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Extended Site Characterization Report: 7500 West Eleventh Street, Tracy, CA. Page 41 However, over the next two years, the concentrations of both diesel and gasoline in f. samples recovered from Well MW-7 exhibited a significant upward trend. As the concentration of those analytes increased, MTBE was no longer detected. That is almost certainly due to its presence being obscured in the chromatographs rather by its actual f ` absence. BY Aril 11 2002 it was evident that there was floating rod-act in Well MW-7 April gp and it was measured to have an apparent thickness of 0.3 ft. 7.3.2.2 Primary Plume to the North of West Eleventh Street At an early stage of the first site characterization program conducted at the 7500 West Eleventh Street in April and May 2000, it was readily apparent to SJC that fuel ._� hydrocarbons that had leaked into the subsurface on that property had migrated down the groundwater gradient to the north side of West Eleventh Street and for some considerable distance beyond. However, although SJC's plan for the site characterization had provided for that eventuality, due to denial of funding for exploratory borings and groundwater- r=j quality monitoring wells located to the east of Chrisman Road and to the north of West Eleventh Street that was imposed by the USTCF at that time, it was not possible to r. determine the complete lateral extent of the plume of affected groundwater. That E=' situation has now been rectified by the drilling of additional exploratory borings PP-15 and PP46 and installation of Monitoring Wells MW-8, MW-9, MW-10 and MW-11 at IF: ] the locations shown on Figure 2. � I The exploratory borings drilled and the groundwater-quality monitoring wells installed to the north of West Eleventh Street in March 2002 permitted the down-gradient extent of the primary plume of affected groundwater emanating from the 7500 West Eleventh Street site to be investigated. As can be seen by inspection of Table 4, with the exception of a trace of a diesel-range hydrocarbon at a concentration of 1.1 mg/Kg detected in a sample recovered from a depth } � of 21 ft BGS in the boring for Well MW-10, no analytes of concern were detected in samples of soil recovered from depths greater than 5.5 ft in any of the holes drilled north of West Eleventh Street. The diesel-range analyte, at a concentration of 5.9 mg/Kg, }r found in a sample recovered from a depth of 5.5 ft. in the boring for Well MW-9 and at 1.9 mg/Kg in a sample recovered from the same depth in the boring for Well MW-10 can be attributed either to local drips and spills that occurred along the shoulders of Chrisman Road or to pieces of bituminous macadam incorporated in the paving sub-base. -a As was predictable, based on the hydrogeologic and geochemical data derived from the »i initial site characterization program and the rounds of groundwater quality monitoring 1 conducted over the following two years, no analytes of concern were detected in the sample of groundwater recovered from monitoring Well MW-9. For that reason, that well was not included in SJC's plan for the extended site characterization program. It was installed at the direction of the SJCEHD. It does, however, serve as an aid to definition of '.. the eastern lateral extent of the primary plume of affected groundwater emanating from the 7500 West Eleventh Street property. The sample of groundwater recovered from Monitoring Well MW-10 (which was included in SJC's plan) on April 11, 2002 was free sic