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i 4.0 ENGINEERING CONSIDERATIONS Ozone effectively destroyed most of the CDCs within 1 hour in this study Some observations that should be taken into consideration when evaluating this technology for full-scale application are provided Ozone Demand. The results of the laboratory study can be used to estimate the size of the ozone generator needed for full-scale application In this study, approximately 450 Mg 03 was applied to the soil-GW mixture in 1 hour, which was about 1 4-1 9 times the dose (230-330 mg 03) required to mineralize COCs initially present in Untreated GW and meet the soil ozone demand The dose required in the field may differ somewhat due to differences in mass transfer efficiency and ozone distribution into the treatment zone between field and laboratory applications Acetone Acetone was generated in the laboratory test Acetone is also susceptible to oxidation by ozone, so increasing the sparge time (or improving the mass transfer efficiency) in the field should result in complete removal of acetone In addition, acetone may be more susceptible to biodegradation than another COCs, so it may quickly naturally attenuate once it leaves the treatment zone Cr(VI) Some Cr(VI) was formed during ozonation of soil and groundwater due to oxidation of soil Cr to water soluble Cr(VI) The available Cr(VI) reducing capacity of lie untreated soil appears to exceed the amount of Cr(VI) that can potentially be generated, indicating that this Cr(VI) should attenuate once it leaves the treatment zone The ability of untreated soil to reduce Cr(VI) present in ozonated water was confirmed in lab tests However, field testing is recommend to confirm that concentrations can be reduced to acceptable levels under field conditions Bromate Bromate was formed during ozonation The amount formed was less than expected based on the amount of bromide lost Evaluation of the fate of bromate was beyond this Scope of Work ' Laboratory Concentrations versus Field Concentrations. It must be noted that post- treatment concentrations of water quality parameters measured in the laboratory may differ from concentrations observed in the field This is due to differences between field and laboratory conditions including soil to liquid ratio, concentration of ozone, duration of sparging and other factors However, the laboratory data does provide information on which tnnrnmPtf-r,,a if any, are likely to be of concern. and in the case of Cr(VI), demonstrates that Cr(VI) is likely to naturally attenuate once it leaves the treatment zone PRIMA Environmental 14 Eva{ of Ozone January 27,2005 ENSR-Unocal 5098