Soil Flushing

Description

Soil flushing is a technology used for extracting contaminants from the soil. It works by applying water to the soil. The water has an additive that enhances contaminant solubility. Contaminants that are dissolved in the flushing solution are leached into the groundwater, which is then extracted and treated. In some cases, the flushing solution is injected directly into the groundwater. This raises the water table into the capillary fringe just above the surface of the water table, where high concentrations of contaminants are found. In many instances, surfactants (i.e., detergent-like substances) or solvents are used as the additive. The effectiveness of this process is dependant on hydrogeologic variables (e.g., type of soil, soil moisture) and type of contaminant.

Limitations and Concerns

Flushing additives may leave small residuals in the soil or groundwater, and should be evaluated on a site-specific basis.

There is the potential of washing the contaminant beyond the capture zone and the introduction of surfactants to the subsurface. The technology should be used only where flushed contaminants and soil-flushing fluid can be contained and recaptured.

Additives must be recovered from the underlying aquifer and, when possible, should be recycled.

Treatment of the recovered fluids forms residual sludges that musty be treated or disposed of.

Recovered groundwater may need treatment to meet appropriate discharge standards.

If used to extract volatile organic compounds (VOCs), air emissions should be treated.

Low permeability soils, such as clays, are difficult to treat with this method.

Surfactants may reduce soil porosity, and therefore should only be used on a case by case basis.

Applicability

Soil flushing technology removes metals, including radioactive contaminants, and VOCs, SVOCs, fuels, and pesticides from soil. It is usually less cost-effective for organic materials.

Technology Development Status

Soil flushing is a developing technology that has had limited use. Typically, laboratory and field treatability studies must be performed under site-specific conditions before soil flushing is selected as the remedy.

Web Links

http://www.lgst.com/matrix/section4/4_8.html

Other resources

None have been identified.