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<br /> ASSOCIATESIV
<br /> I%TC
<br /> I N C .
<br /> MTBE concentrations in EW i appear to be fluctuating over time.
<br /> The change in areal extent of MTBE from the June 3, 2004 monitoring event through the March
<br /> 16-17, 2005 groundwater monitoring event appears negligible (Figure 22).
<br /> ' 4.5.3 TPHg
<br /> During this monitoring period, TPHg concentrations in MWi, MW4, MW6b, MW6c, MW7a
<br /> ' MW7b, MW7c, MW8, MW9a, MW9b, MW9c, MWIOa, MWIOb and MWIOc were not detected
<br /> at method detection limits of 50 bg/L. TPHg was detected in MW2, MW3, MW5, MW6a and
<br /> EWL
<br /> Although some fluctuations were apparent, the overall decline of TPHg in MWI from 54,000
<br /> ug/L on June 3, 2004 in each of the quarterly monitoring events following (i.e., September 13,
<br /> ' 2004 and December 13, 2004 and March 16-17, 2005) was significant. During the March 16-17
<br /> 2005 groundwater monitoring event, TPHg was reported at not detected at method detection
<br /> limits of 50 ug/L for a removal efficiency of 99.9% after approximately 9 months of operation.
<br /> ' TPHg concentrations in MW2 and MW3 appeared to fluctuate during the first quarter. TPHg
<br /> concentrations in MW2 ranged between 1,000 ug/L 1 (i.e., on March 16, 2005) to 1400 ug/L for
<br /> each of the system monitoring events earlier during first quarter. TPHg concentrations in MW3
<br /> ranged from 2,500 ug/L to 4,100 ug/L during the first quarter.
<br /> ' A decline of TPHg in MW4 has accelerated from 4800 ug/L on June 3, 2004 to <50 ug/L on
<br /> December 13, 2004 and remained at not detected at method limits of 50 ug/L during all three
<br /> monitoring events during first quarter. If this reduction was attributed solely to system activities
<br /> ' this would equate to a removal efficiency of 99.0% after approximately 6 months of operation.
<br /> MWS and MW6a show a fairly consistent concentration of TPHg since December 13, 2004.
<br /> ' The successive decline of TPHg in EW 1 was also significant. TPHg was present in
<br /> concentrations of 85,000 ug/L on June 3, 2004. It declined in each of the quarterly monitoring
<br /> ' events following and during the March 16-17, 2005 event, TPHg was reported at 460 ug/L. This
<br /> equates to a removal efficiency of 99.5% after approximately 9 months of operation.
<br /> TPHg maps were also plotted using data from the March 17, 2004, June 13, 2004, September 13,
<br /> ' 2004, December 13, 2004 and March 16-17, 2005.groundwater monitoring events. The March
<br /> 17, 2004 and June 3, 2004 sampling data were obtained prior to system start-up. The March 16-
<br /> 17, 2005 sampling data was information obtained approximately 9 months after system operation
<br /> 1 start-up. Although there are possible reductions in the areal extent of TPHg during this quarter,
<br /> significant reductions of TPHg concentrations are apparent along the injection well corridor
<br /> (Figure 23).
<br /> ' S:1268231QM reports12005 I stQR.doc 11
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