c/EPA
United States
Environmental Protection
Agency
EPA/540/MR-94/527
November 1994
SUPERFUND INNOVATIVE
TECHNOLOGY EVALUATION
Demonstration Bulletin
540MR94527
Radio Frequency Heating
IIT Research Institute
Technology Description: Radio frequency heating (RFH) is
a process that uses electromagnetic energy generated by radio
waves to heat soil in situ, thereby potentially enhancing the
performance of standard soil vapor extraction (SVE) technolo-
gies. An RFH system developed by the IIT Research Institute
(IITRI) was evaluated under the Superfund Innovative Technol-
ogy Evaluation (SITE) Program at Kelly Air Force Base (AFB) in
San Antonio, TX. This demonstration was performed in conjunc-
tion with a technology evaluation being performed by the U.S.
Air Force (USAF) at Site S-1, a former waste disposal site
containing a heterogeneous mix of clayey soils and gravel.
Figure 1 is a schematic diagram of IITRI's RFH system. A 40-
kW radio frequency (RF) transmitter was used as the RF energy
source for the system. The operating frequency and other op-
erational parameters were selected based on soil dielectric
properties.
The four exciter electrodes were installed in a row in the center
of the treatment zone. Two rows of eight ground electrodes
each were installed parallel to and on either side of the exciter
electrode row. Above-ground components connected to the
ground electrodes completed the RF containment system. A
groundwater dewatering system was installed to lower the water
table to below the bottom of the design treatment zone.
The outer casings of most of the ground electrodes were perfo-
rated on the sides facing the treatment zone to permit the
collection of vapors from the soil. The perforated ground elec-
trodes were connected to a manifold that led to the vapor
treatment system. Two perforated vapor extraction pipes were
also installed parallel to the ground surface to prevent buildup of
vapors below the vapor barrier. A vapor barrier covered the
surface of the soil in and around the treatment zone to prevent
heat loss, contaminant migration, and air infiltration.
The vapor extraction system was operated for a period of 8Vz
weeks during which soil heating occurred and for an additional
17 days during which the treated soil was albwed to cool. Soil
cool-down was allowed to continue for approximately another 8
weeks before final soil sampling. Vapors were channeled through
a vapor collection system to a vapor treatment system. Vapors
that condensed in the vapor collection and treatment systems
were collected, and then transferred to a Kelly AFB facility for
further treatment. Uncondensed vapors were burned in a natural
gas flare. The vapor treatment system was site- and contami-
nant-specific and was not evaluated as part of the RFH system.
Waste Applicability: RFH is a potential enhancement for in
situ SVE systems. According to IITRI, their RFH technology is
not currently ready for commercialization. IITRI is continuing
Vapor_Barrier_Perjmete_r _
60 Hz
AC Power
Distribution
Temperature
Measurement
Probe Lines
Figure 1. Schematic diagram of IITRI's RFH system.
Printed on Recycled Paper
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technical development of a system that they believe will be
commercially available in the future. RFH is designed to speed
the removal of volatile organics and to make It possible to
remove semivolatile organics that would not normally be re-
moved by standard SVE technologies. Inorganic, metal, and
other nonvolatile contaminants would not normally be treated by
SVE or RFH technologies. This technology is applicable only to
wastes located above the water table, unless saturated soils can
be effectively dewatered.
Demonstration Results: IITRI's design treatment zone for
the demonstration was a plot of soil 10ft wide, 14.1ft long, and
23.3ft deep. The treatment zone was part of an intermediate
storage area for wastes destined for off-base reclamation, and
the soil was contaminated with mixed solvents, carbon cleaning
compounds, and petroleum oils and lubricants. Temperatures
within and outside the treatment zone were monitored at various
depths throughout the treatment period. Serious operational dif-
ficulties, as exemplified by the melting of copper electrodes,
caused inconsistent and inefficient heating of the treatment zone.
Maximum temperatures within the treatment zone ranged from
more than 1,000°C near the exciter electrodes to less than 50°C
near the bottom corners of the treatment zone. The design
treatment zone contained approximately 3,280ft3 of soil. The
"heated zone" is the area in which a time-weighted average
temperature of at least 150°C was maintained for at least 2
weeks. The heated zone contains an estimated 1,270ft3 of soil.
The heated zone was evaluated independently of the design
treatment zone.
Changes in soil contaminant concentrations were evaluated us-
ing matched pairs of pre- and post-treatment samples, which
were collected as close to one another as possible. Within the
design treatment zone, 28 matched pairs of samples were col-
lected; 9 matched pairs were collected outside the treatment
zone. Both pre- and post-treatment contaminant concentrations
varied considerably, making it difficult to determine statistically
significant removals.
Final statistical analyses have not yet been completed for either
the heated zone or the design treatment zone. Preliminary sta-
tistical analyses for the design treatment zone indicate that total
recoverable petroleum hydrocarbons (TRPH), pyrene, and bis(2-
ethylhexyl)phthalate exhibited statistically significant decreases
(at the 80% confidence interval). Chlorobenzene concentrations
appear to have increased during treatment, potentially due to
volatilization of chlorobenzene present in the groundwater. Sig-
nificant concentrations of 2-hexanone, 4-methyl-2-pentanone,
acetone, and methyl ethyl ketone were found in the post-treat-
ment soils, although virtually no ketones were found before
treatment. Soil temperatures, sometimes as high as 1,000° C,
may have caused partial oxidation of petroleum hydrocarbons.
Alternatively, these ketones may have been volatilized from
groundwater. At this time insufficient data are available to deter-
mine the source of ketones found in post-treatment soils.
An Innovative Technology Evaluation Report and a Technology
Evaluation Report describing the complete demonstration will
be available by summer 1995.
For Further Information:
EPA Project Manager:
Laurel Staley
U.S. Environmental Protection Agency
Risk Reduction Engineering Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
(513) 569-7863
Kelly AFB Project Engineer:
Ms. Victoria Wark
SA-ALC/EMRO
305 Tinker Drive, Suite 2, Building 305
Kelly AFB, TX 78241-5915
(210) 925-1812
Halliburton NUS Project Manager:
Mr. Clifton Blanchard
Halliburton NUS
800 Oak Ridge Turnpike, Suite A600
Oak Ridge, TN 37830
(615)483-9900
Process Vendor:
Mr. Harsh Dev
I IT Research Institute
10 West 35th Street
Chicago, IL60616
(312) 567-4257
USAF RF Program Manager:
Paul F. Carpenter
AL/EQW-OL
139 Barnes Drive, Suite 2
Tyndall AFB, FL 32403
(904) 283-6187
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
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EPA
PERMIT No. G-35
EPA/540/MR-94/527
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