It’s vitally important to never settle for any random pond liner for a sewage lagoon. While a small decorative pond may last with a mid-range liner, the challenging environment of a permanent sewage lagoon is a different story. Only a geomembrane liner, with the right formula and reinforced design, will last for a decade or more when exposed to constant chemical and corrosive exposure. If you need to install the liner in an exposed way for easier cleaning and sludge removal, you’ll find it even harder to get the liner to last multiple decades. Yet careful selection can result in a lagoon that lasts 30 years or more before you need to replace the liner. Prepare for ordering the liners for your sewage ponds and lagoons with this quick guide to selection.
Options for Lagoon Liners
There are more than a dozen general options for lining ponds and nearly all of them have been tested for suitability in holding sewage. Unfortunately, only a handful of modern liner materials work well for this application. The majority of older sewage lagoons leak because of poor liner selection. Here’s a quick round-up of the main liner options marketed for sewage lagoon use and how they stack up to the rest of the competition.
For both new and renovated sewage lagoons, flexible polymer-based geomembranes make the most sense. These flexible materials conform to fit any pond shape you excavate, while the impermeability makes it ideal for controlling seepage in highly sensitive environments. There’s little to no risk to the groundwater under the lagoon unless a leak occurs. If a leak does develop over time, it’s possible to detect it with electrical equipment without even draining the pond. No other liner can compare in durability, cost effectiveness, ease of installation, or customization options as geomembranes like the industry leading reinforced polyethylene (RPE) liners from BTL Liners.
Concrete may seem like a good choice for permanent sewage lagoons and treatment tanks for its strength and durability. However, don’t confuse concrete with an impermeable liquid barrier. On its own, concrete isn’t capable of withholding seepage to the level required by most local authorities. Concrete needs a flexible sheet of impermeable material or a spray-on liner to block the tiny gaps in the surface of this porous material. While concrete can be used for reinforcing large scale in-ground ponds or forming the walls or above ground basins and tanks, you’ll still need a secondary liner to prevent water loss.
Clay is a natural choice for lining ponds where seepage isn’t a major risk. This makes it a poor choice for sewage ponds since the seepage rate is too high. Bentonite clay is the primary material chosen for sealing natural ponds because the tiny particles settle along the bottom and sides to block gaps that let moisture seep out. The effect is too unreliable to use for a high-risk pond like a sewage lagoon. Even for ponds that only contain greywater, with no active sewage component, clay liners aren’t sufficient on their own to keep a lagoon secure over time.
The final option you’ll see marketed for sealing or resealing sewage lagoons is available in the form of a polymer spray. These products claim to be easy to apply, but they don’t compare in durability or leak resistance. Spray-on products require full draining of the pond. At that point, you might as well just spread out a more reliable geomembrane. The spray is difficult to apply in an even layer, leaving behind hidden thin spots that leak. There’s no way to test these materials until the ground is wet. Don’t risk the cost or health hazards of a failing sewage system by trying to rely on a spray-on liner.
Reinforced vs Non-reinforced Liners
All geomembranes used for pond liner are made with extrusion or calendaring techniques that create a single monolithic sheet of material. Yet the addition of a reinforcement grid or tape can make a huge difference in the durability and lay flat function of a finished liner product. Reinforced liners are tougher because these optional additions improve both tear and fold resistance. When a liner folds and forms a wrinkle during installation, the weight of waste pressing down on the material causes it to become a crack over time. Choosing a material like reinforced polyethylene (RPE) is the best way to simplify installation since the liner is easier to smooth out for a tight fit to the excavated ground.
Choosing a Chemical-Resistant Material
Chemical resistance is essential in manufacturing and industrial waste ponds, but it’s also important for sewage lagoons. Various wastewater treatments require the addition of possibly reactive and corrosive chemicals to improve water quality and break down harmful bacteria or nitrates. Without the right materials, the liner of the pond will eventually fail due to constant exposure. Sewage itself is often a corrosive mixture that shortens the lifespan of low-quality geomembranes, especially when concentrated in a commercial or agricultural setting. These are your material options for geomembrane liners and how they stack up when it comes to chemical resistance.
Reinforced polyethylene, or RPE, is the ideal material to use for lining a sewage lagoon. It combines multiple forms of polyethylene to optimize performance. The addition of a reinforcement layer increases tear resistance, so it isn’t easily damaged during installation and prevents roots from doing harm over time. When it comes to chemical resistance, RPE tops the charts. Quality RPE liners, like ArmorPro, can store high concentrations of chlorine and other chemicals used in the sewage treatment process, allowing you to replace small above ground tanks with in-ground storage ponds.
High Density Polyethylene
High density polyethylene, or HDPE, is a tough but brittle liner that isn’t the best choice for most sewage lagoons. It offers a mixed range of chemical resistance and lacks specific resistance to many compounds found in sewage mixtures or water treatment programs. Cold temperatures can also lead to cracking in ponds lined with HDPE, causing hard-to-fix leaks. While it’s a better choice than sheet rubber or PVC, HDPE still is only second or third best after RPE.
Low Density Polyethylene
Low density polyethylene, or LDPE, offers some extra benefits over HDPE by increasing the flexibility of the material. This prevents low temperature or freezing damage and helps the liner conform to the exact curves and corners of the pond. Unfortunately, LDPE is no more resistant to floating than HDPE. Both types of basic polyethylene are prone to rising and floating when used in sewage lagoons, especially if any waste is under the liner to generate methane gases. LDPE also has mixed chemical resistance with susceptibility to a few chemicals used in sewage treatment. While LDPE is most likely better than HDPE or PVC for a sewage lagoon, it still can’t compare to the chemical resistance and durability of RPE products.
Polyvinyl chloride, or PVC, is the most common material used for backyard pond liners. Don’t make the mistake of choosing it for a sewage lagoon, even for a small residential one. PVC has some of the lowest levels of chemical resistance; unless specifically formulated for this purpose. If you’re spending the money for a special blend of PVC material, you’re usually better off buying an RPE product with a similar price that offers other important benefits. PVC liners are flexible but far less durable than all of the polyethylene products listed above. It must be buried because most formulas are particularly weak against UV exposure. If chemical exposure doesn’t cause the PVC liner to fail, when used as a sewage lagoon liner, sun exposure is likely to do it instead. Stick with RPE to enjoy decades of reliable performance without the need to regularly replace the pond liner.
Concerns About UV Exposure
Speaking of UV rays, all flexible geomembrane liners are at risk for damage from the sun when installed in an exposed way. Many liners become exposed over time after being covered thoroughly with gravel, soil, or sand during installation. Wave actions erode bank cover, and the effect is often increased by wind scouring. Letting even a small portion of the total liner become exposed can create major leaks, unless you’ve chosen a material with a high UV damage resistance. As with chemical resistance, RPE is the best choice in this category. Some RPE liners from BTL Liners are rated for multiple decades of exposed installation thanks to the advanced level of sun damage resistance. If these liners are covered and then accidentally exposed, you won’t have to worry about damage occurring as you work to replace the cover material.
Impermeability and Geomembranes
Liners for sewage lagoons must offer as much impermeability as possible to control water loss and seepage that spreads bacteria. Many commercial and residential ponds are built in areas where the local water table also serves as a source of drinking water. While wastewater is naturally filtered as it seeps through layers of soil and rock underground, it needs to spread through a lot of material before becoming clean enough to drink again. A high water table under a lagoon may allow sewage in before it has been properly filtered. An impermeable geomembrane is the most reliable method for controlling this kind of spread. No product is completely impermeable to all water and vapors, but products made of RPE achieve the highest level of impermeability.
The Need for Matching Covers
Many sewage lagoons call for floating or suspended covers to control the gases released from the breakdown of the waste products in the water. Other covers are needed to keep excess rainwater from overfilling the pond or to control odors in crowded areas. Whatever the reason, these covers need to offer just as much chemical resistance as a liner. They’ll also face more UV exposure than even unprotected liners thanks to being installed over the surface of the lagoon. BTL Liners also supplies cover materials for these purposes, including ArmorCover.
Selecting a liner for a sewage lagoon should be a little easier after reading this guide. If you still have questions about the right material for your project, we’re happy to help answer your questions here at BTL liners.