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metals depends on their oxidation state. Therefore, Eh can Indicate the
stability of various chemical species In the waste's chemical environment.
3.3.3 Major Oxide Components
The major oxide components can be used to characterize the mineralo-
gy of the S/S-treated waste. Analytical techniques for determining Si02,
Fe203, A1203, CaO, MgO, and loss on ignition are described in ASTM C 114.
Between 10 and 30% of cementitious solids will be in the form of oxides.
3.3.4 Total Organic Carbon (TOO
The TOC analysis measures the overall level of organic compounds
present in a liquid, sludge, or solid sample. TOC is measured by U.S. EPA
SW-846 Method 9060. This method uses combustion with infrared, thermoconduc-
tivity, or other detection. The TOC results can be used to approximate the
levels of nonpurgeable organic carbon and to estimate the potential for
organic interference in the S/S process.
3.3.5 Oil and Grease
Oil and grease analysis determines the total content of oil and
grease in a sample. This analysis can be done by U.S. EPA SW-846 Method 9070
or 9071. The determination before and after treatment provides a method of
assessing the effectiveness of the S/S process in immobilizing oil and grease
in the waste. Oil and grease analysis of asphaltic solid leachates is
important for determining whether the S/S process aids in stabilizing oil and
grease or whether the asphalt increases oil and grease Teachability. In addi-
tion, oil and grease interfere with cement or pozzolan-based S/S treatment.
3.3.6 Electrical Conductivity
The electrical conductivity of a solution is a measure of its
ability to carry current. Conductivity varies with the concentration and type
of ions present. Solution conductivity can be measured by U.S. EPA Method
120.1 or U.S. EPA SW-846 Method 9050. Conductivity of leachates from untreat-
ed and S/S-treated wastes can be compared to find the relative ionic concen-
trations in the two solutions. In addition, test results from untreated and
S/S-treated waste leachates can be compared with conductivities of natural
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surface and subsurface waters in the vicinity of the demonstration site and/or
potential disposal site. Wide differences in the conductivity of leachate and
natural waters create the potential for the waste leachate to cause conductiv-
ity fluctuations in adjacent receiving waters.
3.3.7 Add Neutralization Capacity (ANC and GANG)
These buffering capacity tests indicate the capacity of the S/S-
treated waste to maintain an elevated pH when exposed to acidic solutions.
The ANC test involves separate extraction of S/S-treated waste samples with
leaching solutions of varying levels of acidity. Ten waste samples are
predried and crushed to a particle size of -100 mesh. Each sample is extract-
ed for 24 hours in one of 10 nitric acid solutions. The acid equivalents per
gram of solid increases incrementally from sample 1 to sample 10. Following
the extraction, the pH of each solution is measured. The amount of decrease
in pH of the leach solutions with each increase in acid concentration indi-
cates the buffering capacity of the S/S-treated waste. Smaller decreases
indicate higher buffering capacity. The higher the buffering capacity, the
greater the possibility of maintaining alkaline conditions conducive to metal
retention. The GANC is a similar test developed to be consistent with the
TCLP test (Isenburg and Moore, 1992).
3.3.8 Alkalinity
Alkalinity indicates the capacity of a solution such as a leachate
to neutralize acid solutions to specific pH levels. It can be measured by
U.S. EPA Method 403.
3.3.9 Total Dissolved Solids (TDS1
The TDS analysis indicates the total quantity of solid material
dissolved in a solution. It can be measured by U.S. EPA Method 209B. The TDS
levels in leaching solutions can be used to track the degradation of S/S-
treated waste solid or leaching of constituents from the sample. TDS is also
a drinking water standard.
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3.3.10 Reactive Cvanide and Sulfide
The analyses for reactive cyanide and sulfide apply to waste
containing cyanide- or sulfide-bearing material. Sulfide can be present in
the waste either as a natural waste constituent or as a binder additive. If
waste exposed to a pH in the range of 2 to 12.5 can generate toxic gases,
vapors, or fumes in sufficient quantity to present a danger to human health or
the environment, it is deemed to contain reactive cyanide or sulfide. The
tests for reactive cyanide and sulfide are described in U.S. EPA SW-846
(1986c) Section 7.3. Testing for reactive cyanide and sulfide may be required
for some RCRA wastes under regulation 40 CFR 261.23-(a)(5).
3.3.11 Reactivity of Silica Aggregates
The test for reactivity of silica aggregates measures the propensity
of silica in the waste to react with alkaline components of Portland cement/
concrete mixtures or similar S/S binders. The potential for silica in suspect
aggregates to react with alkaline compounds is determined by ASTM C 289.
Reactive silica and alkaline compounds combine to form silicate-alkali gels
that expand to cause internal stress in the S/S-treated waste. The internal
stress can result in cracking or spall ing.
3.3.12 Metal Analysis
Metal analyses can be applied to aqueous leach solutions to deter-
mine the concentrations of metals leached from the S/S-treated waste. Metal
analysis tests can also be used, following a suitable strong acid digestion
step, to measure the total metal concentrations in the untreated or S/S-
treated waste. Metals can be determined in accordance with U.S. EPA SW-846
Methods 6010 (analysis by inductively coupled plasma atomic emission spectro-
scopy [ICP]) or 7000 and associated 7000 series methods (analysis by atomic
absorption spectroscopy [AA]). The material should be pretreated with the
appropriate digestion procedure (U.S. EPA SW-846 Methods 3005, 3010, 3020,
3040, and 3050).
3.3.13 Volatile Organic Compounds
The VOC test evaluates the types and concentrations of low-boiling-
point organic materials present in a sample. U.S. EPA SW-846 Method 8240
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describes the extraction and analysis of VOCs by gas chromatography/mass
spectrometry (GC/MS) techniques. This method will quantify most organic
compounds with a boiling point below 200ฐ C. Concentrations of VOCs in
solvent extracts of untreated and S/S-treated wastes can be used to indicate
if the compounds have been stabilized during the S/S process, provided
measures were taken to account for volatilization or degradation. Concentra-
tions of VOCs in TCLP extracts can indicate the aqueous Teachability of the
VOCs from S/S-treated wastes. Extreme caution must be paid to the possible
release of VOCs during waste sampling, handling, storage, treatability test-
ing, or analysis. The potential for volatilization of the organic contami-
nants is so great that a mass balance is generally needed to demonstrate that
a reduction in volatile organic content after treatment is truly due to
immobilization as opposed to volatilization. Although organic leaching may be
low in aqueous leaching tests, this may also be a result of low solubility of
the organic in water rather than immobilization of the organic.
3.3.14 Base. Neutral, and Acid fBNA) Organic Compounds
The analyses for basic, neutral, and acidic organic compounds are
performed by extraction (U.S. EPA SW-846 Method 3510, 3520, or 3540) followed
by GC/MS analysis (U.S. EPA SW-846 Method 8270). Certain BNAs can be target
contaminants for S/S. Measurements of BNAs in solvent extracts of untreated
and treated wastes can determine the fate of organics during the S/S process,
provided measures were taken to account for volatilization or degradation.
Data on concentrations of BNAs in aqueous extracts can be used to assess the
effectiveness of the S/S process in reducing the amount of aqueous Teachable
BNAs. However, like VOCs, certain BNAs have low aqueous solubility. Thus,
the immobilization of such compounds should be evaluated in organic solvent
extracts of appropriate polarity.
3.3.15 Polvchlorinated Biphenyls (PCBs)
The PCB analysis measures the concentration of polychlorinated
biphenyls. PCBs are determined by extraction (U.S. EPA SW-846 Method 3540 or
3520), followed by GC/MS analysis (U.S. EPA SW-846 Method 8080) or by U.S. EPA
Method 608. Quantities of PCBs in solvent extracts of untreated and S/S-
treated wastes can determine the fate of the PCBs during the S/S process,
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provided that measures were taken to conduct mass balances and account for any
PCB volatilization during the treatability study. Conducting aqueous leaching
tests on PCB-contaminated wastes is generally fruitless because of the low
aqueous solubilities of PCB compounds.
3.3.16 Other Contaminant Analyses
Several of the more common waste contaminants not specifically
included in Sections 3.3.1 through 3.3.15 are mercury, pesticides, and
herbicides. Analytical methods are available for measuring such constituents
in either aqueous or organic solvent extracts (see Table 3-4).
3.3.17 Anion Measurements
Anions can be measured by ion chromatography, as described by Water
and Wastewater Standard Method 4110 or by U.S. EPA Method 300. This analysis
is used to determine the concentration of anions in leach solutions.
3.3.18 Interferants Screen
Interferants screening tests involve a series of analyses for
concentrations of materials that can interfere with S/S treatment. The waste
is tested for oil and grease, potassium, sodium, fluoride, chloride, ortho-
phosphate, ammonia, nitrate, and sulfate.
3.4 BIOLOGICAL TESTS
Biological tests applicable to S/S processes include biodegradation
tests and bioassays. Table 3-5 shows some representative biological tests and
presents information about the standard methods for each. Biological tests
are typically conducted only in special circumstances such as testing the
potential biodegradability of organic binders or the aquatic toxicity of the
treated waste.
Biological testing can be used to measure either the degradation of
the matrix leading to release of contaminants or the alteration of contaminant
properties to increase their mobility or toxicity. Standard tests for matrix
degradation exist, but none are available for biologically induced changes in
the contaminants.
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TABLE 3-5. BIOLOGICAL TESTS
Test Procedure
Method
Material
Application
U S L
Purpose
(a)
CO
en
Biodegradation Tests
Biodegradability of plastics ASTM G 21-90,
G 22-76
Biodegradability of paints
Biodegradability of
alkylbenzene sulfonates
ASTM D 3273-86,
D 3274-82,
D 3456-86
To determine whether biodegradation
may decrease long-term stability of
S/S wastes.
To determine whether biodegradation
may decrease long-term stability of
S/S wastes.
To determine whether biodegradation
may decrease long-term stability of
S/S wastes.
Bioassavs
Assessing the hazard of a
material to aquatic organisms
ASTM E 1023-84
XXX To evaluate acute aquatic toxicity at
a point source discharge, e.g., a
leachate collection system. May be
required by state or federal ARARs.
(a)
Testing Application: Biological testing is normally applied as part of an experimental program.
Material Application Guide:
U = Untreated Samples
S = S/S-treated Sample
L = Liquid Sample
-------
Biodegradation tests are used to measure the biodegradability of
various waste materials, almost exclusively organic binders such as asphalt or
plastic. Biodegradation is one possible degradation mechanism for such
binders. At present, the U.S. EPA recommends no particular methods for evalu-
ating the biodegradation of S/S-treated wastes. In general, binders that
produce an alkaline environment (e.g., Portland cement-based processes) are
not favorable for microbial activity; however, this may not be true for
proprietary binders and processes that are tailored to treat organic wastes.
Bioassays are performed only when the proximity of the treated waste
disposal site poses a threat to an aquatic community. If a site undergoing
S/S treatment has a point source discharge, such as from a leachate collection
system, bioassays may be required to meet federal or state ARARs. However,
note that the alkaline nature of many S/S binders may elicit a toxic response
during the bioassay, which may far outweigh any acute toxic response from the
contaminants in the waste.
Although the results of bioassays may provide evidence of reduced
toxicity after S/S treatment, predictions of toxicity from bioassays are
highly site-specific and must be combined with data on exposure pathways for a
specific site. Acute bioassays may be performed rapidly and at low cost, but
they do not predict the response of the test organism to chronic, low-level
contamination. The bioassay techniques that most accurately predict long-term
environmental effects are expensive and time-consuming.
3.5 MICROCHARACTERIZATION
Special methods developed for mineralogic and materials science
testing are applicable to specialized, detailed characterization of materials
for S/S treatment (Hannak and Liem, 1986). These nonroutine tests can be
applied for detailed analysis of the structure of S/S-treated waste or to
better understand the physicochemical form of the target contaminants.
Table 3-6 lists a few of the many tests that can be applied to microcharac-
terization. However, note also that microcharacterization tests provide
special research and problem-solving tools that would not be used in the vast
majority of S/S treatability studies.
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TABLE 3-6. MICROCHARACTERIZATION TESTS
Test Procedure
Method
Purpose(a>
X-Ray Powder Diffraction
Fourier Transform Infrared
(FTIR) Spectroscopy
Scanning Electron Microscopy
(SEM) and Energy-Dispersive
X-Ray Analysis (EDAX)
Nuclear Magnetic Resonance
(NMR) Spectroscopy
Optical Microscopy
Transmitted Light, Reflected
Light, and Polarized Light
ASTM
ASTM
E 1252-88
E 168-88
ASTM C 856-83
ASTM C 295-90
To identify crystalline matrix
and contaminant phases
To identify the presence or
absence of functional groups
in a molecule
To examine the physical
structure and chemical makeup
of the surface of a material
on the microscopic scale
To identify and characterize
molecules
To study microstructure of
S/S-treated waste
(a) Microcharacterization tests are typically applied to treated waste as
part of an experimental program.
3.5.1 X-Ray Diffraction
X-ray diffraction examines the crystal structure of a material.
X-rays are scattered and diffracted by the lattice structure of crystals,
yielding patterns characteristic to various crystals based on the lattice
spacing. The crystalline components of a mixture, including crystalline
phases of the contaminant or contaminants, in amounts of 1% or more can be
identified individually by the X-ray diffraction patterns produced. However,
noncrystalline components are not detected.
3.5.2 Fourier Transform Infrared (FTIR) Spectroscopy
The FTIR Spectroscopy analytical technique can identify the presence
or absence of functional groups within a molecule. The class or type of
compound can be deduced, although positive identification of the exact
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composition of the unknown is not always possible. This technique can be
useful in determining the physicochemical form of the contaminant in either
treated or untreated waste.
3.5.3 Scanning Electron Microscopy (SEH) and
Energy-Dispersive X-ray Analysis (EDXA)
SEM is a technique for examining the surfaces of solid materials.
The method provides a large depth of field, so it is frequently possible to
observe three-dimensional structures in a sample. By adding an EDXA detector
to the SEM, it is possible to obtain simultaneous, multi-element analysis.
This technique can be useful in determining the physicochemical form of the
contaminant in either treated or untreated waste.
3.5.4 Nuclear Magnetic Resonance (NHR) Spectroscopy
NMR spectroscopy identifies and characterizes molecules. Data from
NMR analysis delineate complete sequences of groups or arrangements of atoms
in a molecule. This technique has been used successfully to characterize the
physicochemical form of the contaminant in the treated waste and to help
elucidate the mechanism of contaminant immobilization.
3.5.5 Optical Microscopy
The arrangement of phase structures in a solid sample can be
observed and measured by thin section transmission microscopy or reflected
light microscopy. Optical properties, such as refractive index, also can be
measured. Additional petrographic information can be obtained by using
polarized light microscopy. This is another possible analytical tool for
characterizing contaminant speciation and physicochemical form.
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4 STATUS OF SOLIDIFICATION/STABILIZATION TECHNOLOGY
This chapter of the TRD reviews and summarizes existing literature
on a wide variety of subjects and issues pertaining to S/S technology. A
number of books and summary reports on various aspects of S/S are available.
These resource documents include the following:
ASTM (1989),STP 1033, Environmental Aspects of
Stabilization and Solidification of Hazardous and
Radioactive Hastes, American Society for Testing and
Materials.
ASTM (1992), STP 1123. Stabilization and
Solidification of Hazardous, Radioactive, and Nixed
Wastes, American Society for Testing and Materials.
Conner, J.R. (1990), Chemical Fixation and
Solidification of Hazardous Waste, Van Nostrand
Reinhold.
Czupyrna, G., et al. (1989), In Situ Immobilization
of Heavy-Metal-Contaminated Soils, Noyes Data
Corporation
Pojasek, R. (1979), Toxic and Hazardous Waste
Disposal, Options for Solidification/Stabilization,
Ann Arbor Science Publishers
U.S. EPA (1990e), Handbook on In Situ Treatment of
Hazardous Haste-Contaminated Soils
U.S. EPA (1989b), Immobilization Technology Seminar,
Speaker Slide Copies and Supporting Information
U.S. EPA (1986c), Handbook for Solidification/
Stabilization of Hazardous Hastes
U.S. EPA (1983), Feasibility of In Situ
Solidification/Stabilization of Landfilled Hazardous
Hastes
U.S. EPA (1980), Guide to the Disposal of Chemically
Stabilized and Solidified Haste.
Overview-type information on specific S/S issues can be found in Sections 4.1
through 4.10. Sections 4.1 and 4.2 describe the types of S/S binders and
their binding mechanisms. Applicable waste and contaminant types are dis-
cussed in Section 2.2.3.2. Section 4.3 outlines the interferences to S/S that
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arise from waste constituents. Section 4.4 deals with S/S treatment of
organic contaminants. Section 4.5 discusses air emissions from organic
constituents, particulates, and other emissions. Sections 4.6 and 4.7
describe leaching mechanisms and long-term stability. Sections 4.8 and 4.9
discuss reuse and disposal issues. Section 4.10 gives cost estimates for S/S
testing, materials, and processes. The publications referenced in Chapter 7
provide additional technical details.
4.1 S/S PROCESSES AND BINDERS
Solidification/stabilization processes are "nondestructive" methods
to immobilize the hazardous constituents in a waste. S/S processes are
nondestructive in the sense that they do not remove or reduce the quantities
of these constituents. Typically, S/S processes physically sorb, encapsulate,
or change the physicochemical form of the pollutant in the waste, resulting in
a less Teachable product. Concentrations of contaminants in the treated waste
are often lower than in the untreated waste, primarily because of incidental
dilution by the binder rather than by destruction or removal of the contami-
nants.
S/S processes can generally be grouped into inorganic processes
(cement and pozzolanic) and organic processes (thermoplastic and thermosetting
polymers). In addition to the individual use of inorganic and organic
binders, some systems combine organic with inorganic binders. For example:
Diatomaceous earth with cement and polystyrene
Polyurethane with cement
Polymer gels with silicate and lime cement
The basic S/S processes are generic, and many of the basic materials are
readily available. A variety of additives are used to promote the development
of specific chemical or physical properties. Pretreatment may also be used to
better prepare the waste for treatment by an S/S process.
S/S technology is offered commercially by a large number of vendors.
The specifics of vendor technology are in most cases protected as proprietary
and are not disclosed to the potential user except under agreement of confi-
dentiality. The majority of vendors use conventional S/S technology supple-
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mented by a variety of additives and know-how from previous experience in
applying this technology.
4.1.1 Inorganic Binders
The two principal types of inorganic binders are cement binders and
pozzolanic binders (lime, kiln dust, fly ash). A pozzolan is a material
containing silica or silica and alumina that has little or no cementation
value itself but, under some conditions, can react with lime to produce
cementitious material. Cement-based and pozzolanic processes or a combination
of cement and pozzolans are the methods of choice in the S/S industry today.
This probably is attributable to the low cost of the materials, their applica-
bility to a wide variety of waste types, and the ease of operation in the
field. The most common inorganic binders are:
Portland cement
Lime/fly ash
Kiln dust (lime and cement)
Portland cement/fly ash
Portland cement/lime
Portland cement/sodium silicate
These binders are routinely used to solidify water-based waste
liquids, sludges, and filter cakes. The lime/fly ash process probably has
been used most extensively in the United States, in terms of the total volume
of waste treated. The treatment of flue gas desulfurization (FGD) sludges
from coal-fired power plants accounts for much of the lime/fly ash process
application. Specifications are available for a wide variety of cement and
pozzolanic materials. ASTM standards for these materials include:
C311: Method for Sampling and Testing Fly Ash or
Natural Pozzolans for Use as a Mineral Admixture in
Portland Cement Concrete
C400: Test Methods of Testing Quicklime and
Hydrated Lime for Neutralization of Waste Acid
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C593: Specification for Fly Ash and Other Pozzolans
for Use with Lime
C618: Specification for Fly Ash and Raw or Calcined
Natural Pozzolan for Use as a Mineral Admixture in
Portland Cement Concrete
C821: Specification for Lime for Use with Pozzolans
C911: Specification for Quicklime, Hydrated Lime,
and Limestone for Chemical Uses
C977: Specification for Quicklime and Hydrated Lime
for Soil Stabilization
Most concentrated industrial or Superfund wastes contain complex
mixtures of contaminants, and a generic inorganic binder will frequently
stabilize one contaminant to a greater extent than another. Certain constitu-
ents, such as oils and anions, can retard or prevent the setting of the
binder. Chemicals that interfere with cement- and pozzolan-based processes
are discussed in greater detail in Section 4.3. Complications in the stabili-
zation of certain types of contaminants are discussed in Sections 4.2 and 4.4.
4.1.1.1 Cement Processes
Of the inorganic binders, Portland cement has probably had the
greatest diversity of application to a wide range of hazardous wastes,
especially combined with fly ash. Because cement is a common construction
material, the materials and equipment are mass-produced and generally inexpen-
sive compared with energy-intensive treatment processes such as vitrification
and incineration (McDaniel et al., 1990). Many types of cement have been used
for a variety of purposes, but only those classified as Portland cement, which
is primarily composed of anhydrous calcium silicate, have seen substantial use
in S/S technology (Conner, 1990). Other types of cement, such as alumina or
Sorel cement, have not been used extensively for S/S, primarily because of
their high cost.
Advantages of cement-based processes include (McDaniel et al., 1990
and Conner, 1990):
Availability of materials locally on a worldwide basis
Low cost of materials and mixing equipment
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Use of naturally occurring minerals as raw materials
for the matrix
Ability to make a strong physical barrier under adverse
conditions
Flexibility of tailoring the properties for different
applications
Low variability in composition
Well-known setting and hardening reactions and some
existing data on the immobilization of metals
The disadvantages of cement-based processes include:
Sensitivity of product quality to presence of
impurities at high enough concentrations. (Specific
examples of impurities are discussed in detail in
Section 4.3.)
Porosity of the S/S-treated waste.
Waste volume typically increases due to binder
addition, although not necessarily more than with
other inorganic binders.
Expertise needed for successful application,
although process appears deceptively simple.
The major performance objectives of S/S treatment are to reduce the
mobility of contaminants, minimize free liquids, and, occasionally, to
increase the strength of the waste. Cement-based processes accomplish these
objectives by forming a granular or monolithic solid that incorporates the
waste materials and immobilizes contaminants. The solid matrix forms because
of hydration of silicates in the cement, yielding calcium-silicate-hydrate.
Sufficient free water may be present in the waste material, or additional
water may be needed. In most cases, the bulk of the strength-forming ingredi-
ents are provided as an added cement binder.
ASTM provides specifications for eight types of Portland cement.
Type I is the least expensive and is the most widely used for S/S treatment.
Tricalcium and dicalcium silicates are the major crystalline compounds present
in Portland cement, while tricalcium aluminate and a calcium alumnoferrite are
present in smaller quantities. The cementation process binds free water,
4-5
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increases the pH and alters other chemical properties of the mixture, reduces
the surface area, and increases strength. All these mechanisms contribute to
improved performance characteristics of the treated waste.
Cementation of the waste/binder mixture begins when water is added,
either directly or as part of the waste. Once the cement powder contacts
water, tricalcium aluminate immediately hydrates, causing the rapid setting
which produces a rigid structure. In an idealized setting, the water hydrates
the calcium silicates and aluminates in the cement to form calcium-silicate-
hydrate. Thin, densely-packed fibrils of silicate grow out from the cement
grains and interlace to harden the mixture entrapping inert materials and
unreacted grains of cement. Hydration of tricalcium and dicalcium silicates
results in the formation of tobermorite and crystalline calcium hydroxide.
These compounds account for strength development after the initial setting.
The setting rate is controlled by the amount of gypsum added to the cement.
If sufficient gypsum is present, sulfates combine with tricalcium aluminate to
form calcium aluminate sulfate, which coats the cement particles and retards
hydration reactions.
The ratio of free water to cement (W/C) is a major factor control-
ling the porosity and strength of the final product. With a W/C weight ratio
of about 0.48, the cement will fully hydrate, leaving some water adsorbed in
the pore spaces. If the W/C ratio increases greatly above 0.48, the porosity
increases rapidly and the strength declines. When estimating the required
water addition, it is important to note that the total water content of the
waste is not always available to hydrate the cement. Water that is held by
hydration in the waste material may be unavailable or "bound" and thus not
available to hydrate the cement.
In many applications, the binder is supplemented by additives to
tailor the S/S process to waste-specific conditions. The additives may be
used to modify the characteristics of the fresh mix to improve processing.
For example, lignosulfonic or carboxylic acids can reduce the viscosity and
retard the set of the mix. Low concentrations of calcium chloride accelerate
setting. In other cases, additives may be needed to reduce interferences or
improve the performance of the treated waste.
For cementation reagents to react, they must become wetted with
water. In general, the higher the surface area of the particles, the more
difficult they are to wet. Some additives may even have hydrophobic surfaces
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initially. Many wastes, such as fine particulates and oils, may inhibit the
setting and curing of the cement by interfering with the wetting process
through coating of the reacting surfaces. Addition of surfactants to the
waste may aid in the wetting of reagents, allowing thorough mixing of all
components. Compounds such as alcohols, amides, and specific surfactants aid
in wetting solids and dispersing fine particulates and oil. Flocculants have
a similar effect by aggregating fine particles and film-formers.
The waste constituents can exhibit positive, negative, or inert
contributions to the strength-forming reactions. Wastes with free calcium
hydroxide can contribute to the strength-forming reactions, but excess
hydroxide will increase the pH and increase the solubility of amphoteric
metals. Alcohols and glycols decrease durability, while aliphatic, aromatic,
and chlorinated organics increase set time and often decrease durability.
Inorganic compounds such as boric acid, phospjhates, iodates, sulfates, and
sulfides can slow or prevent setting. Salts of some metals such as manganese,
tin, zinc, copper^and lead can increase set time and reduce strength. Fine
particulates such as silt, clay, or coal dust can coat cement particles and
prevent the growth of calcium-silicate-hydrate crystals from the cement grain.
Inerts such as soils or calcium fluoride do not directly participate in the
cementation reactions but do become trapped in the solid matrix.
Cement-based solidification and stabilization processes have proven
versatile and adaptable. It is possible to form waste/cement composites that
have good strength and durability and that retain wastes effectively.
Sorbents and/or emulsifiers can be added to reduce contaminant migration
through the porous solid matrix, thus improving the leaching resistance of the
treated wastes (U.S. EPA, 1986c).
4.1.1.2 Pozzolanic Processes
Pozzolanic processes generally involve siliceous and aluminosilicate
materials, which do not display cementing action alone but form cementitious
substances when combined with lime or cement and water at ambient tempera-
tures. The primary containment mechanisms are precipitation and physical
immobilization of the contaminant in the pozzolan matrix. Common examples of
pozzolans are fly ash, pumice, lime kiln dusts, and blast furnace slag. The
addition of bentonite can substantially reduce the amount of fly ash required
(U.S. EPA, 1986c, p. 2-11). Pozzolans contain significant amounts of sili-
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cates, which distinguish them from the lime-based materials (U.S. EPA, 1989g).
Typical tests of pozzolanic activity with lime and the strength of lime/
pozzolan mixtures use hydrated lime-to-pozzolan ratios in the range of 1:2 to
1:6 on a weight basis (ASTM C 311 and ASTM C 593). Typically, pozzolanic
reactions occur more slowly than do cement reactions.
Standard testing systems (ASTM C 311) and standard specifications
(ASTM C 593 and ASTM C 618) exist for pozzolanic materials, especially for fly
ash. The specifications take into account the chemical composition (percent
Si02, percent S03), moisture content, and physical properties (fineness,
pozzolanic activity with lime, and specific gravity). Pozzolanic activity
greater than a specified minimum can be expected if the material used meets
the specification for fly ash normally produced from burning either anthracite
or bituminous coal (Type F) or lignite or sub-bituminous coal (Type C). Some
Type C fly ashes have enough lime to be not only pozzolanic but also self-
cementing (U.S. EPA, 1986c).
Lime/fly ash treatment is relatively inexpensive and, with careful
selection of materials, can reliably convert waste to a solid material. In
general, lime/fly ash-solidified wastes are not considered as durable as
Portland cement-treated wastes.
Common problems with lime/pozzolan reactions involve interference
with the cementitious reaction that prevents bonding of materials. The bonds
in pozzolan reactions depend on the formation of calcium silicate and alum-
inate hydrates. Therefore, the interferences are broadly the same as for
cement-based processes (Sections 4.1.1.1 and 4.3).
4.1.1.3 Ettringite Formation Effects
Formation of a calcium aluminate sulfate hydrate (i.e., ettringite)
is typically required early in the curing process to control setting rate.
However, the ettringite then dissolves and reprecipitates as calcium sulfate.
Due to the high content of water of hydration, ettringite increases the volume
of solids when it forms.
If the ettringite is formed while the S/S-treated waste is still
plastic, the material can accommodate the expansive salt. However, if the
ettringite forms after the grout has become rigid, cracking can occur and will
reduce the strength of the product. The formation of this salt, with its
large amount of water of crystallization and consequently large increase in
4-8
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volume, can be destructive to the S/S-treated product. Figure 4-1 is an
idealized representation of the progress of cementation reactions.
4.1.2 Organic Binders
Application of organic binders is usually limited to special waste
types. Inorganic binders are used much more frequently and are generally
favored over organic binders because of cost and ease of application. The
primary niche of organic S/S processes in the commercial sector is to solidify
radioactive wastes or hazardous organics that cannot be destroyed thermally.
Organic binders that have been tested or used for S/S include the
following:
Asphalt (bitumen)
Polyethylene
Polyesters
Polybutadiene
Epoxide
Urea formaldehyde
Acrylamide gel
Polyolefin encapsulations
The basic types of organic S/S processes are: (1) thermoplastic and
(2) thermosetting with organic polymers. Thermoplastic processes involve
blending waste with melted asphalt, polyethylene, or other thermoplastic
binders. Liquid and volatile phases associated with the waste are driven off,
and the waste is contained in a mass of cooled, hardened thermoplastic (U.S.
EPA, 1986c).
Immobilization in thermosetting polymers involves mixing waste with
reactive monomers, which join to form a solid incorporating the waste. Urea
formaldehyde is one thermosetting resin that has been used for S/S processes.
One problem with organic processes is that many use hydrophobic
binders, which are not compatible with water-based wastes unless the waste is
first converted to an emulsion or a solid. Many hazardous wastes are
4-9
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c
o
Porosity
CSH (Long Fibers)
Ettringite
j k i i i
30 1 2 6 12 7 28 90
Curing Time Minutes
Hours
Days
Cement Grains
Ettringite
Ca(OH)2
Dormant
Period
Setting
Hardening
CSH
Monosulfate
Course of cement reactions.
Legend:
CSH = Calcium Silicate Hydrate
C4(A,F)HX = Ferrite Solid Solution
Source: Dole, 1985; figure used with permissiom of author and symposium
proceedings publisher, WM Symposia, Inc., Tuscon, Arizona.
FIGURE 4-1 PROGRESS OF CEMENTATION REACTIONS
4-10
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water-based and require special pretreatment to form an emulsion prior to
treatment by an organic binder.
Organic binders are also subject to deterioration from environmental
factors such as biological action or exposure to ultraviolet light. There-
fore, the long-term stability of organic binders for S/S processes will depend
on the physicochemical characteristics of the disposal or reuse environment
(as in the case of asphalt cement for roadways).
4.1.2.1 Thermoplastic Processes
Thermoplastic processes are used in nuclear waste disposal and can
be adapted to special industrial wastes. The thermoplastic technique for S/S
treatment of waste involves drying and dispersing waste through a plastic
matrix. The waste is mixed into a hot plastic mass which then cools, incorpo-
rating the waste in a rigid but deformable solid. In most cases, the hot
waste/thermoplastic mix is extruded into a container, such as a fiber or metal
drum, to give the final waste form a convenient shape for transport. The most
common thermoplastic material used for waste incorporation is asphalt. When
cost is not a limiting factor, other materials such as polyethylene, poly-
propylene, or wax can be employed for specific wastes to provide containment
in an impermeable medium (U.S. EPA, 1986c).
One advantage of thermoplastic processes is their ability to treat
soluble, toxic materials. For example, thermoplastic processing is one of
the few alternatives applicable to S/S treatment of spray-dried salt (U.S.
EPA, 1986c).
However, compatibility of the waste with the matrix is a limiting
factor in using thermoplastic processes. Most thermoplastic S/S binders are
chemically reduced materials (e.g., solid hydrocarbons) that can react
(combust) when mixed with an oxidizer at elevated temperatures. The reaction
can be self-sustaining or even explosive with perchlorates or nitrates (U.S.
EPA, 1986c).
Other compatibility problems relate to softening or hardening of the
waste/binder mix. Some solvents and greases can prevent asphalt hardening.
Borate salts can initiate hardening at high temperatures, leading to stalled
or clogged mixing equipment. Xylene and toluene can diffuse through asphalt
(U.S. EPA, 1986c). Other interferences have been documented for salts that
dehydrate at elevated temperature and for chelating and complexing agents.
4-11
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Unlike inorganic S/S processes, thermoplastic processes require more
complex, specialized melting and extrusion equipment. Both organic and
inorganic processes require a trained operations staff to ensure safe,
consistent operation. The power consumption for organic processes is higher
than that for inorganic processes because of the need to dry the waste and
melt the matrix material (U.S. EPA, 1986c).
4.1.2.2 Thermosetting Processes
Another type of organic S/S processes uses thermosetting resins such
as urea formaldehyde. This type of process relies on polymer formation to
immobilize the waste (U.S. EPA, 1989g). This technology has been evaluated
for stabilizing radioactive wastes and largely abandoned due to problems with
excess free water and radiolytic decomposition. Thermosetting processes have
also been tested on a limited basis on hazardous wastes such as organic
chlorides, phenols, paint sludges, cyanides, and arsenic as well as flue gas
desulfurization sludge, electroplating sludges, nickel/cadmium battery wastes,
kepone-contaminated sludge, and chlorine product wastes that have been
dewatered and dried (U.S. EPA, 1989g).
Usually, there is no direct reaction between the waste constituent
and the polymer. That is, thermosetting processes do not usually insolu-
bilize, modify, or destroy the hazardous constituents. Rather, the effect of
most thermosetting processes is to microencapsulate the waste, and the process
is potentially applicable to a wide variety of waste types (Conner, 1990).
4.1.3 Additives
S/S processes may be used in conjunction with sorbents or other
additives to improve immobilization of specific contaminants. Additives can
be particularly useful for cement or pozzolan processes to decrease the
mobility of contaminants in the porous, solid products. Additives to cement
or pozzolan processes can also be incorporated to mitigate the effects of
certain inhibitors. Some previously used additives and their applications are
as follows:
Soluble silicates, such as sodium silicate or potassium
silicate. These agents will generally "flash set"
Portland cement to produce a low-strength concrete.
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Soluble silicates can also be beneficial in reducing
interferences from metal ions.
Selected clays to sorb liquid and bind specific anions
or cations. Bentonite can reduce the amount of sorbent
required in low-solids mixtures.
Emulsifiers and surfactants to allow the incorporation
of immiscible organic liquids. Waste turbine oil and
grease can be mixed into cement blends if dispersing
agents are used and if the proper mixing system is
employed.
Certain sorbents (e.g., carbon, silicates, zeolitic
materials, and cellulosic sorbents) can help retain
toxic constituents.
Activated carbon in particular has been used primarily
as a sorbent for organics, although this material will
also sorb at least some metal ions and other
inorganics.
Lime (CaO or Ca(OH)2), soda ash (sodium carbonate,
Na2C03), fly ash, sodium hydroxide (NaOH) and, less
commonly, magnesium hydroxide (Mg(OH)2) are added for
maintaining alkaline conditions.
Ferrous sulfate, sodium metabisulfite/bisulfite, sodium
hydrosulfite, sulfides, blast furnace slag, sodium
borohydride, reductive resins, and hydrazine are added
as reducing agents.
Organophilic clays have been used to increase the
immobilization of certain organic contaminants within
hydrophobic binders. Organophilic clays are clay
minerals, such as montmorillonite, that have been
modified by treatment with a quaternary ammonium
compound that expands the spacing between clay layers,
thus promoting the absorption of organic constituents
between these layers. After treatment, the layer
spacing is reduced by treatment with an alkaline
substance, such as sodium chloride, to immobilize the
absorbed organic constituents in the clays.
Organosilanes have been applied to increase the binding
of metals.
This list is not comprehensive but rather provides examples of additives used.
Note that many additives may work for one constituent but have the opposite
effect for a different constituent. An evaluation of the system performance
of the additive needs to be conducted.
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4.1.4 Pretreatment
Frequently, the ultimate performance of an S/S process can be
improved by pretreating the waste. Improvements can sometimes be made to the
physical characteristics of the waste, to alter metal speciation, to improve
metal immobilization, or to remove problematic organics.
4.1.4.1 Adjustment of Physical Characteristics
Treatment by S/S involves extensive handling and mixing of the
contaminated material. The presence of large pieces of debris or poor
handling characteristics of the waste can interfere with sampling, analysis,
and S/S processing (Barth, 1991).
Some amount of debris or large solids will be encountered in waste
at almost any site. Debris such as wire, broken brick, timbers, tires, scrap
metal, or scrap cloth can be encountered at many industrial or waste disposal
sites. Other sites may have waste-specific debris, such as wood or bark
pieces at a creosote wood preserving site. Large pieces of material present
considerable obstacles to obtaining a representative sample and to character-
izing the waste as well as to performing the treatment.
The preliminary site characterization should identify the presence
of debris. Sample collection should be planned to allow collection of
meaningful characterization data of the waste and the debris. The debris can
either be removed by screening and processed separately or can be broken down
with size-reduction equipment to a size compatible with the S/S processing
equipment.
Mixing requires the ability to handle the waste material. Debris
can damage the mixing equipment and/or prevent good mixing. Excess free
liquid, high viscosity, or caking properties can all present problems in
materials handling. Possible pretreatment methods to improve handling are
drying, pelletizing, or adding sorbents to control liquids.
4.1.4.2 Pretreatment for Inorganic Constituents
Properly formulated inorganic binders can often incorporate metals
and their inorganic salts without extensive pretreatment. In some cases,
however, pretreatment can significantly improve the performance of the S/S
treatment system. Examples include (Conner, 1990):
4-14
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Chemical reduction of hexavalent chromium to the less
soluble and toxic trivalent state
Elimination of problem constituents, for example,
destruction of cyanide or stripping of ammonia
Degrading soluble nickel complexes to ionic nickel
Removing hygroscopic salts such as sodium sulfate by
aqueous extraction.
4.1.4.3 Pretreatment of Organic Constituents
Organic constituents can complicate stabilization in both inorganic
and organic-based S/S treatment systems. Volatile organics can make it
necessary to use expensive off-gas collection and treatment systems. As
described in Section 4.3, organic materials incorporated into the S/S-treated
waste can prevent setting or degrade product quality.
A variety of pretreatment options are available to remove volatiles
and semivolatiles or to control the effects of the organic material prior to
S/S treatment:
Soil washing
Thermal removal
Chemical oxidation
Extraction
Biodegradation
Addition of a sorbent (such as limestone,
diatomaceous earth, clays, activated carbon,
or fly ash) prior to mixing
A study of RODs for Superfund sites where S/S was one component in the
treatment program showed that wastes contaminated with VOCs underwent pre-
treatment more often than any other wastes (U.S. EPA, 1989a).
4.1.4.4 Treatment Trains Involving S/S
In many cases, treatment of wastes containing multiple and diverse
contaminants becomes so complex that S/S treatment becomes just one step in a
4-15
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treatment system or a treatment train. For example, the BOAT treatment for
several RCRA nonwastewater waste types includes one or more other processes
followed by S/S treatment (Table 1-1). The most common BOAT treatments that
prepare waste for S/S are incineration and chemical precipitation. In other
cases S/S treatment can be the initial step in a treatment train. For
example, it can be used to improve materials handling characteristics or to
immobilize metals prior to a different type of treatment.
Pretreatment to mitigate one problem may give rise to problems of
another nature. For example, oxidation of organic contaminants with perman-
ganate leaves a permanganate residue in the waste, and permanganate will
oxidize organic binders such as asphalt. Washing with solvent leaves traces
of solvent that must be removed from the waste prior to S/S treatment.
Incineration can leave certain metals (e.g., chromium) in the ash in their
higher and more mobile oxidation states.
Selection of the appropriate combination of binders, additives, and
pretreatment options for a particular waste requires careful consideration of
the waste material, the contaminants, and the performance objectives of the
project (Sections 2.3 and 2.4).
4.2 IMMOBILIZATION MECHANISMS
Waste stabilization may involve physical mechanisms, chemical
mechanisms, or a combination of the two. Physical stabilization (solidifi-
cation or encapsulation) changes the physical form of the waste but does not
necessarily cause chemical binding of the waste constituents. Chemical
stabilization changes the chemical states of waste constituents to forms with
lower aqueous solubilities. Although the mechanisms of immobilization are
discussed separately for convenience, under actual S/S treatment conditions,
these mechanisms usually do not work independently.
4.2.1 Physical Mechanisms
Physical mechanisms of S/S operate by confining waste constituents
to a certain area or zone in the waste. That is, the waste constituent may or
may not occur in a soluble form, but one or more physical barriers prevent its
mobilization. Containment by a barrier is a satisfactory method as long as
4-16
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the barrier remains stable. Encapsulation is the most commonly used method of
containment, superseding earlier use of sorbents.
Encapsulation techniques use materials that trap waste constituents
in the form of stable solids, preferably as a monolith with high cohesive
strength and low Teachability. Waste constituents are dispersed throughout
an inorganic or organic binder matrix (Section 4.1) that physically isolates
them from groundwater and air. The effectiveness of isolation depends on the
permeability and long-term stability of the matrix and on the degree of mixing
of waste constituents throughout the matrix. In practice, mixing may be less
than ideal, resulting in some of the waste material occupying cavities in the
matrix. Encapsulation of inorganic wastes is generally accompanied by
chemical stabilization, but encapsulation of organic wastes such as oil and
grease, PCBs, pesticides, and volatile compounds usually occurs without
accompanying chemical interactions (Conner, 1990). Encapsulation can be
further described at three levels: microencapsulation, macroencapsulation, and
embedment (Conner, 1990).
The term "microencapsulation" describes a process of adsorbing or
trapping contaminants in the pore spaces of a cementitious material. The
contaminants are fine waste particles that may not be visible to the naked
eye. As the system ages, the waste and matrix may eventually become a
homogeneous material, although this might occur in a time frame of thousands
of years or more (Conner, 1990).
The term "macroencapsulation" describes a process of coating a solid
or cemented waste with an impermeable layer, such as bitumen (thermoplastic)
or amorphous silica (U.S. EPA, 1990e). The success of this method depends on
both effective coating reactions and thorough mixing. "Macroencapsulation"
may also refer to the containment of large waste solids, as in a sealed drum.
The term "embedment" describes a process of incorporating large
waste masses into a solid matrix before disposal. Examples of such wastes are
contaminated debris from remedial actions, laboratory protective equipment,
solid medical wastes (e.g. syringes), and radioactive objects (Conner, 1990).
Embedment is used in situations where it is impractical to reduce the bulk of
the waste but where the waste is hazardous enough to be treated prior to
disposal. In addition, special consideration may also have to be given to the
strength, water permeability, and long-term stability properties of the
matrix.
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Finally, sorbents once were used extensively to prevent the loss of
liquid wastes and to improve handling characteristics. Materials such as
expanding-layer clays and vermiculite were considered attractive for liquid
waste disposal because of their low cost and easy handling. However, the use
of sorbents has greatly diminished since the 1985 landban on bulk liquids in
landfills, although sorbents are currently permitted for certain applications
(Conner, 1990). The main problem with sorbents is that they may become highly
Teachable under certain circumstances, for example, if oversaturation should
occur and load levels become too high.
4.2.2 Chemical Mechanisms
Different chemical mechanisms of S/S are operable for inorganic and
organic wastes. Also, the aqueous chemistries of most inorganic and organic
compounds are fundamentally different, leading to different leaching behav-
iors.
4.2.2.1 Inorganic Wastes
4.2.2.1.1 Basic Chemical Equilibria. The chemistry of inorganic
waste constituents is dominated by hydrolysis reactions. The term "hydroly-
sis" implies that a substance, usually a metal, reacts with water. Hydrolyzed
products can react in the aqueous phase to form new ionic or neutral species,
or they can form precipitates of hydroxides, oxides, or salts (commonly
carbonates, sulfates, and sulfides).
It is useful to compare the solubilities of different metal com-
pounds. Consider the dissolution reaction of a generic compound MJ^:
MA - ซ**<.ซ,> + ^""(aq)
where Ma+ is the cation and A"1" is the anion. The solubility product constant
for this reaction is
Ksp - [M"]'[AT
where square brackets indicate concentration (activity) and Ksp depends only
on temperature and pressure. The solubility product is therefore a constant
4-18
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if temperature and pressure of the solid and solution phases remain fixed, for
example, at the ambient conditions of a disposal site. Frequently, the
solubility product is written as pKsp, where pX = -log10(X).
Table 4-1 lists solubility product values for the hydroxides,
carbonates, sulfates, and sulfides of some regulated metals (higher pK8p means
lower solubility). Table 4-1 shows that the following metals salts have very
low solubility products: Cr(III) hydroxide and sulfides of Cd(II), Pb(II),
Hg(I), and Hg(II). The least soluble barium solid is barium sulfate (barite).
This type of information can be important for deciding which form of a given
hazardous metal is most stable and which metal compounds may be attainable
given specific site conditions and available technology.
Actual concentrations of dissolved species depend on a number of
solution parameters, such as pH, redox potential, and solution composition.
The simplest and most common method of controlling speciation and precipita-
tion is pH adjustment. To illustrate this process, consider the role of a
strong acid in the solubility of a simple metal hydroxide, M(OH)n. According
to the equilibrium expression above, the solubility of M(OH)n is described by
the following reaction:
M(OH)n(t) - rT{aq) + n(OH)-(aq)
TABLE 4-1. pKsp VALUES FOR SELECTED METAL PRECIPITATES<8)
Metal Hydroxide Carbonate Sulfate Sulfide
Ba
Cd
Cr(III)
Pb
HgdD
Hg(i)
2.30
14.30
30.20
19.90
25.52
8.09
11.60
13.48
16.05
9.97
0.50
7.71
1.43
6.17
28.44
27~4>)(c)
48.70
51.42
Galena.
Sources: Means et al. (1991c) and Dragun (1988).
4-19
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To show the dependence on pH directly, the following equation must be sub
tracted from the preceding one, n times:
H20(l) - H+(aq) + (OH)-(aq)
Where K = 14 the result is
M(OH)n(s) + nH+(aq) * M^(8q) + nH20(l)
The solubility constant for this reaction is
Ka =
or upon rearranging terms:
The concentration of M"* ions clearly increases as pH decreases. However, M"*
ions are not necessarily the dominant aqueous species of the metal M at all pH
values and solution compositions. The total dissolved metal is the sum of all
hydrolysis species [M(OH)n~1, M(OH)2n'2, etc.] and complex species [MC03n~2,
MS04n~2, etc.] that form in solution. At sufficiently high or low pH, some
aqueous species can be hydroxylated or protonated. Therefore, these species
are sensitive to pH and they affect the solubilities of the solid phases. The
task of determining which species are present and in what concentrations is
often time consuming and expensive. As an alternative, speciation calcula-
tions can be made if bulk solution compositions are known. Compilations of
thermochemical data that are needed to perform these calculations are avail-
able in the chemistry literature (Means et al . , 1991c).
An investigation of immobilization mechanisms for S/S of cadmium and
lead (U.S. EPA, 1990f) found that, even though Cd(OH)2 and Pb(OH)2 have
comparable and very low solubilities, the degree of leaching from cement
treated wastes differed for the two metals. In leaching tests, cadmium
concentrations were very low, whereas lead concentrations were considerably
higher and could potentially pose a threat to groundwater. The differences
were attributed to the fact that the Cd/cement system involves early formation
4-20
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of Cd(OH)2 which provides nucleation sites for precipitation of C-S-H and
calcium hydroxide and results in Cd being in the form of an insoluble hydrox-
ide with an impervious coating. The Pb/cement system was more complicated in
terms of precipitation reactions. Mixed salts containing hydroxide, sulfate,
and nitrate ions were precipitated. These salts retard the cement hydration
reactions by forming an impervious coating around the cement clinker grains.
Also, as pH in the cement pore water fluctuated during hydration, the Pb salts
undergo solubilization and reprecipitation, resulting in Pb salts on the
surface of cement minerals that are readily accessible to leach water and
apparently are more soluble under basic conditions than a pure lead hydroxide.
4.2.2.1.2 Effect of Alkaline Conditions. Numerous compatible ionic
species form solids by coprecipitation. Therefore, the application of
chemical equilibria based on pure end-members may not be completely valid.
Ferric iron has long been recognized for its ability to flocculate and
coprecipitate toxic metals from solution (Sittig, 1973; LeGendre and Runnel Is,
1975; Swallow et al., 1980). Coprecipitated metals may have solubilities that
are substantially lower than those of either of the pure end-member phases.
For example, the Cr(III) concentrations are many times lower in solutions that
are in equilibrium with coprecipitated Cr(OH)3-Fe(OH)3 than those that are in
equilibrium with pure chromium hydroxide (Sass and Rai, 1987).
The minimum solubility of most metal hydroxides occurs within the
approximate pH range of 7.5 to 11. This implies that solubility increases
under extremely alkaline conditions as well as under acidic conditions
(amphoteric behavior). When the waste material under consideration for S/S
contains a number of different metals, it is possible that their solubility
minima may not entirely overlap. In cases where pH values at these solubility
minima are not too different, it may be sufficient to choose an average pH,
but in cases where pH values are very different, the best recourse may be to
attempt to precipitate the contaminants in a phase or phases other than a
hydroxide.
As an example, suppose that Cd and Cr(III) are the predominant
hazardous constituents in a waste system. Solubility minima occur at
pH ~ 11 to 11.5 for Cd(OH)2 (Brookins, 1988) and pH ~ 8.5 for Cr(OH)3 (Baes
and Mesmer, 1976). In this situation, one might elect to precipitate highly
insoluble CdS by adding a soluble sulfide, such as Na2S, and to precipitate
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Cr(OH)3 by adjusting the pH to 8.5. Note, however, that if barium is present
in the same waste, it has a high solubility in the presence of sulfide. This
example illustrates the need for understanding the waste chemistry as well as
the pertinent chemical equilibria in order to achieve a maximum degree of
chemical stabilization.
Any alkali may be used to control pH, but the common choices are
lime [either CaO or Ca(OH)2], sodium carbonate, or sodium hydroxide. Most
solidification reagents are alkaline and can substitute in part or entirely
for traditional alkalies, acting both as pH controls and as binding agents.
Alkaline binders include Portland cement, cement and lime kiln dusts, Type C
fly ash, and sodium silicate (Conner, 1990).
Buffers provide resistance to rapid changes in pH upon exposure to
acid or base. The presence of pH buffers in stabilized waste is desirable to
maintain the pH at the target value for the long term, thus promoting long-
term stability. Limestone (primarily CaC03) is used to buffer waste acidity;
Na-montmorillonite is also used for this purpose.
4.2.2.1.3 Effect of Redox Potential. Redox potential is another
important solution parameter in S/S technology. An oxidation-reduction, or
redox reaction, is one that involves the transfer of electrons between
products and reactants. Experimentally, the redox potential of a half-cell
reaction is measured by a quantity called "Eh." High Eh voltages indicate
that the solution is oxidizing and low Eh voltages indicate that the solution
is reducing. The redox potential of a waste form can be controlled to convert
the valence states of hazardous metals to valence states that are more
favorable for precipitation.
Among the regulated metals listed in Table 4-1, Cr and Hg have more
than one common oxidation state. The table shows that trivalent chromium
species precipitate as a low-solubility hydroxide. However, Cr(VI) forms
mainly chromate and dichromate species, such as Cr042~ and Cr2072", which do
not form precipitates with low solubility (Eary and Rai, 1987). The table
also shows that mercury in both oxidation states forms very-low-solubility
sulfides. Redox potential has particularly important effects on the regulated
semimetals, such as As and Se, which exhibit a number of different oxidation
states.
4-22
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Table 4-2 lists selected stable solids of As and Se for reference.
A literature review by Means et al. (1991c) shows that calcium arsenate
Ca3(As04)2 is the most stable metal arsenate [As(V)] in oxidizing alkaline
conditions. Under acidic conditions, calcium arsenate becomes unstable
because its calcium source (calcite) is leached away. Another potentially
stable phase for the immobilization of As(V) appears to be basic ferric
arsenate FeAs04ซxFe(OH)3, which forms readily in the presence of ferric
hydroxide. However, basic ferric arsenate is most stable at lower pH.
Under highly oxidizing conditions the selenate ion Se042~ [Se(VI)]
predominates in both acidic and basic solutions (Means et al., 1991c). Barium
selenate appears to be the most stable solid (Elrashidi et al., 1987) but is
fairly soluble (4mM activity). Other metal selenates are even more soluble.
In moderately oxidizing conditions, manganese selenite, MnSe03 [Se(IV)], is
the most stable solid that persists in both neutral and acidic environments
(Elrashidi et al., 1987); at pH 5 the activity of the dominant species HSe03~
is 2.5/iM. According to (Elrashidi et al., 1987), PbSe03 has a solubility
minimum near pH 8. Under highly reducing conditions, selenide [Se(II)]
species predominate (Elrashidi et al., 1987); lead selenide PbSe and tin
selenide SnSe are the most stable solids in both neutral and alkaline condi-
tions. Elemental Se also has a stability region, but it is more soluble than
most of the metal selenides (Elrashidi et al., 1987).
The major reducing agents and their attributes are described by
Conner (1990). The most common agents are ferrous sulfate, Na-metabisulfite/
bisulfite, Na-hydrosulfite, sulfides, Na-borohydride, hydrazine, and reductive
resins. The most widely used reducing agent in S/S technology is ferrous
sulfate, which is used primarily to reduce hexavalent chromium. Its main
disadvantage is that pH must be adjusted below 3 in order for the chromium
reduction reaction to go to completion. The amount of acid needed can
therefore be quite large, particularly if the waste material contains appre-
ciable amounts of alkaline buffers. Na-metabisulfite/bisulfite and soluble
sulfides, such as Na2S, work similarly to ferrous sulfate but require less
acid and alkali to complete a reduction/reprecipitation process. However, Na-
metabisulfite/bisulfite is expensive, and Na2S is unsafe to use at very low pH
because of the possible evolution of toxic H2S. Na-hydrosulfite, Na-boro-
hydride, hydrazine, and freshly precipitated FeS (the Sulfex process) work
under alkaline conditions, which may be more convenient for pretreated wastes.
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TABLE 4-2. pKSD VALUES FOR SELECTED As AND Se PRECIPITATES(8>
Element
As(Y)
As(III)
As(II)
Se(VI)
Se(IV)
Se(-II)
Compound
(arsenates)
Ba3(AsOJ2
Ca3(As04)2
Cd3(As04)2
Mg3(As04)2
Pb,(As04),
FeAs04-xFe(OH)3
As2S3
AsS
(selenates)
BaSeO,
CaSe04-2H20
CdSeO,
PbSe04
(selenites)
BaSeOS
CaSe03-H20
CdSe03
HgSe03
Hg2Se03
MnSe03
PbSe03
(selenides)
BaSe
CaSe
CdSe
CuSe
FeSe
HgSe
PbSe
SnSe
PKSP
50.11
18.17
32.66
19.7
35.39
20.24
29.6
12.3
7.46
3.09
2.27
6.84
6.57
5.44
8.84
13.90
14.23
7.27
12.12
21.86
10.87
35.20
48.10
26.00
64.50
42.10
38.40
(a) Data apply to equilibria at 25ฐC.
Source: Means et al. (1991c).
4-24
-------
Reductive resins (e.g., Amborane) are selective for certain metals and are
used for precious metal recovery. They have potential uses for recovering
hazardous metals such as silver, arsenic, mercury, and antimony (Conner,
1990). Blast furnace slag, a common binder, can serve as a reducing agent.
While adjustment of the redox-sensitive contaminant to its least
soluble oxidation state is an important aspect of chemical stabilization, this
objective eventually will be defeated if the treated waste is placed in a
disposal or reuse environment having a very different oxidation state. Long-
term stability can only be ensured if the oxidation states of the treated
waste and the disposal or reuse environment are similar.
4.2.2.1.4 Hetal Silicates. The behavior of hazardous metals in the
silicate system is critical to cement-based S/S technology. However, full
understanding of the chemical processes involved may be difficult to achieve
because the waste constituents are often heterogeneous mixtures of solutions,
suspended solids, and immiscible liquids. Reactions between metal salts in
solution and soluble silicates have been studied extensively, but their
insoluble products usually have not been well characterized. Metal silicates
are generally nonstoichiometric and poorly crystallized. In fact, their
chemical and physical properties depend considerably upon the conditions under
which they are formed, for example, temperature, concentration, addition rate,
and ionic speciation. The pH is also very important because it affects how
readily soluble silicate (or colloidal silica) adsorbs metal ions. It has
been found that adsorption occurs when the pH is 1 to 2 units below the
hydroxide precipitation point (Her, 1979).
Just how the metal ions are incorporated into the cement structure
is still a matter of debate. Using Portland cement as an example, the
cementitious phase of calcium silicate hydrate, or CSH, forms by a hydration
reaction that takes from 28 days to 1 year to complete (Kantro et a!., 1962):
2Ca3Si05 + 6H20 - Ca3Si207-3H20 + 3Ca(OH)2
It is believed that CSH incorporates metal ions into the silicate matrix
during the hydration reaction (Bhatty and Greening, 1978). The number of
metal ions retained decreases as the CaO:Si02 ratio in CSH increases (Bhatty,
1987).
4-25
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If metals have already been precipitated as low-solubility solids,
they may gradually react with the silicate (if such a reaction is favorable)
as long as free silicate is available; i.e., before it reacts with other ions
in the system, such as calcium. The probable result is that the cementitious
matrix will encapsulate the metal solids as hydroxides, sulfides, carbonates,
etc. (see Section 4.2.1 on physical mechanisms). Continued reaction of metal
ions with silicate will only occur if a continuous source of soluble silica
can be created within the matrix or if the waste is pretreated to dissolve the
metal hydroxides.
4.2.2.1.5 Other Low-Solubility Phases. Another alternative to
precipitating metals as hydroxides is to bind them using insoluble substrates.
Insoluble starch xanthates have been widely used for this purpose since they
became commercially available in 1980 (Conner, 1990). Xanthates are produced
by reacting an organic hydroxyl-containing substrate (R-OH), such as starch,
cellulose, or alcohol with carbon disulfide in the presence of a strong base
such as NaOH (Bricka and Hill, 1987). The structure of a Na-xanthate is
represented by
R-0-C-S-Na
II
S
Xanthates remove metals from solution by exchanging the base metal (Na) for
generally heavier metals, which are bound more strongly. The selectivity for
metal removal increases in the following order (Flynn et al., 1980):
Na ซ Ca-Mg-Mn < Zn < Ni < Cu-Pb-Hg
Wastes stabilized by xanthates are less sensitive to pH and have better sludge
dewatering properties than metal hydroxides. However, the xanthates produce
large quantities of sludge that must be handled like any RCRA material (Bricka
and Hill, 1987).
The effects of typical S/S techniques for binding heavy metals using
cellulose and starch xanthates were investigated by Bricka (1988) and Bricka
and Hill (1987), who found:
4-26
-------
1. Xanthates of Cd, Cr, Hg, and Ni effectively immobilize
these metals when bound with Portland cement.
2. Mercury precipitated by starch xanthate has lower
Teachability than mercury precipitated by hydroxide,
even after solidification.
3. Starch xanthate binds mercury better than cellulose
xanthate.
4. Cd-, Cr-, and Ni-xanthates alone do not have
sufficiently low solubilities for direct disposal; thus
solidification is necessary to achieve acceptable
Teachability levels.
4.2.2.2 Organic Wastes
Aqueous wastestreams containing small amounts (10 to 1000 ppm) of
organic hazardous contaminants are the most treatable organic waste forms
under S/S technology (Conner, 1990). With regard to normal cement-based
methods, containment will be most effective for immiscible liquids and least
effective for soluble liquids (Conner, 1990). It is unclear, however, whether
appreciable chemical reactions take place in the matrix. Losses may be caused
by other factors, such as volatilization, which may be especially important in
S/S processes that involve elevated temperatures (Weitzman et al., 1987).
As with inorganic wastes, organic constituents can undergo reactions
including hydrolysis, change of oxidation state, and precipitation as some
form of salt. Hydrolysis normally involves the loss of a hydroxyl group (-OH)
in exchange for another functional group. Reactions must be catalyzed by a
strong base to proceed at reasonable rates. Oxidation and reduction reactions
can occur naturally in soils, with clays performing the role as catalysts
(Warren et al., 1986). Many substituted aromatics undergo free radical
oxidation. According to Dragun and Helling (1985), this group includes
benzene, benzidine, ethyl benzene, naphthalene, and phenol. On the other
hand, chlorinated aromatics and polynuclear organics are unlikely to be
oxidized under natural conditions (Conner, 1990). Of course, oxidation can be
made to occur by treating the waste with strong oxidizing agents such as
potassium permanganate. However, the possible disadvantages of using such
additives, such as the mobility or toxicity of the additive itself, must be
weighed against the advantages. The mechanism of salt formation by organics
will apply only to the ionized or ionizable organic fraction; it is not
4-27
-------
directly applicable to nonpolar species. The formation of organic salts in
S/S technology is a possible significant mechanism, but it has not been
studied extensively.
One additional area of recent research is the S/S binding mechanisms
of nonpolar organics in organophilic additives such as modified clays and
activated carbon. Modified clays are clays that have been modified by ion
exchange with selected organic compounds that have a positive charged site
hence rendering the clay/organo complex hydrophilic. The binding capacity for
such materials with certain types of organics has been well demonstrated. For
example, Sell et al. (1992) found that sodium bentonite clay, modified with
dimethyl di(hydrogenated tallow) ammonium chloride (LOCKITฎ) can be used to
remove phenol and chlorinated phenols from aqueous solutions. The question
for organophilic additives, however, centers on whether the binding mechanism
entails simple absorption or adsorption, or whether the formation of stronger
covalent bonds between the additive and the contaminant is occurring.
Additional evaluation is necessary.
4.2.3 Concept of Surface Sealing
The concept of "surface sealing" pertains to the situation where the
surfaces of stabilized waste products are sealed, limiting the release of
contaminants and the uptake of matrix-unfriendly components such as salts.
Hockley and van der Sloot (1991) found that "self-sealing" may occur in some
stabilized wastes. They examined the precipitation and dissolution processes
in waste blocks formed from stabilization of coal combustion wastes with
Portland cement and lime that had been exposed to seawater for up to 8 years.
Results indicated that dissolution of calcium hydroxide, calcium sulfite, and
ettringite began at the block surface and proceeded as a moving boundary
toward the interior. Some calcium released by dissolution was reprecipitated
as a carbonate phase, and the remainder was lost to the surrounding seawater.
Magnesium ions infiltrating from the seawater were precipitated, apparently as
a hydroxide phase. Concentration profiles of As, Sb, and B showed that minor
elements also exhibit moving boundary effects, perhaps through association
with the mineral phases. These alteration and leaching processes were
confined to within 10 to 20 mm of the block surface, and many concentration
profiles showed sharp discontinuities at the 10- to 20-mm region.
4-28
-------
These discontinuities could not be explained by the simple
diffusion-based models currently used to interpret leaching data. The sharp
discontinuities in the concentration profiles of nonreactive sea salts led to
the hypothesis that the precipitation of small crystals in pores near the
block's surface restricted diffusion, a process similar to the concept of
"pore refinement" previously identified in the literature on concrete durabil-
ity. This process causes a slowing of all diffusion-controlled processes,
including the degradation of the block matrix and the leaching of contami-
nants.
Similar phenomena have been observed in borosilicate glasses. Upon
leaching, these glasses develop an alteration layer at the glass/water
interface. The alteration layer consists of numerous growths (grouts) that
precipitate and impede glass dissolution and diffusion of glass constituents
into the aqueous phase (Doremus, 1979).
4.3 POTENTIAL INTERFERENCES
S/S processes can be affected by the chemical constituents present
in the waste being treated and by many other factors (e.g., binder-to-waste
ratio, water content, or ambient temperature). The interferences caused by
the chemical constituents of the waste can affect the solidification processes
and/or the chemical stabilization of the treated product as discussed in
Sections 4.3.1 and 4.3.2. Waste-specific treatability studies are needed to
identify and overcome such interferences. General types of interference
caused by the chemical constituents include (U.S. EPA, 1990g):
Inhibition of bonding of the waste material to the
S/S material
Retardation of setting
Reduction of stability of the matrix resulting in
increased potential for Teachability of the waste
Reduction of physical strength of the final product
The exact mechanisms for interference are not known, and because different
wastes respond differently to various types of interferences, limits on
4-29
-------
various interfering agents cannot be set. More study is needed to establish
acceptable levels for interfering agents, both singly and in combination.
4.3.1 Interferences with Solidification
The contaminated materials usually treated by S/S processes are
widely fluctuating, complex mixtures. Even with one waste source, the
concentrations can vary by a factor of ten or more from batch to batch. Many
waste constituents affect cementation chemistry by altering the setting rate
or the properties of S/S-treated waste. Depending on the contaminant type and
concentration, setting rate may be increased or decreased. As an example of
concentration effects, mild accelerators such as chloride or nitrate anions
can slow setting at higher concentrations. Treated waste properties such as
porosity or flexural and compressive strength may be reduced by contaminants.
There is typically a threshold below which the contaminant has no
measurable effect. Because S/S treatment performance is influenced by complex
interactions of waste material and binder, it is usually not possible to
quantify the threshold. Treatability studies are required to determine the
feasibility of treating a specific waste.
Table 4-3 lists substances found to affect cement reactions. Many
of these substances can reduce the ultimate mechanical strength of the waste
form by producing cracking and spall ing. Table 4-4 compiles the characteris-
tics reported to interfere with solidification/stabilization processes and
indicates their potential impacts.
4.3.2 Interferences with Stabilization
Table 4-5 summarizes some typical waste characteristics found to
interfere with the stabilization processes. This table focuses on the effects
of waste constituents on immobilization mechanisms, in contrast to Table 4-4,
which addresses the effects on formation of a solid product. Interferences
with stabilization include chemical incompatibilities and undesirable reac-
tions. Generally, the types of effects reported in Table 4-5 are releases of
noxious gases or effects resulting in the increased leaching potential of the
contaminants.
4-30
-------
TABLE 4-3. SUBSTANCES THAT MAY AFFECT CEMENT REACTIONS:
INHIBITION AND PROPERTY ALTERATION
Substance or Factor Inhibition Property Alteration
Fine particulates X X
Clay X
Silt X
Ion exchange materials X
Metal lattice substitution X
Gelling agents X X
Organics, general X X
Acids, acid chlorides X
Alcohols, glycols X X
Aldehydes, ketones X
Carbonyls X
Carboxylates X
Chlorinated hydrocarbons X X
Grease X X
Heterocyclics X
Hydrocarbons, general X
Lignins X
Oil X X
Starches X
Sulfonates X
Sugars X
Tannins X
Organics, specific
Ethylene glycol X
Hexachlorobenzene X
Phenols X X
Trichloroethylene X
Inorganics, general
Acids X
Bases X
Borates X
Chlorides X X
Copper compounds X
Lead compounds X
Magnesium compounds X
Metal salts X X
Phosphates X
Salts, general X X
4-31
-------
TABLE 4-3. SUBSTANCES THAT MAY AFFECT CEMENT REACTIONS:
INHIBITION AND PROPERTY ALTERATION (Continued)
Substance or Factor Inhibition Property Alteration
Inorganics, general (cont'd)
Silicas X
Sodium compounds X
Sulfates X X
Sulfides X
Tin compounds X
Zinc compounds X
Inorganics, specific:
Calcium chloride X
Copper hydroxide X
Copper nitrate X
Gypsum, hydrate X
Lead hydroxide X
Lead nitrate X X
Sodium arsenate X
Sodium borate X
Sodium hydroxide X
Sodium iodate X
Sodium sulfate X
Sulfur X
Tin
Zinc nitrate X
Zinc oxide/hydroxide X
Adapted from: Conner, J. R. 1990. Chemical Fixation and Solidification of
Hazardous Wastes. Van Nostrand Reinhold, New York. pp. 349-350. Used with
permission of Van Nostrand Reinhold.
4-32
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TABLE 4-4. SUMMARY OF FACTORS THAT MAY INTERFERE WITH SOLIDIFICATION/STABILIZATION PROCESSES
Possible Interfering
Characteristics
Potential Interference Mechanism
Reference
i
CO
to
Semivolatile organics
or PAHs
Oil and grease
Phenols
Nonpolar organics (oil,
grease, aromatic
hydrocarbons, PCBs)
Polar organics (alcohols,
phenols, organic
acids, glycols)
Solid organics (plastics,
tars, resins)
Organics 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.
Marked decrease in compressive strength.
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, phenol
retards 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.
U.S. EPA, 1988c
U.S. EPA, 1988c;
Cull inane and
Bricka, 1989.
U.S. EPA, 1988c;
Cull inane and
Bricka, 1989.
U.S. EPA, 1989g
U.S. EPA, 1989g
U.S. EPA, 1989g;
Wiles, 1987
-------
TABLE 4-4. SUMMARY OF FACTORS THAT INTERFERE WITH SOLIDIFICATION/STABILIZATION PROCESSES (Continued)
Possible Interfering
Characteristics
Potential Interference Mechanism
Reference
i
OJ
-p.
Aliphatic & aromatic
hydrocarbons
Chlorinated organics
Complexing organics
(hydroxycarboxylic
acid, citric acid,
tartaric acid, benzoic
acid, EDTA)
Presence of phenols and
nitrates
Metals (lead,
chromium, cadmium,
arsenic, mercury)
Metal salts
and complexes
Copper, lead, and zinc
Hal ides
Increase set time for cement.
Increase set time and decrease
durability of cement.
Retard setting rate.
Cannot be immobilized with lime/fly ash,
cement, and soluble silicates; fly ash
and cement; or bentonite and cement.
May increase setting time of cements.
Increase set time and decrease
durability for cement or clay/cement.
Detrimental effect on physical
properties of cement-treated waste.
May retard setting, easily leached from
cement and pozzolan S/S-treated waste.
May dehydrate thermoplastics.
U.S. EPA, 1989b
U.S. EPA, 1989b
Dole, 1985
Stegemann et al.,
1988
U.S. EPA, 1989g
U.S. EPA, 1989b
U.S. Army, 1990
U.S. EPA, 1988c
-------
TABLE 4-4. SUMMARY OF FACTORS THAT INTERFERE WITH SOLIDIFICATION/STABILIZATION PROCESSES (Continued)
Possible Interfering
Characteristics
Potential Interference Mechanism
Reference
i
CO
en
Soluble salts of
manganese, tin, zinc,
copper, and lead
Cyanides
Arsenates, borates,
phosphates, iodates,
sulfides, and
carbohydrates
Sulfates
Presence of coal or
lignite
Sodium borate, calcium
sulfate, potassium
dichromate, and
carbohydrates
Reduce physical strength of final
product; cause large variations in
setting time; reduce 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
spall ing in cement S/S. With
thermoplastic solidification may
dehydrate and rehydrate causing
splitting.
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.
U.S. EPA, 1988c
U.S. EPA, 1988c
U.S. EPA, 1988c
U.S. EPA, 1988c
U.S. EPA, 1988c
U.S. EPA, 1986c
-------
TABLE 4-4. SUMMARY OF FACTORS THAT INTERFERE WITH SOLIDIFICATION/STABILIZATION PROCESSES (Continued)
Possible Interfering
Characteristics
Potential Interference Mechanism
Reference
CO
Oxidizers (sodium
hypochlorite,
potassium
permanganate, nitric
acid, or potassium
dichromate)
Nitrates, cyanides
Soluble salts of
magnesium, tin, zinc,
copper, and lead
Flocculants (e.g., ferric
chloride)
Soluble sulfates >0.1% in
soil or 150 mg/L in
water
Soluble sulfates >0.5% in
soil or 2000 mg/L in
water
Inorganic acids
Inorganic bases
May cause matrix breakdown or fire with
thermoplastic or organic polymer S/S.
U.S. EPA, 1989g
Increase setting time, decrease
durability for cement-based.
May cause swelling and cracking within
inorganic matrix, exposing more surface
area to leaching.
Interference with setting of cements and
pozzolans.
Endangerment of cement products due to
sulfur attack.
Serious effects on cement products from
sulfur attack.
Decrease durability for cement (Portland
Type I) or clay/cement.
Decrease durability for clay/cement; KOH
and NaOH decrease durability for
Portland cement Type II & IV.
Colonna et al., 1990
Colonna et al., 1990
Colonna et al., 1990
p. 407
Jones, 1990
Jones, 1990
U.S. EPA, 1989b
U.S. EPA, 1989b
-------
TABLE 4-4. SUMMARY OF FACTORS THAT INTERFERE WITH SOLIDIFICATION/STABILIZATION PROCESSES (Continued)
Possible Interfering
Characteristics
Potential Interference Mechanism
Reference
OJ
Sodium hydroxide
Presence of anions in
acidic solutions that
form soluble calcium
salts (e.g., calcium
chloride, acetate, and
bicarbonate)
Low-solids wastes
Fine particle size
Envi ronmental/waste
conditions that lower
the pH of matrix
Increase early strength at 2 to 5%
concentration but decreased early
strength at 8% level.
Cation exchange reactions leach
calcium from solidified/stabilized
product, increases permeability of
concrete; increases rate of exchange
reactions.
Large volumes of cement or other
reagents required, greatly increasing
the volume and weight of the end
product. Waste may require
reconstitution with water to prepare
waste/reagent mix.
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 >l/4 inch in
diameter not suitable.
Eventual matrix deterioration.
U.S. Army, 1990
Jones, 1990
U.S. EPA, 1988c
U.S. EPA, 1988c
Colonna et al., 1990
p. 407
-------
TABLE 4-5. POTENTIAL CHEMICAL INCOMPATIBILITIES BETWEEN BINDER AND WASTE CONSTITUENTS
Characteristics
Affecting
Process Feasibility
Potential Incompatibilities
Reference
OJ
00
Volatile organics
Use of acidic sorbent
with metal hydroxide
wastes
Use of acidic sorbent with
cyanide wastes
Use of acidic sorbent with
sulfide wastes
Use of alkaline sorbent
with waste-containing
ammonium compounds
Use of alkaline sorbent
(containing carbonates
such as calcite or
dolmite) with acid wastes
Use of carbonaceous
sorbent (carbon,
cellulose) with oily
waste
Use of siliceous sorbent
(soil, fly ash) with
hydrofluoric acid waste
Volatiles not effectively immobilized;
driven off by heat of reaction.
Solubilizes metal.
Releases hydrogen cyanide.
Releases hydrogen sulfide.
Releases ammonia gas.
Releases carbon dioxide which can cause
frothing.
May create pyrophoric waste.
May produce soluble fluorosilicates.
U.S. EPA, 1988c
U.S. EPA, 1986c
U.S. EPA, 1986c
U.S. EPA, 1986c
U.S. EPA, 1986c
U.S. EPA, 1986c
U.S. EPA, 1986c
U.S. EPA, 1986c
-------
4.4 ISSUES DEALING WITH THE STABILIZATION OF ORGANIC WASTES
AND OF MIXED ORGANIC AND INORGANIC WASTES
4.4.1 Introduction
This section focuses on issues related to S/S processing of wastes
in which the primary contaminants are organics or where significant quantities
of organic contaminants are mixed with other types of waste, such as inorgan-
ics. Issues relating to interferences caused by low levels of organics are
discussed in Section 4.3.
Threshold levels for organic interference with S/S processes exist.
However, the actual level depends on the nature of the organic, the waste
matrix, and the binder. Different types of interferences and some guidance on
threshold levels are discussed in greater detail in Section 4.3.
Organic contaminants are more difficult to treat with inorganic S/S
processes than are inorganics such as metals and metal compounds. Organics
generally do not react with an inorganic matrix but instead are sorbed or
encapsulated within pores. The reason organic contaminants do not react is
that many of them are nonpolar and hydrophobic, whereas inorganic S/S binders
are polar and hydrophilic. Therefore, additives with hydrophobic functional
groups are sometimes added to binders to increase the binding affinity for the
organic contaminants. Inorganics may be either entrapped or incorporated into
the chemical structure, depending on the treatment process.
Wastes with very high concentrations of hazardous organic compounds
are generally better suited for treatment by destructive processes such as
incineration, biodegradation, chemical oxidation, and dechlorination. Another
problem with organic contaminants is volatilization. Releases of volatile
organics to the air during S/S treatment will occur whenever volatiles are
present. Both the mixing required in treatment and the heat input (from
exothermic reactions in inorganic processes or external heat input in thermo-
plastic processes) will contribute to the loss of volatile organics. Sec-
tion 4.5 discusses air emissions in greater detail.
However, many industrial wastes and contaminated materials contain
organics at low concentrations, mixed with inorganics, or in a viscous waste
matrix. Application of treatment processes to destroy the organics in such
wastes may be very expensive compared to the benefits and may, in some cases,
be ineffective (Conner, 1990). S/S can be a very viable option. S/S process-
es that have been tested on or applied to various organic constituents are
4-39
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listed in Table 4-6. Note, however, that an entry in this table indicates
only that the binder has been successfully applied at least once in the
stabilization of the indicated contaminant. The degree of stabilization and
the long-term stability of the product are not indicated. Also, an entry in
this table does not imply that the issue of volatilization (as opposed to
immobilization) of the air emissions was properly addressed.
Mechanisms that stabilize organics are not well understood (Sec-
tion 4.2.2). Some stabilization of the organics appears to occur in cementi-
tious systems. However, it has been difficult to determine whether apparent
decreased contaminant mobility is caused by sorption effects, dilution by
reagent additions, sample heterogeneity, or volatilization.
Quantifying the degree of immobilization of organic contaminants in
S/S-treated waste is not as straightforward as for inorganic contaminants.
Aqueous leach tests may provide an estimate of the propensity for the organic
contaminant to be transported in groundwater as a solute, but they do not
provide a good measure of organic immobilization for nonpolar organics that
have low solubility in water. For nonpolar organics, the use of nonpolar
solvent extraction (e.g., the Total Waste Analysis, or TWA) has been recom-
mended. However, this recommendation is still under consideration by EPA
because it is unclear how the results of a solvent extraction relate to the
environmental mobility of a contaminant in groundwater. Also, there are few
if any data that demonstrate that the chemical interaction between an S/S
binder and an organic contaminant is strong enough to resist leaching by an
aggressive nonpolar extractant. Therefore, one of the potential pitfalls of
using S/S technology to treat waste with significant nonpolar organic contami-
nants is the inability to adequately assess the extent of contaminant immobi-
lization attributable to S/S treatment.
4.4.2 S/S Additives Compatible with Orqanics
Testing of additives to improve immobilization of organic compounds
with inorganic binders has shown promising results. These additives include
activated carbon, charcoal, modified clays, and condensed silica fumes (fine
silica particulate prepared by condensing silica fumes).
Ontario Waste Management Corporation's Wastewater Technology Centre
(WTC, 1989, p. 3) investigated the use of S/S systems with the addition of
activated carbon and condensed silica fumes. Tho S/S process was based on
4-40
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TABLE 4-6. S/S PROCESSES TESTED ON OR APPLIED TO ORGANIC-CONTAINING WASTES
Binder
Organic Contaminant
Physical Form
of Waste
Reference
Bitumen
Chemfix"
Fly ash
Kiln dust
Lime and fly ash
Lime and kiln dust
Lime and
neucleophilic reagents
Organic
Portland cement
Portland cement and clay
Oil and gasoline
Oil
Phenol
Oil
Creosote
Phenol
Organics
PCBs and dioxins
PCB
Kepone
Latex
Phenol
Phenol
Substituted phenol
Soil
Sludge
Sludge
SIudge
Sludge
Sludge
Sludge
Sludge
Soil
Sediment
Waste caulk
SIudge
SIudge
Solution
U.S. EPA, 1989g
U.S. EPA, 1989g
Cote and Hamilton, 1984
U.S. EPA, 1989g
U.S. EPA, 1989g
Cote and Hamilton, 1984
U.S. EPA, 1989g
U.S. EPA, 1989g
HazTech News, 1991
Conner, 1990
Conner, 1990
Cote and Hamilton, 1984
Cote and Hamilton, 1984
Sheriff et al., 1989
-------
TABLE 4-6. S/S PROCESSES TESTED ON OR APPLIED TO ORGANIC-CONTAINING WASTES (Continued)
I
4k
ro
Binder
Portland cement and fly
ash
Portland cement,
kiln dust, and a
proprietary agent
Portland cement and
polymer
Portland cement and a
proprietary agent
Portland cement and
soluble silicate
Pozzolan and
Organic Contaminant
Phenol
Pesticides
Kepone
Oil
Vinyl chloride and
ethylene chloride
API separator sludge
PCBs
Kepone
Phenol
Oil
Physical Form
of Waste
Sludge
Sludge
Soil
Sludge
Sludge
Sludge
Soil
Sediment
Sludge
Soil
Reference
Cote and Hamilton, 1984
U.S. EPA, 1989g
U.S. EPA, 1989g
U.S. EPA, 1989g
U.S. EPA, 1989g
U.S. EPA, 1989g
U.S. EPA, 1989g
Conner, 1990
Cote and Hamilton, 1984
U.S. EPA, 1989g
proprietary agent
Sulfur-based
Kepone
Sediment
Conner, 1990
-------
TABLE 4-6. S/S PROCESSES TESTED ON OR APPLIED TO ORGANIC-CONTAINING WASTES (Continued)
Binder
Organic Contaminant
Physical Form
of Waste
Reference
Bentonite clay modified
with dimethyl
di(hydrogenated tallow)
ammonium chloride and
mixed with Type I Portland
cement
Phenol and chlorinated
phenols
Soil
Sell et al., 1992
co
8 Proprietary binder formulation.
Note: An entry in this table does not mean that the binder will work under all conditions or that it
necessarily worked under the conditions of the reported study. In addition, the degree of
solidification/stabilization achieved was not reported in all references, nor was the extent of
contaminant volatilization uniformly addressed.
-------
Portland cement and proprietary additives. The waste was metal-finishing
sludge spiked with 500 mg/kg each of acenaphthene, aniline, bis(2-chloroethyl)
ether, phenol, benzene, and trichloroethylene. WTC found both physical and
chemical mechanisms to be important in containing the contaminants. Activated
carbon was found to be the best additive for immobilizing organic contami-
nants. With the exception of phenol, none of the contaminants tested in this
study were detected in the aqueous leachate. Condensed silica fumes were the
best additive to entrap organic contaminants physically, and the formulation
tested resulted in small increases in waste mass and volume. The physical
containment factor was about ten times better than that of the other cement-
based processes. Further investigation of both additives is needed to define
dosages, applicability to various waste constituents, and long-term stability.
Modified clays can be added with inorganic processes to reduce the
mobility of organic wastes. Investigations by Lagoutte et al. (1990) indicat-
ed that S/S processes using modified clays show promise as an effective
treatment for hazardous waste containing such organic contaminants as penta-
chlorophenol. Some clays, such as bentonite, can be modified by introducing
quaternary ammonium compounds into the spaces between the alumina and silica
layers. These aqueous spaces in the clay are normally hydrophilic and polar,
but they can be made more hydrophobic and less polar by introducing quaternary
ammonium compounds with long-chain alkyl groups or aromatic groups attached.
One common S/S formulation combines Portland cement, treated clay,
and coal fly ash. The addition of coal fly ash produces a high-strength
solid, although the combination generally requires longer curing times than
with Portland cement alone. The residual carbon content of the coal fly ash
has been shown to have an ability comparable to that of activated carbon for
adsorption of organics (Lagoutte et al., 1990). Thus, both the modified clays
and the coal fly ash act to immobilize the organics.
Sheriff et al. (1989) investigated the use of activated charcoal and
tetra-alkylammonium-substituted clays as prestabilization adsorbents for
phenols and chlorinated phenols prior to application of cement-based S/S
processes. Charcoal is a well-known adsorbent, whereas the use of the
substituted clays exploits the hydrophobic properties of the alkyl groups to
fix organic materials within the clay matrix. Wyoming bentonite substituted
with hexadecyltrimethylammonium bromide and benzyl dimethyltetradecylammonium
chloride (Chemical Abstracts Registry Number 139-08-2) was found to be very
4-44
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effective in adsorbing chlorinated phenols with adsorption capacities of
-150 mg of chlorinated phenol per gram of clay. The results indicated a clear
relationship between the chain length of the alkyl ammonium ion in the
exchanged clay and the ability of the clay to adsorb a particular phenolic
compound. Activated charcoal was found to adsorb effectively 180 mg of phenol
or chlorinated phenols per gram of charcoal.
Cost is an important consideration in using additives such as
modified clays and activated charcoal. Most additives are more expensive than
binders such as cement. If a large quantity of additive is needed, the cost
can be prohibitive. However, the additives frequently are effective in low
concentrations. Costs of S/S processes are discussed in greater detail in
Section 4.10.
Many of the additives used to reduce organic mobility in inorganic
binders rely on sorption mechanisms. Sorption, especially with activated
carbon, is at least partially reversible. The long-term performance of any
S/S-treated waste is an important issue that is not fully resolved (Sec-
tion 4.7). Long-term performance of binders that rely on sorption should be
examined with particular attention.
4.4.3 Approach to Evaluating Feasibility of S/S
for Wastes Containing Organics
Figure 4-2 presents a proposed approach in the form of a decision
tree for evaluating the feasibility of S/S for treating organic-bearing
wastes. This decision tree provides guidance for determining whether S/S is
an acceptable alternative for treating a particular waste containing organics.
At the outset of the process, the following information is needed (Wiles and
Earth, 1992):
The quantity of organic material relative to inorganic
contaminants and other materials, including information
on chemical and physical characteristics.
The type and amount of inorganic compounds that would
remain if all organics were destroyed or removed.
The chemical and physical characteristics of residuals
from the destroyed or removed organics.
4-45
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Define Waste Composition
and Contaminants
te contaminants in
concentrations that are
regulated or that pose a slgrtfl-
cant risk to human health or
to the environment?
Organic
Contaminants Only
Mixed Organic and
Metal Contaminants
Metal
Contaminants Only
la
an
for destroying
at a reasonable cost? e.g~
thermal of biological treatment
process
Are
treatment standards
on soluble or total metal
contents?
the organic
contaminants
volatile?
Consider S/S after
appropriate treatablltty
testing.
Consider S/S with appropriate treatabNity
testing Including evaluation of contaminant
votaauatton during treatment
^\have low sokjHKy .^
^"^Vlnwator7^-x^
YES[
Consider S/S with appropriate traataMllty
tMting-, Including valuation of contaminant
Immobilization as measured by leachabiity
h a nonpolar solvent (see Section 4.4.3).
For si organic contaminants, appropriate
treatabilty testing shoukl include an analysis
of possUe contaminant degradation or
transformation reactions and the toxJdty of
any by-products formed.
FIGURE 4-2. GENERAL DECISION TREE FOR S/S APPLIED TO ORGANIC CONTAMINANTS
4-46
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The first step in the decision tree is to evaluate whether the
organic contaminants present in the waste pose a significant hazard or threat
to human health or the environment. This evaluation is carried out as
follows:
Determine whether the waste is either a listed or
characteristic RCRA hazardous waste. If the waste is
not RCRA hazardous, then the following conservative
risk-based approach assuming no containment of the
waste by the S/S process is proposed.
Determine the concentration of the organic present in
the waste to be treated. Determine the compound that
poses the highest health or environment risk (quantity
and toxicity). Then, determine the level and/or
concentration of the highest risk compound that can be
allowed without creating a health or environmental risk
at the given site.
This conservative approach assumes that:
The S/S process will not treat or contain the selected
compound. Therefore, all of it will be released from
the solidified waste; and/or
All of the compound will be released as air emissions
during the S/S process (Wiles and Barth, 1992).
If the concentration of the highest-risk compound is above the level
determined to pose a health or environmental risk at the given site, then
pretreatment to remove or destroy the organic(s) will be required and/or air
emission controls and treatment will be needed on the S/S treatment train.
After determining that the waste contains organic contaminants that
require treatment, then the decision tree in Figure 4-2 addresses the follow-
ing four important issues pertaining to the feasibility and practicality of
using an S/S treatment approach on the organic-bearing waste:
1. Is there an applicable technology that will either
destroy or remove the organic contaminants?
2. Are the organic contaminants volatile and likely to
be released as air emissions during S/S treatment?
3. Do the organic contaminants have low solubility in
water? If so, the inherent potential for migration
4-47
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in groundwater is low and will invalidate the
meaningful ness of aqueous leach tests.
4. Will S/S treatment cause the organic contaminants to
degrade or transform into toxic by-products?
These four issues are discussed further below.
4.4.3.1 Destructive or Removal Technologies Versus S/S
The concern over the use of S/S versus a destructive or removal
technology for treating organic-bearing wastes relates to the hierarchy of
waste treatment that is, all other factors being equal, technologies that
destroy or reduce the amount of contaminants are preferred over technologies
that simply immobilize the contaminants (see Section 1.1.2). Technologies
that are capable of degrading organic constituents to innocuous components
such as C02 and H20, or of separating organic contaminants from inorganic
constituents based on thermal or chemical properties, are preferred over
immobilization technologies. Degradation and separation-based remedies are
permanent, whereas immobilization may lose its effectiveness over time (see
Section 4.7 on Long-Term Performance).
Consequently, S/S treatment typically is not used at sites heavily
contaminated with organic wastes (Wiles and Barth, 1992). Alternative
technologies (e.g., incineration, steam stripping, vacuum extraction,
bioremediation) should be considered first. However, S/S treatment is
frequently appropriate for the residues remaining after the use of one of
these other technologies, or for soils or sludges containing low
concentrations of organics. A well-designed and controlled treatability study
should be conducted to assess S/S effectiveness and to select and design a
proper S/S process (see Section 2).
4.4.3.2 Volatile Organic Contaminants
A wide variety of organic constituents in hazardous waste are
volatile to varying degrees. As indicated in Figure 4-2, when volatiles
comprise the dominant constituents, a destructive or removal technology is
usually preferred. However, there are many cases where volatiles are present
as a relatively minor contaminant, but in concentrations high enough to pose a
potential health or environmental risk. For example, some volatiles, mixed
4-48
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with metals, salts, or semivolatile organics, may respond to S/S without
pretreating to remove the organics. Pretreatment or treatment trains can add
significantly to the cost and the time needed to complete the cleanup. The
difficulty is that volatile contaminants are not always effectively treated
using S/S.
Demonstration that the volatile organic contaminants are being
immobilized during treatability studies greatly complicates the treatability
study. Special precautions have to be made during treatability testing to
assess volatile organic emissions. This means that proper controls must be
used to perform a complete mass balance, in which all organic air emissions
are collected and analyzed during the treatability study, from the point of
waste compositing and mixing through the curing of the treated waste specimen.
The required containment, sampling, and analysis equipment and activities can
more than triple the cost of the treatability study. The testing should be
structured to allow a closed mass balance to fully account for the organic
materials.
Unfortunately, air emissions monitoring during treatability testing
is infrequently carried out as needed, and numerous studies have reported the
apparent immobilization of volatile contaminants when the post-treatment
reduction in contaminant concentration was, in actuality, caused by
volatilization. Nevertheless, volatile contaminants in low concentrations can
be and have been successfully treated using S/S when precautions are taken to
minimize volatilization. Well-designed treatability studies using technology
that can be implemented in the field are needed.
4.4.3.3 Nonpolar Organic Contaminants
The third issue pertains to the low aqueous solubilities of numerous
organic contaminants, both volatile and nonvolatile. Polar organic
contaminants such as carboxylic acids, alcohols, and phenols are typically
very soluble in water. Accordingly, the TCLP aqueous leaching test defines
standards for selected organic contaminants with adequate solubility in water.
However, nonpolar organics such as polyaromatics, benzene,
tetrachloroethane, and hydrocarbons are generally insoluble in water. Hence,
for this latter group of compounds, an aqueous leach test is a meaningless
indicator of the degree of immobilization caused by S/S. Therefore, the use
of a nonpolar solvent extraction (e.g., the TWA) has been recommended.
4-49
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However, this recommendation is still under consideration by EPA because it is
unclear how the results of a solvent extraction relate to the environmental
mobility of a contaminant in groundwater. Also, there are few if any data
that demonstrate that the chemical interaction between an S/S binder and an
organic contaminant is strong enough to resist leaching by an aggressive
nonpolar extractant. Therefore, one of the potential pitfalls of using S/S
technology to treat waste with significant nonpolar organic contaminants is
the inability to adequately assess the extent of contaminant immobilization
attributable to S/S treatment.
4.4.3.4 Degradation and By-Product Formation
The final issue in Figure 4-2 pertaining to the immobilization of
organic contaminants applies to all types of organic contaminants volatile
and nonvolatile, polar and nonpolarin all ranges of concentrations.
Because organic constituents readily undergo chemical transformation reactions
and S/S binders are associated with fairly aggressive chemical environments
(such as increased temperature and alkaline pH), the potential for chemical
transformation or degradation always exists; and a post-treatment reduction in
the concentration of an organic contaminant may be erroneously interpreted as
evidence for immobilization when it, in actuality, may be attributable to
contaminant transformation. Moreover, chemical transformation or degradation
may result in the formation of by-products which can be more or less toxic
than the parent compound. Therefore, it is not sufficient to demonstrate the
extent to which transformation is occurring. The identities of the by-
products and their toxicities must also be characterized. Unfortunately, the
process of detecting and analyzing by-products can be extremely expensive and
can therefore be a deterrent to considering S/S as an option for the treatment
of organics-bearing wastes.
4.5 AIR EMISSIONS AND CONTROL
In considering S/S options, the possibility of air emissions must be
taken into account. Many wastes contain VOCs that can escape into the
atmosphere. Even compounds not generally considered volatile can be released
by the mixing and heating operations involved in S/S. In addition to volatil-
ization, other forms of air emissions, such as fugitive dust or particulates,
4-50
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must be taken into account. The cost of installing and operating equipment to
prevent air emissions can be significant. The local air board or other
cognizant regulatory agency should be consulted to define air emissions
issues.
4.5.1 Volatile Organic Compounds
Volatile organic compounds can escape into the atmosphere during the
mixing and heating steps of the S/S process, and even during sampling, sample
handling, and sample preparation prior to analysis. For example, one study of
volatilization during S/S processing found that an average of 0.11% of the
feed into the process was emitted to the air (Ponder and Schmitt, 1991). As a
general rule, sites contaminated with only volatile contaminants should not be
considered as candidates for S/S (Wiles and Barth, 1992) (see also Sections
4.4 and 2.4). However, volatile and/or semivolatile organic compounds are
frequently present as secondary components in wastes that contain mostly
metallic or other inorganic contaminants.
In wastes containing VOCs, significant VOC losses to the atmosphere
will occur with remediation activities that involve exhumation of the waste.
In situ S/S technology that produces a monolithic product is capable of
reducing VOC losses but not of eliminating them (Spence et al., 1990). Also,
volatiles can continue to escape from a solidified waste form, regardless of
the reduction in pore space and increase in tortuosity.
The quantities of VOCs acceptable for S/S should be based on a risk
assessment for the given site and/or on the result of a treatability study
that includes a mass balance of the organics before, during, and after
treatment. As a worst-case scenario, the risk assessment should assume that
none of the highest risk compounds will be retained by the S/S process and/or
that all the compounds will be lost via air emissions during S/S processing
(Section 4.4).
A system for measuring the emissions of organic compounds from mix-
ing processes such as those used in S/S activities is currently under develop-
ment. This "modified headspace" sampling system, having been demonstrated at
VOC emission rates ranging from less than 1 milligram per minute up to tens of
grams per minute, can be used at the laboratory scale to measure organic
emissions both from the S/S process and from the S/S-treated waste during
curing. Such equipment can also be used in conjunction with a full-scale
4-51
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remediation effort by testing samples of the treated waste from the field in
the laboratory (Weitzman et al., 1990).
4.5.2 Participates and Other Emissions
In addition to gaseous emissions from volatile organics, particulate
releases to the atmosphere from operations associated with S/S treatment can
also be a concern. Possible sources of air pollutants and fugitive dust in a
field S/S project include excavation, the movement of trucks and other heavy
equipment, and the loading and processing of waste and binder materials in the
mixing device. In the study cited in Section 4.5.1 for VOC volatilization, it
was also found that an average of more than 0.01% of the waste feed being
processed was released as particulate emissions (Ponder and Schmitt, 1991).
Care must frequently be taken to reduce the escape of both contaminated
particulates and fugitive dust during treatment. Typical engineering controls
include scrubbers for certain types of air pollutants and wetting the waste or
ground to reduce dust.
Various guidelines exist for determining maximum air emissions of
contaminants and fugitive dust during remediation projects. For example, Toxic
Air Pollutant Source Assessment Manual for California Air Pollution Control
Districts and Applicants for Air Pollution Control District Permits specifies a
risk-screening methodology for evaluating air emissions and a fugitive dust
concentration limit for remediation projects in California (Interagency
Working Group, 1987). The risk-screening methodology is a simple, conservative
estimation of the maximum possible health impacts associated with air emissions
during the duration of the project. If the project fails the initial r1^1<
screening calculation, then a much more detailed risk assessment may have to be
conducted prior to initiating field treatment.
4.5.3 Controlling Air Emissions
Depending on the nature of the anticipated air emissions, it may be
necessary to adopt control measures to ensure that volatile and particulate
emissions are within acceptable levels. Equipment such as air scrubbers or
large enclosures around the treatment area may have to be employed as an
adjunct to the S/S treatment process, thus increasing the complexity and costs
associated with S/S. The U.S. EPA's Office of Air Quality Planning and
4-52
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Standards (OAQPS) is developing guidance for controlling air emissions at RCRA
treatment, storage, and disposal facilities (TSDs). This guidance will
require many S/S processes to incorporate capture and control mechanisms for
volatile constituents. Even those projects involving relatively low levels of
volatile constituents may be affected (Wiles and Barth, 1992). However, apart
from this guidance for TSD facilities, air emissions and controls are
currently assessed on a project-by-project basis.
4.5.4 Significance of the Amended Clean Air Act
The purpose of the Clean Air Act (CAA) is to:
protect and enhance the quality of the nation's air
resources so as to promote the public health and
welfare and the productive capacity of its population
initiate and accelerate a national research and
development program to achieve the prevention and
control of air pollution
provide technical and financial assistance to state
and local governments in connection with the
development and execution of their air pollution
prevention and control programs
encourage and assist the development and operation of
regional air pollution control programs
Within these purposes, waste minimization or pollution prevention is encour-
aged but, in most cases, is not mandated. Under the CAA, regulations have
been promulgated that give industry the choice of either preventing or
controlling air emissions. These regulations include the National Ambient Air
Quality Standards (NAAQS); National Emission Standards for Hazardous Air
Pollutants (NESHAP), which control emission of specific pollutants for
specific industries; and permitting requirements.
Just as the forthcoming RCRA-related guidelines for TSD facilities
will affect S/S operations, the amended Clean Air Act portends increased use
of capture and control mechanisms. Stricter regulations will require more
careful screening of candidate sites for the application of S/S technology.
This screening will be based on the potential to achieve regulatory compliance
and the cost of achieving regulatory compliance.
4-53
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4.6 LEACHING MECHANISMS
After disposal, the S/S-treated waste may eventually come into
contact with water. The S/S processes are aimed at either reducing the
mobility of the contaminants or reducing access of water to the contaminant,
or both. However well the S/S waste is stabilized and isolated from the
hydrosphere in disposal, some transport of contamination from the S/S-treated
waste into the groundwater will eventually occur. Complete immobilization of
contaminants is not a realistic expectation (Bishop, 1988).
This process of slow extraction of contaminants from the S/S-treated
waste by water or some other solvent is called "leaching." Leaching tests are
discussed in Section 3.2. Leaching can occur when the S/S-treated waste is
exposed to stagnant leachant or to a flow of leachant through or around the
waste. Leaching is the general term for complex physical and chemical
mechanisms. These mechanisms mobilize a contaminant and transport it away
from the waste.
In a disposal scenario, the solvent will usually be groundwater.
Leaching occurs when the contaminants in the S/S-treated waste come into
contact with the groundwater. The leachant flow and composition are deter-
mined by the physical properties of the disposal area and any engineered
barriers at the disposal site. Leaching tests may use water, aqueous
solutions of acids or salts, or organic liquids to model various disposal
scenarios, determine waste composition, measure diffusion coefficients, or for
other specific test purposes.
There is significant experimental evidence that, when waste stabi-
lized by cement or similar pozzolanic materials is exposed to acidic water,
significant matrix dissolution occurs. Thus, the leaching rates of contami-
nants from stabilized waste will be a function of both the dissolution rate as
well as the diffusion rate of contaminants into the leachate.
In the Netherlands, a database has been developed to collate,
organize, and analyze information about the leaching of contaminants from
waste and waste-containing materials (de Groot and van der Sloot, 1992).
Organization of the information into a database is intended to assist identi-
fication of systematic trends in leaching behavior and mechanisms.
4-54
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4.6.1 Leaching Associated with Inorganic S/S Processes
The typical S/S-treated waste resulting from use of an inorganic
binder is a porous solid. The pore space contains some mixture of water and
gas, so many different phases can be present. There may be several different
solid phases, each containing contaminants. For example, contaminants may be
present in the cement mineral phases because of substitution in the crystal
structure or as a separate phase, such as a precipitated solid. There can
also be one or more aqueous phases such as an adsorbed layer of fluid as well
as the bulk pore fluid. The sorbed layer may have a different contaminant
composition than the bulk fluid. There can also be one or more nonaqueous
phases if organic contaminants are present (WTC, 1990a).
Prior to introduction of the leachant, the pore system will have
approached equilibrium conditions with the surrounding solid phase. That is,
the contaminants are associated with a specific phase, and there is no net
transfer between the phases. The leachant changes the composition of the
system and disrupts the chemical equilibrium, resulting in the mobilization of
contaminants. The new system may evolve towards a new equilibrium if suffi-
cient time passes with no leachant renewal.
The two basic mechanisms in the leaching process are mobilization
and transport of the contaminant. The leachant mobilizes contaminants within
the pores by dissolving the contaminant. Dissolution results from a combina-
tion of chemical and physical mechanisms. Examples include bulk dissolution
of mineral phases in the S/S-treated waste, washoff of surface contaminants,
changing chemical parameters such as pH or Eh dissolving a formerly insoluble
phase, desorption of contaminants, or other mechanisms (deGroot and van der
Sloot, 1992). Factors that affect the extent of equilibrium concentrations
include the solubility of the constituent and the chemical makeup of the pore
water. Under neutral conditions, the leaching rate is controlled by molecular
diffusion of the solubilized species. However, if the leachant induces acid
conditions, the rate will also depend on the rate of back diffusion of the
hydrogen ion because the pH determines the chemical speciation within the S/S-
treated waste (Cheng, et al, 1992).
As more soluble constituents are leached from a relatively insoluble
solid matrix, a layer deficient in the leached constituents develops. Under
low pH conditions, both H* and the leachable constituents must diffuse through
this layer in opposite directions. The leaching rate in the leached layer
4-55
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should eventually be limited by diffusion of constituents, because H* diffuses
much faster than other species. However, this layer may not be rate-limiting
in the overall process (Cheng and Bishop, 1990). As constituents leach, the
layer may become more porous compared to the unleached solid, so that molecu-
lar diffusion in the pore water and boundary layer phenomena become the
limiting factors (Conner, 1990).
Transport of the mobilized contaminants occurs by bulk advective
flow or diffusion. If water flows within the S/S-treated waste, advective
transport causes contaminants that have been mobilized by reactions in the
pores to flow through the waste. The velocity of leachant moving through the
pores will vary considerably in both magnitude and direction due to the small
size and the tortuosity of the pores (WTC, 1990b). In most S/S-treated waste,
the pores are small and tortuous, so the advective transport is small.
However, contaminant movement still occurs by molecular diffusion (Crank,
1967).
Only a fraction of the pores within the S/S-treated waste are linked
to each other and to the outside to form what is referred to as "connected
porosity." The pores that are not linked to this network are referred to as
"closed porosity." Also, large pore spaces may be connected by small-diameter
pathways, resulting in "occluded porosity." The micromorphology of the matrix
- including the number, size, and degree of connection of the pores - will
determine how quickly water can permeate through an S/S waste (i.e., hydraulic
conductivity) and will influence the leaching process. As might be expected,
leaching occurs most quickly through the connected pores.
In most cases, cement-based monoliths have low hydraulic conductivi-
ty, which limits the amount of leaching water contacting the matrix. However,
it has been shown that the hydraulic conductivity of S/S waste may vary over
several orders of magnitude, from low values typical of compacted clay to
higher values typical of silty soils (Cote et al., 1986). Hydraulic conduc-
tivity of the waste determines whether leaching rates will be controlled by
advection or by molecular diffusion. Advection is more important than
diffusion when hydraulic conductivity is larger than 10"7 cm/s. On the other
hand, slow diffusion limits transport rates when hydraulic conductivity is
lower than 10~7 cm/s. If the hydraulic conductivity of the waste is much
lower than that of the surrounding material, infiltrating water such as
rainwater or groundwater follows the path of least resistance and flows around
4-56
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the waste. In this case, leaching is limited by molecular diffusion in the
connected porosity of the S/S waste matrix because, when contaminants reach
the interface of the S/S waste and surrounding material, they are carried away
by the groundwater. If, on the other hand, the hydraulic conductivity of the
solidified waste is on the same order of magnitude or higher than that of the
surrounding material, water flows around and through the waste. In that case,
the pore water solution is displaced, and leaching takes place largely by
advection (C6t6 and Bridle, 1987, p. 60).
The surface-area-to-volume ratio (SA/V) of a waste product greatly
influences the release of potentially harmful elements to the environment. A
smaller SA/V results in a lower rate of release. The leaching percentage
relative to the total amount of an element present in a waste form is related
to the SA/V, for a given exposure time. Therefore, all measures leading to
products with a smaller SA/V lead to a proportional decrease in leaching
percentage but the long-term quantities released are not decreased (van der
Sloot et al., 1989).
Chemical speciation also influences leaching. Van der Sloot et al.
(1989) found that elements leached from cement-based waste products are mainly
anionic species such as Mo04*~, B033", V043", F", and S042~. These anions are
associated with cationic species typical of cement-based waste forms such as
calcium. Leaching of metals such as copper, cadmium, zinc, and lead typically
is limited when the pH in the pore solution remains above 8 or 9, but can
increase at very high pH (above 11.5 or 12). Van der Sloot et al. (1989)
concluded that chemical speciation of potentially hazardous elements within a
waste product and the interaction of these elements with matrix components
within the pore system are crucial for determining the release rate to the
environment. Also, they suggested that more information on different ways of
contact with water is needed, particularly in relation to pH, to allow
utilization of intrinsic leach parameters in a wide range of environmental
conditions.
For cement-based S/S processes, sulfate can increase leaching rate.
The onset of the leaching rate increase may be delayed, however, so test
results immediately after setting may be misleading. Sulfate either in the
cement or present in the waste causes formation of ettringite, which slowly
hydrates and expands, causing an increase in porosity and possible breakdown
of the waste form. Sulfites and sulfides are also a problem because they may
4-57
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slowly oxidize to sulfate, increasing the solid volume and causing the waste
to crack.
Poon et al. (1985) found that the microstructure of the solidified
waste was important in leaching metals from the cementitious matrix. They
assessed mechanisms of zinc and mercury leaching from cement/silicate stabili-
zation processes using extended leaching tests, scanning electron microscopy,
and powder X-ray diffraction. After an extended leaching period, massive
breakdown of the matrix occurred with a subsequent dramatic increase in
leachate concentration. Once the structural integrity of the stabilized waste
was removed, massive leaching of zinc and mercury occurred.
4.6.2 Leaching Associated with Organic S/S Binders
The thermoplastic and thermosetting resin binder processes operate
mainly by encapsulating the waste. The S/S-treated waste is, therefore, less
porous than the material resulting from S/S processes using inorganic binders.
The leaching process requires the same two fundamental mechanisms discussed in
Section 4.6.1, mobilization and transport. However, the organic binder
systems rely more on denying the leachant access to the contaminant than on
immobilization.
4.6.3 Leaching Hodels
Several models of leaching mechanisms have been developed to predict
the rate of release from the stabilized waste matrix. Modeling is the only
existing method for predicting long-term performance because it is impractical
to conduct empirical leaching tests for hundreds or thousands of years and
because accelerated tests are not well developed.
4.6.3.1 Dissolution/Diffusion Kinetics
The problem of kinetics, with regard to the aqueous dissolution of a
solid or to the preferential dissolution of a chemical species from a solid,
has long been studied. Several factors may be involved. For example, if more
than one kinetic process takes place, it must be determined which (if any) of
the processes controls the overall reaction rate. The shape of the solid, the
existence of any surface-connected porosity, the charge state of the dissolv-
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ing species, and the chemistry of the aqueous medium into which the solid is
dissolving are also considered.
The discussion that follows considers two kinetic processes from a
largely qualitative point of view: the dissolution reaction itself, which
consists of mass transport across the solid/liquid interface, and chemical
diffusion away from this interface into the surrounding aqueous medium. It is
assumed for this specific example that the rate of supply of dissolving
material from the bulk of the solid to this interface occurs quickly. It is
also assumed that the solution is quiescent, so that convective flow does not
contribute to the mass transport. Two fundamentally different types of
systems are considered within this context: a nonporous solid dissolving into
an essentially infinite aqueous medium and a porous solid for which dissolu-
tion takes place principally into the interconnected solution-containing
pores, coupled with diffusive transport through the pores to the solution
outside the material. Idealized models of these two systems are described in
Sections 4.6.3.1.1 and 4.6.3.1.2 to illustrate the concepts in leaching
models.
If the dissolving chemical species is electrically charged, consid-
erations of charge neutrality in the solution become important, as does mass
transport in the solution by electromigration. The species also may react
chemically with other species within the aqueous medium. Diffusing ions may
also react with the matrix in the leaching zone, adsorbing or precipitating,
which can slow their release. Diffusing ions may also react with the matrix
in the leaching zone, adsorbing or precipitating, which can slow their
release. These factors are not considered here. However, a general treatment
of ionic transport within a crevice-like region, which could be applied to
dissolution and diffusive transport in a porous solid, has been presented by
Markworth and Kahn (1985).
4.6.3.1.1 Nonporous Solid. For a nonporous solid, the two kinetic
processes, i.e., dissolution at the solid/liquid interface and chemical
diffusion of the dissolved species away from the interface, occur sequential-
ly. For this case, the interface may be regarded as a spatially localized
"source" of the dissolving species.
At the solid/liquid interface, the flux of matter due to the
dissolution reaction must be equal, point by point, to the diffusive flux in
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the solution to avoid a nonphysical accumulation or depletion of matter at the
interface. Consequently, the slower of the two processes is the one that
dominates the overall kinetics.
Three characteristic values for the aqueous concentration of the
dissolved species are important in describing the overall kinetics for this
case:
1. Ce, the concentration that would exist at the
interface under conditions of thermodynamic
equilibrium.
2. C/, the actual, instantaneous concentration at
the interface.
3. , the far-field concentration, i.e., the
value at distances far from the interface.
The "driving force" for the dissolution reaction depends upon the
difference Ce - C,. If C, < Ce, the net transport of matter across the inter-
face occurs from solid to liquid as the solid dissolves, while the opposite is
true for C, > C9. If these two concentrations are equal, there is no net
transport across the interface. Likewise, the driving force for chemical
diffusion is the difference C, - C., assuming monotonic variation of the
concentration from the interface to the far field. If C, > C., matter
diffuses away from the solid/liquid interface, the converse is true for
C,< Cm.
Two limiting or extreme cases exist for the overall kinetics; one or
the other of these cases is often satisfied in nature.
1. In the dissolution-controlled case, diffusion occurs
rapidly compared to the dissolution reaction so the
driving force required to maintain the diffusive flow
i s very smal 1 and C, = Cn.
Z. In the diffusion-controlled case, diffusion occurs
slowly compared to the dissolution rate. For this
case, dissolution is rapid but a concentration
gradient is needed to drive the diffusion process so
c,sc..
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For dissolution-controlled kinetics, dependence on diffusion-related rate
constants is virtually nonexistent, whereas for diffusion-controlled kinetics,
dependence on dissolution-related rate constants similarly vanishes.
The intermediate case is that for which neither of the two mass
transport processes controls the overall kinetics. For example, the solid is
dissolving when CM < C, < Ce, but it is growing by supply of dissolved species
from solution when Ce < C, < .
Figure 4-3 illustrates the two limiting cases and the intermediate
case. The actual concentration profile of the dissolved species in the
aqueous medium would generally be a complex function of position and time as
well as of the geometry of the dissolving solid.
It should be noted that this view of the dissolution process, which
is widely applied in practice, must be used carefully or be modified in some
cases. One such case, considered by McCoy and Markworth (1987), involved the
dissolution of glasses containing high-level nuclear waste. One question
there concerned how these "impure" materials actually do dissolve. In their
work, McCoy and Markworth assumed that the material dissolves congruently. To
describe this process, they assumed first-order, dissolution-controlled
kinetics, with transport of silicon across the surface/solution interface
being the rate-limiting factor. As another case, consider a dissolving
material which consists of two different, distinct phases, with one phase
tending to dissolve into the surrounding aqueous medium much more rapidly than
the other. The more soluble phase will be preferentially dissolved (i.e.,
leached), leaving behind a material that is enriched in the less soluble
phase. Of course, the microstructure of the material left behind will depend
on the morphology of the two phases prior to dissolution. If, for example,
the more soluble phase exists as an interconnected network, then the leached
portion of the material will consist of a porous structure that likewise
contains a network of interconnected porosity, assuming that the solution can
penetrate into the porous structure as it is being created. This process
could be inhibited if transport of dissolved species through the solution,
within the porous structure or away from the external surface, occurs slowly.
4.6.3.1.2 Porous Solid. The situation differs for a porous solid,
with liquid penetrating and filling the porous structure, where dissolution
can occur along the entire length of the pores. The distinctly sequential
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Solid
Liquid
Dissolution - Controlled
Solid
Liquid
T^- X
Diffusion - Controlled
Liquid
Intermediate Case
FIGURE 4-3. SCHEMATIC ILLUSTRATION OF CONCENTRATION PROFILES, C(x),
CHARACTERISTIC OF SPECIES DISSOLVING FROM A NONPOROUS SOLID INTO
AN AQUEOUS MEDIUM, WITH x BEING THE DISTANCE INTO THE SOLUTION
MEASURED FROM THE SOLID/LIQUID INTERFACE. THE TWO RATE-LIMITING
CASES AND AN INTERMEDIATE CASE ARE SHOWN.
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coupling between the two processes, characteristic of nonporous solids, does
not exist. The "source" of dissolving species, considered to exist at the
pore/solution interface, is not spatially localized as it is for a nonporous
solid. Instead, dissolution can take place along the entire length of the
pores within which the dissolved species is diffusing, the pore walls acting
as a spatially extended "source" of this species to the solution within.
Diffusion of the species takes place within the network of pores until release
occurs at the intersection of the pores with the external surface. Figure 4-4
shows this type of mass-transport kinetics.
4.6.3.2 Examples of Existing Models
The complex relationship between dissolution and diffusion for a
porous solid means that the overall rate of release of dissolved species to
the external surface depends on both dissolution-related and diffusion-related
rate constants, even if one occurs faster than the other.
Godbee and Joy's widely used empirical model (Godbee et al., 1980)
assumes that leaching is controlled by diffusion through the solid, and that a
zero surface concentration exists (i.e., contaminant dissolves into the bulk
liquid from the surface immediately). The equation takes the form:
^1=2
S
0.5
(1)
where an = contaminant loss during leaching period n (mg)
A0 = initial amount of contaminant present in the specimen (mg)
V = volume of specimen (cm3)
S = surface area of specimen (cm2)
tn = time to end of leaching period n (sec)
De = effective diffusion coefficient (cm2/sec)
Models have also been developed to account for other factors and conditions in
the leaching process. For example, where Godbee and Joy's model assumes
leaching from an infinite depth, leaching in cementitious waste forms occurs
in a narrow, but inwardly-moving, leaching zone. A model that addresses this
is discussed in Section 4.6.3.3.
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External
Surface
FIGURE 4-4. ILLUSTRATION OF SPECIES DISSOLUTION WITHIN A POROUS SOLID.
DISSOLUTION ACROSS A PORE WALL IS SHOWN, COUPLED WITH TRANSPORT
THROUGH THE SOLUTION-FILLED PORE TO THE EXTERNAL SURFACE.
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Batchelor (1990) reviewed the theory and application of leaching
models. His results indicate that a variety of mechanistic leaching models
can be developed to describe leaching and predict the effects of process
variables on the performance of solidified wastes. These models are distin-
guished by the assumptions made about the leaching environment and the
chemical and physical mechanisms at work.
Several simple leaching models predict that the fraction of contami-
nant leached is proportional to the square root of leaching time. The
different models assume that contaminants either do not react or react by
linear sorption, by precipitation, or by an undefined mechanism that results
in complete immobilization of part of the contaminant. The observed diffusiv-
ity is the parameter in these models that describes the extent of immobiliza-
tion, and it can be determined by conducting a leaching test. However, these
leach tests cannot themselves describe the type of immobilization occurring.
Each model results in a relationship that shows that the observed diffusivity
is proportional to the effective diffusivity. The effective diffusivity is
the parameter that describes diffusive transport by Pick's law and therefore
describes only physical immobilization. The proportionality coefficient
depends on parameters that describe the particular chemical immobilization
mechanisms assumed for that model.
Batchelor applied mechanistic leach models to describe performance
of solidified wastes in the TCLP test by modifying a simple model to describe
the effect of inward diffusion of acetic acid from the leaching solution.
However, the model did not incorporate changes in the acetic acid concentra-
tion that would be observed over time as pH rises. Batchelor further notes
that mechanistic leach models could also be applied to predict long-term
leaching, to quantify the relative importance of chemical and physical
immobilization mechanisms, to correlate and extrapolate leaching data for
various contaminants and binders, and to predict ultimate performance from
early characteristics of the solidified waste.
Numerous other leaching models have been developed, with a variety
of intended applications. Many of these models are sophisticated and require
an experienced user. For S/S remediation projects requiring application of a
leaching model to evaluate long-term performance, the use of a technical
expert with experience in leaching modeling is strongly recommended.
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4.6.3.3 The Moving Boundary or Shrinking Core Model
A qualitative model of the leaching of cement-based waste forms, in
contact with an acidic leachant, has recently been developed by Cheng et al.
(1992) based on experimental observations. According to this model, acids in
the leachant are thermodynamically favored to be driven into the waste form.
Once inside, they cause the waste form to decompose, leaving a residue (the
leached layer) that is both porous and rich in silica. The unleached core of
the waste form is separated from the leached portion by a very thin boundary
which gradually moves into the core and thus reduces its volume. The thick-
ness of this boundary is only about 100 /tm, but the pH varies from less than 6
on the leached side to greater than 12 within the 100 urn distance.
What is needed is for this general physical model to be quantified,
that is, to be expressed in mathematical form. Then it could be used as a
predictive tool as well as an aid in the interpretation of experimental data.
One way to begin would be to determine the applicability to this problem of
certain mathematical models that have already been developed to describe the
leaching of glasses that contain high-level nuclear waste. Although the
materials, solution chemistry, distance scales, and even the associated
physical processes may not be the same as for S/S wastes, the mathematical
approaches may be applicable, to some extent, to the model of Cheng et al.
(1992). For example, Banba et al. (1985) have developed a one-dimensional
mathematical treatment of a "moving boundary" model for the leaching of
nuclear-waste-containing glasses. This treatment involves a surface layer
that moves into the bulk glass. Also, Harvey et al. (1984) have developed
some diffusion-based mathematical models for leaching of glassy nuclear waste
forms. In this latter work, they described a depleted layer in the waste-form
matrix which is situated between the matrix/leachant interface and a so-called
depletion front. This front is the interface between the depleted and
undepleted matrix and advances into the matrix as leaching progresses. Again,
the mathematical structure of these various models may have some applicability
to the moving boundary model of Cheng et al. (1992).
4.7 LONG-TERM PERFORMANCE
A significant unresolved S/S technology issue is how well the S/S-
treated waste maintains its immobilization properties over time. Although the
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long-term durability of cement is well proved in conventional construction,
some amount of release is virtually inevitable. S/S materials can be deposit-
ed in landfills to provide secondary barriers between natural waters and the
wastes. Contaminant release begins when these secondary barriers permit
natural waters to come into contact with the waste forms (C6t6 and Bridle,
1987). The question is not whether S/S wastes eventually release contaminants
into the environment, but whether the rate of release is environmentally
acceptable. S/S technologies for waste treatment have been in use for only a
few decades, so the number and duration of studies on field-disposed S/S
wastes are limited. Decisions about the acceptability of particular S/S
products must be based on the available shorter-term field data, laboratory
tests, and models of leaching behavior.
There is evidence that elements can be fixed in cementitious
materials for millennia in a variety of geochemical settings (Dole, 1985)1
Ancient grouts from Cyprus and Greece that are 3500 to 2300 years old have
held their trace metal fingerprints, allowing their constituents to be traced
to nearby pits from which they had been mined. These ancient grouts are
composed largely of undifferentiated, amorphous hydrosilicates, even after
thousands of years. The in situ performance of these ancient grouts demon-
strates the effectiveness of these metastable amorphous hydrosilicates in
sequestering a wide range of elements. However, these observations are not
directly applicable to S/S wastes because of differences in the physicochemi-
cal forms of the trace metals in ancient grouts versus modern waste and
differences in the disposal environments in a Mediterranean climate versus the
wetter climate that dominates most of the United States.
4.7.1 Field Studies
There have been only a few studies of the effects of several years'
duration of environmental exposure on S/S-treated waste. The Coal Waste
Artificial Reef Program (CWARP) studied the environmental consequences of
using stabilized coal combustion wastes as construction material for artifi-
cial fishing reefs. On September 12, 1980, some 16,000 blocks of stabilized
waste were released from a hopper barge to form an artificial reef in the New
York Bight. The blocks consisted of coal fly ash and flue gas desulfurization
residues stabilized with lime and Portland cement additives. Blocks recovered
and tested in 1988 indicated little deterioration and no decrease in compres-
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sive strength. Chemical analyses and surveys of biological communities
established on the reef indicated contaminants were successfully immobilized
(Hockley and van der Sloot, 1991).
A Superfund Innovative Technology Evaluation (SITE) field evaluation
examined the long-term performance of S/S treatment of lead and other metals,
oil and grease, and mixed volatile and semivolatile organic compounds using
Portland cement and a proprietary additive. Durability was tested with
weathering tests, by wet-dry and freeze-thaw cycling, and by sampling S/S-
treated waste after 9 and 18 months of burial. The testing showed that lead
and other metals remained highly immobilized, the physical properties of the
S/S-treated waste deteriorated only slightly, and the porosity decreased. The
organic contaminants, however, were not effectively immobilized (de Percin and
Sawyer, 1991).
The demonstrated long-term durability of concrete structures may
help in the analysis of the long-term durability of S/S waste forms. Struc-
tures made with cement have lasted hundreds and even thousands of years.
Long-term durability of a structure is not directly analogous to immobiliza-
tion of contaminants in S/S-treated waste. However, it does indicate the
ability of inorganic binders to resist gross structural degradation from
exposure to the natural environment. Natural mineral deposits occurring in
the environment are another possible analog to certain S/S waste forms. Metal
sulfide deposits, for example, have remained stable for many millions of years
in subsurface geologic formations. In general, mineral leach rates in nature
do not approach those in the laboratory. The same processes that inhibit the
leaching of natural substances also may apply to S/S wastes disposed in
subsurface environments (Conner, 1990), provided that the chemical speciation
of the materials disposed and the disposal environment are the same.
4.7.2 Laboratory Studies
At present, the environmental acceptability of a hazardous waste in
the United States is based primarily upon the EPA's Extraction Procedure
Toxicity Test (EP Tox) or the Toxicity Characteristic Leaching Procedure
(TCLP). Neither test, however, simulates real-world, long-term conditions,
although they may constitute a fairly severe set of conditions for single-
exposure leaching.
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Perry et al. (1992) used TCLP to examine long-term leaching perfor-
mance of four types of wastes contaminated with metals or inorganics. Each
waste was treated with six different commercial stabilization processes. TCLP
was performed on raw waste and at 28, 90, 200, 470 and 650 days after treat-
ment. Results indicated that the effect of time on the TCLP results was highly
waste-dependent. Leachate values for some wastes remained stable over time
while leachate concentrations for other wastes increased over time. In some
wastes, changes in TCLP concentrations did not occur until 90-200 days after
stabilizations. Similar results have been obtained by Akhter and Cartledge
(1991) and Cartledge (1992), except that both increases and decreases in metals
Teachability as measured by the TCLP have been observed with aging. In some
cases, these changes in TCLP data have been associated with changes in the
chemical structure of the stabilized waste, as measured by spectroscopic
analyses. These results suggest that additional evaluation of stabilization is
required to ensure confidence in long-term leaching performance.
The U.S. EPA's Multiple Extraction Procedure (MEP) or other tests
that expose the waste to repeated, sequential leaching can give information on
leach resistance over time. Other sequential or flow-through leaching tests
such as ANSI/ANS/16.1 (see Section 3.2 and Table 3-3) can give information to
support prediction of long-term leach resistance.
By and large, however, attempts to correlate laboratory leaching
tests with field data have not been successful. The EP Tox test, for example,
can be used only to predict the potential for leaching; it cannot predict the
rate of leaching over time (Bishop, 1986). Deviations between the laboratory
and field are sometimes caused by testing materials under oxidized conditions
(open contact with air), while the groundwater in contact with the waste may
be chemically reducing. Laboratory leaching tests use continuous wetting of
the waste with a leachant at controlled temperature. In situ conditions
typically involve periodic contact with water and fluctuations in temperature.
4.7.3 Modeling
Numerical modeling (Section 4.6.3) is another approach to predicting
the long-term performance of S/S-treated waste. Parameters based on the
physical and chemical properties of a waste form can be used in conjunction
with mathematical models to infer long-term leachability, based on assumptions
about the leaching mechanisms and environment (Cote et al., 1986).
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Mathematical models have also been combined with accelerated dynamic leaching
tests to assess the long-term stability of S/S waste forms containing arsenic,
cadmium, chromium, and lead.
Other recent research also indicates that metal leaching follows
diffusion theory and that mathematical models combined with various leaching
tests allow some predictions about metal leaching over time, with particle
size, leachant velocity, and leachant acidity being key variables (Bishop,
1990). Although these models suggest good long-term stability for several
S/S approaches, a test or model that simulates field conditions to a degree
that would allow for confident predictions of long-term stability is lacking.
4.8 USE/REUSE VERSUS DISPOSAL
One of the principal aims of S/S processes is to produce an end
product that is less environmentally threatening than the original waste.
There is an added benefit if the stabilized waste can be put to some practical
end use. The ability to use S/S end products eases the burden of disposing of
the waste and provides obvious economic and environmental advantages over
hazardous waste disposal practices. However, concerns about the long-term
performance of the S/S product and the possible exposure of human or ecologi-
cal receptors to contaminants released from it greatly restrict use/reuse
options, and in practice relatively few S/S-treated wastes have been reused or
recycled to date.
4.8.1 Alternatives
The purpose of use/reuse is to ease the burden on land disposal.
Therefore, use/reuse alternatives, when deemed environmentally safe, can be a
productive alternative to disposal. Possible use/reuse alternatives for
stabilized/solidified waste include construction material for use in concrete,
Portland cement, asphalt, road base material, landfill cover, or agricultural
additives. In addition, some solidified waste may be used in direct water
contact applications, such as for diking material and for forming new land
from lakes, streams, marine waterways, or low-lying swamp areas. Another
potential application is to help solve shoreline erosion problems by install-
ing support structures made from incinerator ash and cement. These structures
are being studied by the State University of New York not only for their
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potential to reuse S/S products, but also for their ecological benefit in
controlling erosion and offering a marine habitat for some species. Another
potential application for S/S products is to construct artificial reefs from
stabilized drilling muds from offshore drilling rigs (Kelley, 1988). In
Europe, there is an emphasis on combining wastes from incineration plants with
fly ash, water, and plaster to form a solid material that can be used to
create sealed landfill reservoirs (Lukas and Saxer, 1990).
Until the long-term performance of S/S-treated waste in such
applications is clearly demonstrated, most S/S products in the United States
will still have to be disposed of in a more cautious manner, which generally
means disposal in a landfill. Environment Canada (WTC, 1990b) has suggested
an overall classification system for S/S waste. Classifications are based on
batch extraction tests to estimate the amount of contaminant available for
leaching and an evaluation of monolithic waste form leaching performance.
Analysis of leaching performance uses mathematical models derived from the S/S
literature with input from a database on S/S waste properties. For the
purpose of this classification system, two utilization and two disposal
scenarios have been selected that require different degrees of contaminant
containment in a S/S waste. The scenarios are briefly described below, in
order of decreasing performance requirements for S/S waste.
S/S wastes that do not qualify for utilization or disposal according
to one of these scenarios would need to be disposed in a secure landfill or
subjected to a more effective treatment process. In a secure landfill,
containment is more a function of engineered barriers and the host geological
setting than of the waste properties. Space in a secure landfill is at a
premium and waste treatment that results in volume increase is usually
undesirable. The performance requirements for S/S wastes disposed in secure
landfills are not addressed here.
Unrestricted Utilization - In an unrestricted
utilization scenario, the S/S waste has a negligible
leaching potential and may be used in any way that a
natural material might be used, on land or in water
(e.g., as a construction material). Once a given
wastestream and S/S process have been approved, the
resulting product becomes exempt from waste
management regulations.
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Controlled Utilization - In this scenario, the
leaching potential of the S/S waste is acceptable
for a specific utilization (e.g., quarry rehabili-
tation, lagoon closure, road-base material). The
environmental impact of S/S waste Teachability
measured by this classification should be assessed
and utilization approved on a site-specific basis.
Segregated Landfill - The S/S waste is not
acceptable for utilization, or utilization is not
possible or practical. The S/S waste is isolated
from other wastes in a segregated landfill which
does not necessarily have an engineered barrier or a
leachate collection system.
Sanitary Landfill - The S/S waste is not acceptable
for utilization and is not acceptable for disposal
in a segregated landfill without special engineered
protection of the environment. Disposal with muni-
cipal garbage in a sanitary landfill is permitted
(WTC, 1990b).
Use/reuse of waste materials was the subject of a recent conference
on Haste Materials in Construction, the Proceedings of the International
Conference on Environmental Implications of Construction with Haste Materials
(eds., Goumans et al., 1991). The focus of this conference was on use/reuse
of waste materials in general. However, several of the studies addressed
wastes treated with S/S technologies. For example, the U.S. EPA Risk Reduc-
tion Engineering Laboratory (RREL) is investigating use of S/S-treated
residues from combustion of municipal solid waste (fly ash, bottom ash, and
combined residues). Wiles et al. (1991a and b) reported that the type of S/S
treatment had little effect on the species of metals found in the municipal
waste combustion residues. Instead, attenuation of metals was attributed to
pH and dilution effects. In another part of this study, Holmes et al. (1991)
investigated the physical properties of S/S-treated municipal waste combustion
residues (bottom ash, air pollution control residue and combined ash).
Results indicated that wastes treated with Portland cement only, that is, with
no proprietary additives, generally produced the most durable test specimens.
Of the three types of residues, the air pollution control residues produced
the least durable test specimens. Kosson et al. (1991) researched the
leaching properties of S/S-treated municipal waste combustion residues using a
variety of leaching tests.
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In addition to the U.S. EPA studies, the conference proceedings
included two other investigations on the use of S/S-treated waste. Wahlstrom
et al. (1991) investigated the properties of S/S-treated soils contaminated
with wood preserving chemicals (As, Cr, Cu) or lead for potential use in
construction of roads or storage areas in landfills. Dijkink et al. (1991)
investigated the potential use of S/S-treated river sediments as building
material in the Netherlands.
4.8.2 Limitations
Although there are many potential ways to use or reuse S/S-treated
waste, there are many nontechnical factors to consider when evaluating any
specific application. Certainly, a key question will be that of liability,
which is related to political, public, and legal questions that are becoming
increasingly sensitive issues of public concern.
Associated with the liability question is the lack of knowledge
about the long-term performance and environmental impacts of S/S waste. The
environmental consequences of the utilization of waste products or materials
containing waste products on the basis of a single type of test (e.g., an
extraction test) is impossible in view of the wide range of scenarios that
will occur in actual use/reuse situations. Test methods to better determine
the leaching mechanisms and characteristics of S/S-treated waste have been
studied by van der Sloot et al. (1989), but much research remains. In
addition, Haste Materials in Construction (eds., Goumans et al., 1991)
contained numerous studies on leaching procedures for evaluating waste
materials proposed for use in construction. In any event, demand will
increase both for beneficial use/reuse of S/S products because of increasing
constraints on land disposal and for technologies that can produce materials
that are environmentally benign. However, the regulatory community is likely
to be unwilling to encourage or permit reuse options unless environmental
risks are clearly and confidently defined.
4.8.3 Compatibility With the Disposal Environment
In evaluating the performance of S/S technologies, the focus is
often on the S/S process itself. What is often overlooked is the fact that
the stabilized waste still must be evaluated in terms of its performance in
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the environment into which it is placed, regardless of whether that environ-
ment is a landfill, a roadbed, or the ocean floor. Often, the interaction of
the stabilized waste and its surroundings is hardly addressed, but the fact
remains that both mobilization and immobilization may occur at the stabilized
waste/soil or stabilized waste/water interface. The stabilized waste and the
site should be evaluated together as a system to realistically assess the
compatibility of the S/S product with the disposal environment. The forces
and elements to which a treated waste is exposed would vary significantly, for
example, depending on whether disposal occurred at the surface, in deep
excavations, or in the ocean.
Environmental compatibility is a major issue at CERCLA sites,
although past studies have generally not considered this factor. Compatibili-
ty with the disposal environment should have a bearing on the design and
conduct of the treatability study as well as what tests are performed.
Hockley and van der Sloot (1991) have modelled the interactions
occurring at the waste-soil interface. They noted that the interactions
between the waste and soil phases lead to phenomena that are not predicted by
consideration of either phase separately, as is the case with most of the
tests currently used to assess the acceptability of a waste for placement in
the environment.
Another possible option to improve environmental compatibility Is to
codispose with the S/S waste material to modify certain physicochemical
characteristics of the disposal environment. Such material could be placed
between the waste and its disposal environment to improve the long-term
performance of the S/S-treated waste. Environment modifiers might include
bentonite or other clays to reduce groundwater infiltration; surface-reactive
materials to adsorb migrating contaminants; or substances to buffer the pH or
redox potential of the disposal environment. With or without the use of modi-
fiers, however, one message clearly communicated by studies of environmental
compatibility is that, to be successful, S/S process selection and design must
consider the S/S product as part of a system that includes the disposal
environment.
4.9 COST INFORMATION
The two major cost categories in remediation by S/S are (a) the
treatability study (laboratory screening and bench-scale study), and (b) full-
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scale remediation. The costs associated with these two efforts are discussed
in this section. Because each project is different, it is very difficult to
generalize the costs of S/S treatment. Hence the costs mentioned in this
section should be regarded as estimates.
4.9.1 TreatabilUv Study Costs
The major cost elements of a treatability study for S/S include
(a) waste and site characterization (Section 2.2); and (b) bench-scale treat-
ability screening and performance testing and associated chemical analyses
(Sections 2.6 and 2.7). Since these studies are expensive, it is important to
strike a balance between collection of enough data to provide statistically
sound results and the available budget. Also, it is important to remember
that the regulators drive the testing and that their requirements must be met
before the treatability study can be accepted and full-scale remediation can
proceed.
4.9.1.1 Waste Characterization and
Establishing Performance Objectives
Waste sampling and characterization is conducted to determine the
type, levels, and spatial distributions of the contaminants, presence of
possible interferants, and for other purposes (Section 2.2). Sampling often
requires the use of drill rings depending on depths to be sampled. Analyses
of waste properties must be conducted in sufficient replication to permit
determination of data quality by statistical methods. Refer to Section 2.2
for guidance. Some of the analytical tests conducted and their estimated
costs are given in Table 4-7. Not all these analyses are necessary for every
waste type.
4.9.1.2 Bench-Scale Testing and Analysis
The level of effort will depend on the number of candidate binder
systems selected for testing, the number of tests performed based on the
design study (or statistical design), and the types of chemical analyses to be
performed, with organic analyses being significantly more expensive than
inorganic analyses (Table 4-7).
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TABLE 4-7. COSTS OF TYPICAL ANALYTICAL TESTS OF UNTREATED AND TREATED WASTES
Analysis
Physical
Particle size analysis
Suspended solids
Density
Permeability
Unconfined compress ive strength
(UCS) of cohesive soils
Unconfined compressive strength
of cylindrical cement specimens
Cone index
Flexural strength
Heat of hydration
Wet/dry weathering
Freeze/thaw weathering
Paint filter test
Atterberg limits
Moisture
Chemical
PH
Oxidation reduction potential
Total organic carbon (TOC)
Oil and grease
Alkalinity
Volatile organic compounds (VOCs)
Semi volatile organics
Base, neutral, and acidic compounds (BNA)
Polychlorinated biphenyl (PCB)
As
Se
Hg
As, Ag, Ba, Cd, Cr, Pb, or Se
Leach Tests
- Extraction
- Extraction
- Volatile organic compounds
- Semi volatile organic compounds
- Pesticides
- Herbicides
- As
- Se
- Hg
- As, Ag, Ba, Cd, Cr, Pb, or Se
Method Unit
ASTM D 422
Standard Method 2092
Various
EPA 9100
ASTM D 2166
ASTM D 1633
ASTM D 3441
ASTM D 1635
ASTM C 186
ASTM D 4843
ASTM D 4842
EPA 9095
ASTM D 4318
Various
EPA 9045
ASTM D 1498
EPA 9060
EPA 413.2
EPA 403
EPA 5030, 8240
EPA 3510, 8270
EPA 3540, 3520, 8270
EPA 3540, 3520, 8080
EPA 3050, 7060
EPA 3050, 7740
EPA 7470
EPA 3010, 6010
EPA 1311 TCLP Metals
EPA 1311 TCLP ZHE
EPA 8240
EPA 3510, 8270
EPA 3510, 8080
EPA 8150
EPA 3050, 7060
EPA 3050, 7740
EPA 7470
EPA 3010, 6010
1991 costs. May vary considerably among various laboratories. Approximate ranges are
quoted prices. There may be some savings of scale if a
"" Furnace atomic absorbtion spectroscopy.
"' Inductively coupled plasma atomic emission spectroscopy.
Cost(a), $
30-160
20
40-240
350-450
25
20-130
20
25
30-75
530
530
10-25
40-100
10-20
10-20
75
50
60-80
35
300-400
600-800
600-1400
150-2001
25-30 ซa
25-30/ซa
20-25
10-20/ซa(c)
given based on
large number of samples are being analyzed.
4-76
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The total analytical cost will depend on the number of samples and
should always include quality assurance samples. Analytical costs are the
major element in treatability testing (usually >50% of the cost). Typical
total costs of bench-scale treatability studies for S/S range from $10K to
$100K, depending on process complexity, number of samples, types of analyses,
and the need to capture and test air emissions. A number of different treat-
ability laboratories are available that will conduct bench-scale treatability
testing for S/S on a service basis.
4.9.2 Full-Scale Remediation Costs
The costs involved in full-scale S/S treatment fall into four major
categories-planning, mobilization and demobilization, treatment, and disposal.
4.9.2.1 Planning
The planning costs are the administrative and engineering planning
costs associated with the remediation. Waste and site characterization
activities and the treatability study are assumed to have been completed
before project planning starts. Planning costs may include permitting,
engineering design (scale-up), equipment and materials procurement, and
preparation of a work plan, quality assurance plan, and/or a health and safety
plan. Permitting can take weeks or months, and costs can be substantial,
especially for uncommon contaminants or complex sites.
Engineering costs involve designing and engineering for full-scale
operation based on bench-scale (treatability testing) data. A pilot- or
field-scale demonstration may be necessary, either to establish scale-up
factors or to satisfy potentially responsible parties (PRPs) and/or regulators
of the feasibility of the cleanup. The actual price of equipment or raw
materials is not included in this category, but the labor involved in procure-
ment is. If the remediation is to be performed through a contractor, contract
procurement costs are also involved.
A site-specific work plan, quality assurance plan, and/or a health
and safety plan are almost always required, and review comments from regulato-
ry agencies and other parties must be addressed. Depending on the magnitude
of the project, planning costs can range from $25K to several hundred thousand
dollars.
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4.9.2.2 Mobilization and Demobilization
Mobilization costs involve transportation of personnel, equipment,
and raw materials to the site, site preparation, and equipment installation
and start-up. Demobilization costs include equipment shut-down and disassem-
bly, and transportation of personnel and equipment from the site. Mobiliza-
tion and demobilization (mob/demob) costs vary depending on type of equipment,
facilities available at the site, decontamination requirements, and the loca-
tion of the site. When large-scale equipment is necessary, mob/demob costs
will range from $25K to $50K or more if extensive site preparation is
involved.
4.9.2.3 Treatment
Treatment costs typically include costs for excavation (if treatment
is ex situ), chemicals, equipment, utilities, labor, and sampling and analy-
sis. Full-scale S/S treatment services are offered by a variety of firms,
including S/S vendors, remediation companies, and construction companies
certified to conduct hazardous waste remediation. Full-scale treatment should
not be undertaken by anyone not fully qualified and certified, including OSHA
safety certifications.
Excavation applies to sites containing contaminated materials that
are to be stabilized by plant mixing. Excavation equipment consists of
typical earth-moving equipment, which can be rented along with an operator at
most sites. Cost for excavation ranges from about $0.85/yd3 to $4.09/yd3
(U.S. EPA, 1987b).
Chemical costs depend on the type of chemicals required for the
binder system and the amounts as determined by the waste-to-binder ratio.
Table 4-8 shows the costs of some typical stabilization chemicals. If
chemicals are transported for large distances, the transportation costs may
equal or exceed the chemical costs.
Equipment costs other than for excavation are based on the type of
equipment selected for materials handling and processing. Qualified S/S
vendors and remediation firms will own the necessary equipment and charge a
use-rate based on the time it is used. Equipment can also be purchased (for
large and long-term projects), in which case depreciation costs should be
considered, or rented (for smaller sites). Customary equipment includes
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TABLE 4-8. COSTS OF TYPICAL STABILIZATION CHEMICALS
Chemicals Costs $/Ton $600
IWT-HWT 20M(C) $300
Concrete admixtures $ 2 - 12/gallon
(a> 1991 Costs obtained from suppliers. Costs may vary based on suppliers and
the location of the site.
(b) Proprietary additive
(c> Proprietary modified clay binder
backhoes, front-end loaders, storage tanks, mixers, conveyors, etc. Sometimes
equipment and its operators are available for an hourly, weekly, or monthly
charge. The purchase costs of different types and sizes of equipment, and
estimates of their rental costs are mentioned in the Handbook for Stabiliza-
tion/Solidification of Hazardous Waste (U.S. EPA, 1986c).
Table 4-9 shows the major unit cost elements for S/S treatment with
cement by typical stabilization techniques (in-drum mixing, in situ mixing,
plant mixing, and area mixing as defined in Section 2.8.2). These are the
unit costs for mixing only and exclude the numerous other cost elements such
as mobilization and demobilization, engineering and administration, and health
and safety. In addition to processing equipment, personal protective equip-
ment may be needed, including Tyvek suits, respirators, decontamination
equipment, etc.
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TABLE 4-9. COMPARISON OF MAJOR COST ELEMENTS OF SOLIDIFICATION/STABILIZATION WITH CEMENT
I
CO
o
Cost, $/Cubic Yard
Category
Labor, overhead, and
profit
Equipment and metering
Conveyance
Pretreatment
Monitoring and testing(a)
Reagents and mixing
materials
Offsite disposal
(nonhazardous waste)
Supplies
TOTAL
In-Drum Mixing
216.30
65.40
NA
NA
115.40
31.10
NA
84.60
512.80
In Situ
1.40
1.60
NA
NA
4.00
31.10
NA
0.60
38.70
Plant Mixing
1.10
0.70
1.40
0.50
3.10
31.10
3.10
0.80
41.80
Area Mixing
3.00
3.00
NA
5.10
31.10
NA
1.30
43.50
-------
Utilities normally Include water and electricity. Sometimes the
remediation may have to provide its own energy supply, such as diesel genera-
tors. If pretreatment is necessary, other sources of heat, such as oil, gas,
or steam may be needed.
Labor costs are based on the number of equipment operators, supervi-
sory personnel, and managers, as well as the number of hours of operation. An
important factor in remediation can be the stand-by time. If operations are
not scheduled appropriately or if unanticipated delays such as stop work
orders are incurred, equipment or personnel will go unutilized. For example,
if the operation runs short of a chemical, or if a piece of equipment breaks
down, the entire operation may have to be temporarily halted. Another type of
work stoppage is when sampling and analysis of treated waste show that the
stabilization is ineffective. Clearly, some types of work stoppages can be
avoided or minimized by effective planning. Other types of stoppages are less
controllable, such as stop work orders issued by regulators so that they can
review preliminary data.
Sampling and analysis are conducted during full-scale remediation to
determine whether the treated process is achieving the performance goals for
chemical and physical properties. A sampling and analysis and/or quality
assurance plan will be prepared during planning. Implementation of the plans
may be a significant part of the remediation cost. Particularly during the
early stages of full-scale treatment, it may be necessary to have samples
analyzed on a rush basis, in order to minimize standby time while waiting for
data. Note that with rush fees, analysis costs can be 2 or 3 times higher
than fees for normal turnaround-time analyses.
If a full-scale demonstration precedes full-scale cleanup, regulato-
ry approval for the full-scale cleanup may be contingent on results of the
demonstration. If the initial demonstration shows deficiencies in the
process, then process modifications followed by additional demonstration runs
will have to be conducted until the process is working satisfactorily. As
discussed in Section 2.8, demonstration runs prior to full-scale processing
are highly recommended for refining the process and verifying that process
scale-up in the field has been accomplished satisfactorily. However, this
step has potentially significant cost impact on the project, particularly if
several demonstration runs need to be conducted prior to full-scale treatment.
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4.9.2.4 Final Disposal
When field treatment is completed, the S/S-treated waste has to be
disposed of as planned. In some cases, depending on the characteristics of
the treated waste and on regulatory approval, the S/S-treated waste can be
returned to its original location. Some final steps such as compacting or
capping (with the associated costs) may be required.
However in other cases, the treated waste cannot be disposed of on
site. Then arrangements have to be made to transport the treated waste to a
sanitary or secure landfill, again depending on waste characteristics and
regulatory policy. Tippage fees at sanitary landfills typically range from
approximately $10 to $50/ton and for secure (RCRA-permitted) landfills range
from $100 to $300/ton. Added to this is the cost of waste transport to the
landfill. The cost for transportation by covered bed dump truck or roll off
box carrier typically ranges from $0.15/yd3-mile to $0.60/yd3-mile. Costs
include the actual charge for hauling; demurrage (charge for truck waiting
time); and training, licensing, and protective clothing for the truck operator
(if required) (U.S. EPA, 1987b). Because there are far fewer secure landfills
than sanitary landfills, the transportation distance to secure landfills will
generally be much greater.
4.9.3 Estimates of Stabilization Costs
Table 4-10 lists the estimated costs registered in the records of
decision (RODs) for CERCLA sites. Because costs in this table are estimates,
there is no indication whether or not the remediation was actually accom-
plished for that cost. Total costs vary according to type of contaminants
and amount of wastes. Missing from this table is information on necessary
pretreatment steps and other project-specific requirements that may signifi-
cantly impact total cost. In general, a relatively straightforward S/S
project involving more than 5,000 to 10,000 tons of waste should cost in the
range of $100 to $150/ton of waste processed. Below this amount, unit costs
can increase because of fixed costs; above 10,000 tons, unit costs can
decrease because of economics of scale. Therefore, the higher unit costs in
Table 4-10, some of which greatly exceed the $100 to $150/ton range, are
almost certainly inflated by pretreatment requirements or other factors.
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TABLE 4-10. ESTIMATED TREATMENT PROJECT COSTS MENTIONED IN THE RODs FOR SUPERFUND SITES
WHERE STABILIZATION HAS BEEN SELECTED AS A COMPONENT OF THE REMEDIAL ACTION
I
00
CO
Site
Love Canal, NY
Marathon Battery, NY
Alladin Plating, PA
Amnicola Dump, TN
Davie Landfill, FL
Independent Nail , SC
Burrows Sanitation, MI
Outboard Marine
Media
Soil
Sediment/soil
Soil
Soil
Soil /sludge
Sediment/soil
Sludge/soil
Sediment
Vol ume
7,500 cy
23,700 cy
12,000 cy
400
75,000 cy
6,200 cy
250 cy
5,700 cy
Contaminants
dioxin
Cd, Co,
Cr
Ni,
As, Cd, Cr, cyanide,
Pb, Hg, PAH,
pesticides, VOC
As, Cd,
Pb, Hg,
Cd, Cr,
Zn
Cr, Cu,
PCB
Cr, cyanide,
sul fides
cyanide, Ni,
Pb, Zn
Project Unit
Cost, $ Cost, $/cy Includes planning, sampling, and pretreatment costs as well as direct S/S process costs.
Source: Based on data contained in U.S. EPA (1989a).
-------
4.9.4 Case Study
A treatability study and field demonstration/cleanup of 1800 cubic
yards of lead-contaminated soil conducted by Battelle (Means et al., 1991b) at
Port Hueneme, California, demonstrates the various aspects of an S/S field
project and the associated costs. To establish a baseline concentration on
the amount of lead in the soil before treatment, 18 grab samples (and two
blind replicates) of the untreated soil were collected and analyzed for total
and soluble lead. Because the levels of lead in these samples varied greatly,
seven additional samples were collected. Total lead levels averaged 178
(ฑ162) mg/kg in the soil. The EP Tox average of 0.9 mg/L lead was lower than
the U.S. EPA standard (5 mg/L lead). Previous data on the Cal WET test,
however, showed that the average of 11.7 mg/L lead exceeded the STLC estab-
lished by California (5 mg/L). (See Section 3.2 for further discussion of
leaching tests.)
The bench-scale treatability study involved evaluating two stabili-
zation techniques, a sulfide-based process and a silicate-based process.
Eleven samples were treated with the sulfide process, which involved adding a
hydrated sodium sulfide solution in water, low-alkaline Portland cement, and a
small amount of detergent. Ten samples were treated with the silicate
process, which involved adding sodium silicate instead of the sulfide. The
sulfide process was used in this instance as an alternative to the silicate
process to determine the relative attributes of the two processes. Although
the sulfide process produced slightly lower soluble lead values than the
silicate, the silicate process was concluded to be the preferable based on
ease of application in the field.
The stabilization formulation used in the field was the same as that
used during bench-scale testing; no additional testing to determine optimum
ratio was done in this case. During the field demonstration, eight sets each
of pre- and post-stabilization samples were collected and analyzed for pH,
total lead, and Cal WET test. The average Cal WET test results were reduced
from 11.7 mg/L before stabilization to 2.7 mg/L after stabilization. After a
number of discussions with cognizant regulatory agencies, the treated soil was
released for placement in a sanitary landfill.
Table 4-11 provides cost details for this project. A pug mill was
rented for the mixing of soil, cement, silicate, and bicarbonate. Most of the
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TABLE 4-11. STABILIZATION COSTS FOR AN 1800-CUBIC-YARD SITE
CONTAMINATED WITH LEAD
1. Bench-Scale Treatabilitv Study/Planning
Chemist, 8 hrs 0 $50/Hr. $ 400
Chemical Analysis, 12 samples each
TTLC, STLC, and pH 3,240
Project Manager, 16 hrs. @ $95/hr 1.520
Subtotal $5,160
2. Move Soil from Storage Hut to Work Area
End-dump trucks, 2 trucks x 1 day
each x $55/hr $ 880
Field supervision, 8 hrs @ $78/hr 624
Laborers, 2 x 8 hrs each @ $30/hr 480
Plastic sheeting, 10 rolls 0 $120/roll 1.200
Subtotal $3,184
3. Steam Clean Storage Hut (Subcontracted) $4,000
4. Power Sieving
Power screen @ $4,000/wk
including mobilization/demobilization $4,000
Front-end loaders, 2 loaders x
1 day each (? $90/hr 1,440
Field supervision, 8 hrs @ $78/hr 624
Laborers, 2 x 8 hrs each @ $30/hr 480
Subtotal $6,544
5. Debris Disposal
Front-end loader, 1 loader x 1 day
@ $90/hr $ 720
End-dump trucks, 2 trucks x 10 trips
each x 1 hr/round-trip @ $55/hr 1,100
Field supervision, 10 hrs (? $78/hr 780
Laborers, 2 x 10 hrs each
@ $30/hr 600
Tippage at landfill, 300 tons
(? $18.70/ton 5.610
Subtotal $8,810
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TABLE 4-11. STABILIZATION COSTS FOR AN 1800-CUBIC-YARD SITE
CONTAMINATED WITH LEAD (Continued)
6. Stabilization (approximately 4 working days
and 10 hour-days, including mobilization/demobilization)
Cement, 150 tons 0 $0.04/lb $12,000
Sodium silicate solution, 150 tons
0 $0.08/lb 24,000
Sodium bicarbonate, 15 tons
0 $0.10/lb 3,000
Freight for chemical deliveries 3,000
Plastic sheeting, 5 rolls 0 $120/roll 600
Pugmill and components, including
mobi1i zati on/demobi1i zati on 29,000
Front-end loaders, 2 loaders x 40 hrs
each 9 $90/hr 7,200
End-dump trucks, 1 truck x 40 hrs
0 $55/hr 2,200
Baker tank, 1 month 0 $30/day 900
Field supervision, 40 hrs 0 $78/hr 3,120
Project Manager, 24 hrs 0 $95/hr 2,280
Chemist, 32 hrs 0 $50/hr 1,600
Laborers, 2 laborers x 40 hrs
each 0 $30/hr 2,400
Travel and subsistence for contractor
staff, 5 persons x 7 days
each 0 $100/day 3,500
Industrial hygiene monitoring and
oversight 2,000
Analytical fees, rush basis (100%
surcharge) 1.080
Subtotal $97,880
4-86
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TABLE 4-11. STABILIZATION COSTS FOR AN 1800-CUBIC-YARD SITE
CONTAMINATED WITH LEAD (Continued)
7. Post-Treatment at Pro.iect Closure Activities
Chemical analysis, TTLC, STLC, and
pH on 12 samples, normal turnaround $3,240
Regulator meetings concerning disposal
options, Project Manager 20 hrs
I? $95/hr 1,900
End-dump trucks, 4 trucks x 25 trips each
x 1 hr/round trip @ $55/hr 5,500
Front-end loader, 1 truck x 25 hrs
@ $90/hr 2,250
Reporting and documentation, Project
Manager, 16 hrs @ $95/hr and
secretary, 16 hrs @ $40/hr 2.160
Subtotal $15,050
Grand Total - Expenses $140,628
Contractor Fee 9.372
Total Cost $150,000
other equipment, such as dump trucks, power screen, and front-end loaders, was
also rented. A number of other cost elements are itemized to provide the
reader with the variety of typical cost elements for an S/S treatment project
and the stages of the project in which they were incurred. Note, however,
that the unit costs associated with this project were fairly modest compared
to those for other larger-scale S/S projects (e.g., Table 4-9). The total
cost of the cleanup of 1800 cubic yards (approximately 2,430 tons) was
$150,000, for an average of $83/cu yd or $62/ton.
4-87
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5 TECHNOLOGY SHORTCOMINGS AND LIMITATIONS
This chapter discusses some of the shortcomings and limitations of S/S
technology pertaining to S/S processes/binders, waste form and treatability/per-
formance testing, and other issues. The topics discussed should be viewed as
examples of issues rather than an exhaustive list of technology limitations.
5.1 PROCESS/BINDER CONSIDERATIONS
5.1.1 Hierarchy of Waste Management
As discussed in Chapter 1, technologies that lead to the recycling,
recovery, or reuse (3R) of some portion of the contaminant or waste material
are preferred over treatment technologies in the waste management hierarchy.
Technologies such as incineration that destroy the contaminant also are
typically preferred over S/S processes. However, S/S is still an important
treatment option because of its versatility and effectiveness (Section 1.1).
5.1.2 Scale-Up Uncertainties
Process scale-up from bench-scale to full-scale operation involves
numerous complex issues that should not be taken for granted. These issues
are no less important for S/S technology than for any other remediation
technology. Variables such as ingredient flow rate control, materials mass
balance, mixing, and materials handling and storage, as well as the unpredict-
ability of the outdoor elements compared with the more controlled environment
in the laboratory, all may affect the success of a field operation. These
potential difficulties underline the need for a field demonstration prior to
full-scale implementation (Section 2.8).
5.1.3 Proprietary Binders
The nature of the S/S business at present is such that most vendors
protect their exact binder formulations as proprietary or trade secret.
Relatively few formulations are covered by patent. The proprietary designa-
tion protects the formulations from being readily recognized by competitor
vendors (Section 4.1). The reality is that there are several different
generic binder systems that are used by the majority of S/S vendors, and each
vendor has its own variations in the form of special additives.
5-1
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Binder ingredients are frequently designated in the literature as,
for example, "fly ash A" or "proprietary additive." As a result, the report
on a treatability study lacking information on binders and additives has no
technology transfer value, and the ability to evaluate the data in terms of
chemical mechanisms is absent, because binder chemistry is unknown or
unreported.
5.1.4 Binder "Overkill
Too much of a particular binder ingredient can lead to unnecessary
expense and even to an improperly stabilized waste form. For example, many
metals are amphoteric, meaning that they are soluble under both acidic and
basic conditions (Section 4.2). The metal will be at minimum solubility when
a sufficient base (in the form of an S/S ingredient) is added to make the
waste moderately alkaline. Too much base will cause the metal to resolubilize
and/or make the waste hazardous by virtue of the RCRA corrosivity
characteristic (i.e., pH >12.5).
5.2 WASTE FORM/CONTAMINANT ISSUES
5.2.1 Complications of Phvsicochemical Form of the Target Contaminants
In a recent S/S field demonstration (Means et al., 1991b), the
unsatisfactory degree of stabilization of the copper and lead was a direct
result of their encapsulation in organic coatings of various types (antifoul-
ing compounds, pigments, etc.). People conducting S/S treatability tests
frequently measure the type and amount of contaminant present, but, in complex
waste forms such as sandblasting grit, the type and amount of contaminant do
not provide sufficient information. It is important to understand the
physicochemical form of the contaminant as well. However, the chemical
analyses necessary to characterize the physicochemical form of the contaminant
can be expensive and nonroutine (Section 3.5).
5.2.2 Interferences and Incompatibilities
As discussed in Section 4.3, numerous chemical constituents may
interfere with various S/S processes. Thus, specific chemical incompatibili-
ties should be recognized and avoided.
5-2
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5.2.3 Volatile Organic Contaminants
Several studies have been performed that strongly indicate the
inadvisability of using S/S as the principal remediation technology for
organic wastes, particularly wastes containing hazardous volatile organics
(Wiles and Barth, 1992). The following guidance is provided based on the
current state of knowledge about using S/S for treating organics
(Section 4.4):
According to the hierarchy of waste management, treat-
ment by a destructive technology (e.g., incineration)
is preferable to contaminant immobilization (e.g., by
S/S) because the former processes eliminate the con-
taminant and the concern over the long-term stability
of the S/S process. The same is true for removal
processes, such as thermal desorption, that concen-
trate the contaminant into a much smaller volume of
material which can then be either reused as a raw
material or incinerated and destroyed.
Generally, S/S should not be used to treat a site
containing only organic waste. Alternative
technologies (e.g., incineration, steam stripping,
vacuum extraction) should be used to remove and/or
destroy the organics. If residues remain after this
primary treatment, S/S treatment may be effectively
used to stabilize the residue. However, a well-
designed and controlled treatability study should be
conducted to assess S/S effectiveness and to select
and design a proper S/S process.
There are exceptions to avoiding S/S treatment of
organic wastes. For example, if the organic is
generally not mobile through air, soil, and water
(e.g., low levels of oil and grease), then S/S may be
an acceptable, cost-effective treatment alternative
for a given site. Careful attention must be paid to
any existing state and federal environmental regula-
tions concerning the particular organic contaminant
(e.g., dioxins, etc.). Treatability studies must be
performed incorporating appropriate test methods to
evaluate the organic waste's potential for escape.
Based on existing data, volatile organic compounds
(VOCs) usually cannot be treated by current S/S
technology. Whether a site containing VOCs as a minor
constituent can be treated by S/S will depend on
specific conditions existing at the site.
Available data also indicate that semivolatile organic
compounds generally cannot be effectively treated by
5-3
-------
current S/S techniques. Whether a site containing low
to moderate concentrations of semivolatile organics
should be treated using S/S also depends upon site-
specific factors.
Notwithstanding the above factors, there are situa-
tions in which S/S can be a satisfactory treatment
method for wastes containing organics. When S/S
treatability tests are performed on such matrices, it
is important to understand that (a) aqueous leaching
tests will be a meaningless indicator of the degree of
immobilization for organic compounds having low
solubility in water and (b) in the aggressive chemical
environments associated with certain binders, certain
organic contaminants may be degraded or transformed
into by-products that, in some cases, may be as toxic
as or more toxic than the parent compounds.
5.2.4 Multlcontaminant Wastes
Wastes containing a large number of contaminants are generally more
difficult to stabilize than wastes containing one or a few contaminants,
particularly when the multiple contaminants have widely varying chemistries
(Section 4.2). The problem is that a given type of binder might be more
compatible with an organic waste than with a primarily metallic waste.
Therefore, when both organics and metals occur in the same waste form, the
binder selected will not be optimal for both types of contaminants. On a more
specific level, because metal chemistry varies widely, metals will respond
differently to the same binder. As a general rule, a physical encapsulation
process (solidification) may be the best compromise for a multicontaminant
waste, whereas a chemical stabilization process may be the best approach when
there is only one contaminant or when the contaminants present have similar
chemical properties.
5.2.5 Limitations of Cement-Based Waste Forms
The weaknesses of cement-based waste forms are as follows:
The fate of the waste species within the waste form is
unknown.
They are porous solid bodies.
The total volume of material to be disposed of usually
increases.
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Small changes in the waste composition or mix
proportions can alter the properties, sometimes
without the knowledge of those utilizing the waste
form.
Managers and operators charged with the task of waste
disposal frequently do not understand the complexity
of the heterogeneous material they are attempting to
create.
It is of utmost importance that users of these waste forms be aware
of these weaknesses and their ramifications. In most instances, problems
originating from the weaknesses can be avoided or circumvented. Future
research is expected to help explain and overcome these weaknesses (McDaniel
et al., 1990).
5.2.6 Sample Heterogeneity
Solid wastes can be highly heterogeneous in composition, both
macroscopically and microscopically. A person can analyze two different
portions of the sample and obtain two very different analytical results.
Therefore, sample heterogeneity should be recognized as a possible causative
factor when explaining treatability data that are discrepant or difficult to
interpret.
5.3 TREATABILITY AND PERFORMANCE TESTING ISSUES
5.3.1 Testing Limitations
Several unresolved issues pertain to S/S processes. In particular,
tests that have been developed to assess technology performance are not
applicable to every disposal scenario. Testing methodologies must be tailored
to the specific nature of the S/S-treated waste. Personnel involved in
treatability testing should be aware of the various tests' limitations when
interpreting the data (Chapter 3).
Examples of the limitations of treatability studies and S/S-treated
waste testing based on actual field experience are as follows:
Although the principal objective of the site sampling
is to obtain a sample that is representative of the
waste as a whole, variation from sample to sample is
common and must be considered when interpreting the
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analytical data. Many factors affect site sampling.
If the goal is a single composite sample, site debris,
such as large boulders or rocks, timbers, shingles,
etc., usually should be segregated by physical
screening before samples are collected from a wide
range of locations, in order to produce a repre-
sentative sample.
No single leaching methodology is suitable for all
waste forms or target contaminants, and none of the
leaching methodologies is calibrated in terms of
contaminant migration in actual groundwater. The TCLP
does not provide data on long-term stability; in fact,
different results are frequently obtained when the
TCLP test is conducted on the same stabilized waste at
different cure times. Leach tests in general are
probably most useful for assessing the relative
stabilization efficiencies of different binders.
Some leaching test methods are more appropriate for
metals, some are not applicable to nonvolatile
organics, and others are applicable only to monolithic
wastes that do not change in surface area appreciably
during testing. Batch methods usually do not use
sufficient acid to exhaust the acid-neutralizing
capacity of most stabilized waste forms. Sequential
methods accelerate leaching to assess long-term
performance. The interpretation of results is
difficult, however. Accelerated leaching in the
laboratory may occur by different mechanisms than the
longer term leaching that occurs in the field.
At times it is appropriate to modify a standard
leaching protocol to address a specific issue.
Examples include the following:
- Eliminate the leachate filtration step to address
colloidal contaminant transport.
- Use site-specific groundwater as the leachant
instead of the generic leachant specified in the
procedure.
- Consider use an organic solvent (e.g., acetone) as
the leachant instead of an aqueous leachant for
addressing the S/S of organic contaminants (see
Section 4.4.3 for discussion of pros and cons).
- Determine when it is appropriate to create an
artificial surface area prior to leaching (e.g.,
by crushing).
- Deionized water can be more aggressive than acid
in some cases.
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Microbes may eventually affect the long-term
performance of certain waste forms, particularly
organic binders (Section 3.4). However, these
microbial reactions can be very slow, and accelerated
tests that are generally recognized and approved and
that closely simulate real-world biochemical reactions
are not available.
Bioassay data may conflict with chemical data.
There are limitations to interpreting and applying the
results of physical tests. For example:
- The unconfined compressive strength test is not
appropriate for noncohesive substrates and is not
a direct indicator of constructability.
- No correlation has been identified between the
physical strength of a waste form and its leaching
behavior.
- Permeability measurements are difficult to conduct
and are subject to wide variation. Also, large
differences have been observed between values
measured in the laboratory and in the field for
the same substrates.
With the exception of a small group of "regulatory"
tests, no performance standards or acceptance criteria
exist for many tests. In fact, acceptance criteria
should vary, depending on waste composition, disposal
or reuse site characteristics, and other factors.
This leaves much to the interpretation of individual
S/S project personnel.
In general, the bench-scale treatability study should
exceed the performance criteria established for the
project. That is, a margin of safety should be
established that allows for the greater variability of
the process when implemented in the field, especially
in the area of mixing. The necessary magnitude of the
safety margin, however, is unknown and probably varies
from project to project (Sections 2.6 and 2.7).
5.3.2 Long-Term Performance
The long-term performance of treated waste is not clearly under-
stood, and no definitive test procedures exist to measure or assess this
property. The TCLP is not an adequate measure of long-term leaching.
Monitoring data from field disposal sites are needed to detect the premature
deterioration of solidification or stabilization of previously processed
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wastes. Because of the uncertainties surrounding long-term performance,
wastes previously treated using S/S and disposed of may have to be retrieved
and retreated in the future (Section 4.7).
5.3.3 Reproducibilitv
The reproducibility of treatability data can be poor because of
sample heterogeneity, uneven mixing, the complexity of S/S chemical reactions,
and other reasons. Timing is also a critical variable. It is not unusual to
see different analytical results when samples from the same treatability study
are cured for different periods of time prior to leaching.
5.3.4 Limitations in S/S Treatability Reference Data
S/S processes would be used more successfully if experiences were
shared more effectively. However, well-documented S/S treatability data are
scarce. Many of the common reporting deficiencies are as follows:
1. Proprietary binders (Section 5.1.3). Without spe-
cific information on binder characteristics the
process is not reproducible, and the treatability
data have no technology transfer value.
2. Incomplete treatabilitv data and data gaps.
Certain types of data that are needed to evaluate
the stabilization efficiency and help understand
the chemical mechanism(s) of stabilization are
frequently missing, for example:
Baseline soluble metal concentrations in the
untreated waste. This is needed as a point of
comparison for the soluble metal concentra-
tions in the treated waste so that the percent
reduction attributable to treatment can be
assessed.
Total metal concentration in the untreated
waste and the treated waste. The latter is
necessary to demonstrate that a low post-
treatment soluble metal concentration is not
attributable simply to sample heterogeneity.
Binder-to-waste ratio. This is needed to
estimate the volume expansion of the waste
during treatment and the effect of dilution on
posttreatment soluble metal concentrations.
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oH of the leachate from the untreated and
treated wastes. This is an important para-
meter for interpreting the performance data.
Frequently, high soluble-metal concentrations
are due to pH. The pH parameter should be
routinely measured at the conclusion of leach
testing.
Extent of dilution from binder ingredients.
This can be estimated from the binder/waste
ratio, where given, but should be carefully
characterized in each treatability study so
that the performance data can be corrected for
dilution. Frequently, a significant propor-
tion of the reduction in soluble metal concen-
tration in the treated waste can be attributed
to dilution from the binder ingredients.
3. Data reliability. Many treatability reports do
not indicate whether data were collected under an
appropriate quality assurance/quality control
(QA/QC) program. Therefore, many existing S/S
performance data have unknown validity.
4. Treatability procedures. Similarly to data
reliability, the frequent absence of detailed
treatability procedural information greatly limits
the technology transfer value of a treatability
study. The success or failure of a treatability
study may depend on small variations in the
amounts of the ingredients and in the order and
timing of ingredient addition.
5. Bias of existing S/S performance data toward
successful treatability studies. Treatability
projects that achieved a high degree of metal
stabilization are reported more frequently in the
literature than projects in which the treatment
systems worked poorly. Therefore, the existing
S/S database is probably biased toward the most
successful treatability studies.
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6 CURRENT RESEARCH AND FUTURE DEVELOPMENT NEEDS
6.1 CURRENT RESEARCH
Solidification/stabilization is the subject of active research aimed
at improving the range and efficiency of S/S process application. Some of
that research is described in sections 6.1.1 through 6.1.8.
6.1.1 Binders
Experimental Study of S/S Treatment of Hazardous Substances.
Statistically designed treatability studies are being applied to identify envir-
onmentally acceptable and economically feasible methods for S/S processing of
organic and inorganic wastes. The work focuses on inexpensive pozzolanic bind-
ers such as fly ash, silica fume, lime kiln dust, cement kiln dust, and ground
blast furnace slag. Waste types tested include electric arc furnace dust (K061)
and arsenic-contaminated soil (Fan, L.T., 1991, personal communication).
Improvement In S/S Treatment of Hazardous Inorganic Hastes by Silica
Fume (Microsilica) Concrete. A preliminary experimental program is being
conducted to assess the potential of silica fume concrete for solidifica-
tion/stabilization of K061 metal arc dust from steel manufacturing. TCLP
leaching tests are being used to investigate the effectiveness of the various
methods of S/S processing. The study is testing S/S process performance for
condensed silica fume and cement binder or fly ash, cement kiln dust, and
cement binder. It was concluded that silica fume concrete can significantly
enhance the stabilization of furnace arc dust as compared with the other S/S
processes. The results were based on studying the concentration of metals in
the leachant as specified by U.S. EPA (Fuessle and Bayasi, 1991).
Physical and Chemical Aspects of Immobilization. Recent studies are
using sodium as an internal marker for physical retardation. Almost any
product will contain some Na, K, or Cl, which can be used independently as
indicators for tortuosity. The difference between the mass transfer coeffi-
cients for Na and other elements derived from leaching tests, such as the
modified ANSI/ANS/16.1, reflects the contribution of chemical retention in the
product matrix to the overall mass transfer coefficient for the product. The
types of release mechanisms that can be distinguished are:
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dissolution
surface wash-off
diffusion (de Groot and van der Sloot, 1990)
Evaluation of Solidification/Stabilization of RCRA/CERCLA Wastes.
U.S. EPA Risk Reduction Engineering Laboratory is sponsoring a project to do
bench-, pilot-, and field-scale evaluation of the performance of cementitious
binders in S/S treatment of metal-contaminated wastes over time (Irish
Erickson, 1992, personal communication). Performance will be measured in
terms of lab Teachability tests, solids composition and actual water quality
of infiltration/runoff. Field measurements will extend over at least 5 years,
while smaller tests are intended to simulate field results at a much-acceler-
ated pace. The University of Cincinnati protocol for accelerated weathering
testing described below can be tested in this project.
6.1.2 Mechanisms
Review and Analysis of Treatabilitv Data Involving S/S Treatment of
Soils. This project is using geochemical equilibria models to determine
minimally soluble forms of the eight Toxicity Characteristic Leaching Proce-
dure (TCLP) metals. Emphasis is on identifying physicochemical forms of these
metals that are relevant to the stabilization or solidification of typical
hazardous wastes and the chemical conditions needed to produce the physico-
chemical forms of these metals.
These data are being analyzed to identify empirical or theoretical
geochemical relationships that appear to govern the success of S/S applied to
metal-contaminated soils. Relationships for multiple metal systems are being
quantified, where possible (Means et al., 1991c).
Morphology and Hicrochemistry of S/S-Treated Waste. Scanning
electron microscopy and X-ray diffraction techniques along with solvent
extractions are being used to investigate waste/binder interactions. The
objectives of these investigations are to better understand S/S processes by
characterizing the binder phase composition and structure and the distribution
of the contaminants in the solid phases, and to determine if microstructure
can be correlated to macroscale physical properties (U.S. EPA, 1990f; and
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several other papers in preparation). Contaminant distribution data include
analysis of the contaminant concentration, chemical forms and crystal struc-
ture, and binding mechanisms in each phase.
Fate of PCBs in Soil Following Stabilization with Quicklime.
Several researchers have reported destroying polychlorinated biphenyls (PCBs)
in contaminated soil by applying quicklime. These reports are based on
retrospective data from site remediation programs, anecdotal information and
results of one bench-scale project. Accordingly, an investigation was
conducted to verify claims that use of quicklime alone can promote decomposi-
tion of PCBs. Synthetic soil samples were spiked with three PCBs and treated
with quicklime and water. Significant PCB losses (60% to 85%) were evidenced
after five hours of treatment. However, evaporation and steam stripping at
elevated temperature conditions, rather than PCB decomposition, accounted for
most of the losses observed. Low levels of partially dechlorinated PCBs were
detected in lime-treated samples, but the quantities were stoichiometrically
trivial. The amounts of observed dechlorination products were not dependent
on the duration of lime treatment, and no evidence of phenyl-phenyl bond
cleavage was found. The use of quicklime alone as an in-situ treatment for
removal of PCBs is not supported by these results (U.S. EPA, 1991c).
S/S Treatment of Salts of As. Cd. Cr. and Pb. The behaviors of
various metal salts in cement-based S/S processes are being studied through
leaching tests, conduction calorimetry, and solid-state NMR. The research is
aimed at identifying the chemistry involved during cement hydration reactions
in S/S processes treating metal salts (U.S. EPA, 1990f).
The Nature of Lead. Cadmium, and Other Elements in Incineration on
Residues and Their Stabilized Products. A detailed laboratory study of metal
species in raw and S/S-treated wastes is being conducted to test how the
chemical nature and binding state affect Teachability. Focus will be on the
application of sophisticated surface analysis techniques to characterize
poorly crystalline inhomogeneous metal forms. Existing geochemical models
will be applied to test if they can predict the formation of solubility-
controlling solid phases as determined analytically (Eighmy et al., 1992).
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6.1.3 Interferences
Factors Affecting the S/S Treatment of Toxic Waste. Research on
interfering agents is being done to quantify the physical and performance
characteristics of S/S-treated waste containing interfering chemicals. The
data are being analyzed to determine whether physical properties can be
correlated with durability and leach resistance. Interferences from inorgan-
ics such as Pb, Cd, and Zn and from sulfates and organics such as oil, grease,
hexachlorobenzene, trichloroethylene, and phenol are being studied (Jones
et al., 1992).
Effects of Selected Waste Constituents on S/S-Treated Waste Leach-
ability. The effects of 10 common waste constituents on the strength and
contaminant immobilization of S/S-treated waste were studied. The contami-
nants were cadmium, chromium, mercury, and nickel. The potential interferenc-
es were nitrate salts, sodium hydroxide, sodium sulfate, and five organic
substances. The S/S binders tested were Portland cement, cement plus fly ash,
and lime/fly ash (Jones et al., 1992).
6.1.4 Organics and Air Emissions
Roles of Organic Compounds in Solidification/Stabilization of
Contaminated Soils. Organic compounds pose problems for solidification/
stabilization processes in three ways:
1. Nontarget organics can interfere with the
immobilization of target metals.
2. Target organics are more difficult to stabilize
than metals.
3. Some organics can volatilize during mixing with treat-
ment agents, leading to unacceptable air emissions.
The University of Cincinnati, on behalf of the U.S. EPA, is evaluating the
effectiveness of S/S processing for organic/metal wastes, in terms of organic
immobilization and organic-induced effects on metal immobilization. Organic
emissions during S/S processing are being measured. Polyaromatic hydrocarbons
(PAHs) will be used in this project to represent a common class of organic
compounds of concern in waste remediation.
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Measurement of Volatile Emissions from S/S-Treated Haste. Although
the mechanical strength and leaching characteristics of S/S-treated wastes
have been investigated, few data are available on the emissions of organics
from the S/S process and from the treated waste. Acurex Corporation at
Research Triangle Park, North Carolina, is developing organic measurement
methods and using them to test S/S-treated waste to address this data gap. A
"Wind Tunnel" system, a "Modified Headspace" sampling system, and a "Sample
Venting" system have been developed and are being used to measure organic
releases from S/S-treated waste (Weitzman et al., 1990).
Field Assessment of Air Emissions From Hazardous Waste S/S Process-
Infl. The U.S. EPA is collecting information to develop standards necessary to
control air emissions from hazardous waste treatment, storage, and disposal
facilities. Field tests have been conducted to quantify emissions of vola-
tile, semivolatile, and particulate emissions from S/S treatment processes
(Ponder and Schmitt, 1991).
S/S Treatment of Metal Hastes Contaminated with Volatile Orqanics.
S/S-treatment of sludge contaminated with about 1% metal ions and about 0.04 %
VOCs was tested. Waste sludge containing 11 metal contaminants was spiked
with 8 VOCs. Four different cement based S/S processes were applied to treat
sludge samples (Spence et al., 1990).
Immobilization of Orqanics in S/S Haste Forms. U.S. EPA RREL is
sponsoring a laboratory study to investigate (1) the immobilization of target
organics by selected S/S formulations and (2) the effects of nontarget
organics on the immobilization of target metals. Initial studies will be
performed on spiked soils to systematically vary relative contaminant concen-
trations (Trish Erickson, U.S. EPA, personal communication, 1992).
6.1.5 Test Methods
Method Development. Laboratory and field test methods are needed to
support optimum binder selection, assess short-term and long-term performance
of S/S-treated waste, and allow better correlation of laboratory and field
tests. A project is being conducted to study these three areas (U.S. EPA,
1991a):
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Evaluate the effect of sample size and configuration on results
from leaching tests.
Assess durability tests such as ANSI/ANS/16.1 and the accelerated
aging/weathering protocol being developed through cooperative
agreement between the U.S. EPA and the University of Cincinnati.
Evaluate methods to monitor S/S-treated waste in situ.
Investigation of Test Methods for Solidified Waste. An effort was
conducted with Environment Canada to evaluate several leaching and physical
property measurement methods. This research is leading toward development of
a protocol for evaluating S/S-treated waste. The protocol is based on the
measurement of several physical, engineering, and chemical properties of S/S-
treated wastes to allow different use and disposal scenarios to be evaluated.
Several of the testing methods in the protocol have been evaluated in a
cooperative project with industry initiated by Environment Canada. Others are
methods recommended by standards organizations in the fields of hazardous and
radioactive wastes. Finally, some properties of S/S wastes were measured
using methods in the developmental stage (Stegemann and Cote, 1991).
Critical Characteristics of Hazardous S/S-Treated Waste. The
physical and chemical characteristics of the waste affect performance, as do
the climatic (temperature and humidity) conditions during curing and after
placement in the final disposal or reuse environment. This research is being
conducted to determine the critical characteristics affecting waste perfor-
mance and how to measure them. The work is leading to quality control proce-
dures for use in the field to better assure performance of S/S-treated waste
(Wiles and Howard, 1988).
Advanced Test Methods. A program evaluating test methods for
construction materials and stabilized waste is ongoing at Enegieonderzoek
Centrum Nederland (ECN). Aspects being dealt with are changes within the
product with time, problems in determining the proper geometrical surface
area, boundary conditions for modeling the release from products, development
of a three-dimensional leaching model, and chemical speciation within a waste
form. Testing involves radionuclide tracers in specific chemical forms in the
S/S-treated waste (van der Sloot, ECN, personal communication, 1991).
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Assessment of Lonq-Term Durability of Solidified/Stabilized Hazard-
ous Waste Forms Lab Component and Field Component. U.S. EPA RREL is
sponsoring a laboratory study of synthetic and real hazardous wastes to
develop a protocol for accelerated weathering testing of cementitious waste
forms. Durability testing is focused on the use of elevated temperature or
acid to speed degradation reactions.
A field project is also being conducted to develop and utilize
sampling and analysis methods that allow assessment of waste form durability
after various periods of exposure to field conditions. Early efforts are
concentrating on detection of the interface between buried waste forms and
adjacent fill material. Subsequent work will focus on sampling to obtain
surficial (<1 cm) weathered material for analysis as well as bulk sampling.
The observed weathering patterns will be compared with those induced under
laboratory or lysimeter conditions. (Irish Erickson, U.S. EPA, personal
communication, 1992).
6.1.6 Leaching and Transport Models
Contaminant Profile Analysis. Chemical and X-ray diffraction
analysis methods are being used to determine the composition profiles in
blocks of S/S-treated waste that have experienced long-term leaching. These
analyses evaluate the actual release from S/S-treated waste and provide
insight into the processes occurring within the waste during leaching (Hockley
and van der Sloot, 1991).
The Binding Chemistry and Chemical Leaching Mechanism of Hazardous
Substances in Cementitious S/S Binders. Type I Portland cement samples
containing the soluble nitrates of the priority pollutant metals chromium,
lead, barium, mercury, cadmium, and zinc have been investigated using therm-
ogravimetric and Fourier-transform infrared techniques, including diffuse
reflectance. The major vibrational bands and thermal stability of the
carbonate, sulfate, silicate, water, and nitrate species have been tabulated
in comparison to uncontaminated Portland cement. Immobilization mechanisms
and their effect on contaminant leaching are being studied (Ortego et al.,
1989; Ortego, 1990; and Ortego et al., 1991).
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Development of a Numerical Three-Dimensional Leaching Model. The
overall goal of this research effort is to improve the fundamental understand-
ing of binding chemistry and leaching mechanisms in S/S-treated waste and to
apply this understanding to development of improved S/S technology and of
improved methods for predicting the environmental impacts of disposing of S/S-
treated waste. This work is taking the approach of developing mechanistic
leach models and developing characterization methods that can be used with the
leach models. An underlying theme throughout this research is the need to
separately describe the physical and chemical immobilization mechanisms. A
set of simple leach models has been developed based on various simple reaction
systems and rectangular geometry. Irreversible immobilization, reversible
linear sorption, reversible precipitation, and reaction between a precipitate
and inwardly diffusing reactant are the mechanisms considered in the simple
leach model. A general numerical three-dimensional leaching model is being
developed based on the Crank-Nicholson finite difference algorithm (Batchelor,
1991, personal communication).
Acid Leaching Rate and Advancement of Acid Front In S/S-Treated
Waste. This program is studying the behavior of leaching of a cement-based
waste form. The investigations indicate that acids in the bulk solution
diffuse through the pores of the waste form leading to a reduction in pH and
dissolution of metals.
The dissolved metals leach out of the solid matrix into the bulk
solution, leaving a leached layer on the surface of the waste form. A sharp
leaching boundary was identified in every leached sample, using pH indicators.
The movement of the leaching boundary was found to be a single diffusion-
controlled process. Studies were conducted using both static and semidynamic
leaching procedures (Cheng and Bishop, 1992).
Leaching Test Methods and Models. Several leaching mechanisms,
including dissolution of the matrix, washoff of surface contaminants, and
diffusion-controlled release, were studied. A variety of leach testing
methods were described and the capabilities compared. A diffusion model for
leaching was developed (de Groot and van der Sloot, 1992).
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Review and Analysis of Treatabllltv Data Involving Solidifica-
tion/Stabilization of Soils. A paper study of existing treatability data for
S/S of 18 metals and application of geochemical models is being conducted to
identify factors controlling metal solubility. The data base contains
approximately 2600 records representing approximately 80 studies. Despite the
volume of data, inconsistent data collection and procedural uncertainties
limit interpretation. No statistically significant correlations could be
found when post-treatment parameters were tested against measured waste
characteristics. However, subsets of the data base will continue to be tested
to identify chemical controls as the modeling work proceeds (Means et al.,
1991a).
6.1.7 Compatibility with Disposal or Reuse
Assessment of Long-Term Durability of S/S-Treated Waste. The
mechanisms governing the durability of S/S-treated waste are not well under-
stood. Studies are needed to examine how the disposal environment interacts
to modify the physical and chemical performance of the waste. In one study,
S/S-treated waste is being tested to quantify waste form performance and
examine degradation mechanisms. Testing involves accelerated freeze/thaw and
wet/dry cycles and various environments, such as high or low pH, high pres-
sure, high- or low-redox potential. Conventional and advanced large-scale
leaching tests are being performed. The S/S-treated waste is being character-
ized by sophisticated techniques such as laser holography, acoustic stress
wave testing, and dye injection (Bishop et al., 1990a).
Effect of Curing Time on Leaching. The effect of curing time on
metal leaching, as measured by the TCLP test, is being studied in synthetic
wastes for a variety of metal contaminants. Initial results indicate a
significant effect of curing time, both on TCLP results and on the chemical
structure of the stabilized waste as evidenced by spectroscopic analyses
(Akhter and Cartledge, 1991; Cartledge, 1992). Both increased and decreased
leaching is being observed, depending on the metal contaminant, binder, and
other factors. These observations underline the limitations of the TCLP test
as an indicator of the long-term leaching of stabilized waste and emphasize
the need for other types of leaching data.
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Field Performance of S/S-Treated Waste. Solidification/stabilization
is used at CERCLA sites and in other waste treatment applications. However,
durability of S/S-treated waste remains unclear due, in part, to the relative
newness of the technology and the lack of information from sites currently
applying S/S processes. A three-phase project is under way (U.S. EPA, 1991b):
Identify sites using S/S processes.
Core sample and test S/S-treated waste from several
sites.
Design and implement a program to solidify
representative wastes by various S/S processes and
monitor the wastes over an extended period.
Utilization and Disposal. The performance of S/S-treated waste
depends on the environment the material is exposed to as well as the treated
waste and contaminant properties. The Waste Technology Centre in Canada is
developing an evaluation protocol as a decision-making tool for management of
S/S-treated waste. One factor in the protocol is identification and defini-
tion of use and disposal scenarios. Scenarios include unrestricted use,
approved use, sanitary landfill, segregated landfill, and secure landfill
(WTC, 1990b).
6.1.8 Treatability Tests and S/S Process Application
Superfund Innovative Technology Evaluation (SITE) Program. The SITE
Program was established to accelerate the development and use of innovative
cleanup technologies at hazardous waste sites across the country. The Demon-
stration Program of SITE focuses on field demonstration of emerging site
remediation technologies. The Demonstration Program has 37 active tests,
including the eight low-temperature S/S technologies summarized in Table 6-1.
Municipal Waste Combustion Residue S/S Program. Vendors of S/S
processes are cooperating with the U.S. EPA Office of Research and Development
Risk Reduction Engineering Laboratory to demonstrate and evaluate the perfor-
mance of S/S processes for treating residues from the combustion of municipal
solid waste (MSW). The program includes four S/S processes: cement, silicate,
cement kiln dust, and a phosphate process. The aim of the project is to
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TABLE 6-1. SUPERFUND INNOVATIVE TECHNOLOGY EVALUATION PROGRAM:
SOLIDIFICATION/STABILIZATION TECHNOLOGIES
Developer
Solidification/
Stabilization
Technology
Applicable
Waste Media
Applicable Waste
Inorganic
Organic
Chemfix Technologies, Inc.
Metairie, LA
HAZCON, Inc.
Brookshire, TX
International Waste
Technologies/Geo-Con, Inc.
Wichita, KS
S.M.W. Seiko, Inc.
Redwood City, CA
Separation and Recovery
Systems, Inc. (SRS)
Irvine, CA
Silicate Technology Corp.
Scottsdale, AZ
Soliditech, Inc.
Houston, TX
Wastech, Inc.
Oak Ridge, TN
Soluble silicates and
silicate setting agents
Cement and proprietary
additive
In situ silicate and
proprietary additives
In situ proprietary
binder
Lime and proprietary
additives
Silicate, cementitious
material, and proprietary
additives
Pozzolan or cement and
proprietary liquid
additives
Proprietary
Soil, sludge,
other solids
Soil, sludge
Soil
Metals
Metals
Soil, sediment Nonspecific
Metals
Liquid/solid Low-level
metals
Groundwater, Metals,
sludge, soil cyanide,
ammonia
Soil, sludge Metals
High-molecular-
weight organics
Not an inhibitor
PCBs, other
nonspecific
organic compounds
Semi volatile
organic compounds
Specific for
acidic sludges
with at least 5%
hydrocarbons
High-molecular-
weight organics
Nonspecific
Soil, sludge, Nonspecific, Nonspecific
liquid waste radioactive
Nonspecific = Technology is generally applicable to that waste type.
Sources: U.S. EPA, 1988d and Barth, 1991)
-------
enhance the environmental performance of S/S-treated MSW combustion residue in
a range of final environments. The final environment may be disposal in the
land or use as roadbed aggregate, building blocks, or artificial reefs for
shore erosion control (Wiles et al., 1991a and b).
Leaching Mechanisms and Performance of S/S-Treated Hazardous Waste
Substances 1n Modified Cementitious and Polymeric Matrices. In this study, a
latex polymer additive is being used with Portland cement to treat inorganic-
and organic-contaminated waste. The latex polymer is used to reduce the
porosity of the S/S-treated waste in order to improve immobilization (Daniali,
1990).
Stabilization Potential of L1me In.lection Multistage Burner
Product Ash Used With Hazardous Distillation Residues. A study is under way
to investigate the trace metal binding mechanisms in S/S high-sulfur coal fly
ash and flue gas desulfurization (FGD) sludges. Fly ash and sludge from a
typical wet FGD process and dry flue gas desulfurization by-product from a
demonstration LIMB process are being evaluated. The latter material contains
substantial portions of available lime and may prove amenable as a solidifying
agent with the fly ash. This work is being done to characterize the waste,
determine the solidified/stabilized waste formulation, and measure the
influence of liquid/solid ratio on metal leaching from the waste forms (Bishop
et al., 1992; Dusing et al., 1991).
Stabilized Incinerator Residue in a Shore Protection Device. The
goals of this research are to stabilize potentially toxic incineration
residues and to use the stabilized material to construct energy-deflecting or
absorbing structures to reduce shore erosion. The initial phases of the
project will deal with developing the proper mix design for stabilized
materials in high-wave energy environments and with determining their engi-
neering properties, leachate characteristics, and potential toxicity to
organisms. Permits will be secured to construct a model wave deflec-
tor/absorber in a marine system. The actual construction will occur in the
next phase (Swanson, 1990).
6-12
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6.2 FUTURE DEVELOPMENT
For more than 20 years, S/S processes have been used to treat
industrial and radioactive waste. More recently, the technology has been used
to treat contaminated soils at CERCLA sites, fly ash, incinerator ash, and
metal-contaminated sludges.
Despite extensive application and considerable research, there still
are areas that could profit from additional effort. An increased under-
standing of S/S mechanisms, interferences, leaching behavior, and long-term
performance would all help to improve process efficiency and increase confi-
dence in the technology. Some areas to consider for future research are
summarized in sections 6.2.1 through 6.2.8.
6.2.1 Binders
Increase immobilization performance by modifying
existing binders.
Develop advanced binders to minimize volume increase
inherent in most existing S/S processes.
Develop advanced binders with better tolerance to
organic contaminants and interferences.
Determine factors affecting optimum binder addition
rate. Too much of a particular binder ingredient
can lead to an improperly stabilized waste form.
For example, many metals are amphoteric, meaning
that they are soluble under both acidic and alkaline
conditions. The metal will be at minimum solubility
when a sufficient base (S/S ingredient) is added to
make the waste moderately alkaline. Too much base
will cause the metal to resolubilize and/or make the
waste hazardous by virtue of the RCRA corrosivity
characteristic (i.e., pH >12.5).
6.2.2 Mechanisms
Develop an understanding of chemical speciation and
how it affects immobilization.
Gain understanding of S/S process bonding mechanisms
with presently used binders and additives.
Gain understanding of microstructure and chemistry
of the complex interactions among binder phases and
contaminants (McDaniel et al., 1990).
6-13
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6.2.3 Interferences
Organic matter in the waste can prevent setting of
the S/S-treated waste or reduce the strength or
immobilization performance of the final product.
Research is needed to determine threshold levels for
interfering organic compounds with inorganic and
organic S/S binders.
Interfering agents should be classified into groups
based on similarity of interference mechanisms.
Once the mechanisms are defined and interferences
grouped, control parameters could be set for
interfering chemicals such as volatile organics,
insoluble organics, soluble organics, soluble salts,
sulfates, and ammonia.
6.2.4 Organics and Air Emissions
Develop methods to efficiently remove organic
contaminants from sludge, soil, and soil-like wastes
(Barth, 1990).
Develop methods to determine whether bonding occurs
between binder and organic waste. Increased
understanding of the mechanisms for organic
immobilization will speed development of better
binders for organic contaminants.
6.2.5 Test Methods
Characterize the chemical interaction within the
S/S-treated waste and at the waste/soil interface by
diffusion tube measurements with radiotracers.
Develop methods to more accurately predict and
measure the performance of S/S processes and
products in the laboratory and to improve the
correlation of laboratory results with performance
in the field (McDaniel et al., 1990).
Develop and evaluate simple methods for deter-
mination of metal speciation for use in binder
evaluation and selection.
Develop and evaluate methods for inexpensive
determination of metal speciation.
Develop better test methods for detailed research of
S/S-treated waste performance (e.g., X-ray
fluorescence, computer imaging, laser holography).
6-14
-------
Identify factors affecting scale-up of treatability
test results to determine the safety margin needed
in performance measures. Scale-up from bench-scale
to field-scale involves a number of variables that
cannot be exactly replicated in the bench-scale
experiments, e.g., field-curing conditions, degree
of mixing, and ingredient control, among others.
Therefore, the results of the bench-scale tests
should exceed the performance measures for the field
project by a wide enough margin to allow for unknown
contingencies. As a general rule, if a bench-scale
test meets the field performance measures by only a
slim margin, then one may expect problems with full-
scale implementation.
Quantify the effect of the small-scale treatability
test environment on S/S-treated waste performance.
The jar environment promotes good contact between
the binder and waste form and can enhance the degree
of stabilization.
6.2.6 Leaching and Transport Models
Develop approaches to better predict field
performance from laboratory results.
Quantify containment release rates by diffusion and
advection over long-term exposure to environmental
conditions. Use the transport data to evaluate the
acceptability of the release rates.
The TCLP does not fully address the main leaching
mechanisms for many organics. In many cases, the
organics in leachates are associated with
particulate matter. Methods need to be developed to
assess the fraction of organics mobilized by
mechanisms not directly related to diffusion or
dissolution such as sorption on particulates.
Develop better, more economical, and more rapid
leaching tests that allow reliable prediction of
long-term performance of S/S-treated waste.
6.2.7 Compatibility with Disposal or Reuse
Identify and validate methods to produce S/S-treated
waste that can be reused or recycled (Barth, 1990).
Determine the long-term physical durability and
contaminant retention properties of S/S products by
the following means:
6-15
-------
- Define the physical and chemical environments
for various end uses.
- Develop accelerated weathering tests.
- Define biodegradation potential.
- Determine the relative merits of granular
versus monolithic materials.
Analyze the conditions needed for long-term
environmental protection for S/S-treated waste
placed in a disposal or use environment. Analysis
will include determination and evaluation of the
ultimate release pathways.
Evaluate and develop criteria for reuse of S/S-
treated waste (e.g., bricks or subgrade fill).
6.2.8 Treatabilitv Tests and S/S Application
Determine the effectiveness of S/S processes and
equipment for treating contaminated soil and
impounded liquid.
Determine effectiveness of mixing methods (including
in situ methods).
Evaluate effectiveness of slag addition or other
pretreatment options to alter the valence states of
metal contaminants prior to S/S processing.
Establish a database recording important
characteristics of S/S processing, such as binders,
waste characteristics, interferences, and
performance.
Develop expert systems to aid in planning and
evaluating treatability studies, S/S processes, and
pretreatment options. The expert systems can be
used to screen potential S/S processes for specific
waste types and contaminated site conditions.
Develop real-time QA/QC methods for S/S process
control.
Evaluate uses, based on experience with S/S
treatment of industrial sludge, for similar wastes
such as dredged materials from harbors and waterways
or ashes and residues from combustion of coal and
municipal solid waste.
Develop strategies to optimize sample collection and
analysis to increase efficiency and reduce cost.
6-16
-------
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APPENDIX A
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS
INTRODUCTION
This section summarizes the steps in the technology screening
process for S/S technology. It provides a checklist of the material described
in detail in Chapter 2. The organization of the checklist parallels the
organization of Chapter 2, integrating the issues covered in that section into
a user-friendly format. The checklist worksheets help the uninitiated user to
follow orderly and comprehensive screening procedures. The screening could be
repeated at several stages throughout a project, as appropriate. For the
first use, the checklist would serve as a tool to guide preparation of test
plans. The checklist would then be applied at major milestones, such as
selection of an S/S process or completion of bench-scale screening, to review
progress, identify weaknesses in the project, and develop methods to improve
the testing. Later in the testing the checklist would be applied to review
and evaluate the project.
INSTRUCTIONS
Each major subheading in the checklist is followed by 1) a brief
statement or question that clarifies the scope and aspect of S/S technology
covered in that section and 2) a series of questions to guide evaluation of
the S/S project with respect to that aspect. The question can be evaluated as
"favorable," "neutral," "unfavorable," "not known," or "not applicable."
"Favorable" means lower complexity or a higher probability of success for the
S/S project. "Neutral" means that the issue has a known effect but the effect
is not significant to the outcome of the project. "Unfavorable" means greater
challenges to S/S technology. "Not known" means there is high probability of
an effect but the magnitude and/or direction are not known. "Not applicable"
means a low probability of any effect. The questions are typically clarified
or elaborated with notes in the "Issues" column. In most cases the evalua-
tions are qualitative, but in a few cases quantitative performance criteria
are given as guidance. Typically, an answer of "yes" to the question equals a
favorable condition. Cases where the reverse is true are noted.
A summary sheet for tallying the responses for each subheading is
provided at the conclusion of this chapter. The purpose of the summary sheet
A-l
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is to assist in identifying trends or possible weaknesses in the treatability
study.
Not every issue listed in the checklist is applicable to every
treatability study. Irrelevant issues should be ignored. It is hoped that,
through consideration of the issues contained herein, future S/S treatment
projects can be improved in terms of both planning and conduct.
A-2
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SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS
Indicator
*L 3 t+5 *ป *ป
2 55 CJ O O
Information Requirements* it, Z D Z Z Issues
1 SITE-SPECIFIC BASELINE INFORMATION
REQUIREMENTS
1.1 Waste Sampling - Do the waste samples
accurately reflect the chemical and physical
characteristics of the entire volume of the
waste?
1. Are preliminary field surveys available?
2. Are waste sampling procedures
documented and consistent with guidance
in SW-846 (U.S. EPA, 1986a) and/or
other agency guidance?
3. Are sampling locations statistically
randomized?
4. Is sample variability addressed by
statistical analysis?
5. Were samples composited prior to
analysis?
6. Were debris, large rock fragments,
vegetative material, etc. removed prior
to analysis?
7. Is material available sufficient for pilot-
scale testing?
8. Is some material being archived for
possible later tests?
Planning for sampling
Representativeness, holding times,
chain-of-custody, etc.
Representativeness
Representativeness
Composites preferred for
comparative treatability testing but
do not define extremes in waste
composition. Variation is
particularly important for testing
of continuous processes, e.g., pug
mill mixing.
Representativeness
Need to support waste
characterization and bench- and
pilot-scale tests.
QA/QC
* An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-3
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
I S ง ซ o
Information Requirements* t, Z D Z Z Issues
1.2 Waste Acceptance - Is the waste material
toxicity low enough to allow contact handling
needed for S/S testing and application?
1. Was a representative sample analyzed
prior to shipping?
2. Is waste composition in compliance with
shipping regulations?
3. Is the hazard to S/S workers acceptably
low?
1.3 Waste Characterization - Is there an
adequate, statistically valid database to
support selection of binding agents?
1 . Is historical information available?
2. Does characterization include a "total
waste analysis"?
3. Were TCLP data generated on the
untreated waste?
4. Have other hazard characteristic tests
been performed or are they known to be
unnecessary?
5. Have other chemical analyses been
performed to establish baselines and
possible S/S interferences?
6. Have baseline physical characteristics of
the untreated waste been measured?
Identification of chemical hazards
Toxicity and U.S. DOT shipping
regulations
Worker safety
Optimize data collection
Identify target contaminants
Baseline leaching data; RCRA
toxicity characteristic
Ignitability, corrosivity, reactivity,
toxicity, infectivity
pH, redox potential, acid
neutralization capacity, etc.;
Interferants screen, e.g., oil and
grease, salt content, nitrate,
sulfate, etc.
UCS, specific gravity, Paint Filter
Test, permeability, etc.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-4
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
.2
.c
ฃ >t ฃ
2 SOD.
e5 "3 o fl P*
5 fl 5 ซ <
5 fl <*5 <- *-
5 S a o o
Information Requirements* u, Z ^) Z Z Issues
7. Are any other data available on the
physico-chemical form of the target
contaminants?
1.4 Site Characterization - Are fundamental site
characteristics established to give baseline
data for the design of the treatment system?
1. Does the site support the setup and
operation of S/S equipment?
2. Are necessary resources close to the
site?
Water, gas, electricity
Supplies and chemicals
Equipment
Access routes
Disposal facilities
3. What proportion of the waste occurs
above the groundwater table (or
uppermost aquifer)?
100% = favorable
4. Has the total waste volume been
estimated, measured, or calculated?
5. Does the waste contain debris that may
interfere with field treatment?
no = favorable
X-ray diffraction, SEM-EDXA,
microscopy, spectroscopy, etc.
Available space, topography,
excavation difficulty, climate
Design flexibility
Excess water can make excavation
difficult and require dewatering of
waste material.
Smaller volumes, more limited
treatability study; larger volumes,
more extensive treatability study
Pretreatment and handling
requirements; interferences may
be process-specific.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-5
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
ฃ 33 a o o
Information Requirements* u, Z D Z Z Issues
6. What are the textural characteristics of
the waste?
dry, granular = favorable
clayey, sludge, or liquid = neutral
hard, blocky = unfavorable
7. How heterogeneous is the distribution of
the target contaminant(s) within the
waste?
fairly homogeneous = favorable
1.5 Quality Assurance/Quality Control - Is
QA/QC sufficient to determine and document
data quality?
1. Does the analytical laboratory
performing the analyses on the untreated
waste possess appropriate
qualifications/certifications?
2. Are the characterization data collected
under an appropriate QA/QC program,
or is there some other indication of the
quality of the analytical measurements?
3. Are there a sufficient number of
replicates analyzed to permit a statistical
analysis of the results?
4. Is a second analytical laboratory
available for interlaboratory verification
on a portion of the more critical
measurements?
Pretreatment and handling
requirements
More analytical data needed to
compensate for higher variability.
CLP, other
qualifications/certifications
Blind replicates, duplicates,
bracketed calibration, standard
additions, blanks, etc.
Mean, standard deviation,
confidence intervals, etc.
Data accuracy, interlaboratory
verification
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-6
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
Information Requirements*
Issues
2 PERFORMANCE OBJECTIVES
2.1 Regulatory Requirements - Have CERCLA
and RCRA regulatory-driven requirements
been considered in developing performance
requirements?
1. Is the site close to possible receptors of
noise, fugitive dust, volatiles, or odors?
2. Is the site close to sensitive
environmental areas such as floodplains,
wetlands, or the breeding grounds of
protected species?
3. Are the primary contaminants metals or
organics, or both?
metals = favorable
metals and organics = neutral
organics only = unfavorable
4. If mostly metals, how many metals are
present in regulated concentrations?
1 = favorable
2-3 = neutral
4 or more = unfavorable
5. If arsenic and chromium are among the
target contaminants, have their valence
states been determined?
Possible source of location-
specific ARAR
Possible source of location-
specific ARAR
S/S BDAT for many metals; some
types of organics may require
pretreatment unless present in low
concentrations.
Potential for incompatible
chemistries; complex wastes are
more difficult to satisfactorily
stabilize
Toxicity issues; may affect binder
selection; data may also be
inferred from waste origin in
some cases.
* An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-7
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
4)
3
1
6 S ฃ ซ <
I 8 'a ซ ซ
Information Requirements* n, Z p z z Issues
6. If mercury, nickel, tin, arsenic or lead is
among the target contaminants, are
analyses planned for organic (e.g.,
tetraethyl lead, tributyl tin,
organoarsenic) or other unusual and
toxic forms (e.g., nickel carbonyl)?
7. Does the waste contain volatile organic
contaminants and, if so, in what
concentrations?
no or < 50 ppb = favorable
8. Does the waste contain other high
hazard or special contaminants, such as
PCBs, dioxins, pesticides,
chlorophenols, radionuclides, or
cyanide?
no = favorable
2.2 Technical and Institutional Requirements -
Have technical and institutional factors been
considered in developing performance
requirements?
1. Will testing determine the leaching (e.g.,
TCLP) or physical properties (e.g.,
compressive strength) of treated waste?
2. Are reagent costs consistent with project
economics?
3. Does the waste contain compounds that
may decompose or volatilize to produce
off-gas?
no = favorable
Toxicity issues; may affect binder
selection; data may also be
inferred from waste origin in
some cases.
Levels of concern will vary with
the contaminant; S/S not
demonstrated for volatiles;
probable release during mixing
and curing; pretreatment probably
necessary.
Levels of concern vary with the
contaminant; pretreatment will
likely be necessary; S/S may not
be preferred approach, unless a
strong rationale is provided.
Demonstrate basic feasibility.
Calculate binder cost per volume
of stabilized waste.
Off-gas treatment increases
processing costs.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-8
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
i
1 8 'a ซ ซ
Information Requirements* u, Z P Z Z Issues
4. Will the waste mix well with the binder?
5. Does the waste interfere with setting or
cause unfavorable reactions with the
binder?
no = favorable
6. Is the waste/binder mixture fluid and
amenable to material handling and
mixing?
7. Does S/S increase waste volume
significantly?
no = favorable
8. Is the S/S-treated waste amenable to
placement?
9. Is the binder material subject to possible
biodegradation?
no = favorable
10. Are longer-term leaching tests on the
treated waste planned?
3 INITIAL TECHNOLOGY SCREENING
3.1 Technology Screening/Feasibility Study -
Has S/S been compared to other treatment
alternatives and been found to be the most
appropriate technology?
Good mixing and wetting is
needed to ensure a strong,
uniform product.
Interferences should be identified.
Pumpable waste/binder mix makes
handling easier.
Large volume increase raises costs
and increases disposal problems.
Need long-term structural integrity
and ability to support heavy
equipment soon after placement.
Long-term stability
TCLP is not a good indicator of
long-term stability.
* An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-9
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
ซ e -a
ซ ill
i i I a *
1 ง 'a o ซ
Information Requirements* it, Z D Z Z Issues
3.1.1 CERCLA Technology Screening
1. Do the selected methods protect human
health and the environment?
2. Do the selected methods meet ARARs?
3. Do the selected methods reduce toxicity,
mobility, or volume?
4. Do the selected methods minimize
impact to human health and the
environment?
5. Do the selected methods reliably
maintain low residual risk to human
health and the environment?
6. Do the selected methods allow efficient,
cost-effective application at the site?
7. Are the selected methods likely to
receive state acceptance?
8. Are the selected methods likely to
receive community acceptance?
3.1.2 Technology Screening at RCRA TSD
Facilities
1. Is the waste banned under another
regulatory system such as TSCA?
yes = not suitable for S/S
Methods should attain threshold
criteria.
Methods should attain threshold
criteria.
Methods should provide good
trade-off of primary balancing
criteria.
Methods should provide good
trade-off of primary balancing
criteria.
Methods should provide good
trade-off of primary balancing
criteria.
Methods should provide a good
trade-off of primary balancing
criteria.
Modifying criteria are evaluated
after the public comment period.
Modifying criteria are evaluated
after the public comment period.
Review waste for suitability of
S/S treatment.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-10
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (confd)
Indicator
5 1 I * <
| 5 ซ3 3 "8
Information Requirements* ft, 5z t5 Z Z Issues
2. Is the waste classified as "not suitable"
for S/S or land disposal under the
landbans, or is a technology other than
S/S recommeded as BOAT?
yes = not suitable for S/S
3. Is the waste not yet covered or extended
under landbans?
yes = S/S not required
4. Does the generator certify that the waste
meets landban requirements?
yes = S/S not required
S. Is the waste restricted or banned under
site permit conditions or otherwise
unacceptable to a TSD facility?
yes = not suitable for S/S
6. Is treatment required to prepare waste
for a TSD facility's S/S system?
yes = less favorable
3.2 General Criteria for Not Using S/S - Is the
waste compatible with S/S technology?
1. Is the waste amenable to recycling,
reuse, or recovery technology, all other
factors being equal?
no = favorable for S/S
Adherence to RCRA landban and
BDAT recommendations
Landban requirements
Landban requirements
Permit compliance
Treatment process complexity
Recycling, reuse, and recovery
are preferred over treatment or
disposal.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-ll
-------
SOLIDIFICATION/STABIUZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
Information Requirements*
55 ง a o o
(2 55 5 S5 S5
2. Is the waste treatable by a destruction
technology, all other factors being
equal?
no = favorable for S/S
3. Are there ARARs that cannot be
satisfied by existing S/S technology?
no = favorable for S/S
4. Is S/S waste treatment inefficient or
expensive when compared to another
remedy?
no = favorable for S/S
5. Does the waste exhibit poor mixing,
incompatibility, or other unacceptable
characteristics?
no = favorable for S/S
6. Does the waste contain volatile organics
or a large fraction of total organics?
no = favorable for S/S
4 WASTE/BINDER COMPATIBILITY
LITERATURE SCREENING - Has a
comprehensive review and selection process
found a group of test S/S binder formulations
that have a high probability of providing good
stabilization?
Contaminant destruction is
preferred over disposal.
Can S/S meet regulatory
requirements?
Cost effectiveness
Amenability to S/S
Organics can be difficult to
stabilize.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-12
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
Information Requirements*
5 ง (3
n, 55 |5
*
o
Issues
1. Are interferences and chemical
incompatibilities considered as part of
the binder selection?
2. Has metal chemistry been considered in
the binder formulation?
3. Is S/S-treated waste compatible with the
planned end use?
4. Are the S/S costs known, and are they
competitive with other treatment and
disposal methods?
5. Does the S/S process have a proven
track record on similar wastes?
5 LABORATORY BENCH-SCALE
SCREENING OF THE WASTE/BINDER
MIXTURES - Although laboratory screening can
be conducted in a variety of ways, it is typically
an interactive process involving two sequential
steps. A wide range of formulations are given
simple tests. Then a more refined group are
tested against more complex or demanding
criteria. Test criteria and issues are discussed
below.
Pozzolanic binders are
incompatible with high
concentrations of oil, grease,
organics, chlorides, and other
soluble salts. Sodium sulfite
binder is incompatible with acids.
Formation of metal hydroxides is
an important stabilization
mechanism with alkaline binders;
however, high pH can increase
the solubility of some metals
(e.g., As and Cr).
Possible end use includes disposal
such as landfill, monofUl, or
burial or reuse as fill, road base,
or construction material.
Cost is a consideration but should
be secondary to performance.
While proven performance is
desirable, innovative methods
should not be discouraged.
* An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-13
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
"8
'ง,
g fi 1 * <
> 3 <3
5 5 d o o
Information Requirements* u* Z D Z Z Issues
1. Has an appropriate pretreatment step
been devised, if necessary?
2. Have at least 3 to 4 different binders
been selected for bench-scale testing?
3. Are several different binder-to-waste
ratios used in the testing?
4. Have waste/binder compatibility issues
been considered in selecting a binder?
5. Is laboratory testing being based on
composite or "worst-case" samples, or
both?
issue was considered = favorable
6. Are any chemical additives to the binder
carefully monitored and controlled?
7. Are several rounds of bench-scale
testing performed, i.e., have the most
successful processes been adapted to the
site-specific waste form?
8. Are the chemical compositions of the
binder and of any other chemicals added
during S/S (e.g. , fairy dust) known?
9. Are all of the additives mentioned in
item 8 above nontoxic and
nonhazardous?
Highly toxic constituents;
contaminants that do not respond
well to S/S; interferants; debris
Maximize potential for successful
treatability study.
Cost/benefit; excess binder may
hinder S/S process.
Target contaminants; interferants;
compatibility with disposal
environment
Composite best for process
comparison; may be necessary to
design for worst case.
Reproducibility, interpretability,
sensitivity analysis
Process optimization is an
iterative process; ability to
"engineer" solutions to treatability
problems
Hazardous properties
Corrosivity (pH), reactivity (free
sulfide or lime), etc.
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-14
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
1 1 1 1 f
Information Requirements* u, Z P Z Z Issues
10. Are there any new ARARs that result
from the binder additives?
no = favorable
11. Is there provision for a third party or
regulatory agency to observe the
treatability study?
12. Were anticipated field conditions
simulated during waste curing?
13. Were the samples allowed to cure for an
appropriate time period prior to
analysis?
14. Does the test program cover critical
ARARs?
IS. Does the test plan provide for split
samples to be sent to a second
laboratory?
16. Does the test include good statistical
design, replication, blind controls,
laboratory QA/QC, etc?
17. Is the waste volume increase resulting
from binder additions determinable from
the test?
Toxicity and hazard
characteristics, e.g., pH, reactive
sulfide, metal leach criteria,
volatile emissions, dust, etc.
Objectivity
"Jar effect" enhances performance
28 days recommended before
UCS testing for most pozzolans
Leaching and critical
chemical/physical properties
Intel-laboratory comparison to
increase confidence in results
Data accuracy and reliability
End use compatibility, economical
feasibility
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-15
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
S I S S S
Information Requirements* it, Z D Z Z Issues
6 BENCH-SCALE PERFORMANCE
TESTING/PROCESS OPTIMIZATION - Does
the bench-scale performance test demonstrate that
the S/S-treated waste meets predetermined
performance standards?
1. Are the guidelines applied in the bench-
scale screening also considered in the
bench-scale performance testing?
2a. If subsurface disposal is anticipated, are
appropriate physical tests being
conducted?
2b. If surface or near-surface disposal is
anticipated, are the appropriate physical
tests being conducted?
2c. Is the longer-term stability of the waste
toward leaching being evaluated?
2d. For wastes containing organic
contaminants with low aqueous
solubilities, are leaching tests in an
organic solvent being conducted?
2e. Are there any technical reasons to
suspect that colloidal contaminant
transport may be important at this site?
no = favorable
2f. Is there any technical reason for
conducting leach tests with site-specific
groundwater as leachant?
no = favorable
Completeness and consistency
e.g., UCS, permeability etc.
e.g., wet/dry, freeze/thaw, etc.
e.g., multiple extraction
procedure, ANSI/ANS/16.1, etc.
Aqueous leachate is a meaningless
indicator of process effectiveness
because of low solubility of
contaminant.
Assess in leach test by modifying
or eliminating filtration step.
e.g., humic-rich groundwater, or
groundwater with other
completing ligands (e.g.,
carbonate, fluoride, high chloride,
etc.)
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-16
-------
SQLIPIFJCATION/STABIUZATIQN TECHNOLOGY SCREENING WORKIH1ETI (งงst'd)
Indieator
2g, If fee binder ie biodegradable, Is
biodegndatioa perfermanee tMt being
งงBdซgtง4?
iate u apatite system, are Jeaehate
bieasgays being performed?
% Ais sp^ifie biading ftgefot proportiM
3. Is ft total metal analysis being performed
on the same sybsample as the leach test?
4, Have the leaching perfonnanee data
been @งfF@gt@d for dilution by binder
additives?
5. Is there a safety margin is the
performance data compared to the
performance criteria?
6. Is the process impleraentable in the
field?
7, Is the bulking factor (volumetric
expansion งf thง waste due to binder
additives and water) compatible with
disposal constraints?
< 25 ซ expansion = favorable
Waits form lability
Lmefaate teiidty tง atimtig
eeงiyงteffl
pH aad reaetive งซlflde
aaalyiea fงf iulfldง=gงitaiaiflg
trefttmeat งbeaieali
h}งdงgfiditiงfl teits fef
Aefaงplastie งr งfeer งrgafliง
biflden
Iliffliaate falee aegativei,
lubtnet งut iffงgl งf dilufies,
Mixiag, iBgredieat eงBtfงl, aad
euriag eBvifงBfflj8tซ are set iง
well @งatfeUed in the field,
Material! handling iงiuงงs prงงงซs
งงfflplesiityi ffljxiflg, Ihreughput,
asd iterage fequireffl8Stง
Criteria will vary depeadiag งB
the lite,
An answer of *yes" to a question indicates a favorable condition unless otherwise indicated.
A-17
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
a s a o o
Information Requirements* CL, z p z z Issues
8. Is the estimated cost of field treatment
reasonable?
< $100/ton = favorable
$100 - $150/ton = neutral
9. Does the process or binder selected have
a successful track record for this type of
waste?
10. Does the test plan provide for split
samples to be sent to a second
laboratory?
11. Is there provision for a third party or
regulatory agency to observe the bench-
scale performance study?
12. Does the study simulate field conditions
as closely as possible during curing?
13. Is the S/S-treated waste allowed to cure
for the appropriate period of time?
14. Is the amount of performance testing
consistent with the guidance provided in
Section 2.7.2 regarding project risk?
15. Does the analytical laboratory
performing the analyses on the treated
waste possess appropriate
qualifications/certi fi cations?
Will vary depending on several
factors, such as waste volume,
binder type, and process
complexity. Includes both
operating and capital costs.
Innovative processes may require
slower implementation, e.g.,
mandatory pilot-scale test, more
extensive field performance data.
Interlaboratory comparison to
increase confidence in results
Objectivity
Representative of field
conditions
Improve use of data for
scale-up
Test reliability
The greater the risk, the more
performance testing is needed.
CLP, other qualifications/
certifications
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-18
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
1 !
* <
1 ง "a ซ ซ
Information Requirements* fc fc D 5Z Z Issues
16. Were the performance data collected
under an appropriate QA/QC program,
or is there some other indication of the
quality of the analytical measurements?
17. Have a sufficient number of replicates
been analyzed to permit a statistical
analysis of the results?
7 PILOT-SCALE AND FIELD
DEMONSTRATIONS
7. 1 The Need for Process Scale-Up - Is
technical, regulatory, and institutional
confidence in the S/S binder and
binder/waste ratio high enough to obviate the
need for bench-scale testing?
1. Has the binder been used successfully in
field applications?
2. Does the waste to be treated have
physical and chemical characteristics
similar to waste successfully treated in a
prior field application?
3. Are site surroundings similar?
4. Are regulatory requirements similar?
5. Are process scale-up issues well
understood?
Binder replicates, duplicates,
bracketed calibration, standard
additions, blanks, interlaboratory
verification, etc.
Mean, standard deviation,
confidence intervals, etc.
Field application increases
confidence.
Similar wastes' characteristics
imply similar binder
performance.
Particular attention should be
given to complex mixtures and
possible interferences.
Review site-specific performance
and institutional issues.
Site-specific regulatory issues and
ARARs
Material handling
Mixing
Vapor evolution
* An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-19
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
Information Requirements*
d I
I I i
i
Issues
6. Are process costs known?
7. Is waste reasonably homogeneous and
well characterized?
7.2 Scale-Up Issues - Do your pilot-scale tests
address the major remediation steps?
1. Is the performance of earth-moving or
other waste removal equipment known?
2. Is the performance of material-handling
equipment known?
3. Is the storage and handling system for
the S/S binder known?
4. Is waste pretreatment needed to improve
material handling?
5. Is waste pretreatment needed to improve
binder compatibility or efficiency?
6. Are the mixing system for the S/S
binder and the waste disposal approach
known?
7. Is the S/S-treated waste disposal
approach known?
Pilot plant test will improve
accuracy of cost estimate.
Waste composition variations can
affect S/S binder performance.
Throughput
Free liquid handling
Operator safety
Throughput
Caking/Plugging
Spillage
Inventory needs
Throughput
Space
Size adjustment by crushing
and/or screening
Moisture adjustment
Blending, homogenization, pH
adjustment, volatile organic
removal
In situ, batch, continuous
Handling, placement, compaction,
moisture content, final closure and
capping
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-20
-------
SOLIDIFICATION/STABILIZATION TECHNOLOGY SCREENING WORKSHEETS (cont'd)
Indicator
I
Information Requirements*
3 55 Z
Issues
7.3 Analytical Testing of the Treated Waste - Is
sampling and analysis of pilot plant S/S-
treated waste sufficient to determine
performance?
1. Is basic testing included?
2. Are additional tests required?
Leaching and physical strength
Permeability, moisture content,
chemistry
An answer of "yes" to a question indicates a favorable condition unless otherwise indicated.
A-21
-------
SUMMARY SHEET
I. Site:
II. Reviewer:
IH. Date:
IV. Review Summary:
I
f
1
1.1 WASTE SAMPLING
1.2 WASTE ACCEPTANCE
1.3 WASTE CHARACTERIZATION
1.4 SITE CHARACTERIZATION
1.5 QUALITY ASSURANCE/QUALITY CONTROL
Subtotal, Waste and Site Characterization
2.1 REGULATORY REQUIREMENTS
2.2 TECHNICAL AND INSTITUTIONAL REQUIREMENTS
2.3 APPROACH TO SETTING PERFORMANCE CRITERIA
Subtotal, Performance Objectives
3.1 TECHNOLOGY SCREENING/FEASIBILITY STUDY
3.2 GENERAL CRITERIA FOR NOT USING S/S
Subtotal, Initial Technology Screening
A-22
-------
SUMMARY SHEET (Continued)
4. WASTE/BINDER COMPATIBILITY SCREENING
Subtotal, Waste/Binder Compatibility Screening
5. BENCH-SCALE LABORATORY SCREENING
Subtotal, Bench-Scale Laboratory Screening
6. BENCH-SCALE PERFORMANCE OBJECTIVES
Subtotal, Bench-Scale Performance Testing/Process Optimization
7.1 THE NEED FOR PROCESS SCALE UP
7.2 SCALE UP ISSUES
7.3 ANALYTICAL TESTING OF THE TREATED WASTE
Subtotal, Pilot-Scale and Field Demonstration
i S & * <
i i ง i i
A-23
-------
APPENDIX B
DRAFT REPORT: SAMPLING AND ANALYTICAL PROCEDURES
Note: The sampling and analytical procedures document presented in this
appendix was developed for sampling piles of waste material contaminated
with copper and lead. The document is included here only as an example
and has been modified to protect client confidentiality.
B-l
-------
DRAFT REPORT
SAMPLING AND ANALYTICAL PROCEDURES
February 25, 1992
by
Andrea Leeson
Jeffrey Means
Gregory Headington
Bruce Buxton
BATTELLE
Columbus Division
505 King Avenue
Columbus, Ohio 43201-2693
(B-2)
-------
TABLE OF CONTENTS
1.0 INTRODUCTION 1
2.0 PROJECT SCOPE 2
3.0 SAMPLING PROGRAM 7
4.0 ANALYSIS PROGRAM 8
5.0 STATISTICAL DESIGN 10
5.1 Overview 10
5.2 Approach 10
5.2.1 NUMBER OF SAMPLES PER WASTE PILE 10
5.2.2 GRID SIZE 14
5.2.3 SELECTION OF GRIDS 14
5.2.4 SAMPLING METHOD WITHIN A GRID 16
6.0 SAMPLING EQUIPMENT AND OPERATION 17
6.1 Dipper 17
6.2 Stainless Steel Spoon or Scoop 19
6.3 Glass Tube Thief 19
6.4 Auger and Thin-Wall Tube Sampler 21
7.0 SAMPLE COLLECTION AND PRESERVATION 25
7.1 Sample Collection 25
7.2 Sample Preservation 26
8.0 PERSONAL PROTECTIVE EQUIPMENT AND DECONTAMINATION 27
8.1 Personal Protective Equipment 27
8.1.1 SAMPLING 27
8.1.2 CLEANING OPERATIONS (DECONTAMINATION) 27
8.2 Decontamination 27
9.0 SAMPLE CUSTODY, LABELING, PACKAGING, AND TRANSPORTATION 30
9.1 Sample Custody 30
9.2 Sample Labeling 30
9.3 Sample Packaging 33
9.4 Sample Transportation 34
(B-3)
-------
TABLE OF CONTENTS
(Continued)
10.0 SAMPLE QUALITY ASSURANCE AND QUALITY CONTROL 35
10.1 Rinsate Blanks (Equipment Washes) 35
10.2 Laboratory Quality Control and Certification 35
10.2.1 MATRIX SPIKE ANALYSIS 35
10.2.2 MATRIX SPIKE DUPLICATES 36
10.2.3 METHOD BLANK TESTS 36
LIST OF TABLES
TABLE 2-1. SUMMARY OF COPPER AND LEAD LEVELS IN WASTE BOXES 4
TABLE 2-2. SUMMARY OF COPPER LEVELS IN WASTE PILES 5
TABLE 2-3. SUMMARY OF LEAD LEVELS IN WASTE PILES 6
TABLE 5-2. SAMPLE SIZE REQUIRED TO DEMONSTRATE COMPLIANCE WITH
REGULATORY THRESHOLD (RT) AS A FUNCTION OF
ANTICIPATED AVERAGE CONTAMINATION LEVEL (X) AND
COEFFICIENT OF VARIATION 11
TABLE 5-2. RANDOM NUMBERS TABLE -15
LIST OF FIGURES
FIGURE 2-1. SCHEMATIC DIAGRAM OF WASTE PILES 3
FIGURE 6-1. SCHEMATIC DIAGRAM OF DIPPER 18
FIGURE 6-2. SCHEMATIC DIAGRAM OF GLASS TUBE THIEF 20
FIGURE 6-3. SCHEMATIC DIAGRAM OF AUGERS AND THIN-WALL TUBE
SAMPLER 22
FIGURE 9-1. CHAIN-OF-CUSTODY SHEET 31
FIGURE 9-2. SAMPLE LABEL 32
(B-4)
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DRAFT REPORT
FOR
SAMPLING AND ANALYTICAL PROCEDURES
1.0 INTRODUCTION
[The introduction is specific to each project and should briefly describe the project
background and objectives.]
(B-5)
-------
2
2.0 PROJECT SCOPE
The existing waste consists of three accumulated piles of material situated on pavement in
an approximately rectangular shape (Figure 2-1). Approximate estimates of the dimensions of the
piles are: Pile 1: 43 ft by 27 ft and 2 ft deep; Pile 2: 53 ft by 38 ft and 2 to 2.5 ft deep; and Pile
3: 53 ft by 20 ft and 3 ft deep.
A preliminary sampling of the waste was conducted by Battelle to obtain an estimate of the
number of contaminants of concern as well as the concentrations. In addition, previous sampling
of other similar which had been collected in rolloff boxes and stored in the parking area was
analyzed in order to obtain a better estimate of the contaminants likely to be found in the piles.
Copper and lead were the primary contaminants from both sampling surveys. Average
concentrations of copper and lead from the rolloff boxes and piles are shown hi Tables 2-1, 2-2,
and 2-3. These preliminary measurements of the metal concentrations were used to design the
sampling program.
The waste tends to be fairly uniform in consistency throughout, but possible variations in
metal concentrations require that samples be collected at varying locations, both spatially and as a
function of depth. Specific details of the sampling design are discussed in the following section.
(B-6)
-------
I
N
BuMtng
A 215
}
*
I
r
-------
TABLE 2-1. SUMMARY OF COPPER AND LEAD LEVELS IN WASTE BOXES
Results by Analytical Methods Copper Lead
STLC
Regulatory Threshold (mg/L) 25 5.0
Mean (mg/L)1 35 2.2
Coefficient of Variation 0.97 0.43
TTLC
Regulatory Threshold (mg/kg) 2500 1000
Mean (mg/kg)1 3240 28
Coefficient of Variation 0.33 0.40
1 Samples which contained nondetectable concentrations were used in calculations as
the mean between 0 and the detection limit.
(B-8)
-------
TABLE 2-2. SUMMARY OF COPPER LEVELS IN WASTE PILES
Results by Analytical Methods
STLC
Regulatory Threshold (mg/L)
Mean (mg/L)1
Coefficient of Variation
TTLC
Regulatory Threshold (rag/kg)
Mean (mg/kg)1
Coefficient of Variation
1
25
45
0.33
2500
2550
0.14
Pile*
2
79
0.91
3080
0.27
3
31
0.85
2600
0.11
Average of four samples.
(B-9)
-------
TABLE 2-3. SUMMARY OF LEAD LEVELS IN WASTE PILES
Results by Analytical Methods
STLC
Regulatory Threshold (mg/L)
Mean (mg/L)1
Coefficient of Variation
TTLC
Regulatory Threshold (mg/kg)
Mean (mg/kg)1
Coefficient of Variation
1
5.0
3.0
0.23
1000
66
0.21
Pile*
2
2.0
0.26
58
0.11
3
2.4
0.33
64
0.05
Average of four samples.
(B-10)
-------
7
3.0 SAMPLING PROGRAM
The sampling design will be of a random grid layout. Piles 1 and 3 will be gridded into
equal surface areas by marking a coordinate every 3 ft, both horizontally and laterally. Due to the
variation in size between piles, this will result in approximately 130 grids for Pile 1 and
approximately 120 grids for Pile 3. Each grid will have a surface area of 9 square ft. Pile 2 will
be gridded into equal surface areas by marking a coordinate every 4 ft, both horizontally and
laterally. This will result in approximately 125 grids. Each grid will have a surface area of 16
square ft. The grid areas will be numbered consecutively so that sample locations may be
referenced.
Six different samples will be collected along with two blind replicates for each pile.
Location of the sampling points will be selected for each of the sampling locations from a random
number table (see Section 5.2.3).
Trained technicians will be required to collect samples of waste from the piles using the
techniques described in Sections 5.0 through 10.0. Composite samples will be collected from each
randomly selected grid. Composite sampling will consist of collecting five subsamples from each
of two different depths in the randomly selected grid for a total of ten subsamples. The depths will
be 0.5 ft from the surface of the pile and approximately 0.5 ft from the pavement. Subsamples
will be collected from four corners of the grid in addition to one subsample from the center. The
subsamples will then be composited in a tray and mixed using a stainless steel or Teflon spoon.
The composited sample will be split and placed into two or three precleaned polyethylene bottles
for analysis as follows:
500 cc from all sampling points. These samples will be sent to the primary
analytical laboratory.
1000 cc from all sampling points. These samples will be archived in the event that
additional analyses are required.
500 cc from 1 out of 10 sampling points. These samples will be sent to a separate
analytical laboratory to verify results from the primary laboratory.
This type of sampling versus a single grab sample will provide a better estimate of the
mean concentration of the contaminants within the sampling grid and, correspondingly, a better
estimate of the mean concentration of the contaminants in the waste pile.
(B-ll)
-------
8
4.0 ANALYSIS PROGRAM
One sample from each pile will be analyzed for the seventeen California Assessment
Manual (CAM) metals plus Cr (VI). Total metal concentration is to be compared to California
Total Threshold Limit Concentrations (TTLCs) for the seventeen metals plus Cr (VI) using
appropriate methods as found in "Test Methods for Evaluating Solid Waste, Physical/Chemical
Methods", SW-846, 3rd Edition. The remaining samples need be analyzed for only total copper
and lead since previous testing has shown these to be the major metals. The waste will be
analyzed for soluble metals using the following two methods:
The Toxicity Characteristic Leaching Procedure (TCLP) will be carried out on 1
out of 5 samples in future sampling programs to ensure the waste is. not a RCRA
waste. The waste piles which are now undergoing analyses have already been
tested by this method.
Soluble metal concentrations using the California Title 22 Waste Extraction Test
(WET), to be compared with the California Soluble Threshold Limit
Concentrations (STLCs) standards for these metals.
The total metal analyses (all 17 metals plus Cr(VI)) are conducted first and are conducted
to determine major metals for subsequent analysis. A major metal is one whose total concentration
is ten times above the STLC for that metal. Then all the remaining samples are analyzed for total
metals content for just the major metals. Finally, any sample whose total metal concentration is ^
ten times its STLC should be analyzed by the WET to determine any STLC exceedances. The
approach to analysis described in this paragraph is relatively simple, quick, and cost-effective.
It is important to inform the analytical laboratory to use as large a sample volume as
possible for analyses in order to obtain an accurate, representation of the metal concentrations in
each sample. A minimum of 100 g of sample should be used for the WET and a minimum of 5 g
of sample should be used for acid digestion.
The analytical laboratory must meet the following quality control and quality assurance
standards:
The minimum acceptable detection limit is 100 times lower than TTLCs and 10
times lower than STLCs for WET analysis.
(B-12)
-------
Results from spike analyses must be provided to demonstrate the accuracy and
reproducibility of laboratory methods. An error of ฑ 20% is acceptable.
Also, in future sampling programs we recommend mat approximately one out of ten
samples be analyzed for total metal concentrations of all 17 CAM metals plus CR(VI). It is not
necessary or cost-effective to analyze every sample for all 17 metals. However, a representative
fraction of the samples used needs to be completely characterized in order to determine the major
metals present.
Additional details on the statistical design of the sampling program are provided in Section
S.O. Sampling equipment and operation, sample collection and preservation, personal protective
equipment and decontamination, and quality assurance and quality control are discussed in Sections
6.0 through 10.0.
(B-13)
-------
10
5.0 STATISTICAL DESIGN
An overview of the sampling effort will be discussed first followed by details on each
aspect of the sampling design. The overview is intended to provide a general understanding of
how the waste will be sampled. The details which follow the overview will include information on
how the number of samples and grid sizes were selected, as well as detailing the method for
selection of the grids and the sampling method within a grid.
5.1 Overview
Each waste pile will first be subdivided into either 3 ft by 3 ft grids (Piles 1 and 3) or 4 ft
by 4 ft grids (Pile 2). Random sampling will then be used to select six grids for sampling. Within
each of these grids, ten samples will be taken and composited, five samples from each of two
levels.
The key elements which must be defined for this type of sampling design include: 1) the
number of samples; 2) the grids (spatial area) to be sampled; 3) the selection of the grids; 4) the
sampling method within a grid; and 5) the estimators used to characterize the population.
5.2 Approach
5 J.I NUMBER OF SAMPLES PER WASTE PILE
Factors affecting the number of samples which should be collected are the homogeneity of
the contaminant in the waste, the desired confidence interval, and the cost per sample. Based on
previous sampling at the site (Tables 2-1 - 2-3), an estimate of the number of samples which would
provide statistical confidence in the results may be determined.
In order to provide a basis for the determination of the number of samples to acquire per
pile, a table was generated which compares the coefficient of variation of a sample set (standard
deviation/mean) versus K, which is a ratio of the mean of the sample set to the regulatory
threshold (Table 5-1). In order to generate this table, the sample mean, standard deviation, and
sample size are related to determine an upper bound, Ty, which represents the highest value for
the
(B-14)
-------
11
TABLE 5-1. SAMPLE SIZE1 REQUIRED TO DEMONSTRATE COMPLIANCE WITH
REGULATORY THRESHOLD (RT) AS A FUNCTION OF
ANTICIPATED AVERAGE CONTAMINATION LEVEL (X)
AND COEFFICIENT OF VARIATION
K ป 100X/RT
CV
0.1
0.5
0.9
1.3
1.7
2.0
0.1
0.5
0.9
1.3
1.7
2.0
0.1
0.5
0.9
1.3
1.7
2.0
1 These
10
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
sample sizes cc
30
80% CONFIDENCE
1
1
1
1
1
1
90% CONFIDENCE
1
1
1
2
2
2
95% CONFIDENCE
1
1
2
3
3
4
>rrespond to a statistical
50
LEVEL
1
1
1
2
2
3
LEVEL
1
1
3
4
5
6
LEVEL
1
2
4
6
8
10
power of 50%
70
1
2
4
6
8
9
1
3
8
13
18
21
1
5
13
22
29
35
at a
90
1
15
38
63
87
103
2
34
108
147
202
239
3
55
145
242
332
393
contamination level
x, and were calculated assuming a lognormal probability distribution for the metal
concentrations, along with assumptions mat the standard deviation of the
measurements is known, and that spatial correlation effects are not important.
(B-15)
-------
12
concentration that is plausible based on the samples taken. If To is found to be below the
regulatory threshold, then it is decided that the true average concentration is also below that
threshold. From an environmental point of view, the use of Tv is probably most defensible
because it requires that an area be demonstrated free of contaminants at the regulated levels.
TU is calculated from the statistical formula shown below:
-.+-ฃ (5.D
where m is the mean of the log-transformed metal concentrations:
i t (Xj) (5.2)
n
where: t(Xj) = the log-transformed metal concentrations
n = sample number
g^ = the (1-a) percentile point of the standard normal distribution
a = the standard deviation of the log-transformed metal concentrations
The sample sizes shown in Table 5-1 have been generated by assuming an average metal
concentration (x), a standard deviation (a), and a desired Ty to give a range of CVs (cr/x) and Ks
(lOOx/RT). In order to use Table 5-1, it is necessary to either assume an expected x and CV or a
small preliminary sample should be taken to provide an estimate of x and the CV. These values
can then be used to select an appropriate sample size. The mean and standard deviation of the
sample set may be calculated in the standard method as shown. The mean of a sample set may be
calculated as follows:
(5.3)
n
The standard deviation of the sample set may be calculated as follows:
-------
13
* - N n-\ y'
The coefficient of variation (CV) is simply the ratio of the sample standard deviation to the
sample mean:
CV = - (5.5)
From Table 5-1, one can see that as the K value increases or the coefficient of variation
increases, a greater number of samples are required to demonstrate compliance. In other words, as
the expected sample mean approaches the regulatory threshold, it will require many more samples
to demonstrate that the actual metal concentration in the waste is below the threshold.
As shown by the preliminary sampling (Tables 2-1 - 2-3), the results demonstrated that
most of the waste in the piles contain copper concentrations above the regulatory thresholds for
both soluble and total metals content, although a high coefficient of variance was often found with
these results. Theoretically, additional sampling of any pile of waste might result in finding the
metal concentrations to be below the regulatory limits (although this is not recommended for these
particular piles because the soluble copper content is too high); however, one must balance the cost
of sampling with the likelihood of being able to dispose of the waste as nonhazardous.
Although the calculations in Table 5-1 show that in some cases one sample would be
sufficient to demonstrate compliance, this would be difficult to justify from a regulatory
perspective. From a statistical standpoint, a minimum of six samples per waste pile (where a
waste pile is equal to 300 yd3 or less) would provide relatively good confidence in the calculated
average metal concentration. The number of samples required if, for example, the average metal
concentration is expected to be close to the regulatory threshold and the coefficient of variation is
high, can be as high as 390 samples, which would clearly be economically unfeasible. Therefore,
it is recommended that six samples per pile be taken to determine the average metal concentration.
If waste piles generated in the future are significantly larger than those now in question, sample
size should increase proportionally.
(B-17)
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14
5.2.2 GRID SIZE
The grid size selected was based upon the area required to collect the samples and a "rule
of thumb" that for a sample of size n, there should be 20 x n grids. There are six samples to be
taken from each waste pile, therefore, 120 grids would be adequate. This number of grids
indicates a grid size of 3 ft by 3 ft would be appropriate for Piles 1 and 3 (generating
approximately 130 and 120 grids, respectively), while a grid size of 4 ft by 4 ft would be
appropriate for Pile 2 (generating approximately 125 grids).
For sampling of other piles, the following steps may be followed:
1) Determine the number of samples to be taken as discussed in the previous section.
2) Multiply the number of samples, n, by 20 to determine the number of grids
required per strata.
3) Based upon the dimensions of the pile, determine the size of the grids required.
For example, to take 5 samples from a waste pile with dimensions of 40 ft by 50 ft
would require 100 grids. Selecting a grid size of 4.5 ft by 4.5 ft would yield
approximately 100 grids.
5.2.3 SELECTION OF GRIDS
Grid areas should be numbered consecutively. Selection of the grids for sampling will be
done randomly. In order to select the grids, use the set of random numbers shown in Table 5-2.
Select the first, middle, cr last three digits from each five-digit number, but decide which digits
will be selected prior to beginning. Choose any number randomly in the table as a starting point.
From this number, go down the column, then to the top of the next column on the right, until six
numbers have been selected with no repetitions. If a number is selected for which there is no grid,
select the next consecutive random number. For example, if we choose to select the middle three
digits from the five-digit number and we begin in the seventh column, proceeding down column 7
would give us the numbers 46, 119, 75, 22, 95, and 130. The grids corresponding to these
numbers would then be selected for sampling.
(B-18)
-------
15
TABLE 5-2. RANDOM NUMBERS TABLE1
Lin*/ Col.
1
2
3
4
S
6
7
8
9
10
11
12
13
14
IS
16
17
18
19
20
21
22
23
24
25
(1)
10480
22368
24130
42167
37570
77921
99962
96301
89S79
85475
28918
63S53
09429
1036S
07119
S108S
02368
01011
52162
07056
48663
54164
32639
29334
02488
(2)
15011
48573
48360
33093
39975
06907
72905
91977
14342
36857
69578
40961
93969
61129
97338
12765
21382
54092
53916
97628
91245
S8492
32363
27001
33062
(3)
01536
25595
22527
06243
81637
11008
56420
05463
63661
53342
88231
48235
52636
87529
71048
51821
52404
333^2
46369
33787
85828
22421
05597
87637
26834
w
02011
SS393
97265
61680
16656
42751
69994
07972
10281
53988
33278
03427
92737
85689
08178
51259
60288
94904
58586
09998
14346
74103
24200
87308
07351
(5)
81647
30995
76393
07856
06121
27756
96872
18876
17453
53060
70997
49626
88974
48237
77233
77452
89368
31273
23216
42698
09172
47070
13363
S8731
19731
(ซ)
91646
89198
64809
16376
91782
53498
31016
20922
18103
59533
79936
69445
33488
52267
13916
16308
19885
04146
14513
06691
30168
25304
38005
00256
92420
(7)
59179
27982
15179
39440
60468
16602
71194
94595
57740
38867
56865
18663
36320
67689
47564
60756
55322
18594
83149
76988
90229
76468
94342
45834
60952
(8)
14194
53402
24830
53537
81305
70659
18738
56869
84378
62300
05859
72695
17617
93394
81056
92144
44819
29852
98736
13602
04734
26384
28728
15398
61280
(S)
62590
93965
49340
71341
49884
90655
44013
69014
25331
08158
90106
52180
30015
01511
97735
49442
01188
71585
23495
51851
59193
58151
35806
46557
50001
(10)
36207
34095
32081
57004
60672
15053
48840
S004S
12566
17983
31595
20847
08272
26358
85977
53900
65255
85030
64350
46104
22178
06646
06912
41135
67658
(11)
20969
52666
30680
00849
14110
21916
63213
18425
58678
16439
01547
12234
84115
85104
29372
70980
64835
51132
94738
88916
30421
21524
17012
10367
32586
(12)
99570
19174
19855
74917
06927
81825
21069
84903
44947
11458
85590
90511
27156
20285
74461
63990
44919
01915
17752
19509
61666
15227
64161
07684
86679
(13)
91291
39815
63348
97758
01263
44394
10634
42508
05585
18593
91610
33703
30613
29975
28551
75601
05944
92747
35156
2S62S
99904
96909
18296
36188
50720
|1ซ)
90700
99505
58629
16379
54613
42880
12952
32307
56941
64952
78188
90322
74952
89868
90707
40719
55157
64951
35749
58104
32812
44592
22851
18510
94953
1 Ott, L. 1984 An Introduction to Statistical Methods and Data Analysis.
Second Edition, Duxbury Press, Boston
(B-19)
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16
5.2.4 SAMPLING METHOD WITHIN A GRID
Spatial composite sampling will be used to characterize the waste within a grid. Five
subsamples will be taken within each grid from the corners of the grid and the center at a depth of
0.5 ft from the surface. An additional five subsamples will be taken in the same manner from a
depth of 0.5 ft from the pavement. These ten subsamples will then be composited via mixing in a
lined container into a homogenous sample for the various analyses.
(B-20)
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17
6.0 SAMPLING EQUIPMENT AND OPERATION
The following pieces of equipment will be used to perform sampling of the waste placed in
roll-off bins, grit piles, and the rinsate water. The two main requirements for the sampling
equipment are:
The tool must not contribute any chemical contamination to the sample, and
The tool must be capable of collecting a representative sample.
Stainless steel equipment is generally the most durable and is often used for sampling
sludge, sediments, and soils. The following paragraphs below discuss the pieces of sampling
equipment which are recommended for use in sampling the waste and the rinsate water resulting
from decontamination.
6.1 Dipper
A dipper consists of stainless steel, glass, or Teflon beaker constructed with or clamped to
the end of a handle (Figure 6-1). Dippers are used for sampling tanks, bins, outfalls, and
discharge. The following precautions should be observed:
A stainless steel dipper should have a riveted handle not a soldered handle, because
metals from the solder could leach into and contaminate the sample.
Use only Teflon, stainless steel, or glass to sample wastes containing organic
materials.
When using a beaker clamped to a pole, the handle and clamp should be painted
with a 2-part epoxy or other chemically-inert paint when sampling either alkaline
or acidic materials.
(B-21)
-------
18
Telescoping Stainless Steel
(optional)
Length determined based on
necessary reach
FIGURE 6-1. SCHEMATIC DIAGRAM OF DIPPER
(B-22)
-------
19
Procedures for Use:
1. Decontaminate the dipper, clamp, and handle (see Section 6.2).
2. In tanks, turn the dipper so the mouth of the dipper faces down and insert it into
the waste material. Turn dipper right side up when dipper is at desired depth.
Allow dipper to dill completely as shown by the cessation of air bubbles. When
sampling drums, submerge the dipper to the desired depth, allow the beaker to fill.
3. Raise dipper and pour the sample material into an appropriate container.
4. Decontaminate the dipper.
6.2 Stainless Steel Spoon or Scoop
A stainless steel spoon or scoop is the simplest, most direct method for collecting soil
samples. In general, the procedure is used to sample the first three inches of surface soil.
However, samples from greater depths and samples of sludges, sediments and bulk samples may
also employ this technique in some situations.
Procedures for use:
1. Collect and composite samples from the top three inches of soil.
2. Mix the samples in a lined container, then deposit in the appropriate container.
3. Wipe sample containers clean of surface contamination.
4. Place in individual plastic bags in an insulated ice chest with freezer packs if
refrigeration is necessary.
6 J Glass Tube Thief
A hollow glass tube is a simple tool which is used to sample liquids from drums (Figure 6-
2). The advantages of using a glass tube thief include inexpensive cost, ease of disposal, its
availability in variable lengths, and capability to sample a vertical column of waste. The tool
(B-23)
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20
5' - Length depends on
depth of sample
container
FIGURE 6-2. SCHEMATIC DIAGRAM OF GLASS TUBE THIEF
(B-24)
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21
consists of a glass tube, typically between 8 and 16 mm in diameter. This device will be used to
sample the drums containing rinsate from the decontamination of the dipper.
Procedures for use:
1. Decontaminate the glass tube (see Section 6.2)
2. Slowly insert the tube into the waste container. This should be done at a rate
which permits the level of the liquid inside and outside the sampler to remain the
same. If the level of waste in the sampler tube is lower inside than outside, the
sampling rate is too fast and may yield a non-representative sample.
3. When the tube contacts the bottom of the waste container, place a rubber stopper
or attach a squeeze bulb over the exposed end of the sampling tube. The use of a
squeeze bulb improves the ability of a glass tube to retain very viscous fluids
during sampling. It is important that none of the fluid comes in contact with the
rubber squeeze bulb. If using your thumb, ensure your hands are protected by
gloves which are resistant to the chemicals sampled. With the end of the tube
plugged, slowly draw the tube from the waste container. In order to enable the
sampler to retain the fluid in the glass tube, the glass tube may be withdrawn at an
angle such that the thumb may be kept over the end of the glass tube.
4. Place the end of the glass tube in the sample container and remove plug from the
end of the tube.
5. Repeat steps 2 through 5 until the required amount of sample has been collected.
6. Place the contaminated glass tube in a plastic storage tube for subsequent cleaning,
as described in Section 6.2. If used to sample a drum of waste, the glass tube may
be disposed in the drum prior to reseating the bung. Notch the glass with a steel
file to avoid shattering the glass when breaking long pieces.
6.4 Auger and Thin-Wall Tube Sampler
The system consists of an auger bit, a series of drill rods, a "T" handle, and a thin-wall
corer (Figure 6-3). The auger bit is used to bore a hole to the desired sampling depth and is then
withdrawn. The auger tip is replaced with the tube corer, lowered down the borehole, and forced
into the soil at the completion depth. The corer is then withdrawn and the sample collected.
Alternatively, the sample may be recovered directly from the auger. This technique
however, does not provide an "undisturbed" sample as would be collected with a thin-tube
(B-25)
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22
L_L
V
FIGURE 6-3. SCHEMATIC DIAGRAM OF AUGERS AND THIN-WALL TUBE SAMPLER
(B-26)
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23
sampler. When the soil is rocky, it may not be possible to force a thin-tube sampler through the
soil or sample recovery may be poor. Sampling directly from the auger may be the only viable
method. Several auger types are available: bucket type, continuous-flight (screw), and pesthole
augers. Bucket types are good for direct sample recovery, are fast, and provide a large volume of
sample. When continuous flight (screw) augers are used, the sample may be collected directly off
the flights, however, this technique will provide a somewhat unrepresentative sample as the exact
sample depth will not be known. The continuous-flight augers are satisfactory for use when a
composite of the entire soil column is desired. Pesthole augers have limited utility for sample
acquisition as they are designed more for their ability to cut through fibrous, heavily rooted,
swampy areas. In soils where the borehole will not remain open when the tool is removed, a
temporary casing may be used until the desired sampling depth is reached.
Procedures for use:
1. Attach the auger bit to a drill rod extension and attach the "T" handle to the drill
rod.
2. Clear the area to be sampled of any surface debris (twigs, rocks, litter). It may be
advisable to remove the first 8 to 15 cm of surface soil from a 30-cm diameter area
around the drilling location.
3. Begin drilling, periodically removing accumulated soils. This prevents accidentally
brushing loose material back down the borehole when removing the auger or
adding drill rods.
4. After reaching desired depth, slowly and carefully remove auger from boring.
(Note: When sampling directly from auger, collect sample after auger is removed
from boring and proceed to Step 10).
5. Remove auger top from drill rods and replace with a precleaned thin-wall tube
sampler. Install proper cutting tip.
6. Carefully lower corer down borehole. Gradually force corer into soil. Take care
to avoid scraping the borehole sides. Do not hammer the drill rods to facilitate
coring as the vibrations may cause the boring walls to collapse.
7. Remove corer and unscrew drill rods.
8. Remove cutting tip and remove core from device.
(B-27)
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9. Discard top of core (approximately 2.5 cm) which represents material collected by
the core before penetrating the layer in question. Place remaining core into sample
container.
10. Verify that a Teflon liner is in the cap if required. Secure the cap tightly.
11. Label the sample bottle with the appropriate sample tag. Label the tag carefully
and clearly, addressing all the categories or parameters. Complete all chain-of-
custody documents and record in the field logbook.
(B-28)
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25
7.0 SAMPLE COLLECTION AND PRESERVATION
7.1 Sample Collection
The following procedures will be followed for sampling waste from waste piles:
1. Identify the specific pile which will be sampled.
2. Construct the sampling grid as described in Section 5.2.3.
3. Go to the random numbers table (Table 5-2) and select six numbers. Each number
represents the grid unit which will be sampled.
4. Use the appropriate instrument to obtain the sample. Follow the recommended
procedures for use as stated in Section 6.0.
5. Collect a composite sample from each randomly selected grid. Composite
sampling will consist of collecting five subsamples at two different depths (0.5 ft
from the surface and 0.5 ft from the pavement) from each corner of the randomly
selected grid in addition to one sample from the center for a total of 10
subsamples. The samples will then be composited in a tray and mixed using a
stainless steel or Teflon spoon. The composited sample will be placed in
precleaned polyethylene bottles for analysis.
6. From each sampling point, split the composite sample into a 500 cc subsample for
the analytical laboratory and a 1000 cc subsample to archive. From 1 out of 10
sampling points, reserve 500 cc of the composite sample to send to a separate
analytical laboratory. No preservation is required for samples. Rinsate blanks
must be preserved with a solution of nitric acid. This can be provided in the
sample jar by the analytical laboratory. Holding time for the samples is 6 months,
unless sampling for mercury which has a holding time of 28 days.
7. The collection of the sample does not require filling the sample jar in any special
manner.
8. Discard the outer latex gloves after each sample into an appropriate container and
then replace them for the next sampling event.
9. For the rinsate blank (which will be required once for every twenty samples),
simply run deionized water over the sampling instrument after it has been
decontaminated.
(B-29)
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10. The sampler must pay attention while filling the sample bottle for the rinsate blank
due to the fact that the sample bottle will have a preservative already in it. If the
bottle were to be overfilled during collection, some of the preservative would be
lost resulting in insufficient preservative remaining in the bottle and an inaccurate
analysis.
7.2 Sample Preservation
No preservatives will be required for the sampling of the waste itself. Only the rinsate
blank (equipment washing) will require a preservative of nitric acid in order to lower the pH of the
sample below 2. The analytical laboratory can provide the sample containers containing the
appropriate quantities of preservative for this. Caution should be exercised when these samples are
collected to prevent accidental exposure by splashing.
(B-30)
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27
8.0 PERSONAL PROTECTIVE EQUIPMENT AND DECONTAMINATION
8.1 Personal Protective Equipment
8.1.1 SAMPLING
The following personal protective equipment shall be worn during the sampling of the
waste:
Tyvek suit
Latex gloves (two pairs)
Dust protector
Safety glasses with splash shields (only necessary for when rinsate blanks
(equipment washes) are collected).
8.10, CLEANING OPERATIONS (DECONTAMINATION)
The following personal protective equipment shall be worn during all cleaning operations
for sampling equipment:
Safety glasses with splash shields
Latex gloves (water decontamination)
Neoprene or nitrile gloves (when using solvents)
Tyvek or cloth coveralls
8.2 Decontamination
Decontamination (cleaning) of sampling devices prior to and after use is required.
Decontamination is important so that material from a previous sampling event does not contaminate
subsequent samples. Decontamination should be performed as follows:
(B-31)
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28
Scrub the sampling tool with a brush in a laboratory-grade detergent (Alconox,
Liquinox, or the equivalent) and tap water solution
Rinse with water
Rinse again with deionized water or the equivalent
If sampling for organic contamination, rinse a final time with pesticide-grade
isopropanol or pesticide-grade acetone or methanol (a minimal amount is necessary
for rinsing and this should be conducted under a fume hood or hi the open, but
never in a closed room without adequate ventilation)
Allow sampling tool to air dry
Wrap in aluminum foil or other similar protective covering to avoid contamination
before the next use
No eating, smoking, drinking, chewing, or any hand to mouth contact will be
permitted during cleaning operations.
The following are cleaning procedures for the glass tube thief:
Wash thoroughly with laboratory detergent and hot water using a brush to remove
any paniculate matter or surface film
Rinse thoroughly with hot tap water
Rinse with at least a 10 percent nitric acid solution
Rinse thoroughly with tap water
Rinse thoroughly with deionized water
Rinse twice with solvent and allow to air dry for at least 24 hours
Wrap completely with aluminum foil to prevent contamination during storage
The following are cleaning procedures for stainless steel sampling equipment:
Wash thoroughly with laboratory detergent and water with a brush
Rinse thoroughly with tap water
Rinse thoroughly with deionized water
If sampling for organic contamination, rinse twice with solvent and allow to air dry
(B-32)
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29
Wrap completely with aluminum foil
Rinse with tap water after use in the field
Decontamination wash waters should be collected and containerized separately from solvent
rinses in a 55-gallon drum. Since potentially hazardous wastes are being rinsed from sampling
equipment, the collected rinse waters should be handled and sampled for hazardous constituents
using a glass tube thief prior to disposal. The storage area should have a drum staged for the
disposal of rinse waters and one for disposal of solvents. Upon filling the rinse water drum, it
should be sampled for metals to determine if it must be disposed of as a hazardous waste or down
the industrial drain. The contents of the solvent drum may be recycled.
(B-33)
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30
9.0 SAMPLE CUSTODY, LABELING, PACKAGING, AND TRANSPORTATION
9.1 Sample Custody
The purpose of a sample chain-of-custody is to document the possession of a sample from
the time of collection, through all transfers of custody, until it is delivered to the analytical
laboratory. This requires that a form (Figure 9-1) be filled out in permanent ink and sent along
with the samples to the storage area. This form will contain the following minimum information:
Sample number
Date and time of collection
Shipyard location
Waste type
Signature of collector
Preservation
Container type
Analysis request
Appropriate notations relative to sample integrity and handling practices
Signature of all persons involved in the chain of possession
Inclusive dates and times of possession
9.2 Sample Labeling
A sample label is applied to a sample container before a sample of waste is collected
(Figure 9-2). The label will be completely filled out with permanent ink. It will contain the
following information:
(B-34)
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31
0
Batielle
Form No..
CHAIN OF CUSTODY RECORD
Culumbut
Pfoj No.
Piojtct Till.
SAMPLERS:(Slgnttural
DATE
TIME
SAMPLE I.D.
SAMPLE TYPE <
EVS
Rtnurki
RdinquistMd by: (Slgiutun)
Rซcปlvซd by: (Signalura)
Rซllnqu!thซd by: (Sigiutun)
DatefTlnn
Rซdlved by:
(Signซtur*|
Rtllnqulihซd by: (Slgnitura)
Diu/TlnM
Rtcalnd by:
(Slgiutur*)
Rillnquislud by: (Slgnitur.l
Datt/Tim*
Rtc.lv.d by:
(Slgnatur*)
R*llM|uldiซd by: (Slgntluct)
DiM/Tlim
Rioilxd foe LabMitory by:
(Sigiutunl
DaU/Tlim
Rซnurkซ
Pป3ซ.
of.
FIGURE 9-1. CHAIN-OF-CUSTODY SHEET
(B-35)
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SAMPLE NO.
SAMPLE MATRIX
SAMPLE PRESERVATIVE
SAMPLING LOCATION
ANALYSIS REQUIRED
INITIALS OF SAMPLER &
TIME AND DATE OF COLLECTION
FIGURE 9-2. SAMPLE LABEL
(B-36)
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Sample number
Date and hour the sample was taken
Sampler's initials
Sampling site
Tests required, if known
Preservative used, if any
9.3 Sample Packaging
The laboratory will typically provide all sample containers, preservatives, and packaging
for transportation of samples. Proper preparation of sample containers for transport to the
laboratory is essential to prevent breakage of containers and spillage of potentially hazardous
material. The following steps will be taken during sample packaging:
Ensure sample container is labeled correctly
After sampling activities are complete, clean the outer surface of all sample
containers
Wrap each glass container with plastic insulating material (bubble wrap) and
enclose in a plastic bag to prevent contact with other sample containers. Plastic
containers also should be placed into bags, however, bubble wrap is not needed.
Place sample containers in thermally-insulated, rigid ice chests which contain ice or
reusable ice packs if the temperature must be held at 4ฐC. If the sample does not
need to be held at 4ฐC, an ice chest is not required. However, an ice chest is a
lightweight, rigid, and easily secured container in addition to being thermally
efficient.
Ensure the chain-of-custody forms are filled out and secure the inside the sample
chests. Packers should retain one copy.
(B-37)
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9.4 Sample Transportation
Transport samples to the laboratory as soon as possible after collection.
(B-38)
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10.0 SAMPLE QUALITY ASSURANCE AND QUALITY CONTROL
10.1 Rinsate Blanks (Equipment Washes)
Equipment washes serve as checks of field decontamination procedures. They are obtained
after final wash and decontamination of equipment by pouring reagent-grade water
into/through/over a decontaminated piece of sampling equipment. The water is collected in
appropriate sample containers and transported to the laboratory with other samples. The equipment
blanks are analyzed in the same manner as the field samples. Equipment blanks should be
collected prior to each sampling event at each sampling site. However, once good equipment
decontamination technique (equipment blanks are "clean") has been demonstrated, the frequency of
equipment wash samples may be reduced to an occasional basis. Initially, one rinsate blank
(equipment wash) will be collected for every twenty samples taken.
10.2 Laboratory Quality Control and Certification
Laboratory quality control procedures are instituted to ensure the reliability of analytical
data obtained throughout the sampling effort. Procedures include the analysis of laboratory
samples to measure the accuracy and precision of laboratory procedures. A laboratory duplicate
should typically be analyzed one time in twenty samples. Any analytical laboratory used should
have current certification from the state of California for performing all the necessary chemical
analyses.
10.2.1 MATRIX SPIKE ANALYSIS
Matrix spike analyses are performed to assist the accuracy of laboratory methods. Spiked
samples are used to determine if chemical interferences are occurring. One spike analysis per
sample set is generally adequate.
(B-39)
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10.2.2 MATRIX SPIKE DUPLICATES
Matrix spike duplicates are used to evaluate the reproducibility of the analytical
procedures. A field sample is analyzed and the results are compared to the original matrix spike
sample test results. In general, this is only necessary for large numbers of samples (>30).
10.2.3 METHOD BLANK TESTS
Method blank tests are performed in the laboratory by analyzing distilled, deionized water
for all analytical methods employed by the laboratory. Method blanks are analyzed for each
matrix to verify that laboratory-induced contaminants are identified and distinguished from
environmental contaminants of concern.
(B-40)
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APPENDIX C
GLOSSARY OF SOLIDIFICATION/STABILIZATION TERMS AND ABBREVIATIONS*
AA - atomic absorption spectroscopy, a microcharacterization method.
ANC - Acid Neutralization Capacity, a chemical test.
ANS - American Nuclear Society.
ANSI - American National Standards Institute.
ANSI/ANS/16.1 - American Nuclear Society test 16.1, a leaching test.
AOC - area of contamination.
APC - air pollution control.
API - American Petroleum Institute.
ARAR - applicable or relevant and appropriate requirement. These are cleanup
standards, standards of control, and other substantive requirements, criteria,
or limitations promulgated under federal, state, or local environmental laws
or facility siting laws that: (1. applicable) specifically address a hazardous
substance, pollutant, contaminant, remedial action, location, or other
circumstance found at a CERCLA site or (2. relevant and appropriate) address
problems or situations similar to those encountered at a CERCLA site (40 CFR
300.5, pp. 7 and 12).
ASTM - American Society for Testing and Materials.
absorption - assimilation of fluids into interstices (ASTM D 653, p. 129).
acidity - the quantitative capacity of materials to react with hydroxyl ions.
additives - materials included in the binder to improve the S/S process.
Examples of some types of additives are: (1) silicates or other materials
that alter the rate of hardening, (2) clays or other sorbents to improve
retention of water or contaminants, or (3) emulsifiers and surfactants that
improve the incorporation of organic compounds.
adsorption - attraction of solid, liquid, or gas molecules, ions, or atoms to
particle surfaces by physiochemical forces. The adsorbed material may have
different properties from those of the material in the pore space at the same
temperature and pressure due to altered molecular arrangement (after ASTM
D 653 and Parker, 1989, p. 37).
advection - unidirectional, progressive bulk movement, such as water under the
influence of a hydraulic gradient.
alkalinity - the quantitative capacity of aqueous media to react with hydrogen
ions.
*Acronyms and abbreviations are listed at the beginning of each letter of the
alphabet.
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anion an Ion that is negatively charged.
asphalt a brown, black, hard, brittle, or plastic bituminous material
composed principally of hydrocarbons. It is found in nature or can be
prepared by pyrolysis of coal tar, certain petroleums, and lignite tar. It
melts on heating and is insoluble in water but soluble in gasoline.
BDAT Best Demonstrated Available Technology.
BNA base, neutral, and acid (organic) compounds, a chemical analysis
identification.
bentonite a clay formed from volcanic ash decomposition and largely composed
of montmorillonite and beidellite. Usually characterized by high swelling on
wetting.
binder a cement, cementlike material, or resin (possibly in conjunction with
water, extender, or other additives) used to hold particles together.
bitumen naturally occurring or pyrolytically obtained dark or black colored,
tarry hydrocarbons consisting almost entirely of carbon and hydrogen, with
very little oxygen, nitrogen, or sulfur.
buffer a solution selected or prepared to minimize changes in pH (hydrogen
ion concentration). Also known as buffer solution.
CAA Clean Air Act.
Cal WET California Waste Extraction Test, a leaching test.
CERCLA Comprehensive Environmental Response, Compensation, and Liability
Act.
CERCLA hazardous substance any substance, pollutant, or contaminant as
defined in CERCLA sections 101(14) and 101(33), except where otherwise noted
in the Hazard Ranking System (see 40 CFR 302.4).
CERCLA hazardous wastestream any material containing CERCLA hazardous
substances that was deposited, stored, disposed, or placed in or that migrated
to a site being evaluated by the HRS; any material listed in the NPL.
CERCLA waste a term with no regulatory meaning that is often used as a
shortened form of CERCLA hazardous wastestream.
CFR Code of Federal Regulations.
CLP Contract Laboratory Procedures.
COE U.S. Army Corps of Engineers.
CRN Core Research Needs for Containment Systems.
CSH Calcium Silicate Hydrate.
CWA- Clean Water Act.
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CHARP-Coal Waste Artificial Reef Program.
cation a positively charged atom or group of atoms.
cement a mixture of calcium aluminates and silicates made by combining lime
and clay while heating.
characteristic waste see RCRA characteristic waste
clay fine-grained soil or the fine-grained portion of soil that can be made
to exhibit plasticity (putty-like properties) within a range of water contents
and that exhibits considerable strength when air-dry.
colloid the phase of a colloidal system made up of particles having
dimensions of 1 to 1000 nanometers and which is dispersed in a different
phase.
colloidal system an intimate mixture of two substances, one of which, called
the dispersed phase (or colloid), is uniformly distributed in a finely divided
state through the second substance, called the dispersion medium.
compressive strength (unconfined or uniaxial compressive strength) the load
per unit area at which an unconfined cylindrical specimen of soil or rock will
fail in a simple compression test. Commonly the failure load is the maximum
that the specimen can withstand in the test.
contaminant typically undesirable minor constituent that renders another
substance impure.
corrosiveness characteristic exhibiting the hazardous characteristic of
corrosivity due to extreme pH or failing under the test conditions defined in
40 CFR 261.22.
DLT Dynamic Leach Test, a leaching test where the specimen is exposed to an
actual or simulated flow of the leachant.
DQO Data Quality Objective, a planned quantitative measure of precision,
accuracy, and completeness of data.
ORE destruction-removal efficiency. The combined efficiencies of one or
more processes intended to reduce the target contaminant(s). The ORE may be
expressed as a ratio or percentage.
density, apparent (of solids and liquids) the mass of a unit volume of a
material at a specified temperature. Only the volume that is impermeable is
considered.
density, bulk (of solids) the mass of a unit volume of the material at a
specified temperature.
diffusion movement of molecules towards an equilibrium driven by heat or
concentration gradients (mass transfer without bulk fluid flow).
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diffusivity diffusion coefficient, the weight of material, in grams,
diffusing across an area of 1 square centimeter in 1 second due to a unit
concentration gradient.
dimensional stability the ability of the solidified/stabilized waste to
retain its shape.
disposal facility a facility or part of a facility at which waste is
intentionally placed into or on any land or water, and at which waste will
remain after closure.
durability the ability of solidified/stabilized wastes to resist physical
wear and chemical attack over time.
ECN Energieonderzoek Centrum Nederland (Netherlands Energy Research
Foundation).
EDXA energy dispersive X-ray analysis, a microcharacterization method.
EE/CA Economic Evaluation/Cost Analysis, CERCLA technology screening process
for a removal action 40 CFR 300.415.
ELT Equilibrium Leach Test, a leaching test where, under the conditions of
the test, an equilibrium between the specimen and the leachant is attained.
EP Tox Extraction Procedure Toxicity Test, a regulatory leaching test used
since 1980 to determine if a waste is toxic (40 CFR 261, Appendix II).
embedment the incorporation of waste masses into a solid matrix before
disposal.
emulsifier a substance used to produce an emulsion of two liquids which do
not naturally mix.
emulsion a colloidal mixture of two immiscible fluids, one being dispersed
in the other in the form of fine droplets.
ettringite a mineral composed of hydrous basic calcium and aluminum sulfate.
The formula for ettringite is Ca6Al2(S04)3(OH)12-26 H20.
extender an additive whose primary function is to increase the total bulk of
the S/S-treated waste.
F6D flue gas desulfurization, a pollution abatement process.
FR Federal Register.
FS Feasibility Study, a study undertaken to develop and evaluate options for
a treatment process.
FTIR Fourier transform infrared spectroscopy, a microcharacterization
method.
FY fiscal year.
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fly ash the finely divided residue from the combustion of ground or powdered
coal and which is transported from the firebox through the boiler by flue gas.
free water water that i s free to move through a soi1 or rock mass under the
influence of gravity.
freeze/thaw cycle alternation of a sample temperature to allow determination
of weight loss and visual observation of sample disintegration resulting from
phase change from water to ice.
GC/MS gas chromatography/mass spectrometry.
grout as used in soil and rock grouting, a material injected into a soil or
rock formation to change the physical characteristics of the formation. The
term "grout" is not used in this document but is frequently encountered in the
S/S industry as a synonym for the term "binder."
HCB hexachlorobenzene.
HRS Hazard Ranking System, the primary mechanism for considering sites for
inclusion on the NPL.
HSL Hazardous Substance List, a list of designated CERCLA hazardous
substances as presented in 40 CFR 302.4.
HSWA Hazardous and Solid Waste Amendments of 1984.
hazardous characteristics ignitable, corrosive, reactive, and toxic as
defined in 40 CFR Part 261.10.
hazardous waste see RCRA hazardous waste, CERCLA hazardous substance, and
CERCLA hazardous wastestream.
heat of hydration (in S/S reactions) the heat generated due to the reaction
of cementitious or pozzolanic materials with water.
hydrate a compound containing structural water.
ICP inductively coupled plasma atomic emission spectroscopy.
ignitability characteristic exhibiting the hazardous characteristic of
ignitability as defined in 40 CFR 261.21.
immobilization the reduction in the ability of contaminants to move through
or escape from S/S-treated waste.
incineration a treatment technology involving destruction of waste by
controlled burning at high temperatures.
inhibitor a material that stops or slows a chemical reaction from occurring.
Used in this document to apply to stopping or slowing of the setting of S/S-
treated material.
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Interference (S/S) an undesirable change In the setting of the S/S material
resulting in lower strength, poorer leach resistance, or evolution of noxious
or hazardous gases, or other degradation of the S/S-treated material.
1on an atom or molecule which by loss or gain of one or more electrons has
acquired a net electric charge.
Interstitial see pore water.
kaolin a variety of clay containing a high percentage of kaolinite.
kaolinite a common clay mineral having the general formula Al2(Si205)(OH4).
kiln a heated and usually rotating enclosure used for drying, burning, or
firing materials such as ore or ceramics. In this document "kiln" typically
refers to a kiln used for production of lime or cement.
kiln dust fine particulate by-product of cement production or lime
calcination.
LDR Land Disposal Restriction.
LIHB Lime Injection Multistage Burner.
LRT Liquid Release Test.
Teachability a measure of release of constituents from a waste or
solidified/stabilized waste. Leachability is one measure of the mobility of a
constituent. High Teachability means high constituent mobility.
leachant liquid that comes in contact with a material either from natural
exposure (e.g., water in a disposal site) or in a planned test of
Teachability. The typically used leachants are pure distilled water or water
containing salts, acids, or both.
leachate any liquid, including any suspended components in the liquid, that
has soaked, percolated through, or drained from material during leaching.
leaching the release of constituents from a solid through contact with the
leachant. The leaching may occur by either natural mechanisms at waste sites
or as part of a laboratory leaching test.
leaching agent leachant.
leaching rate the amount of a constituent of a specimen or solid waste form
which is leached during a unit of time (usually normalized by sample volume,
area, or weight).
leaching resistance the inverse of Teachability. High leach resistance
means low contaminant mobility.
leaching test exposure of a representative sample of contaminated waste,
S/S-treated waste, or other material to a leachant under controTTed conditions
to measure the release of constituents.
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lime specifically, calcium oxide (CaO); also loosely, a general term for the
various chemical and physical forms of quicklime, hydrated lime, and hydraulic
hydrated lime.
listed waste see RCRA listed waste.
long-term stability the ability of solidified/stabilized wastes to maintain
their properties over time while exposed to the environment.
MCL maximum concentration limit.
HEP Multiple Extraction Procedure, a leaching test in which the sample is
repeatedly leached with fresh batches of leachant.
MSDS-Material Safety Data Sheet.
NSW municipal solid waste.
HWEP Monofilled Waste Extraction Procedure, a leaching test.
macroencapsulation a process of encasing a mass of solid or S/S-treated
waste in a protective layer, such as bitumen (thermoplastic).
meq mi 11i equi valent.
mlcroencapsulation containment of the contaminants on a microscopic or
molecular scale.
mlcrostructure the structure of an object or material as revealed by a
microscope at a magnification over 10 times.
mixer machine employed for blending the constituents of grout, mortar, or
other mixtures.
modified clays clays (such as bentonite) that have been modified by ion
exchange with selected organic compounds that have a positive charged site
(often a quarternary amine), hence rendering the clay/organo complex
hydrophobic.
monolith a free standing solid consisting of one piece.
monomer a simple molecule which is capable of combining with a number of
like or unlike molecules to form a polymer.
montmorillonite a group of clay minerals characterized by a weakly bonded
sheet-like internal molecular structure; consisting of extremely finely
divided hydrous aluminum or magnesium silicates that swell on wetting, shrink
on drying, and have ion exchange capacity.
multimedia air, land, and water.
NAAQS National Ambient Air Quality Standards.
NCP National Oil and Hazardous Substances Contingency Plan, provides the
organizational structure and procedures for preparing and responding to
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discharges of oil and releases of hazardous substances, pollutants, and
contaminants (40 CFR 300.1).
NESHAP National Emission Standards for Hazardous Air Pollutants.
NMR nuclear magnetic resonance spectroscopy, a microcharacterization method.
NPL-National Priorities List, list of CERCLA sites (40 CFR Part 300
Appendix B).
NRC U.S. Nuclear Regulatory Commission.
NYSC-HWM New York State Center for Hazardous Waste Management.
OAQPS-Office of Air Quality Planning and Standards (of the U.S. EPA).
OSHA Occupational Safety and Health Act; Occupational Safety and Health
Administration.
PAH polynuclear aromatic hydrocarbon.
PCB polychlorinated biphenyl.
PFT Paint Filter Test, a physical characterization test.
ppb part per billion.
ppm part per million.
PRP - potentially responsible party, potentially liable for the contamination
and cleanup of CERCLA sites.
percolation movement of water under hydrostatic pressure or gravity through
the smaller interstices of rock, soil, wastes, or S/S-treated wastes.
performance criterion a measurable performance standard set for an
individual property or parameter.
performance indicator an easy-to-measure property or parameter selected to
characterize the S/S process or S/S-treated waste.
permeability a measure of flow of a fluid through the tortuous pore
structure of the waste or S/S-treated waste. It is expressed as the
proportionality constant between flow velocity and the hydraulic gradient. It
is a function of both media. If the permeating fluid is water, the
permeability is termed as hydraulic conductivity.
phase (of a material) a region of a material that is physically distinct and
is homogeneous in composition and morphology.
polymer a chemical with repetitive structure formed by the chemical linking
of single molecules (monomers).
pore a small cavity or void in a solid.
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pore size distribution variations in pore sizes in solids; each material has
its own typical pore size distribution and related permeability.
pore water water contained in voids in the solid material.
porosity the ratio of the aggregate volume of voids or interstices to the
total volume of the medium.
Portland cement a hydraulic cement produced by pulverizing clinker
consisting essentially of hydraulic calcium silicates, usually containing one
or more of the forms of calcium sulfate.
pozzolan a siliceous or siliceous and aluminous material, which in itself
possesses little or no cementitious value but will, in finely divided form and
in the presence of moisture, chemically react with calcium hydroxide at
ordinary temperatures to form compounds with cementitious properties. The
term is derived from an early source of natural pozzolanic material, Pozzuoli,
Italy.
QA/QC Quality Assurance/Quality Control.
QAPjP Quality Assurance Project Plan.
QAPP Quality Assurance Program Plan.
3Rs recovery, reuse, and recycle.
RCRA Resource Conservation and Recovery Act.
RCRA characteristic waste any solid waste exhibiting a characteristic of
ignitability, corrosivity, reactivity or toxicity, as defined in 40 CFR 261,
Subpart C.
RCRA hazardous waste- any RCRA solid waste, as defined by 40 CFR 261.3, that
is not excluded from regulation under 40 CFR 261.4 and that meets any one of
the characteristic or listing criteria (including mixtures) described in
40 CFR 261.3(a)(2). For more detail, see 40 CFR 260, Appendix I.
RCRA listed waste any solid waste listed in 40 CFR 261, Subpart D; or a
mixture that contains a solid waste listed in 40 CFR 261, Subpart D that has
not been excluded under the provisions of 40 CFR 261.3 in accordance with 40
CFR 260.20 or 40 CFR 260.22.
RCRA solid waste any garbage, refuse, or sludge; or any solid, liquid, semi-
solid or contained gaseous material that is: (1) discarded, (2) no longer to
be used for its original purpose, or (3) a manufacturing or mining by-product
and is not excluded by the provisions of 40 CFR 261.4(a). For more detail,
see 40 CFR 260, Appendix I. Also note that the definition of solid waste
includes materials that are not "solids" in the normal sense of the word.
RI Remedial Investigation, a process undertaken by the lead agency to
determine the nature and extent of the problem presented by a CERCLA site (40
CFR 300.430(d)).
RI/FS Remedial Investigation/Feasibility Study, see RI or FS.
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ROD-Record of Decision, a document prepared to explain and define the final
remedy selected for a CERCLA site (40 CFR 300.430 (f)(4)(i)).
RP Responsible Party, persons or corporate entities found to be responsible
for contamination and cleanup at a CERCLA site.
RPM-Remedial Project Manager, the official designated by the lead agency to
coordinate, monitor, or direct remedial or other response actions under
subpart E of the NCP (40 CFR 300.5).
RREL Risk Reduction Engineering Laboratory (of the U.S. EPA).
reactivity characteristic - exhibiting the hazardous characteristic of
reactivity as defined in 40 CFR 261.23.
redox abbreviation for oxidation-reduction, now accepted as a word.
residual liquid free liquid remaining in the S/S-treated waste after
treatment.
SARA Superfund Amendments and Reauthorization Act.
SDWA- Safe Drinking Water Act.
SCE sequential chemical extraction, a leaching test with a variety of
aqueous chemicals used sequentially to characterize the contaminant bonding.
SEN scanning electron microscopy, a microcharacterization method.
SET Sequential Extraction Test, a leaching test with a series of sequential
acid extractions used to determine the sample buffering capacity.
SITE Superfund Innovative Technology Evaluation.
SRS Separation and Recovery Systems, Inc.
S/S solidification/stabilization, used in this document to encompass the
variety of processes that may contribute to increased physical strength and/or
contaminant immobilization.
S/S-treated waste a waste liquid, solution, slurry, sludge, or powder that
has been converted to a stable solid (granular or monolithic) by an S/S
treatment process.
STLC Soluble Threshold Limit Concentration, limit applied to Cal WET
leaching results (Ca 22 California Code of Regulations 66699).
silica fume very fine silica dust produced by condensation of silica fumes.
sludge in this document, sludge means a viscous semi-solid or fluid
containing contaminants requiring treatment. The regulatory definition is any
solid, semi-solid, or liquid waste generated from a municipal, commercial, or
industrial wastewater treatment plant, water supply treatment plant, or air
pollution control facility with the exception of specific exclusions such as
the treated effluent from a wastewater treatment plant (40 CFR 260.10).
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solid waste see RCRA solid waste.
solidification a process in which materials are added to the waste to
convert it to a solid or to simply improve its handling and physical
properties. The process may or may not involve a chemical bonding between the
waste, its contaminants, and the binder. In solidification, the mechanical
binding of contaminants can be on the microscale (microencapsulation,
absorption, or adsorption) or the macroscale (macroencapsulation).
solubility the maximum concentration of a substance dissolved in a solvent
at a given temperature.
solubility product a type of simplified equilibrium constant defined for and
useful for equilibria between solids and their respective ions in solution.
solution a single, homogeneous phase of liquid, solid, or gas in which a
solute is uniformly distributed.
sorption a general term used to encompass the processes of adsorption,
absorption, desorption, ion exchange, ion exclusion, ion retardation,
chemisorption, and dialysis.
stability the stabilization and solidification provided by an S/S process.
stabilization a process by which a waste is converted to a more chemically
stable form. The term may include solidification, but also includes chemical
changes to reduce contaminant mobility.
storage the holding of hazardous waste for a temporary period, at the end of
which the hazardous waste is treated, disposed of, or stored elsewhere (40 CFR
260.10).
surfactant surface-active agent, a soluble compound that reduces the surface
tension of liquids, or reduces interfacial tension between two liquids or a
liquid and a solid.
TCE trichloroethylene.
TCLP Toxicity Characteristic Leaching Procedure, the primary leach testing
procedure required by 40 CFR 261.24 and the most commonly used test for degree
of immobilization offered by an S/S process.
IDS total dissolved solids.
TOC total organic carbon, a chemical analysis.
TRD Technical Resources Document.
TSCA Toxic Substances Control Act.
TSD treatment, storage, and disposal facility (RCRA).
TTLC Total Threshold Limit Concentration, limit applied to Cal WET leaching
results (Ca 22 California Code of Regulations 66699).
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TWA Total Waste Analysis, total concentration of priority pollutants,
organics, and metals in the waste
technology screening the logistic of technology selection, evaluation, and
optimization. A treatment technology properly screened prior to full-scale
implementation has the highest probability of success in the field.
thermoplastic resin an organic polymer with a linear macromolecular
structure that will repeatedly soften when heated and harden when cooled; for
example styrenes, acrylics, cellulosics, polyethylenes, vinyls, nylons, and
fluorocarbons.
thermosetting resin an organic polymer that solidifies when first heated
under pressure, and which cannot be remelted or remolded without destroying
its original characteristics; for example epoxies, melamines, phenolics, and
ureas.
tortuosity the ratio of the length of a sinuous pathway between two points
and the length of a straight line between the points.
toxicity characteristic exhibiting the hazardous characteristic of toxicity
as defined in 40 CFR 261.24.
transportation the movement of hazardous waste by air, rail, highway, or
water (40 CFR 260.10).
treatability study a study in which hazardous waste is subjected to a
treatment process to determine: (1) whether the waste is amenable to the
treatment process, (2) what pretreatment (if any) is required, (3) the optimal
process conditions needed to achieve the desired treatment, (4) the efficiency
of a treatment process for a specific waste or wastes, or (5) the
characteristics and volumes of residuals from a particular treatment process
(40 CFR 260.10).
treatment any method, technique, or process, including neutralization,
designed to change the physical, chemical, or biological character or
composition of any hazardous waste so as to neutralize such waste, or so as to
recover energy or material resources from the waste, or so as to render such
waste non-hazardous, or less hazardous; safer to transport, store, or dispose
of; or amenable for recovery, amenable for storage, or reduced in volume (40
CFR 260.10).
triaxial compression compression caused by the application of normal stress
in lateral directions (ASTM D 653, p. 152).
triaxial shear test (triaxial compression test) a test in which a
cylindrical specimen encased in an impervious membrane is subjected to a
confining pressure and then loaded axially to failure.
UCS unconfined compressive strength, the load per unit area at which an
unconfined cube or cylindrical specimen of material will fail in a simple
compression test without lateral support.
U.S. DOE United States Department of Energy.
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J.S. DOT United States Department of Transportation.
U.S. EPA United States Environmental Protection Agency.
VOC volatile organic compound, an organic compound with a low boiling point.
WDW wet/dry weathering.
WET see Cal WET, a leaching test.
WTC Wastewater Technology Centre, formerly of Environment Canada.
wet/dry cycle alternation of soaking and drying a sample to allow
determination of material loss and visual observation of sample disintegration
resulting from repeated soaking and drying cycles.
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