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Resources Control Board as required by AB2886 The electronic delivery receipt is attached in Appendix <br /> C <br /> During the fourth quarter 2004, the average DO levels in observation wells (MW-3 through MW-10) varied <br /> in the range of 1 4 mg/L to 4 4 mg/L, while the average DO levels in background monitoring wells (MW-1 <br /> and MW-2)were in the range of 1 6 mglL to 2 1 mg/L During the fourth quarter 2004, higher DO levels in <br /> the range of 2 5 mglL to 6 2 mglL were observed in wells MW-7 and MW-9 (located approximately 10 feet <br /> from the infection point) The DO levels in the observation wells continue to be generally greater than the <br /> background monitoring wells, and is likely due to ozone infection DO levels in the observation wells are <br /> consistent with levels measured during previous monitoring events <br /> Concentrations of COD and hetetrophic plate counts appear to correspond to changes in GRO <br /> concentrations for wells MW-4, MW-6, and MW-8 (Figures 11 through 16) COD and heterotrophic plate <br /> counts serve as secondary indicators to evaluate oxygen sinks and to evaluate whether biodegradation is <br /> occurring Given the COD and heterotrophic plate count variations observed at wells MW-4, MW-6, and <br /> MW-8, it appears that biological activity is occurring at the site <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 /> LIMITATIONS <br /> This report was prepared in general accordance with accepted standards of care that existed at the time <br /> this work was performed No other warranty, expressed or implied is made Conclusions and <br /> recommendations are based on field observations and data obtained from this work and previous <br /> investigations It should be recognized that definition and evaluation of geologic conditions is a difficult <br /> and inexact art Judgments leading to conclusions and recommendations are generally made with an <br /> incomplete knowledge of the subsurface conditions present More extensive studies may be performed to <br /> reduce uncertainties This report is solely for the use and information of our client unless otherwise noted <br /> I <br /> K\Bp-Arco for URS\5469\Quarkerly\2004\Arco_5469_4Q04 doc 5rRAru5 <br />