Leak Detection for
Landfill Liners
Overview of Tools for Vadose Zone
Monitoring
Karen Mix
Technology Status Report prepared for the U.S. E.P.A. Technology
Innovation Office under a National Network of Environmental Management
Studies Fellowship
August 1998
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»B« Leak Detection for
Landfill Liners
Overview of Tools for Vadose Zone
Monitoring
^K ^M
Karen Hix
is;
!!
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I
Technology Status Report prepared for the U.S. E.P.A. Technology
Innovation Office under a National Network of Environmental Management
Studies Fellowship
August 1998
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NOTICE
This document was prepared by a National Network of Environmental Management Studies
grantee under a fellowship from the U.S. Environmental Protection Agency. This report was not
subject to EPA peer review or technical review. The U.S. EPA makes no warranties, expressed
or implied, including without limitation, warranty for completeness, accuracy, or usefulness of
the information, warranties as to the merchantability, or fitness for a particular purpose.
Moreover, the listing of any technology, corporation, company, person, or facility in this report
does not constitute endorsement, approval, or recommendation by the U.S. EPA.
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FOREWORD
Identifying leaks in landfill liners is an essential part of waste management. EPA's Technology
Innovation Office (TIO) provided a grant through the National Network for Environmental
Management Studies (NNEMS) to prepare a technology assessment report on identifying leaks in
landfill liners. This report was prepared by a senior undergraduate student from Virginia Tech
during the summer of 1998. It has been reproduced to help provide federal agencies, states,
consulting engineering firms, private industries, and technology developers with information on
the current status of this technology.
About the National Network for Environmental Management Studies (NNEMS)
NNEMS is a comprehensive fellowship program managed by the Environmental Education
Division of EPA. The purpose of the NNEMS Program is to provide students with practical
research opportunities and experiences.
Each participating headquarters or regional office develops and sponsors projects for student
research. The projects are narrow in scope to allow the student to complete the research by
working full-time during the summer or part-time during the school year. Research fellowships
are available in Environmental Policy, Regulations, and Law; Environmental Management and
Administration; Environmental Science; Public Relations and Communications; and Computer
Programming and Development.
NNEMS fellows receive a stipend determined by the student's level of education and the
duration of the research project. Fellowships are offered to undergraduate and graduate students.
Students must meet certain eligibility criteria.
About this Report
This report is intended to provide a basic summary and current detection of leaks hi landfill
liners. It contains information gathered from a range of currently available sources, including
project documents, reports, periodicals, Internet searches, and personal communication with
involved parties. No attempts were made to independently confirm the resources used.
While the original report included color images, this copy is printed in one color. Readers are
directed to the electronic version of this report to view the color images; it is located at
http://clu-in.org.
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TABLE OF CONTENTS
Page
1. PURPOSE 3
1.1 Monitoring background 3
1.2 Overview of leak sensor options 4
1.3 Cost 5
1.4 Other types of leak detection 5
2. ESTABLISHED SENSORS 6
2.1 Electrical 6
2.1.1 Two electrode method 6
a. Advantages 7
b. Disadvantages 7
c. Example- Sandy Lane landfill 7
2.1.2 Electrode grid method 7
a. Advantages 7
b. Disadvantages 8
c. Example 1- Sandy Lane landfill 8
d. Example 2- WESTEC' s Electronic Leak Detection System 9
2.2 Diffusion hoses 9
a. Advantages 9
b. Disadvantages 9
c. Example-Siemens'LEGS 10
2.3 Capacitance sensors 10
a. Advantages 11
b. Disadvantages 11
c. Example- Troxler's Sentry 200 EMMS 11
2.4 Tracers 12
a. Advantages 12
b. Disadvantages 12
c. Example 1- Tracer Research Corporation's Automatic Leak Detector 12
2.5 Electro-chemical sensing cables 13
a. Advantages 13
b. Disadvantages 13
c. Example 1- Noverflow's SMART CABLE 13
d. Example 2- Raychem's TraceTek 14
2.6 Other 15
a. Visual inspection 15
b. Wires in geotextiles 15
3. EMERGING TECHNOLOGIES 15
3.1 Geosynthetic Membrane Monitoring System 15
1
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3.2 SEAtrace 17
3.3 FLUTe ideal system 18
3.4 Other 19
a. LIDAR 19
b. Acoustic monitoring 20
4. CONCLUSION 20
Appendix A- Overview grid 21
Appendix B- Contact information- available sensors 22
Appendix C- Contact information- emerging technologies 23
Appendix D- Web sites 24
References 25
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1. PURPOSE
Identifying leaks in landfill liners is an essential part of waste management. Several types
of leak detection tools can be installed in addition to monitoring wells to identify leaks soon after
they occur. This paper provides an overview of some tools for vadose zone monitoring, as well
as the advantages, disadvantages, and costs associated with them.
1.1. Monitoring background
Federal law requires all landfills to include a leak detection system above the bottom
composite liner. The system must consist of a layer of granular drainage materials with a slope of
at least one percent, so any leachate which passes through the top liner will drain into the sump at
the bottom of the unit, where its volume is recorded.(40 CFR 264.301) This system establishes
what volume of leachate has leaked through the top liner, but it does not indicate whether or not
leachate is leaking through the bottom liner.
In addition, all landfills are required to install a groundwater monitoring system. The
system must consist of both up gradient and down gradient wells which allow sampling of the
groundwater in the uppermost aquifer, as shown in figure 1. The number, spacing, and depths of
the required wells are dependant on the geologic and hydrologic properties of the area. (40 CFR
258.51)
Upgradient Wefl
Landfill
"i - ' ": -r7«-=i_^ ^K*1*" ;- ?'-"»^_
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Downgradient Wdls
n
:-; Saturated Zone <.;>
^^^^^:^^^^^^?!^^^^^ ~
" : -. . .. e . ' ;;.
Sandstone'.; ." -. , Sandstone
Figure 1:
Cross section of a traditional groundwater monitoring system. (GAO, 1995)
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By collecting groundwater samples and analyzing them, landfill operators can usually
detect contaminant plumes caused by leaks in the landfill liner. One limitation of this method is
that it does not prevent the groundwater from becoming contaminated. Another limitation is the
expense of comprehensive monitoring for all groundwater which comes in contact with a landfill.
Because most landfills are lined with geomembranes, most leaks are point sources, not
widespread. If there is no monitoring well in the path of a plume, it is possible for the front of the
plume to pass by the line of wells at the point of compliance without being detected. Installing
enough monitoring wells to be sure of intercepting a narrow plume in any position can be
prohibitively expensive. (Godfrey, 1987)
California has especially rigorous monitoring requirements. State law requires testing for
leakage in the vadose zone under waste disposal sites. (CA Code) The two most common ways
to comply with this requirement are lysimeters, which collect pore water for later removal and
testing, and soil core sampling. Both of these methods require laboratory testing and neither can
easily pinpoint the location of the leak. (Daniel, 1987)
1.2 Overview of leak detection options
In addition to the monitoring methods required by law, some landfill owners are choosing
to install systems of leak detection sensors. These sensors permit early leak detection without
laboratory analysis, and often locate the leak.
Several different types of sensors provide these benefits. Some work by electrical
methods, measuring the resistivity or dielectric constant of the soil. Others work by chemical
methods, either analyzing soil vapor or reacting directly to leachate. These sensors are often
dependant on the composition of the leachate. Still others use tracer chemicals to detect leaks.
Use of these technologies is not widespread, mainly because of cost Most must be installed
during construction and are not applicable to existing landfills.
Each of the leak detection systems available has different advantages and disadvantages.
The perfect vadose zone monitoring system has not yet been designed, but the ideal system
would:
- Be affordable
- Be durable enough to last through the life of the landfill and the 30 year post-closure period
- Locate leaks and determine their sizes
- Be automated
- Be applicable to all types of landfills and all types of leachate
- Provide full spatial monitoring for the entire area below the landfill
Research on new sensors for leak detection at landfills is ongoing, but it is also limited because
the market for this optional extra level of detection is extremely small.
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1.3 Cost
The main reason leak detection sensors are not more widely used at landfills is the cost.
By law, sensors may only be used in addition to monitoring wells, not in place of them.
Therefore, it is uncommon for a landfill owner to choose to install leak detection sensors. The
owner has no way of knowing whether or not a major leak will ever occur, so the benefits of
detecting a hypothetical future leak earlier do not outweigh the immediate costs of installing a
vadose zone leak detection system.
A comparison compiled by Inyang (Rumer, 1995) of monitoring costs for a hypothetical
landfill showed that sensors can be less expensive than monitoring wells. Inyang compared the
cost of monitoring a 20,000 ft2 area for 20 years with monitoring wells to the cost of monitoring
the same area with the Raychem system for electro-chemical monitoring, (see section 2.5 d) The
costs are broken down in the following table:
Cost comparison for monitoring wells vs. electro-chemical sensing
Monitoring technique
Groundwater
monitoring wells
Well installation
Chemical analyses
Operation and management
Total cost
Electro-chemical sensing
Central electronic unit
Sensing cables
Connecting cables
Sensor installation
Operation and management
Total cost
Unit cost (S)
5,000
18,000 per well
100,000
Number required
3
3
Total item cost
15,000
54,000
100,000
169,000
5,000
1,200
300
400
120,000
1
3
3
3
5,000
3,600
900
1,200
120,000
130,700
(Rumer, 1995)
Although the cost of me electro-chemical system is lower than that of the monitoring
wells, the entire system would cost $299,700, which is substantially more than the wells alone.
1.4 Other types of leak detection
This report includes information on permanently emplaced monitoring systems which
detect leaks in the vadose zone. Surface geophysical techniques such as ground penetrating radar
will not be covered; nor will direct push site characterization techniques or sampling techniques
such as lysimeters.
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Most of the techniques used for locating leaks in subsurface barriers are not readily
applicable to landfills. For more information on ground penetrating radar, electrical resistance
tomography, and other subsurface barrier monitoring techniques, refer to the following report
Rumer, R.R. and J.K. Mitchell, eds. 1996, "Assessment of Barrier Containment Technologies: A
Comprehensive Treatment for Environmental Remedial Application." Product of the
International Containment Technology Workshop. National Technical Information Service,
PB96-180583.
2. ESTABLISHED SENSORS
2.1 Electrical
There are two main ways of detecting leaks using electrical methods: the two electrode
method and the electrode grid method. Both leak detection techniques utilize the insulative
properties of geomembrane liners. The first method detects the flow of current from one
electrode to another through a hole hi the insulative liner. The second method depends upon the
liner to insulate the containment area so that only leachate which has escaped into the soil will be
detected.
2.1.1 Two electrode method
The first method requires installing one electrode inside the landfill, and another in the
ground outside the containment area. Electrical current is introduced into the containment area by
the electrode inside the landfill. Because of the electrical resistance of the liner, the current will
not flow to the electrode in the ground if there are no holes in the liner. Flow of current from one
electrode to the other indicates a leak, as shown in figure 2. (White et al, 1997)
Current Beetricalnoienl
electrode pasced into
Receirag electrode
Synthetic
liner
(HOPE)
in liner
Figure 2:
The flow of electrical current through a landfill with a defect in the synthetic liner. (Adapted from White et al,
1997)
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a. Advantages
The two electrode method can be especially useful for detecting leaks in pre-existing
landfills because this technique does not require the installation of any sensors below the liner.
b. Disadvantages
This method indicates only the existence of a leak, not the number, size or location.
Current flow can be caused by one leak or several, and by large or small leaks. In order to
determine the location of the leak, a map of the voltage distribution must be determined. This is
achieved by passing voltmeters systematically over the liner within several inches of the surface.
An area of high voltage indicates a leak. Because voltmeters cannot be passed directly over the
liner if the landfill has begun accepting solid waste, the two electrode method is popular for use
in liquid containment basins and on solid waste disposal cells which have not yet begun
accepting waste. (Laine et al, 1993)
c. Example- Sandy Lane landfill
Sandy Lane Landfill is located on a major aquifer in the United Kingdom and within one
kilometer of a public well. The site was originally a sandstone quarry. In order to receive
permission to begin planning and construction, its designers decided to include an electrical
monitoring system in the plans.
The system included a combination of the electrode grid method which will be discussed
in section 2.1.2 and a version of the two electrode method. Instead of a single electrode being
placed outside the liner, a grid of electrodes was installed below the liner to allow leak location.
A single electrode was installed in the sand protection layer above the liner as the current source
for liner integrity testing. If the electrode grid below the liner detects current from the electrode
inside, it indicates that a breach has occurred in the liner. (White et al, 1997) For more
information on the electrode grid, see section 2.1.2 c.
2.1.2 Electrode grid method
The second method makes it possible to actually locate leaks in active and closed solid
waste landfills. It requires installing a grid of electrodes beneath the primary liner during
construction. The electrodes are used to energize the area around the liner and to measure the
resulting voltage of the soil near each electrode. Because leachate has a higher electrical
conductivity than either soil or water, an area of a difference in voltage indicates that leachate has
escaped from the liner at that location.
a. Advantages
This system involves simple, durable components that can last for several decades. It
monitors the entire area below the liner, not just certain points. In addition to detecting leachate
releases, the electrode grid can also detect holes in the liner before waste is placed in the cell in
the manner described above in section 2.1. Current is introduced into the protective soil layer. If
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the current is detected by the electrodes, it has passed through a hole in the insulative
geomembrane liner.
b. Disadvantages
This system is not applicable to existing landfills because the electrodes must be installed
during the construction of the cell.
c. Example 1- Sandy Lane landfill
Sandy Lane landfill, which was introduced in section 2.1.1 c, can also detect leaks by the
electrode grid method. The monitoring system was installed when the landfill was built in 1995.
The lower liner is underlain by a grid of stainless steel monitoring electrodes spaced 20 meters
apart, as shown in figure 3. This distance was chosen based on mathematical modeling and
small-scale testing. Multicore cables connect the electrodes to each other and to the control
equipment, which is housed in the weigh station. The area around the electrodes was backfilled
with bentonite enhanced sand because of its high conductivity.
r
Insulating 23nun high-density
polyethylene liner
Domestic waste
Sand protection
brer
v* w ^ ^*
-rcH.* «f mnnitiintMr I1
Sand* tnr
Grid of monitoring ^Beattnite enhanced sand
electrodes
Figure 3: A cross section showing the position of the grid below Sandy Lane landfill. (White et aL 1997)
The system was first used to verify the continuity of the liner after it was installed. One
intentional and one unintentional hole were located and repaired. During the first year of
operation, monitoring was conducted monthly. Data collection typically took one to two hours
All voltage irregularities were found to correspond to holes in the geomembrane. After the first
year, monitoring was conducted according to a schedule based upon past data.
In the event of significant contamination of the area below the landfill, the monitoring
system can be used to map the pollution plume as it moves toward the monitoring wells, both in
the vadose zone and in the groundwater. Initially, the system was installed over an area of 30,000
meters. The system is being installed in other cells as they are constructed. (White et al, 1997)
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d. Example 2-WESTEC's Electronic Leak Detection System
The Electronic Leak Detection System produced by Westec, Inc. consists of an exterior
patch panel installed during the construction of the liner system. Electrical nodes are connected
to the panel in a grid with 100 feet of space between nodes.
The system can detect leaks as small as 50 gallons. It runs on 12 volt batteries. After the
installation of the system, it must be calibrated by introducing a controlled amount of simulated
leachate below the liner and monitoring the subgrade response. (VendorFACTS, 1997)
Analysis of a positive reading reveals the size of a leak, in addition to its existence and
location. Computer processing of the data produces a three dimensional graphic image of the
leak. The cost of the system is typically less than a third of the cost of the geosynthetic liner.
(Robison, 1996)
The system has been installed in over 20 million square feet of containment facilities at
ten sites in the western United States since its first installation in 1987. In 1995, the system was
installed at a landfill in Italy. (VendorFACTS, 1997) The largest installation of this technology
has been operating at a gold mine in Elko, Nevada for eleven years. (Robison, 1996)
2.2 Diffusion hoses
Diffusion hoses were originally developed for detecting leaks hi pipes. A diffusion hose
system consists of a network of vapor-permeable tubes emplaced in the ground under the landfill.
After a set period of time, the gas in the hose is pumped out through a detector which records
contaminant concentration as a function of pumping time, as shown in figure 4. By observing the
time at which contaminants were detected, the leak location can be determined within one or two
meters. Because the vapors of a leak diffuse into the tube at a concentration proportional to the
concentration in the soil, the approximate leak size can be determined by analyzing the vapor
concentration inside the tube. The identification of the composition of the leak is possible by
sampling the contaminated gas as it passes out of the detector and analyzing it by gas
chromatography or other laboratory methods. (Stammler, 1985)
a. Advantages
Diffusion hoses are widely available for tank and pipeline use. The system is automatic,
so it is not necessary for a technician to spend time running tests. This autonomy reduces the cost
of operation.
b. Disadvantages
In order to be detected by the diffusion hose system quickly, the leachate must produce
vapor. If the leachate does not produce any vapor, the system will not detect the leak until the
leachate comes directly into contact with the hose and the liquid itself diffuses into the tube. If
the leachate produces no vapor, the diffusion hoses must be placed very close together to produce
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a high probability of intercepting a leak at any point in the liner. This would increase the cost
significantly.
small leak very small leak
Cone
m
entration (ppm)
-10000
-1000
-100
-10
Pipeline
fpl
m\ } . ii
\ 1 ~* , 1 ^«t / Pumpmg every
leaked materials diffuse / 24hours
into sensor hose /
sensor hose
hzgepeak
1 snallpeak
v H . .
-
1 i
...[..
12345678
ftaopinstin*
Distance (km)
Figure 4:
Schematic of die leak detection and location method of a diffusion hose. (Stantmler, 1985)
c. Example- Siemens' LEOS
The hose of the LEOS leak detection system, manufactured by Siemens, is composed of
several layers of durable plastic. The tube is filled with purified air, which is later evacuated and
tested for contamination with semiconductor gas sensors. When the alarm threshold is crossed,
the location and concentration distribution of the leak are displayed. Leaks can be located to an
accuracy of 0.5% of the length of the hose. ( LEOS Leak Detection System page)
2.3 Capacitance sensors
Capacitance sensors measure the soil's dielectric constant, which is a measure of how well
the soil resists a change in the electric field. The dielectric constant of dry soil is around 5 and the
dielectric constant of water is around 80. When soil becomes moistened.by a leak, its dielectric
constant increases. Measuring the change in dielectric constant of an area over time can indicate
whether or not a leak has occurred there.
The sensors work by frequency domain technology, which means they resonate at a
harmonic frequency dependent on the dielectric constant of the soil around the probe. From the
frequency, the moisture content can be determined with the calibration curve. (VendorFACTS,
1997) Capacitance sensors are commonly used in agriculture to determine irrigation schedules.
10
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a. Advantages
Capacitance sensors are readily available for purchase, as several companies market them for
agricultural use. They can be programmed to take moisture readings automatically.
b. Disadvantages
Moisture content is the only quantity measured by capacitance sensors, so they measure all
moisture, not specifically leachate. They must be installed far enough above the highest water
table to be sure the probe doesn't detect groundwater. Each probe only measures the dielectric
constant of the soil immediately surrounding it, so the more complete the leak detection coverage
desired, the more probes are necessary, and the more the system will cost. The probes must be
buried during construction of the landfill.
c. Example- Troxler's Sentry 200 EMMS
The Sentry 200 Environmental Moisture Monitor System is produced by Troxler Electronic
Laboratories. The system consists of a central unit, the ProbeReader Plus, and up to eight probes
which can be connected to the reader by coaxial cable. The ProbeReader must be connected to a
data logging system for information retrieval. Each probe costs 51,000 and each ProbeReader
costs 54,700. The system is capable of taking measurements either continuously or at regular
intervals. It can run on either 12 volt batteries, which last four hours, or AC electrical current.
Each probe measures the dielectric constant of the approximately 1.5 liters of soil
surrounding it. The probes should be kept 12 inches away from metal structures. (Vendor
FACTS, 1997) The probes are 12 inches long and two inches in diameter, as shown in figure 5.
They weigh eight pounds apiece. The outside of the probe is made of stainless steel, high density
polypropylene, and fiberglass epoxy laminant, making the probe resistant to corrosion and
breakage. (Troxler Sentry 200 Environmental Moisture Monitor Page)
(TO
2 in.
12m.-
Figure 5:
The dimensions of the probe for the Environmental Moisture Monitor System. (Adapted from the Troxler Sentry
200 EMM System Page)
11
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In April of 1995, the Sentry 200 EMMS was installed at San Marcos Landfill in San Diego,
California. Sixty probes and eight ProbeReader Plus units were installed. The total cost of the
project was $219,000, including equipment, engineering, and installation costs. The system
automatically measured moisture levels four times per day, and a person collected and examined
the data every two weeks. (VendorFACTS, 1997)
2.4 Tracers
Using tracers as a method of leak detection originated for use in storage tanks and pipelines,
but tracers can be used to detect leaks in any type of containment facility, including landfills.
Sample collection probes must be inserted in the ground around the perimeter of the landfill. To
test for leaks, a volatile chemical tracer is injected into the landfill. If the tracer is detected at the
sampling points, a leak exists.
a. Advantages
The composition of the leachate is unimportant, as the properties of the tracer are known.
Tracer systems can be used on any type of containment facility. Also, tracers can be used to
detect leaks at any stage in the life of the landfill because the probes are placed around the
perimeter of the facility. The volatile tracer travels through the soil gas to the probe.
b. Disadvantages
Most tracer systems do not usually find the location of the leak, they only determine whether
or not leaks exist. In addition, many systems require soil gas samples to be manually collected
and analyzed by a technician, which increases operations costs. Systems which automatically
collect and analyze samples are rare.
c. Example- Tracer Research Corporation's Automatic Leak Detector
Tracer Research Corporation provides leak detection services to its clients, which include
Texaco Refining and Marketing and almost all US Air Force bases. They have applied their
TracerTight systems not only to thousands of petroleum storage and transport facilities, but also
to hazardous waste sewer systems and landfill liners. (VendorFACTS, 1997)
One of its products, the Automatic Leak Detector (ALD 2000), is an automated system
capable of continuously collecting and analyzing samples for the presence of tracer and
hydrocarbons in the soil. Sample data can be collected on a remote computer via a modem.
(Tracer Research Corporation page)
The Tracer Research Corporation's soil gas probes are five feet long and weigh two pounds
each. The number of sampling probes necessary depends upon the size of the area to be
monitored. The TracerTight system costs around $15,000. (VendorFACTS, 1997)
12
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2.5 Electro-chemical sensing cables
Electro-chemical sensing cables were originally designed for detecting leaks in storage tanks
and pipelines. Most detect hydrocarbons, but the cables can also be made permeable to specific
contaminants or to water. For example, Lawrence Livermore National Laboratory is developing a
carbon tetrachloride-specific cable.
The target contaminant causes a physical or chemical change in the sensing cable. This
change either initiates or interferes with electrical or optical signals. Many electrical cables detect
leaks by measuring the drop in voltage in the cable caused by contact with contaminants. Most
fiber optic cables operate by measuring either a change in the optical attenuation of the cable or
the fluorescence of the contaminant when it comes in contact with an organic dye. Most of the
reactions are reversible. Cables which utilize a reversible reaction do not need to be replaced
after a leak occurs. (Rumer et al, 1995)
a. Advantages
Chemical sensing cables are widely available, especially for detecting hydrocarbons. If the
composition of the leachate which will be produced by a landfill is known, a sensing cable which
is compatible to the leachate can be installed during construction.
b. Disadvantages
The cables only detect a narrow range of contaminants. Each landfill must verify that a
particular cable would detect the specific type of leachate that will be produced there. No
company has developed a cable specifically tailored to detecting leachate. Further research is
necessary to determine the extent of the applicability of sensing cables to landfills.
c. Example 1- Novel-flow's SMART CABLE
Noverflow Inc. is developing two types of fiber optic leak detection cables. Both detect
organic corrosives and petroleum hydrocarbons. They are applicable to both industrial and
municipal landfills.
Type I sensors are cut on contact with the contaminant because of swelling and degradation
of the polymer coat. An optical time domain reflectometer sends a light pulse along the cable and
measures the amount of time it takes to reflect back to determine the distance to the cut, and
therefore the location of the leak. These cables can monitor distances of up to 50 miles.
Contaminants modify Type n sensors to change the refraction of light pulses traveling
through the cable. A light emitting diode and a photo detector are used to detect the leak. This
sensor is reversible unless enzymes have been incorporated into it to test for a specific chemical.
This type of cable can only monitor distances of up to 100 feet because the cables are made of
fibers with high optical attenuation.
13
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Units can be configured to be powered by solar energy, eliminating the need for batteries
or other power sources The cables cost S2.00 per foot. This cost includes an optical time domain
reflectometer. (VendorFACTS, 1997)
d. Example 2- Raychem's TraceTek
Raychem manufactures a wide variety of electrical leak detection cables. One detects
water, another detects conductive liquids, another detects fuels, and still another detects organic
solvents.
The cables all function on the same general principle. The cable contains two circuit
loops, one of which carries a current and the other of which contains an alarm. When electrical
contact is made between the two circuits, the alarm is tripped, as shown in figure 6. Contact is
made in some cables by a conductive fluid which carries current from one circuit to the other. In
others, electrical contact is made by direct wire contact. The conductive polymer sleeve which
surrounds the inner sense cables expands on contact with the target contaminant. The outer
containment braid forces the polymer to expand inward, squeezing the sense wires together. The
location of the leak is then calculated automatically. (Raychem Leak Detection and Location
page)
Inner Separator Braid
!T
rWire
Sex&Wire
Conductive Polymer Sleeve
/\A/\A/\/\AA/\
Witiumt Leak
With Leak
V = High Irnp*dance Voltmeter I = Constant Current Soorc*
Figure 6:
A diagram of Raychem's TT 500
hydrocarbon sensor, as well as a
schematic of the leak detection
mechanism. When a leak causes the
conductive polymer sleeve to swell.
wires come into contact with each
other, and the circuit including the
alarm is completed. (Sandberg et al.
1991).
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2.6 Other
a. Visual inspection
Venice Park Recycling and Disposal Facility in Lennon, Michigan has a system which
makes it possible to locate leaks visually. Piping networks ran along both the primary and
secondary liners. Operators can send a camera into the piping system where a leak is suspected to
locate where liquids are entering the pipe. (Dunson, 1996)
b. Wires in geotextiles
A system of placing electrically conducting wires inside geotextiles for use hi leak
detection has been patented by Koberling, a German company. When the wires come in contact
with leachate, they short circuit, signifying a leak. The main limitation is that the wires, once
shorted out, cannot easily be replaced. (Stammler, 1986)
3. EMERGING TECHNOLOGIES
3.1 Geosynthetic Membrane Monitoring System
The Sandia National Laboratories are currently developing geomembranes with
embedded fiber optic sensors. Sensors were first incorporated into materials and structures for
defense and space applications. These "smart" structures have been used to help monitor
weapons tests, naval ships, and the space shuttle. (Boms, 1997) The Sandia labs are now
applying the same strategy to environmental needs.
By incorporating fiber optics into geomembranes, the Sandia labs have produced a
membrane which can be monitored for strain. This capability is especially useful for detecting
stretching and tearing hi geomembranes used as landfill liners and caps. Strain detection is
possible because the fiber optic lines are crimped into small folds called microbends. The
microbends are either distributed evenly along the entire optical fiber or the fiber may have short
sections of microbends a few meters apart, as shown in figure 7. As the geomembrane tears or
stretches, the microbends flatten out, changing the way optical signals are reflected through
them. (Geosynthetic Membrane Monitoring Systems page)
Optical fibers can be incorporated into geomembranes in several ways. The sensors can
be extruded along with the geomembrane during manufacture, or the factory can laminate, glue,
or weld them on afterwards. The Sandia National Laboratories have determined hot shoe welding
to be the most promising attachment technique. (Borns, 1997)
15
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Smart Geomembrane Concept
Geomembrane
Plane View
Field Connector for Optical Fibers
Geomembrane
Cross-Section
0.02 to 0.12
Up To 25'
Fiberoptic Cable
Fiber Optic Connector
Fiber Optic Fibers Located
Parallel to Welded Edge
_M
of
Figure?:
A schematic showing the configuration of the geosynthetic ]
Monitoring Systems page)
obrane monitoring system. (Geosynthetic Membrane
In addition to testing several different methods of attachment, the Sandia labs have also
tested several different types of sensors: absorption-type, bragg grating, mircobend, and others.
They expect the variety of possible combinations of sensor types and attachment methods to
allow them the flexibility they need to meet the specific needs of individual sites. (Borns, 1997)
Field scale testing on the Geosynthetic Membrane Monitoring System was completed in
October, 1997. For the test, a 43 x 4.5 m section of geomembrane was installed as a cap over a
test facility which was designed to simulate both local and general subsidence. The strain in the
membrane was measured for three months as water and air were drained from fabric bladders and
intertubes in the test cell. The data provided by the sensors indicated the location and magnitude
of the subsidence. (Boms, 1998)
Although the Department of Energy has discontinued funding the project, the Sandia labs
are conducting ongoing research on optical fiber sensors for fluid level, leak detection and
moisture content (Borns, personal correspondence) Their goal is to keep the cost of
incorporating sensors at or below 20% of the cost of the geomembrane. (Geosynthetic Membrane
Monitoring Systems page)
16
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3.2 SEAtrace
Sandia National Laboratories are working together with Science and Engineering
Associates, Inc. to develop SEAtrace, a leak detection system which uses gaseous tracers.
SEAtrace is capable of determining the location, size, and start time of a leak by analyzing data
with an inverse global optimization code. (Barrier Verification and Monitoring System page)
SEAtrace requires a multipoint monitoring system to be installed outside the liner, as
shown in figure 8. Then a tracer gas (usually sulfur hexaflouride or carbon dioxide) is injected
inside the containment area. If the gas reaches the monitoring ports, the amount of tracer in the
soil gas at each monitoring point is measured over time. The global optimization code uses these
parameters to find the best fit solution for the location, size, and duration of the leak.
The SEAtrace system has undergone proof-of-concept field testing in Technical Area 3 at
Sandia National Laboratories. It was shown to be capable of locating a leak to within 0.5 meters
and determining its size to within 0.2 meters. (Williams et al, 1997)
/ SEAtrace Monitoring
and Analysis System
Tracer Injection
Barrier
Contaminant
Phune
Ports
Cross Section
Figure 8:
Diagram of the SEAtrace system for subsurface barrier monitoring. (Earner Verification and Monitoring System
page)
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3.3 FLUTe ideal system
Flexible Liner Underground Technologies (FLUTe) have designed their version of an
ideal landfill monitoring approach. The system consists of a layer of coarse materials underlain
by a layer of fine materials and another layer of course materials, (sand-silt-gravel, for example)
The fine layer widens the leak and must be capable of wicking leachate horizontally for 30 feet
or more. Two tiers of perforated pipes connected to surface manifold pipes are installed inside
the layers to collect vapor samples and to allow access for moisture sensors and logging tools, as
shown in figure 9. Pipes made of a geologic material (such as vitrified clay) are recommended to
allow electrical and radiation based monitoring devices to be used inside the pipes.
Routine monitoring is accomplished by drawing the pore vapor out of the system through
a charcoal filter which can then be analyzed for contamination. The air is drawn out through the
manifold which connects the upper tier of pipes. Fresh air is allowed in through the manifold
which connects the lower layer of pipes. In this way, all the air in the pipes and the monitoring
layers is drawn through the filter
inlet
Surface manifold of lower pipes
\L
lower pipes
upper pipes
Top View
-
Surface manifold of upper pip
outlet
Side View
lower pipe
Figure 9:
Top view and cross section diagrams of the FLUTe piping system. (Keller, 1995)
IS
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If contaminants are detected on the filter, the location and size of the leak can be
determined by towing logging tools through the pipes. This is best accomplished by using
SEAMIST, a versatile everting liner system which makes it possible to perform many monitoring
tasks including transporting equipment safely inside a horizontal well. The leak can be directly
sampled by using the SEAMIST system to wick pore liquid samples through the pipe. Because
no instruments are permanently emplaced in the ground, new technologies can be used in the
existing access system as they are developed.
Once the leak has been located, the FLUTe system can also be used to control the leak.
One option is to control or heat the air flow hi the system to dehydrate the leak and keep it from
flowing. Other options are to freeze the leak or contain it by injecting a sealant into the upper
coarse bed with tubing emplaced in the upper pipes. (Keller, 1995)
The estimated cost of installing the system is approximately $100,000 per acre in 20 acre
increments. About 70% of the cost is for the installation of the layered bed materials. There are
also lower cost options such as installing only one tier of piping. The SEAMIST canister costs
about $7,000 and the liner costs $10 to $20 per foot
Los Alamos National Laboratory is currently using a form of the FLUTe ideal design in
passages beneath radiation waste pits in TA-54. The University of Texas is monitoring
experimental cover designs with the SEAMIST system in horizontal passages in Hudspeth,
Texas.
To monitor exiting landfills, horizontal wells can be drilled beneath the liner. FLUTe has
developed a method of using an everting water driven liner to help drill horizontal wells which
contain less mud than conventionally drilled wells. These wells can be used for towing logging
instruments under the landfill and for wicking pore liquid samples with the SEAMIST system.
(Keller, personal correspondence)
3.4 Other
a. LEDAR
There is some interest in using Light Detection and Ranging as a leak detection
technique. LIDAR is similar to RADAR, but instead of sending and receiving radio waves to
determine distances by remote sensing, it uses light waves.
LIDAR is widely used to measure atmospheric conditions. It may also be possible to use
it underground. If a horizontal perforated tube is installed down gradient of the landfill just above
the water table, it may be possible to use LIDAR to detect the contaminant vapors which enter
the tube. This system would not prevent groundwater contamination, but it would improve the
probability of detecting a plume before it passes the point of compliance. This technique could be
applied to both new and existing landfills.
19
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One example of lasers currently being used for leak detection is Lasersonic, a system
produced by Laser Imaging Systems. Sodium hexaflouride is placed inside the object to be tested
as a tracer gas. When the Lasersonic is pointed at the object, any gas which has escaped into the
air strongly absorbs the light energy of the laser, then releases it as sound energy. Lasersonic
receives the sound energy and finds the location of the leak. (Laser Imaging Systems page)
b. Acoustic monitoring
As leachate flows through soil, it makes a slight noise. Fluids moving through coarse
sand or gravel at 10 mm/s or more have been shown to produce a detectable level of sound. The
sound waves below a landfill can be monitored by installing wave guides in a layer of coarse
material beneath the liner and connecting them to geomicrophones. The wave guides are metal
rods 10 to 20 mm in diameter and up to 100 m in length. If the wave guide has a geomicrophone
at both ends, the location of the leak can be determined because the time the sound took to travel
to both ends is known. (Stammler, 1985)
Acoustic methods are often used to detect gas leaks from pipes and valves. Non-
Destructive Testing International, for example, markets the Computerized Leak Analyzer, which
acoustically detects gas leaks, especially in boilers and steam-operated systems. (Clan page)
Argonne National Research Facilities includes a laboratory specifically for research in this area
called the "Acoustic Leak Detection Laboratory." (Argonne National Laboratory page)
Palmer Environmental markets a liquid leak detector for underground pipes called the
Corralog leak manager. The instrument uses two microphone sensors to listen to the noise
produced by the leak, then locates the leak on the pipe by comparing the time taken by this noise
to reach the two sensors at either end of the pipe section. (Breworld page)
4. CONCLUSION
Vadose zone sensors provide more complete spatial monitoring for possible landfill leaks
than wells alone, so they allow fewer leaks to go unnoticed. Another advantage of sensor systems
is that leaks which are detected in the vadose zone can be managed earlier than would have been
possible if they were discovered only when they reached the monitoring wells.
Each of the systems available has different advantages and disadvantages. The perfect
vadose zone monitoring system has not yet been designed, but the ideal system would be
affordable, durable enough to last through the life of the landfill and the 30 year post-closure
period, automated, and applicable to all types of landfills and leachates. It would provide full
spatial monitoring for the entire area below the landfill and locate leaks and determine their
sizes. Further research and development is necessary to create a system with these attributes.
Although the ideal system has not yet been developed, landfill managers who wish to
avoid unexpected remediation expenses down the road do have options to limit their risk. Those
who are willing to pay for extra monitoring during construction of the landfill can decrease the
possibility of having to pay for a significant cleanup later on.
20
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Appendix A- Overview grid
monitoring
technique
2 electrode
method
electrode grid
method
diffusion hoses
capacitance
sensors
tracers
sensing cables
Geosynthetic
Membrane
Monitoring
System
SEAtrace
FLUTe system
LIDAR
installable
anytime
X
X
X
locates
leak
X
X
X
some
X
X
X
determines
size
X
X
X
X
widely
available
X
X
reusable
X
X
X
X
X
some
X
X
X
X
tests
automatically
X
X
21
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Appendix B-Contact information- available sensors
Technology or location
Sandy Lane Landfill
WESTEC's Electronic
Leak Detection System
Siemens' LEGS
Troxler's Sentry 200
Environmental Moisture
Monitor System
Tracer Research
Corporation's
Automatic Leak
Detector
Raychem's TraceTek
Noverflow's Smart
Cable
Address
Christopher White
Aspenwall and Company Ltd.
SY4 2HH
United Kingdom
Rob ertH. Panning
Director of Business Development
5250 Neil Rd.
Suite 300
Reno, NV 89502
Siemens Nixdorf
Informationssysteme
Aktiengesellschaft
Geschaftsstelle Magdeburg
Wemer-von-Siemens-Ring 14 a
D-391 16 Magdeburg
Ken Brown
Product Support Manager
3008 Cornwallis Rd.
Research Triangle Park, NC 27709
Doug Mann
VP of Sales and Marketing
3755 N Business Center Drive
Tucson, AZ 85705-2944
MS 110/7568
300 Constitution Dr.
Menlo Park, CA 94025
Dr. Joe Hopenfield
President
1724 Yale Place
Rockville, MD 20850
Email
Chris.White@
Apinwall.
co.UK
RPanning@
westec-
Inc.com
Frank-Stefan.
Becker@
uk.siemens.de
sales@
tracertight.com
cheminfo@
raychem.com
noverflow@
aol.com
Phone
(702) 828-
6800
fax- (702)
828- 6820
49 (0) 391
/6 33-16 10
fax- 49 (0)
391/6
33-16 12
(919) 549-
8661
fax- (919)
549- 0761
(800) 394-
9929
fax- (520)
293- 1306
(800) 553-
1737
(303) 340-
1625
fax- (301)
762-3511
22
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Appendix C- Contact information- emerging technologies
Technology or location
Geosynthetic Membrane
Monitoring System
SEAtrace
FLUTe
system
Address
David 3. Boms
Sandia National Laboratories
Department 6621
MS 0719
P.O. Box 5800
Albuquerque, NM 87185-0719
Sandy Dalvit Dunn
Science and Engineering
Associates, Inc.
1570 Pacheco, Suite D-l
Santa Fe,NM 87501
Carl Keller
1640 Old Pecos Trail
Suite H
Santa Fe, NM 87505
Email
djboms@
sandia.gov
sddunn@
seabase.com
ckmist@
aol.com
Phone
(505) 844 -
7333
fax- (505)
844-0543
(505)
983-6698
(505) 983-
3199
fax- (505)
983-3476
23
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Appendix D- Web sites
Available sensors
Company
Siemens' LEOS
Troxler's Sentry 200
Tracer Research Corporation's
Automatic Leak Detector
Raychem's TraceTek
Web page address
htrp://w2.siemens.de/infoshop/umwelt/ums03_e.htm
http://www.troxlerlabs.com
http://www.tracertight.com
http://www.raychem. com/products/chemelex/
tracex.htm
Emerging technologies
Technology
Geosynthetic Membrane
Monitoring System
SEAtrace
Web page address
http://www.sandia.gov/eesector/enytopics/monitor/
gmms/emms.html
ht^p://www.sandia,gov/eesector/em/topics/monitor/
seatrace/seatrace.html
24
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geomembrane strain monitoring system during subsidence." in press.
Borns, D.J. 1998. Email to author. 30 June.
Boms, D. J. 1997. "Geomembrane with incorporated optical fiber sensors for geotechnical and
environmental applications." Proceedings of the International Containment Technology
Conference, St. Petersburg, Florida, p. 1067-1073.
Breworld. "Breworld press releases." (August 1998).
California Health and Safety Code. Article 9.5. Section 25208.8.
Daniel, David. February, 1987. "Under ground, over the water table." Civil Engineering, v.57, p.
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Dunson, Cheryl L. March 1996. "Technology today: landfills with vision." World Wastes, v.39,
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Laine, Daren and Darilek, Glenn. August, 1993. "Detecting leaks in geomembranes." Civil
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25
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Troxler Electronic Laboratories, Inc. "The Troxler Sentry 200 Environmental Moisture Monitor
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US Code of Federal Regulations, Title 40
Vendor FACTS 3.0. EPA's Field Analytical and Characterization Technology System database.
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26
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White, C.C. and Barker, R.D. Summer, 1997. "Electrical leak detection system for landfill
liners: a case history." Ground Water Monitor Remediation, v.17, n.3, p.153-159.
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