To the editor:
Efforts toward achieving zero leaks in a waste containment system (“Achieving Zero Leaks on a Budget” in the June/July issue of Geosynthetics) are certainly laudable. Authors Gilson-Beck and Toepfer do a good job of explaining how electrical leak detection surveys can minimize leaks in a geomembrane liner system at the end of liner system placement in a cost-effective manner. However, readers should be cautioned that even the highest-quality electrical leak detection systems are subject to limitations on the size of the defect they can detect. These size limitations are greater when the survey is conducted after placement of an overlying protective soil layer versus on a bare liner. Furthermore, leaks may develop over the service life of the liner system, during and after waste placement. Electrical leak detection is an invaluable quality assurance tool. Moreover, defects that cannot be detected by electrical leak detection surveys may be so small as to be insignificant with respect to the performance of the containment system. However, until a continuous monitoring system with the appropriate resolution is developed and implemented, leaks that develop after the leak detection survey has been conducted (i.e., after the end of liner system construction) cannot possibly be detected by an end-of-construction leak detection survey and, therefore, achieving zero leaks remains an ideal that cannot be verified. Despite this limitation, electrical leak detection surveys are a valuable tool to minimize leakage through geosynthetic liners.
Edward Kavazanjian Jr., Ph.D., P.E., Ira A. Fulton Professor of Geotechnical Engineering, Arizona State University, Tempe
Response from the authors:
The electrical leak location (ELL) survey partnered with rigorous construction quality assurance (CQA) can yield zero leaks for a project lifetime. Zero leaks have been achieved, verified and maintained in numerous double-lined impoundments approaching seven or more years of service life using these components. Site conditions, poorly written specifications, poor or absent CQA and/or imperfect application of ELL methods cause leaks to be missed. Inferior welds or sheet conditions, which may pass an initial ELL survey but fail later, must be identified and fixed during construction.
There is no limit to how small a leak an ELL survey can locate. If the hole can transmit water, it can carry current, and the current will be detectable through some approach. After protective cover is placed, geomembrane damage is unlikely. Incorporating a bare geomembrane survey prior to cover placement followed by a dipole survey after cover soil placement yields the benefits of increased sensitivity to locate smaller damage associated with installation while finding any defects caused by cover material placement.
Exposed geomembranes are subject to post-construction damage. A continuous monitoring program—such as a double-lined facility or a permanent electrical leak detection system—is ideal. However, the same could be achieved through periodic ELL method application.
Abigail Gilson-Beck, Senior Engineer/Director of Liner Integrity Services, TRI Environmental, Austin, Texas
Glen Toepfer, President, CQA Solutions, Toledo, Ohio