United States
                  Environmental Protection
                  Agency
          Office of Solid Waste
          and Emergency
          Response (5102G)
                                 EPA 542-F-98-002
                                 October 1996
                                 www.ciu-m.com
v>EPA      Recent  Developments  for In Situ Treatment
                  of Metal  Contaminated Soils
                  Fact Sheet and Order Information
   This report (EPA 542-R-97-004) provides status information on four in situ technologies for treating
   soil contaminated with metals:
   • Electrokinetic remediation  •  Phytoremediation  • Soil flushing •  Solidification/stabilization
   The report discusses different techniques currently in practice or under development; identifies
   vendors and summarizes performance data; and discusses technology attributes that should be
   considered during early screening of potential remedies.
SUMMARY

Metals are prevalent at most Superfund sites. Almost
three-quarters of these sites with signed Records of
Decision (ROD) are contaminated with metals as the sole
contaminant group (approximately 16%) or in combination
with other contaminant groups such as volatile or semi-
volatile organic compounds.  In situ remedies should be
capable of providing cost savings, when compared with
traditional disposal methods, and are being selected  more
frequently at Superfund sites. However, relatively few
alternatives exist for the in situ treatment of metals.

This report provides hazardous waste cleanup
professionals with a status update on available and
promising technologies for in situ remediation of soil
contaminated with heavy metals. The report is intended
to assist in screening new technologies early in the remedy
evaluation and selection process.

Electrokinetics

Electrokinetic remediation relies on the application of low
density direct current between electrodes placed in the
soil. Contaminants  are mobilized in the form of charged
species, particles, and ions. Several organizations are
   source of
   contaflnrnation
                 ,-- 'plume' of „
                 contaminants.
   direction of
   grouhdwater flow
current
lines
Contaminated Plume Stopped by Electrokinetic Fence
developing technologies for the enhanced removal of
metals by transporting contaminants to the electrodes
where they are removed and subsequently treated above
ground.

Experience with this technology is limited to bench and
pilot scales, with the notable exception of a metal removal
process that has been commercially operated by a single
vendor in Europe and recently licensed in the United
States. Limited performance data from this vendor
illustrate the potential for achieving removals greater than
90 percent for some contaminants.

A broad range of metals is potentially treated by this
technology. The commercial applications in Europe
treated copper, lead, zinc, arsenic, cadmium, chromium,
and nickel. There is also potential applicability for
radionuclides and some types of organic compounds.
Electrokinetics also can be used to slow or prevent
migration of contaminants by configuring cathodes and
anodes in a manner that causes contaminants to flow
toward the center of a contaminated area of soil. The
practice has been named "electrokinetic fencing."

Phytoremediation

This technology is in the early  stage of commercialization,
and in the future may provide  a low cost option under
specific circumstances.  At the  current stage of
development  for treatment of metals, this process is best
suited for sites with widely dispersed contamination at low
concentrations where only treatment of soils at the surface
(that is, within depth of the root zone) is  required.

Two basic approaches for metals remediation include
phytoextraction and phytostabilization. Phytoextraction
relies on the uptake of contaminants from the soil and
their translocation into aboveground plant tissue, which is
harvested and treated.  Although hyperaccumulating trees,
shrubs, herbs, grasses, and crops have potential, crops seem
to be most promising because of their greater biomass

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production. Nickel and zinc appear to be the most easily
absorbed, although preliminary tests with copper and
cadmium are encouraging. Significant uptake of lead,
a commonly occurring contaminant, has not been
demonstrated in any of the plants tested thus far.
However, one researcher is experimenting with soil
amendments that make lead more available for uptake
by plants,

Soil Flushing
Soil flushing involves extraction of contaminants from
soil using water or other suitable aqueous solutions.
Although additives such as acids and chelating agents
have had limited commercial use for full-scale ex situ
soil washing projects, they have not been demonstrated
as feasible for in situ applications.

Soil flushing has been selected at seven Superfund sites
with metals present; however, at six of those sites,
organic contaminants are  the primary targets.  Soil
flushing is most effective in removing hexavalent chrome,
            Spray Application
             **"  ,. "** /""*"

                        Pump
                                   Graundwaler
                                   Treitment
Pump
 ~
                                 Groundwater
                                  Treatment

                         — Contaminated Area
  Lcachate
  Collection
   1
                     Low Permeability
                          Zone
              due to its solubility in water. Two soil flushing remedies
              are currently ongoing at Superfund sites, with some
              preliminary data available from a hexavalent chrome
              application.

              Solidification/stabilization
              This process (also referred to as immobilization) changes
              physical characteristics of the waste in order to immobilize
              contaminants. Metals are commonly remediated by ex situ
              solidification with pozzolans and possibly other additives.
              This technology also can be adapted to an in situ technique
              through the use of various proprietary- augers that provide
              mechanisms for reagent delivery and mixing.  In situ
              treatment likely will have a cost advantage over
              ex situ applications for larger volumes and for depths
              greater than 10 feet.  However, in situ immobilization is
              rarely selected for Superfund use, largely because of
              concerns with thoroughness of mixing and long-term
Typical Soil Flushing System (Surface Sprinklers)
A second in situ solidification technique involves
vitrification where an electrical current is passed between
electrodes to melt soil and incorporate metals into a
vitrified product.  This technology is commercially available
and has been successfully used at two Superfund sites.

Both processes are broadly applicable to a range of
metals.  Vitrification uses a hood to capture mercury and
other volatile metals, such as lead and arsenic, which may
be partially vaporized during operations.  Vitrification is
best suited for wastes that are difficult to treat, such as
mixtures of organics and metals.

ORDER  INFORMATION

This report (EPA 542-R-97-004) is available free from the
EPA National Center for Environmental Publication and
Information (NCEPI) at 800-490-9198 or 513-489-8190, or
fax 513-489-8695. It is also viewable and downloadable
from the Internet at http://www.clu-in.com
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