United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/016 Apr. 1988
&ER& Project Summary
Review and Evaluation of the
Influence of Chemicals on the
Conductivity of Soil Clays
K. W. Brown
Soil lined facilities have been used
extensively for the containment and
disposal of waste liquids. Often slowly
permeable natural clay-rich deposits
were relied upon to retard the move-
ment of liquids. More recently,
remolded layers of clay soils with
hydraulic conductivities of 10~7 cm s~1
have been constructed with the inten-
tion of retaining liquids. The hydraulic
properties of both natural deposits and
remolded clays have been characteris-
tically evaluated by using water or
dilute solutions of CaSO* as the per-
meating fluid. Many landfills and
surface impoundments have been
designed, built, and used across the
country with the approval of state and
federal regulating agencies, based on
the conductivity standard of 10~7 cm
s~1 or less, as determined with water.
Such facilities have received a wide
range of waste liquids with properties
that differ greatly from those of water.
Water is well known for its ability to
hydrate clay soils by causing them to
swell, resulting in low conductivities.
Many organic liquids are known to
cause the interlayer spacing of smec-
titic clays to decrease from those that
occur when the same clay is wetted
with water. Thus, organic liquids could
possibly cause clay-rich soils to shrink
and crack, which could result in
increasing the conductivity of soils
expected to retain organic liquids.
A series of experiments were under-
taken to determine if organic liquids
would increase the conductivity of
clay-rich soils, to determine if changes
were dependent on the clay mineral-
ogy, and to determine the mechanism
by which any changes in conductivity
could be explained. A theoretical
evaluation of the influence of dielectric
properties of liquids on the thickness
of the double layer between adjacent
clay minerals suggests that the spacing
should decrease when liquids with
dielectric constants lower than those
of water wet the surfaces. Most com-
mon organic liquids have dielectric
constants considerably lower than
water, suggesting that they should
cause clay-rich soil to shrink. An x-ray
observation of smectitic clay minerals
wetted with organic liquids confirmed
that the D-spacings were less than
those observed with water. Floccula-
tion studies using dispersed clays
indicated that smectitic, micaceous,
and kaolinitic clays flocculated rapidly
when they were added to organic
liquids, which were only sparingly
water soluble, and also flocculated
when placed in a solution of water
soluble liquids that contained greater
than 50% organic liquid. Observation
of bulk samples indicated that water
wetted specimens containing each of
the three above-mentioned clays
swelled more than when similar sam-
ples were wetted with organic liquids.
Laboratory studies of conductivities
using a range of organic liquids includ-
ing both polar and nonpolar solvents,
waste sorbents, and commercial petro-
leum products in fixed wall perme-
ameters indicated that the conductiv-
ities to organic liquids were two to
three orders of magnitude greater than
those to water. Observation of the soils
permeated with dye-labeled organic
liquids revealed the formation of struc-
tural units near the surface. The organic
liquids had also moved through cracks
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that penetrated the soil, which origi-
nally had a massive structure. Field test
cells were set up using three clays and
two organic waste liquids. The conduc-
tivity measurements in the field con-
firmed the laboratory findings. The
nonpolar solvent waste containing
xylene, which was used to permeate
the 1.5 M square and 15 cm thick field
test section of compacted clay, broke
through many of the replications within
two weeks. The acetone waste took as
long as two years to break through the
test sections; however, in the end,
sections of each type of clay were also
permeated by the acetone waste.
It thus appears that organic liquids,
which are only sparingly soluble, in
water, or water soluble organic liquids
in concentrations greater than 50% will
descicate clays, causing them to shrink
and crack. The liquids are then able to
flow through the soil much more
rapidly than when the soils are wetted
with water.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Many landfills and surface impound-
ments depend on compacted soil liners
as either the primary or secondary means
for retarding the movement of chemicals
to the ground water. Even though com-
pacted soil liners are to have a conduc-
tivity of 1 x 10~7 cm s"1 or less, reports
continue to appear documenting the
leakage of liquid organics from clay lined
facilities. One possible cause for this is
that liners installed in the field have
seepage paths such as cracks or flaws.
A second possibility for the rapid move-
ment of organics through compacted soil
is that the chemicals interact with the
soil matrix in such a way as to increase
the conductivity.
A previous laboratory study revealed
that compacted clay soils exposed to
concentrated organic liquids underwent
large conductivity increases. Uncertain-
ties associated with the equipment used,
pressure gradients used, and represen-
tativeness of the data necessitated
further study. This project was, therefore,
conducted to provide additional data on
the effect of hydraulic gradient on
conductivity measured in the laboratory,
to study the effect of dilute organic
solutions on the conductivity of com-
pacted soils, to provide field cell verifi-
cation of laboratory measurements of
conductivity, and to develop a mechanis-
tic explanation for the observed data.
Methods
The conductivity of three soils of
differing mineralogies (mica, kaolinite,
and bentonite) when permeated with
water, acetone, and xylene at hydraulic
gradients of 31, 91, 181, and 272 was
measured using fixed wall permeame-
ters. Soils were tested at moisture
contents equivalent to the moisture
content at the time of compaction
(hereafter referred to as nonsaturated)
and after the passage of one pore volume
of water (hereafter referred to as satu-
rated) to evaluate the effect of moisture
content on conductivity. The conductivity
of each soil to dilute concentrations of
organics was measured in the laboratory
through the use of 0, 60, 80, and 100%
ethanol and 0,60,80, and 100% acetone
solutions as the permeants. Conductiv-
ities were also measured using waste
organic chemicals and a group of petro-
leum products.
To document whether or not the
laboratory measurements provided an
accurate estimate of how the soils
behave under field conditions, special
field cells were constructed. Each cell
was 1.5 m x 1.5 m x 1.8 m tall and
equipped with a removable platform. A
100-mil HOPE liner was installed in each
cell, followed by a leachate collection
system. Above this, a 15-cm thick layer
of compacted soil was installed in two
lifts. Four perforated barrels were placed
on top of the liner, and the cell was
backfilled with soil and capped with soil
and plastic to exclude rainfall. Approx-
imately 1400 L of dyed-tagged xylene or
acetone were pumped into the four
perforated barrels through a standpipe.
Leachate was collected twice weekly,
quantified, and subsampled for analysis.
Leachate volumes and times were used
to calculate the conductivity and the
number of pore volumes that passed
through the soil. After the conductivity
was measured at 2 x 10~7 cm s"1 or
greater, each cell was disassembled, and
the clay liner was visually observed and
sampled for analysis.
To elucidate the effects of organic
chemicals on the f locculation and disper-
sion state of the clay fraction of the soils.
each of the soils was subjected to partic
size analysis using 0, 50, 60, 70, 80, ar
100% by volume acetone and 0, 20, 5i
60, 70, 80, 90, and 100% by volurr
ethanol. The apparent % clay in eac
solution was compared to that measure
in water. The bulk shrinkage or swellir
of compacted samples of each so
exposed to water, acetone, and xyler
was measured using a volume chanc
apparatus. Changes in D-spacing of th
bentonite were measured using standai
x-ray analysis of bentonite equilibrate
with solutions containing 0, 2, 5, 50, 6(
80, and 100% by volume acetone an
0, 20, 40, 60, 80, and 100% by volum
ethanol. Additional measurements of th
mobility of clay particles in variou
solutions and exposed to an electric.
field were made. Measurements wer
converted to electrophoretic mobility an
zeta potential.
Results and Conclusions
Laboratory testing using three soil
and numerous chemicals verified th
data that concentrated organics increas
the conductivity of compacted soil. N
consistent significant effect of hydrauli
gradient or initial moisture content on th
final conductivity could be found. Con
centrated organic solvent wastes, as we
as petroleum products including kerc
sene, diesel fuel, gasoline, and motor o
all resulted in dramatic increases i
conductivity of all three soils teste
(Table 1). Increases ranged from one t
five orders of magnitude and general!
were least for the bentonite soil. Con
centrated organic solvents, acetone ani
xylene, resulted in similar conductivit
increases. A representative figure depict
ing the influence of concentrated organi
solvents on the conductivity of com
parted soil as a function of the pon
volumes of effluent is given in Figure 1
Presaturated soil conditions resulted ii
the passage of typically 0.1 to 0.7 pon
volumes of water at initial conductivities
followed by a very rapid increase ii
conductivity. When the soils were no
saturated before exposure to solvents
the conductivity rose immediately t<
values often two to four orders o
magnitude greater than the initial con
ductivity to water. Solvent concentra
tions in leachate from the non-saturatei
soils ranged from 95 to 100% from th<
very first appearance of leachate. For th(
presaturated soils, only 0.2 to 0.7 pon
volumes passed through the soil before
solvent concentrations of 95 to 1009(
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Table 1. Mean Conductivity of Each Soil to Each Fluid Tested
Fluid CC1 CC2
CC3
Water
Acetone
Xylene
Gasoline
Kerosene
DieselFuel
Motor Oil
3.61 x 1Q-*b*
5.05 x 10~5b
1.76x10'*a
1.96x 10~4a
1.49x10'*a
5.17 x 10'*b
6.13x10'*b
2.58 xW8b
1.41 x10'eb
7. 28x10'* a
9.07 x10'sa
9.10x10'sa
4.53x10'5ab
2.13 x 10'eb
1.57xW'ab
2.51 x 1Q-7b
I.OOxW'a
6.19 x W~5b
5.68x10'5b
6.29x10'7b
9.48 x10'7b
"Values in a given column followed by the same letter do not differ significantly (P = 0.05).
were reached, thus indicating that only
the water from the large macropores was
displaced.
Field tests confirmed the laboratory
data. For the kaolinitic and micaceous
soils exposed to xylene, only two to three
days elapsed until leachate appeared.
When acetone was the permeant, 21 to
28 days elapsed before leachate began.
The bentonite soil exposed to xylene and
acetone required 70 and 704 days,
respectively, before the appearance of
leachate. Agreement between laboratory
and field data is summarized in Table 2.
Conductivity to pure acetone in the
laboratory averaged about 1.5 orders of
magnitude greater than the conductivity
to water. Laboratory measurements with
waste acetone from the field experiment
showed only slight increases in conduc-
tivity. The conductivities measured in the
field, however, were a full order of
magnitude greater than the laboratory
value. Laboratory measurements with
pure xylene indicated conductivities
three to four orders of magnitude greater
than that to water. Conductivities of
waste xylene permeated in the laboratory
averaged 2.5 orders of magnitude greater
than laboratory values with water. Field
conductivities to waste xylene averaged
two orders of magnitude greater than
water. It thus appears that laboratory
testing using fixed wall permeameters
and elevated hydraulic gradients can
provide a reasonable field estimate
response of compacted clay liners to
organic liquids. Visual observations of
the dissected clays indicate that the
organic liquid moved through only a
small fraction of the pores.
A study of the mechanism causing the
observed changes in conductivity was
undertaken. It was found that as the
concentration of organics in water
increased there was a concentration at
which the suspended clay flocculated.
The point at which the apparent clay
content was 0.5 of the actual clay content
was reached when the solution dielectric
constants ranged from 31 to 49 for the
three soils tested (Table 3). A decrease
in the basal spacing of the bentonite soil
to values below that observed with water
was found to occur when the dielectric
constant of the solution reached 28 and
47 for ethanol and acetone solutions,
respectively. Electrophoretic mobility and
10'
10'
|;
10'
10"
° Rep 1
• Rep 2
Mica
Xylene
Presaturated
Gradient 91
W
10'
CC3
Xylene
Gradient 91
• Rep1
°Rep2
Lab Value with
Water 1.6x10'"
1/0 1 2
Pore Volume
1 2
Pore Volume
Figure 1.
Conductivity of presaturated and nonsaturated mica soil to xylene measured with
a fixed wall permeameter at a gradient of 91.
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Table 2. Conductivities of Three Soils to Water. Pure Chemical, and Wastes in Both Laboratory and Field Cells
Kaolinite
Mica
Bentonite
Average
Laboratory
Conductivity
to Water
1.1 x JO'8
J.5xJO'a
3.5xJO~*
Laboratory
Conductivity to
Pure Acetone at
a Gradient
of 181
3.7 x10~*
4.5xJO'a
1.5 x JO'7
Laboratory
Conductivity to
Waste Acetone
at a Gradient
of 181
4.6 x JO'9
2.4xJO~"
Field Cell
Conductivity to
Waste Acetone
at a Gradient
of?
7.7 xJO'"
J.OxJO'7
3.4x10'"
Laboratory
Conductivity to
Pure Xylene at
a Gradient
of 181
J.OxJO'4
2.2 x JO'5
1.5x10'*
Laboratory
Conductivity to
Waste Xylene at
a Gradient
of 181
6.1 x JO'*
6.4 x JQ-*
8.5 x JO'7
Laboratory
Conductivity t
Waste Xylene ,
a Gradient
of 7
J.J x J0'e
2.1 xW*
J.3xJO'7
zeta potential served as indicators of the
bulk charge on the clay particles. Meas-
urements indicated that changes in these
parameters also occurred in the dielectric
constant range of 26 to 41. Increased
hydraulic conductivities were observed
for solutions having dielectric constants
below 35 to 50. These data coupled with
that of the other portions of the project
indicate that as organic chemicals
permeate the soil, they cause it to shrink
and crack and thereby increase the
hydraulic conductivity.
The full report was submitted in
fulfillment of Cooperative Agreements
CR-808824 and CR-811663 by Texas A
& M University under the sponsorship
of the U.S. Environmental Protection
Agency.
Table 3. Dielectric Constants at Which the Apparent Clay Concentrations Reached 0.5. the
d-Spacing Dropped Below J.8 NM. the Electrophoretic Mobility was Midway
Between Zero and the Plateau, the Zeta Potential was Midway Between Zero and
the Plateau, and the Hydraulic Conductivity Increased
Acetone
Ethanol
K
M
B
K
M
B
Apparent
Clay
Content
31
37
38
30
33
49
Electro-
Basal phoretic
d-Spacing Mobility
31
26
47 37
28
31
28 38
Zeta
Potential
35
26
41
32
30
39
Conductivity
48
35
-
50
-
45
Average
36
31
41
35
31
40
K. W. Brown is with Texas A&M University, College Station, TX 77843.
Walter E. Grube. Jr., is the EPA Project Officer fsee below).
The complete report, entitled "Review and Evaluation of the Influence of
Chemicals on the Conductivity of Soil Clays," (Order No. PB 88-170 808/
AS; Cost: $25.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22J6J
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
U.S.OFRGIALfvl
/^""".fX B
Penalty for Private Use $300
EPA/600/S2-88/016
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