x>EPA
United States
Environmental Protection
Agency
EPA/540/MR-94/520
August 1994
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
In Situ Vitrification
Geosafe Corporation
Technology Description: in Situ Vitrification (ISV) is de-
signed to treat soils, sludges, sediments, and mine tailings con-
taminated with organic and inorganic compounds. The process
uses electrical current to heat (mett) and vitrify the soil in place.
Organic contaminants are decomposed by the extreme heat into
simple gases, which then rise through and escape from the
molten soil. Inorganic contaminants are trapped within the molten
soil, which cools and solidifies into a glassy monolith.
The ISV technology demonstrated by Geosafe Corporation
(Richland, Washington) operates by means of four graphite elec-
trodes, arranged in a square, and inserted into the soil to be
treated. A pattern of electrically conductive graphite containing
glass frit is placed on the soil in paths between the electrodes.
When power is fed to the electrodes, the graphite and glass frit
conducts the current through the soil, heating the surrounding
area and melting directly adjacent soil. Molten soils are electri-
cally conductive and can continue to carry the current which
heats and melts soil downward and outward. The electrodes are
allowed to progress down into the soil as it becomes molten,
continuing the melting process to the desired treatment depth. As
treatment progresses, a "cold cap" of solidified material forms at
the surface. When all of the soil in the treatment area becomes
molten, the power to the electrodes is discontinued and the
molten mass begins to cool. The electrodes are cut near the soil
surface and are allowed to settle into the molten soil to become
part of the melt. (One setting of four electrodes is referred to as a
"melt.") After the molten soil cools a glass and crystalline vitrified
material remains.
The organic contaminants in the soil undergoing treatment are
pyrolyzed (heated to decomposition without oxygen) and are
generally reduced to simple gases. The gases migrate through
the molten soil and/or the adjacent dry zone to the surface, often
following the path of the electrodes where the mass is least
viscous. Gases at the surface are collected in a stainless steel
hood placed over the area being treated. The hood is hexagonal
and approximately 60 ft (18 meters) in diameter. It is sealed at
the soil surface with clean fill and kept at a negative pressure
during treatment to prevent the gases from escaping out of the
system. Gases from the hood are treated in an off-gas treatment
system, comprising a quencher, a scrubber, a demister, HEPA
filters for particulates, and activated carbon adsorption to process
the off-gas before releasing the cleaned gas through a stack. A
thermal oxidizer can be used after the off-gas treatment system,
if necessary, to polish the off-gas before release to the atmo-
sphere. A generator-run back-up gas treatment system is also
connected to the hood, and is designed to be activated automati-
cally in case of power interruption.
Inorganic contaminants in the soil are generally encapsulated in
the molten soil which hardens to a vitrified mass that has charac-
teristics similar to volcanic obsidian. The vitrified soil is dense
and hard, and significantly reduces the possibility of leaching
from the mass over the long term. Since the vitrification process
removes most of the void space in the soil, as well as destroys
the organic contamination, a volume reduction of 20 to 50% is
achieved by the technology, leaving a subsidence volume at the
top of the treated block. This volume is backfilled with clean soil
immediately after treatment.
A large area of contaminated soil is treated by consecutive melts,
which are spaced to overlap along the edges and form one
continuous monolith. Treatment of each melt occurs at a rate of-
approximately four to six tons per hour. The melt performed
during the Demonstration Test took approximately 10 days to
complete.
Demonstration Approach: A Demonstration Test of ISV was
conducted at the Parsons Chemical Site in Grand Ledge, Michi-
gan. The demonstration was performed in conjunction with cleanup
operations occurring at the site under the direction of EPA Re-
gion V. Soil at the site was contaminated with low levels of
pesticides and mercury. Before treatment with ISV the contami-
Off-gas collection hood
I
Off-gases to
treatment
Bectroda
Soil surface
tionductive beating
Figure 1. Diagram of an ISV treatment mett.
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nated soil was staged in open concrete trenches designed for
nine treatment settings. The trenches were lined with cobble and
wood, and surrounded by clean soil.
Prforto the Demonstration Test, treatment of the staged areas by
the Geosafe ISV system had been ongoing for several months as
a part of the Parsons site cleanup action. The Demonstration
focused on the treatment of Cell 8. This cell was selected for
Demonstration Test sampling by the SITE Program because Re-
gion V data indicated that this was the most contaminated cell.
This cell was treated relatively late in the melt order to give the
developer a chance to shake down and optimize the equipment
and procedures before the SITE demonstration.
The effectiveness of the ISV technology was investigated through
sampling of solid, liquid, and gas matrices. The soil in the treat-
ment cell was sampled before treatment and analyzed for pesti-
cides and metals. During the test samples of the scrubber water
were collected before, during, and after the treatment of Cell 8.
Gas samples from the thermal oxidizer stack were collected
during treatment of Cell 8 and were analyzed for volatile and
somivolatile organic compounds, pesticides, dioxins/furans, met-
als, HCI, and participates. Continuous emission monitoring for
total hydrocarbons, oxygen, and carbon monoxide was conducted
throughout treatment by the developer. After the soil in the Cell 8
was treated by the technology, samples of the vitrified material on
the surface were collected and analyzed for pesticides and met-
als. The TCLP (toxicity characteristic leaching procedure) was
also performed on these samples to determine the teachability of
pesticides and mercury in the vitrified material. Additional samples
of the treated material will be collected after the treated soil has
completely cooled and solidified (approximately one year after
treatment).
A detailed economic analysis of this full-scale technology applica-
tion will be performed utilizing collected data (i.e., power usage,
labor requirements, waste generation, maintenance needs, etc.).
This data was collected by the developer and the SITE program
during the course of operation.
Preliminary Results: Preliminary evaluation of the post-treat-
ment data suggests the following conclusions:
* The technology treated the soil as expected, completing the
melt in 10 days. During this time approximately 330 yd3 (250 m3)
of contaminated soil was vitrified according to Geosafe melt
summaries. Approximately 613,OOOkWh of power was applied
to the total soil volume during vitrification of Cell 8. This total soil
volume exceeds the contaminated soil volume because clean
fill and surrounding uncontaminated soil are treated as part of
each melt.
• The cleanup levels specified by EPA Region V for chlordane,
4,4-DDT, dieldrin and mercury were met. Pesticide concentra-
tions were reduced to non-detectible levels in the vitrified soil.
• The solid vitrified material collected was subjected to TCLP for
mercury and pesticides. The test results indicated that leach-
able mercury was well belowthe regulatory guidelines (40 CFR
part 261.24), arid no target pesticides were detected in the
leachate.
• Samples of the stack gas after the off-gas treatment system
were collected during the Demonstration Test to characterize
process emissions. There were no target pesticides detected
in the stackgas samples. Metal emissions were below regula-
tory requirements during the Demonstration Test. Continuous
emission monitoring of the gas showed that total hydrocarbon
and carbon monoxide emissions were in compliance with EPA
Region V limits.
--•• Scrubber water generated during the Demonstration Test
contained partially oxidized semivolatile organics (phenolics),
volatile organics, mercury, and other metals. The scrubber
water required secondary treatment before ultimate disposal.
• The system ran continuously for approximately 10 days with
only minor operational problems. System operation was inter-
rupted for routine maintenance such as electrode segment
addition and adjustment.
Key findings from the demonstration, including complete analyti-
cal results and the economic analysis, will be published in an
Innovative Technology Evaluation Report. This report will be
used to evaluate the Geosafe ISV technology as an alternative
for cleaning up similar sites across the country. Results will also
be presented in a SITE Technology Capsule and a videotape.
For Further Information:
EPA Project Manager:
Teri Richardson
U.S. Environmental Protection Agency
Office of Research and Development
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7949
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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PERMIT No. G-35
EPA/540/MR-94/520
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