United States
Environmental Protection
Agency
Municipal Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-041 Mar. 1984
4>EPA Project Summary
Assessment of Innovative
Techniques to Detect Waste
Impoundment Liner Failures
M. J. Waller and J. L Davis
Recommendations were developed
for monitoring systems that will detect
leaks in both new and existing landfill
liner systems. Both solid and liquid
impoundment sites were considered,
but liquid waste impoundments were
emphasized. The study was conducted
in two phases. First a literature review
was performed to establish the state-
of-the-art in the leak detection field and
to identify candidate methods. Second,
a multiple-objective ranking matrix was
designed and used to rank candidate
techniques according to a predefined
set of parameters covering pertinent
technical, economic, and operational
objectives.
Results indicate that no single
technique or group of techniques can
detect liner failure or leachate leaks
with absolute certainty in either
existing or planned sites. Several
techniques used in combination will
improve conventional water quality
monitoring techniques at existing sites.
In planned lined landfills, several
techniques hold promise for future
development.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search 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
Despite the many lined impoundment
and disposal sites in use throughout the
country, methods to monitor the
performance of liners have not been
adequately developed. When liner
failures occur at a site, a monitoring
system should provide warning before
significant environmental damage can
occur. Furthermore, such a system must
be capable of locating a leak precisely so
that repairs can be made. Finally, the
monitoring system must be nondestruc-
tive to the liner. Efforts to determine the
precise locations of liner leaks may be
repaid many times in terms of reduced
environmental damage, and resulting
costly litigation, and by reduced costs for
subsequent repairs.
During the course of this program,
recommendations were developed for
monitoring systems that will permit
effective in situ detection of leaks in both
new and existing landfill liner systems.
Both solid and liquid impoundment sites
were considered, but emphasis was
placed on liquid waste impoundments.
Because assessing liner performance
and detecting leaks varies in approach
and complexity between existing and
planned sites, each situation was
considered separately. At existing sites,
any leak detection program is almost
totally site-dependent because of
considerations such as site area, depth of
impoundment, and the presence of
waste already in the landfill. Sites still in
the planning stage can be tailored to a
monitoring program. Thus it may be
possible to emplace a leak detection
system directly under a planned site
before construction, or even to select a
configuration for site layout that will
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readily lend itself to a routine monitoring
program.
At the outset of this program, the
primary objective for each candidate
detection technique was the ability to
pinpoint a landfill liner failure within a
maximum area of 0.1 m2 (1 ft2). But
because of restrictions placed on
detection systems at existing sites (which
in most cases will limit them to surface
use), this goal was broadened to
encompass any system that could
feasibly improve current conventional
monitoring techniques. Thus any system
with the potential to detect a leachate
plume before it contacts the groundwater
was reviewed and evaluated. In the case
of detection techniques applied to
planned disposal sites, the 0.1 m2 (1 ft2)
goal was retained. Thus plume detection
at existing sites is distinguished from
actual leak detection at planned sites.
Program objectives were met in two
study phases. First, a literature review
established a state-of-the-art in the leak
detection field and then identified a list of
possible candidate methods. Second, a
multiple objective ranking matrix was
designed and executed. This tool was
used to rank candidates according to a
predefined set of parameters covering
pertinent technical, economic, and
operational objectives. The program
results in the information needed to set
priorities for research and development
and to allocate resources for future devel-
opment of promising leak detection
techniques.
Technical Considerations
To help define potential leak detection
systems, the study identified certain
phenomena that were expected to be
associated with liner leaks. Various leak
detection techniques for locating or
identifying these phenomena were then
selected. A review was also made of
techniques that had been applied in
various environments for a variety of
purposes, as well as those that seemed to
have conceptual application to the leak
detection problem. Phenomena that
might yield to leak detection techniques
include the following:
• Leachate conductivity,
• Subgrade and landfill materials,
• Groundwater flow fields, and
• Liner and soil distress.
Various geophysical techniques might
be applied to detecting these phenomena
under favorable site conditions. Some of
these techniques were selected for
review and evaluation here based on the
following criteria:
1. The ability to "sense" beyond their
point of application to a depth
greater than 30 m (33 yd),
2. The ability to be applied in situ with-
out harming the liner,
3. The ability to improve conventional
groundwater monitoring techniques
at existing sites, and
4. The ability to detect a leakwithinO.1
m2 (1 ft2) at planned sites.
Some geophysical techniques apply to
both existing and planned sites, whereas
others may be used in either one or the
other.
The performance of a leak detection
system depends on the site environment
and the landfill contents. Any particular
site may be subject to natural or cultural
interferences that can degrade
performance of the monitoring system.
Geophysical sensing techniques have
inherent limitations on their ability to
detect leaks, particularly at existing
waste sites. Many of the geophysical
methods are limited by the waste and
background materials, which render
surface measurements far from ideal. In
many cases, geophysical methods may
not be at all useful for detecting leaks
under a site and may only be able to detect
changed conditions over time in the
unsaturated zone before a contaminant
reaches the groundwater. Borehole
methods improve the probability of
detecting leaks because potentially they
can reveal conditions under the site and
do not have to sense through it. Borehole
geophysical techniques are most useful
when the distance between boreholes is
not greater than about 30 m (33 yd),
though this distance varies depending on
soil type and conductivity of the host
material. Most techniques fail to
penetrate at greater distances.
Detecting leaks at sites that might
undergo construction at some future date
is not simple, but it is much less complex
than for existing sites. A variety of
sensing systems can be placed near the
liner to detect the presence of leachate or
its effects, or to evaluate the mechanical
integrity of the liner itself. Ultimately, it
may be advantageous to design a system
combining several geophysical
techniques for monitoring conditions
such as the presence of leachate and the
occurrence of mechanical failures.
At planned sites, the goal of detecting
leaks within a 0.1-m2 (1 ft2) range
becomes a very real possibility.
Eventually it may be possible to design an
inbuilt system to meet the needs of any
site in terms of cost and technical
precision. Thus a small site or a municipal
landfill with nonhazarous wastes could
use a relatively inexpensive system
monitored quarterly or twice a year. For
vast impoundments of hazardous liquid
wastes, where the cost of liner failure
would be great, it will eventually be
possible to build in a continuous monitor-
ing system with equipment and
procedures designed for cell-by-cell
monitoring and daily retrieval, processing,
interpreting, analyzing, recording, and
storing of liner performance data.
State-of-the-Art Review
Based on these technical considera-
tions, a literature search was conducted
to identify possible candidate methods
being investigated in the laboratory or
applied in the field. Five data bases were
searched, including GeoRef, EnviroLine,
Pollution Abstracts, NTIS, and DOD
Documentation Center, followed by a
manual search.
The literature review provided little
information on actual leak detection
techniques in existing or planned lined
landfills. Considerably more information
was available regarding the problem of
leachate plume detection at existing
sites. But in no case was successful
leachate leak detection reported before it
was detected by groundwater quality
monitoring, which assumes fairly wide-
spread contamination. This finding does
not so much reflect the limitation of
current geophysical leak detection
techniques as it indicates the state-of-
the-practice in groundwater quality
monitoring. During the review, no cases
were found in which techniques were
actually being applied in the field to eval-
uate liner integrity.
All possible leak detection techniques
reviewed in the course of the survey are
summarized in Table 1. Techniques that
have seen application in the field to detect
a leachate plume include HF Pulse
Techniques, electromagnetics, resitivity,
and seismic techniques. Resistivity tech-
niques appear to have had the greatest
field application; these are followed by
electromagnetic techniques, which are
beginning to see wide application both for
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Table 1. Summary of Candidate Methods
Technique
SP
What is Measured
in the Ground Used from
Range Meters
Leachate Prop-
erties in Contrast Estimated
Area/ Extent to Host Medium Cost for Leak
of Anomaly Properties Detection _
Electric:
Resistivity
Resistance over a
length versus
horizontal and
vertical position
Surface
borehole
2:J Low
Voltage generated
by electrochemical
actions
Surface
borehole
<1
Meters
Low
Electromagnetic:
Low Frequency
Electromagnetic
High Frequency
Electromagnetic
A coustic:
Seismic
A coustic
Emission
For Planned Sites:
TOR Grid
Conductivity versus
horizontal and
vertical position
Surface
Dielectric properties Surface
versus horizontal borehole
and vertical position
Elastic properties Surface
versus horizontal and borehole
vertical properties
Sounds emitted from Borehole
fluid flow in soils
Dielectric properties Parallel wires
versus position on in one
transmission line direction
<100
2:J
Moderate
Moderate
High
DC Grid
Change of res/stance Parallel wires
of a wire due to in two
corrosion caused by directions
leak
<1000's
-Size of grid
spacing
High
leachate plume identification and areal
site surveys. A number of other tech-
niques were identified that are either
conceptually applicable or have seen field
use in related applications such as
petroleum exploration or extensive site
evaluations.
Multiple Objective Ranking
Matrix
Finally, a multiple objective ranking
matrix was structured to compare the
candidate methodologies with regard to a
defined set of criteria. The criteria defined
earlier for geophysical techniques were
included. Techniques were eliminated
from the matrix if they were not identified
n the literature survey as having at least
the potential for producing satisfactory
results. Also, only techniques that posed
no significant risk factors to the operators
or to the environment were considered.
Thus any technique that could not
possibly work without substantial
penetration of the dumpsite and the liner
was rejected from further consideration.
This limitation severely reduces the
number of techniques that can be used at
existing sites and also the probability of
success in detecting leaks under the
waste site.
The completed matrix evaluates each
technique on the following parameters:
• Technical factors (such as range,
resolution, lateral extent, flow direc-
tion, etc.)
Sensitivity (soil type, waste type, and
cultural noise)
Data reduction (data acquisition
time, interpretation time, etc.)
Impacts (safety, site disruption, and
site safety and liability)
Economic factors (capital cost, in-
stallation cost, etc.)
System capabilities (operator skill,
portability, survivability, and avail-
ability)
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Since some of the parameters are more
vital for success than others, a weighted
scale was devised. The weighted curve
applied to the matrix parameters appears
in Figure 1. All the values are given on a
relative scale of 1 to 10.
Matrix Results
Matrix results are summarized and
displayed in Tables 2 and 3. The average
values for all parameters tend to group
around 6.7, except for the two grid
techniques, which are about 7.8. Clearly,
no significant variation exists among the
technrques. Considering the conditions
under which methodologies were
included in the matrix, this consistency is
neither surprising nor unreasonable.
All of the techniques are very sensitive
to the soil and waste type, with an
average sensitivity value of about 4. This
value indicates that probably none of the
techniques will work in certain situations
found in a typical waste dumpsite. The
two grid techniques are less sensitive to
the site conditions because they are only
feasible for planned sites where optimum
conditions can be selected.
All the values in the impacts group
have very high ratings because the only
techniques that were considered were
those that had no significant risk factors
for the operators or the waste dumpsite.
Lower values were given if the technique
required the use of holes for short rods on
the site or if boreholes near it were
necessary. Obviously, if any risk exists for
the operator or the site, the technique is
impractical. This limitation severely
reduces the number of techniques that
can be used, and with it the probability of
success for detecting leaks under the
waste site.
All of the values in the technical factors
group for existing sites tend to be about
6.7. This result appears to be
discouraging at first, and it certainly
indicates the difficulty of using any of the
geophysical or other techniques for
monitoring or detecting leaks from an
existing waste dumpsite. Clearly no
single technique stands out as superior
for detecting leaks in existing sites. This
matrix makes it abundantly clear that a
composite of techniques must be used to
solve this complex problem, particularly
in existing sites. Nearlyall the techniques
are sensitive to the various electrical
properties of a leachate in the host
medium. The exceptions are the seismic
and acoustic mission techniques, which
are sensitive to the elastic properties and
density changes caused by a leak or the
Technical
Factors
Sensitivity Data Impacts
Reduction
Figure 1. Weighting curve applied to matrix parameters.
Economic
Factors
System
Capabilities
acoustic emission from the fluid flow from
a leak. A composite geophysical survey
can be designed to monitor a complex of
material properties, thus enhancing
confidence in the survey results.
Note that techniques evaluated for
planned sites received overall higher
scores, This result reflects the reality of
the problem described in both the
literature survey and the matrix results.
Landfill liner integrity and performance
monitoring programs will be easier to
design when they are included and
planned for at the conception of a total
waste disposal program. Note that
despite the problems associated with
geophysical techniques, they still hold
greater promise of success under
optimum site conditions than do the
conventional monitoring methods. Leak
detection at existing lined sites is and will
continue to be more problematic. But
skillful use of the techniques described
here should often lead to leak detection
before extensive groundwater contamin-
ation occurs.
Table 2. Applied Methods Summary of Ranking Matrix
Technique
Significance of Values
Mutual Inductance
VHF Wave Tilt
HF Pulse Surface
Tech-
nical
Factors
±1
6.2
6.1
7.2
Sensi-
tivity
±1.7
4.3
3.7
4.7
Data
Reduc-
tion
±1.7
8.4
7.4
7.5
Impacts
±1.7
1O.O
10.0
10.0
Eco-
nomic
Factors
±1.7
1O.O
10.0
7.6
System
Capabil-
ities
±1.7
1O.O
10.0
6.8
A verage
of All
Param-
eters
±1.5
7.1
6.7
7.1
Resistivity
Schlumberger/Wenner
Resistivity
6.9
4.0
6.3
9.4
8.5
8.6
6.6
Pole-dipole
SP Surface
Seismic Surface
7.1
5.3
7.5
4.0
3.5
4.0
6.3
8.4
6.7
9.4
10.0
10.0
8.2
10.0
8.6
7.9
9.2
9.9
6.5
6.6
6.9
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Table 3. R&D Methods Summary of Ranking Matrix
Technique
Seismic
Surface to Borehole
Seismic
Borehole to Borehole
HF Pulse
Borehole to Borehole
Tech- Data
nical Sens/- Reduc-
Factors tivity tion Impacts
Average
Eco- System of A/I
nomic Capabil- Param-
Factors ities eters
Significance of Values +1
+ 1.7 ±1.7 +1.7
±1.7 ±1.7 +1.5
7.4 4.0 6.7 9.2
7.3 4.7 6.7 9.2
7.2 4.7 7.5 10.0
Resistivity
Borehole to Borehole 6.5 4.4
Resistivity Borehole 5.6 4.3
Induced Polarization 6.6 4.0
CW/HF
Borehole to Borehole 6.8 4.0
CW/HF Surface 6.2 4.0
SP Borehole 4.8 3.8
6.8
8.1
6.7
10.0
9.8
9.4
7.7
7.7
7.2
8.7
8.8
7.4
9.9
9.9
7.7
8.0
8.6
8.3
5.0
5.1
8.4
10.0
10.0
9.5
6.1
6.6
9.5
5.9
7.2
9.2
6.7
6.8
7.1
6.8
6.7
6.4
6.1
6.0
6.4
Planned Sites
TDR Grid
DC Grid
Acoustic Emission
8.5
7.2
6.1
6.7
6.7
4.5
6.8
8.1
9.8
10.0
10.0
6.8
7.9
8.6
9.7
8.0
8.3
8.7
7.8
7.8
6.8
Conclusions and
Recommendations
Results of the survey and the ranking
matrix indicate that no single technique
currently exists that is applicable in all or
even many situations, particularly in
existing sites. Each geophysical
technique has both theoretical and site-
specific limitations. Further research is
needed to demonstrate the advantages
and limitations of a number of the
candidate methods in various dumpsite
configurations. Such investigations
should include both solid and liquid sites
in various soil types, and they should
include an array of techniques used in a
composite mode. The optimum
configuration for planned sites that are to
be monitored may be long trenches up to
30 m (33 yd) wide. This shape should
reduce the range limitations that exist
with geophysical monitoring techniques.
Though no single technique or group of
techniques has been identified as a
solution to the leak detection problem,
the group of techniques reviewed and
evaluated here can be applied systemat-
ically and synergistically to existing lined
sites with the eventual hope of detecting
leachate contamination before damage
occurs to the groundwater. Cetainly such
techniques should be applied routinely in
conjunction with water quality sampling
at any site identified as a potential
problem. In the case of planned sites,
several solutions hold promise for future
development.
The full report was submitted in fulfill-
ment of Contract No. 68-03-3029 by
EarthTech Research Corporation under
the sponsorship of the U.S. Environ-
mental Protection Agency.
M. J. Waller and J. L Davis are with EarthTech Research Corporation, Baltimore,
MO 21227.
Carlton C. Wiles is the EPA Project Officer fsee below).
The complete report, entitled "Assessment of Innovative Techniques to Detect
Waste Impoundment Liner Failures," (Order No. PB 84-157 858; Cost: $ 14.50,
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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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