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• Results
<br /> Results of field and analytical parameters collected to date to evaluate and optimize the performance of
<br /> the ozone infection system are presented in Tables 4 and 5 The TPHG, benzene, and MTBE
<br /> concentrations observed in all the groundwater monitoring wells during fourth quarter 2003 are presented
<br /> in Figure 4 Change in DO concentrations for select observation and background monitoring wells are
<br /> presented in Figure 5 The historical TPHG, benzene, and MTBE concentration variation over time at
<br /> select monitoring wells (MW-4 through MW-8) are illustrated graphically in Figures 6 through 10
<br /> TPHG and benzene concentrations were observed to have increased in groundwater samples collected
<br /> from MW-4, MW-5, and MW-8 since the previous sampling event (September 9, 2003) The highest
<br /> increase of TPHG (from 9,300 µg11- to 17,000 gg/L) and benzene (from 1,700 pg/L to 3,400 pglL) was
<br /> observed in samples collected from MW-4 Since the previous sampling event, MTBE concentrations
<br /> were observed to decrease in groundwater samples collected from MW-5, MW-6, and MW-10, while an
<br /> increase in concentrations were observed in groundwater samples collected from MW-1, MW-3, MW-8,
<br /> and MW-9 The highest decrease in MTBE concentration (from 49,000 pg/L to 46,000 µg/L) was
<br /> observed in samples collected from MW-6, while the highest increase (from 23,000 pg/L to 28,000 pg/L)
<br /> was observed in samples collected from MW-8 Petroleum hydrocarbons and BTEX constituents were
<br /> not reported in groundwater samples collected from MWA through MW-3, MW-7, or MW-9 1,2-DCA was
<br /> reported in groundwater samples collected from MW-4, MW-7, MW-9 and MW-10 at concentrations of 96
<br /> pg/L, 2 3 pg/L, 6 5 µgll- and 1 3 pg/L, respectively TBA, DIPE, ETBE, TAME, EDB, or ethanol were not
<br /> reported in any of the groundwater samples collected from the site Analytical data were submitted to the
<br /> State Water Resources Control Board as required by AB2886 The electronic delivery receipt is attached
<br /> in Appendix C
<br /> Samples from wells MW-4, MW-6, and MW-7 were analyzed beyond the EPA recommended hold times
<br /> The results were accepted with qualification because the reported results were within the historical data
<br /> ranges The initial results reported for MTBE and benzene in samples collected from wells MW-1, MW-5,
<br /> MW-8, and MW-10 may have been biased high as demonstrated by high surrogate recoveries Samples
<br /> were re-analyzed for MTBE, but the re-analysis was performed outside the EPA recommended hold time
<br /> Both the initial benzene and the re-analyzed MTBE results were accepted with qualification, as the results
<br /> were within historical data range
<br /> During fourth quarter 2003, the average DO levels in observation wells (MW-3 through MW-10) varied in
<br /> the range of 1 33 mg/L to 7 55 mg/L while the average DO levels in background monitoring wells (MW-1
<br /> and MW-2) were in the range of 1 18 mglL to 3 07 mg/L The higher DO levels in observation wells as
<br /> compared to the background monitoring wells are probably due to ozone infection Comparison of
<br /> COD/TOC data and petroleum hydrocarbon concentrations between third and fourth quarter appear to
<br /> correlate An increase in total iron concentrations was observed in monitoring wells MW4 through MW-9
<br /> Stratus will check these monitoring wells during the first quarter 2004 for potential iron oxide precipitates
<br /> that may exist The heterotrophic plate counts have increased or decreased corresponding to either TOC
<br /> or petroleum hydrocarbon concentration in wells MW-1, MW-4 through MW-7, and MW-10
<br /> Based on the field and laboratory data collected to date, the ozone infection system appears to be
<br /> supplying ozone and oxygen to the subsurface as designed
<br /> P IBp-Arca for URS154691Quarterly120031Arco_5469 4Q03 doc 57-RAT-U5
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