Perhaps we should start by discussing what is not adequate to meet contemporary specifications for water treatment plants. Traditional options have included:
- Concrete: Because it’s strong and durable, concrete can seem like a viable option for water treatment tanks, sewage lagoons and holding ponds of all types. However, on its own, concrete is not considered an impermeable barrier because it’s subject to cracking and shifting. Even with a secondary flexible covering or impermeable material, seepage can occur, and it may not be able to meet regulatory standards for environmental protection. Surface gaps can allow liquids to penetrate the porous concrete and escape to surrounding soil.
- Clay: Compacted soil and clay can be effective if potential seepage isn’t a problem. That is not the case for a sewage pond, nor is it suitable for most industrial wastewater containment. Although Bentonite clay can be a option for natural ponds because its small particles will block gaps along the sides and bottom of the pond, it is unreliable for high-risk containment of potentially toxic substances in a sewage lagoon. Clay is not considered ample protection even for greywater containment ponds that don’t contain actual fecal sewage.
- Polymer Sprays: Like other products that claim easy installation and adequate protection, there are inherent problems and long-term effectiveness, durability and performance might be questionable. In addition, any spray-on product is not only difficult to apply evenly, but its reliability is extremely difficult to test. Such products also require additional site preparation and can be risky if relied upon for long-term, lasting protection.
Geomembranes Are the Best Choice
Flexible, polymer-based geomembranes are the sensible choice for both new and renovated sewage lagoons, but not all geomembranes are created equal. Because such liners are flexible and will conform to any pond shape that is planned, they are good for sensitive environments. The impermeable nature of the material prevents seepage and eliminates risk to groundwater except in highly unusual circumstances. In most modern settings, that risk is typically detectible using electronic sensors installed in tandem with lagoon construction. The options for size customization are almost unlimited, and geomembrane liners compare favorably with other options in terms of cost, durability, installation ease and long-term efficacy. Versatile liners of reinforced polyethylene (RPE) are industry-leaders.
Assuring Membrane Impermeability
Impermeability is supremely important. Liners for sewage lagoons must prevent seepage and leaks to the highest extent that is possible for as long as possible. That is especially important in areas where the water table also serves as a source of drinking water. Even though any water that penetrates natural terrain is naturally filtered to some extent as it travels through subsurface layers of soil, sand and rock, it takes time and a relatively long journey before it is once again suitable for human consumption. A high-water table near or under a sewage lagoon is at risk if the lagoon leaks. A highly impermeable membrane is the best protection against this type of contamination, and RPE liners provide the best protection currently available.
