Installation and Testing of Landfill Liners

The material used for liners and caps is only as good as long as it’s installed properly, says Doug DeCesare, the solid waste section manager in HDR Engineering’s Nebraska/Iowa engineering department.

Installation is critical for the effectiveness of geomembranes in landfills in not enabling water to stream through tears or pinholes, adds Don Hullings, Cornerstone Environmental Group client manager.

Boyd Ramsey, GSE Environmental chief engineer, concurs. He recommends for guidance is the International Association of Geosynthetic Installers (IAGI). “They have a qualification program for both the installer and the actual staff that works on the site, so if I were building a site that I was going to depend on, I’d use an IAGI-certified installer and IAGI-certified welders”

Quality construction assurance is another critical component. For that, Ramsey recommends The Geosynthetic Institute. “It has a certification program for construction quality assurance and it includes a practical examination and a resume qualification phase,” he says.

Installation is usually overseen by construction quality assurance (CQA) technicians, says Farmen. “When the material arrives on site, they’re inspecting it to make sure the material they’re receiving at the project matches the rolls or the identification numbers for what material was produced for that job,” he says.

That goes back to the manufacturing plant where rolls of material are produced. Samples are collected from the rolls and sent to a lab for material testing.

“It’s got to meet a myriad of both raw material properties and requirements as well as finished product requirements,” says Todd Farmen, principal environmental engineer with Arcadis USA. “For a liner, they’ll make sure its carbon black content is accurate or within a specified range. They’ll want to make sure its thickness is within a specified range, so they usually do sampling at the plant while it’s being manufactured.”

Once approved by the engineer and the data reviewed, the product is sent to the site, and the CQA technicians are responsible to make sure that the site is getting the rolls that were produced for the job and it matches the rolls that were sampled, says Farmen.

“Then during deployment of the material, they’re making sure that the right equipment is being used, that the subgrade or whatever surface the material is going on is properly prepared and tested,” he adds. “As it’s going in, they’re testing seams and overlaps—there’s a lot of tests they use out in the field to make sure that the seaming is done properly and you’re producing a liner system that is intended by the design.”

Another important factor is ensuring that the material covering the geosynthetic is being laid down correctly and that the right equipment from a ground pressure standpoint is being used, says Farmen.

“Is adequate thickness being put in? All of those different things that a CQA person would monitor throughout the construction—whether it’s a cap or a liner, soils or geosynthetics—they’re usually on top of everything and making sure the contractors who are doing the installation are following the requirements,” he says. “It’s really very important because it affects the overall performance of the integrity of the material that you’re putting in.”

Burns & McDonnell does a lot of quality assurance testing on the liner and the clay to make sure it’s meeting permeability requirements with the different lifts, says Doran. “Typically they’re putting in three or four lifts to get that two-foot thickness,” he says. “You do a lot of quality control testing on the membrane to make sure that the seams are good.”

Fred Doran, senior environmental engineer for Burns & McDonnell, does electric connectivity testing on the geomembrane after the drainage layer goes on top of the membrane, which could be a sand or gravel, to identify any holes that might occur from a survey stake, rock or any other object that could create a hole, says Doran. “In every project, we’ve found something,” he notes.

Ramsey points out that there are several mechanisms in place for a liner integrity survey, which uses a variety of site-dependent electrical methods to verify the barrier function of the liner both before and after the soil is placed on top.

“Abigail Beck at the Texas Research International has done a lot of work putting statistics together to show these are the chances of a leak with this level of leak detection, these are your chances of leak without these level of leak detection, and it is something that benefits the product and gives you a much higher probability of success,” he says.

DeCesare says that in many cases—depending on his company’s client and site location—”our qualifications for liner installation have to meet a certain threshold. That’s one way to minimize the opportunity for an unqualified installer because that’s problematic.”

Dan McGrath, associate and senior consultant for Golder Associates, points out that proper installation starts with a properly prepared subgrade.

“It doesn’t do any good to deploy this fantastic geomembrane material on a sub-grade that’s going to poke holes into it and make it leaky,” he says.

Geomembrane material typically comes in rolls that are unfurled in site-specific sizes on a prepared subgrade and then welded. PVC material sections are glued, he says. In addition to CQA inspection to identifying deployment errors that may have damaged the liner, seams that aren’t quite complete, wrinkles or shortcomings in the deployment itself, there are a variety of destructive and non-destructive seam test methods to verify seam integrity, McGrath says.

Such methods usually involve spark testing, pressure, or vacuum. “Testing to verify the seam integrity and then to verify the strength of those seams, they can cut samples out of the seam itself and test them for strength,” he adds. “Ideally, testing shows that the seam is as least as strong as the material itself to verify if any kind of settlement occurs, physical stressors on the liner system as a whole will behave as a unit. You don’t want the leak point to be at the seam to come apart like a zipper.”