This technique is based on the in situ delivery of chemical oxidants to the contaminated media to destroy the contaminants by converting them to harmless compounds. Typical oxidants applied in this process include hydrogen peroxide, potassium permanganate, ozone and dissolved oxygen. A common application of this procedure, based on Fenton’s Reagent, involves the addition of hydrogen peroxide and an iron catalyst to the contaminated area, generating a hydroxyl free radical:

H2O2 + Fe2+=> Fe3+ + OH + OH* (1)

This free radical is capable of oxidising complex organic compounds, such as TCE, PCE, dichloroethylene (DCE), benzene, polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyl (PCBs), with any residual hydrogen peroxide decomposing into water in the subsurface. Fenton’s Reagent oxida­tion is most effective in acidic environments (pH 2-4) and becomes ineffective under moderate to strongly alkaline conditions.84 Ozone can oxidise con­taminants directly or through the production of hydroxyl radicals and is also most effective in acidic conditions. Due to its instability and high reactivity, ozone is produced onsite and requires injection via closely spaced delivery points. Permanganate is typically provided as a liquid or as solid potassium permanganate (KMnO4) but is also available in sodium, calcium or magnesium salts. Permanganate reactions occur at a slower rate compared to ozone and peroxide and, depending on the pH, can destroy the contaminant through direct electron transfer or free radical oxidation. An advantage of permanga­nate use includes an operable pH range of 3.5 to 12.84

This method was used in a field study at the A/M Area of the Savannah River Site where undissolved dense non-aqueous phase liquid (DNAPL), including TCE and PCE, contamination was present. The treatment test operated over six days and used hydrogen peroxide and iron sulfate to generate hydroxyl radicals to destroy approximately 600 pounds of DNAPL-contaminated soil in the target area. After the trial period, 94% of the targeted DNAPL was destroyed85 at a total cost of $511k for the project demonstration.

104 Richard Kimber, Francis R. Livens and Jonathan R. Lloyd