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P Only Tests. The pH increased by approximately 1 pH unit in both of the H2O2 Only tests. ORP and sulfate were not significantly affected. Treatments employing acid with or without iron (Tests 4 and 5 and Tests 8 and 9) increased the concentrations of Cr(VI) and sulfate and affected the concentrations of several metals. The concentrations of vanadium, magnesium, calcium, chromium, iron, manganese, cobalt, and nickel increased, often by an order of magnitude . The concentration of barium decreased, presumably due to precipitation of barium sulfate (the acid used in these tests was sulfuric acid). The concentration of sulfate increased to 4,0004,400 mg/L due to the acid. Addition of acid did not result in a permanent decrease in pH in the H202 /Acid tests (Tests 4 and 5), which were sampled after 48 hours, due to the high buffering capacit� of the soil (see Section 3 .5). A small decrease in pH was observed in the 5 % H2O2/Fe +/Acid test, which was sampled after 24 hrs. The 2% H202/Fe2+/Acid tests showed a significant drop in pH, but was due to poor mixing in this reactor (the stir bar became embedded in the soil while the reaction was running overnight.) In tests using chelated iron (Tests 6 and 7) the concentrations of chromium, iron, cobalt, nickel and copper increased. In most cases, the increase was at least an order of magnitude. The increase was presumably due to chelation of metals form the soil phase. The pH increased by about 0.5 pH units, which was less than when H202 Only was used. The concentration of sulfate increased to 27-30 mg/L . The concentration of arsenic was not affected by treatment with either H202 Only or H2O2/Acid. However, arsenic was completely removed to below the reporting limit of < 0 .005 mg/L when either chelated iron or acidified iron was used. 3.4 Off-Gas Formation/Longevity of H2O2 The rate at which off-gases were generated for each of the oxidant systems are shown in Figure 1 . H2O2 decomposition was rapid in these tests—in most cases, 75-99% of the off-gases were generated within 60 minutes. 3.5 Buffering Curves The change in soil pH after addition of acid is shown in Figure 2 . Addition of up to 100 mmol H+/kg soil (50 mL of pH 1 acid to 50 g soil) initially decreased the pH to 5 . 1 , but the pH attenuated to 7.3 within 7 days. Thus, the soil can easily buffer any added acid. However, the amount of acid needed to maintain low pH for an extended length of time would be significant. PRIMA Environmental, Inc. 15 Eval of Peroxide February 8, 2007 Cambria—G Street, Davis