Technical Note by D.B. Narejo and G.Q. Memon - IGS - International ...

Technical Note by D.B. Narejo and G.Q. Memon
COMPATIBILITY OF GEOSYNTHETIC CLAY
LINERS WITH THREE PENNSYLVANIA MUNICIPAL
SOLID WASTE LEACHATES
ABSTRACT: The free swell of three commercially available geosynthetic clay liners
is evaluated using the Geosynthetic Research Institute test method GCL 1. Leachate
from three Pennsylvania municipal solid waste landfills is used in the test procedure.
It is seen that the swelling of all three geosynthetic clay liners is significantly affected
by the composition of the landfill leachates; however, the magnitude of the decrease
in swelling varies with each leachate. Since the permeability of clays is inversely related
to their swell potential, a significant drop in free swell may indicate an increase
in permeability. Therefore, a significant drop in free swell as compared to de-ionized
water may indicate incompatibility of a geosynthetic clay liner with the service environment
in question.
KEYWORDS: Geosynthetic clay liners, Compatibility, Leachates, Landfills, Free
swell.
AUTHORS: D.B. Narejo, Applied Geoscience and Engineering, Inc., 1300 New
Holland Road, Reading, PA 19607, USA, Telephone: 610-777-5027, Telefax:
610-777-4276 and G.Q. Memon, P.O. Box 19016, Pittsburgh, PA 15213, USA,
Telephone: 412-621-5751, Telefax: 412-624-0135.
PUBLICATION: Geosynthetics International is published by the Industrial Fabrics
Association International, 345 Cedar St., Suite 800, St. Paul, MN 55101, USA,
Telephone: 1/612-222-2508, Telefax: 1/612-222-8215. Geosynthetics International is
registered under ISSN 1072-6349.
DATES: Original manuscript received 5 August 1995, accepted 2 October 1995.
Discussion open until 1 May 1996.
REFERENCE: Narejo, D.B. and Memon, G.Q., 1995, “Compatibility of
Geosynthetic Clay Liners with Three Pennsylvania Municipal Solid Waste Leachates”,
Geosynthetics International, Vol. 2, No. 5, pp. 889-892.
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NAREJO AND MEMON D Compatibility of GCLs with Municipal Solid Waste Leachates
1 INTRODUCTION
The compatibility of geosynthetic materials with the end use environment requires
serious consideration. For polymeric materials, such as geomembranes and geotextiles,
compatibility is usually evaluated according to Environmental Protection Agency
(EPA) Method 9090, or a modified form of it. For compacted clay liners the EPA Method
9100 is usually recommended for the same purpose. Since geosynthetic clay liners
(GCLs) are composites of clay and polymeric materials, it may be necessary, in some
critical applications, to evaluate the compatibility of the polymeric material according
to EPA Method 9090 and the clay according to EPA Method 9100.
The EPA Method 9100 is time consuming, thus, it may be desirable to estimate the
compatibility of the clay component of GCLs with a leachate by evaluating its free
swell. Free swell tests may be performed according to Geosynthetic Research Institute
(GRI) test method GCL 1 or a similar test.
In general, the higher the swell potential of a clay, the lower its permeability and vice
versa; e.g. montmorillonite possesses a higher swell potential and lower permeability
than kaolinite. Similarly, a liquid that causes a decrease in swell potential will also
cause an increase in permeability; e.g. when using diesel and benzene as permeants, the
free swell of GCLs will be lower and permeability higher than with de-ionized water.
Should a GCL show incompatibility with a particular service environment, some of
the following options may be considered:
1. Use a different type of GCL.
2. If possible, modify the clay component of the GCL to obtain compatibility with the
service environment.
3. Use a compacted clay liner; however, the question of compatibility still remains.
2 GEOSYNTHETIC CLAY LINERS USED IN STUDY
Three commercially available GCLs were used in this study. The GCLs are identified
as Type 1, Type 2 and Type 3. The clay component, including any fibers and adhesive,
was separated from each GCL sample type and used to perform the free swell tests.
3 LEACHATES USED IN STUDY
The leachate for these tests was obtained from three municipal solid waste landfills
in the state of Pennsylvania. The landfills were selected such that the organic and ionic
leachate concentrations ranged from mild to high. Consequently, the leachates in this
paper are identified as mild, medium and harsh. The harsh leachate had the highest concentration
of organics and ions, the mild leachate had the lowest, and the medium leachate
had concentrations of organics and ions between the two.
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NAREJO AND MEMON D Compatibility of GCLs with Municipal Solid Waste Leachates
4 TEST METHOD
The GRI test method GCL 1 was used to perform all of the free swell tests. The test
method requires 100 g of the clay component of the GCL together with any associated
fibers and adhesive. The specimen is then hydrated with de-ionized water. The clay is
spread evenly on the bottom of a 150 mm diameter California Bearing Ratio (CBR)
mold which has a porous steel base plate. A porous steel loading plate with an extension
rod is placed on top of the clay imposing a dead weight of approximately 0.68 kPa. The
CBR mold is placed in a container and de-ionized water is added to the container and
the CBR mold. The total swell after 24 hours, and the time-swell curves are recorded.
In this note only the total swell values are reported.
5 TEST RESULTS
The free swell values for the GCLs with de-ionized water and the different leachates
are given in Table 1. The de-ionized water was used as the control. All values of free
swell were recorded after 24 hours as required by the test procedure. The percentage
decrease in free swell (Table 1) was calculated using the following equation:
(Free swell) water − (Free swell) leachate
(Free swell) water
× 100 = % decrease in free swell (1)
It can be seen from Table 1 that the percentage decrease in the free swell values for
Type 1 and Type 2 is approximately the same; however, the lowest Type 1 free swell
value was obtained using the harsh leachate, whereas the lowest Type 2 free swell value
was obtained using the medium leachate. The response of Type 3 to the leachates is significantly
different from both Type 1 and Type 2. The maximum percent decrease in
free swell for Type 3 is approximately one half of the percent decrease in free swell for
Type 1 and Type 2. Moreover, Type 3 gives the smallest value of percent decrease in
free swell for the harsh leachate. This demonstrates that the Type 3 clay could be more
compatible with the harsh leachate than the Type 1 and Type 2 clay materials.
6 CONCLUSIONS
The free swell of three commercially available GCLs was evaluated using leachate
from three municipal solid waste landfills. The effect of each leachate on the free swell
of the GCLs was found to be significantly different. The lowest free swell value for the
Type 1 clay was obtained using the harsh leachate, the medium leachate for the Type
2 clay and the mild leachate for the Type 3 clay. This indicates that different GCLs may
show different levels of compatibility with different service environments. A quick and
preliminary indication of the compatibility of GCLs to service environment may be obtained
using the GRI test method GCL 1.
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NAREJO AND MEMON D Compatibility of GCLs with Municipal Solid Waste Leachates
Table 1. Free swell values of GCLs according to GRI test method GCL 1.
GCL Type 1
Leachate type
Free swell
Decrease
(mm)
(%)
De-ionized water (control) 15.4 -
Harsh leachate 5.6 64
Medium leachate 6.6 57
Mild leachate 8.0 48
GCL Type 2
Leachate type
Free swell
Decrease
(mm)
(%)
De-ionized water (control) 20.7 -
Harsh leachate 8.9 57
Medium leachate 8.0 61
Mild leachate 10.0 51
GCL Type 3
Leachate type
Free swell
Decrease
(mm)
(%)
De-ionized water (control) 12.0 -
Harsh leachate 9.5 21
Medium leachate 9.0 25
Mild leachate 8.0 34
7 RECOMMENDATIONS
The GRI test method GCL 1 may be used to obtain a preliminary estimate of the compatibility
of the clay component of GCLs to the intended service environments. Furthermore,
empirical correlations can be established between the permeability of the clay
component of GCLs and the free swell value obtained according to the GRI test method
GCL 1. Once such empirical correlations are established, a preliminary estimate of the
permeability of the clay component of GCLs can be evaluated based on free swell values.
REFERENCES
U.S. Environmental Protection Agency, “EPA Method 9090 - Compatibility Test for
Wastes and Membrane Liners”, USEPA, Washington, DC, USA.
GRI GCL 1,“Standard Test Method for the Swell Measurement of Clay Component of
GCLs”, Geosynthetic Research Institute, Drexel University, Philadelphia, PA, USA.
U.S. Environmental Protection Agency, “EPA Method 9100 - Saturated Hydraulic Conductivity,
Saturated Leachate Conductivity and Intrinsic Permeability”, USEPA,
Washington, DC, USA.
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