According to the American Society for Testing and Materials (ASTM) D-6747, "The principle behind these techniques is to place a voltage across a synthetic geomembrane and then locate areas where electrical current flows through discontinuities in the geomembrane. Other electrical leak paths such as prevent pipe penetrations, flange bolts, steel drains, and batten strips on concrete and other extraneous electrical paths should be electrically isolated or insulated to prevent masking of leak signals caused by electrical current flowing through those electrical paths. The only electrical paths should be through leaks in the geomembrane. This electric detection method of locating leaks in geomembranes can be performed on exposed geomembranes, on geomembranes covered with water or on geomembranes covered with an earthen material layer, or both." The figure below provides a visual description of an exposed discontinuity in the primary geomembrane by using sophisticated leak detection equipment.
Why It Works
Electrical leak detection methods implement a physical, real-world circuitry consisting of magnetic fields and current density. The geomembrane, or liner, acts as an electrical insulator and emulates a current barrier. Two temporary electrodes are required to energize the commercial application: a source electrode and a ground electrode. When the application is energized and saturated, localized ripple-effects of high current density occurs only at the leaks. Measurements are collected and scans are made with leak detection probes and equipment to pinpoint the exact location of the leaks.
Single - Lined Systems
For single-lined systems with soil or liquid, a source electrode will be connected to the material covering the liner (operations layer), while a ground electrode will be connected to earth ground. It is crucial for systems that are single-lined to have an electrical isolation perimeter or trench throughout the entire cell if feasible. An electrical isolation trench consists of an area of exposed geomembrane or liner that electrically separates the operations layer with earth ground (subgrade). Excavating the isolation trench to a width of approximately 2 feet will be sufficient. In addition, the overall isolation perimeter will also increase the leak detection sensitivity.
Double - Lined Systems
For double-lined systems, the source electrode will also be connected to the material covering the liner, but the ground electrode will be connected to an electrode either in between the liners or in the Leak Detection Zone (LDZ). During the construction of the cell, copper-plate electrodes or copper-wire electrodes may be required prior to the installation of the primary liner to increase the leak detection sensitivity. Prior flooding of the LDZ and/or pre-wetting of the material between the geomembranes may also be required. Since the liner is an electrical insulator, an isolation perimeter or trench may not be necessary.