In the past, rubbish was taken to abandoned sand or stone quarries, burnt and then covered with soil. Many of these old ‘tips’ were poorly designed with numerous problems, such as odours, air pollution, litter, vermin and, in some cases, contamination of ground water.
Modern day landfills in Australia are designed to overcome these problems and must comply with strict government regulations. These landfills are still situated in mainly old quarries, but they have many features that help overcome the problems of the past.
They are used to dispose of rubbish collected from homes, shops, businesses, and in some cases, building sites. Special landfills are set aside for rubbish that is considered toxic or hazardous waste.
A typical landfill pit is lined with a layer of clay and sometimes a plastic liner as well. This prevents any liquid (called leachate) from seeping into the surrounding soil and ground water.
In order to pack as much rubbish as possible in a landfill, the rubbish is compacted by heavy vehicles, excluding the air from the rubbish. In these airless conditions, the rubbish only breaks down slowly.
The gases given off by the slowly rotting material are mainly a mixture of carbon dioxide and methane – called landfill gas. Some of this gas is extracted through special pipes and, in many cases, sent to a special facility where it is used to generate electricity. As landfill gas can only be produced by rotting organic material, reducing this material from going to landfill can reduce the quantities of landfill gas generated.
Any water that was in the rubbish or is formed during breakdown is squeezed out of the rubbish and leaches (or percolates) through the layers of rubbish and sand or soil to the bottom of the landfill (or sumps) where it is collected in special pipes and pumped to leachate storage ponds. The leachate, which can be made up of many different chemicals, is either treated or disposed of to the sewers.
In 2010, after the drought broke in southeastern Australia, a number of old landfills began experiencing problems with unusually high levels of odour coming from the landfill. Before the drought broke, the water table sat below the landfill causing no problems. However, after the drought broke, the large amount of rain that fell trickled down into the water table, raising it to a level above the bottom of the landfill.
In new lined landfills, this caused no problem, but in old landfills (or even some old cells) which were unlined, water from the water table percolated into the landfill, blocking the gas collection pipes. This meant that more landfill gas rose to the surface and was released into the surrounded air. To correct the problem, the landfill operators had to introduce measures to remove the excess water.