A bottom liner is a layer of impermeable material that is installed at the base of a landfill to prevent leachate from contaminating groundwater. Leachate is a liquid that forms when water seeps through the waste and picks up pollutants, such as chemicals and heavy metals.
The bottom liner typically consists of multiple layers of material, including a geomembrane liner made of high-density polyethylene (HDPE) or another impermeable material, a geosynthetic clay liner (GCL) made of bentonite clay, and a layer of sand or gravel for drainage. These layers work together to create a barrier that prevents leachate from reaching the soil and groundwater below.
The design and installation of a bottom liner are critical to the long-term effectiveness of a landfill. The liner must be able to withstand the weight of the waste and the stresses of settling and compaction, and it must be carefully constructed to ensure that there are no gaps or tears that could allow leachate to escape.
In addition to the bottom liner, landfills also require a cover system to prevent rainwater from entering the landfill and to control odors and emissions. The cover system typically includes layers of soil and other materials that are compacted and graded to create a barrier between the waste and the outside environment.