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Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA, Page 58 out and disposed at a permitted facility. That action, together with removal of soil from beneath the area where fuel dispensers had been located, was highly effective in improving groundwater quality beneath the West Eleventh Street frontage of the subject I property and was very economical to implement. Its effectiveness can be evaluated by consideration of the groundwater-quality data in Table 4. From a situation where floating product was present on the groundwater, by May 11, 2000, in a sample of groundwater recovered from Monitoring Well MW-3, the concentrations of TPH(d) had fallen to 2,800 µg/L, TPH to 11,000 L with benzene toluene ethyl benzene and total xylene isomers at concentrations of 5,600 p.glL, 160 µg/L, 830 µglL and 710 µg/L, respectively. On that date, the concentration of MTBE in that well was 10,000 µg/L. Continuing reduction of the concentrations of analytes of concern have occurred, so that by April 11, 2002, the concentrations of TPH(d) had fallen to 200 µg/L, TPH(g) to 330 µg/L, with benzene, toluene, ethyl benzene and total xylene isomers at concentrations of 85 µg/L, 4.8 µg/L, 16 µg/L and 12 µg/L,respectively, and the concentration of MTBE had fallen to -.-� 170 µg/L. Floating product is currently present in the groundwater around MW-7 on the north side 3 of West Eleventh Street. When measured on April 11, 2002, it had an apparent thickness of 0.3 ft, SJC believes that removal of the floating product in that area is essential if the components of fuel hydrocarbons affecting groundwater throughout the area of the primary plume shown on Figure 13 are to be reduced to acceptable values. (Such values would permit closure of the site by on-going water-quality monitoring during a period of intrinsic bioremediation that is expected to readily proceed when the high concentrations .. of fuel hydrocarbons in that area have been reduced.) SJC further recommends that removal of the floating product and the consequent reduction of high concentrations of analytes of concern in the groundwater beneath the = � north side of West Eleventh Street should be achieved by use of the same techniques that successfully removed the floating product and reduced the high concentrations of f analytes of concern along the south side of that street in 1998. The design for implementation of removal of floating product and extraction of groundwater affected by high concentrations of components of fuel hydrocarbons on the j north side of West Eleventh Street can be developed after a detailed study of that location, particularly with respect to locations of underground utilities, the stability of the sands that underlie the surficial fill and shallow clays, and other civil and.geotechnical engineering specifics. However, it is expected that the remediation of the area would be based on the following concepts: An excavation that parallels the street would be opened in the northern shoulder of West Eleventh Street, having dimensions on the order of 100 l ft. long by 10 ft. wide, the bottom of which would be some 15-20 ft. BGS, so that the affected sand aquifer at that depth would be exposed. The actual dimensions and the method of excavation would be determined following a detailed engineering study, but the excavation may be performed within shored walls or achieved by opening short trenches, the SJC a