DOWNLOAD NEWEST WEBINAR: Effect of Elevated Temperatures on Geosynthetics - Presented by Dr. Timothy Stark, University of Illinois

Dedicated to advancing the use of fabricated geomembranes through education, research, and technology transfer.

WHY?
Factory fabrication reduces field welding, reduces installation time and costs, allows modular construction and provides consistent seam and liner quality.

Frequently Asked Questions

What are fabricated geomembranes?

Fabricated geomembranes are geosynthetic lining materials that are flexible enough for panels to be joined in a factory environment to create large “single” panels of material that may be folded, rolled, and transported efficiently to a containment or project site. There, the large panels are unrolled into position and unfolded without damage. This reduces the number of seams that must be conducted in the field, which facilities faster, lower cost installations. Standard testing verification methods are available to ensure the factory seam quality too.

Applications of note include aquaculture, canals, decorative ponds, exposed or floating covers, hydrocarbon containment, reservoirs, sewage lagoons, tank liners, mining works, wastewater, and more.

What are some of the main items to consider when choosing a membrane?

There are several items to consider, including:.

1.     Design life – Make sure your membrane life expectancy and warranty meet your project requirements.

2.     UV Stability – If you are specifying an exposed membrane make sure you are choosing a membrane that can handle UV and weather exposure for the duration of its life.

3.     Chemical compatibility – Not all membranes do well with certain chemicals. Make sure you understand what the membrane will be faced with over its entire life and then choose the membrane that can handle these requirements

4.     Dimensional stability – This is especially critical when using a covered membrane as wrinkles can cause several delays in construction and can create long term weaknesses to your overall liner system design.

5.     Flexibility – A lot of projects require membranes to contour to uneven subgrade or even need to allow for differential settlement in base materials. You need to make sure your membrane can handle these requirements long term.

6.     Construction schedule and location – Projects can require tight deadlines and/or difficult remote access. Understand your installation process and what time and equipment it is going to require to complete your job.

7.     Regulations – Make sure your membrane will meet and/or exceed your specific state or federal requirements for your application. Also please contact the FGI if you find that your state or governing body does not allow you to use the membrane that best fits your project.

Why should I look at using fabricated membranes over HDPE?

The goal is not to use a specific membrane. The goal is to use the correct membrane for your project. Our goal at the FGI is to educate and guide people to use the proper membrane that fits the project goals and requirements.

What is an acceptable level of content of recycled PVC in a PVC Geomembrane?

The use of recycled materials depends on a few things.  Source of the recycled components: In house like, or higher quality, compound/resin recycled materials, sourced post industrial, sourced post consumer. Each manufacturer qualifies the materials to be recycled and then needs to determine the % that their equipment can process while meeting the required specifications. Could be 5% to 100%.

Are there different quality types of PVC being sold?

Yes; Industrial Grade (Does not meet 7176 and intended to be buried for more than 1 year, but less than 10 or short term exposed application or less  than 2 years), 7176 Grade  (Meets 7176 requirements and intended for up to 20 year buried application), and 7176 w/UV (Meets 7176 and intended for up to 20 year Exposed or Buried application.) 

Does thicker membrane merit the price increase --and perform better long-term for my application?

It can, but not necessarily.  Attention to quality control steps like subgrade prep,  welding test results, supervised cover operations, and minimizing traffic over the membrane are better guarantors of performance and durability than extra thickness.  

If we specify fabricated panels instead of roll goods for an installation, does that mean fewer seams, patches and destructive testing?

Yes,  as a rule installers will face 70% less seaming and fewer butt seam patches; moreover, industry standard quality control measures on pre- fabricated geomembranes often entail other methods than frequent destructive testing and the associated patch-work.

Do fabricated geomembranes expand and contract as much as the HDPE and LLDPE roll goods we’ve used in many ponds?

Polyethylene is a plastic material that expands and contracts with temperature swings - about 2% across the pond width and length. Pre-fabricated membrane liners are typically scrim-reinforced or a variety of rubber-like formulations (Polypro, EPDM, PVC, etc.) that do not tend to wrinkle or trampoline as much in the field.

Can you install a PVC when it is very cold (-10F)?

Not a good idea.  Too close to the temperature where the liner gets brittle.

Can you use a double track wedge weld on 36 mil RfPP and air pressure test the seam?

No.  It is possible to damage the geomembrane, exposing some scrim and creating a pathway for air to escape.

Is PVC environmentally “friendly”?

Not only does PVC outlast and outperform many competitive materials, but because 50 percent of its base polymer comes from common salt, an inexpensive, renewable resource, it is also much preferred to materials that rely 100 percent on petrochemical feedstocks and those that deplete forests or ore reserves.

Do rats and rodents eat the PVC geomembrane?

It is only possible to eat the geomembrane at an edge, fold, or seam onto which the animal can grip. Since PVC geomembranes have 80% less field seams than polyethylene geomembranes, the likelihood of having an edge, fold, or seam is significantly less. However, it is important to note the following information about PVC geomembranes:

  1.  they possess no compounds that have any food or nutritional value to rats and rodents,
  2.  the materials are not addictive, and
  3. the reason for an animal eating through a geomembrane is probably to obtain access to the other side for food, warmth, or some other reason.
Does PVC decompose and create groundwater hazard when it is subjected to landfill leachate?

PVC is a highly stable material that is extremely resistant to the aggressive chemical environment found in landfills. Any plasticizers released when PVC is buried under these conditions would constitute minuscule amounts over an extended period of time and thus present no threat to human health or the environment. Forensic studies show the liner to be in excellent condition after 30 years of burial.

Is smoke from the wedge welding process hazardous?

The concentration is non-toxic and wedge welding outdoors poses no risk.

Is chlorine, the raw material used to make PVC toxic – since “natural” organochlorides are not known to exist?

Numerous instances of natural organochlorides exist. In fact, life itself could not exist without chlorine chemistry.

What design features are essential for baffle curtains?

Curtains are effective ways to maximize the flow and settling processes in waste-water, sedimentation and various industrial lagoons. Baffle curtains are often made of reinforced Polypropylene (RPP). More corrosive fluids may require use of Cool-Guard, XR-5 or reinforced PVC products.. Flexible and durable, any material needs proper hardware and attention (e.g. never leave it flapping in the wind) to assure long-term service. Floats can be built into the top edge and often weights hold the curtain bottom where it can best function. Never assume the liner material can handle the stresses (without reinforcement) around cables, chains, anchor points and flow through windows.

Is it possible to weld flexible (plasticized) PVC to rigid PVC pipe by hot air welding?

The difficulty with hot air welding is that the melting point of the rigid and flexible PVC may not match up well enough to make welding in this method easy.However, this problem has an easy solution. You can solvent bond flexible PVC to rigid PVC pipe quite easily. Normally, PVC pipe cement is a mixture of THF (tetrahydrofuran) mixed with dissolved PVC pipe resin (and a few other chemicals to slow the reaction). The main ingredient is THF. That is the same solvent used to weld flexible PVC liner materials. Using THF to weld rigid to flexible PVC is a fairly common procedure. Make sure all the pieces are pre-cut and fit together. Slide a THF laden brush between the surface of the liner and the pipe you want to weld. A little roller pressure and it should set up nicely.

How might we address in the field polyethylene (PE) wrinkling and/or tenting in different climates?

Polyethylene is an excellent liner for many applications – both covered and uncovered. Because PE expands and contracts up to 2% over width and length, expect it to shift in the course of installation [LLDPE and HDPE slightly more than RPE (reinforced) membranes]. Polyethylene sheets expand or contract within hours of deployment. Overnight, movement follows temperature changes. Remember to focus on anchor trench back-fill at the best time & temperature. If uncovered (no water, dirt or ballast anchors on the liner), shifts can stress the membrane at pipe boots and attachment to structures. Installers typically leave enough liner in anchor trenches so inches (or feet) can shift out of trench into the cell as temperatures fluctuate. Beware “locking in” that anchor trench in a hurry — only to find the next morning the membrane tightened up and toes of slope lifting off the subgrade. Weight at slope bottoms minimize the effect (sandbags, ballast bags or tubes). Filling with liquid is the best way to assure PE membranes stay in contact with subgrade at all points within a cell (even a foot or two depth).

Welding PE membranes at relatively cold times – followed by hot stretches – may lead to wrinkling throughout a cell. That doesn’t mean “too much liner” was installed: only that it expanded (and will continue to do so in cycles until covered or filled). As with back-fill of an anchor trench, keep that in mind for determining safest times to cover a PE liner with soils or gravel.

Want to know more about FGI Membership? 
Get in touch with us to discuss becoming a member.