Soil washing removes adsorbed contaminants from soil particles. The process involves excavating the contaminated soil and washing it with a leaching agent, a surfactant, or chelating agency or adjusting the pH (U.S. EPA 1990c). Sometimes extraction agents are added to enhance the process. The process reduces the volume of contaminant; however, residual suspended solids and sludges from the process may need further treatment since they contain a higher concentration of contaminant than the original. The technology is effective for halogenated semivolatiles, fuel hydrocarbons, and inorganics (U.S. EPA 1993a).
The technology, however, is less effective when the soil contains a high percentage of silt and clay particles or high organic content. In addition, this technology reduces the volume of the contaminants, but the toxicity of the contaminants is unchanged.
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