As a class, geomembranes work well as floating covers for lagoons and covers because of their durability, flexibility, stretch resistance, UV resistance, and chemical compatibility. However, individual geomembrane products are challenging to choose correctly. Other geosynthetics feature distinct visual differences, but almost all geomembranes tend to be smooth, solid, and available only in black or white. This similarity is confusing because while geomembranes' construction and material makeup vary substantially from product to product, the amount of reflection and specific surface texture is often the only visible difference between them.
There are dozens or even hundreds of formulations used to make geomembrane liners and covers. We've identified a few basic categories where most geomembranes can be sorted based on similar compositions or features. We'll introduce these categories next. We invite you to use this information to help you select the best cover for your operation.
Synthetic Rubber Polymers:
Chlorosulfonated Polyethylene (CSPE) is a modern, rubber polymer formula designed to overcome many of the limitations of PVC and other materials and was once the primary geomembrane for floating covers.
Pros:
- Outstanding resistance to UV and ozone
- Good performance at low temperatures
- Good resistance to chemicals, acids, and oils
Cons:
- Thermal welding is possible for only a brief period after manufacture.
Ethylene Propylene Diene Monomer (EPDM) is best known as a roofing material but is also suitable for lining decorative backyard ponds.
Pros:
- Good resistance to UV and ozone
- High strength characteristics
- Good low-temperature performance
- Available in thick sheets that are resistant to tears and friction
Cons:
- Stiff and heavy enough to make installation difficult for large covers
- Low resistance to oils, hydrocarbons, and solvents
- Poor seam quality
Polyethylenes
High-Density Polyethylene (HDPE) is frequently employed for all kinds of water containment, including challenging applications such as heap leach and tailings ponds.
Pros
- Broad chemical resistance
- Good weld strength
- Good low-temperature properties
- Relatively inexpensive
Cons
- Potential for stress cracking from sustained low-grade pressure
- A high degree of thermal expansion
- Poor puncture resistance
- Poor flexibility
Low-Density Polyethylene (LDPE) is similar to HDPE but has a slightly different molecular configuration, which gives it other physical properties
Pros
- Fairly inexpensive
- Welded seams
- Soft, flexible, pliable
- Less prone to stress cracking
Cons
- Prone to lengthwise deformation and tears
- Less resistant to UV rays & oxidation
- Less resistant to chemicals
Reinforced Polyethylene (RPE) geomembranes include layers of HDPE and LDPE bonded around a core reinforcement scrim. The combination makes a material that is exceptionally durable and shares many of the benefits of both types. Additional layers or coatings can contribute even more beneficial properties.
Pros
- High chemical resistance
- Excellent UV damage resistance
- Extremely resistant to tears, punctures, and wear
- Tolerant of temperature extremes
- Resistant to stretching and deformation
- Lightweight and flexible for easy shipping
- Suitable for custom shaping and factory assembly
Cons
- Relatively stiff
- More expensive than other solutions
- Limited research on the expected lifespan
Polyvinyl Chloride
In its rigid form, polyvinyl chloride (PVC) is readily recognized as those ubiquitous white pipes used in plumbing, but it's also available as a flexible sheet geomembrane. PVC geomembrane is inexpensive and popular in many installations where cost is an overriding factor. PVC is commonly rendered flexible and pliable by the addition of liquid plasticizers, which can be eroded by UV, heat, and certain aggressive chemicals over time. PVC ages quickly as the plasticizers disperse, rendering it brittle and prone to damage. Worse, the plasticizers often include harmful compounds that spread into the contained water itself.
Pros:
- Highly flexible
- Easy to work with and seam
- Widely available
Cons:
- Poor innate resistance to UV and ozone
- Poor resistance to weathering
- Poor performance at both high and low temperatures
- Vulnerable to tears unless reinforced
- Can leach its chemicals into wastewater, adding complexity to the treatment process
Polypropylene
Polypropylene is innately flexible without the need for plasticizers that create problems with many other geomembranes.
Flexible Polypropylene (fPP) A variety of other additions can be introduced while fPP is in its liquid state to enhance the attributes of the finished product.
Pros:
- Extremely lightweight
- Highly resistant to most acids and alkalis
- Resistant to stress cracking and friction wear.
- Stretchable without breaking or deforming
- Resistant to tears, scratches, and punctures
- Pliable until -50°C
Cons:
- Susceptible to UV damage
- Limited resistance to hydrocarbons and chlorinated water
Reinforced Polypropylene (RPP) Considered one of the longest-lasting geomembrane liners currently available, RPP is manufactured with a reinforcing scrim layer to boost durability, while specialized coatings provide additional targeted enhancements. BTL's AquaArmor PP-45 (https://www.btlliners.com/aquaarmor) is an excellent example, rated for 20-year UV exposure.
Pros:
- Unprecedented resistance to UV and weathering
- Excellent chemical resistance
- Welded seams
- Excellent abrasion, puncture, and tear resistance
- Manufactured in large-scale single panels
- Excellent impermeability, less likely to pass through condensation than polyethylene
Cons:
- Limited resistance to hydrocarbons and chlorinated water
EIA Geomembranes
EIA (Ethylene Interpolymer Alloy) geomembranes are made by applying a polymer-formulated coating to a PVC base fabric. Many geomembranes have coatings added to enhance performance, but EIA is unique because it is an alloy of PVC and DuPont™ Elvaloy®. Using PVC as the base, with its poor history of plasticizer durability, may seem odd, but Elvaloy is different. Other plasticizers are liquid and rest passively on the contact points between PVC molecules, making them vulnerable to erosion. In contrast, Elvaloy is a solid with a natural attraction to PVC at the molecular level, making it essentially impossible to separate the two once they've formed an alloy.
The reinforced version of EIA geomembranes includes a woven nylon scrim sandwiched between two layers of EIA, which adds significant dimensional stability. EIA-R geomembranes are available from several manufacturers, but the properties of BTL's XR lines are substantially better than the competition. BTL's AquaArmor XR - 3 PW is NSF certified for
Pros:
- High UV resistance
- Resistant to weathering
- Good chemical resistance, including chlorine, chloramines, and hydrocarbons
- Low thermal expansion
- Thinner and more durable than other geomembrane options
- Will not leach plasticizers
- Available in large scale panels
Cons:
- Relatively expensive
- Wicking to scrim layer possible in exposed edges (degree depends on manufacturer)
- Overheating during welding can leave adjacent areas vulnerable to tears
Making the Choice
Once you've prioritized your needs and compared available products, it's time to make the decision. Keep in mind that longevity and durability are critical factors in evaluating cost. The material used to construct the floating cover will largely determine if it achieves your goals and lasts for years. Improper material selection leads to a product that cracks in the cold, peels apart in the sun, or sinks below the water's surface despite the use of floats. Wastewater facilities tend to operate long-term, so it's not cost-effective to be replacing critical materials every few years.
BTL Liners offers several exceptional options suitable for wastewater floating covers. The AquaArmor line includes a reinforced polypropylene geomembrane (PP - 45) and a reinforced EIA geomembrane (XR - 3 PW). Both are NSF-61certified for potable water and are superior to other geomembranes for this application. Give BTL's expert staff a call for help evaluating your project's needs and answering your questions. Quotes are free and easy to request.
