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CAP Addendum:Former FuJQ Station, 7500 West Eleventh Street, Tracy, Page 3 Eleventh Street. The revised distance is 80 ft. Based on the above assumptions, it is estimated that the area of the subsurface beneath the Navarra Site that is currently affected by LNAPL is not greater than 9,200 fl2. �^cur_4 �i^v lS � 2.t.4 Total Volume of LNAPL in Subsurface Taking the porosity of the soil in the formation to be 0.3 (The San Joaquin Company Inc. 2002), the actual thickness of floating product to be 0.05 ft. (Section 2.1.1), and the areal extent of floating product to be 9,200 ftZ (Section 2.1.3) yields an estimated total volume of LNAPL of 138 ft3, or 1,050 gallons. - ,,f acrw w/rc 'Orr: „?Oz c - 2.1.5 Recoverable FloatinzProduct Due to adsorption of liquid-phase hydrocarbons onto soil particles, a significant portion of LNAPL present in a zone just above and below the water table does not flow freely out of the soil when the water table falls, nor when clean water flows into the soil pores from up-gradient locations. Thus, the volume of LNAPL that can actually be extracted from the in situ soil by any given remediation technology (other than removal by excavation) is frequently considerably less than the total volume of non-aqueous phase hydrocarbons present in the soil mass. The relationships between the apparent thickness of floating product measured in a well, the actual thickness in the adjacent formations, and the amount of product that is recoverable are complex and are affected by. soil-specific and LNAPL-specific parameters and the dynamics of the hydrogeologic regime prevailing at any given moment. As was also explained in the CAP, various methods have been developed to make approximate estimates of the volume of recoverable LNAPL in an aquifer. However, application of different methods results in a very wide range of estimated recoverable volumes for the same in situ conditions. For example, curves of the relationship between the volume of LNAPL in porous media for any given depth of LNAPL in a well have been developed from numerical analytical models. Among the most conservative of the methods is that developed by Farr, Houghtalen and McWhorter (1990). However, when the thickness of the LNAPL in the well is as low as 0.05 ft., that methodology predicts zero recoverable LNAPL. Alternately, a very conservative estimate of the recoverable volume of LNAPL can be made using the procedure developed by Testa and Paczkowski (1989). Their method employs a single parameter that is dependent upon soil type to estimate the volume of recoverable product from a unit volume of affected soil. They estimated the oil retention capacity of soil to range from 5 Uma (0.34 gal/ft) for gravel to 40 L/m3 (2.96 gal/ft) for silty sand. Adopting the value for silty sand, it is estimated that the volume of recoverable free product in the subsurface under the 7500 W. Eleventh Street Site would be 2.96 gallons of floating product per cubic foot of affected soil. `"~- 2.1.6 Order of Magnitude Estimate of Volume of LNAPL to be Recovered As was described in Section 2.1.3, the estimated area of the subsurface affected by