A Field Demonstration of GSE Leak Location Liner: Distance Testing

TECHNICAL NOTE
A Field Demonstration of GSE Leak Location Liner:
Distance Testing
Conductive geomembranes have been available for many years
and are relatively common to the geosynthetic market. GSE
developed the first conductive geomembrane over 20 years ago
as a way to improve the efficiency and accuracy of liner integrity
surveys by establishing a uniform electircal field beneath the liner
that was superior to the soil, subgrade, or other geosynthetic
product. In the past, electrical connections between the
geomembrane panels were assumed to be efficient, but no field
demonstration had been conducted to prove this assumption.
Liner integrity testing traditionally was done in small sections using a brush, probes or
multiple probes or other localized apparatus because this was the most efficient way
to pinpoint the location of the leak and make repairs. In addition, carrying an electric
charge over large distances was difficult. Recent advancesin welding technology,
however, have dramatically reduced the occurance of false positives and highlighted
the benefits of “distance” testing of conductive geomembranes and the measurement
and the testing of the entirety of the barrier system at one time. This is most beneficial
in the situation where the barrier system is being monitored for leakage or changes in
electrical conductivity. In this situation the distance that an electrical signal or current
may be conducted is a critical design parameter and thus a practical field demonstration
is valuable.
Protocol and Set Up
When geomembrane is installed, panels are connected using various methods in order to
form a physical bond, an electrical bond, or both. A dual track wedge weld is described
in ASTM 5820 and connects the panels both physically and electrically by creating a
hollow channel within the center of the weld that can be pressure tested. If the channel
holds air pressure for longer than a few seconds, it is reasonably assumed that the welds
on both sides of the channel are complete. The electrical connection in the conductive
layer inside the weld (between the unbonded edge of the geomembrand and the bottom
conductive layer) must be broken in order to prevent a false positive electrical signal. If
the electrical conductivity in this layer is not disrupted, a false positive will be transmitted
during surveying and the results will indicate a leak where no hole exists. The welding
technology used under the trademark GSE IsoWedge creates a break in the conductive
layer of the weld and is protected by patent in most countries. Figures 1 and 2 on the
following page illustrate these two circumstances.
GSEworld.com
GSE Leak Location Liner
Authors
B. J. Ramsey
GSE Environmental
Suzhou, PRC
N. Liu
Shanghai Jiao Tong
University
Shanghai, PRC
E. Geutebrück
Texplor GmbH
Potsdam, Germany
Field Demonstration of GSE Leak Location Liner
Figure 1. Conductive geomembrane weld with false positive result potential.
Figure 2. Conductive geomembrane weld with proper conductivity break.
Another proven method of connection is the contact weld which is installed to create an electrical connection
between two panels (rolls) of conductive geomembrane. It is common practice to connect the two adjacent
panels electrically by placing a small section of geomembrane underneath the continuous geomembrane
such that the conductive surfaces are in contact, as illustrated below. Again the current assumption is that
this provides sufficient electrical conductivity and in practice that appears to be the case; however, this is
commonly used only to monitor single panel to single panel connections. Multiple connections across a long
distance have yet to be reported.
Figure 3. Conductive geomembrane weld with proper conductivity break and panel to panel connections.
This Information is provided for reference purposes only and is not intended as a warranty or guarantee. GSE assumes no liability in connection with the use of this Information.
Specifications subject to change without notice. GSE and other trademarks in this document are registered trademarks of GSE Environmental, LLC in the United States and certain
foreign countries.
Field Demonstration of GSE Leak Location Liner
Test Description
Five sections each measuring 40 meters in length by 30-40 centimeters in width of GSE Leak Location
Liner, 2.0 mm, HDPE Geomembrane were laid end to end and connected both physically and electrically
using under laid strips of conductive geomembrane, again approximately 30-40 centimeters in width, cut
from the cross direction of the strips These smaller “cut sections” were inverted and the two conductive
sides were hot air tack welded together. After the tack weld was cool, an extrusion weld was placed
on the top of the two connected strips. This followed the typical extrusion welding sequence of light
grinding to clean and roughen the surface followed immediately by extrusion welding with welding rod
made from a similar material. Four such connections were made using the same construction and layout.
The connections are pictured below. The completed installation was measured with a 50 meter tape and
was approximately 200 meters long.
Photo 1. Test pad splice during construction.
Photo 2. Test pad splice being welded.
Following construction of the strip, a Texplor combimodule was attached to the west end of the strip and white
nonwoven polyester geotextile was placed atop the geomembrane. This geotextile strip was saturated with water.
Additionally, the weather during the entire testing was a very light drizzle and very wet conditions. The welding and
connections were conducted under tents. A 500 millivolt signal was propagated through the system successfully.
Furthermore, after the system stabilized, a 2 centimeter diameter hole was placed in the strip at the end opposite the
monitoring module. This change in the signal response was very rapidly noticeable and consistent in variation from
the non-hole condition.
Photo 3. Monitoring module during testing.
Photo 4. “Hole end” during testing.
This Information is provided for reference purposes only and is not intended as a warranty or guarantee. GSE assumes no liability in connection with the use of this Information.
Specifications subject to change without notice. GSE and other trademarks in this document are registered trademarks of GSE Environmental, LLC in the United States and certain
foreign countries.
Field Demonstration of GSE Leak Location Liner
The analysis of the measured MSS® data and the comparison with the base measurement showed clearly that the EFT®tracer sent from the source propagated the length of 200 m on the bottom of the conductive liner, passed the hole at
the end of teststrip and travelled back 200 m on the surface to the sensor in the MSS® CombiModul (Fig. 4)..
Compared with the natural electrical flow in the tight situation only 5% of EFT-tracer energy sent from the source in the
MSS® CombiModul passed the test liner strip.
After the SP tests, a 2 centimeter diameter hole was placed in the strip at the end opposite the monitoring module,
approximately 200 meters away. With the hole in the strip, the signal response change was very rapidly noticeable and
consistent in variation from the non-hole condition. Compared with the SP base measurement data, over 80% more
electrical energy reached the sensor in the MSS® CombiModul in 200 meters distance (Fig. 4). In general, alarm criteria
in the monitoring system are fulfilled when > 50% of the tracer energy reaches the sensor.
Figure 4. MSS® result: Electrical response – test
Conclusions
The surveying and monitoring of geosynthetic systems via electrical liner integrity surveys is a complicated process,
but it has been established to be repeatable, technically viable, and a powerful method for improving the quality and
performance of geosynthetic barrier systems. One of the most effective proven methods is an electrical leak location
survey that is conducted after initial cover soil placement above (on) the geomembrane (Beck, 2012). The placement of
cover soil on the geomembrane has been reported to be the most dangerous time and the most likely to result in a loss
of barrier capability (Nosko). Further, electrically conductive geomembranes have a very strong history at supporting
and improving the performance of liner integrity surveys (Beck, 2015). However, prior to this paper, the distance
of electrical coverage had not been demonstrated with a field trial over a length of 2-3 panel widths. This test has
demonstrated electrical conductivity of a conductive geomembrane over a 200 meter length and across 4 field seams.
This range of coverage can be useful to design engineers in formulating monitoring plans, monitoring unit spacing and
creating CQA (Construction Quality Assurance) programs, requirements and methodology.
This Information is provided for reference purposes only and is not intended as a warranty or guarantee. GSE assumes no liability in connection with the use of this Information.
Specifications subject to change without notice. GSE and other trademarks in this document are registered trademarks of GSE Environmental, LLC in the United States and certain
foreign countries.
Field Demonstration of GSE Leak Location Liner
REFERENCES
ASTM D5820 - 95(2011) Standard Practice for Pressurized Air Channel Evaluation of Dual Seamed Geomembrane,
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with Water or Earth Materials”, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA.
ASTM D7240. Standard Practice for Leak Location using Geomembranes with an Insulating Layer in Intimate Contact
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ASTM D7703. Standard Practice for Electrical Leak Location on Exposed Geomembranes Using the Water Lance
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This Information is provided for reference purposes only and is not intended as a warranty or guarantee. GSE assumes no liability in connection with the use of this Information.
Specifications subject to change without notice. GSE and other trademarks in this document are registered trademarks of GSE Environmental, LLC in the United States and certain
foreign countries.
Field Demonstration of GSE Leak Location Liner
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Landfill Symposium
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This Information is provided for reference purposes only and is not intended as a warranty or guarantee. GSE assumes no liability in connection with the use of this Information.
Specifications subject to change without notice. GSE and other trademarks in this document are registered trademarks of GSE Environmental, LLC in the United States and certain foreign
countries. 26OCT2015