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
The bottom and sides of a landfill cell are lined with a 1m-thick layer of compacted clay (B) and a 2mm-thick plastic liner (C). These layers stop pollution getting into the groundwater (A). A geotextile mat (D) covers the plastic liner to stop rocks and gravel from tearing it. Collection pipes (E) run through the bottom of the cell to remove liquid that drains through the layers.
A layer of gravel (F), a drainage layer (G), and a layer of soil (H) cover the pipes. These layers allow the liquid to move through to the pipes. The cell is then ready for layers of waste (I, J) which are compacted and covered with soil. Over time, the leachate will be pumped out of the cell and collected in a tank (K). Sometimes, the leachate is pumped back through the cell to help with the breakdown process.
Soil is used to cover the top layer of the cell each night. This helps reduce odour, stop litter being blown away, and stop vermin and scavengers from feeding off the garbage.
What happens when the landfill is full?
When a landfill cell is full, it is 'capped' to stop rainwater from soaking into the layers of garbage. The cap is made of a layer of compacted clay and a layer of soil.
A capped landfill can be turned into a recreational area such as parkland and sporting fields. It will not have housing built on it as it will produce gas for around 20 years.
Gas and dust emissions
Only a small amount of oxygen can get into a landfill cell. This means the rubbish breaks down in anaerobic conditions. When organic rubbish breaks down in anaerobic conditions, it produces landfill gas. The two main parts of landfill gas are methane (CH4) and carbon dioxide (C02).
When these gases and dust go into the air, they have a greenhouse effect and add to global warming. Landfills currently make up around 3% of Australia’s greenhouse gas emissions.
Groundwater pollution
When water and other fluids pass through the layers of waste they make a liquid called leachate. As the fluid filters through, it dissolves chemicals of organic and inorganic matter. Leachate is usually polluted and acidic.
Leachate that soaks into groundwater creates health risks to humans and the environment. If groundwater polluted by leachate leaks into wetlands or streams, it will affect aquatic species and their habitat. Most modern landfills are designed to stop this from happening.
