Geosynthetic Clay Liner
A geosynthetic clay liner (GCL) is a composite barrier that functions as a hydraulic constraint in landfill waste containment. GCLs are made of two durable geotextiles encapsulating a layer of natural sodium bentonite clay that swells to form a low-permeability barrier.
Unlike geomembranes, which require welding to join sections, GCLs are often joined by overlap seaming and adhesive bonding. This allows the GCL to repair itself if damaged without needing additional field welding.
Benefits
The use of clay as a barrier to liquids has been used for thousands of years. While the technology behind it has evolved, the basic principle remains the same. The primary function of any containment barrier is to control advective contaminant transport while also providing strong diffusive contaminant retardation properties. This dual requirement often requires the use of multiple barriers and is a common challenge in landfill, lagoon and pond applications.
A geosynthetic clay liner (GCL) is a manufactured barrier layer consisting of a competent layer of sodium bentonite clay attached or adhered to a geotextile or flexible geomembrane. The bentonite clay swells when it encounters a liquid, forming a highly impermeable barrier with low permeability. Geotextile layers provide added strength and puncture resistance to the GCL.
GCLs are designed to replace traditional compacted clay liners for many of the same applications. Their simple installation and improved hydraulic performance make them an ideal alternative. The natural sealant nature of the GCL’s sodium bentonite enables it to seal around penetrations, self-heal punctures, and self-seam at overlaps. The bentonite has a strong affinity for water and swells upon hydration to form a tight seal Geosynthetic clay liner with a saturated hydraulic conductivity typically less than 5 x 10-9 cm/sec, which is significantly lower than the permeability of traditional compacted clay lines.
GCLs are ideal for a wide variety of applications including landfills, wastewater management systems, industrial waste ponds, and engineered/constructed wetlands. They can also be used to cap petroleum-impacted soil or waste, and for the containment of stormwater in pipeline trenches and spillways.
Installation
GCLs are typically used as a bottom liner in landfill applications, but can also be used for other containment purposes. They can replace a layer of compacted clay, or work in conjunction with other traditional liner materials such as geomembranes.
In general, GCLs are manufactured composite liners that consist of a durable geotextile outer layer and a uniform layer of low-permeability sodium bentonite clay core. The bentonite clay is a naturally occurring material that expands when hydrated under confinement, creating a hydraulic barrier. The GCLs can be held together by either needle-punched fibers or stitch bonding, or glued to the underlying geotextile with an adhesive.
Some manufacturers also offer prefabricated bentonite clay blankets for use in landfill liners and other environmental projects. These are often called “clay mats” or “bentonite blankets.” They can be cut to size and placed in the same way as a regular GCL.
Once the GCL is in place, it is covered with its intended substrate material (generally soil or another geosynthetic). The GCL should be covered before a rainfall or snow event occurs. The cover should be carefully placed to avoid damage to the GCL or underlying materials.
The GCL should be closely monitored while being deployed and covered, as any damage to the liner can impact its hydraulic properties. It is important that a CQA inspector be present to monitor the handling, placement and covering of the GCL.
Maintenance
In order to keep GCLs performing properly, it is important to maintain them with regular inspections. The inspections should be completed by a professional engineer or hydrologist. The GCL product should be visually inspected and mechanically checked for any defects such as a puncture or a shift. If the GCL has been damaged, it should be patched immediately with a geotextile patch that extends at least 30 cm (12 in.) beyond the damaged area and is adhesive or heat bonded to the product. This ensures that the GCL patch will not shift during backfilling with soil or subsequent seaming of materials over the GCL.
A GCL is a geocomposite that contains a layer of low-permeability sodium bentonite clay sandwiched between layers of geotextile fabric. When it comes into contact with a liquid, the bentonite swells up, forming a hydraulic barrier. GCLs are commonly used as an alternative to traditional compacted clay liners and geomembranes in landfills, lagoons and ponds.
A GCL can also be used as a secondary liner for earthen spill containment berms. These berms are designed to Geo Bag Sand Bag prevent hazardous materials from spilling and contaminating the surrounding environment. In addition to preventing toxic substances from entering the environment, these berms can also stop rough terrain such as rocks and sticks from poking through the liners, which would cause contamination.
Secondary Containment
While landfills are designed to contain hazardous waste, it’s important for them to have secondary containment in case of a leak or other disaster. This is where geosynthetic clay liners come in. These barriers prevent seepage and contaminant movement, protecting the environment and the people and animals who live around the site.
Many states and governmental agencies have laws in place that require sites with potentially harmful seepage to be contained. Using GCLs can help meet those requirements, and they’re much easier to install than other liner options.
GCLs are used to line a wide range of landfill capping and containment structures, including leachate liners and SUDs pond liners. The natural clay mineral, sodium bentonite, swells on contact with water to create a highly impermeable barrier. GCLs are a more efficient and cost-effective alternative to traditional compacted clay lines or geomembranes, and they can be used in conjunction with those materials.
They’re also resistant to varying weather conditions, which can cause a decrease in the effectiveness of traditional compacted clay liners. GCLs are not susceptible to the freeze-thaw and desiccation-rewetting cycles that can affect compacted clay barriers, which allows them to retain their low permeability in extreme weather. GCLs are also less likely to experience performance decreases due to chemical incompatibilities, which can be a problem with some types of compacted clay barriers.