ASTM D6747 provides guidance for method selection.
Yes, if the GCL s adequately conductive. All GCLs come from the manufacturer with sufficient moisture, but can be desiccated during placement. Encapsulated GCLs are unable to wick moisture from the subgrade. To check for conductivity, place both electrodes in the GCL about 100 ft (33 m) apart and see if current flows. For more information on encapsulated GCL desiccation see the Beck et. al. (2008) publication in the “Resources” section of this website.
A newly installed geocomposite. Both a dried-out GCL and a new geocomposite may need slight irrigation during installation.
No. The LDS will have to be backfilled with water to introduce a conductive medium below the geomembrane. Alternatively, Leak Location Liner, a conductive geomembrane product manufactured by GSE can be specified as the primary liner.
If the cover soil is in contact with the subgrade soil around the periphery of the cell, the liner must be exposed around the periphery to isolate soil above the liner from soil under the liner.
No, unless you are surveying a double liner and the conductive medium in the LDS is totally isolated from ground.
Survey sensitivity depends on the method used and the site conditions. Any hole large enough to allow water through can technically be located by the water puddle method for exposed geomembranes, including pinholes. The sensitivity of the dipole method for earth-covered liners will depend on the site isolation, the mineralogy and moisture content of the subgrade and cover soils, and the degree of contact of the subgrade and cover soils through the hole. Generally, the minimum sensitivity for two feet of cover soils is a hole with a ¼” diameter. Frequently, much smaller holes can be detected.
This occasionally happens even when the methods are applied correctly. This typically happens when the “blind hole” is not placed or drilled per the ASTM standard guide. A “blind hole” is to be drilled at least 10 meters from the edge of the survey area for a dipole method survey. When the hole is drilled, the geomembrane material must be completely removed to represent a leak with the diameter of the drill bit. Geomembranes like reinforced polypropylene are difficult to drill in this manner. Care must be taken not to remove the subgrade material when a hole is drilled. Good hole contact must be represented. For a water puddle survey, blind holes should not be drilled in areas where the liner is trampolining or at the peak of a wrinkle.
Yes. Anyone performing an electrical leak location survey should be aware of the potential electrical hazards and should inform anyone in the area of the dangers before turning on the power source.
Water in the form of ice is not conductive. Sometimes a dipole survey area can freeze overnight; you will have to wait until it thaws back out to recommence surveying.
If you protect the equipment you can survey in a light rain, but if the single liner is exposed and the slopes are fully wet, current will conduct through the water film up the slopes to the subgrade and sensitivity will be lost. If the liner is covered with soil, electrical isolation will be lost at the perimeter of the survey area if the isolation trenches develop a film of water.
There are several minimum qualification requirements for the methods, most circulated by established leak location service providers. TRI has authored a non-biased specification for leak location methods with minimum qualifications comparable to similar industry methods, which is found in the “Resources” section of this website.
Do not wait for extraordinary circumstances to do good action; try to use ordinary situations.
Jean Paul Richter