotted in both plan view and cross sectional views, <br />the apparent volume of the petroleum hydrocarbon-impacted area prior to remediation <br />encompasses approximately 42,665 cubic yards, and yields approximately 552 gallons of <br />gasoline, which is equivalent to 3,450 pounds of gasoline. Mass/volume calculations are <br />included in Appendix C. <br />Figures 5 and 6 depict selected soil sample locations and the estimated extent of TPH-g <br />concentrations adsorbed in soil in cross sectional view; Figures 7, 8, and 9 depict the <br />estimated lateral extent of TPH-g in plan view. <br />Based on historic soil samples collected at the site, AGE has divided the maximum <br />adsorbed hydrocarbon impact at the site. The three intervals, described in detail below are <br />located at 5 to 30 feet bsg, 30 to 60 feet bsg and from 60 to 75 feet bsg. The intervals were <br />determined based on the topology of the soil plumes when modeled in plan view. <br />Advanced GeoEnvironmental, Inc.