Concerns about manure seepage from self-sealing lagoons and even clay-lined lagoons are driving the market for new synthetic membrane liners. The liners, widely used in other containment applications, are now being installed in lagoons on some hog farms. The liners are being used in addition to, or as an alternative to clay liners.
Synthetic Liners The most common type and most effective material for a lagoon liner is high density, polyethylene (HDPE). This same liner is also suitable for slope erosion control. Lining only the slopes will only provide erosion protection above the water line. It does not protect groundwater from leaks.
HDPE liners are also available with rough (textured) surfaces to help enhance slope stability where the liner will be covered with soil. The liners may also be used in conjunction with clay or doubled up to provide assurance that leaks can be detected before extensive contamination can occur.
Smooth HDPE liners have been formulated, tested, and demonstrated to provide resistance to chemicals, ultraviolet sun rays, and thermal aging. Membrane life expectancy in excess of 20 years can be achieved for most applications.
HDPE lining materials are available with thickness of up to 0.1 in. or more. Many animal or agricultural waste applications to date have utilized a liner thickness 0.04 in. even though a thicker HDPE geomembrane may be a more dependable and economic selection for long-term life expectancy in areas where the clay content in soils is lower.
The surface to be lined is prepared and rolled smooth. Any sharp objects are removed. A geotextile or drainage composite under layer may be necessary or desirable to protect the liner and vent underground gas in some installations.
The liner is then laid out in panels typically in excess of 22 ft. wide and as long as necessary. Each panel is heat welded to the next. Pressure checks are conducted on each weld to assure that the seams do not leak. Additional layers of protection are placed below all discharge pipes, pumps or other equipment that might rest on the liner. After the entire liner is completed and tested, 6 to 12 in. of water or soil is placed on top of the liner bottom for protection and to stabilize the liner position.
Puncture Potential Though liners are resistant to rupture by the same natural causes that affect clay liners, they may be subject to mechanical damage. For economic reasons, the thinnest material possible is desired to line lagoons. Protective measures may reduce the chances of puncture or tear to an acceptable level.
The potential benefits of synthetic liners outweigh the potential damage factors. Membrane liners offer the advantages of dependable containment with lower permeability, long life expectancy, faster installation and easy maintenance.
Achieving Zero Leakage A few producers like Iowa Select Farms, Iowa Falls, IA, are using designs that allow immediate detection of leaks. They are using a multi-layered, synthetic liner system.
The liner is manufactured and installed by GSE Lining Technology, Inc. of Houston, TX. It includes a layer of liner membrane separated from the clay subgrade by a geocomposite drainage layer. The drainage layer allows detection, collection and disposal of leaks that might be caused in the primary liner and minimizes leakage loss even if the liner is punctured. The composite layer acts not only as a second layer of protection against leaks; with the installation of a collection sump and pump, it also drains fluid from any possible leak into a collection pipe so that integrity can be monitored. Digestion of the organic matter contained in the waste water and unacceptable odors caused by the products of decomposition can be controlled by floating covers manufactured from the same or similar membranes as the containment liner. In some cases anaerobic digestion of waste in a covered pond can generate sufficient methane to allow economically viable collection and use of the methane.