Hydrogen peroxide is particularly effective when it reacts with ferrous iron (Fe2+ ) to produce Fenton's Reagent. Ferrous iron may be naturally present in the subsurface soils and/or groundwater, or it can be added as a catalyst solution together with the hydrogen peroxide to produce this aggressive chemical reaction. Hydrogen peroxide in the presence of ferrous iron (Fe2+ ) reacts to form hydroxyl radicals (OH•), ferric iron (Fe3+ ), and hydroxyl ions (OH- ). The hydroxyl ions are very powerful oxidizers, and react particularly with organic compounds. The hydroxyl radicals break the petroleum hydrocarbon bonds of common petroleum constituents such as benzene, toluene, ethylbenzene, and xylene, as well as.