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Geological rechAks Inc. Page 10 Sinclair'trucking Project No.: 1.030.2 November 1,2005 The largest percentage of contamination remaining is in the deep region between 10.5 and 14 feet bgs remain in the area around MW-4. The following summarizes the data and 1 assumptions used in the remaining mass balance estimates: Figure 8: Remaining_Contamination - Shallow + TPH-G contours were generated using soil data gathered from shallow soil samples collected prior to the soil excavation activities. The contours were generated by Surfer 7.0® contour generating software using soil samples collected between 6 and 10.5 feet bgs • The calculations are performed as described in Section 2.4: Post-Excavation Mass Estimate Calculations. I + The area of the core and ring were taken from the remaining plume boundaries less the excavated soil. • The thickness of the shallow TPH-G contamination is assumed to be 4.5-feet, primarily occupying the depths between 6 and 10.5 feet bgs. • Historical depth-to-groundwater measurements average 11.25 ft bgs. + Mass balance calculations assume the entire 4.5-foot thick units consist of uniform contaminant concentrations. • Contaminated soil removed during soil boring and monitoring well installation activities was not subtracted from the overall mass volume. ® Natural attenuation was not used in determining remaining mass. Figure 9: Remaining Contamination - Deep • TPH-G contours were generated using soil data gathered from shallow soil samples collected prior to the soil excavation activities. The contours were generated by Surfer 1 7.00 contour generating software using soil samples collected between 10.5 and 14 feet bgs. + The calculations are performed as described in Section 2.4: Post-Excavation Mass ' Estimate Calculations. + The area of the deep core and deep ring were taken from the remaining plume boundaries less the excavated soil. 1 • The thickness of the deep TPH-G contamination is assumed to be 3.5-feet, primarily occupying the depths between 10.5 and 14 feet bgs. • Historical depth-to-groundwater measurements average 11.25 ft bgs. 1 • Mass balance calculations assume the entire 3.5-foot thick units consist of uniform contaminant concentrations. + Contaminated soil removed during soil boring and monitoring well installation activities i - was not subtracted from the overall mass volume..- • Natural attenuation was not used in determining remaining mass. i 1