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ratios (that is, more soil, less water) Specifically, the amount chromium oxidized was lower when the soil to liquid ratio was 1 1 than when it was 12 or 1 5 Thus, in the sub- surface, where the amount of soil is much greater than the amount of liquid, the mass of chromium oxidized may be lower than observed in the laboratory testing 3.5 Natural Attenuation/Reduction of Cr(VI) Three tests were conducted to evaluate the ability of Cr(VI) to naturally attenuate if it is indeed produced during in situ treatment Cr(VI) can potentially be generated from naturally occurring soil-chromium by strong oxidants such as ozone and Peroxone In PRIMA Environmental's experience, such CT(VI) may naturally attenuate, but this is site specific and may occur very quickly(within days) or take several weeks or months 3.5.1 Total Cr(VI) Reducing Capacity (Walkley Black Method) The total Cr(VI) reducing capacity of untreated field moist and air-dried soil was measured These measurements should be considered the maximum amount of Cr(VI) that can be reduced, and not representative of potential field conditions because of the extreme conditions (heat and very low pH) used in the test The total Cr(VI) reducing capacity of air-dried soil was 6,800,000 µg/kg while that of field moist soil was . 7,300,000 ug/kg Because air-dried soil presumably did not contain significant concentrations of hydrocarbons, the similarity of the air-dned and field moist results indicates that hydrocarbons are not responsible for most of the soil's reducing capacity This was important to demonstrate because hydrocarbons will not be present after treatment with ozone or Peroxone 3.5.2 Available Cr(VI) Reducing Capacity (Bartlett Method) The available Cr(VI) reducing capacity of untreated field-moist and air-dried soil was measured The values obtained were lower than the total Cr(VI) reducing capacities (Section 3 5 1) because the procedure used is milder than that of the total Cr(VI) reducing capacity The available Cr(VI) reducing capacity of air-dried COMP7 soil ranged from 20,000-21,000 µg/kg while that of field-moist soil ranged from 21,000-27,500 gg/kg The similarity of the air-dried and field moist results indicates that hydrocarbons are not responsible for most of the soil's reducing capacity because air-dried soil presumably did not contain significant concentrations of hydrocarbons This was important to demonstrate because hydrocarbons will not be present after treatment with ozone or Peroxone The available Cr(VI) reducing capacity of C4MP7 soil indicates that the soil can reduce more Cr(VI) than it can generate The available Cr(VI) reducing capacity is 20,000 to 27,500 µg/kg soil, while the amount of Cr(VI) produced during oxidation was equivalent to about 200-1,150 µg/kg soil (See Section 3 4 2) This implies that the volume of untreated soil needed to reduce the Cr(VI) is smaller than the volume of soil that generated the Cr(VI) PRIMA Environmental 18 Eva] of Peroxone June 1,2005 ETIC-Exxon#3942