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1.0 INTRODUCTION Bench-scale treatability testing was conducted on soil and groundwater collected at former ExxonMobil #3942 site in Stockton, California, which contained diesel range total petroleum hydrocarbons (TPH-d), gasoline range total petroleum hydrocarbons (TPH-g), BTEX compounds (benzene, toluene, ethylbenzene and xylenes), and methyl-t-butyl ether (MTBE) Testing was conducted to evaluate and compare the abilities of ozone (03) and Peroxone (a mixture of ozone and hydrogen peroxide) to destroy petroleum hydrocarbons in soil and groundwater at the site, and to determine whether removal was due to volatilization (by sparging) or to destruction (via chemical oxidation) This was accomplished by comparing the effect of sparging with a chemically inert gas (nitrogen) to the effect of sparging with ozone The effect of each treatment on hexavalent chromium [(Cr(VI)] (which can be formed by oxidation of naturally occurring trivalent chromium) and other secondary water quality parameters were also evaluated The effects of each treatment on secondary water quality parameters, including hexavalent chromium [(Cr(VI)], were also evaluated The potential fate of Cr(VI), which was sometimes formed by ozone and Peroxone,was also assessed 1.1 Ozone and Peroxone Background Ozone (03) is a strong oxidant that can destroy a wide range of organic compounds, including TPH-g, BTEX, and MTBE Compounds may be completely mineralized to carbon dioxide (CO2) and water (H2O), although intermediates such as acetone may be seen if they react more slowly than the parent compounds Potential intermediates of MTBE oxidation include t-butyl alcohol (TBA) and acetone Iron and other metal ions in soil and groundwater can increase the effectiveness of ozone by reacting with ozone to form hydroxyl radicals (Bower, K C and C M Miller "Filter Sand-Phosphate Buffer Effect on 2,4-Dimtrotoluene Ozonation," J Environ Eng February 2002, 131-136, and references therein) Because the hydroxyl radical is an even stronger oxidant than ozone, its formation will reduce the likelihood of oxidation by-products Peroxone is a mixture of ozone and hydrogen peroxide (H2O2) This combination may also generate hydroxyl radicals as well as other radicals, potentially making Peroxone an even stronger oxidant than ozone alone Furthermore, Fenton-type reactions, which provide an additional source of hydroxyl and other radicals, may occur if iron present in the sub-surface reacts with H2O2 Equations 1-4 show the reactions for conversion of benzene (C6HO, toluene (C7H8), ethylbenzene (CgH,o) and xylenes (C$141fl) to carbon dioxide (CO2) and water (H20) by ozone Chemical reactions cannot be written for TPH-g and TPH-d because TPH-g and TPH-d are complex mixtures of chemicals The stoichiometnc ozone requirements for the complete mineralization of each hydrocarbon are given in Table 1 In practice, a greater-than-stoichiometric dose of 03 will usually be required because 03 is a non- selective oxidant that will react with natural organic matter and other non-target June 1,2005 ETFC-Exxon#3942