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 typically found. In many instances, surfactants
(i.e., detergent-like substances) or solvents
are
used as the additive. The effectiveness of this process is dependent on
hydrogeologic
variables (e.g., type of soil, soil moisture) and the type of
contaminant.
Limitations
and Concerns
Flushing
additives may
leave small residuals
in the soil or groundwater, and they should be evaluated on a
site-specific
basis.
Flushing may
spread the
contaminant beyond the capture zone or to introduce surfactants to the
subsurface, so 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 must
be treated or disposed.
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 they should only be used on a case-by-case basis.
Applicability
Soil flushing
technology
removes metals (including radioactive
contaminants), VOCs, SVOCs,
PCBs, fuels, and pesticides
from soil. It may also be used to remove ordnance compounds from soil.
Technology
Development Status
Soil flushing is
proven
technology. 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.frtr.gov/matrix2/section4/4-6.html
http://www.clu-in.org/download/remed/flush_o.pdf
http://www.clu-in.org/download/citizens/insituflushing.pdf
Other
resources
See http://www.clu-in.org/products/isf/
for a project database.