SPECIAL SESSION: Panel Discussion – How to Write a Good Geomembrane Spec
Organized by: FGI
Tuesday, Feb. 7th 1:30 – 3:00 pm
Join Panelists: Edward Silva, Ray Peebles, Neil Nowak, and Patrick Elliott with Moderator Timothy Stark leading this discussion on the importance of writing a good geomembrane specification and not using an old specification that may or may not be for the type of geomembrane intended for the current project. In particular, the panelists will discuss the most important parameters of a geomembrane specification for a particular application, such as functionality, longevity, and constructability.
Some of the important parameters to consider when preparing a specification may include: chemical resistance, ability to accommodate differential settlement, dimensional stability to control wrinkles, ability to factory fabricate large panels to reduce field time and exposure, and seam strengths but properties should be keyed to the application of the geomembrane. For example, if there are concerns about subgrade compaction, specifying a material with higher multiaxial elongation properties may be desirable.
It is also important that engineers understand that most material types can have very different properties, and it is important that designers select an appropriate geomembrane to meet project requirements. This will help avoid confusion or blended specifications. Finally, the importance of specifying relevant and consistent properties, e.g., long-term durability in terms of plasticizer retention instead of OIT values for a PVC geomembrane. Afterward, the panelists will answer your questions about writing a good geomembrane specification.
By Ali Khatami, Ph.D, P.E., SCS Engineers National Expert
Leachate seeping out of a landfill slope can be a major issue during the active life of a landfill, and waste operators undertake significant efforts to control and manage it. Uncontrolled seeps can cause soil erosion on the slope, odor issues, and unpleasant scenery on the landfill slope which is visible to adjacent public roads or properties. Leachate can also travel beyond the liner boundaries into perimeter ditches.
Leachate also can seep below the final cover, and that causes a different set of problems. Leachate seeps below final landfill covers are rarely discussed because of the general consensus that they become inactive after construction of the final cover system. That may be true under certain conditions, but very often, leachate seeps remain active as long as the source of water remains active and continues discharging through the seep locations. Leachate seeps below final covers can potentially:
If the final cover geomembrane is not welded to the bottom liner geomembrane, leachate seeping to the toe of the slope can reach the landfill perimeter ditch and contaminate the surface water, or it can percolate into the ground and cause ground water contamination that may be detected in nearby groundwater monitoring wells. Leachate seep also may enter the perimeter berm structure and saturate the berm to the point that the stability of the landfill slope becomes a concern.
If the final cover geomembrane is welded to the bottom liner geomembrane, the only way to address the accumulation of leachate under the cover at the toe of the slope is to open the geomembrane, remove the leachate, and close the geomembrane again. However, this process does not solve the seep problem, which will continue to recur.
SCS has designed various leachate toe drain systems to collect and dispose of leachate that flows below the final cover geomembrane. Leachate toe drains have become a standard feature in the final cover designs for some of our clients who have experienced the benefits of the system.
If you have leachate seep issues at your landfill, please contact SCS. We can develop a design specific to your landfill and the conditions at your facility. We also provide construction recommendations and a preliminary cost estimate for implementation of the system. SCS has extensive experience with the permitting of these systems; we prepare modification applications for permitting purposes and obtain approval from the state regulatory agency. SCS can also prepare the construction plans. We also offer design-build options, employing our SCS Field Services Construction group to construct the system, which often can be a cost-effective way to implement your system.
Questions? Contact Ali Khatami, PhD, PE, LEP, CGC, is a Project Director and a Vice President of SCS Engineers. He is also our National Expert for Landfill Design and Construction Quality Assurance. He has nearly 40 years of research and professional experience in mechanical, structural, and civil engineering. Dr. Khatami has acquired extensive experience and knowledge in the areas of geology, hydrogeology, hydrology, hydraulics, construction methods, material science, construction quality assurance (CQA), and stability of earth systems. Dr. Khatami has applied this experience in the siting of numerous landfills and the remediation of hazardous waste contaminated sites.