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1 Geological Teclacfcs Inc. Page 6 Sinclair Trucking Project No.: 1030.2 November 1,2005 o Each percentage is multiplied by the corresponding concentration and the sum of the three products is divided by 100 percent to reach the average concentration in a given ' area. ® 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. o Mass balance calculations assume the entire 4.5-foot thick units consist of uniform ' contaminant concentrations. e UST and septic tank volumes are small and not subtracted from the overall mass volume. a Contaminated soil removed during soil boring and monitoring well installation activities ' was not subtracted from the overall mass volume. e Natural attenuation was not used in determining remaining mass. ' Fi.Rure 5: Pre-Excavation Deep ® TPH-G contours were generated using soil data gathered from deep soil samples collected prior to the soil excavation activities. The contours were generated by Surfer 7.00 ' contour generating software using soil samples collected between 10.5 and 14 feet bgs. e The heaviest contamination is found in bi-lobal contours near the southern end of the former UST and surrounding MW-4. This bi-lobal contamination encompasses an area of approximately 1,175-ft2. This area, called the deep core, has an average concentration of 5,000 mg/Kg. The deep core occupies the space inside and including the 4,000 mg/Kg contour line. ' m Average concentration was determined by the percentage of the core or ring occupied by a specific contour concentration. o The deep core is 1,175-ft2. ' o 8,000 mg/Kg contour covers 21.9-ft'and represents 1.9% of the core area o 6,000 mg/Kg contour covers 297.2-ft'and represents 25.3%o of the core area o 4,000 mg/Kg contour covers 856-ft2 and represents 72.8% of the core area ' o Each percentage is multiplied by the corresponding concentration and the sum of the three products is divided by 100 percent to reach the average concentration in a given area. ' • The area between the non-detect and the 4,000 mg/Kg contours is approximately 4,825-ft2 and is called the deep ring. The largest portion of the ring lies between the non-detect and the 2,000 mg/Kg contour lines. To be conservative 1,000 mg/Kg was used as an ' average for the area between non-detect and 2,000 mg/Kg. The deep ring has an average concentration of 1,435 mg/Kg. • Average concentration was determined by the percentage of the core or ring occupied by ' a specific contour concentration. o The deep ring is 4,825-ft2. o 2,000 mg/Kg contour covers 2,100-ft2and represents 43.5% of the deep ring o ND<1 mg/Kg contour covers 2,725-ft2 and represents 56.5% of the deep ring o Each percentage is multiplied by the corresponding concentration and the sum of the two products is divided by 100 percent to reach the average concentration in a given area.