United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-87/097 Feb. 1988
Project Summary
Geosynthetic Design
Guidance for Hazardous Waste
Landfill Cells and Surface
Impoundments
G. N. Richardson and R. M. Koerner
Geosynthetic compounds beneath
and above hazardous waste materials
in a landfill cell provide the primary
separation between leachate generated
within the cell and the surrounding
environment. This report provides
recommendations for the design of
these geosynthetic components—the
polymer flexible membrane liners,
textiles, nets, grids, and composites
used to limit the flow of leachate and
used for the drainage and filtration
components (the leak collection and
removal system). Design guidance is
also given for ancillary components
including ramps, berms, and
standpipes.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH . to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Because the use of geosynthetics in
hazardous waste disposal cells and
surface impoundments is an emerging
technology with only relatively recent
expertise, a need exists to develop design
guidance for the users and for the
regulators who must review the design.
The report emphasizes the analyses of
field conditions and laboratory-measured
properties of the components that are
needed to properly design these compo-
nents. Construction and long-term phys-
ical considerations are also reviewed, but
chemical considerations are not.
Geosynthetics
The geosynthetics considered here are
the flexible membrane liners, textiles,
grids, nets, and composites that are used
as structural components of hazardous
waste or surface impoundment facilities.
• Geomembranes are sheets made of
impermeable synthetic polymers with
additives to improve the physical or
long-term aging characteristics. The
geomembranes are used to prevent
water flow into and out of hazardous
waste or impounded material (fluid).
• Geotextiles are woven, nonwoven,
and knit synthetic fibers made of
polypropylene, polyester, or polyeth-
ylene. Geotextiles have relatively high
permeability allowing liquid to move
through the fabric while preventing
the passage of soil particles. They can
also be used to provide tensile
strength to soils and to bridge discon-
tinuities in the subgrade.
• Geogrids are made of extruded pol-
ypropylene or polyethylene by punch-
ing a regular pattern of holes into
sheeting and drawing the sheeting
uniaxially or biaxially to increase its
modulus and strength. They are used
principally as reinforcement material
and can provide limited planar flow
capacity.
• Geonets are extruded nets formed by
extruding and bonding up to three
layers of polymer rods oriented at
acute angles to each other. They have
significant capacity of planar flow and
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are commonly used with geotextiles
to form systems for leachate or
surface water collection/removal.
• Geocomposites are high-drainage
polymerics that are made of a built-
up open drainage core covered with
geotextile that acts as a filter. They
are used to provide drainage with such
applications as lateral drains in
roadways.
Design Guidance
Currently, the design of hazardous
waste cells and surface impoundments
is based on a mix of regulator-based
minimum requirements (which are
briefly described), of performance-based
engineered designs, and of empirical
rules-of-thumb. In this report, the anal-
yses needed to properly design a syn-
thetic component—analyses based on
calculated field conditions and
laboratory-measured component proper-
ties—are given. By using performance-
based design, the designer/regulator is
allowed to properly evaluate the true
degree of protection against failure
provided by regulatory minimums or
rules-of-thumb.
The use of geosynthetic components
beneath, within, and above the cell, and
the construction and fabrication of caps,
drainage, and filtration and subgrade are
each discussed.
Each design consideration is derived
from specific equilibrium equations and
then illustrated with typical applications
(see Figure 1 for one example) for
components used:
• beneath the cell, e.g., leachate collec-
tion/removal system transmissivity,
flexible membrane liners, and filters
• within the cell, e.g., ramps, interior
berms, standpipes, etc.
• above the cell, e.g., surface water
collection/removal systems
A potential failure mode is established
A (Figure 1), a design procedure is
developed based on calculated service
conditions under field conditions F, and
then a calculated design ratio G with
minimum values is recommended for
each design procedure. Because specific
geosynthetic material properties B are
needed to determine the design ratio in
each design procedure, a suggested
range of values, based on available data,
is given C. Test procedures D and
Cell Component:
Cons deration:
VERIFY THAT L
Required Material Properties
Draft WIG Minimum
Range
Analysis Procedure:
(O
V
LEAll-
(Q CALCULATE MAXIMUM Nle>P.MAu
P •* FlMAL.
LA&OR ATOB.Y
P ATA
i
FltLO
t?e.F'Kj£
PR =
rt
Design Ratio:
References:
Figure 1. Example design calculations for leachate collection and removal system.
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andard
Example:
UT.
* SLOPE. &M
RA.T6
4-^hu
z 7-46.MO"M'lk
- / —
= t
- A-
- f
- i
I ~
'---A A A A
(4")
-A-
L_
.75 1.00 1 25
HYDRAULIC GRADIENT
NORMAL STRFSS ,PSF
O 200
• 2000
D 5000
• 10000
A 15000
A 20000
14
7.46x10"
T,
If
Example No. 3.1
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relevant standards E for each test are
referenced when available.
The equations of equilibrium are based
on "freebody" diagrams that express
both the direction and magnitude of
forces acting at a given point in the
geosynthetic component and reflect the
need for the sum of the forces to be equal
to zero in a given plain for equilibrium
conditions to exist. When a clear limit
is known for the performance of the
geosynthetic, a design ratio is calculated:
DR = allowable material performance
calculated actual material service
conditions
Although a minimum value of 1.0 for the
design ratio would be needed to prevent
an undue amount of stress or strain or
both, the performance limits of the
components and the service conditions
can not be accurately defined and a
design ratio considerably larger than 1.0
is needed to ensure satisfactory
performance.
Tests for the index properties for
geomembranes and geotextiles and for
the performance properties for geomem-
branes, geotextiles, and geonets/com-
posites are summarized in the append-
ices. The index tests provide a means of
quality control for the manufacturer and
are usually independent of actual field
conditions. Because the performance
tests try to simulate true in-situ environ-
ments and are site-specific for the given
field conditions, each test must be
carefully reviewed to determine its
applicability for each design situation.
Construction and Fabrication
The general requirements for success-
ful installation of a flexible membrane
liner and its drainage/filtration compo-
nents are outlined: their delivery, stor-
age, and quality control and quality
assurance. Proper preparation of the
subgrade is also touched upon.
The full report was submitted ir
fulfillment of CR No. 68-03-3338 by Soi
& Material Engineers, Inc., under the
sponsorship of the U.S. Environmenta
Protection Agency
The EPA author. Robert P. Hartley (also the EPA Project Officer, see below),
is with Hazardous Waste Engineering Research Laboratory, U S.
Environmental Protection Agency, Cincinnati, OH 45268; G. /V. Richardson
is with Soil and Material Engineers. Inc.. Gary. NC 27511; and R. M. Koerner
is with Geosynthetic Research Institute, Drexel University, Philadelphia, PA
19014..
The complete report, entitled "Geosynthetic Design Guidance for Hazardous
Waste Landfill Cells and Surf ace Impoundments." (Order No. PB 88-131 263 /
AS; Cost: $25.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
EfllWTflo «-3<
* : U .£ I
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Official Business
Penalty for Private Use $300
EPA/600/S2-87/097
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