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CAP Addendum:Former Fuefteg Station, 7500 West Eleventh Street, Tracy, C�%O Page 8 Comparison of that mass with the 4,625,025 grams total mass of contaminants in the subsurface in the area affected by LNAPL reflects the extremely low solubility of TPHd and TPHg in groundwater. 2.2.1.5 Total Mass of Contaminants Removed from Extraction Trench The total mass of fuel hydrocarbons removed from the extraction trench will be the sum of the mass of contaminants removed by excavation of soil to form the trench, the mass of LNAPL extracted from the trench and the mass of fuel hydrocarbons in the contaminated water that is pumped from the trench that will be in addition to the LNAPL that will be pumped. 2.2.1.5.1 Mass of Contaminants Removed by Excavation of Soil When the extraction trench is excavated it will be 15 ft. deep and four feet wide and its length over the area estimated to be affected by LNAPL will be 80 ft. Using a unit weight for the soil in the trench of 120 lb/ft3, the weight of soil that will be excavated is estimated to be 576,000 lbs, or 261,269 Kg. The concentration of fuel hydrocarbons in that area can be represented by the concentrations of fuel hydrocarbo around Monitoring Well MW-7, which as computed in Section 2.2.1.2 abo , is 29.43 m g. Thus, the mass of fuel hydrocarbons to 'be removed from the subsurface en the extraction trench is formed will be 138,324 grams. 1,70 J� iutorraG� '�— cess 2.2.1.5.2 Mass of Contaminants Removed by Extraction of LNAPL As was discussed in Section 2.2.1.1, the total estimated volume of LNAPL is 1,050 gallons, which has a mass of 3,179,746 grams. However, given the limitations of the state of the art related to such computations, it is difficult to estimate how much of that mass will be extractable. In Section 2.1.5 above, different methodologies yielded a range for the volume of extractable LNAPL ranging from zero to 1,050 gallons. For the purpose of estimating the mass of fuel hydrocarbons that will be removed from the subsurface by pumping LNAPL from the water surface in the extraction trench, we will conservatively assume that the extractable volume is 525 gallons. That volume would have a mass of 1,589,873 grams*. *Note: If, as might be predicted by the Testa and Paczkowski method (see Section 2.1.5) 100% of the LNAPL in the subsurface, i.e. 1,050 gallons, could be recovered it would have a mass of 3,179,746 grams. 2.2.1.5.3 Mass of Contaminants Removed by Extraction of Groundwater It was proposed in the CAP that the total volume of LNAPL and groundwater to be pumped from the extraction trench would be 10,000 gallons. Subtracting the conservative portion of that volume that is conservatively estimated to be represented by LNAPL, i.e.,