ASTM D7909-14

4.1 Geomembranes are used as low-permeability barriers to control liquids from leaking from landfills, ponds, and other containments. The liquids may contain contaminants that, if released, can cause damage to the environment. Leaking liquids can also erode the subgrade. Leakage can result in product loss or otherwise prevent the installation from performing its intended containment purpose. For these reasons, it is desirable that the geomembrane have as little leakage as practical.

4.2 Geomembrane leaks can result even when the quality of the subgrade preparation, the quality of the material placed on the geomembrane, and the quality of the workmanship are not deficient.

4.3 Electrical leak location methods are an effective final quality assurance (QA) measure to locate previously undetected leaks in electrically insulating geomembranes. Practices for these implementations are contained in Guide D6747 and Practices D7002, D7007, D7240, and D7703.

4.4 It is important to realize that the detection of leaks depends not only on the capabilities of the leak location equipment, procedures, and experience of the leak location practitioner but also on local site conditions that are not under the control of the leak location practitioner. In particular, to detect a leak, there shall be an electrical conduction path through the leak and through the materials above and below the leak to allow sufficient electrical current through the leak for detection. For some site conditions, such as a leak not making contact with the subgrade, dry geotextile, or geocomposite above or below the leak; dry materials above or below the leak; degree of isolation between the materials above and below the geomembrane; and other factors, may preclude the detection of leaks. Therefore, the use of a properly placed blind actual leak is also a test of site preparations and conditions.

4.5 It is not necessarily proper to conclude that, if a blind actual leak is not detected, a leak location survey, using the proper relevant ASTM International standard, has no validity. Real leaks that have more favorable site conditions and larger leaks may still be detected.

4.6 The importance of blind actual leaks is to provide an additional measure to assess whether the site conditions are proper for a leak location survey and that the electric leak location survey is performed correctly and completely. The use of blind actual leaks provides: (1) a check that the equipment is operating properly, (2) a test for proper survey coverage, and (3) a check that all survey data (results) have been assessed to confirm a proper survey has been done. These all result in a high likelihood that significant-sized leaks are detected.

1.1 This guide is for placing blind actual leaks in geomembranes before performing an electrical leak location survey. The geomembranes can be bare (not covered) or can be covered with water or moist soil.

1.2 This guide is intended to serve as an additional quality control/quality assurance (QC/QA) measure to ensure that leaks through the geomembrane are detectable, site conditions are proper for leak location surveys, and a valid and complete leak location survey is performed. Because various leak location practitioners use a wide variety of equipment to perform these surveys and have a wide range of expertise, placement of blind actual leaks by the owner or owner’s representative helps ensure that the leak location survey is being performed correctly and completely.

1.3 Placing blind actual leaks can also assist in determining whether or not the site conditions permit the flow of electric current through leaks, which is necessary for detecting leaks using electrical methods.

1.4 For clarification, this guide is in addition to the typical placement of the artificial or actual leaks placed as described in the relevant ASTM International standards for the various leak location methods.

1.5 Placing blind actual leaks should be done with the consent and knowledge of all involved parties and specifically the “owner” of the geomembrane. Geomembranes are typically purchased and installed by dedicated geosynthetic installers who “own” the geomembrane until the ownership gets transferred to the end user. A project meeting should be set up with the owner, the consultant, the geosynthetic installers, and the leak location contractor. The intention to use blind leaks should be clearly stated by the owner or consultants or both and the scope and number to be placed should be understood by all parties. The consultant should broadly identify to the lining contractor a location that can be easily repaired after the test. It is critical that all actual blind holes be included on the liner documentation and repair record drawing.

1.6 Leak location surveys can be used on geomembranes installed in basins, ponds, tanks, ore and waste pads, landfill cells, landfill caps, and other containment facilities. The procedures are applicable for geomembranes made of electrically insulating materials. (Warning—The electrical methods used for geomembrane leak location could use high voltages resulting in the potential for electrical shock or electrocution. This hazard might be increased because operations might be conducted in or near water. In particular, a high voltage could exist between the water or earth material and earth ground or any grounded conductor. These procedures are potentially very dangerous and can result in personal injury or death. The electrical methods used for geomembrane leak location should be attempted only by qualified and experienced personnel. Appropriate safety measures shall be taken to protect the leak location operators as well as other people at the site.)

1.7 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.