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Landfill

A landfill is a site designated for the purpose of waste disposal by burial. All waste collected from transfer stations and by commercial and domestic garbage trucks, is sent to landfill and buried on site. The Council operated landfill in Logan, is the Browns Plains Landfill.

In Logan, 40-60 domestic garbage trucks visit the Browns Plains Waste and Recycling Facility to drop off their load of waste every day. Each truck has the capacity to hold the waste from between 550 – 600 (240L) domestic garbage bins. That means there is an average of 28,750 household garbage bins being emptied into the SmartTiP landfill on any given day. There are also Commercial and Industrial (C&I) and Construction and Demolition (C&D) services in addition to this.

A typical landfill site is divided into a series of ‘cells’. Waste materials are dumped into the cell, then spread out and compressed using a large compactor, before being covered with soil. Compaction of the waste material after dumping maintains site stability and also ensures more space is available to fit the maximum amount of rubbish in the remaining cell. Once the cell is full, it is capped and covered with soil and dumping commences in the next cell. At Logan City Council’s Browns Plains Landfill, the current working cell should take three years to fill at the rate of one Olympic sized swimming pool every four days.

How does a landfill cell work?

Landfill cells are specifically designed and carefully prepared to minimise the contamination of groundwater by leachate. The following image shows the various layers of a landfill cell:Landfill Cell

  • A: Groundwater
  • B: Compacted clay
  • C: Plastic liner
  • D: Leachate collection pipe
  • E: Geotextile mat
  • F: Gravel
  • G: Drainage layer
  • H: Soil
  • I: Old garbage layer
  • J: New garbage layer
  • K: Leachate collection tank

A one meter thick layer of compacted clay (B) and a two millimetre thick plastic liner (C) are set into the bottom of a new cell to avoid the contamination of groundwater (A) by garbage and leachate. The plastic liner is then covered by a geotextile mat (D) that keeps it from being torn or punctured by the nearby rock and gravel layers (the plastic liner and geotextile mat also line the cell walls). Leachate collection pipes (E) run through the base of the cell and remove liquid as it drains through the layers.

A layer of gravel (F), a drainage layer (G), and a layer of soil (H) are successively laid down on top of the pipes. These layers allow the leachate to move through to the collection pipes. The Cell is then ready to be filled. Layers of waste (I, J) are dumped and compacted into the cell and covered with soil. Over time, the leachate is pumped out of the cell and collected in a tank onsite (K).  In some instances, the leachate can be pumped back through the cell to aid in the decomposition process of the waste materials.

At night, the working layer of the cell is covered with soil to reduce odour, prevent litter being blown away and to prevent vermin and scavengers from feeding off the garbage.

What happens when the landfill is full?

When a landfill cell has been filled, a ‘cap’ is placed on top to prevent rainwater from soaking into the layers of garbage. Cap construction involves a layer of compacted clay being laid on top of the cell, followed by a layer of soil. The cell can then be regenerated by planting trees or grass on top of the soil layer.

Although a completed landfill site may be regenerated, the land cannot be reclaimed for housing purposes. A completed landfill site will continue to produce gas (Environmental Issues Associated with Landfills: Page 8) for around 20 years, increasing to a peak at 10 years and then gradually dropping off. In the meantime, the completed cell can be converted into recreational areas such as parkland, sporting fields, wildlife reserves, golf courses and more.

Gas and dust emissions

When waste is buried underground in landfill, very little oxygen can enter the cell, meaning decomposition takes place under anaerobic conditions.  When organic waste (e.g. garden waste and food waste) breaks down in these anaerobic conditions of a landfill, it produces gas (landfill gas). The two main components of landfill gas are methane (CH4) and carbon dioxide (C02). When released into the atmosphere, both methane and carbon dioxide have a greenhouse effect and significantly contribute to atmospheric (global) warming. Landfills currently account for around 3% of Australia’s Greenhouse gas emissions.

Similarly, dust particles from landfill operations and other gases from waste decomposition, comprising of various elements, escape into the atmosphere and can contribute to the warming effect.

Groundwater contamination

Leachate is the name given to the liquid that is created inside a landfill cell when water and other fluids pass through the various layers of decomposing waste. As the fluid leaches, it dissolves chemicals of organic and inorganic matter that are present in the landfill. Although the composition of leachate varies throughout the landfill, it is usually contaminated and acidic.

If leachate is allowed to permeate through to the groundwater it may present several risks to human health and the environment. Leachate-contaminated groundwater may discharge into wetlands or streams where it can affect aquatic species and their habitat. Most modern day landfills, including the Browns Plains Landfill, take a range of mitigating actions to prevent this from occurring.

Limited site space

Perhaps one of the greatest issues associated with modern landfills is the space required for their construction. Landfill sites occupy very large areas of land, and with the amount of waste Australians are currently producing, this space is filling up almost as fast as it can be prepared.