|Committee Proposes Performance-Based Detection of Geomembrane Leaks
Chemicals or waste seeping through leaks in geomembranes can result in pollution and fines. To test these plastic liners, ASTM Subcommittee D35.10 on Geomembranes has drafted Standard Practices for Electrical Methods for Locating Leaks in Geomembranes Covered with Water or Earth Materials.
Governmental environmental regulators are beginning to require geomembrane leak location tests, primarily for landfills, says chief author Glenn Darilek, P.E., an electrical engineer. Each leak location contractor seems to use different equipment and procedures, so there is a need for standards to be sure the client is obtaining the desired leak detection performance. Electrical leak location methods are still evolving, so a performance-based standard has been written. This approach will promote further innovation, and will not show preference for any practitioners equipment or procedures.
Although electrical leak location methods for geomembranes have been in commercial use for more than 15 years, the emphasis for geomembrane construction quality assurance has been on performing destructive tests of geomembrane seams, explains Darilek, a principal engineer with Leak Location Services, Inc., San Antonio, Texas. But now the geomembrane industry, engineers, owners, and regulators are realizing that it does not make sense to concentrate on obtaining maximum strength for seams that are not placed in stress, and practically never fail in service, while ignoring the wide spread problem of leaks in the geomembranes.
The proposed standard applies to plastic geomembrane liners that fortify landfills, ponds, tanks, and other applications, typically 1 to 1.5 mm thick (0.04 to 0.06 in.), Darilek says. He describes a typical landfill installation: One or two layers of geomembrane are typically installed on a prepared sub grade. Then a layer of drainage gravel or sand is installed on the geomembrane to protect the geomembrane and allow leachate from the waste to be drained away for proper disposal. In the process of installing the drainage layer, heavy equipment can easily damage one or both geomembranes, negating their impermeable barrier function. However, if a proper electrical leak location test is performed, these leaks can be located and repaired before waste is placed into the landfill. The standard procedures will ensure that a proper electrical leak location test is performed, which will provide optimum benefit for the owner, rate-payers, and environment.
To properly specify an electrical leak location test for a geomembrane, one must specify that a certain-sized leak can be found, he continues. Furthermore, it is not sufficient to demonstrate that the leak can be found by performing the measurements directly over the leak. Instead the leak detection sensitivity must be demonstrated with the worst-case conditions where the leak is midway between the nearest measurement points. The standard practices will ensure that the specified leak detection sensitivity will be demonstrated and documented under these worst-case conditions. Therefore, the new standard will improve the reliability of any electrical leak location test for geomembrane liners covered with water or earth materials.
According to Darilek, landfill liners and final caps, industrial ponds, geomembrane-lined tanks, and even golf course water hazards and decorative ponds can be improved with the proposed standard. There have been some unusual applications including moisture control systems for clay tennis courts, fountains, and drainage pipes, he says. One new application will be for a drainage system under a highway where the roadbed will be constructed below the water table.
While ASTM D 6747, Standard Guide for Selection of Techniques for Electrical Detection of Potential Leak Paths in Geomembranes, describes several electrical leak location methods, the proposed standard focuses on practices for water-covered and soil-covered geomembrane systems, Darilek says. Another subcommittee group is developing a standard practice for the water puddle system, he adds.
Subcommittee D35.10 is part of ASTM Committee D35 on Geosynthetics.
The subcommittee requests comments from geomembrane leak location contractors and other stakeholders on the draft Standard Practices for Electrical Methods for Locating Leaks in Geomembranes Covered with Water or Earth Materials, to balance review by geomembrane design engineers on the subcommittee.
Contact Darilek (phone: 210/408-1241). Committee D35 meets Jan. 15-16 in Tampa, Fla. For meeting or membership details, contact Maxine Topping, manager, Technical Committee Operations, ASTM International (phone: 610/832-9737). //
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