Mobile leak detection
Mobile leak detection is also an electrical procedure that makes use of the insulating properties of HDPE geomembrnaes. The procedure involves a check for any electrical contact with the underside of the geomembrane generated as a result of damage. Use of this technique means there is no need to pre-stall cables when the liner is constructed.
Types of methods
There is a general difference between the techniques used to survey exposed geomembranes and geomembranes which are already covered. However, it should be noted that most damage occurs when geomembranes are covered by the drainage and protective layers; only minimal damage usually occurs during installation of the actual liner.
In the case of both methods, the quality of results depends on the experience of the operator using the system. Results are not generally automatically recorded.
Inspection of exposed geomembranes
This is undertaken by means of scanning with a high-voltage brush. If the brush comes into contact with a leak, then a current flows and is detected by the instrument. An alarm signal is generated and the operator can mark the location of the leak.
This technique is best used on geomembranes with an electrically conducting underside. Unloaded liners are not generally in contact with the substrate at all points and hence an adequate electrical contact between the leak and the substrate or soil is not guaranteed.
This technique is typically used for the scanning of exposed, uncovered basins.
Inspection of covered geomembrnaes
The top side of the covering is scanned. This dipole survey method is employed throughout the world. There is a corresponding ASTM standard. The experience of the technician is not the only important factor determining the reliability of results. Project-specific details, such as the depth of the covering, the layer construction and various other factors can influence the quality of the result.