Sanitary Landfills

In Australia, we call landfills the “tip” because it’s what you tip your waste into, in the USA we call it the “dump”. But whatever you call them, sanitary landfills are by far the most common waste disposal method for solid municipal and industrial waste in the world (37% of waste globally).

In the USA alone there are over 1,250 landfill facilities. The goal of these facilities is to prevent environmental contamination and to protect public health by collecting and storing waste in the safest manner possible.

Chart showing Australia’s waste generation destinations (Click to expand)

To accomplish these two goals, sanitary landfills are often located away from water courses and high above any groundwater aquifers. They are also located away from cities, but not too far away because cities are the source of most municipal wastes. Landfills are often built with water in mind because water is a solvent and will dissolve, collect and transport any hazardous wastes or contaminants in the solid waste. Water is also useful while the landfill is active to support biological activity that degrades waste. Recently, the emission of the greenhouse gas methane (34 times more powerful than CO₂ as a greenhouse gas) from rotting food in anaerobic conditions (the largest component of municipal waste) has led to innovative solutions to recover and use methane from constructed landfills.

Diagram of a typical U.S. sanitary landfill (Click to expand)

Landfills are typically constructed using engineered mounds of layered waste on top of an impermeable layer of clay or other waterproof material. Keeping control of the water in the landfill is paramount and landfills are often designed with leachate pipes (perforated pipes below the waste but above the waterproof layer) that collect water that has percolated down through the landfill and waste materials. This water can then be treated and released or used for other activities. The leachate pipes and pumps prevent the accumulation of water underneath the landfill and on top of the water proof layer, making leaks into groundwater or nearby waterways less likely. Other vertical pipes may be used to collect methane gas that can be used on site to generate electricity. Once a landfill is “full” or is no longer used (e.g. the urban area has grown around the landfill and residents don’t want an active, smelly landfill near their homes), the landfill will be capped with an impermeable clay layer or phytocapped (using soil and plants) to prevent water infiltration into the landfill. Essentially, the landfill is sealed. Groundwater monitoring wells outside the landfill are active during the life of the landfill and after to detect contamination from the landfill if it leaks into the groundwater.

Sanitary landfills are a great improvement on open or unregulated dumping. It is much easier to manage the environmental impacts of millions of tons of waste in several places than it is to deal with widely distributed litter and uncontained waste. However, there are still environmental issues with sanitary landfills including poorly sited landfills near water courses or close to groundwater supplies, inadequate wetness that decreases decomposition rates of degradable waste, and too much water that manages to leak either through or around the waterproof liner of the landfill. Landfills are often considered unfit for most purposes after they are closed, although clever use of soils and plants (i.e. phytocapping) can convert some completed landfills into parks and open woodlands that provide some ecological benefits. Building new landfills is getting more difficult too. If land is scarce or it’s politically unpopular to site new landfills in suburban or exurban areas, governments may export their solid waste to other countries with less stringent environmental or health regulations.