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i LVA RTC
<br /> F� A S S O C I A T E S I N C ,
<br /> During the first quarter 2005 monitoring period, benzene concentration levels were at consistent
<br /> levels of not detected at method detection limits of 0.5 ug/L in MW5, MW6a, MW6b, MW6c,
<br />' MW7a, MW7b, MW7c, MW8, MW9a, MW9b, MW9c, MW1Oa, MW10b and MW10c.
<br /> Composite benzene concentration maps were plotted using data from March 17, 2004, June 3,
<br />' 2004, September 13, 2004, December 13, 2004 and during the March 16-17, 2005 events. The
<br /> March 17, 2004 and June 3, 2004 sampling data were obtained prior to system start-up. The
<br /> March 16-17, 2005 sampling data was information obtained approximately 9 months after system
<br /> operation start-up. Reductions in the areal extent of benzene are apparent over time. Significant
<br /> reductions of benzene concentrations are apparent along the injection well corridor (Figure 21).
<br /> 4.5.2 MTBE
<br /> During this quarter MW6c had the highest MTBE concentrations successively followed by EW1,
<br /> MWI, MW6b, MW4 and MW2, MW7c, MW10b, MW7b and MW7a. The MTBE
<br /> concentrations in MW7a and MW7b are below typical clean-up levels (Table 2).
<br /> MTBE concentrations in MW 1 have historically fluctuated but appear to be declining in the first f
<br /> quarter of 2005. The fluctuating MTBE concentrations in MW 1 may be a result of periods of
<br /> system operation and non-operation. The concentration of MTBE has decreased from 190,000
<br /> ug/L prior to system startup to 4,300 ug/L during the March 16-17, 2005 groundwater monitoring
<br /> event. DO also increased significantly after system start-up in MW from 0.36 mg/L on 3 June to
<br /> 5.17 mg/L during the March 16-17, 2005 event.
<br /> ' In MW2, MTBE concentrations have remained similar or decreased only slightly from June 3,
<br /> 2004 (140 ug/L) to March 16-17, 2005 (94 ug/L). DO has fluctuated after system start-up in
<br /> ' MW2 from 1.39 mg/L on June 3, 2004 to 2.26 mg/L during the March 16-17, 2005 monitoring
<br /> event
<br /> ' MTBE has not been detected in MW3 at or above method detection limits since March 13, 2003.
<br /> ' DO has increased overall in MW4 since system start-up in June, 2004 and MTBE concentrations
<br /> may be decreasing slowly with increasing time.
<br /> ' During this monitoring period, MTBE concentrations remain at below action levels for MW5,
<br /> MW7a and MW7b. MTBE concentrations remain not detected at method detection limits for
<br /> MW6a, MW8, MW9a, MW9b, MW9c, MW10a, and MW10c.
<br /> MTBE concentrations have increased from the December 13, 2004 groundwater monitoring
<br /> event in MW6b, MW6c and MW7c.
<br /> MTBE concentrations in MW10b although decreasing from the December 13, 2004 groundwater
<br /> monitoring event remain similar.
<br /> ' S:1268231QM reports12005 IstQR.doc 10
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