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EXlended P1utne Definition:-75ao W 111h S1., Tracy,CA, Page 26 by high concentrations of analytes of concern were pumped from the open tank pit in December 1998. Additionally, the concentrations of analytes of concern in the groundwater sample recovered from Monitoring Well MW-13, which is some 90 ft. down-gradient from Monitoring Well MW-3, are significantly lower than .those detected in the groundwater recovered from Monitoring Well MW-7, which is 80 ft. down-gradient from Monitoring Well MW-13. The concentrations of analytes of concern in the groundwater sample recovered from Monitoring Well MW-13 were higher than the concentrations detected in the sample recovered from up- gradient Monitoring Well MW-3. These results are consistent with SJC's interpretation, made at the time that the underground storage tanks were exhumed, that when floating product was being pumped from the tank pit, it was being drawn into the pit from a radial distance on the order of some 110 ft. (i.e., a distance equal to that from the pumped tank pit to the former location of the fueling station's pump islands, where the fuel had been released due to leaks in piping at that location). No floating product was detected in any of the wells tested for the presence of LNAPL (Le., Wells MWFP-1 through MWFP-5 and MW-7, MW-13 and MW-14) during the April 2004 monitoring round. However, as is discussed in Section 5.0 and recorded in Table 4, f significant thicknesses of floating product had been detected in Monitoring Well MW-7 prior to being removed from that well by a series of dedicated purging operations begun in November 2003. The last purging under that LNAPL removal program was performed on March 30, 2004. Subsequently, on April 22, 2004, that well was again purged, but in that instance, as was also the case on January 25, 2004, it was a routine pre-sampling purge performed as part of the scheduled quarterly groundwater-quality monitoring round. The absence of floating product in any of the wells used to assess the distribution of LNAPL in the interior of the primary plume of affected groundwater emanating from the Navarra Property is not inconsistent with SJC's prior observations and hydrogeologic and contaminant transport assessments. As was discussed above, the location of Monitoring Well MW-13 is well within the radial influence of the LNAPL pumping operations of December 1998, during which steep gradients were generated in the direction of the former tank pit from which floating Product was pumped (The San Joaquin Company Inc. 2001g). In the work plan for the site characterization work reported herein (The San Joaquin Company Inc. 2003a), SJC made a general estimate that it was possible that LNAPL may have advanced down-gradient within the interior of the plume to a point some 30 ft. north of Monitoring Well MW-7. No floating product was detected in MWFP-3, which is approximately 32 ft. F down-gradient from MW-7 and no more than a trace of analytes of concern were found in the soil samples recovered from the boring in which MWFP-3 is installed (see Table 2). It is, of course, recognized that estimations of the velocity and distribution of LNAPL are subject to significant uncertainties, even at sites where the mass hydraulic conductivity and the rate of migration of volatile components of fuel hydrocarbons such as MTBE have been well characterized. The principal uncertainty in the estimate is the retardation factor related to the flow of the long-hydrocarbon chain components of fuel hydrocarbons that are the principal constituents of LNAPL. However, given these inherent difficulties of estimation, L1t a sic