Why covered geomembrane leak location (dipole) is crucial on any impervious work

To protect geomembranes from heavy machinery damage during site operations, most im-pervious works will include a natural material layer (for drainage and/or protection) overtop of the geo-synthetic layer. Whether the natural material is sand, clay, gravel, or comprised of multiple types of mate-rial, a covered liner electrical leak location (ELL) survey, or dipole survey, can be performed on it to verify the integrity of the geomembrane underneath. Certain limitations would obviously need to be con-sidered, such as the thickness of the protection layer, and will be discussed later in this paper.
The integrity of a geomembrane can also be verified prior to it being covered; an exposed liner leak loca-tion survey verifies the quality of the geomembrane installation phase and the skill of the installer. If only the dipole survey is conducted then there is room for argument when the time comes to decide who should pay for the repairs. The dipole survey should be prioritized because of the nature of holes it de-tects. Exposed geomembrane leak location methods will detect pinholes, bad extrusions, knife cuts, and other equivalently small defects. The dipole survey, however, will detect rock punctures, tears from heavy machinery, and other larger defects that allow for greater leakage.
This paper will explain how the dipole survey works, and, based on more than 15 years of field experi-ence, will discuss the types of damage and size of holes that can be found with the dipole method, statis-tics on the number of defects found, and the main parameters that affect its efficiency. Information will be given to understand better how to improve a site’s conditions for performing the survey, in order to attain maximum sensitivity and thereby increase the potential of finding smaller holes.