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Work Plan for Ref ned Plume Definition and Management of Floating Product-7500 W 11th St., Tracy. CA. Page 17 groundwater that has been observed from the results of the groundwater-monitoring program that has been conducted at the site (see Figure 4). These considerations suggest that, prior to its removal from that area, floating product extended along the southern side of West Eleventh Street over a distance of some 80 ft., and on the northern side of that street in the 7 ti �kekpl, vicinity of Monitoring Well MW-7, it has an east to west extent of some 100 ft. * 4 From the above estimates of the lateral extent of the remaining plume of floating product in the subsurface, we estimate that the plan area of the subsurface affected by floating product is 15,000 ft2. 5.2.4 Volume Estimate for Engineering Design Pu oses �. Using the estimates for actual thickness, recoverable volume per unit area, and the areal extent of the floating product remaining in the subsurface beneath and to the north of West Eleventh Street (Sections 5.2.1, 5,2.2 and 5.2.3, respectively), the following estimates for the total volume and the recoverable volume of the free product can be made. 5.2.4.1 Total Volume Taking the porosity of the soil in the formation to be 0.30 (The San Joaquin Company Inc. 2002c), the actual thickness of floating product to be 0.33 ft. (Section 5.2.1), and the areal extent of floating product to be 15,000 ft (Section 5.2.3) yields an estimated total volume of LNAPL of 1,485 ft3, or 11,000 gal. 5.2.4.2 Recoverable Volume Taking the volume of recoverable product per unit area of affected subsurface of the soil in the formation to be 0.05 gal/ft2 that we estimated in Section 5.2.2 by use of Farr, et al's solution curves and the areal extent of floating product to again be 15,000 ft2, yields an estimated total recoverable volume of LNAPL of 750 gal. Alternatively, an estimate of the amount of recoverable product can be made based on the procedure developed by Testa and Paczkowski (1989). For a soil having a porosity of 0.30, the total pore space available for occupation by LNAPL is 2.24 gal/R3. Subtracting a floating product retention capacity of 1.7 gal/ft3, which is in the mid-range of the values presented by Testa and Paczkowski, the recoverable volume of floating product in the subsurface is approximately 0.5 gal/ft3. This, in turn, yields an estimated volume of recoverable floating product in the assumed 15,000 ft2 area over which LNAPL is distributed of 7,500 gal. .� The large disparity between the estimates of the total volume of recoverable floating product beneath the site that are presented in the above paragraphs - 750 gallons v. 7,500 gallons - is, unfortunately, typical of the range of uncertainty that is confronted by the design engineer concerned with floating product remediation system design. However, the estimation exercise is of value because it provides an order-of-magnitude estimate of the total volume of floating product that will have to be efficiently managed by any remediation technology implemented at the 7500 West Eleventh Street site. It is clear that such a system must be sic