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I CLEARWATER GROUP Fenton's Reagent Protocol INTRODUCTION Hydrogen peroxide (11202) is the most common peroxide in commerce and a common chemical oxidizer used for in-situ remediation applications. Pure hydrogen peroxide and its aqueous solutions are clear liquids resembling water. Unlike water, hydrogen peroxide has a slightly sharp and distinctive odor. Low concentrations of hydrogen peroxide are sold in drug stores (typically at 3% concentration) as a mild antiseptic. HISTORY Hydrogen peroxide is one of the earliest chemical oxidants to be discovered and used in industry. It was discovered in the late 1700s and was commercialized in the early 1800s. Hydrogen peroxide works as a remedial treatment chemical in two ways: it produces free radicals and is a strong oxidizing agent. H.J.H. Fenton (1893, 1894), a British professor, described the exothermic and somewhat violent reaction of hydrogen peroxide with iron salts (ferrous sulfate). Fenton' s chemistry or Fenton's reagent uses a transition metal catalyst or an acid to enhance the oxidation chemical reaction of hydrogen peroxide by producing the hydroxyl radical, h l For in-situ chemical oxidation, the metal catalyst is usually provided by iron oxides within the soil or fill material, or added separately as a solubilized iron salt, such as iron sulfate. In addition, pH adjustment using an acid, such as sulfuric (H2SO4), is common since the chemical oxidation is more rapid and efficient under lower pH conditions (pH 2 to 4 is optimal). Fenton's chemistry has been well documented for over 100 years and has been in use in water treatment plants (Barb et al., 1950). IN-SITU REMEDIAITION Although Fenton's chemistry has been documented for well over 100 years, it has been employee safety and handling issues that have kept large numbers of environmental contractors from using in-situ chemical oxidation technology. Although this technology can be used safely, significant safety planning, worker training, personal protective equipment, on-site supervision, and monitoring must be an integral part of all oxidation projects. The chemical processes which essentially result in the destruction of petroleum hydrocarbons, and other volatile organic compounds, are well documented by Watts et al. (19909 1991 , and 1992), Watts and Stanton (1994), Arnarante (2000), Leethem (2002), and Kelly et al. (2002). Jacobs and Testa (2003) and Jacobs (2001), among others, have described oxidant delivery systems. CHEMICAL PROCESS When chemical oxidant H202 is injected at concentrations of 10 to 35% into the subsurface, it decomposes readily into reactive hydroxyl radicals (HO*) and water. The hydroxyl radical in the subsurface can be used to rapidly mineralize hydrocarbon, solvent, and other contaminants to water and carbon dioxide. This reaction is enhanced 1