Enhanced Geomembrane CQA through proper application of geomembrane leak location surveys
Historically, geomembrane construction quality assurance (CQA) has focused on destructive testing of welded seams to verify seam strength and integrity. Paradoxically, seams are not subject to significant stress and practically never fail in service, while holes and construction damage in the geomembrane are a much more widespread problem. The historical approach fails to evaluate how well the geomembrane performs in providing a liquid barrier, which is the primary function of a geomembrane. More recently, CQA efforts have focused on verifying liquid barrier performance using electrical leak location surveys. Engineers, installers, regulators, and owners are starting to rely on these surveys to evaluate geomembrane performance. The only function of a geomembrane is to prevent liquid flow. It is certainly prudent to spend a fraction of a percent of the construction cost of a landfill to test the performance of the geomembrane. So now a total approach is needed that incorporates a sound design that considers the most relevant and cost-effective CQA requirements, construction monitoring and testing, proper preparations for leak location surveys, and effective geomembrane leak location surveys.
Geomembrane leak location surveys using electrical methods have been used commercially for more than 20 years. Leak locations surveys are conducted on bare geomembranes, geomembranes covered with soil, and geomembranes covered with water. Industry standards have been developed for all the major electrical methods. Optimum leak detection sensitivity depends not only on the proper performance of the survey itself, but also on the design of the liner system and the proper preparation of the liner system prior to testing. The electrical method is used to detect electrical current flowing through holes in the geomembrane. The liner system design and leak location preparations should take this into consideration. Certain landfill liner designs can reduce leak detection sensitivity and hinder the detection of holes. At the same time, the detection of smaller holes requires special preparations and considerations. This paper discuses a total approach to geomembrane CQA from design to pre-construction preparation to leak location field surveys, and makes specific recommendations for enhanced geomembrane leak detection performance.