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3.4 Formation of Cr(VI) by Ozone and Peroxone <br /> Strong oxidants such as ozone and Peroxone can potentially convert naturally occurring <br /> chromium in the soil to water-soluble Cr(VI) The effect of ozone and Peroxone on the <br /> formation of Cr(VI) from soil and groundwater at this site was variable and complex In <br /> some tests (eg the Hydrocarbon Removal test discussed in Sections 3 2 and 3 3), the <br /> concentration of Cr(VI) was very low—between 3 1 and 5 1 µg/L In other tests (see <br /> Section 3 4 1) the concentration was very high—in one case reaching 570 µg/L The <br /> cause of this variability is unclear, but appears to be related to the formation of <br /> permanganate, Mn04, which was present in all tests showing high C(VI) concentrations, <br /> but not in tests with low concentrations of Cr(VI) (Formation of Mn04- from soil <br /> manganese during ozonation is known to occur, and the ability of MnO4- to oxidize soil <br /> chromium is well-established ) <br /> The tests performed to assess the formation of Cr(VI) are described in this section Tests <br /> designed to address the potential natural attenuation of Cr(VI) are discussed in Section <br /> 35 <br /> 3.4.1 Effect of Soil to Liquid Ratio on Cr(VI) Concentration <br /> . The concentrations of Cr(VI) in tests using different soil to liquid ratios are shown in <br /> Table 9 The conditions of these tests were similar to those of the COC Removal test <br /> (Section 3 2), except for the soil to liquid ratio However, in these tests, the waters were <br /> pink (due to Mn04-) and the concentrations of Cr(VI) ranged from 170- 570 gg/L, which <br /> was in stark contrast to the COC Removal test in which the water was colorless (no <br /> Mn04 was formed) and Cr(VI) was < 10 gg/L There was no correlation between the <br /> Cr(VI) concentration and soil to liquid ratio <br /> Table 9. Effect of Soil to Liquid Ratio on Aqueous Cr(VI). <br /> Soi1:Liquid Aqueous Cr(VI), n/L Cr(VI) Formed, gg/kg soil <br /> Ratio <br /> Ozonesparge Peroxone Ozones arge Peroxone <br /> 1 1 200 240 200 240 <br /> 1 2 230 570 460 1140 <br /> 1 5 230 170 1150 850 <br /> 3.4.2 Oxidizable Cr(VI) <br /> To estimate the amount of soil chromium that could potentially be oxidized during in situ <br /> treatment, the amount of Cr(VI) formed per mass of soil was calculated for the soil to <br /> Ilquid ratio tests (Section 3 4 1, Table 9) The results Indicate that 200-1,150 µg <br /> Cr(Vl)/kg soil can be formed, with lower amounts corresponding to higher soil to liquid <br /> PRIMA Environmental 17 Eval of Peroxone <br /> June 1,2005 ETIC-Exxon#3942 <br />