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APPENDIX C ADSORBED MASS & VOLUME CALCULATIONS STALLWORTH AUTO SALES 602 North California Street, Stockton , California Impacted Soil Mass/Volume Assumptions: • Utilizing Figures 3 through 7, the mass distribution of total petroleum hydrocarbons quantified as gasoline (TPH-g) can be estimated for impacted soils at the site. To estimate the mass, the adsorbed plume has been split into three depth discrete zones and three contoured zones of 1 , 000 mg/kg , 100 mg/kg , and 1 mg/kg . • Figures 5 , 6 and 7 were generated using computer assisted design software . The software has a specific function to calculate the area of a selected object, such as each area between the above referenced TPH-g isoconcentration intervals . • The area and volume of each contoured zone can be estimated utilizing the computer-assisted design software and the program can be used to determine the area between the above referenced 1 , 000 , 100 and 1 mg/kg contoured zone intervals (Figures 7) , and then multiplying the area by the height of the contoured zone . • Height used for estimating the mass were determined by the three depth discrete zones and estimated from cross sections A-A' and B-B' . For the 10 to 25 foot interval the height was determined to be 15 feet. For the 25 to 65 foot interval the height was determined to be 35 feet. For the 65 to 100 foot interval the heights were determined to be 7 feet (1 , 000 mg/kg contour) , 8 feet ( 100 mg/kg contour interval) and 40 feet ( 1 mg/kg contour interval). • The volume can be calculated by the formula : V = AREA•h , where "area" is determined through the design software ( Figures 5 , 6 and 7) and "h" is the height as determined as contoured in cross section . • The average TPH-g concentration in the each depth discrete zone was estimated by summing the contour isoconcentration lines and the soil sample concentrations within the selected area and dividing by the total number of samples . ADSORBED SOIL PLUME MASS CALCULATIONS 10 to 25 foot zone: • >1 ,000 mg/kg (Inner zone) : The sum of 61 -15 (1 ,400 mg/kg), B1 -25 (5,600 mg/kg), VW3-20 (6 ,800 mg/kg ),.VW 3-25 (2 ,200 mg/kg ), VW 1 -20 (2 ,900 mg/kg ), VW 1 -25 (2 ,700) and the 1 ,000 mg/kg contour line; average = 3,228 mg/kg (equivalent to 0 .003228) . • 1004 ,000 mg/kg (middle zone) : The sum of the 1 ,000 mg/kg contour line and the 100 mg/kg contour line; average = 550 mg/kg (equivalent to 0 .00055) . • 1 - 100 mg/kg (Outer zone) : The sum of 62-25 (5 . 1 mg/kg ) , 133-20 (6.8 mg/kg ) the 1 mg/kg and the 100 mg/kg contour lines average = 28 mg/kg (equivalent to 0 .000028) . Advanced GeoEnvironmental, Inc.