EPA/600/A-92/202
Geosynthetlcs '91 Conference
Atlanta, USA
The Resistance of Membranes in Cover Systems to Root Penetration by Grass
and Trees
Robert E. Landreth
U. S. Environmental Protection Agency, USA
ABSTRACT
Increased emphasis in being placed on multi-layered cover systems for waste
management facilities to minimize the need for further maintenance and to minimize
the infiltration of moisture into the unit. These cover systems contain geosynthetic
materials that perform specific design, drainage and barrier functions.
A major concern is long-term (greater than 30 years) performance of materials
used, especially barrier materials. Grasses and woody plants planted or growing
naturally on the cover may produce root systems capable of penetrating the barrier
materials. The U.S. Environmental Protection Agency has undertaken a study to
evaluate the resistance of commercially available membranes to the penetration force
of grasses and trees.
This paper will describe the issues of concern, the experimental set-up, and
the results from three lysimeters excavated after two growing seasons.
INTRODUCTION
The state of the art in landfill technology has improved significantly in the
past few years through research, design experience, and regulatory requirements. The
construction of cover systems, at closure, for waste management facilities at first
seems simple, but high-confidence techniques remain to the developed. One of the
primary goals of a cover system is to have minimum maintenance while still performing
its intended function-minimizing moisture infiltration. While maintenance is
maintained it is reasonable to expect mowing to occur at least annually if not more
often. Mowing at this frequency should minimize the establishment of deep rooted
vegetation. One issue that has not been clearly resolved for maintenance-free cover
systems is whether roots from natural vegetation will develop to the point of
penetrating the membrane barrier layer. This paper will discuss a small in-house
study to investigate the potential for woody plant roots to penetrate commercially
available membranes.
The literature contains relatively few reports on root penetration of membranes
although it is well recognized that plant systems (grasses) easily grow upward
through membranes unless the natural seed bearing soil is sterilized before membrane
placement. Laboratory studies Dexter (1986), and Stolzy and Berkley (1968) have
shown that roots do exert a pressure but probably insufficient to penetrate

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Geosynthetlcs '91 Cont«rence
Atlanta, USA
membranes. These studies also indicate that the root after encountering strong
untilled sub-soil will grow horizontally until the soil dries out, at which the plant
may die, or until weak planes of resistance allow for the continued downward growth.
The U.S. Department of Agricultural (USDA) El kins and Van Sickle (1984) has
investigated the use of roots from selected grasses to penetrate plow pans to
increase the production of agriculture crops.
One of the early studies to investigate the ability of membranes to resist
root penetration was by the Soil Conservation Service at Utah Station Lauritzen
(1953). This study evaluated fiberglass reinforced asphaltic membrane, paper-backed
membrane, asphaltic coated asbestos membrane, butyl-coated fiberglass and a sprayed
membrane. Alfalfa was planted and the extent of root penetration noted. The results
indicated the asphaltic coated asbestos liner to be more resistant than other
asphaltic liners tested and that the butyl liner also showed no penetration of the
roots. Additional tests using different plants was planned.
In a study by the Bureau of Reclamation U.S. Dept. of Interior, Bureau of
Reclamation (1961) nutgrass roots penetrated 0.15 mm and 0.2 mm (6 and 8 mil)
polyethylene and 0.2 mm (8 mil) vinyl plastic films. Roots and rhizomes of Johnson
and nutgrass in another test series were able to penetrate 0.13 mm (5 mil); 0.15 mm
(6 mil); 0.2 mm (8 mil) and 0.25 mm (10 mil) polyethylene and 6.2 mm (8 mil) vinyl
and 0.63 mm (25 mil) butyl rubber.
These studies clearly suggest that grass root penetration through membrane
should be considered. The membrane materials used in the studies were relatively
thin in comparison to currently recommended membrane thickness U.S. Environmental
Protection Agency (USEPA) (1989) for use in cover systems.
The experimental landfill test cells employed for this study are located at the
USEPA Center Hill Research Facility in Cincinnati, Ohio. The test cells were
originally installed to evaluate the impact of co-disposing industrial wastes with
municipal solid wastes (U.S. Environmental Protection Agency (USEPA) (1985). At the
completion of that project the wastes were removed and the test cells were cleaned.
EXPERIMENTAL FACILITIES AND TEST PLAN
The facility consists of fifteen outside cells buried in the ground. The cells
are 1.8m (6 ft) in diameter and 3.6 m (12 ft) deep although the total depth was not
a consideration in the design of the experiment. They are constructed of 4.76 mm
(3/16 in.) steel covered with a coal-tar epoxy. The test cells were back-filled with
a washed pea gravel to a depth of 2.7 m (9 ft.), the membrane under consideration
placed on the bottom and up and over the side, and then finished filling with a good
quality top soil, Figure 1. In selected cells the membrane was slit with a knife to
simulate tears or punctures in the membrane. Each test cell was planted with six
tree seedlings obtained from the local Soil Conservation Service. The types used for
this study were black walnut, Eastern Redbud, River Birch Tulip and Mountain Ash.
Blue grass was then seeded and fertilized to complete the cover system.
Four commercially available membranes that might be used in waste management
facilities for landfill cover systems were selected for the study. An additional
material from a local hardware store was used for comparison to the higher quality
membranes. The commercially available materials and their physical properties are
shown in Tables 1 and 2.

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Geosynthetlcs '91 Conference
Atlanta, USA
The test plan was relatively simple. Once the vegetation and trees had
established themselves, estimated to take 2 to 4 years, the system would be stressed
to determine the fate of the root system. Stressing the vegetation would be
accomplished by covering the test cells with shields to reject rainfall. Water would
be introduced under the membranes to encourage the roots to grow through the membrane
for moisture. Depending on growth performance the cells would be dissected (4 to 6
years) to determine the fate of the roots and the performance of the membrane
barrier.
PRELIMINARY RESULTS
The initial development of the grasses and trees were hampered by a drought in
the Cincinnati area. However, external watering helped to establish a good strand
of grass and only a few trees were lost. It should be noted that natural growth of
weeds, primarily Johnson grass, was also established and thrived in this environment.
As mentioned previously the test cells had been used in a co-disposal research
study using industrial wastes. Selected wastes used in the co-disposal study were
later defined as hazardous requiring sampling inside and outside of the cells for
potential contamination. As part of the Center Hill permit, test cell contents
suspected of containing hazardous wastes were removed. Trees from each test cell to
be removed were transplanted to other cells that were to remain in the study.
Fortunately, the removal of the test cell contents allowed for a preliminary review
of growth of the roots and performance of the membranes.
As expected there was an abundance of root mass near the top of each cell. At
the edge, immediately adjacent to the membrane, the root mass was at its maximum
density. However, when the soil was removed and the membrane could be pealed back
from the test cell wall there was no evidence of any root penetration. Figure 1 and
2 illustrates the root masses near the edge.
Figure 1. Root Mass within the Soil Matrix
305

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Geosynthetlcs '91 Conference
Atlanta, USA
Figure 2. Root Mass at Edge of Tank
The tree roots had not developed to the full depth of the soil. However, the
Johnson grass roots had reached the bottom of the top soil. Figure 3 shows the root
from Johnson grass reaching the membrane. The root split and was growing
horizontally across the top of the membrane. This same phenomenon was observed in
severally other locations of the test cells that were disassembled.
Figure 3. Johnson Grass Roots at Soil Membrane Enterface
306

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Geosynthetlcs "91 Conference
Atlanta, USA
Table 1. Analytical and Physical Properties of Unreinforced FMls
Prooertv
Direction
of test
PVC
LLDPE
CPE
Analytical properties




Volatiles at 1Q5+2°C, %
Extractables, %
Ash, %
Carbon black content, %
Specific gravity of FMl
Density of polyethylene, g/cm3

0.46
35.23b
1.65
i! 243
0.14
2.28c
2.27
0.945
0.936
0.14
14.30d
L349
Physical orooerties




Thickness, ml

20.0
20.2
30.6
Tensile properties:
Tensile at yield, psi
Machine
Transverse

2340
2550

Elongation at yield, psi
Machine
Transverse
¦ • •
20
15
« • •
Tensile at break, psi
Machine
Transverse
2990
2815
3985
3650
1785
1550
Elongation at break, %
Machine
Transverse
335
345
875
920
325
495
Stress at 100% elongation, psi
Machine
Transverse
1435
1895
1925
1875
1255
780
Tear strength, ppi
Machine
Transverse
360
345
775
715
280
215
Hydrostatic resistance, psi

72
140
98
Puncture Resistance
Thickness, mil
Stress, lb
Elongation, in.

20.0
31.1
0.69
20.4
32.7
1.00
30.5
41.3
0.99
WC = polyvinyl chloride; LLDPE
CPE = chlorinated polyethylene
Extraction solvent: 2:1 blend of
Extraction solvent: methyl ethyl
dn-Heptane
linear low-density polyethylene;
carbon tetrachloride and methyl alcohol
ketone
307

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.Geosynthetlcs '91 Conference
Atlanta, USA
Table 2. Analytical and Physical Properties of
Fabric-Reinforced Chlorosulfonated Polyethylene FML
Direction
	Property	of tests	Val ues
Analytical properties
Volatiles, %	0.24
Extractables, %	6.15
Specific gravity	1.518
Physical properties
Thickness, mil	37.9
Tensile properties:
Breaking strength of fabric8, lb Machine	265
Transverse	310
Elongation of fabric, % Machine	20
Transverse	27
Breaking strength of rubber, lb Machine	180
Transverse	265
Elongation of rubber, % Machine	60
Transverse	80
Ply adhesion, ppi Machine	9
Transverse	10
Hydrostatic resistance, psi	418
Puncture resistance, lb	186
"Grab test
308

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Geosynthetlcs '91 Conference
Atlanta, USA
SUMMARY AND CONCLUSIONS
The potential detrimental action of vegetation roots penetrating membrane
barriers used in waste management cover systems is being investigated in fifteen test
cells. The vegetation consisted of both grasses and trees with some intrusion of
Johnson grass. Although the study was initiated under drought conditions a good
stand of grass was developed and the trees are growing well.
Early dissection of 3 test cells established that a good root mass was
developing from grass and weed root masses had reached the membrane surface but there
was no evidence of any damage to the membranes.
These results represent only a short period of generation in the life of a
landfill cover. The RREL plans to operate the test cells for several more years.
ACKNOWLEDGEMENTS
The author wishes to acknowledge the Water Saver Company of Denver, CO and the
Gundle Lining Systems of Houston, TX for providing the membranes used in the study.
We also appreciate the assistance of Dr. Henry Haxo of Matrecon, Inc., Alameda, CA
for providing the analytical data for the membranes.
REFERENCES
Dexter, A.R., (1986) "Model Experiments on the Behavior of Roots at the
Interface Between a Tilled Seed-Bed and a Compacted Sub-soil", Plant and Soil.
95, 149-161.
Elkins, Charles B., and Van Sickle, K., (1984) "Punching Holes in Plowpans",
Solutions., July/August, pp. 38-41.
Lauritzen, C.W., (1953) "A Test of Durability of Canal Lining Materials is
Their Ability to Resist Root Penetration", Farm and Home Science. September,
pp. 58-59.
Stolzy, L.H. and K.P. Berkley, (1968) "Mechanical Resistance Encountered by
Roots Entering Compact Soils", Soil Science Vol. 105, No. 5, pp. 297-301.
U.S. Dept. of Interior, Bureau of Reclamation, (1961) "Resistance of Canal
Lining Materials to Penetration by Plant Growth Progress Report No. 1",
Chemical Engineering Laboratory Report No. W-2, November 15, Denver, Colorado.
U.S. Environmental Protection Agency (USEPA), (1985) "Evaluation and Disposal
of Waste Materials within 19 Test Lysimeters at Center Hill," Report No.
EPA/600/2-86-035, Office of Research and Development, Hazardous Waste
Engineering Research Laboratory, Cincinnati, OH. NT IS PB-86-176336.
U.S. Environmental Protection Agency (USEPA), (1989) Technical Guidance
Document: Final Covers an Hazardous Waste Landfills and Surface Impoundments
Report No. EPA/530-SW-89-047 Office of Solid Waste and Emergency Response,
Washington, D.C.
309

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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completr "
¦ 			^
1. REPORT NO.
EPA/600/A-92/202
2.
3- PB 9 3— 106714
4. TITLE ANDSUBTITLE

to Root
5. REPORT DATE
The Resistance of Membranes in Cover Systems
Penetration by Grass and Trees
6. PERFORMING ORGANIZATION CODE
7. AUTHORISI
Robert E. Landreth
RREL/WMDDRD/MSWRMB (513)569-7871
8.PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADORESS
RREL/WMDDRD/MSWRMB

10. PROGRAM ELEMENT NO.
5995 Center Hill Avenue
Cincinnati, OH 45224


11. CONTRACT/GBANT NO.
12. SPONSORING AGENCY NAME AND AOORESS
Risk Reduction Engineering Laboratory--Cincinnati, OH
13. TYPE OF REPORT AND PERIOD COVERED
Published Paper
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 45268

14 SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES Pj^O jGCt
Geosynthetics 191 Conference
Officer = Robert E. Landreth
Atlanta, Georgia, 2/26-28/9]
(513)569-7871
, Volume 1, p
.303-309
16. ABSTRACT
Increased emphasis is being placed on multi-layered cover systems for waste management
facilities to minimize the need for further maintenance and to minimize the
infiltration of moisture into the unit. These cover systems contain geosynthetic
materials that perform specific design, drainage and barrier functions.
A major concern is long-term (greater than 30 years) performance of materials used,
especially barrier materials. Grasses and woody plants planted or growing
naturally on the cover may produce root systems capable of penetrating the barrier
materials. The U.S. Environmental Protection Agency has undertaken a study to
evaluate the resistance of commercially available membranes to the penetration force
of grasses and trees.
This paper will describe the issues of concern, the experimental set-up, and the
results from three lysimeters excavated after two growing seasons.
17.
KEY WORDS AND DOCUMENT ANALYSIS

J. DESCRIPTORS
b.lOENTIFIERS/OPEN ENDED TERMS
c. COSATl FieJd/Group

Geosynthetics
Cover Systems
Landfi11s
^oots

18. DISTRIBUTION STATEMENT

19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
9
RELEASE TO THE PUBLIC

20. SECURITY CLASS (This pagei
UNCLASSIFIED
22. PRICE
EPA F«m 2220-1 (R«». 4-77) previous edition is obsolete

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