Neutralization And Detoxification

In situ neutralization and detoxification involves injecting a substance into groundwater that neutralizes or destroys a contaminant. The technology is limited to contaminants that can be neutralized or degraded to nontoxic byproducts. Neutralization and detoxification is applicable to both organic and inorganic compounds. Selecting a treatment agent depends on the type of contaminant and the characteristics of the subsurface environment such as tem

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perature, permeability, pH, salinity, and conductivity. Examples of in situ treatment agents include hydrogen peroxide that can be injected directly into groundwater through existing monitoring wells or subsurface drains (Vigneri 1994). Hydrogen peroxide produces the hydrogen free radical OH, an extremely powerful oxidizer which progressively reacts with organic contaminants to produce carbon dioxide and water.

Other in situ neutralization and detoxification technologies include precipitation and polymerization. Precipitation involves injecting substances into the ground-water plume which form insoluble products with the contaminants, thereby reducing the potential for migration in groundwater (U.S. EPA 1985). This technique is mainly applicable to dissolved metals, such as lead, cadmium, zinc, and iron. Some forms of arsenic, chromium, and mercury and some organic fatty acids can also be treated by precipitation (Huibregts and Kastman 1979). The most common precipitation reagents include hydroxides, oxides, sulfides, and sulfates. As with other in situ techniques, precipitation is only applicable to sites with aquifers having high hydraulic conductivities. The major disadvantages of precipitation are that it can only be applied to a narrow, specific group of chemicals (mainly metals); that a potential groundwater pollutant may be injected; that toxic gases (as in sulfide treatment) may form; and that the pre-cipate may resolubilize (U.S. EPA 1985).

In situ polymerization involves injecting a polymerization catalyst into the nonaqueous organic phase of a contaminant plume to cause polymerization (U.S. EPA 1985). The resulting polymer is gel-like and nonmobile in the groundwater flow regime. Polymerization is a specific technique that is applicable to organic monomers such as styrene, vinyl chloride isoprene, methyl methacrylate, and acrylonitrile (Huibregts and Kastman 1979). In a hazardous waste site where groundwater pollution has occurred over time, any organic monomers originally present would most likely have polymerized upon contact with the soil (U.S. EPA 1985). Therefore, in situ polymerization is a technique most suited for groundwater cleanup following land spills or underground leaks of a pure monomer. The major disadvantages of polymerization include its limited application and the difficulty of initiating sufficient contact of the catalyst with the dispersed monomer (Huibregts and Kastman 1979).

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