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-
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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

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  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

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