In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
POPS-WASTES APPLICABILITY (REFS. 4 AND 16):
ISTD is a thermally enhanced in-situ treatment technology that uses conductive heating elements to
directly transfer heat to environmental media. ISTD can heat soil or sediment in situ to average
temperatures of 1,000 degrees Fahrenheit (°F), and as a result has been used to treat compounds with
relatively high boiling points. Some of these include semivolatile organic contaminants (SVOCs) such
as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), pesticides, and
herbicides. Pilot- and full-scale applications have been performed where ISTD has been used to
remove PCBs, and where dioxins and furans were trace contaminants. TerraTherm is the sole vendor
for ISTD. According to TerraTherm, laboratory-scale work and extrapolation techniques have
suggested the potential applicability of ISTD to POPs other than PCBs, dioxins, and furans (including
aldrin, dieldrin, endrin, chlordane, heptachlor, DDT, mirex, hexachlorobenzene, and toxaphene);
however, these contaminants have not yet been treated using ISTD on a full- or pilot-scale basis. ISTD
has been used to treat contaminants in most hydrogeologic settings, including beneath structures.
POPs Treated:
Other Contaminants Treated:
PCBs, dioxins, and furans, aldrin, chlordane, dieldrin, and endrin
Hexachlorocyclopentadiene, isodrin, VOCs, SVOCs, oils, creosotes,
coal tar PAHs, gasoline and diesel range organics, and MTBE
Well-field
TECHNOLOGY DESCRIPTION (REFS. 2,4,13 AND 16):
OVERVIEW
ISTD involves simultaneous application of heat and vacuum to subsurface soils. There are three basic
elements in an ISTD process: (1) application of heat to contaminated media; (2) collection of desorbed
contaminants through vapor extraction; and (3) treatment of collected vapors. Figure 1 presents a
typical ISTD system.
Figure 1
Typical ISTD System
ISTD has been used at full scale
to treat PCBs, PAHs, dioxins,
and chlorinated volatile organic
compounds (CVOC). At the
temperatures achieved by the
ISTD process, volatiles metals
such as mercury may also be
recovered.
In-Situ Heating
ISTD uses surface or buried
electrically powered heaters to heat contaminated media. The most common setup uses a vertical
array of heaters placed inside wells drilled into the remediation zone. A less common setup uses the
same type of heaters installed horizontally on the surface of the contaminated zone. This method of
heating (often called blanket heating) is typically used when contamination is shallow (usually 1 to 3
feet below ground surface (bgs)). Figure 2 illustrates the two different methods of heating.
ISTD heaters can attain temperatures as high as 1,600 degrees °F, and can produce average media
temperatures exceeding 1,000 °F. Heat originates from a heating element and is transferred to the
subsurface largely via thermal conduction and radiant heat transport, which dominates near the heat
sources. There is also a contribution through convective heat transfer that occurs during the formation
of steam from pore water present in the soil or sediment.
The thermal conductivity values of a wide range of soil types (e.g., clay, silt, sand, gravel) vary only by
a factor of approximately four. Therefore, the rate of heat transfer from the linear heaters to the
surrounding media is radially uniform. When heating commences, the temperature profile in the
remediation zone is characterized by large gradients, and temperatures decrease sharply with distance
from the source. Overtime, superposition of heat from adjacent heaters tends to even out these
differences.
Vapor cap
Source: TerraTherm™ Inc.
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
Figure 2
Blanket and Thermal Well Heating
Source: TerraTherm™ Inc.
Vapor Extraction
As the matrix is heated, adsorbed and liquid-
phase contaminants begin to vaporize. A
significant portion of organic contaminants
either oxidize (if sufficient air is present) or
pyrolize once high soil temperatures are
achieved. Desorbed contaminants are
recovered through a network of vapor-
extraction wells.
Vapor extraction wells are also heated to
prevent condensation of contaminants inside
the well. A vacuum is applied to these wells to
induce air flow through the contaminated
media creating a zone of capture.
Contaminant vapors captured by the
extraction wells are conveyed to an offgas
treatment system for treatment prior to
discharge to the atmosphere.
Offgas Treatment (Ref. 2)
TerraTherm offers two different methods of
vapor treatment. One treats extracted vapor
without phase separation (Figure 1), and the
other cools heated vapor, separates the resulting phases, and manages each phase separately.
The vapor treatment option depicted by Figure 1 uses a thermal oxidizerto break down organic vapors
to primarily carbon dioxide and water. Stack sampling has demonstrated that toxic pollutants in offgas,
including dioxins, are substantially below regulatory standards. When influent vapors contain
chlorinated compounds, hydrogen chloride (HCI) gas is produced. In such cases, the exhaust from the
thermal oxidizer is passed through an acid gas scrubber to capture HCI gas.
The other vapor treatment option uses a heat exchanger to cool extracted vapors. The resulting liquid
phase is then separated into aqueous and nonaqueous phases. The nonaqueous phase liquid (NAPL)
is usually disposed of at a licensed treatment storage and disposal facility. The aqueous phase is
passed through liquid-phase activated carbon adsorption units and then released into the environment.
Cooled, uncondensed vapor is passed through vapor-phase activated carbon adsorption units and then
vented to atmosphere.
Although setup varies from site to site, several components of the remediation system including
heaters, blowers, and offgas treatment equipment are either standard or adaptable to new situations,
with equipment reused from site to site. Downhole wells may not be salvageable and may be plugged
and abandoned in place.
STATUS AND AVAILABILITY (REFS. 4 AND 5):
ISTD is a patented technology originally developed by Shell Oil. While U.S. Patent rights were donated
to the University of Texas (UT), patent rights outside the U.S. were retained by Shell. TerraTherm
holds the exclusive license to this technology from both UT and Shell, and is currently the only vendor.
ISTD has been commercial for several years. Its ability to remove PCBs from contaminated soil was
first demonstrated more than 6 years ago. As shown on Table 1, ISTD has been used at six POP-
contaminated sites. Implementation at four of these sites was full scale, and the other two were pilot
scale.
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
Table 1
Performance of ISTD at POPs Contaminated Sites (Refs. 2, 4 and 7)
Site Name
Former South
Glens Falls
Dragstrip,
Moreau, New
York
Tanapag
Village, Saipan,
NMI
Centerville
Beach,
Ferndale, CA
Missouri
Electric Works,
Cape
Girardeau, MO
Former Mare
Island Naval
Shipyard,
Vallejo, CA
Former Wood
Treatment
Area,
Alhambra, CA
Year
1996
1997-
1998
1998-
1999
1997
1997
2002-
2005
Scale
Full
Full
Full
Pilot
Pilot
Full
Contaminant
PCB
1248/1254
PCB
1254/1260
PCB 1254
Dioxins and
Furans
PCB 1260
PCB
1254/1260
Dioxins
Concentration
Initial
5,000
(Max)
10,000
(Max)
860
(Max)
3.2 (Max)
20,000
(Max)
2,200
(Max)
18
(Mean)
Final
<0.8
<1
<0.17
0.006 '
< 0.033
< 0.033
0.01
Goal
2
10
1
1
2
1
1
Units
mg/kg
mg/kg
mg/kg
ug/kg
TCDD
mg/kg
mg/kg
ug/kg
Note:
Avg Average concentration
Max Maximum concentration
mg/kg Milligrams per kilogram (or parts per million)
NMI Northern Mariana Islands
ND Below detection limit
TCDD Tetrachlorodibenzodioxin equivalents
ug/kg Micrograms per kilogram (or parts per billion)
1 Final concentration presented as average of residual concentrations in treatment area.
DESIGN (REF. 12):
Key design factors for ISTD include the number and depth of heater wells and vacuum wells, as well as
the requirements for electrical power and treatment of off gasses. These factors are affected by the
type of contaminants present, concentration of the contaminants, extent of contamination, soil type,
hydraulic conductivity, permeability, thermal properties, location of the water table, availability of site
facilities such as electrical power supply, and regulatory issues.
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
THROUGHPUT (REF. 5):
ISTD has been used to treat volumes as low as a few hundred cubic yards to greater than 20,000 cubic
yards in 6 to 9 months. Factors affecting cleanup durations can include type of contaminants,
cleanup/remedial goals, and site geology.
WASTES/RESIDUALS (REFS. 3 AND 5):
Wastes produced by ISTD are likely to result from the treatment of extracted vapors, and vary
according to the type of treatment they are subjected to. Offgas treatment options that employ phase
separation techniques could produce process wastes such as NAPL, spent liquid- and vapor-phase
activated carbon, and inorganic salts as waste products. For example, the treatment of chlorinated
vapors in a thermal oxidizer results in the production of HCL gas. A wet or dry acid gas scrubber used
to neutralize HCI gas will produce inorganic salts as a waste product.
NAPL is typically transported off site for disposal at a licensed facility. Spent activated carbon may
either be disposed of, or regenerated at a licensed facility. Inorganic salts produced from neutralization
processes are typically considered nonhazardous and are consequently disposed of as nonhazardous
waste.
MAINTENANCE (REF. 4):
Maintenance associated with ISTD includes the occasional replacement of heater elements. ISTD
operation is typically characterized by less than 5% downtime. Other maintenance needs include
treatment media replacement and thermal oxidizer refueling.
LIMITATIONS (REF. 4):
The following are some of the limitations of this technology:
• ISTD cannot address contaminants that do not volatilize with in the temperature range of
approximately 15-1000°C.
• As long as liquid water remains within the remediation zone, the temperature that can be
attained is limited to the boiling point of water (212 °F). Once the water is boiled off, higher
temperatures can be attained. A continuing source of water influx into the treatment zone will
undermine the ability of this technology to produce temperatures necessary for the removal of
POPs. For this reason, formation dewatering and implementation of water control measures
are needed prior to the implementation of ISTD in high-permeability, water-saturated zones.
• Though not always the case, cost can be a limiting factor. Unit costs for treatment are
influenced by several factors including scale of the project, depth of the treatment zone, depth
to water table, air emission controls, cost of labor and cost of power. However, in general, unit
costs in USD range from $200 to $600 per cubic yard corresponding to treatment volumes
ranging from less than 5,000 to approximately 15,000 cubic yards for POP-type contaminants.
Larger volumes may have lower unit costs. Treatment costs for VOC contaminants are lower.
FULL-SCALE TREATMENT EXAMPLES:
Centerville Beach (Refs. 6, 8,10 and 14)
The Centerville Beach Naval Facility is a 30-acre site in Ferndale, California that was used for
oceanographic research and undersea surveillance. The site was decommissioned in 1993.
Operations at the site lead to contamination of a particular area with PCBs. The PCB of concern was
Aroclor 1254 which was present in concentrations ranging from 0.15 to 860 milligrams per kilogram
(mg/kg). Dioxins and furans were also present at a maximum concentration of 3.2 micrograms per
kilogram (ug/kg) as 2,3,7,8-tetrachlorodibenzodioxin (TCDD) equivalents. The contaminated medium
was primarily silty clay. Groundwater was encountered below the contaminated zone at depths
exceeding 60 feet bgs.
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
From September 1998 through February 1999, approximately 1,000 cubic yards of PCB-contaminated
soil was treated using ISTD. Heater and vapor extraction wells were installed in a zone measuring 40
feet long, 30 feet wide, and 15 feet deep. The wells were installed 6 feet apart. Two sealed vacuum
blowers were used in parallel for vapor extraction. Offgas was treated using a flameless thermal
oxidizer (with greater than 99.99% demonstrated treatment efficiency), and two granular activated
carbon units configured in series. The total cost of the implementation in USD was approximately
$650,000.
The treatment goal was 1 mg/kg for PCBs and 1 ug/kg TCDD equivalent fordioxins and furans.
Remediation took place between September 1998 and February 1999. Treatment goals were met in
the bulk of the treatment area; however, one portion (178 cubic yards) still contained elevated
concentrations of PCBs. This was found to be caused by a previously undiscovered bank of PCB-
containing electrical conduits emanating from outside the treatment zone and passed into the treatment
area. Excavation and disposal was subsequently used to remove this area of contaminated soil and
the associated conduits.
Alhambra (Refs. 3, 9, 17 and 18)
Southern California Edison's (SCE) Alhambra Combined Facility occupies approximately 33 acres and
is currently used for storage, maintenance, and employee training. SCE carried out wood treatment
operations in SCE's 2-acre former wood treatment area between 1921 and 1957. The total volume of
contaminated soil was estimated to be 16,200 cubic yards of soil. The contaminated zone included a
variety of buried features including treatment tanks, the structural remains of the former boiler house
and tank farm, and various buried utilities. The contaminants of concern were PAHs,
pentachlorophenol (PCP), and dioxins. Total PAHs were present in site soils at a maximum
concentration of 35,000 mg/kg and an average concentration of 2,306 mg/kg. PCP was present at a
maximum concentration of 58 mg/kg and an average concentration of less than 1 mg/kg. Dioxins were
present at a maximum concentration of 0.194 mg/kg and an average concentration of 0.018 mg/kg
(expressed as 2,3,7,8-tetrachloro-dibenzodioxin [TCDD] Toxic Equivalency Quotient [TEQ]). The soil in
the remediation zone was composed of silty sands, inter-bedded with sands, silts, and clays. The
average thermal treatment depth was approximately 20 feet bgs and extended to 100 feet bgs in some
areas. The depth to the water table was greater than 240 feet bgs. The treatment goals were 0.065
mg/kg (expressed as benzo(a)pyrene [B(a)P] toxic equivalents) for PAHs; 2.5 mg/kg for PCP, and
0.001 mg/kg for dioxins (expressed as TEQ).
Remedial action at the site was conducted in
the site. The overall ISTD system for the two
vacuum and 654 heater-only wells) at a
7.0-ft spacing between thermal wells, as
well as an insulated surface seal, thermal
oxidizer, heat exchanger, and granular
activated carbon for off-gas treatment.
The ISTD began cleanup operations for
Phase I of the remediation of Area of
Concern (AOC)-2 in February 2003.
Confirmation soil samples were submitted
to DTSC in July 2004 which confirmed that
the cleanup goals for Phase I of AOC-2
had been achieved. Phase 2 of the
cleanup began in July 2004 and was
scheduled for completion by October 2004.
two phases. Each phase addressed a different area of
phases consisted of 785 thermal wells (131 heater-
Figure 3
Phase-1 Soil Sampling Results
30000
Goal: 65 |jg.'Kg
• Dioxins (2,37,8-TCDD TEQ)
Goal: ' ug"«J
ISO 048
23 0.01
Hie-1 leatmenl In lor in
Sampling Period
Source: TerraTherm™ Inc.
HcsMrealmenl
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
However, a previously undiscovered volume of free product made it necessary to reduce in-situ
temperatures in order to control organic contaminant concentrations in the offgas treatment system
influent. This resulted in an anticipated 10-month increase in the cleanup duration. Phase 2 of the
cleanup is expected to end in August 2005. The total cost of the implementation in USD was
approximately $10 million.
Rocky Mountain Arsenal Hex Pit (Ref. 15)
The Hex Pit was a former disposal pit at the U.S. Department of Army's Rocky Mountain Arsenal
(RMA). Shell Oil Company leased a portion of the RMA from 1952 to 1982 to manufacture pesticides.
The pit was used from 1947 to 1975 to dispose of residues from distillation and other processes used in
the production of hexachlorocyclopentadiene (hex), an ingredient in the manufacture of pesticides.
The main part of the Hex Pit measured approximately 94 ft by 45 ft, and varied from 8 to 10 ft deep.
The pit contained a total of 2,005 cubic yards of waste-contaminated materials, of which 833 cubic
yards was estimated to be waste.
The Hex Pit consisted primarily of soil and waste material originally disposed of in the pit. The
impacted soil (silty sand) was stained dark brown, rust orange, or black, and at times included granules
or globules of hex. Black, tar-like, relatively pure hex residue occurred in distinct solid layers of waste
(approximately 1-foot thick). Hex was not detected in groundwaterdowngradient of the Hex Pit
boundaries.
The contaminants of concern were hex, aldrin, chlordane, dieldrin, endrin, and isodrin. Only hex,
chlordane, and dieldrin had treatment goals. The treatment goals were 760 mg/kg, 67 mg/kg and 335
mg/kg respectively. Laboratory tests indicated that Hex Pit wastes could be effectively treated by the
ISTD process.
ISTD at the Hex Pit was designed to heat a treatment soil volume of 3,198 cubic yards, extending from
0 to 12 ft bgs and 5 ft laterally beyond the boundaries of the Hex Pit. Thermal wells on 6-foot centers
were installed in a hexagonal arrangement. A total of 266 wells were installed, of which 210 were
heater-only and 56 were heater-vacuum wells.
The target treatment temperature based on the boiling point of COCs was 325 °C. All heater-only wells
reached their operating temperatures in early March 2002. Treatment was expected to last 85 days
and end in May 2002. However, twelve days after commencement, corrosion was observed in some of
the well manifolds. Subsequent investigation and assessment determined that unforeseen
concentration of HCL gas and production of HCL (liquid) in the vapor conveyance system, resulting
from the highly concentrated wastes in the Hex Pit, had caused corrosion. Corrosion damage to the
ISTD system was significant. A determination was made that replacements with necessary corrosion
resisting matrices was cost prohibitive. Wastes were excavated and capped.
STATE CONTACT (CENTERVILLE
BEACH):
California EPA
Dept. of Toxic Substances
Control (DTSC)
Ms. Christine Parent
Phone: (916)255-3707
Email: CParent@dtsc.ca.gov
STATE CONTACT (ALHAMBRA):
California EPA
DTSC
Mr. Tedd E. Yargeau
Phone: (818)551-2864
Email: tyargeau@dtsc.ca.gov
VENDOR CONTACT:
Mr. Ralph Baker
TerraTherm™, Inc.
Tel: (978)343-0300
Email: rbaker@terratherm.com
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In Situ Thermal Desorption for
Treatment of POPs in Soils and Sediments
PATENT NOTICE:
ISTD is covered by a total of 22 U.S. patents, with 6 patents pending. TerraTherm is the exclusive
licensee through the University of Texas and Shell.
REFERENCES:
1. Baker, Ralph and Kuhlman, Myron. 2002. 2nd International Conf. on Oxidation and Reduction
Technologies for Soil and Groundwater, ORTs-2, Toronto, Ontario, Canada. A Description of
the Mechanisms of In-Situ Thermal Destruction (ISTD) Reactions. Nov. 17-21
2. Baker, Ralph, TerraTherm, Inc. 2004. Email to Chitranjan Christian, Tetra Tech EM Inc.,
Regarding Questions on ISTD. October27, Novembers, 15, 24 and 29.
3. Baker, Ralph, TerraTherm, Inc. 2004. Telephone Conversation with Chitranjan Christian,
Tetra Tech EM Inc., Regarding Questions on ISTD. October 29.
4. Heron, Gorm, TerraTherm, Inc. 2004. Email to Chitranjan Christian, Tetra Tech EM Inc.,
Regarding Questions on ISTD. October 15.
5. Heron, Gorm, TerraTherm, Inc. 2004. Telephone Conversation with Chitranjan Christian,
Tetra Tech EM Inc., Regarding Questions on ISTD. October 15.
6. Parent, Christine, California EPA, DTSC. 2004. Telephone Conversation with Chitranjan
Christian, Tetra Tech EM Inc., Regarding Questions on ISTD implementation at Centerville
Beach. November 2.
7. Stegemeier, G.L., and Vinegar, H.J. 2001. "Thermal Conduction Heating for In-Situ Thermal
Desorption of Soils," Chapter 4.6, pages 1-37. Chang H. Oh (ed.), Hazardous and Radioactive
Waste Treatment Technologies Handbook, CRC Press, Boca Raton, FL.
8. TerraTherm Environmental Services. 1999. Naval Facility Centerville Beach, Technology
Demonstration Report, In-Situ Thermal Desorption. November.
9. TerraTherm Inc. Case Study-Alhambra. Online Address:
http://www.terratherm.com/CaseStudies/WS%20Final%20Alhambra%20Sheet.pdf.
10. TerraTherm Inc. Case Study - Centerville Beach Naval Facility. Online Address:
http://www.terratherm.com/CaseStudies/WS%20Centrvll-Tesi.pdf.
11. TerraTherm Inc. Case Study- Former Mare Island Naval Shipyard. Online Address:
http://www.terratherm.com/CaseStudies/WS%20BADCAT.pdf.
12. TerraTherm Inc. Feasibility Screening. Online Address:
http://www.terratherm.com/default.htm.
13. TerraTherm Inc. ISTD Process Description. Online Address:
http://www.terratherm.com/default.htm.
14. Tetra Tech EM Inc. 2000. Draft Final Closeout Report. Naval Facility Centerville Beach,
Ferndale, California. February.
15. Todd, Levi. Year. Publication or Report. Lessons Learned from the Application of In Situ
Thermal Destruction of Hexachlorocyclopentadiene Waste at the Rocky Mountain Arsenal.
Month.
16. U.S. Environmental Protection Agency. 2004. In Situ Thermal Treatment of Chlorinated
Solvents Fundamentals and Field Applications. EPA 542-R-04-010. March.
17. Yargeau, Tedd, California EPA, DTSC. 2004. Email to Chitranjan Christian, Tetra Tech EM
Inc., Regarding Questions on ISTD implementation at Alhambra. December 22.
18. Yargeau, Tedd, California EPA, DTSC. 2004. Telephone Conversation with Chitranjan
Christian, Tetra Tech EM Inc. Response to Questions on ISTD implementation at Alhambra.
November 2.
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