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<br /> A S S Q C I A T E S I N C
<br /> 4.5 Analysis of System Effectiveness
<br /> Figures 14 through 20 are crossplots of benzene and MTBE over time. Figures 21, 22 and 23
<br /> show the areal distribution of benzene, MTBE and TPHg, respectively, based on isoconcentration
<br /> maps over time.
<br /> 4.5.1 Benzene
<br /> During the fourth quarter monitoring period, benzene levels in on site wells, MW1, MW2, MW3,
<br /> MW4 and EW 1 declined. Benzene concentrations in MW5 and MW8 appeared to remain non-
<br /> detected at method detection limits. During the fourth quarter, benzene was reduced to non-
<br /> detected at method detection limits level (<0.5 ug/L) in MW4.
<br /> Prior to remediation system start-up on June 17, 2004 at the Jamar property, benzene
<br /> concentrations appeared to decline in MW2, MW3, MW4, MW5 and MW8. Declining trends in
<br /> benzene concentration were not evident, however, in MW1 and EW1 prior to remediation
<br /> startup.
<br /> During the fourth quarter monitoring period, concentrations of benzene in MWI at
<br /> approximately 7.5 from IW2 and in EW1 placed at approximately 9.0 feet from IW1 declined
<br /> These are the closest Spargepoint® to any on site well. The successive decline of benzene in
<br /> • MW 1 from the 37,000 ug/L on June 3, 2004 in each of the monitoring events following (i.e., July
<br /> 16, 2004, August 13, 2004, September 13, 2004 and December 13, 2004) was significant. During
<br /> the 13 December event, benzene was reported at a concentration of 0.8 ug/L for a removal
<br /> efficiency of 99.9% after approximately 6 months of operation. The successive decline of
<br /> benzene in EW1 from the 35,000 ug/L on June 3, 2004 in each of the monitoring events
<br /> following was also significant. During the 13 December event, benzene was reported at 0.8 ug/L
<br /> for a removal efficiency of 99.9% after approximately 6 months of operation.
<br /> The decline of benzene in MW2 may have accelerated only after initial mixing during the July
<br /> 16, 2004 monitoring event. If the reduction in benzene was attributed solely to system activities
<br /> (i.e., from the 1500 ug/L on June 3, 2004 to 36 ug/L on December 13, 2004) this would equate to
<br /> a removal efficiency of 97.6 % after approximately 6 months of operation. Dissolved oxygen
<br /> (DO) concentrations after initially increasing in the August 13, 2004 monitoring event have
<br /> successively declined but are still above pre start-up levels. The increase in DO after system
<br /> start-up would indicate influence by the C-SpargeTM process)
<br /> The reason for the decline of benzene in MW3 is not clearly related to the effects of system
<br /> operation. The trend appears to have been in ongoing previously at a similar and could reflect
<br /> seasonal variation. However, DO concentrations, which could be a result of system operation
<br /> increased (i.e., in the December 13, 2004 groundwater monitoring event) when compared with
<br /> previous events. More data is needed to evaluate this well.
<br /> MW4 is approximately 16 feet from the closest sparge point (IW4). The decline of benzene in
<br /> MW4 may have accelerated after system start-up from the 1,500 ug/L on June 3, 2004 to later
<br /> monitoring events (i.e., July 16, 2004, August 13, 2004, September 13, 2004, December
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