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• DIPE (0 69 µg/L) was reported in well MW-10 1,2-DCA was reported in wells MW-7 (1 7 µg/Q, MW-9 (2 6 pg/L), and MW-10 (2 2 gg/L) TBA, ETBE, TAME, EDS, or ethanol were not reported in any of the wells The petroleum hydrocarbon concentrations generally appear to have decreased since the operation of ozone infection Analytical data were submitted to the State Water Resources Control Board as required by AB2886 The electronic delivery receipt is attached in Appendix C Historical groundwater monitoring and chemical analytical data are included in Appendix D During the first quarter 2005, the average DO levels in observation wells (MW-3 through MW-10)varied in the range of 140 mg/L to 6 7 mg/L, while the average DO levels in background monitoring wells (MW-1 and MW-2) were in the range of 15 2 mg/L to 6 4 mg/L During the first quarter 2005, higher DO levels in the range of 4 05 mg/L to 8 86 mg/L were observed In wells MW-7 and MW-9 (located approximately 10 feet from the infection point) The DO levels In the observation wells continue to be generally greater than the background monitoring wells, and is likely due to ozone infection DO levels in the observation wells are consistent with levels measured during previous monitoring events Concentrations of COD and hetetrophic plate counts generally appear to correspond to changes in GRO concentrations for wells MW-4, MW-6, and MW-8 (Figures 11 through 16) COD and heterotrophic plate counts serve as secondary Indicators to evaluate oxygen sinks and to evaluate whether biodegradation is occurring Given the COD and heterotrophic plate count variations observed at wells MW-4, MW-6, and MW-8, it appears that biological activity is occurring at the site Based on the field and laboratory data collected to date, the ozone infection system appears to be supplying ozone and oxygen to the subsurface as designed LIMITATIONS • This report was prepared in general accordance with accepted standards of care that existed at the time this work was performed No other warranty, expressed or implied is made Conclusions and recommendations are based on field observations and data obtained from this work and previous investigations It should be recognized that definition and evaluation of geologic conditions is a difficult and inexact art Judgments leading to conclusions and recommendations are generally made with an Incomplete knowledge of the subsurface conditions present More extensive studies may be performed to reduce uncertainties This report is solely for the use and information of our client unless otherwise noted K ft-Arco for URS\5469\Quarterly\2005\Arco_5469_IQ05 doc 57'RATU5