United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-83-016 April 1983
v>ERA Project Summary
Effects of Organic Solvents on the
Permeability of Clay Soils
K. W. Brown and D. C. Anderson
This laboratory study examines the
suitability of using water alone to test
the permeability of compacted clay
liners of hazardous landfills and surface
impoundments. Traditional permeabil-
ity tests using water alone qualified four
clay soils for lining hazardous waste
facilities on the basis of low
permeabilities (1 x 10~7 cm sec-1). But
these same clays underwent large
permeability increases when tested
with basic, neutral polar, and neutral
nonpolar organic fluids. They also
showed potential for substantial per-
meability increases when exposed to
concentrated organic acids.
This Project Summary was developed
by EPA's Municipal Environmental
Research Laboratory. Cincinnati, OH.
to announce key findings of the
research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Knowledge of the permeability- a main
criterion used to judge whether a
compacted soil liner will prevent
movement of leachates below or adjacent
to a disposal facility-is needed to
determine a liner's suitability for use as a
containment system. However, little
information is available concerning the
impact of waste fluids on the permeability
of clay liners. Also, no simple perme-
ability test method has been developed
that is suitable for use with a range of
possible waste fluids.
The report begins with a brief state-of-
the-art review of the use of clay liners in
hazardous waste landfills and surface
impoundments. The review examines the
physical classes of fluid-bearing
hazardous wastes, the leachates they
generate, and the predominant fluids in
these leachates. Available information is
also summarized on native soils used to
construct compacted clay liners.
A description is then given of the
comparative permeability testing that
was conducted with four compacted clay
soils and a wide range of possible waste
fluids. Potential interactions between
waste fluids and clay liners are evaluated,
and the permeability of typical clay soils is
examined.
State-of-the-Art Review
Overview
RCRA regulations concerning
hazardous waste disposal facilities
(effective November 19, 1981) prohibit
the landfill disposal of drums containing
free liquids. Furthermore, the regulations
prohibit the disposal of bulk liquids in
hazardous waste landfills unless the
landfill has an "adequate liner" and a
"leachate collection .and removal
system."
Hazardous wastes placed in landfills
can be categorized into the following four
physical classes: aqueous-inorganic,
aqueous-organic, organic, and sludges.
This categorization was used, for
example, in a report to Congress in 1974.
Leachate Generated by
Hazardous Waste
Two leachates should be investigated
to determine the effects of a waste on the
permeability of a liner. The first, or
primary leachate, is made up of all the
flowable constituents of the waste-the
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fluids (solvents) and the dissolved compo-
nents (solutes). The secondary leachate is
that generated from water percolating
through a disposal facility, and it consists
of water, the waste solvent, and the
solutes.
The solvent phase of the leachate
usually has the greatest impact on clay
liner permeability. However, nearly all
literature describing the permeability of
clay liners consider water only as the
leachate. Water is viewed as the carrier
fluid, and organic chemicals are
considered to be present only in trace
quantities. Such is not always the case,
however, since many wastes have an
organic fluid phase.
In addition to the fluid and dissolved
phases of leachates, a suspended phase
may also be present (e.g., inorganic
pigments suspended in an organic fluid
saturated with paint).
Fluids in Hazardous Waste
Leachate
Organic fluids may be classified into
four groups: Organic acids, organic
bases, neutral polar organics, and neutral
nonpolar organics. The most important
fluid property affecting soil permeability
is viscosity. Any slow-viscosity fluid is
leachate and able to extract organic
components from otherwise dry waste.
Organic Acids
Organic acids are organic fluids with
acidic functional groups such as phenols
and carboxylic acids. These fluids may
react with the dissolved clay soil
components through a variety of
mechanisms. Anaerobic decomposition
byproducts are an ever present source of
organic acids in waste impoundments.
Organic Bases
Though it is not clear whether organic
bases can dissolve certain components of
clay minerals, they have been implicated
in dissolving clay liners. Adsorption of
organic bases by clays is rapid and nearly
irreversible, and it yields a porous matrix
that is structurally stable under either
aqueous or organic fluid flow.
Neutral Polar Organics
Polar compounds compete with water
for adsorption sites on the negatively
charged clay surfaces. The adsorption of
an organic fluid to clay changes the
behavior of the latter, including possibly
its permeability. Examples of such polar
compounds are alcohols, aldehydes,
ketones, glycols, and alkyl halides.
Neutral polar organic fluids tend to
reduce the surface tension of water, and
hence the viscosity. The decreased
viscosity would significantly increase
the permeability of a soil when measured
with that fluid.
Neutral Nonpolar Organics
Neutral nonpolar organic fluids have
low water solubilities and little polarity
with which to compete with water for
adsorption sites on clay minerals. In the
presence of hydraulic gradient, however,
nonpolar fluids move downward through
a clay without being appreciably attenu-
ated by clay minerals. Examples of non-
polar organic fluids are aliphatic and
aromatic hydrocarbons.
Water
Water strongly adsorbs to clay surfaces
in multiple layers and forms large
hydration spheres around inorganic soil
cations. Because of these properties,
certain clay soils swell and seal upon
hydration and shrink and crack when
water is displaced or extracted. Clay
surfaces of a liner are initially water-wet.
But if a percolating organic fluid has a
higher affinity for the clay surface than
does water, the clay may become
organic-wet. Since the clay surface is
negatively charged, polar or positively
charged components of organic leach-
ates will have an affinity for interlayer
surfaces of an expandable lattice clay.
The water solubility of an encroaching
fluid will improve its access to the clay
surface since water on the clay surface
may be several layers thick.
Components of Clay Softs
A clay soil is a porous mixture of air,
water, organic matter, and inorganic
minerals. Approximately 40% of the clay
soil by volume is pore space (occupied by
air and water) and 60% is solids. Of the
solids, trace amounts to 15% is organic
matter, and 85% to 99% or more is
organic minerals. The inorganic minerals
include sand (0.05 to 2.0 mm), silt-sized
rock fragments (0.02 to 0.05 mm), and at
least 35% clay-sized particles (0.002
mm). These clay-sized particles consist of
rock fragments smaller than silt and a
variety of clay minerals.
Pore space in clay soils is largely
determined by the structural
arrangements of solid soil components. "
Pore-size distribution determines the
permeability of clay soils to fluids.
Solid components that dominate the
behavior of clay soils are organic matter,
clay minerals, and cations adsorbed to
clay minerals. Organic matter generally
imparts structure to clay soil and results
in larger pores and higher permeability.
But the low permeability usually
associated with clay soils is due largely to
characteristics of clay minerals and
associated cations.
Soil organic matter consists of partially
decomposed plant and animal residues
and humus. The addition of organic
matter can transform clay soils with
normally low permeabilities into highly
pervious soils. For example, organic
wastes have been added to farmland for
centuries to improve the soil structure,
but the addition of organic sludges to clay
soils at hazardous wasteland treatment
facilities may destroy the long-term
integrity of clay liners.
The mineral fraction of native clay soils
and subsoils is usually of mixed
composition. Several clay mineral
species are normally present, with one or
two species dominating. Four of the most
widespread species are 2:1 expandable
layer smectites, 2:1 nonexpendable layer
illites, 1:1 nonexpendable layer
kaolinites, and multiple form 1:1 halloy-
sites.
Exchangeable cations are positively
charged ions that are reversibly adsorbed
to negatively charged clay surfaces. Both
the composition of exchangeable cations
and the resulting equilibrium
concentration of the cations in soil water
will greatly affect the permeability of a
compacted clay soil.
Failure Mechanisms of
Clay Liners
Failure mechanisms of clay liners are
defined here as any interaction of the
compacted clay soil liner that can sub-
stantially increase its permeability.
Climatological cycles (wet-dry, freeze-
thaw, etc.) are widely understood to
cause much of the structural
development and permeability increases
in clay soils. Our main concern here,
however, is to investigate the little
understood inservice environments of
remolded and compacted clay soil liners
used for hazardous waste landfills and
surface impoundments. The main failure
mechanisms studied in this context are
(1) dissolution and piping and (2) volume '
changes.
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Dissolution and Piping
Dissolution and piping rtave
complimentary effects on clay liner per-
meability, so they are considered
together. As a dissolving agent erodes
pore walls, the released fragments of soil
tend to clog pores unless they are piped
out of the compacted clay soil. Piping is
the active erosion of soil from below the
ground surface that results from
substratum pressure and the concentra-
tion of seepage in localized channels.
Both organic and inorganic acids and
bases react with and often dissolve
portions of compacted clay soils. Acids
dissolve aluminum, iron, and silica,
which erodes the lattice structure of clays
and releases undissolved fragments for
migration with a percolating leachate.
Acids may also oxidize native organic
matter and dissolved calcium carbonate
nodules.
Pore sizes of compacted clay soils are
not usually large enough to transport
slaked fragments produced by reactive
acids or bases. Thus pore clogging and at
least a temporary decrease in clay liner
permeability will result. But if the clay
liner is placed atop strata containing
pores large enough to pipe soil
fragments, or if the clogging fragments
are dissolved, permeability increases can
eventually occur.
Volume Changes
Volume changes occur in clay soils
from bulk and interlayer shrinkage. Bulk
shrinkage can usually be identified by
visual inspection for cracks, fissures,
joints, faults, slickensides, shears,
channels, ice wedges, planes, and
chambers. Interlayer shrinkage is
manifested by shifts in pore size
distribution and may not be detected
visually, but its impact on clay liner per-
meability can be just as dramatic.
Volume changes in clay liners occur
when there is a change in the water
content of clay. Such changes may occur
if an organic leachate extracts water from
the clay liner. The magnitude of volume
change depends on the clay mineral type,
arrangement of clay particles, size of clay
particles, surface area per unit weight of
clay, and the kind and proportion of
cations adsorbed to the clay.
Swelling of compacted clay soils is a
complex result of many interacting
mechanisms. Swelling is related to the
presence of clay minerals, organic
compounds adsorbed to clay surfaces,
„ and exchangeable cations and to fabric or
structural arrangement of clay particles,
overburden pressure, and Atterberg limit
values of clay soils. Though swelling
tends to decrease permeability of clay
soils, it simultaneously indicates
potential for shrinkage if the soil
environment is substantially altered.
Interlayer spacing of clay minerals
refers to spacing between adjacent basal
surfaces. Changes in interlayer spacing
of clay may affect its bulk volume, pore
size distribution, and thus permeability.
Factors affecting this spacing include the
clay mineralogy, properties of the fluid,
and the exchangeable cations adsorbed
to the clay minerals.
Permeability Measurements
of Clay Soils
Because of the large variety of waste
fluids placed in hazardous waste landfills
and impoundments, there is great need
fora qualitative permeability test that can
rapidly determine potential effects of
waste fluids on the permeability of clay
liners. Such a test should use
standardized procedures and readily
available equipment to simplify training
of laboratory personnel and to allow
intercalibration by independent
laboratories. The test method developed
for this study was designed to meet these
objectives.
The permeability tests conducted for
this study do not attempt to reproduce
typical field conditions and are not
suitable for exact determinations of field
permeability values. But they are useful
for performing rapid comparative studies
to evaluate the potential influence of
waste fluids on permeability of
compacted clay soil liners.
Materials and Methods
Five steps were followed to provide a
basic perspective on the permeability of
clay liners to organic fluids:
1. Delineation of physical classes of
organic liquid-bearing hazardous
wastes.
2. Description of leachates generated
by various waste classes.
3. Interpretation of the types of fluid
contained by various waste
leachates.
4. Evaluation of characteristics of
clay soils used to line disposal
facilities.
5. State-of-the-art review of mecha-
nisms of interaction between
organic fluids and clay soils that
may alter the permeability of clay
liners.
Data gathered during these phases of the
study were then used as guides for
choosing clay soils and methods for com-
parative permeability studies.
Fluids Studied
Seven organic fluids and water were
selected for the comparative permeability
studies. The four classes of these organic
fluids were acidic, basic, neutral polar,
and neutral nonpolar.
All organic fluids used in this study
were reagent grade (pure), whereas
actual waste leachates are normally a
mixture of fluids combined with various
organic and inorganic solutes. Also, waste
leachates often contain suspended parti-
cles that could clog or coat soil pores. This
study used pure fluids to eliminate
variables other than fluid properties that
could effect the resulting permeability
values.
Glacial acetic acid represented the
acidic organic fluid class, and aniline
stood for the basic organic fluids. Three
neutral polar organic fluids (methanol,
acetone, and ethylene glycol) were
chosen along with two neutral nonpolar
organic fluids (heptane and xylene).
Water (0.01 N CaSO4) was used as a
control fluid to establish the baseline
permeability of each soil core.
Clay Soils Studied
Four native clay soils with diverse
mineralogical or chemical properties
were selected for this study. Two of the
soils (noncalcareous smectite and
calcareous smectite) had predominantly
smectitic clay minerals but different
chemical properties. The two other soils
(mixed cation kaoliniate and mixed cation
illite) contained predominantly kaolinitic
and illitic clay minerals, respectively. In
addition, each soil was characterized by
the following:
1. Permeability of less than 1 x 10'7
cm sec"' when compacted at
optimum water content.
2. Geographic extent of at least 1
million ha.
3. Deposits thick enough to permit
economical excavation for use as
clay liners.
4. Minimum clay mineral content of
35% by weight.
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After collection the clay soils were
broken into clods the size of golf ba Ms and
airdried. The soils were then ground
sufficiently to pass through an ASTM No.
4 sieve (4.75 mm) and stored at room
temperature in large drums before
testing.
Permeability Test
Considerations
Steps were taken to minimize sources
of error in soils of low permeability (leaks,
trapped air, volatile losses, and turbulent
flow or channeling along the soil
chamber wall) and to eliminate inherent
dangers associated with organic fluids
under pressure. Other steps were taken
to ensure accurate permeability values,
including increasing the hydraulic gradi-
ent to reduce the time needed for testing
and to minimize trapped air.
Procedures
Compacted soil cores were used to
evaluate permeability to organic fluids.
These were prepared at or above
optimum water content. After
compaction, the soil cores were mounted
on permeameter base plates and fitted
with fluid chambers and permeameter
top plates (Figure 1). Each top plate was
then fitted with a pressure inlet connec-
ting it to a pressurized air source via the
pressure distribution manifold (Figure 2).
After the soils were seated at low
pressure, the selected air pressure was
applied to the permeameter fluid
chamber until stable permeability values
were obtained with the standard
leachate. Pressure was then released,
and permeameters were disassembled.
The core was next examined for signs of
swelling or deterioration.
Any soil that had expanded out of its
mold was removed with a straight edge,
ovendried, and weighed to estimate the
percent of swelling. Additional standard
leachate was then passed through the
three soils that had swollen to ensure
that permeability was not affected by the
excess soil removal.
Next, the remaining standard leachate
was removed and replaced with the
organic fluids for all but the control
permeameter. After passage of 0.5 to 2.0
pore volumes of organic fluids, the
permeameters were depressurized and
disassembled, and the cores were
dissected to determine whether
structural changes had occurred in the
compacted clays. Curves for organic fluid
breakthroughs were determined simply
_ Pressure Input
vPVT*/n!?'f'*r-!
////fly /TV
Permeameter
Top
Teflon
Gaskets
— Permeameter
Base
Porous Stone
Outlet
Teflon Tubing
Figure 1. Schematic of the compaction permeameter.
by measuring the organic fluid volume
(with immiscible fluids) or by
thermoconductivity gas chromatography
(with miscible fluid).
Results and Discussion
Relative Performances of the
Four Clay Soils
When the four soils used in this study
were evaluated with the traditional per-
meability test using water (0.01 N CaS04),
the resultant permeabilities were lower
than 1x10-' cm sec-'. But these same
clay soils underwent large increases in
permeability when basic, neutral polar,
and neutral nonpolar organic fluids were
used in place of water. They also showed
the potential for substantial permeability
increases when exposed to concentrated
organic acids. Permeability data are
summarized in Table 1.
Of the four clay soils studied, the
noncalcareous smectitic clay showed the
lowest initial permeability but the least
resistance to increases in permeability
when exposed to organic fluids. The
calcareous smectitic clay had intermed-
iate initial permeability, but it showed a
much greater resistance to permeability
changes than its noncalcareous counter-
part. The result was that the
noncalcareous clay generally had a
higher final permeability than the
calcareous smectitic clay. In addition, of
the two smectitic clay soils, the
noncalcareous tended to yield organic
fluids in the effluent after less fluid had
passed through the soil.
Though the kaolimtic clay soil had the
highest initial permeability of the four
soils studied, it nearly always showed the
greatest resistance to permeability
changes. Organic fluids generally
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appeared in the effluent of this soil after
passage of greater fluid volumes than
with the illitic or noncalcareous smectitic
clay soils.
The illitic clay soil had both intermedi-
ate initial permeability and resistance to
permeability changes. But the organic
fluids tended to appear in the effluent of
the illitic clay soil after passage of less
fluid than with the other clay soils.
Overall, the kaolinitic and calcareous
smectitic clay soils performed best of the
four clays studied. These two clays
showed greater resistance to
permeability increases, and organic
fluids appeared in their effluent after
passage of more fluid (larger pore volume
values) than the illitic or noncalcareous
smectitic clay soils. Note, however, that
all four clay soils showed permeabilities
Figure 2. Schematic of the compaction permeameter test apparatus.
greater than 1 x 10~7 cm sec-1 when
exposed to several of the organic fluids
tested.
Relative Effects of Organic
Fluids on Permeability of
Clay Soils
Organic acids apparently affect perme-
ability by mechanisms that are different
from those of other organic fluids studied.
The operative mechanisms for perme-
ability changes with acetic acid appeared
to be dissolution of soil particles followed
by piping of the particle fragments
through the soil. A sharp initial permea-
bility decrease resulted as the migrating
particle fragments clogged the fluid-
conducting pores. But permeability then
i ncreased gradu al ly (with two of the soi Is)
as acid dissolved the soil particles that
clogged the pores.
No dissolution or piping was observed
for the soils permeated by the weak
organic base (aniline) or the neutral
organic fluids, These fluids tended to
cause permeability increases by altering
the structural fabric of the soil.
Neutral nonpolar fluids caused initial
permeability increases of approximately
two orders of magnitude. The soils so
treated tended, however, to reach rela-
tively constant permeability at that point.
The basic and neutral polar fluids showed
continuous permeability increases with
no apparent tendency to reach maximum
values. Though the large viscosity of
ethylene glycol and aniline slowed the
Table 1. Permeability of Four Clay Soils to Water 10.01 N CaSOJ*
Permeability (cm seer'1)
Fluids to Which the Soil
Column Would be Exposed
Water (O.O1N CaSOJ
Acetic Acid
Aniline
Ethylene Glycol
Acetone
Methanot
Xylene
Heptane
Noncalcareous
Smectite
2. 14(±O.26) x 70-a
t.59f±0. 191 x 70-9
2.91(±0.23)x JO-9
1.39(±Q. 14) x 70-9
7. 14(±0. 101 x 70-9
7.55r±0.77M70-9
1.44(±0.21lx 70-9
1. 51 (±0.1 3) x 70-9
Calcareous
Smectite
7.77{±0.64)x tO-9
6.48(±0.11)x 70-9
3.86(±0.19)x JO-9
4.67(±0.64)x1&*
3.47{±O.66)x 70-9
5.07(±0.52)x JO'9
5.62(±0.11)x JO-9
3.62(±0.37J x 70-9
Mixed Cation
Kaolinite
1.92(±0. 18)x10-*
1.30<±0.3S) x 70-8
1.51 (±0.12) x 10-o
1.55(±0.35)x 70-8
2.01 (±0.1 2) x 70-8
1.46(±0.42)x10-*
1.77(±0.1B)x10-*
1.87(±O.1O)x1O-*
Mixed Cation
Illite
6.07(±3.88) x 70-9
7.31 (±0.93) x 70-9
3.87(±1.62) x 70-9
6.75(±1.52)x 70-9
3.06(±0.69) x 70-9
5.54(±1.S2) x 70-9
3.51 (±1.1 3) x 70-9
4.26(±0.99) x 70-9
All Permeameters
1.63(±0.50) x 70-9
4.98(±J.60)x 70-9
7.77(±0.25) x 70-8
5.14(±2.20) x 70-9
"Values for individual columns represent mean ± one std. dev. of 2-7 permeability measurements.
Values given under the designation "Aft Permeameters" represent mean ± one std.dev. for all soil columns of a given soil type.
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rate at which these fluids increased
permeability relative to the less viscous
acetone and methanol, all four fluids
increased the permeability of soils as
compared with values obtained with
water (0.01 N CaSO4).
The full report was submitted in
fulfillment of Grant No. R806825010 by
Texas A&M University under the sponsor-
ship of the U.S. Environmental Protection
Agency.
K. W. Brown andD. C. Anderson are with Texas A&M University, College Station,
TX 77845.
Robert E. Landreth is the EPA Project Officer (see below).
The complete report, entitled "Effects of Organic Solvents on the Permeability of
Clay Soils," (Order No. PB83-179 978; Cost: $16.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield. VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
. S. GOVERNMENT PRINTING OFFICE-.l983/659-095/1936
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