Standard Guide for Placement of Intentional Leaks During Electrical Leak Location Surveys of Geomembranes

Abstract

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, D7703, D7953, and D8265. 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. 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 leak is also a test of site preparations and conditions. 4.5 It is not necessarily proper to conclude that, if a leak is not detected, a leak location survey using the proper relevant ASTM International standard has no validity. Other leaks that have more favorable local conditions and larger leaks may still be detected. 4.6 The importance of blind leaks is to provide an additional measure to assess whether the site conditions throughout the entire survey area are proper for a leak location survey and that the electric leak location survey is performed correctly and completely. The use of blind 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. 4.7 The placement of blind leaks should not replace hiring a reputable and qualified leak location practitioner to perform the electrical leak location survey. Many site-specific issues and technical limitations can preclude the detection of leaks, but a non-expert will find it difficult to impossible to determine whether the non-detection of leaks is due to survey performance errors or issues with site conditions. It is therefore important to achieve a satisfactory resolution to any issues with the non-detection of leaks but, much more importantly, to check leak location practitioner references and qualifications before hiring. In addition to checking references from previous clients, qualifications should include reports from at least three projects completed, similar in cross section to the proposed project, where leaks were found. The report output should provide indisputable evidence that the survey was performed effectively. 4.8 It is important to note that the placement of leaks may affect the sensitivity of the electrical leak location survey for geomembranes covered with soil or water or both. The placement of leaks larger than the leaks present in the lining system may preclude detection of those smaller leaks, especially for highly conductive cover materials.