United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/070 June 1993
Project Summary
LDCRS Flow from Double-Lined
Landfills and Surface
Impoundments
Rudolph Bonaparte and Beth A. Gross
A study, sponsored by the U.S. Envi-
ronmental Protection Agency (EPA), on
measured flows from leakage detec-
tion, collection, and removal systems
(LDCRSs) of 28 double-lined landfills
and 8 double-lined surface impound-
ments indicated
— all landfills with geomembrane top
liners leaked;
— landfills with composite top liners
had LDCRS flows from consolida-
tion water;
— 60% of surface impoundments with
geomembrane top liners leaked;
— landfill flows were within the ex-
pected range; those from impound-
ments were lower;
— facilities constructed with rigorous
construction quality assurance
(CQA) report leakage of less than
1,000 liters per hectare per day (L/
hd).
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
Liquid flows have been observed from
LDCRSs of many landfills and surface
units. The purpose of this report is to
summarize and evaluate field data on flows
from double-lined landfills and surface im-
poundments. In January 1992, the Liner/
Leak Detection System Rule was made
final. In this final rule, the concept of an
action leakage rate (ALR) was defined as
"the maximum design leakage rate that
the leak detection system can remove with-
out the fluid head on the bottom liner
exceeding one foot." The preamble to the
final rule states that the Agency believes
units meeting the minimum requirements
would not require ALRs below 1,000 L/hd
for landfills and 10,000 L/hd for surface
impoundments. These flow rates are re-
ferred to as EPA's recommended ALRs.
The Study
Because the types of liners
(geomembrane and composite) and the
types of drainage materials (granular,
geonet, other geosynthetic) influence the
frequency, the source, and the rates of
flow from LDCRSs, they are separated in
this report into Group I (with geomembrane
top liner and geonet drainage material),
Group II (geomembrane and sand drain-
age material), Group III (composite top
liner and geonet), and Group IV (compos-
ite and sand).
To evaluate LDCRS flow data, potential
sources of flow must be identified. Leak-
age through a geomembrane usually oc-
curs because of defects in the membrane.
Calculated leakage rates through com-
posite liners range from 0.01 to 90 L/hd;
through geomembrane liners, 400 to 6,300
L/hd. The calculated leakage rates from
geomembrane top liners are two to five
orders of magnitude greater than those
calculated for composite liners. Further, it
may take from several months to many
years for liquid to flow through the clay
components of a composite liner, but only
several days to several years through the
geosynthetic clay liner. The flow through
Printed on Recycled Paper
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a geomembrane liner can occur almost
instantaneously.
Source of Flow
Construction Water
Construction water is the precipitation
that percolates into the LDCRS before the
top liner is placed (Figure 1). Some of this
water can be retained by capillary tension
to the drainage material; the rest flows by
gravity from the LDCRS. The kind of drain-
age material affects the flow rate and du-
ration of flow.
Compression Water
As an LDCRS's granular material com-
presses under the weight of the overlying
waste or impounded liquid, not only does
the pore volume and porosity of the
LDCRS decrease, the capillary tension of
water in the pores increases as the soil
particles are packed more densely.
The flow rate of compression water from
granular material initially is small and fre-
quently negligible in comparison with flow
rates from other sources.
Consolidation Water
When a landfill or impoundment is be-
ing filled, thick layers of compacted natu-
ral clay, or bentonite-treated soil, will con-
solidate and expel water into the LDCRS
drainage layer. Because geosynthetic clay
liners are put in place dry, they do not
contribute additional liquid to the LDCRS.
The flow rate from consolidated water may
range from 10 to 1,500 L/hd. For most
landfills, consolidation will end near the
end of the landfill's active life. For some
plastic clay materials, compression water
may be a significant source after the end
of the landfill's active life.
Infiltration Water
If there is a sustained groundwater table
above the bottom of the bottom liner or if
it is a composite liner with a clay layer
undergoing consolidation or secondary
compression, infiltration water can migrate.
The infiltration through clay layers will be
relatively small; through geomembrane
bottom liners, it can be very great and
occur quickly.
Data Collection
Data on LDCRS flow rates were col-
lected from 76 monitored cells in 28
double-lined landfill facilities and from 17
monitored ponds from 8 double-lined sur-
face impoundment facilities.
Under EPA's January 1992 final rule,
owners/operators are required to monitor
the rate of flow from LDCRSs. These are
the data used here.
Flow rate measurements ranged from
the simple (calculating the flow quantities
based on changes in liquid depth in the
sump) to the complex (using tipping buck-
ets and flumes and recording the flow
data with automated data-logging sys-
tems).
The most common method used in-
volved a flow meter equipped with a me-
chanical accumulator; the change in flow
volume was divided by the time since the
last measurement.
For the study, the measured flow rates
for a specific time were compared with
calculated flow rates (from different
sources) during the same time period. This
method involved
Geomembrane
A = Top Liner Leakage
B = Construction Water and Compression Water
C = Consolidation Water
D = Infiltration Water
Figure 1. Potential flow sources from LDCRSs (from Bonaparte and Gross).
2
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— identifying potential sources based on
double-liner system design, climate,
hydrogeology, and operating histories;
— calculating flow rates from each po-
tential source;
— calculating time frames for flows from
potential sources;
— evaluating potential flow sources by
comparing measured flow rates with
calculated flow rates at specific points
in time.
The chemical constituents in the landfill
or impoundment liquid were compared with
those of the LDCRS flow to determine
whether a flow source is top-liner leakage.
Approximately 90% of the landfills in the
U.S.A. are located in relatively moist cli-
matic regions.
Results
This methodology was used to evaluate
the sources of flow from the 93 individu-
ally monitored cells (Table 1). Flow-rate
data included information from end of con-
struction, active cells and ponds, closed
cells and ponds, and those with CQA pro-
grams where information was available.
Group I
Landfills — All seven cells appeared to
have top-liner leakage with average flow
rates from 0 to 220 L/hd and maximum
flow rates about seven times greater than
average values.
Surface Impoundments — Only two of
the six ponds have had flow since the
start of operation. These six ponds were
all subject to ponding tests, or leak loca-
tion surveys, or both as part of the owner's
internal or Ihird party CQA programs, and
holes identified during these surveys or
tests were repaired. The observed leak-
age rates were smaller than those calcu-
lated from landfills and much smaller than
those calculated for ponds.
Group II
Landfills — Excluding one landfill cell,
which was constructed differently, flow
rates at all other 12 were attributed to top-
liner leakage, with average rates attrib-
uted to top-liner leakage ranging from 0 to
2,200 L/hd and maximum flow rates about
five times larger than average values. At
the six cells where CQA was not imple-
mented, larger flow rates were attributed
to top-liner leakage.
Surface Impoundments — Flow rates at
three of five impoundments were attrib-
uted to top-liner leakage and construction
water.
Chemical quality testing of LDCRS
liquids indicated top-liner leakage in both
ponds shortly after they began operating;
after repairs, the average measured flow
rate decreased significantly.
Group III
Landfills — Thirty of 31 cells exhibited
flows from LDCRSs during active life, with
average flow rates from 0 to 1,300 L/hd;
24 cells had flows less than 500 L/hd.
Based on calculated breakthrough times
for seepage through the top liner, LDCRS
flows primarily came from consolidation
water. For the 17 closed or covered cells,
LDCRS flows may have resulted from con-
tinuing consolidation secondary compres-
sion of the clay component.
Surface Impoundment — From avail-
able active-life data, flow was attributed to
consolidation water with top-liner leakage
in one pond. For both landfills and surface
impoundments, the flow rate of consolida-
tion water decreased over time.
Group IV
Landfills — For the seven cells with
GCL as part of the composite liner, one
had no flow, five had average flow rates
of 50 L/hd or less, and one had an aver-
age of 120 L/hd. The flow rate could be
accounted for by a combination of com-
pression and continuing drainage of the
sand LDCRS drainage layer or leakage
through the geomembrane top-liner on the
side slopes.
For the five active cells with a com-
pacted clay layer as a component of the
Table 1. Flow Measurements from Four Types of Facilities
Top Liner
Group
I Geomembrane
II Geomembrane
III Composite
IV Composite
"Surface impoundment.
Drainage
Material
Geonet
Sand
Geonet
Sand
Landfills
3
7
10
Landfill
Cells
7
18
37
14
SI*
2
3
2
1
SI
Ponds
top liner, three had flows less than 200 U
hd, with a range of 40 to 500 L/hd.
Surface Impoundments — For one pond,
the flow was zero from month 20 to 43
after construction. The other averaged flow
rates from 2 to 1, 120 L/hd, primarily from
consolidation water and leakage through
the geomembrane top liner on the side of
the pond.
Conclusions
EPA's recommended ALR for landfills
is 1,000 L/hd. Implementing a CQA pro-
gram appears to consistently limit top leak-
age rates to less than 1,000 L/hd. Of the
21 landfill cells in Groups I and II for
which data are available, 14 had CQA
programs, 7 did not. None of the 14 with
CQA programs had flow rates greater than
1,000 L/hd, and 11 of these had rates
less than 200 L/hd. Of the seven cells
without a CQA program, one had rates
less than 200 L/hd and five had rates
greater than 1,000 L/hd.
Of the 42 landfill cells in Groups III and
IV for which data are available, only 3
averaged flow rates greater than 1,000 L/
hd; 34 averaged less than 500 L/hd.
The facilities examined in the report typi-
cally had LDCRS flows less than the ALR
values given in the final rule. F:or Groups I
and II landfills, the primary LDCRS flows
were from top-liner leakage. For Groups
III and IV landfills, the primary LDCRS
flows were from consolidation water.
About 60% of the surface impoundments
with geomembrane top liners leaked, but
generally the flows were less than 300 U
hd, considerably less than EPA's 10,000
ALR. Maximum flow rates greater than
the recommended ALRs did, however, oc-
cur.
Recommendations
The information in the report provides a
preliminary understanding of how landfills
and surface impoundments perform. Fu-
ture studies are needed to expand this
information. Added data from more units
meeting EPA regulations should be gath-
ered. From this data base can be an-
swered such questions as what is the
quantity and chemical quality of the
leachate being generated? of the liquid
flow from LDCRSs? does this vary geo-
graphically? is there any indication that
one type of design performs better than
another?
These answers are needed to deter-
mine the long-term effectiveness of land-
fills and surface impoundments.
'U.S. Government Printing Office: 1993 — 750-071/60248
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Rudolph Bonaparte and Beth A. Gross are with GeoSyntec Consultants,
Atlanta, GA 30342.
Robert E. Landreth is the EPA Project Officer (see below).
The complete report, entitled "LDCRS Flow from Double-Lined Landfills and
Surface Impoundments," (Order No. PB93-179885; Cost: $19.50, 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
Official Business
Penalty for Private Use
$300
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POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/070
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