v°/EPA
United State*
Environmental Protection
Agency
Saparffoxj
Office of Emergency and
RerwcSaf Response
Washinyton, DC 20460
Office of
Research and Development
Cincinnati, OH 45268
EPA/540/S-92/015
May 1993
Engineering Bulletin
Solidification/Stabilization
of Organics and Inorganics
Purpose
Section 121(b) of the Comprehensive Environmental Re-
sponse, Compensation, and Liability Act (CERCLA) mandates
the Environmental Protection Agency (EPA) to select remedies
that "utilize permanent solutions and alternative treatment
technologies or resource recovery technologies to the maxi-
mum extent practicable" and to prefer remedial actions in
which treatment "permanently and significantly reduces the
volume, toxicity, or mobility of hazardous substances, pollut-
ants, and contaminants as a principal element." The Engineer-
ing Bulletins are a series of documents that summarize the most
current information available on selected treatment and site
remediation technologies and related issues. They provide
summaries of and references for this information to help reme-
dial project managers, on-scene coordinators, contractors, and
other site cleanup managers understand the type of data and
site characteristics needed to evaluate a technology for poten-
tial applicability to their Superfund or other hazardous waste
site. Those documents that describe individual treatment tech-
nologies focus on remedial investigation scoping needs. Ad-
denda are issued periodically to update the original bulletins.
granular consistency resembling soil. During in situ operations,
S/S agents are injected into and mixed with the waste and soil
up to depths of 30 to 100 feet using augers.
Treatability studies are the only means of documenting the
applicability and performance of a particular S/S system. Deter-
mination of the best treatment alternative will be based on
multiple site-specific factors and the cost and efficacy of the
treatment technology. The EPA contact identified at the end of
this bulletin can assist in the location of other contacts and
sources of information necessary for such treatability studies.
It may be difficult to evaluate the long-term (>5 year)
performance of the technology. Therefore, long-term monitor-
ing may be needed to ensure that the technology continues to
function within its design criteria.
This bulletin provides information on technology applica-
bility, the limitations of the technology, the technology descrip-
tion, the types of residuals produced, site requirements, the
process performance data, the status of the technology, and
sources for further information.
Abstract
Solidification refers to techniques that encapsulate hazard-
ous waste into a solid material of high structural integrity.
Encapsulation involves either fine waste particles
(microencapsulation) or a large block or container of wastes
(macroencapsulation) [1, p. 2]*. Stabilization refers to tech-
niques that treat hazardous waste by converting it into a less
soluble, mobile, or toxic form. Solidification/Stabilization (S/S)
processes, as referred to in this document, utilize one or both of
these techniques.
S/S technologies can immobilize many heavy metals, cer-
tain radionuclides, and selected organic compounds while de-
creasing waste surface area and permeability for many types of
sludge, contaminated soils, and solid wastes. Common S/S
agents include: Type 1 Portland cement or cement kiln dust;
lime, quicklime, or limestone; fly ash; various mixtures of these
materials; and various organic binders (e.g., asphalt). The
mixing of the waste and the S/S agents can occur outside of the
ground (ex situ) in continuous feed or batch operations or in
the ground (in situ) in a continuous feed operation. The final
product can be a continuous solid mass of any size or of a
•[reference number, page number]
Technology Applicability
The U.S. EPA has established treatment standards under
the Resource Conservation and Recovery Act (RCRA), Land
Disposal Restrictions (LDRs) based on Best Demonstrated Avail-
able Technology (BDAT) rather than on risk-based or health-
based standards. There are three types of LDR treatment
standards based on the following: achieving a specified con-
centration level, using a specified technology prior to disposal,
and "no land disposal." Achieving a specified concentration
level is the most common type of treatment standard. When a
concentration level to be achieved is specified for a waste, any
technology that can meet the standard may be used unless that
technology is otherwise prohibited [2].
The Superfund policy on use of immobilization is as fol-
lows: "Immobilization is generally appropriate as a treatment
alternative only for material containing inorganics, semi-volatile
and/or non-volatile organics. Based on present information,
the Agency does not believe that immobilization is an appropri-
ate treatment alternative for volatile organic compounds (VOCs).
Selection of immobilization of semi-volatile compounds (SVOCs)
and non-volatile organics generally requires the performance of
Printed on Recycled Paper
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oEPA
United State*
Environmentaf Protection
Agency
Office of
Remedial Reeponee
Washington, DC 20460
Office of
Research and Development
Cincinnati, OH 45268
Superfund
May 1993
Engineering Bulletin
Solidification/Stabilization
of Organics and Inorganics
Purpose
Section 121(b) of the Comprehensive Environmental Re-
sponse, Compensation, and Liability Act (CERCLA) mandates
the Environmental Protection Agency (EPA) to select remedies
that "utilize permanent solutions and alternative treatment
technologies or resource recovery technologies to the maxi-
mum extent practicable" and to prefer remedial actions in
which treatment "permanently and significantly reduces the
volume, toxicity, or mobility of hazardous substances, pollut-
ants, and contaminants as a principal element." The Engineer-
ing Bulletins are a series of documents that summarize the most
current information available on selected treatment and site
remediation technologies and related issues. They provide
summaries of and references for this information to help reme-
dial project managers, on-scene coordinators, contractors, and
other site cleanup managers understand the type of data and
site characteristics needed to evaluate a technology for poten-
tial applicability to their Superfund or other hazardous waste
site. Those documents that describe individual treatment tech-
nologies focus on remedial investigation scoping needs. Ad-
denda are issued periodically to update the original bulletins.
granular consistency resembling soil. During in situ operations,
S/S agents are injected into and mixed with the waste and soil
up to depths of 30 to 100 feet using augers.
Treatability studies are the only means of documenting the
applicability and performance of a particular S/S system. Deter-
mination of the best treatment alternative will be based on
multiple site-specific factors and the cost and efficacy of the
treatment technology. The EPA contact identified at the end of
this bulletin can assist in the location of other contacts and
sources of information necessary for such treatability studies.
It may be difficult to evaluate the long-term (>5 year)
performance of the technology. Therefore, long-term monitor-
ing may be needed to ensure that the technology continues to
function within its design criteria.
This bulletin provides information on technology applica-
bility, the limitations of the technology, the technology descrip-
tion, the types of residuals produced, site requirements, the
process performance data, the status of the technology, and
sources for further information.
Abstract
Solidification refers to techniques that encapsulate hazard-
ous waste into a solid material of high structural integrity.
Encapsulation involves either fine waste particles
(microencapsulation) or a large block or container of wastes
(macroencapsulation) [1, p. 2]*. Stabilization refers to tech-
niques that treat hazardous waste by converting it into a less
soluble, mobile, or toxic form. Solidification/Stabilization (S/S)
processes, as referred to in this document, utilize one or both of
these techniques.
S/S technologies can immobilize many heavy metals, cer-
tain radionuclides, and selected organic compounds while de-
creasing waste surface area and permeability for many types of
sludge, contaminated soils, and solid wastes. Common S/S
agents include: Type 1 Portland cement or cement kiln dust;
lime, quicklime, or limestone; fly ash; various mixtures of these
materials; and various organic binders (e.g., asphalt). The
mixing of the waste and the S/S agents can occur outside of the
ground (ex situ) in continuous feed or batch operations or in
the ground (in situ) in a continuous feed operation. The final
product can be a continuous solid mass of any size or of a
•[reference number, page number]
Technology Applicability
The U.S. EPA has established treatment standards under
the Resource Conservation and Recovery Act (RCRA), Land
Disposal Restrictions (LDRs) based on Best Demonstrated Avail-
able Technology (BOAT) rather than on risk-based or health-
based standards. There are three types of LDR treatment
standards based on the following: achieving a specified con-
centration level, using a specified technology prior to disposal,
and "no land disposal." Achieving a specified concentration
level is the most common type of treatment standard. When a
concentration level to be achieved is specified for a waste, any
technology that can meet the standard may be used unless that
technology is otherwise prohibited [2].
The Superfund policy on use of immobilization is as fol-
lows: "Immobilization is generally appropriate as a treatment
alternative only for material containing inorganics, semi-volatile
and/or non-volatile organics. Based on present information,
the Agency does not believe that immobilization is an appropri-
ate treatment alternative for volatile organic compounds (VOCs).
Selection of immobilization of semi-volatile compounds (SVOCs)
and non-volatile organics generally requires the performance of
Printed on Recycled Paper
-------
a site-specific treatability study or non-site-specific treatability
study data generated on waste which is very similar (in terms of
type of contaminant, concentration, and waste matrix) to that
to be treated and that demonstrates, through Total Waste
Analysis (TWA), a significant reduction (e.g., a 90 to 99 percent
reduction) in the concentration of chemical constituents of
concern. The 90 to 99 percent reduction in contaminant
concentration is a general guidance and may be varied within a
reasonable range considering the effectiveness of the technol-
ogy and the cleanup goals for the site. Although this policy
represents EPA's strong belief that TWA should be used to
demonstrate effectiveness of immobilization for organics, other
teachability tests may also be appropriate in addition to TWA to
evaluate the protectiveness under a specific management sce-
nario. "To measure the effectiveness on inorganics, the EPA's
Toxicity Characteristic Leaching Procedure (TCLP) should be
used in conjunction with other tests such as TCLP using distilled
water or American Nuclear Society (ANS) 16.1 [3, p. 2].
Factors considered most important in the selection of a
technology are design, implementation, and performance of
S/S processes and products, including the waste characteristics
(chemical and physical), processing requirements, S/S product
management objectives, regulatory requirements, and econom-
ics. These and other site-specific factors (e.g., location, condi-
tion, climate, hydrology, etc.) must be taken into account in
determining whether, how, where, and to what extent a par-
ticular S/S method should be used at a particular site [4, p.
7.92]. Pozzolanic S/S processes can be formulated to set under
water if necessary; however, this may require different propor-
tions of fixing and binding agents to achieve the desired immo-
bilization and is not generally recommended [5, p. 21]. Where
non-pumpable sludge or solid wastes are encountered, the site
must be able to support the heavy equipment required for
excavation or in situ injection and mixing. At some waste
disposal sites, this may require site engineering.
A wide range of performance tests may be performed in
conjunction with S/S treatability studies to evaluate short- and
long-term stability of the treated material. These include total
waste analysis for organics, leachability using various methods,
permeability, unconfined compressive strength (DCS), treated
waste and/or leachate toxicity endpoints, and freeze/thaw and
wet/dry weathering cycle tests performed according to specific
procedures [6, p. 4.2] [7, p. 4.1], Treatability studies should be
conducted on replicate samples from a representative set of
waste batches that span the expected range of physical and
chemical properties to be encountered at the site [8, p. 1 ].
The most common fixing and binding agents for S/S are
cement, lime, natural pozzolans, and fly ash, and mixtures of
these [4, p. 7.86] [6, p. 2.1]. They have been demonstrated to
immobilize many heavy metals and to solidify a wide variety of
wastes including spent pickle liquor, contaminated soils, incin-
erator ash, wastewater treatment filter cake, and waste sludge
[7, p. 3.1] [9]. S/S is also effective in immobilizing many
radionuclides [10]. In general, S/S is considered an established
full-scale technology for nonvolatile heavy metals although the
long-term performance of S/S in Superfund applications has yet
to be demonstrated [2].
Traditional cement and pozzolanic materials have yet to be
shown to be consistently effective in full-scale applications treat-
ing wastes high in oil and grease, surfactants, or chelating
agents without some form of pretreatment [11] [12, p. 122].
Pretreatment methods include pH adjustment, steam or ther-
mal stripping, solvent extraction, chemical or photochemical
reaction, and biodegradation. The addition of sorbents such as
modified clay or powdered activated carbon may improve ce-
ment-based or pozzolanic process performance [6, p. 2.3].
Regulations promulgated pursuant to the Toxic Substances
Control Act (TSCA) do not recognize S/S as an approved treat-
ment for wastes containing polychlorinated biphenyls (PCBs)
above 50 ppm. It is EPA policy that soils containing greater
than 10 ppm in public/residential areas and 25 ppm in limited
access/occupational areas be removed forTSCA-approved treat-
ment/disposal. However, the policy also provides EPA regional
offices with the option of requiring more restrictive levels. For
example, Region 5 requires a cleanup level of 2 ppm. The
proper disposition of high volume sludges, soils, and sediments
is not specified in the TSCA regulations, but precedents set in
the development of various records of decision (RODs) indicate
that stabilization may be approved where PCBs are effectively
immobilized and/or destroyed to TSCA-equivalent levels. Some
degree of immobilization of PCBs and related polychlorinated
polycyclic compounds appears to occur in cement or pozzolans
[15, p. 1573]. Some field observations suggest polychlorinated
polycyclic organic substances such as PCBs undergo significant
levels of dechlorination under the alkaline conditions encoun-
tered in pozzolanic processes. Recent tests by the EPA, how-
ever, have not confirmed these results although significant
desorption and volatilization of the PCBs were documented
[13, p. 41] [14, p. 3].
Table 1 summarizes the effectiveness of S/S on general
contaminant groups for soils and sludges. Table 1 was pre-
pared based on current available information or on professional
judgment when no information was available. In interpreting
this table, the reader is cautioned that for some primary con-
stituents, a particular S/S technology performs adequately in
some concentration ranges but inadequately in others. For
example, copper, lead, and zinc are readily stabilized by
cementitious materials at low to moderate concentrations, but
interfere with those processes at higher concentrations [12, p.
43]. In general, S/S methods tend to be most effective for
immobilizing nonvolatile heavy metals.
The proven effectiveness of the technology for a particular
site or waste does not ensure that it will be effective at all sites or
that treatment efficiencies achieved will be acceptable at other
sites. For the ratings used in Table 1, demonstrated effective-
ness means that at some scale, treatability tests showed that the
technology was effective for that particular contaminant and
matrix. The ratings of "Potential Effectiveness" and "No Ex-
pected Effectiveness" are both based upon expert judgment.
When potential effectiveness is indicated, the technology is
believed capable of successfully treating the contaminant group
in a particular matrix. When the technology is not applicable or
will probably not work for a particular combination of contami-
nant group and matrix, a no expected effectiveness rating is
given.
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
Table 1
Effectiveness of S/S on General Contaminant
Groups for Soil and Sludges
jfl^""
a
6
i
1
*
2
'1
0)
QC
Contaminant Groups
Halogenated volatiles
Nonhalogenated volatiles
Halogenated semivolatiles
Nonhalogenated semivolatiles
and nonvolatiles
PCBs
Pesticides
Dioxins/Furans
Organic cyanides
Organic corrosives
Volatile metals
Nonvolatile metals
Asbestos
Radioactive materials
Inorganic corrosives
Inorganic cyanides
Oxidizers
Reducers
Effectiveness
Soil/Sludge
a
a
•
.
V
T
T
V
V
•
•
•
•
•
"
•
•
KEY: • Demonstrated Effectiveness: Successful treatability test
at some scale completed.
T Potential Effectiveness: Expert opinion that
technology will work.
a No Expected Effectiveness: Expert opinion that
technology will/does not work.
Another source of general observations and average re-
moval efficiencies for different treatability groups is contained
in the Superfund LDR Guide #6A, "Obtaining a Soil and Debris
Treatability Variance for Remedial Actions," (OSWER Directive
9347.3-06FS, September 1990) [16] and Superfund LDR Guide
#6B, "Obtaining a Soil and Debris Treatability Variance for
Removal Actions/ (OSWER Directive 9347.3-06BFS, Septem-
ber 1990) [17]. Performance data presented in this bulletin
should not be considered directly applicable to other Superfund
sites. A number of variables such as the specific mix and
distribution of contaminants affect system performance. A
thorough characterization of the site and a well-designed and
conducted treatability study are highly recommended.
Other sources of information include the U.S. EPA's Risk
Reduction Engineering Laboratory Treatability Database (acces-
sible via ATTIC) and the U.S. EPA Center Hill Database (contact
Patricia Erickson).
Technology Limitations
Tables 2 and 3 summarize factors that may interfere with
stabilization and solidification processes respectively.
Physical mechanisms that can interfere with the S/S pro-
cess include incomplete mixing due to the presence of high
moisture or organic chemical content resulting in only partial
wetting or coating of the waste particles with the stabilizing
and binding agents and the aggregation of untreated waste
into lumps [6]. Wastes with a high clay content may clump,
interfering with the uniform mixing with the S/S agents, or the
clay surface may adsorb key reactants, interrupting the poly-
merization chemistry of the S/S agents. Wastes with a high
hydrophilic organic content may interfere with solidification by
disrupting the gel structure of the curing cement or pozzolanic
mixture [11, p. 18] [18]. The potential for undermixing is
greatest for dry or pasty wastes and least for freely flowing
slurries [11, p. 13]. All in situ systems must provide for the
introduction and mixing of the S/S agents with the waste in the
proper proportions in the surface or subsurface waste site envi-
ronment. Quality control is inherently more difficult with in situ
products than with ex situ products [4, p. 7.95].
Chemical mechanisms that can interfere with S/S of ce-
ment-based systems include chemical adsorption, complex-
ation, precipitation, and nucleation [1, p. 82]. Known inor-
ganic chemical interferants in cement-based S/S processes
include copper, lead, and zinc, and the sodium salts of arsen-
ate, borate, phosphate, iodate, and sulfide [6, p. 2.13] [12, p.
11]. Sulfate interference can be mitigated by using a cement
material with a low tricalcium aluminate content (e.g., Type V
Portland cement) [6, p. 2.13]. Problematic organic interferants
include oil and grease, phenols [8, p. 19], surfactants, chelating
agents [11, p. 22], and ethylene glycol [18]. For thermoplastic
micro- and macro-encapsulation, stabilization of a waste con-
taining strong oxidizing agents reactive toward rubber or as-
phalt must also be avoided [19, p. 10.114]. Pretreating the
wastes to chemically or biochemically react or to thermally or
chemically extract potential interferants should minimize these
problems, but the cost advantage of S/S may be lost, depend-
ing on the characteristics and volume of the waste and the type
and degree of pretreatment required. Organic polymer addi-
tives in various stages of development and field testing may
significantly improve the performance of the cementitious and
pozzolanic S/S agents with respect to immobilization of organic
substances, even without the addition of sorbents.
Volume increases associated with the addition of S/S agents
to the waste may prevent returning the waste to the landform
from which it was excavated where landfill volume is limited.
Where post-closure earthmoving and landscaping are required,
the treated waste must be able to support the weight of heavy
equipment The EPA recommends a minimum compressive strength
of 50 to 200 psi [7, p. 4.13]; however, this should be a site-specific
determination.
Environmental conditions must be considered in determin-
ing whether and when to implement an S/S technology. Ex-
tremes of heat, cold, and precipitation can adversely affect S/S
applications. For example, the viscosity of one or more of the
Engineering Bulletin: Solidification/Stabilization ofOrganics and Inorganics
-------
Table 2.
Summary of Factors that May Interfere with Stabilization Processes *
Characteristics Affecting Processing Feasibility
VOCs
Use of acidic sorbent with metal hydroxide wastes
Use of acidic sorbent with cyanide wastes
Use of acidic sorbent with waste containing ammonium compounds
Use of acidic sorbent with sulfide wastes
Use of alkaline sorbent (containing carbonates such as calcite
or dolomite) with acid waste
Use of siliceous sorbent (soil, fly ash) with hydrofluoric acid waste
Presence of anions in acidic solutions that form soluble
calcium salts (e.g., calcium chloride acetate, and bicarbonate)
Presence of halides
Potential Interference
Volatiles not effectively immobilized; driven off by heat of reaction.
Sludges and soils containing volatile organics can be treated using a
heated extruder evaporator or other means to evaporate free water and
VOCs prior to mixing with stabilizing agents.
Solubilizes metal.
Releases hydrogen cyanide.
Releases ammonia gas.
Releases hydrogen sulfide.
May create pyrophoric waste.
May produce soluble fluorosilicates.
Cation exchange reactions - leach calcium from S/S product
increases permeability of concrete, increases rate of exchange
reactions.
Easily leached from cement and lime.
Adapted from reference 2
Table 3.
Summary of Factors that May Interfere with Solidification Processes
Characteristics Affecting
Processing Feasibility
Organic compounds
Semivolatile organics or poly-
aromatic hydrocarbons
(PAHs)
Oil and grease
Fine particle size
Halides
Soluble salts of manganese,
tin, zinc, copper, and lead
Cyanides
Sodium arsenate, borates,
phosphates, iodates, sulfides,
and carbohydrates
Sulfates
Potential Interference
Organics may interfere with bonding of waste materials with inorganic binders.
Organics may interfere with bonding of waste materials.
Weaken bonds between waste particles and cement by coating the particles. Decrease in unconfined
compressive strength with increased concentrations of oil and grease.
Insoluble material passing through a No. 200 mesh sieve can delay setting and curing. Small particles
can also coat larger particles, weakening bonds between particles and cement or other reagents.
Particle size >1 /4 inch in diameter not suitable.
May retard setting, easily leached for cement and pozzolan S/S. May dehydrate thermoplastic
solidification.
Reduced physical strength of final product caused by large variations in setting time and reduced
dimensional stability of the cured matrix, thereby increasing leachability potential.
Cyanides interfere with bonding of waste materials.
Retard setting and curing and weaken strength of final product.
Retard setting and cause swelling and spading in cement S/S. With thermoplastic solidification may
dehydrate and rehydrate, causing splitting.
* Adapted from reference 2
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
Table 3
Summary of Factors that May Interfere with Solidification Processes * (continued)
Characteristics Affecting
Processing Feasibility
Phenols
Presence of coal or lignite
Sodium borate, calcium
sulfate, potassium
dichromate, and
carbohydrates
Nonpolar organics (oil,
grease, aromatic
hydrocarbons, PCBs)
Polar organics (alcohols,
phenols, organic acids,
glycols)
Solid organics (plastics, tars,
resins)
Oxidizers (sodium
hypochlorite, potassium
permanganate, nitric acid,
or potassium dichromate)
Metals (lead, chromium,
cadmium, arsenic, mercury)
Nitrates, cyanides
Soluble salts of magnesium,
tin, zinc, copper and lead
Environmental/waste
conditions that lower the
pH of matrix
Flocculants (e.g., ferric
chloride)
Soluble sulfates >0.01% in
soil or 1 50 mg/L in water
Soluble sulfates >0.5% in
soil or 2000 mg/L in water
Oil, grease, lead, copper,
zinc, and phenol
Aliphatic and aromatic
hydrocarbons
Chlorinated organics
Metal salts and complexes
Inorganic acids
Inorganic bases
Potential Interference
Marked decreases in compressive strength for high phenol levels.
Coals and lignites can cause problems with setting, curing, and strength of the end product.
Interferes with pozzolanic reactions that depend on formation of calcium silicate and aluminate
hydrates.
May impede setting of cement, pozzolan, or organic-polymer S/S. May decrease long-term durability
and allow escape of volatiles during mixing. With thermoplastic S/S, organics may vaporize from heat.
With cement or pozzolan S/S, high concentrations of phenol may retard setting and may decrease short-
term durability; all may decrease long-term durability. With thermoplastic S/S, organics may vaporize.
Alcohols may retard setting of pozzolans.
Ineffective with urea formaldehyde polymers; may retard setting of other polymers.
May cause matrix breakdown or fire with thermoplastic or organic polymer S/S.
May increase setting time of cements if concentration is high.
Increase setting time, decrease durability for cement-based S/S.
May cause swelling and cracking within inorganic matrix exposing more surface area to leaching.
Eventual matrix deterioration.
Interference with setting of cements and pozzolans.
Endangerment of cement products due to sulfur attack.
Serious effects on cement products from sulfur attacks.
Deleterious to strength and durability of cement, lime/fly ash, fly ash/cement binders.
Increase set time for cement.
May increase set time and decrease durability of cement if concentration is high.
Increase set time and decrease durability for cement or clay/cement.
Decrease durability for cement (Portland Type 1) or clay/cement.
Decrease durability for clay/cement; KOH and NaOH decrease durability for Portland cement Type III
and IV.
* Adapted from reference 2
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
materials in the mixture may increase rapidly with falling tem-
peratures or the cure rate may be slowed unacceptably [20, p.
27]. In cement-based S/S processes the engineering properties
of the concrete mass produced for the treatment of the waste
are highly dependent on the water/cement ratio and the de-
gree of hydration of the cement. High water/cement ratios
yield large pore sizes and thus higher permeabilities [21, p.
177]. This factor may not be readily controlled in environmen-
tal applications of S/S and pretreatment (e.g., drying) of the
waste may be required.
Depending on the waste and binding agents involved, S/S
processes can produce hot gases, including vapors that are
potentially toxic, irritating, or noxious to workers or communi-
ties downwind from the processes [22, p. 4]. Laboratory tests
demonstrate that as much as 90 percent of VOCs are volatilized
during solidification and as much as 60 percent of the remain-
ing VOCs are lost in the next 30 days of curing [23, p. 6]. In
addition, if volatile substances with low flash points are in-
volved, the potential exists for fire and explosions where the
fuel-to-air ratio is favorable [22, p. 4]. Where volatization
problems are anticipated, many S/S systems now provide for
vapor collection and treatment. Under dry and/or windy envi-
ronmental conditions, both ex situ and in situ S/S processes are
likely to generate fugitive dust with potentially harmful impacts
on occupational and public health, especially for downwind
communities.
Scaleup for S/S processes from bench-scale to full-scale
operation involves inherent uncertainties. Variables such as
ingredient flow-rate control, materials mass balance, mixing,
and materials handling and storage, along with the weather
compared to the more controlled environment of a laboratory,
all may affect the success of a field operation. These potential
engineering difficulties emphasize the need for a field demon-
stration prior to full-scale implementation [2].
Technology Description
Waste stabilization involves the addition of a binder to a
waste to immobilize waste contaminants effectively. Waste
solidification involves the addition of a binding agent to the
waste to form a solid material. Solidifying waste improves its
material handling characteristics and reduces permeability to
leaching agents such as water, brine, and inorganic and or-
ganic acids by reducing waste porosity and exposed surface
area. Solidification also increases the load-bearing capacity of
the treated waste, an advantage when heavy equipment is
involved. Because of their dilution effect, the addition of bind-
ers must be accounted for when determining reductions in
concentrations of hazardous constituents in S/S treated waste.
S/S processes are often divided into the following broad
categories: inorganic processes (cement and pozzolanic) and
organic processes (thermoplastic and thermosetting). Generic
S/S processes involve materials that are well known and readily
available. Commercial vendors have typically developed ge-
neric processes into proprietary processes by adding special
additives to provide better control of the S/S process or to
enhance specific chemical or physical properties of the treated
waste. Less frequently, S/S processes combine organic binders
with inorganic binders (e.g., diatomaceous earth and cement
with polystyrene, polyurethane with cement, and polymer gels
with silicate and lime cement) [2].
The waste can be mixed in a batch or continuous system
with the binding agents after removal (ex situ) or in place (in-
situ). In ex situ applications, the resultant slurry can be 1)
poured into containers (e.g., 55-gallon drums) or molds for
curing and then off- or onsite disposal, 2) disposed in onsite
waste management cells or trenches, 3) injected into the sub-
surface environment, or 4) re-used as construction material
with the appropriate regulatory approvals. In in situ applica-
tions, the S/S agents are injected into the subsurface environ-
ment in the proper proportions and mixed with the waste
using backhoes for surface mixing or augers for deep mixing
[5]. Liquid waste may be pretreated to separate solids from
liquids. Solid wastes may also require pretreatment in the form
of pH adjustment, steam or thermal stripping, solvent extrac-
tion, chemical reaction, or biodegradation to remove excessive
VOCs and SVOCs that may react with the S/S process. The type
and proportions of binding agents are adjusted to the specific
properties of the waste to achieve the desired physical and
chemical characteristics of the waste appropriate to the condi-
tions at the site based on bench-scale tests. Although ratios of
waste-to-binding agents are typically in the range of 10:1 to
2:1, ratios as low as 1:4 have been reported. However, projects
utilizing low waste-to-binder ratios have high costs and large
volume expansion.
Figures 1 and 2 depict generic elements of typical ex situ
and in situ S/S processes, respectively. Ex situ processing
involves: (1) excavation to remove the contaminated waste
from the subsurface; (2) classification to remove oversize de-
bris; (3) mixing; and (4) off-gas treatment. In situ processing
has only two steps: (1) mixing; and (2) off-gas treatment.
Both processes require a system for delivering water, waste,
and S/S agents in proper proportions and a mixing device (e.g.,
rotary drum paddle or auger). Ex situ processing requires a
system for delivering the treated waste to molds, surface
trenches, or subsurface injection. The need for off-gas treat-
ment using vapor collection and treatment modules is specific
to the S/S project.
Process Residuals
Under normal operating conditions neither ex situ nor in
situ S/S technologies generate significant quantities of contami-
nated liquid or solid waste. Certain S/S projects require treat-
ment of the offgas. Prescreening collects debris and materials
too large for subsequent treatment.
If the treated waste meets the specified cleanup levels, it
could be considered for reuse onsite as backfill or construction
material. In some instances, treated waste may have to be
disposed of in an approved landfill. Hazardous residuals from
some pretreatment technologies must be disposed of accord-
ing to appropriate procedures.
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
Figure 1.
Generic Elements of a Typical Ex Situ S/S Process
S/S Binding
Agent(s)
Excavation
0)
1
VOC Capture
and
Treatment
^-
Classification
(2)
1
Oversize
Rejects
1
Crusher
^ Mixing
(3)
t
Water
Off-Gas
Treatment
(optional)
(4)
_*^ Stahili7Ad/
Media
— *- Rc
Solidified
Residuals
Figure 2.
Generic Elements of a Typical In Situ S/S Process
Water— ^
S/S Binding — *»
Agent(s)
^
Mixing
(1)
Stab
Medi
lized/Solidified
a
Off-Gas
Treatment
(optional)
(2)
^ Residuals
Site Requirements
The site must be prepared for the construction, operation,
maintenance, decontamination, and ultimate decommission-
ing of the equipment. An area must be cleared for heavy
equipment access roads, automobile and truck parking lots,
material transfer stations, the S/S process equipment, set up
areas, decontamination areas, the electrical generator, equip-
ment sheds, storage tanks, sanitary and process wastewater
collection and treatment systems, workers' quarters, and ap-
proved disposal facilities (if required). The size of the area
required for the process equipment depends on several factors,
including the type of S/S process involved, the required treat-
ment capacity of the system, and site characteristics, especially
soil topography and load-bearing capacity. A small mobile ex
situ unit could occupy a space as small as that taken up by two
standard flatbed trailers. An in situ system requires a larger area
to accommodate a drilling rig as well as a larger area for auger
decontamination.
Process, decontamination, transfer, and storage areas should
be constructed on impermeable pads with berms for spill reten-
tion and drains for the collection and treatment of stormwater
runoff. Stormwater storage and treatment capacity require-
ments will depend on the size of the bermed area and the local
climate. Standard 440V, three-phase electrical service is usually
needed. The quantity and quality of process water required for
pozzolanic S/S technologies are technology-specific.
S/S process quality control requires information on the
range of concentrations of contaminants and potential
interferants in waste batches awaiting treatment and on treated
product properties such as compressive strength, permeability,
teachability, and in some instances, contaminant toxicity.
Performance Data
Most of the data on S/S performance come from studies
conducted for EPA's Risk Reduction Engineering Laboratory
under the Superfund Innovative Technology Evaluation (SITE)
Program. Pilot scale demonstration studies available for review
during the preparation of this bulletin included: Soliditech, Inc.
at Morganville, New Jersey (petroleum hydrocarbons, PCBs,
other organic chemicals, and heavy metals); International Waste
Technologies (IWT) process using the Geo-Con, Inc. deep-soil-
mixing equipment, at Hialeah, Florida (PCBs, VOCs); Chemfix
Technologies, Inc., at Clackamas, Oregon (PCBs, arsenic, heavy
metals); Im-Tech (formerly Hazcon) at Douglassville, Pennsyl-
vania (oil and grease, heavy metals including lead, and low
levels of VOCs and PCBs); Silicate Technology Corporation
(STC), at Selma, California (arsenic, chromium, copper, penta-
chlorophenol and associated polychlorinated dibenzofurans and
dibenzo-p-dioxins). The performance of each technology was
evaluated in terms of ease of operation, processing capacity,
frequency of process outages, residuals management, cost, and
the characteristics of the treated product. Such characteristics
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
included weight, density, and volume changes; DCS and mois-
ture content of the treated product before and after freeze/
thaw and wet/dry weathering cycles; permeability (or
permissivity) to water; and teachability following curing and
after the weathering test cycles, teachability was measured
using several different standard methods, including EPA's TCLP.
Table 4 summarizes the SITE performance data from these sites
[20] [24] [25] [26] [27] [28].
A full-scale S/S operation has been implemented at the
Northern Engraving Corporation (NEC) site in Sparta, Wiscon-
sin, a manufacturing facility which produces metal name plates
and dials for the automotive industry. The following informa-
tion on the site is taken from the remedial action report. Four
areas at the site that have been identified as potential sources of
soil, groundwater, and surface water contamination are the
sludge lagoon, seepage pit, sludge dump site, and lagoon
drainage ditch. The sludge lagoon was contaminated primarily
with metal hydroxides consisting of nickel, copper, aluminum,
fluoride, iron, and cadmium. The drainage ditch which showed
elevated concentrations of copper, aluminum, fluoride, and
chromium, was used to convey effluent from the sludge lagoon
to a stormwater runoff ditch. The contaminated material in the
drainage ditch area and sludge dumpsite was then excavated
and transported into the sludge lagoon for stabilization with
the sludge present. The vendor, Geo-Con, Inc., achieved stabi-
lization by the addition of hydrated lime to the sludge. Five
samples of the solidified sludge were collected for Extraction
Procedure (EP) toxicity leaching analyses. Their contaminant
concentrations (in mg/l) are as follows: Arsenic (<.01); Barium
(.35 -1.04); Cadmium (<.005); Chromium (<.01); Lead (<.2);
Mercury (<.001); Selenium (<.005); Silver (<.01); and Fluoride
(2.6 - 4.1). All extracts were not only below the EP toxicity
criteria but (with the exception of fluoride) met drinking water
standards as well.
Approximately three weeks later DCS tests on the solidified
waste were taken. Test results ranged from 2.4 to 10 psi, well
below the goal of 25 psi. One explanation for the low DCS
could be due to shear failure along the lenses of sandy material
and organic peat-like material present in the samples. It was
determined that it would not be practical to add additional
quantities of lime into the stabilized sludge matrix because of its
high solids content. Therefore, the stabilized sludge matrix
capacity will be increased to support the clay cap by installing
an engineered subgrade for the cap system using a stabilization
fabric and aggregate prior to cap placement [29].
The Industrial Waste Control (IWC) Site in Fort Smith,
Arkansas, a closed and covered industrial landfill built in an
abandoned surface coal mine, has also implemented a full-scale
S/S system. Until 1978 painting wastes, solvents, industrial
process wastes, and metals were disposed at the site. The
primary contaminants of concern were methylene chloride,
ethylbenzene, toluene, xylene, trichloroethane, chromium, and
lead. Along with S/S of the onsite soils, other technologies used
were: excavation, slurry wall, french drains, and a landfill cover.
Soils were excavated in the contaminated region (Area C) and a
total of seven lifts were stabilized with flyash on mixing pads
previously formed. A clay liner was then constructed in Area C
to serve as a leachate barrier. After the lifts passed the TCLP test
they were taken to Area C for in situ solidification. Portland
cement was added to solidify each lift and they obtained the
DCS goal of 125 psi. With the combination of the other tech-
nologies, the overall system appears to be functioning property
[30].
Other Superfund sites where full scale S/S has been com-
pleted to date include Davie Landfill (82,158 yd3 of sludge
containing cyanide, sulfide, and lead treated with Type I Port-
land cement in 45 days) [31 ]; Pepper's Steel and Alloy (89,000
yd3 of soil containing lead, arsenic, and PCBs treated with
Portland cement and fly ash) [32]; and Sapp Battery and
Salvage (200,000 yd3 soil fines and washings containing lead
and mercury treated with Portland cement and fly ash in roughly
18 months) [33], all in Region 4; and Bio-Ecology, Inc. (about
20,000 yd3 of soils, sludge, and liquid waste containing heavy
metals, VOCs, and cyanide treated with cement kiln flue dust
alone or with lime) in Region 6 [34]. All sites required that the
waste meet the appropriate leaching test and UCS criteria. At
the Sapp Battery site, the waste also met a permeability crite-
rion of 10'6 cm/s [33]. Past remediation appraisals by the
responsible remedial project managers indicate the S/S tech-
nologies are performing as intended.
RCRA LDRs that require treatment of wastes based on
BOAT levels prior to land disposal may sometimes be deter-
mined to be Applicable or Relevant and Appropriate Require-
ments (ARARs) for CERCLA response actions. S/S can produce a
treated waste that meets treatment levels set by BOAT but may
not reach these treatment levels in all cases. The ability to meet
required treatment levels is dependent upon the specific waste
constituents and the waste matrix. In cases where S/S does not
meet these levels, it still may in certain situations be selected for
use at a site if a treatability variance establishing alternative
treatment levels is obtained. Treatability variances may be
justified for handling complex soil and debris matrices. The
following guides describe when and how to seek a treatability
variance for soil and debris: Superfund LDR Guide #6A, "Ob-
taining a Soil and Debris Treatability Variance for Remedial
Actions" (OSWER Directive 9347.3-06FS) [16], and Superfund
LDR Guide #6B, "Obtaining a Soil and Debris Treatability Vari-
ance for Removal Actions" (OSWER Directive 9347.3-06BFS)
[17]. Another approach could be to use other treatment tech-
niques in conjunction with S/S to obtain desired treatment
levels.
Technology Status
In 1990,24 RODs identified S/S as the proposed remediation
technology [35]. To date only about a dozen Superfund sites
have proceeded through full-scale S/S implementation to the
operation and maintenance (O&M) phase, and many of those
were small pits, ponds, and lagoons. Some involved S/S for off-
site disposal in RCRA-permitted facilities. Table 5 summarizes
these sites where full scale S/S has been implemented under
CERCLA or RCRA [7, p. 3-4].
More than 75 percent of the vendors of S/S technologies
use cement-based or pozzolanic mixtures [11, p. 2]. Organic
polymers have been added to various cement-based systems to
enhance performance with respect to one or more physical or
8
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
-------
Table 4. Summary of SITE Performance Data
Site
Vendor Technology
Pretreatment
Post Treatment
Imperial Oil Co. /
Champion Chemical Co.
Morganville, NJ
Soliditech: Urrichem reagent, water,
additives, Type II Portland cement
Bulk density: 1.14 to 1.26 g/cm3
Permeability: Not determined
DCS: Not determined
Lead-TCLP Extract 0.46 mg/l
Bulk density: 1.43 to 1.68 g/cm3
Permeability: 8.9x10* to 4.5x1 a7 cm/s
UCS: 390 to 860 psi
Lead-TCLP extract: <0.05 to <0.20 mg/l
CE Electrical Service Shop
Hialeah, PL
IWT-DMS/Geo-Con:
In situ injection of silicate additive
Bulk density: 1.55 g/ml
Permeability: 1.8x102 cm/s
UCS: 1.2 to 1.85 psi
Bulk density: 1.88 g/ml
Permeability: 0.24x10' to 21x107 cm/s
UCS: 300 to 500 psi
Portable Equipment
Salvage Co.
Clackamas, OR
Chemfix: polysilicates and dry
calcium containing reagents
TCLP-Extractable (Pb, Cu, Zn):
12 to 880 mg/l
Hydraulic cond. (CSS-13):
2.4x10" to 2.7x10* cm/s
Bulk density: 2.0 to 2.6 g/cmj
TCLP-Extractable (Pb, Cu, Zn): 0.024 to 47 mg/l
Hydraulic cond. (CSS-14): 4.6x1 a7 to 1.2x10" cm/s
Bulk density: 1.6 to 2.0 g/cm1
USC (14, 21, 28 days): 131,136,143 psi
Immersion UCS (30, 60,90 days): 177,188, 204 psi
Douglasville
Douglasville, PA
Imtech (Hazcon): Chloranan™,
water and cement
Bulk density: 1.23 g/ml
Permeability: 0.57 cm/s
TCLP-Extractable Pb: 52.6 mg/l
Bulk density (7, 28 days): 1.95,1.99 g/ml
Permeability (7, 28 days): 1.6x10', 2.3x10* cm/s
TCLP-Extractabte Pb (7,28 days): 0.14,0.05 mg/l
UCS (7,28 days): 1447,113 psi
Selma Pressure Treating
Wood Preserving Site
Selma, CA
Silicate Tech Corp.:
alumino-silicate compounds
Arsenic-TCLP: 1.06 to 3.33 ppm
Arsenic-Distilled HX) TCLP: 0.73 to 1.25 ppm
PCP-TWA:1983to8317ppm
Bulk density: 1.42 to 1.54 g/cm
Arsenic-TCLP: 0.086 to 0.875 ppm
Arsenic-Distilled H20 TCLP: < 0.01 to 0.012 ppm
PCP-TWA:14to158ppm
Bulk density: 1.57 to 1.62 g/cm
Permeability: 0.8x107 to 1.7x1 a7 cm/s
UCS: 259 to 347 psi
UCS - Unconfined Compressive Strength
TCLP - Toxicity Characteristic Leaching Procedure
TWA - Total Waste Analysis
-------
Table 5. Summary of Full Scale S/S Sites
Site
independent Na8, SC
Midwest, US Plating
Company
Unnamed
Marathon Steel,
Phoenix, AZ
Alaska Refinery
Unnamed, Kentucky
Nfcfteitoery
Velsicol Chemical
Amoco Wood River
Pepper Steel & Alloy,
Miami, PL
Victory, Onto
Wood Treating,
Savannah, CA
Chem Refinery, IX
API Sep. Sludge,
Puerto Rico
Metaplating, W1
Contaminant
Cu, Cr, Ni
Pb/soit2-100ppm
Pb, Cd
Oil/oil sludges
Vinyl chloride
Ethylene dichloride
Oil skidges, Pb, Cr, As
Pesticides and organics (resins,
etc.) up to 45% organic
Oil saturated soil
Pb-1 000 ppm
PCBs-200 ppm
As-1 -200 ppm
Waste add
PCBs(<50Oppm>
dtoxirtt
Creosote wastes
Combined metals, sulfur, oft
sludges, etc>
API separator sludges
Ni-750 ppm
Cr-220 ppm
Physical Form
Solid/soils
Sludge
*•**
Dry-landfill
Sludges, varla We
Sludges, variable
SKidges, variabte
Sludges, variable
Soils
Sludgy (viscous)
Sludges
Stodges
(synthetic 08 sludges)
Sludges
Sludges
Binder
Portland cement:
Portland cement
Portland cement and
proprietary ingredient
Portland cement and silicates
Portland cement and
Portland cement and
proprietary ingredient
K8ndt»st(highCaO content)
Portland cement and kiln dust,
proprietary ingredient
J*W|Jt8et«y Ingredient
Pozzolanic and proprietary
ingredient
Lime and fcttndtist
Kiln dust
Portland cement and
proprietary ingredient
Portland cement and
proprietary ingredient
tfene
Percentage Binder(s)
Added
20%
20%
CememC1S*ao%)
proprietary ($%}
Varied 7-1 5%
(cement)
Varied 50+
Varied 25+
*ft*is4mi
Varied (cement 5-15%)
-30%
3RSSU .
20%
NA
50% cement
-4 % proprietary
10-25%
Treatment (batch/
continuous In Situ)
In Situ
:*»
Concrete batch plant
Coi>cr«te t»tch ptant
In Situ
in Situ
In Situ
Continuous feed (mixer
proprietary design)
1*** . •
In Situ
&Bte«—
Concrete batch plant
InSttu
-------
chemical characteristics, but only mixed results have been
achieved. For example, tests of standardized wastes treated in
a standardized fashion using acrylonitrile, vinyl ester, polymer
cement, and water-based epoxy yielded mixed results. Vinyl
and plastic cement products achieved superior UCS and leach-
ability to cement-only and cement-fly ash S/S, while the acry-
lonitrile and epoxy polymers reduced UCS and increased leach-
able TOC, in several instances by two or three orders of
magnitude [36, p. 156].
The estimated cost of treating waste with S/S ranges from
$50 to 250 per ton (1992 dollars). Costs are highly variable
due to variations in site, soil, and contaminant characteristics
that affect the performance of the S/S processes evaluated.
Economies of scale likely to be achieved in full-scale operations
are not reflected in pilot-scale data.
EPA Contact
Technology-specific questions regarding S/S may be di-
rected to:
Carlton C. Wiles or Patricia M. Erickson
U.S. Environmental Protection Agency
Municipal Solid Waste and Residuals
Management Branch
Risk Reduction Engineering Laboratory
5955 Center Hill Road
Cincinnati, OH 45224
Telephone: (513) 569-7795 or (513) 569-7884
Acknowledgments
This bulletin was prepared for the US Environmental Pro-
tection Agency, Office of Research and Development (ORD),
Risk Reduction Engineering Laboratory (RREL), Cincinnati, Ohio,
by Science Applications International Corporation (SAIQ under
contract No. 68-C8-0062 (WA 2-22). Mr. Eugene Harris served
as the EPA Technical Project Manager. Mr. Gary Baker was
SAIC's Work Assignment Manager. This bulletin was written by
Mr. Larry Fink and Mr. George Wahl of SAIC. The authors are
especially grateful to Mr. Carlton Wiles and Mr. Edward Bates of
EPA, RREL and Mr. Edwin Barth of EPA, CERI, who have contrib-
uted significantly by serving as technical consultants during the
development of this document.
The following other EPA and contractor personnel have
contributed their time and comments by participating in the
expert review meetings or peer reviews of the document:
Dr. Paul Bishop
Dr. Jeffrey Means
Ms. Mary Boyer
Mr. Cecil Cross
Ms. Margaret Groeber
Mr. Eric Saylor
University of Cincinnati
Battelle
SAIC-Raleigh
SAIC-Raleigh
SAIC-Cincinnati
SAIC-Cincinnati
Engineering Bulletin: Solidification/Stabilization of Organics and Inorganics
11
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12
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