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December 22, 1998 41017 002 Harding Lawson Associates Mr Michael Kith PHSIEHD Page 7 Final Sampling Round ' A total of seven confirmation samples (T-17 through T-23) were collected on July 21 following the second phase ofoverexcavation that was performed to define the vertical and lateral extent of impacted soil in the two areas where hydrocarbons were detected in the second sampling round • Four soil samples (T-17 through T-20) were collected following additional excavation of impacted soil from the area where T-8 and T-9 had been collected Sample T-17 was collected to define the lateral extent ' to the inside of the excavation, samples T-18 and T-19 were collected to define the lateral extent to the outside of the excavation, and sample T-20 was collected from a depth of 11 0 feet bgs to define the vertical extent • No detectable BTEX was present in any of these four samples • TPHd was detected with a concentration range of 4 to 280 mg/kg • TPHmo was detected with a concentration range of 14 to 1,800 mg/kg ' + Three soil samples (T-21 through T-23) were collected following additional excavation of impacted soil from the area where T-12 had been collected Sample T-21 was collected to define the lateral extent to the �1 inside of the excavation, sample T-22 was collected to define the lateral extent to the outside of the 1 excavation, and sample T-23 was collected from a depth of 11 5 feet bgs to define the vertical extent • No detectable BTEX was present in any of these three samples ' In samples T-21 and T-23, detectable TPHd and TPHmo were not detected • In sample T-22, TPHd and TPHmo were detected with a concentrations of 12 and 49 mg/kg, respectively Soluble Analyses A total of seven samples (T-3, T-8,T-9, T-12, T-18, T-19, and T-20)were analyzed to determine the soluble fractions of TPHd and TPHmo in these samples • Sample T-3 did not contain detectable soluble TPHd or TPHmo However, hydrocarbons eluting in the diesel time window when quantified against a diesel standard were reported to sample T-3 as 1,800 micrograms per liter(ug/L) The laboratory indicated that 1 the chromatogram for the soluble TPHd fraction in T-3 appeared to be that of biomass or plant fats The laboratory indicated that a silica gel filtration of the extract would remove such hydrocarbons but that all the extract had been used in the run Because the sample T-3 had exceeded the holding time, it was decided that additional soluble data would be collected on other samples and the silica gel filtration process would be utilized to eliminate potential false positives due to non-diesel hydrocarbons These data would provide a basis for corroboration of the non- diesel nature of the hydrocarbons in sample T-3 Samples T-8, T-9, T-12, T-18, T19, and T-20 were analyzed for soluble fractions of TPHd and TPHmo and the silica gel filtration of the WET procedure extract was performed The corresponding total i3