How our Landfill Works

It is only in the last few decades that waste has been managed scientifically even though the connection between disease transmitted by vermin from waste dumps has been know for 100 years.

The first "sanitary" landfills were holes in the ground or disused quarries where deposited garbage was periodically covered over with burden to reduce odour and control rodents. Although reducing offensive smells these old style "tips" created ground water contamination and the risk of fire or explosion from accumulated methane generated within the waste pile.

Dulverton was the first landfill in Tasmania designed to handle domestic and commercial waste sustainably. The landfill is better described as a waste hill and is shown schematically below:

The landfill is constructed as a series of cells. The chosen site is first levelled but with a slight incline to ensure all liquid drains in the same direction. The whole area is covered with a 1000mm layer of compacted clay and a 300mm layer of gravel to promote leachate drainage.

This combination provides an impervious barrier to liquid percolating through the landfill from moisture in the waste and from rain. This percolating liquid leaches contaminants from material in the waste pile - hence its name, leachate.

The leachate is collected in a pond. Some evaporates and the balance is reticulated back into the landfill where it fuels biological breakdown. In the process the water is split into its component hydrogen and oxygen. The oxygen aids biological activity and the hydrogen finishes up as methane and hydrogen sulphide (rotten egg gas). As the volume of these gases increase with size and age of the landfill they are either flared off or used beneficially to generate power.

Waste from municipal and other sources is dumped on the working area of the cell, spread evenly to about 300mm and compacted. The compacted area is covered with a layer of inert waste to minimise odour and the risk of rodents. The waste cell is thus built up layer by layer until it reaches its maximum height, then it is capped with a layer of clay to prevent rain ingress.

The landfill is designed and constructed to ensure that run off from rainfall is kept separate from leachate. Indeed leachate control is one of the most important aspects of landfill management and involves monitoring ground water via a series or bores around the site.

Capping a landfill cell does not end there. Each cell when complete is covered with soil and re-vegetated. Financial provisions are made to manage the site for 30 or more years - until all biodegradable material has broken down and is no longer a potential environmental hazard.