United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-91/002 Mar. 1991
EPA Project Summary
Compilation of Information on
Alternative Barriers for Liner and
Cover Systems
David E. Daniel and Paula M. Estornell
On June 7-8,1990, a workshop at-
tended by approximately 75 people was
held In Cincinnati, OH, to present and
discuss alternative barriers for liner and
cover systems for landfills, waste im-
poundments, site remediation projects,
secondary containment structures, and
other facilities. In some cases, the ma-
terials are being considered as an extra
component of a liner or cover system,
e.g., to back up a flexible membrane
liner (FML), and in other cases the al-
ternative barriers are being considered
as a substitute for a thicker layer of
compacted, low-permeability soil.
This report contains a compilation
of Information available concerning al-
ternative barrier materials and summa-
rizes the main points brought out in the
workshop. There are four main alterna-
tive barrier materials currently being
produced. Three of them consist of a
thin layer of bentonite sandwiched be-
tween two geotextiles and the fourth
consists of a thin layer of bentonite
glued to an FML. All of the materials
appear to have a. very low hydraulic
conductivity to water (between 1 x 10-10
cm/s and 1x10-* cm/s, depending upon
the conditions of testing). All of the
materials are seamed in the field by
overlapping sheets of the material and
relying upon the bentonite to form its
own seal when it hydrates. Data on the
hydraulic integrity of the seams are
much less complete compared to data
on the materials themselves. The ex-
pansive nature of bentonite provides
the bentonitic blankets with the capa-
bility of self-healing small punctures,
cracks, or other defects. The materials
have many advantages, including fast
installation with light-weight equipment.
The most serious shortcomings are a
lack of data, particularly on field per-
formance, and the low shear strength of
bentonite. The advantages of alternative
barrier materials are significant, and the
materials warrant further evaluation.
This Project Summary was developed
by EPA's Risk Reduction Engineering
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
On June 7-8, 1990, a workshop at-
tended by approximately 75 people was
held in Cincinnati, OH, to present and dis-
cuss alternative barriers for liner and cover
systems. Alternative barriers are thin,
manufactured,' low-permeability materials
that are being used and being proposed
for use in liner and cover systems for
landfills, waste impoundments, site
remediation projects, secondary contain-
ment structures, and other facilities. In some
cases, the materials are being considered
as an extra component of a liner or cover
system, e.g., to back up a flexible mem-
brane liner (FML); and in other cases, the
alternative barriers are being considered
as a substitute for a thicker layer of com-
pacted, low-permeability soil.
There are four principal alternative bar-
rier materials currently being produced.
Three of them consist of a thin layer of
bentonite sandwiched between two geo-
Printed on Recycled Paper
-------
textiles, and the fourth consists of a thin
layer of benton'rte glued to an FML All of
the materials are seamed in the field by
overlapping sheets of the material and re-
lying upon the benton'rte to form its own
seal when it hydrates.
The purpose of this report is to summa-
rize available information concerning al-
ternative barrier materials, to identify
concerns about the materials, and to iden-
tify research needs.
Procedure
This report was prepared from various
sources, including reports prepared by in-
dependent testing laboratories that have
tested the products for the manufacturers,
a very limited amount of information in the
literature, and information presented at the
workshop. The information was collected,
compiled, categorized, analyzed, and
summarized in this report. Concerns about
the materials and research needs were
identified based upon discussions at the
workshop.
Results and Discussion
One of the alternative barrier materials
is Bentomat,* which consists of 11b/ft2 (4.9
kg/m2) of benton'rte sandwiched between
two geotextiles that are needlepunched
together. Limited direct shear and tilt table
tests produced failure along the contact
between the Bentomat and adjacent mate-
rials, not through the benton'rte. Hydraulic
conductivity of small specimens perme-
ated in the laboratory with water was found
to vary with effective confining stress but is
generally in the range of 1O* to 1D* cm/s for
confining stresses of 8 to 12 psi (55 to 82
kPa). Practically no data were available on
hydraulic properties of overlapped seams
or hydraulic properties when the material
was permeated with liquids other than wa-
ter.
Claymax consists of 1 Ib/ft2 (4.9 kg/m2)
of benton'rte sandwiched between and glued
to two geotextiles. When sheared in-plane
underfully hydrated and drained conditions,
the angle of internal friction of the bento-
n'rte is approximately 10°. Hydraulic con-
ductivity of small laboratory specimens was
found to vary from approximately 1 x 8*
cm/s at an effective confining stress of 2
psi (14 kPa) to 3 x 10'10 cm/s at an effective
confining stress of 30 psi (207 kPa). Hy-
draulic conductivity to chemicals was found
to vary with the chemical and to be very
sensitive to whether or not the benton'rte
was prehydrated with water prior to intro-
duction of the chemical. The material pos-
sesses some self-healing capacity and is.
able to recover, to some extent, bw hy-
draulic conductivity if the material desic-
cates and then rehydrates or if the material
is punctured. Under carefully-controlled test
conditions, overlapped seams were found
to self-seal, provided the minimum recom-
mended overlap width (6 in. or 150 mm)
was provided.
Gundseal consists of 1 Ib/ft2 (4.9 kg/m2)
of benlbnrte "glued to a 20:mil (0.5 mm)
high density polyethylene (HOPE) sheet.
Practically no data were available on the
hydraulic conductivity of the bentonite or
the shear strength of the material. Under
carefully-controlled test conditions, over-
lapped seams were found to self-seal, even
with as little as 1.5 in. (38 mm) of overlap.
Bentofix is similar to Bentomat in that
bentonite is sandwiched between two
geotextiles that are needlepunched to-
gether. The angle of internal friction for in-
plane shear through the bentonite was
found to be approximately 30° in one series
of tests. The hydraulic conductivity of small
samples of the material is reported to be
approximately 1 x 10"9 cm/s. Information on
other characteristics of the material could
not be located.
Various other alternative materials have
been proposed. Flyash-benton'rte-soil mix-
tures show promise in terms of providing
low hydraulic conductivity and high strength.
Super-absorbent geotextiles, such as
Fibersorb, have been proposed. Sprayed-
on geomembranes, applied to a bentonitic
blanket material, have been manufactured.
Conclusions and
Recommendations
There are fundamental differences be-
tween low-permeability, compacted soils
and the alternative barriers identified in
this report. The alternative barrier materials
should not be thought of as "equivalent"
barriers. For example, the alternative barri-
ers are all much thinner than compacted
soil barriers and can never be equivalent
in this respect. However, it is conceivable
that the alternative barrier materials may
be able to provide equivalent hydraulic
functions and serve other important func-
tions adequately well.
The potential advantages of alternative
barriers (compared to low-permeability,
compacted soil) are (1) rapid and simple
installation of the alternative barrier; (2) the
potential for a more predictable end-product
with manufactured, alternative barriers; (3)
a more predictable cost for alternative
barriers that in some instances may be
Tnuchlower: than for'compacted soil; (4)
the possibility of utilizing light-weight
equipment to install alternative barriers,
which minimizes the risk of damaging un-
derlying materials, e.g., FMLs; and (5) the
possibility of developing a detailed data
base on an alternative barrier material so
that the data base does not have to be
recreated for every project.
The main disadvantages of alternative
barrier materials are (1) a general lack of
data aind independent research; (2) lack of
field experience and performance data; (3)
vulnerability to puncture; (4) the possibility
of chemical attach of the bentonite; (5)
uncertainties about performance of seams;
and (6) low shear strength of bentonite.
The research needs, in order of priority,
appear to be (1) characterization of the
shear strength of the materials; (2) deter-
mination of the hydraulic properties of the
materials for both water and waste liquids;
(3) documentation of performance of
seams; and (4) determination of probable
long-term performance in the field and
useful life.
The full report was submitted in partial
fulfillment of Cooperative Agreement Num-
ber CR-815546-01-0 with the University of
Texas under the sponsorship of the U.S.
Environmental Protection Agency.
* Montton of trade names or commercial products does
not constitute endorsement or recommendation for
lisa.
•&U S. GOVERNMENT PRINTING OFFICE: 1991/548-028/20179
-------
-------
David E. Daniel and Paula Estornell are with the University of Texas, Austin, TX
78712.
Walter E. Grubs, Jr., is the EPA Project Officer (see below).
The complete report, entitled "Compilation of Information on Alternative Barriers for
Liner and Cover Systems," (Order No. PB91-141846/AS; Cost: $17.00, 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA PERMIT NO. G-35
Official Business
Penally for Private Use $300
EPA/600/S2-91/002
------- |