Harmful Effects of Landfills

Design of a Landfill

• To identify the hazards associated with landfills, an understanding of landfill design can prove helpful. A typical landfill has four key components: the natural hydrogeologic setting of the landfill, which should consist of a stable area with limited exposure to groundwater; a bottom liner; a leachate collection system; and a cover. Any one of these four components can provide a path for environmental contamination.

Landfill Liner Hazards

• Liner hazards depend on the type of liner used in a landfill. Clay liners are susceptible to fractures and cracking, allowing leachate to leak out. Diffusion can also allow organic compounds such as benzene to leach through 3 inches of clay in about five years. Other chemicals can cause the clay liner to degrade. Plastic liners made from high-density polyethylene can become compromised by several household chemicals and other products, allowing leaks to form. Composite liners combine both liner types. However, they will still eventually develop leaks. An average 10-acre landfill will have a leak rate of between 0.2 and 10 gallons a day.

Landfill Collection System Hazards

• Water that enters a landfill becomes contaminated by contact with the waste and settles in the bottom. Collection systems use networks of pipes above the liner to collect this leachate, pumping it out and delivering it to wastewater treatment plants. However, if this system fails, the level of leachate will build. The pressure is the primary force that fuels liner leaks. These pipes can become clogged due to several causes, including the presence of excessive amounts of silt and mud, growth of microorganisms and chemical precipitates. Chemicals can also weaken the pipes, allowing them to become crushed.

Landfill Cover Hazards

• Landfill covers are physical caps placed over a landfill when it is closed to prevent water from entering, and thus preventing the formation of leachate. Typical covers consist of three layers: an impervious layer of clay or a liner, a permeable layer of gravel to promote runoff and a layer of topsoil with vegetation to stabilize the lower layers. However, a number of processes can compromise a cover, including erosion by rain and wind, the roots of shrubs and trees that can penetrate the cover, burrowing and soil-dwelling animals, exposure of the clay or liner to sunlight and the settling of the landfill contents.