Natural Liners
Clay liners are typically the only type of natural liner that is suitable for use in a landfill, although they aren’t used on their own. Dense, highly compacted clay has low permeability and can be used to line the bottom and sides of a landfill. On the plus side, it’s a natural substance which blends naturally into the environment over time. A major weakness to the use of clay is the amount (typically 2 feet or more) that’s required to establish an acceptable seal. This volume used as a daily cover, for example, would quickly occupy a great deal of valuable space within the landfill and would limit the amount of trash it could contain. Clay is also very heavy, unwieldy, and difficult to work with during installation.
In places where clay is chosen for the base liner, bentonite clay is typically preferred. Bentonite can be transported as a lightweight powder form and then mixed with water on-site before it’s applied and compacted. A unique property of bentonite is its ability to absorb water and expand, filling air pockets and tiny cracks. This ability to self-repair is particularly valuable over the life of a landfill but is still not enough to make bentonite liner suitable as a standalone option.
An improved combination option for clay is called a geosynthetic clay liner (GCL). In a GCL liner, bentonite powder is distributed evenly between woven and non-woven geotextiles. When exposed to moisture, the bentonite absorbs it and expands, filling and eliminating air spaces. When installed properly, the bentonite clay has a low permeability and is suitable to use in place of a simple clay barrier. GCLs are best used as a separation between two different types of soils to prevent contamination between layers, such as in the base layer.
The way GCLs are fabricated allows for precise calculation of liner required, preventing overspending. However, they are still heavy and cumbersome to work with and installation is very labor intensive. Worse, damp conditions may make installation impossible since the clay would likely absorb even more moisture and make the panels virtually impossible to move. The cost of labor, in addition to this kind of expensive delay, could completely consume any potential cost savings.
Synthetic Liners
Geomembranes are synthetic membranes used to control fluid or gas migration. These membranes are typically manufactured in very thin continuous sheets, although other configurations are possible.
Landfill installations require durable, reliable, impermeable geomembranes for every face exposed to leachate. This includes each of the sides as well as the primary, secondary and even tertiary base layers. The best options for strong, flexible and chemically resistant liners come from BTL’s ArmorPro series. Built on XR technology, these products are designed to outlast high-density polyethylene (HDPE), chlorosulfinated polyethylene (CSPE) and polypropylene when exposed to the toughest contaminants, temperature extremes and UV light.
While it’s true that geomembrane liners are better at eliminating leaks and seepage, they’re also vulnerable to damage during installation and some materials are not well suited to withstand stretching and elongation during repeated compaction. In waste that’s not been carefully sorted, protruding roots and stones could puncture and tear the liner, especially when heavy compaction is applied. Resistance to degradation from UV rays (sunlight) is also a significant feature.
The XR-3 geomembrane is an affordable, durable option for landfill liners. It’s constructed with a nylon woven reinforcement layer sandwiched between EIA coatings that are minimally degradable even in an adverse environment. XR liners offer maximum containment and protection for even highly challenging substances. Whenever it’s necessary to minimize or prevent toxic leachate from moving into nearby rivers, underlying aquifers or surrounding soil, the ArmorPro series of XR liners from BTL Liners are an outstanding choice.
Composite Liners
Geocomposites are a combination of materials that are typically used individually. In leachate management systems, a layer of gravel or some other permeable material allows leachate to filter through and collect on a chemically resistant (HDPE) layer, which is the first barrier to incursion into the environment. A composite liner would combine both layers in a single product. For example, a grid or pockets of gravel may be fused to an impermeable HDPE layer. The gravel permits collection of leachates while the HDPE layer prevents movement into the underlying soil. Underneath this collection layer and primary barrier is a leachate detection system. Detection systems differ but are typically composed of a layer of permeable material and a web of moisture sensors. These sensors are monitored to alert operators of leaks. The detection layer is underlaid with an impermeable HDPE liner to contain any leachate that does manage to pass through the primary liner. Underneath the secondary liner there is often one or more layers of geosynthetic clay liner.
Other Substrates
Landfills are complex structures, and there are other uses for geotextiles throughout. To avoid potential problems with punctures and tears, engineers will often call for additional layers of nonwoven geotextile underlayment to be installed above and/or below the geomembrane. The underlayment essentially acts as a pillow, evening out any protrusions or sharp edges.
Geogrids are structural materials used to improve stability of cover soil atop a synthetic liner, or as soil reinforcement on steep slopes.
Geonets can be used as drainage layers in the place of gravel or sand, and often use less vertical space than the natural materials, thus increasing usable capacity for the landfill.
