Electrical Techniques
Geomembrane Leak Location
Detail
Geomembrane leak location surveys (GLLS) involve applying an electrical potential either side of synthetic geomembranes in order to identify holes and tears. These are commonly introduced during emplacement of the protective cover but may also result from later weld failures/puncturing during loading with waste of fluid.
The GLL method relies on the extremely high electrical resistivity of liner materials (such as HDPE and PVC) which prevents current flow across the geomembrane except through any holes or tears. This results in anomalously high potential gradients in the protective cover material above any holes which can be mapped over the surface of the liner using a pair of roving potential electrodes (see figure).
The high contact resistances (resistance to current flow) encountered at holes means that a high-voltage current source is generally required in order to induce current flow through any holes. The method has been used to successfully locate small holes (<5mm) below up to 1m of protective cover. For cells with a single geomembrane, current is passed across the liner using two current electrodes; one outside the cell (sink) and the other within the protective cover material (injector). In the case of double lined landfills the outer (sink) electrode is placed in the sandwich between the two liners. The sensitivity of the survey is primarily dependent on adequate isolation of the material outside the cell from the protective cover material above. Poor isolation, due to tying in of the geomembrane within anchor trenches, results in high levels of noise around the edges of the cell. Isolation is generally not a problem on double lined cells where the sandwich is effectively isolated from the material above.
A typical leak location system for use on soil covered landfills comprises a high voltage (+1000V) current regulated power supply and a pair of mobile non-polarising potential electrodes. Voltages are logged automatically to a digital data logger, enabling immediate download and processing of the data in the field for interpretation and quality control.
A modified leak location system is available for use on fluid covered and uncovered liners, such as leachate lagoons and ornamental lakes and cell side slopes where there is no soil cover. Due to the low amplitude of the anomalous signals within water the system has a built in amplifier and provides an audible indication of any anomalies.
