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3.5.3 Long-term Cr(VI) Reducing Capacity The long-term Cr(VI) reducing capacity tests used ozone-treated or Peroxone-treated site groundwater and untreated site soil to assess whether Cr(VI) generated during treatment could be reduced as predicted by the total and available Cr(VI) reducing capacity tests discussed in Sections 3 5 1 and 3 5 2 A long-term test using clean, untreated groundwater and untreated soil was also performed for comparison The results of the long-term reducing capacity tests are shown in Table 10 The results clearly indicate that Cr(VI)potentially generated during ozone or Peroxone treatment can attenuate once the Cr(VI) contacts untreated soil For example, within 15 days, complete removal of Cr(VI) was seen in the Ozone sparged test in which the Cr(VI) was generated solely by treatment with ozone Complete removal was seen almost immediately (within 3 days) in the Peroxone-treated test spiked with 560 µg/L Cr(VI) and using a 1 1 soil to liquid ratio Partial removal was seen in the Peroxone test that was spiked with 750 gg/L Cr(VI) and using a 1 4 soil to liquid ratio The reason for this difference is uncertain but is probably due to residual ozone in the 750 mg/L test which inhibited Cr(VI) attenuation by competing with Cr(VI) for reducible species in the untreated soil It should be noted that the initial concentration of Cr(VI) in most of these tests was • greater than or equal to the highest concentration observed after treatment with ozone or Peroxone (570 mg/L) and that all of this Cr(VI) was reduced Even in the test spiked with 750 µg/L Cr(VI), 520 µg/L of Cr(VI)was reduced 3.6 Ozone Demand The ozone demand of soil and water was measured These values are estimates that can be used as guidance to determine the size of an ozone generator that would be needed for field application of either ozone or Peroxone The concentration of ozone over time in the groundwater demand and soil demand tests is shown in Figures 1 and 2, respectively The ozone concentration decreased much more rapidly in the first 15 minutes in the presence of groundwater than in the absence of groundwater GWODo,was therefore calculated for all data points using Eqn 9 and found to range from 110 to 1$0 mg 03/L groundwater Based on the concentration of BTEX in untreated IP groundwater and the stoichiometric doses given in Table 1, the expected GWOD., was 320 mg 03/L of groundwater This value is about 2-3 times the measured demand Possibly, hydrocarbons were volatilized during set-up of GWODoz test Clearly, however, the groundwater does not exert an unexpectedly high demand Pk1MA Environmental 19 Eva]of Peroxone June 1,2005 ETIC-Exxon#3942