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Table 5 Summary of Contaminant Mass Balance Calculation CCT Stockton Railyard 1645 Cherokee Road Stockton,California Assumptions: Non-detectable results are calculated as one half the reporting limit. Soil density of 1.4 tons per cubic yards of soil. Soil porosity is o.3 One gallon of diesel is approximately 6.8 pounds The impacted soil volume is estimated based on results from previous investigations. Petroleum Hydrocarbons are uniformly distributed within volume of impacted soil. The soil contaminant mass removal calculation is based on an average concentration of TPH-d from soil samples collected from B-1 through B-11,excluding B-6,and the tonnage of waste soil removed as reported by others(CLS Environmental,2006). The soil contaminant mass remaining calculation is based on an average concentration of TPA-d from soil samples collected from B-6 and 13-12 through 13-16. Results from soil boring B-17 were not used in the concentration average as these results are not representative of the soil onsite.The volume of impacted residual soil is based on a nominal radius around observed impacted areas(13-17,MW-g,MW-7),and an average 5400t thickness of impacts within the capillary fringe in these areas. The groundwater contaminant mass removal calculation is based on an average concentration of TPH-d from grab groundwater samples collected B-1 W,B-1 through B-q and monitoring well sampling data from MW-1 through MW-4. The volume of groundwater removed is based on the reported soil tonnage removed(CIS Environmental,2006),nominal density of 1.4 tons/cubic yard and an observed average thickness of saturated soil in the bottom 30 feet of the approximately So- foot deep excavation. A nominal porosity of o.30 was assumed. The groundwater contaminant mass remaining calculation is based on an average concentration of TPH-d from grab groundwater samples collected 13-12 through B- 17 and monitoring well sampling data from MW-5 through MW-7.The volume of saturated residual soil is based on the radius of the too ug/L isoconcentration contour,a water column thickness of 10 feet(MW-5)and an assumed porosity of 0.30.