Description

Soil flushing is an in-situ extraction of inorganic and organic compounds from soil, and is accomplished by passing extractant solvents through the soils using an injection and recirculation process. Solvents may include: water, water-surfactant mixtures, acids, bases (for inorganics), chelating agents, oxidizing agents, or reducing agents. Soil washing consists of similar treatments, but the soil is excavated and treated at the surface in a soil washer.

A simplified drawing of the soil washing process is illustrated in Figure 11.15.6. The contaminated soil is removed to a staging area, then sifted to remove debris and large objects such as rocks. The remaining material enters a soil scrubbing unit, is mixed with a washing solution, and agitated. The washing solution may be water, or may contain some additives like detergent to remove contaminants. Then the washwater is drained and the soil is rinsed with clean water. The heavier sand and gravel particles in the processed soil settle out and are tested for contaminants. If clean, these materials can be used on site or taken elsewhere for backfill. If contaminated, these materials may undergo soil washing again.

The contaminated silt and clay in the washwater settle out and are then separated from the washwater. The wash-water, which also contains contaminants, undergoes wastewater treatment processes for future recycling use. This wastewater may contain additives that interfere with the wastewater treatment process. If so, the additives must be removed or neutralized by pretreatment methods before wastewater treatment. The silts and clays are then tested for contaminants. If clean, these materials can be used on the site or taken elsewhere for backfill. If contaminated, these materials may undergo soil washing again, or be collected for alternate treatment or off-site disposal in a permitted RCRA landfill.

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