United Stales
Environmental Protection
Agency
Hazardous
Research Laboratory
Cincinnati OH
Research and Development
EPA/600/S2-88/035 198S
Project Summary
The Electrical Leak Location
Method for Geomembrane
Liners
Glenn T. Darilek and Jorge O. Parra
An electrical method for locating
leaks in geomembrane liners was
developed and demonstrated for a
wide variety of applications.
Geomembrane liners are sheets of
elastomeric material used to prevent
the leakage of waste and to prevent
rainwater from Infiltrating solid waste
landfills and surface impoundments.
When no leaks are present, a voltage
applied between the material in the
liner and the earth under the liner
produces a relatively uniform
electrical potential distribution in the
material in the liner. Leaks are
located by mapping the anomaly in
the potential distribution caused by
current flowing through a leak. A
computer simulation model of
layered earth sequences above and
below an insulating liner with a leak
was developed to efficiently predict
the effect of a wld© range of
parameters on the leak signature.
Tests on a double-lined physical
model demonstrated the applicability
of th© method for a variety of
drainage layers under various test
conditions such as leak size,
@laetrod@ depth, and presence of
protective cover soil. Leaks smaller
than 0.8 mm in the primary liner can
b© reliably located to within 10 mm,
Leaks in th® bottom liner can b@
dat®et@d, but not located. The
electrical l«*k location method was
successful In finding m teak in a full
impoundmtnt that had b««n
fully tested using the vacuum box
method.
The method was adapted for
locating leaks in the geomembrane
liner of landfill cover systems. Scale
model tests demonstrated the
applicability of the method under a
wide range of cover soil thicknesses
and leak sizes. Special non-
polarizing electrodes were used to
locate leaks as small as 3 mm under
600 mm of cover soil.
This Project Summary was devel-
oped by EPA's Hazardous W»9t«
Engineering Research Laboratory,
Cincinnati, OH, to announce key
findings of the research project that is
fully documented in a separate report
of the same title (see Protect Report
ordering information at
Introduction
The most common method of disposal
of solid and hazardous wastes is in
landfills and surface impoundments. To
prevent contamination, geomembrane
liner systems are often installed
the landfill or impoundment to form an
essentially impermeable barrier that
prevents th© migration of contaminant
liquids. Installation practices and
operational factors can result in m
the form of punctures or
seams. An electrical
was develQptd to
in gaomembrane liners to
liners have and
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ptoperly and that no damage has oc-
Curred-
Technical Discussion
Figure 1 shows ihe basic electrical
teak location method for detecting and
locating leaks in a geomembrane liner
The teak location method makes use of
the high electrical resistivity of the
geomembrane liner material When no
leaks are present, a voltage impressed
across the liner produces a relatively
uniform voltage potential distribution in
the material above the liner If She liner is
physically punctured or separated.
conductive fl'jid flows through the leak
establishing a conductive path for current
flow, which produces an anomaly in the
measuzed potential in the vicinity of the
teak. Therefore, leaks can be located by
measuring the potential distribution
patterns in the material covering the
liner The electrical leak location method
can be used in liquid impoundments, as
a pre-service inspection of solid waste
landfills, and to locate leaks in the final
cover for landfills or impoundments. The
method will not damage the liner
Computer Simulation Model
Research Approach
A computer model was developed to
investigate the performance capabilities
of the electrical leak location method.
The model can accommodate various
electrical and dimensional parameters in
the three layers comprising the lined
impoundment or landfill The electrical
anomaly of a circular hole in a thin.
highly resistive layer was used to model
the response of a geomemtorana lined
impoundment or landfill containing a
damaged geornembrcne liner. The waste
material, the liner, and the soil under the
liner are simulated by infinite horizontal
layers The secondary potential for a leak
m a geomembrane liner is in the form of
an integral equation, which includes a
three-layer medium Green's function
Multiple circular leaks m the thin resistive
liner can also be modeled
To verify the validity of the modeling
technique, synthetic leak signatures were
computed and compared with fieid data
measured under the same conditions.
The excellent agreement between ex-
perimental and synthetic model data
verified the accuracy of the general
solution for predicting leak signatures.
Parametric Study
Model studies of the electrical leak
detection survey technique were made to
characterize the performance of the
method r-nder various conditions of the
electric?* arameters of ths waste
matena' > •: ~> measurement electrode
array, i '•*,• measurement dipole depth and
proximit, to the leak, Ihe size and
number of teaks, and the impoundment
depth Figure 2 shows a typical family of
leak anomaly responses illustrating the
effects of various measurement depths
for a single leak located in a liquid waste
impoundment A substantial improve-
ment m detection sensitivity is obtained
when the potential array is closer to the
leak The peak-to-peak anomaly
amplitudes for different waste layer
resistivity values were calculated. When a
constant current is injected, the teak
detsctatoility is increased linearly with trie
resistivity of the waste material.
Figure 3 shows the peak-to-peak
anomaly responses calculated fur various
dipole offset distances from the leak
center as a function of Ihe survey height
above the liner An improvement in leak
detectabiiity is observed for survey lines
located within a radius of 10 cm from ths
leak center when the depth of the c's-
tector is increased.
Field data can be acquired in
gaomembrane-liquid impoundments
using either horizontal or vertical dipole
detectors Figure 4 shows that the
horizontal dipole response is stronger
than the vertical dipole response because
of the closer proximity of the two
electrodes to the plane of the liner.
However, it may be more practical to
make subsurface survey scans using a
vertical dipoie detector rather than a
horizontal dipole detector With a vertical
dipole, the leak can be more easily and
accurately located because the leak is
located at the peak of the unipolar
response The horizontal dipole detector
exhibits a bipolar anomaly in which the
Key
s = electrode spacing
h = depth of the water
pw = resistivity of the liquid
PS = resistivity of the soil under the
liner
a = radius of the leak
zm = depth of electrodes
x = offset distance Irom the leak
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Current Source
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Figure 3.
leak location corresponds with the
crossover between {he bipolar leaks
Multiple ieaks can be resolved with less
ambiguity when a vertical dipole is used
Figure 5 shows a typical vertical dipote
anomaly response of a leak in this case.
the ieak is directly associated with the
maximum anomaly response
The detection capabilities for multiple
leaks m a geomembtane-hned im-
poundment were analyzed by computing
leak signatures for two leaks oiiented
radially away from the current source.
Figure 6 shows horizontal dipole leak
signatures computed for two survey
depths when the leaks are spaced two
meters apart As expected, when the
horizontal separation between leaks
becomes less than the horizontal dipole
spacing, separate resolution ol the two
leaks is lost When leaks at3 located at
separations approximating the horizontal
dipote detector spacing, the resolution is
poor. However, when measurements are
acquired using a small dipoie detector
spacing, the resolution is improved.
Results of the Computer
Simulation Model Study
The derived geomembrane leak
detection model is an important and
significant analysis technique for leak
location and assessment of damaged
geomembrane liners. This technique can
be implemented as an aid in planning
surveys and processing leak survey data
acquired in lined impoundments or
landfills The computed leak tesponses
point out the practical importance of
performing the survey measurements
near the bottom of the impoundment.
The results also indicate that the
horizontal dipole detector spacing must
be less than the leak separation or a
vertical dipole must be used to improve
leak resolution. The injected current must
be increased to offset the effect of lower
measured leak anomaly attributed to
lower resistivity of the liquid.
Instrumentation for Scale Model
Tests and Full-Scale Field
Evaluations
Instrumentation was assembled to test
the electrical leak location method on
outdoor physical modeis and at full-
scale field installations. A simplified block
diagram of the electronic components is
shown m Figure 7 A transmitter provides
the current needed to generate potentials
•n the impoundment. The receiver
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ISm
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0.0004 m
O.01
Ffgun 4,
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nr
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Leak
Liner
Horizontal Dipole Response
0.15
Height Above L'ner, h-i™ !ml
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025
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Figure S.
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Transmitter
To Current
Return
Electrode
To Current
Source Electrode
in Water
Recorded
Data to
Processing
Measurement
Electrodes
Figun 7.
Current Electrode
Figure 8.
measures the resultant potentials, which
are then logged by the computer. For
full-scale field surveys, a dual-drum
electric logging winch is equipped with
the logging cable and a nylon rope
drawn through a remote sheave. The
electrodes are suspended from two floats
to make potential gradient meas-
urements.
Double Liner (Model Tests
Background
Double-lined facilities are required to
meet EPA minimum technology stand-
ards for hazardous waste impoundments
By placing the current return electrode in
electrical contact with the liquid-
saturated drainage layer located between
the two liners, the electrical teak location
method is applicable for detecting and
locating leaks in the upper liner. Simple
electrical continuity tests between the
drainage layer and the earth can also
determine the existence of a significant
leak in the bottom iiner, but not the
location of that leak.
Research Approach
A scale model with dimensions of 3 m
x 3 m was used to test the electrical leak
location method for locating leaks with
various impoundment configurations.
including different types of drainage
layers, various types of leaks, and a
protective soil cover over the primary
liner An electrode support bar was used
to position the potential electrodes at a
constant depth as close as possible to
the liner. Tests were conducted using
various electrode materials and geo-
metries to determine the best and most
practical electrode configurations for
electrical leak location surveys in liquid-
filled impoundments.
Results of Double Uner
Model Tests
Figure 8 is a contour plot of the data
for a leak with a diameter of 5.1 mm with
a drainage layer consisting of a sandy
loam soil layer placed over the geotextile
mat, which is then placed over the
geonet material. The location of the leak
is clearly indicated by the dipolar contour
pattern. The potential gradient pattern
caused by the current injection electrode
is also evident in the data. Other tests
indicated that a leak with a diameter of 25
mm and a 15-cm slit leak produce
anomaly characteristics very similar to
the leak with a diameter of 5.1 mm.
However, the larger leaks required less
voltage to produce the same anomaly
amplitude.
The characteristic dipolar negative-
to-positive transition of trie leak anomaly
was clearly indicated for a leak with a
diameter of 5.1 mm on tests conducted
with a protective soil cover with a
thickness of 15 cm placed over the
geomembrane iiner. The approximate
location of the leak can be determined
from the contour data, but the dipolar
pattern is weaker.
Figure 9 shows the relative leak
anomaly amplitudes for various elec-
trodes when the centerlines of the
electrodes were scanned directly over
the leak and 15 cm offset from the leak.
The sensitivity of the stainless steel and
carbon electrodes was comparable.
When the electrodes were scanned
directly over the leak, the anomaly
amplitudes were inversely related to the
length of the electrodes. However, when
the electrodes were scanned along a line
15 cm from the leak, the 30-cm line
electrode produced the largest anomaly.
Most importantly, the leak anomaly was
barely detected when the localized point
electrodes passed within 15 cm of the
leak, where the longer electrodes
produced easily detectable anomalies.
Locating Leaks in Cover
Systems
Background
Geomembrane liner material is widely
used for landfill final cover systems. An
impermeable cap is placed over the
hazardous waste to prevent rainwater
from percolating through the waste and
leaching chemicals that could migrate
into groundwater or surface water. The
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Scan Over Leak
Figure 9.
electrical leak location method was
adapted to make surface soil potential
measurements to locate leaks in final
cover system geomembrane liners.
Polarization noise is caused by electro-
chemical reactions at the interface
between the soil and metal electrodes.
This noise can be reduced to a signif-
icant degree by using half-ceil elec-
trodes. These electrodes typically
consist of a plastic tube with a porous
ceramic tip. Electrical contact is made
through a metal electrode in a saturated
salt solution in the half-cell.
Research Approach and Results
Experiments were conducted using a
physical model with dimensions of 5 m x
5 m. Figure 10 is a plot of the measured
leak anomaly for several soil cover
thicknesses. Although the peak-to-
peak amplitude of the anomaly
decreases rapidly with increasing soil
cover, the leak was easily detected for all
of the soil cover depths tested. Tests
were performed with 60 cm of soil cover
to show that electrode contact noise is
reduced significantly when the
electrodes are inserted in the ground to a
depth of approximately 25 mm or when
the dry ground surface is scraped off
prior to the measurements.
3O-cm
Line
Scan Offset IS cm
Protected
2S-cm
Line
Leak Diameter = 3 mm
ll
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8 T
r
o
1
1234
Distance (Meters!
15.2 cm Soil 25.4 cm Soil
-'30.5 cm Soil • 61 cm Soil
Figure 10.
Other Leak Location
Methods for Cover Systems
The infrared imaging technique was
evaluated for detecting subtle
temperature differences in the soil cover
related to localized areas of low thermal
conductivity caused by the drainage of
soil moisture through a leak in the
underlying geomembrane. The hypo-
thesis was that during early morning or
immediately after sunset, when solar
heating was introduced or removed, heat
would not be conducted as well in the
slightly drier soil above a large leak in the
geomembrane, which would result in a
detectable temperature difference
associated with the leak. The tests
indicated that the infrared imaging
technique was not applicable because no
temperature anomalies were detected,
even with only 67 mm of soil cover.
Other methods for detecting leaks in
the geomembrane liner of cover systems,
including ground-penetrating radar,
tracer gas, the electromagnetic induction
method, encapsulated chem-icals, and
electronic transponders, were analyzed.
Ground-penetrating radar was judged to
offer the highest likelihood of success.
Under suitable conditions, the method
can detect areas of concentrated
moisture beneath the geomembrane liner
caused by leaks in the liner. However,
the success of the method depends upon
the soil having only moderate
conductivity and, hence, reasonably low
dissipation of electro-magnetic energy.
Ground-penetrating radar may offer the
additional capability of mapping the
depth of the soil cover and the lateral
extent of the seepage through a leak.
Liner Resistivity Tests
Research Approach
Tests were conducted to measure
electrical resistance changes in liners
over a period of time to determine
whether the electrical resistance of the
liner materials changes after exposure to
waste liquids, thereby reducing the
usefulness of the survey technique. The
tests were performed in triplicate using
five different types of liner material
exposed to four different liquids. The
liner materials tested included polyvinyl
chloride, high-density polyethylene, two
thicknesses of chlorosulfonated poly-
ethylene, and chlorinated polyethylene.
The liquids used in the tests included
sodium hydroxide solution, pH of 10;
sulfuric acid solution, pH of 1; sodium
chloride solution, 10 percent by weight;
and deionized water.
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Results of Liner Resistivity Tests
The test results indicated that the
measured resistance values were at least
two orders of magnitude higher than the
resistance needed to allow the practical
application of the electrical leak location
method. The electrical leak detection
technique will not be affected for liner
systems constructed from the materials
tested under exposure to these liquids
Field Demonstration Surveys
Full-scale surveys at the Southwest
Research Institute test impoundment
were performed to detect and locate four
small circular leaks, each 079 mm m
diameter. Tho impoundment was filled
with water to a depth of approximately 46
cm. The contour plot of the data shown
in Figure 11 graphically indicates the
locations of the four leaks. The contour
plot, together with the potential plots for
each survey line, provide a
straightforward means to analyze and
interpret the data for leak detection and
location purposes.
The electrical leak location method
was demonstrated at another full-scale
impoundment in the San Antonio. Texas
area. Although the complete liner had
been tested previously using the vacuum
box method, a 2.0-cm long leak was
found. The characteristic leak anomaly
was clearly evident on scan lines as far
away from the leak as 15m, and no
false indications were obtained
Conclusions and
Recommendations
An electrical method for detecting and
locating leaks in geomembrane liners for
hazardous waste impoundments and
landfills has been developed and
demonstrated successfully in a wide
variety of applications The project
demonstrates the validity and usefulness
of the electrical leak location method for
testing the integrity of the geomembrane
for single and double liners and final
cover systems. The technique is cost
effective for construction quality
assurance and in-service performance
monitoring.
The computer simulation mode! effi-
ciently and accurately predicts the effect
of a wide range of measurement
parameters on the leak signature. The
computer simulation model indicates that
leak location sensitivity is increased very
significantly when the electrodes are
scanned as close to the liner as possible.
For a given level of injected current, leak
25 r
is
9)
1
W 15 20 25 30 35
Meters
Figure 11,
location sensitivity increases propor-
tionally with the resistivity of the material
on the liner
Tests on a double-lined model
demonstrated that the method can be
applied to a wide variety of double liner
configurations of drainage layers with
various test parameters such as leak
size, electrode depth, and protective soil
cover. Leaks smaller than 0.8 mm in
diameter can be reliably iocated. Leaks
can be detected from distances greater
than 15 m from the leak. Linear
electrodes oriented perpendicular to the
scan direction, with scans offset by ap-
proximately the length of the electrodes,
produce the highest likelihood of
detecting all leaks compared with
surveys using localized electrodes. The
electrical leak location method is less
sensitive for locating leaks in
geomembrane liners with liquid and
protective soil cover over the liner The
shape and size of the leak have littie
effect upon the shape of the leak
signature However, the leak size affects
the leak current, thereby increasing the
amplitude of the leak signature. A simple
continuity test can indicate the presence,
but not location, of leaks in the bottom
liner.
The electrical leak location method is
also an effective meihod for locating
leaks in geomembrane liners of waste
impoundment or landfill final cover
systems Non-polarizing half-cell
electrodes were used to greatly reduce
the polarization voltage noise. The
method was very successful in locating
leaks as small as 3 mm under 60 cm of
soil cover.
The most promising method studied
for locating leaks in final cover systems,
other than the electrical leak location
method, is ground-penetrating radar.
Limited testing using infrared imaging
was unsuccessful in detecting localized
areas of low thermal conductivity caused
by drainage of soil moisture through a
leak.
Laboratory tests indicated that there
was no significant decrease in the
resistivity of typical liner materials during
a 13-week exposure to water, salt water,
acidic solution, and basic solution.
Exposure of these typical liner materials
to these chemicals had no effect on the
applicability of the electrical leak location
method.
The equipment and procedures for
conducting full-scale leak location
surveys also can detect leaks with a
diameter of 0.8 mm up to 1.5 m away
from the leak. A leak was found in an
impoundment that had been fully tested
using the vacuum box method.
The electrical leak location method has
been developed to the stage of industry
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use for nonhazardous applications,
including pro-service leak location
surveys for impoundments and landfills
and surveys of nonhazardous in-service
impoundments. Additional development
will bring the method into application for
hazardous material impoundments and
for final cover systems. The electrical
leak location method should be
demonstrated at one or more field
installations for final cover systems and
for a liner with a protective soil cover in
place. The ground-penetrating radar
technique should be evaluated for
detecting leaks in final cover systems.
Methods should be developed to repair
in-service geomembranes.
Glenn T, Darilek and Jorge O. Parra are with the Southwest Research Institute.
San Antonio, TX 78284.
Charles J. Moench, Jr., is the EPA Protect Officer (see below).
The complete report, entitled "The Electrical Leak Location Method for Geo-
membrane Liners," (Order No. PB 88-220 496'AS; Cost: $19.95, subject to
change) will be available onfy from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
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
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-33
Official Business
Penalty for Private Use $300
EPA/600/S2-88/035
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