SEPA
United States
Environmental Protection
Agency
Solid Waste and
Emergency Response
Publication 9200.5-224FS
EPA 540/F-95/031
PB95-963315
January 1997
Engineering Forum Issue Paper:
Thermal Desorption Implementation Issues
John Blanchard, PE1 and Robert Stamnes, PE2
Office of Emergency and Remedial Response
Quick Reference Fact Sheet
This issue paper identifies issues and summarizes experiences with thermal desorption as a remedy for volatile organic
compounds (VOCs) in soils. The issues presented here reflect discussions with over 15 Remedial Project Managers (RPMs)
and technical experts. This fact sheet has been developed jointly by the Engineering Forum and Office of Emergency and
Remedial Response, with assistance from the Office of Research and Development. EPA's Engineering Forum is a group
of professionals, representing EPA Regional Offices, who are committed to identifying and resolving the engineering issues
related to remediation of Superfund and hazardous waste sites. The Forum is sponsored by the Technical Support Project.
The information presented here is advisory in nature, should be verified for its applicability to a given site, and is not intended
to establish Agency policy. RPMs should consult their regional management before applying the recommendations cited in
this paper for appropriateness at their site.
Thermal desorption (TD) is a commonly used separation process that EPA has selected as a "presumptive remedy" for
VOCs, in which contaminated soils, sludge, or other wastes are heated so that volatile and semivolatile organic compounds
are driven off as gases (Superfund Directive 9355.0-FS; EPA 540-F-93-048; PB93-963346). The TD process is designed
to separate organics from the matrix, but not to destroy them (although some thermal destruction may occur). Air,
combustion gas, or inert gas (such as nitrogen, which may be introduced to impede combustion) is introduced to the waste
stream, and carries the volatilized contaminants to air pollution control equipment. The volatilized contaminants generally are
condensed onto cooled surfaces or adsorbed on activated carbon beds for subsequent treatment, reuse, or ultimate
disposal. After cleaning, the off gas is vented to the atmosphere. Consult the bibliography at the end of this fact sheet for
additional details. In addition to volatilizing constituents in the waste medium, the thermal desorption process may also result
in the partial breakdown of compounds and reformation of new compounds, which can form new contaminants of concern
(dioxins, furans) in the treatment residuals.
Index
page
Site Characterization 1
Record of Decision (ROD) and Applicable or Relevant
and Appropriate Regulations (ARARs) 2
Remedial Design (RD) 2
Implementation and System Performance 3
Air Emissions Control 5
Community Involvement 5
Bibliography 5
Site Characterization and Remedy Selection
Before remedial technologies for soil treatment can
be evaluated for a site, investigations should be
conducted to identify the contaminants present, the
soil type and structure, and other site features. Key
soil and constituent parameters are discussed in the
Implementation and System Performance section of
this fact sheet.
Treatability testing is often used at the remedy
screening level to provide a quick and relatively
inexpensive indication of the appropriateness of TD
as a remedial technology. Treatability studies (TS)
will indicate if heating the medium to a specific
temperature for a specific period of time results in
meeting VOC soil remediation goals for contaminant
removal. There is disagreement among experts as to
the necessity of treatability testing at the TD design
level. A vendor may be in the best position to decide
if a TS is required after considering soil matrix,
'John Blanchard, PE
U.S. Environmental Protection Agency (5203G)
Office of Emergency & Remedial Response
Washington, DC 20460
"Robert Stamnes, PE
U.S. Environmental Protection Agency
Region 10 (OEA-095), 1200 Sixth Avenue
Seattle, WA 98101
Page 1
-------
contaminant level, and treatment standard variables.
To supplement site characterization data, some
RPMs have stated that treatability tests should be
performed during the Remedial Investigation (Rl).
The availability of site-specific treatability test results
would allow more accurate treatment cost quotes for
the Feasibility Study (FS).
Record of Decision (ROD) and Applicable or
Relevant and Appropriate Regulations (ARARs)
Many factors can affect the time and cost required to
implement TD as a treatment technology. As one
way to streamline the process, an RPM suggested
that RODs explicitly permit more flexibility with
thermal treatment technologies. For example, the
language in the ROD for one site stated that "thermal
treatment" was the remedy, thus allowing either
thermal desorption or incineration.
The movement and preparation of soils for ex situ
treatment presents many issues. Reducing the soil
aggregate size to meet the feed system requirements
and reducing soil or sludge moisture content by
blending or de-watering are specific concerns. Ex situ
TD also has the potential for generating nuisance
odors and dust, as well as other more serious
emissions resulting from on-site excavation.
The RPM should always consider the requirements
and costs of materials handling when evaluating any
remedy. For a site heavily contaminated with VOCs,
and where excessive materials handling is required,
in situ treatment technologies, such as soil vapor
extraction, may be more appropriate and less costly.
Experts have noted that on a typical thermal
desorption project, the requisite review by state
regulatory agencies can be lengthy. Reducing the
number of times that a regulatory agency must
review the design would shorten the schedule. In the
experience of one RPM, the most difficult task was
determining the state's requirements or other Appli-
cable or Relevant and Appropriate Requirements
(ARARs) that would be imposed on the system. Most
EPA Regions try to meet substantive state require-
ments rather than obtain state permits. The best
advice for keeping a project on schedule is to meet
early and often with state air and hazardous waste
permitting personnel.
Thermal desorption is a physical separation tech-
nology, not a destruction technology. A variety of TD
systems may be used to separate (vaporize) VOCs
and semivolatile organic compounds (SVOCs) from
Thermal Desorption Process
Vapor
Contaminated Soil
Soil redeposited or reused
Organic Iquid for
further treatment
or disposal
Water for reuse
Further treatment or
|Yea disposal
soil. The vaporized organics are then collected by
condensation or carbon adsorption. Please note,
however, that TD systems that vaporize and then
burn organic contaminants are considered incinera-
tors for the purpose of RCRA regulation—thermal
desorbers may well meet RCRA definitions for
incinerator, boiler, industrial furnace, or miscellane-
ous unit regardless of the operator's intentions.
To compare costs of operating a specific TD system
with those of other ex situ technologies, one expert
recommends considering only those costs associated
with operations from the time the soil is removed from
a screened pile until the time the processed soil is
placed in the discharge pile. The costs involved in
transporting and screening soil prior to treatment and
removing or backfilling the treated discharge pile are
common to all types of ex situ technologies at sites
and should be costed and compared separately.
Direct-fired thermal desorbers operating at high
temperatures and thermal desorbers equipped with
afterburners (or other types of oxidizers) also are
considered to be incinerators, and must meet the
more stringent RCRA Subpart O incinerator emission
requirements rather than RCRA Subpart X
requirements for thermal desorbers.
Remedial Design (RD)
Some experts have suggested that after remedy
selection, but before or during remedy design,
specific vendors or contractors should be offered the
opportunity to perform remedy treatability studies to
demonstrate that their product will meet the goals of
the project. The vendors should be allowed some
flexibility in how the tests will be conducted because
the vendor knows best what data are needed to
evaluate their systems. A treatability study performed
by the contractor who will remediate the site would
Page 2
-------
prevent selecting an unsuitable system, limit
unforeseen problems associated with site-specific
soils and contaminants, and thereby reduce the
overall costs of site remediation. The RPM should
verify that the contracting strategy used for the project
will allow this.
The tendency of dry, clayey soils to agglomerate can
slow treatment processes and lower the efficiency of
the thermal desorption process. The problem can be
resolved by retrofitting the soil feeding system with a
shredder that breaks up the clay balls to the proper
diameter, and a screener, which removes oversized
objects. The problems associated with saturated
clays are far more difficult to overcome, since wet,
plastic clays cannot be screened and tend to smear
when handled. Chemical de-watering agents or
drying can be used in certain cases, depending upon
clay mineralogy; it is best to consult with the vendors
or contractors for the specific TD systems being
considered, for their experience and recommenda-
tions.
Several RPMs believe that noise pollution issues do
not receive enough attention during the planning and
design phases. Some TD systems produce high deci-
bel levels and operate 24 hours per day. Possible
solutions include adding mufflers or housing the
desorberin a pre-engineered building.
Implementation and System Performance
Key soil characteristics influencing TD effectiveness
at a given site include soil plasticity, particle size
distribution, heat capacity, concentration of humic
material, metals concentration, and bulk density. Key
constituent characteristics include concentrations,
boiling point range, vapor pressure, octanol/water
partition coefficient, aqueous solubility, thermal
stability, and dioxin formation.
Other factors affecting TD performance are the
maximum bed temperature, total residence time,
organic and moisture content, and feedstock proper-
ties. Since the basis of the process is physical
removal from the medium by volatilization, bed
temperature is a primary factor in determining end-
point concentrations. Soils having a high proportion of
Schematic Layout of Typical Thermal Desorption Facility
GENERATOR
TRAILER
CONTROL
TRAILER
TREATED MATERIAL
ACTIVATED CARBON
TRAILER
IMPACTED MATERIAL
PageS
-------
sand and gravel are easier to handle and treat than
finer, more cohesive silts and clays. Processing rates
for the finer soils generally are lower and therefore
per unit costs are higher.
Experts have stated that most TD units easily can
handle feedstock moisture content as high as 15
percent. With moisture content at 15 to 25 percent,
there is some reduction in throughput, but with only
inconsequental impacts on cost. When moisture
content is higher than 20 percent, impacts on cost
can become significant. Moisture in the material acts
as a heat sink because it must be evaporated from
the soil along with the organic contaminants.
However, there is no upper limit on acceptable feed
soil moisture content as long as it can be reduced to
economically reasonable levels before treatment.
Soils having high moisture content can be de-watered
(by filter press or other means) or mixed and blended
with dry materials before they are fed into to the TD
system.
Experts have stated that the mixing of soil and sweep
gas (sweep gas is used to transfer the volatilized
organics and water to the off gas treatment system)
within the TD unit is crucial for promoting efficient
contaminant removal. However, excessive mixing
also may lead to undesirable carryover of soil to the
to the air pollution control equipment (APCE) system.
Almost all thermal desorption systems are designed
to accept materials no larger than 1 to 2 inches in
diameter. Although TD can be used for all types of
contaminated soils, clays must be shredded and
mixed with sand to be able to move through the feed
processor. At one site, excavation uncovered cobbles
that required separation from the feedstock. The
cobbles were steam-cleaned and returned to the
treated soil. The wastewater generated from this
steam cleaning was used to wet the feedstock to the
optimum moisture level for treatment. At another site,
the volume of soil remaining after treatment was
roughly two-thirds of that originally estimated
because of the significant amounts of oversized
material.
Sludges at one site were found to be full of large
debris and required de-watering and screening prior
to treatment. The screened debris was transported to
a RCRA landfill for disposal. Placement of chemical
additives in the sludge also should be considered
carefully, because additives can affect the load-
bearing potential of the treated soil and result in
material unsuitable for backfill intended to support
pavement or an overlying structure.
Dust control is another important consideration in the
implementation of TD. At one site, dust was
generated by the convection of hot air across the end
of the TD unit as treated solids were discharged. To
address this type of problem, contractors have
installed dust control systems which include a
quenching water spray at the point where dry treated
soil leaves the TD oven. At one site, a dust control
shed was constructed to house both the water-
quenched soil awaiting treatment and the dust
discharge pile. An 18-inch diameter pipe was
installed in the shed and a vacuum truck was used to
collect fugitive dust from the air within the shed. It
should be noted that TD processing of sandy
sediments does not create a significant dust problem
since the relatively large particles that remain after
processing do not become airborne.
RPMs have stressed that more obscure parameters
should be considered when evaluating or designing
a TD system. For example, media that are highly
basic or acidic may corrode the processing system
components. Also, high levels of sulfur in the
untreated soil can form sulfuric acid in the TD system
and cause significant corrosion.
Several RPMs have recommended that greater
emphasis be placed on the adherence to process
drawings, specifications, and descriptions developed
during the RD phase and on oversight during the RA
phase to reduce the occurrence of technical prob-
lems (e.g., equipment failure) during implementation
of the remedy.
Proof-of-Process (POP) performance tests typically
are conducted to verify that the TD system is
achieving soil treatment goals, and that air emissions
are below allowable limits. One issue concerning
POP tests centered on the representativeness of TD
test conditions, which are governed by the represen-
tativeness of the soil tested. If POP tests are
conducted with blends of soils collected from various
locations at the site, it becomes critical to ensure that
any contaminant "hot spots" are properly recognized
and tested.
RPMs have recommended that TD systems be shut
down following the performance test until EPA has
reviewed and approved the data. To facilitate the
review process, the RPMs recommend that the
chemical analysis of samples be expedited even if
additional costs are incurred. Any potential benefits
(economic or otherwise) from continuing operation
during the review period may be outweighed by the
risks associated with continuing operation without
Page 4
-------
better knowledge of how well the system is perfor-
ming.
Air Emissions Control
Several APCE systems have been evaluated by
RPMs under field conditions. RPMs state that a
system that removes particulates, cools and
condenses vapors, and adsorbs residual vapors on
carbon beds typically is recommended over thermal
oxidation (which must meet the more stringent
requirements of an incinerator) and a scrubber to
eliminate the products of incomplete combustion.
However, there are possible drawbacks to the
condenser/adsorption system. Contaminant concen-
trations in the vapor may be too high to be treated
effectively, and therefore would not meet the cleanup
goals. In such a case, the thermal oxidation process
may be more appropriate.
Experts have noted that at most sites contaminated
with chlorinated aromatics there is a strong possibility
thatdioxins orfurans also are present, and would be
removed from the soils and sediments during TD
treatment. The APCE must be designed to deal with
this possibility, and the POP test should include
measurements to detect and quantify dioxin in
exhaust emissions.
Soils at one site contained a significant amount of
wood chips. During the first performance test,
embers from the wood chips burned holes in the
walls of the dust collection bags. A cyclone collector
(centrifuge) was added to remove the embers.
However, the cyclone was not effective in removing
the fine dust from the gas stream prior to the
afterburner and stack. The feed rate had to be
reduced to less than 60 percent of capacity to
prevent excessive emissions of particulate matter.
Operation of the desorption system in a way that
increases heat transfer to the contaminated soil
usually increases carryover of dust to the APCE and
creates problems. As an example, off-gas may burn
holes in the baghouse filter media, and cause the
induction fan to fail. The holes would then allow
particulate matter to pass through the bag walls and
clog the carbon adsorption bed. The bed would then
have to be regenerated more often during the
cleanup process.
Community Involvement
The focus and level of community interest varies at
each site. Community relations efforts should begin
early, include risk communication in nontechnical
terms, and afford numerous opportunities for the
public to view the process. Members of the
community should be encouraged to visit the site and
observe as much of the actual system as possible
without compromising their safety. The community
should be shown how air emissions will be controlled
to safe levels, both in a fact sheet and further at
public meetings.
Public acceptance of thermal desorption may be
adversely affected by confusion with incineration
technologies, which do not enjoy public confidence.
When presenting TD to the public, the differences in
air emissions from alternative remedial technologies
and APCE should be compared and explained. The
public should be made aware of the safeguards that
will prevent atmospheric releases of toxic gases.
Selected Bibliography
Remediation Case Studies: Thermal Desorption,
Soil Washing, and In Situ Vitrification.
U.S. EPA, Office of Solid Waste and Emergency
Response, Technology Innovation Office. March
1995
EPA-542-R-95-005, PB95-182945.
This report contains six case studies on thermal
desorption at Superfund sites, and describes
contaminants treated, media and quantities, project
durations, costs, and performance. The report is a
publication of the Federal Remediation Technologies
Roundtable.
A Citizen's Guide to Thermal Desorption.
U.S. EPA, Office of Solid Waste and Emergency
Response, Technology Innovation Office. July 1996
EPA/542/F-92/0036, PB92-232396.
This fact sheet presents in lay terms the
technologies, processes, and applicability of thermal
desorption technology. It may be a useful handout to
communities associated with possible thermal
desorption systems.
VISIT! Database (Version 5.0) — Vendor Informa-
tion System for Innovative Treatment Technolo-
gies
U.S. EPA, Office of Solid Waste and Emergency
Response, Technology Innovation Office. July 1994
EPA/542/R-94/003, PB94-213634.
This database provides current information on
innovative treatment technologies for the remediation
PageS
-------
of contaminated sites. VISIT! contains technology
information submitted by developers, manufacturers,
and suppliers of innovative treatment technology
equipment and services.
Combustion Emissions Technical Resource
Document (CETRED). Draft.
U.S. EPA, Office of Solid Waste and Emergency
Response, Washington, DC, May 1994
EPA530/R94/014
This text contained the initial technical analysis by
the U.S. EPA concerning potential emissions of
dioxins/furans and particulate matter (PM). CETRED
represents the current state of analysis of EPA
technical staff in the Office of Solid Waste as regards
the emission levels of PM and dioxins/furans
achievable by the best controlled sources. Approx.
330 pp.
Estimation of Air Impacts for Thermal Desorption
Units Used at Superfund Sites. Air/Superfund
National Technical Guidance Study Series
U.S. EPA, Office of Emergency and Remedial
Response, Washington, DC, April 1993. 54 pp.
EPA/451/R-93/005, PB93-215630
The report provides procedures for estimating the
ambient air concentrations associated with thermal
desorption. Procedures are given to evaluate the
effect of the treatment rate and contaminant
concentrations on the emission rates and on the
ambient air concentrations at selected distances from
the treatment area. Health-based ambient air action
levels are also provided for comparison to the
estimated ambient concentrations.
XTRAX Model 200 Thermal Desorption System,
OHM Remediation Services Corporation: SITE
Demonstration Bulletin.
U.S. EPA, Office of Solid Waste and Emergency
Response, Washington, DC, May 1993
EPA540-MR-93-502
EPA and Environment Canada both have prog-
rams that support emerging innovative technology
development and technical evaluation demonstra-
tions. EPA's Superfund Innovative Technology Evalu-
ation (SITE) Program and Environment Canada's
Development and Demonstration of Site Remediation
Technologies (DESRT) Program present an
evaluation of cost and performance based on a
demonstration of the XTRAX technology. The
XTRAX™ Model 200 thermal desorption System
developed by Chemical Waste Management, Inc., is
a low-temperature process designed to separate
organic contaminants from soils, sludges, and other
solid media.
Innovative Site Remediation Technology, Vol. 6,
Thermal Desorption.
Office of Solid Waste and Emergency Response,
Technology Innovation Office. November 1993
EPA/542/B-93/011, PB94-181716
The monograph on thermal desorption is one
of a series of eight on innovative site and waste
remediation technologies that are the culmination of
a multi-organization effort involving more than
100 experts over a two-year period. The thermal
desorption processes addressed in this monograph
use heat, either direct or indirect, ex situ, as the
principal means to physically separate and
transfer contaminants from soil, sediment, sludge,
filter cakes, or other media. Thermal desorption is
part of a treatment train; some pre- and post-
processing is necessary.
Contaminants and Remedial Options at Wood
Preserving Sites
U.S. EPA, Office of Research & Development,
Cincinnati, OH. October 1992. 178 pp.
EPA/600/R-92/182, PB92-232222
The report provides information that facilitates the
selection of treatment technologies and services at
wood preserving sites, in order to meet acceptable
levels of cleanliness. It identifies the sources and
types of wood preserving contaminants,
characterizes them, and defines their behavior in the
environment. It addresses the goals in technology
selection and describes the principal remedial options
for contaminated wood preserving sites. It also
considers ways to combine these options to increase
treatment efficiency. Finally, this remedial aid
provides a comprehensive bibliography, organized by
its relevance to each section, to complement the
information offered in these pages.
Thermal Desorption Treatment: Engineering
Bulletin
U.S. EPA, Office of Research & Development,
Cincinnati, OH. February 1994. 11 pp.
EPA 540-S-94-501, PB94-160603
The bulletin discusses various aspects of the
thermal desorption technology including applicability,
limitations of its use, residuals produced, perfor-
mance data, site requirements, status of the
technology, and sources of further information. The
Page 6
-------
document is an update of the original bulletin
published in May 1991.
Thermal Desorption Remedy Selection Guide for
Conducting Treatability Studies under CERCLA
U.S. EPA, Office of Emergency and Remedial Re-
sponse, Washington, DC. September 1992. 47 pp.
EPA 540-R-92-074A, PB93-126597
The manual focuses on thermal desorption
treatability studies conducted in support of remedy
selection prior to the Record of Decision (ROD). It is
a standard guide for designing and implementing a
Acknowledgements
treatability study to evaluate the effectiveness of
thermal desorption on a site-specific basis. The
manual describes, discusses, and defines the
prescreening and field measurement data needed to
determine if treatability testing is required. It also
presents an overview of the process for conducting
treatability tests, and discusses the applicability of
tiered treatability testing for evaluation of thermal
desorption technologies. The elements of a treat-
ability study work plan also are defined, and detailed
information on the design and execution of the
remedy screening treatability study are provided.
The assistance of the Engineering Forum members is greatly appreciated:
Rich Ho, Region 2
Chet Janowski, Region 1
Paul Leonard, Region 3
Frank Vavra, Region 3
For Further Information
John Blanchard, PE
U.S. Environmental Protection Agency (5203G)
Office of Emergency and Remedial Response
401 M Street, SW
Washington, DC 20460
(703) 603-9031
Email: blanchard.john@epamail.epa.gov
Marta Richards
U.S. Environmental Protection Agency
National Risk Management Research Laboratory
26 West Martin L. King Drive
Cincinnati, OH 45268
(513)569-7692
Email: richards.marta@epamail.epa.gov
Thermal desorption has been selected as the remedy for VOCs or SVOCs in soils at the sites or operable units
listed below. Some sites are currently operating, and some are in the design phase. This list has been adapted
from the "Innovative Treatment Technologies: Annual Status Report (Eighth Edition)," September 1996 (EPA
542-R-96-010). This list is not comprehensive.
Aberdeen Pesticide Dumps, OU 1 & OU 4, NC
Acme Solvent Reclaiming, Inc., OU 3, IL
American Chemical Services, IN
American Thermostat (Phase 1), NY
American Thermostat (Phase 2), NY
Anderson Development (ROD Amendment), MI
Arlington Blending and Packaging Co., OU 1, TN
Cannon Engineering/Bridgewater, MA
Ciba-Geigy (Macintosh Plant), OU 2, AL
Ciba-Geigy (Macintosh Plant), OU 4, AL
Clare Water Supply, MI
Claremont Polychemical, NY
Drexler - RAMCOR, WA
Duell-Gardner Landfill, MI
PCX-Washington Site, NC
Fort Lewis Military Reservation, Solvent Refined Coal Plant, WA
Fulton Terminals, Soil Treatment, NY
GCL Tie and Treating, NY
General Motors/Central Foundry Division, OU 1 & OU 2, NY
Harbor Island, WA
Industrial Latex, OU 1, NJ
Jacksonville Naval Air Station, OU 2, FL
Lipari Landfill Marsh Sediment, NJ
Lockheed Shipyard Facility/Harbor Island, OU 3, WA
Lockheed/Martin (Denver Aerospace), CO
Martin Marietta Corp., W C Astronautics Facility, CO
Marzone Inc./Chevron Co. Superfund Site, OU 1, GA
McKin, ME
Metaltec/Aerosystems, OU 1, NJ
Naval Air Station, Cecil Field Site 17, OU 2, FL
Ott/Story/Cordova Chemical, MI
Ottati & Goss, NH
Outboard Marine/Waukegan Harbor, OU 3, IL
Potter's Septic Tank Service Pits, NC
Pristine (ROD Amendment), OH
Re-Solve, MA
Reich Farms, NJ
Reilly Tar and Chemical, IN
Page 7
-------
Rentokil, VA Solvent Savers, NY
Reynolds Metals Company Study Area Site, (RMC), NY South Andover Salvage Yards, OU 2, MN
Sand Creek Industrial, OU 5, CO U.SA. Letterkenny SE Area, OU 1,PA
Sangamo/Twelve-Mile/Hartwell PCB, OU 1, SC Universal Oil Products, NJ
Sarney Farm, NY Valley Park TCE Site, Wainwright OU, MO
Saunders Supply Co, OU 1, VA Waldick Aerospace Devices, OU 1, NJ
Sherwood Medical, NE Wamchem, SC
Smith's Farm Brooks, OU 1, KY William Dick Lagoons, OU 3, PA
PageS
------- |