United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada, OK 74820
Research and Development
EPA/600/SR-94/005 March 1994
&EPA Project Summary
Determination of Capillary
Pressure-Saturation Curves
Involving TCE, Water and Air for a
Sand and a Sandy Clay Loam
J. H. Dane, M. Oostrom, and B. C. Missildine
The contamination of aquifers and
other groundwater by Non-Aqueous
Phase Liquids (NAPLs) such as
chlorinated solvents, has become a
major concern in many areas of the U.S.
Characterization and modeling of these
contaminants require accurate and
realistic data for the fluids and media
involved. Most capillary pressure (Pc) -
saturation (S) curves are determined
with a pressure or tension apparatus
that often contains a porous medium
sample of more than 5 cm in height. If
the porous medium sample consists of
a rather coarse material and the
interfacial tension between the wetting
and non-wetting fluid is sufficiently low,
itisnotinconceivablethatlargechanges
in S occur overthe height of the sample.
Using the standard procedure of
measuring the outflow volume of one of
the flu ids, from which average values of
S are calculated, can therefore result in
substantial errors. In this study, a
method is proposed to measure PC-S
drainage and imbibition relationships
for TCE/air and TCE/water systems at
points along a 0.94-m long sand column
and a 0.94-m long sandy clay loam
column with the help of a gamma
radiation system and from knowledge
of the fluid pressure distributions in the
porous media at hydraulic equilibrium.
The results showed that the S-values of
the fluids present in the sand, either
TCE and air or TCE and water, changed
from complete saturation to their
residual values, and vice versa, over P
changes ranging from 2.5 to 10 cm of
water pressure. For the sandy clay
loam the changes in S of the fluids
were less dramatic with changes in Pc,
making the use of a pressure cell more
acceptable, although the PC-S curves
will still not be as accurate as for the
method used in this study.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, 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
Dense non-aqueous phase liquids
(DNAPLs), such as trichloroethylene
(TCE) are the cause of many current
ground-water contamination problems. An
essential component in understanding and
simulating multiphase fluid flow is the
accurate determination of the hydraulic
properties of the different fluids involved.
It has been standard procedure to use
pressure cells to determine capillary
pressure (Pc)-saturation(S) curves, where
pc =pnw-pw=2°/r(Pnw= pressure of the
non-wetting fluid; Pw = pressure of the
wetting fluid; o is the interfacial tension;
and r is the radius of curvature at the
interface of the two fluids). The interfacial
tension at 20°C between TCE and air is
only 30 mN/m, and 38 mN/m between
TCE and water, as compared to 72 mN/m
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between water and air. The height of the
pressure cell may therefore be critical during
the displacement of one fluid by another if
S changes rapidly with small changes in Pc,
as is the case for coarser materials (the
density of TCE is 1.456 g/cm3 and its
viscosity ratio with respect to water 0.52,
both at 20°C). The main objective of this
study was therefore to explore an improved
way to determine Pc-S curves for TCE/air
and TCE/water during wetting and drainage
of the wetting fluid (hysteresis loops) in a
sand and a sandy clay loam. Two additional
factors of importance for simulation and
cleanup purposes are the Revalues atwhich
the non-wetting fluid starts to displace the
wetting fluid and the values forthe residual
saturation of TCE. These values were
determined as well.
Materials and Methods
A 1.0-m long glass column experiment
was designed to allow accurate Pc-S
information to be collected at any given
point along the column. The column (i.d. =
7.5 cm), with Teflon end caps, was first
filled uniformly to a height of 0.94 m with
Flintshot 2.8 Ottawa (medium) sand and
later with a sandy clay loam (25% non-
swelling clay, 20% silt and 55% sand). The
outlet at the bottom of the column was
connected to a TCE supply (or drainage)
bottle by Teflon tubing. This bottle was also
used to adjust the fluid pressures in the
column by lowering or raising it.
For the TCE/air combination, the initially
air-saturated column was subjected to the
following cycles:
• Saturation fromthe bottom, by slowly
raising the bottle, until TCE was
ponded on the surface. It was not
possible to displace all of the air in
this manner, so a certain amount of
air should be considered trapped.
• TCE displaced by air by stepwise
lowering the bottle.
• Air displaced by TCE by stepwise
raising the bottle.
H2 O/TCE - System
100-\
20
40 60 80 100
Pressure, Dynes cm'2 (xlOOO)
120
140
Figure 1. Graphical display of fluid pressures in a TCE/water system when the TCE level in the
supply/drainage bottle is 85.7 cm above the reference level. At 51.5 cm above the
reference level the pressure in the TCE is PTCE = Pnw = (85.7 - 51.5) x 1.456x 1000 =
49,800 dynes/cm2, while the water pressure PH20 = Pw= (96 - 51.5) x 1 x 1000 =
44,500 dynes/cm2. Therefore, Pc = Pnw - Pw = 5,300 dynes/cm2 or 5.3 cm of equivalent
water pressure.
• Upon reaching equilibrium after each
step change (no more flow from or
into the supply bottle), dual-energy
gamma radiation measurements
were taken at the desired locations
to determine the volumetric TCE
content, 9TCE.
Pc-values were obtained from knowledge
of the height of the TCE-level in the supply/
drainage bottle. Corresponding S-values
were calculated from S = 6TCE/porosity. By
matching the corresponding Pc and S-
values, Pc-S data points were obtained.
Upon completion of the TCE/air
experiments, a 2-cm layer of water (top of
water at 96 cm above reference level) was
maintained on the soil surface to displace
the TCE by water, or vice versa, and Pc-S
curves were determined for TCE/water in a
similar manner as described for TCE/air.
The dual-energy gamma radiation system
now determined both 6TCE and the
volumetric water content, 6W An example
of the Pc determination for a TCE/water
system is shown in Figure 1. The TCE-level
in the supply/drainage bottle forthis example
was at 85.7 cm.
The Pc-S data were fitted with the van
Genuchten curve fitting procedure. The Pc
entry value for the non-wetting fluid was
taken as 1/a.
Results and Discussion
The full explanation of this research is
reported in the full report. It contains
extensive data tables and parameter values
forthe van Genuchten function obtained for
many different imbibition and drainage
cycles, plus graphical representations of
both the acquired and fitted data.
Average values for the bulk density,
porosity, 9TCE, and S as measured at nine
locations along the TCE-saturated column
are listed in Table 1 for both the sand and
sandy clay loam.
Flintshot 2.8 Ottawa Sand
An example set of TCE saturation data
during the displacement of TCE by air (TCE
drainage) is given in Table 2 and graphically
displayed in Figure2. An exampleofsimilar
results, obtained during the displacement
of air by TCE (TCE wetting), is illustrated in
Figure 3. The solid lines in Figures 2 and 3
represent the curves as fitted by the van
Genuchten procedure. It should be noted
that the fitted curves look somewhat
awkward at times, because they only
connect points calculated from measured
Pc-values. To appreciate the amount of
hysteresis, the fitted van Genuchten
functions are shown without values. Based
on actual measurements, these valueswere
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Table 1. Average values for the bulk density (pj, the corresponding porosity (e) based on a particle density of 2.65 g/cm3, and the average
volumetric TCE content (0-TCE) during TCE saturated conditions (upon TCE wetting into dry soil). N is the number of observations for
each location, z is the distance to the reference level, and S is the degree of TCE saturation.
Location
Z
cm
g/crrf
N
e
cm3/cm3
0-TCE
cm3/cm3
N
S
Flintshot Sand
1
2
3
4
5
6
7
8
9
1
2
3
4
5
6
7
8
9
91.5
81.5
71.5
61.5
51.5
41.5
31.5
21.5
11.5
91.5
81.5
71.5
61.5
51.5
41.5
31.5
21.5
11.5
1.52
1.48
1.47
1.45
1.51
1.50
1.49
1.48
1.48
1.25
1.24
1.22
1.23
1.24
1.23
1.23
1.22
1.27
92
92
92
92
92
92
92
92
92
Sandy
253
253
253
253
253
253
253
253
253
0.426
0.440
0.446
0.454
0.431
0.433
0.438
0.442
0.443
Clay Loam
0.528
0.531
0.538
0.535
0.531
0.536
0.537
0.539
0.521
0.332
0.360
0.376
0.371
0.353
0.359
0.356
0.365
0.361
0.443
0.445
0.454
0.439
0.446
0.453
0.462
0.446
0.444
5
9
11
13
17
17
19
21
21
48
48
48
48
48
48
48
48
48
0.78
0.82
0.84
0.82
0.82
0.83
0.81
0.83
0.82
0.84
0.84
0.84
0.82
0.84
0.84
0.86
0.83
0.85
Table 2. Volumetric TCE content (0-TCE) as a function of capillary pressure (Pc),
expressed in cm of equivalent water pressure, during displacement of TCE with
air in a 1-m long column filled with Flintshot 2.8 Ottawa sand. Location #3.
d-TCE
cm3/cm3
0.376
0.380
0.369
0.371
0.374
0.320
0.230
0.150
0.113
0.092
0.066
0.060
0.055
0.049
0.045
0.045
0.042
0.045
0.038
0.039
Pc
cm
0.0
0.9
2.3
3.8
4.5
5.2
6.0
6.7
7.4
8.2
8.9
10.3
11.8
13.2
14.7
16.2
17.6
18.3
19.1
19.8
d-TCE
cm3/cm3
0.040
0.044
0.045
0.046
0.038
0.043
0.044
0.037
0.041
0.044
0.044
0.038
0.043
0.038
0.037
0.039
0.040
0.044
0.046
0.042
Pc
cm
20.5
21.3
22.0
22.7
23.4
24.9
26.4
27.8
29.3
30.7
32.2
32.9
33.6
34.4
35.1
35.8
36.5
37.3
38.0
38.7
d-TCE
cm3/cm3
0.038
0.042
0.036
0.033
0.042
0.044
0.038
0.042
0.040
0.041
0.038
0.041
0.033
0.033
0.039
0.047
0.041
0.027
PC
cm
39.5
40.9
42.4
43.8
45.3
46.7
47.5
48.2
48.9
49.7
50.4
51.1
51.8
52.6
53.3
54.0
55.5
56.9
the data points in Figure 4. The sets of data
evaluated in the full report showed that S
changes from its maximum to its minimum
value, and vice versa, over a capillary
pressure difference of about 5.5 cm of
equivalent water pressure. The data also
show that ignoring hysteresis can have a
major effect on S.
A similar presentation is given for the
results obtained during the displacement
of TCE by water (Figure 5) and for the
displacement of water by TCE (Figure 6).
Representation of hysteresis is shown again
using the fitted van Genuchten functions in
Figure 7. The change in S with capillary
pressure is again very rapid, especially for
the (water) wetting curve. The amount of
hysteresis in this case is even more
pronounced than for the TCE/air system.
The average value forthe van Genuchten
parameter a during the displacement of
TCE by air was 0.155 (st. dev. = 0.020),
which means that the average air entry
value into a TCE saturated system is 6.5
cm of equivalent water pressure (st. dev. =
0.7 cm).
For the TCE/water system the pressure
in the TCE must, on average, be at least
12.0 cm higher (st. dev. 0.6 cm) than in the
water before it will displace the water.
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700 -i
8
6
4-
2-
10 -
S-
6-
2-
FS 2.8 Sand
Location 3
TCE Displaced by Air
Figure 2.
0.0 0.2 0.4 0.6 0.8 1.0
Degree of TCE Saturation
TCE drainage curve at location 3 for a Flintshot 2.8 Ottawa sand containing
TCE and air.
100
o
Q.
6 -
4-
2 -
10 -
8 -
6 -
4-
2 -
FS 2.8 Sand
Location 3
Air Displaced by TCE
0.0
^ ' I ' I
0.2 0.4 0.6
Degree of TCE Saturation
0.8
1.0
Figure 3.
TCE imbibition curve at location 3 for a Flintshot 2.8 Ottawa sand containing TCE and
air.
During the displacement of TCE by air
and of TCE by water, the degree of TCE
saturation had rapidly attained theirresidual
values. Based on actual measurements,
these values were 0.085 (number of
measurements = 150) and 0.050 (number
of measurements = 506) for the TCE/air
and TCE/water, respectively. Subsequent
flushing of the column with water had no
measurable impact on the residual S-value
of 0.050.
Sandy Clay Loam
The experimental setup and procedure
for the sandy clay loam soil was the same
as for the Flintshot 2.8 sand. Example
graphs for the TCE saturation data during
the displacement of TCE by air (TCE
drainage) and forthe displacement of air by
TCE (TCE wetting) are shown in Figures 8
and 9, respectively. The amount of
hysteresis becomes obvious from the fitted
curves (Figure 10). It is obvious that
changes in S with Pcare much more gradual
and that hysteresis is less profound than
forthe sand (Figures 4 and 7).
Example graphs of the results obtained
during the displacement of TCE by water
and the displacement of water by TCE are
presented in Figures 11 and 12, respectively.
Due to the similarity in data and the limited
range in S-values, several measurement
locations were combined into one graph
and the PC-S wetting and drainage curve
for the combined data sets was used to
demonstrate the amount of hysteresis
(Figure 13).
The average value for a during the
displacement of TCE by air was 0.055 (st.
dev. =0.012), which meansthatthe average
air entry value into this TCE-saturated
system was 18.3 cm of equivalent water
pressure (st. dev. = 3.4 cm).
For the TCE/water system, the pressure
in the TCE was, on average, at least 24.0
cmhigher(st. dev. 1.4cm)than inthewater
before displacement of the water occurred.
In considering the two porous medium
systems used in this study, the data show
very rapid changes in saturation with only
very small changes in capillary pressure in
the medium sand for both the TCE/air and
TCE/water systems. The use of alternative
procedures, such as the use of pressure
cells, should therefore be avoided for
coarser materials. The changes in
saturation with capillary pressure were more
gradual for the sandy clay loam, which
would result in smallerdifferences between
the Pc-S curve determined with a pressure
cell and the "true" curve. Although both
media exhibited considerable hysteresis, it
was most pronounced forthe medium sand
containing TCE and water. The average air
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100 —i
2 -
10 —
8 •
6 •
4-
2-
FS 2.8 Sand
Location 3
TCE/Air
entry value for the TCE/air systems was
6.5 cm for the medium sand and 18.3 cm
forthe sandy clay loam. Forthe TCE/water
systems the average TCE entry value was
12.0 cm forthe medium sand and 24 cm for
the sandy clay loam. The average measured
TCE residual saturation forthe sand was
0.085 when TCE was displaced by air and
0.050 when it was displaced by water.
\
Drainage
Wetting
0
I
0.2
I
0.4
1 1
0.6
0
8
\
1.0
Degree of TCE Saturation
Figure 4. TCE drainage and imbibition curve at location 3 for a Flintshot 2.8 Ottawa sand
containing TCE and air.
10 —
9-
8-
7-
6-
5-
> 4-
3-
2-
FS 2.8 Sand
Location 3
TCE Displaced by Water
0.0
0.2
0.4
0.6
0.8
\
1.0
Degree of Water Saturation
Figure 5. Water imbibition curve at location 3 for a Flintshot 2.8 Ottawa sand containing TCE
and water.
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3-
2-
10 —
9'
8 •
7'
6.
5 -
3-
2-
FS 2.S Sand
Location 3
Water Displaced by TCE
0.0 0.2 0.4 0.6
Degree of Water Saturation
0.8
\
1.0
Figure 6. Water drainage curve at location 3 for a Flintshot 2.8 Ottawa sand containing TCE and
water.
2-
10 —
8-
6-
4-
2-
FS 2.8 Sand
Location 3
TCE/Water
Drainage
Wetting
0.0 0.2 0.4 0.6
Degree of Water Saturation
0.8
1.0
Figure 7. Water imbibition and drainage curve at location 3 for a Flintshot 2.8 Ottawa sand
containing water and TCE.
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p
100 9~
7-
6-
5-
7-
6-
5'
4-
3'
2-
1
Sandy Clay Loam
Location 4
TCE Displaced by Air
0.0
0.2
o
T
0.8
\
1.0
0.4 0.6
Degree of TCE Saturation
Figure 8. TCE drainage curve at location 4 for a sandy clay loam containing TCE and air.
2-
100-
8-
6-
4-
2-
10-
8-
6-
4-
2-
1
0.0
\
0.2
Sandy Clay Loam
Location 4
Air Displaced by TCE
\
0.4
\
0.6
\
0.8
\
1.0
Degree of TCE Saturation
Figure 9. TCE imbibition curve at location 4 for a sandy clay loam containing TCE and air.
1
-------
700-|
8
6
2-
± 10 -
I 8\
o° 6-\
2-
0.0
Wetting
Sandy Clay Loam
Location 4
TCE/Air
\ ' \
0.2 0.4
\ ' \
0.6 0.8
\
1.0
Degree of TCE Saturation
Figure 10. TCE drainage and imbibition curve at location 4 for a sandy clay loam containing TCE
and air.
2-
10 —
8-
6 -
4-
2-
1
Sandy Clay Loam
Location 4
TCE Displaced by Water
0.0
\
0.2
\
0.4
\
0.6
\
0.8
\
1.0
Degree of Water Saturation
Figure 11. Water imbibition curve at location 4 for a sandy clay loam containing TCE and water.
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2-
10 —
3 6-
|
4-
2-
Sandy Clay Loam
Location 4
Water Displaced by TCE
0.0 0.2 0.4 0.6 0.8
Degree of Water Saturation
1.0
Figure 12. Water drainage curve at location 4 for a sandy clay loam containing TCE and water.
2 -
10 —
8 -
2-
Sandy Clay Loam
Water-TCE
0.0
\ ' \ ' \ ' \ ' \
0.2 0.4 0.6 0.8 1.0
Degree of Water Saturation
Figure 13. Water imbibition curve (combined data of locations 5, 6, and 7) and drainage curve
(combined data of locations 3 and 4) for a sandy clay loam containing TCE and water.
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J. H. Dane and B. C. Missildine are with Auburn University, Auburn University, AL
36849. M. Oostrom is with the Battelle Pacific Northwest Laboratory, Richland, WA
99352.
James W. Weaver is the EPA Project Officer (see below).
The complete report, entitled "Determination of Capillary Pressure - Saturation Curves
Involving TCE, Water and Air for a Sand and a Sandy Clay Loam," (Order No.
PB94-130 754/AS; Cost: $27.00, 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:
Robert S. Kerr Environmental Research Laboratory
U. S. Environmental Protection Agency
Ada, OK 74820
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-94/005
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