Diagram — The design of a modern landfill site

The diagram illustrates the structure of a modern landfill site for domestic rubbish and the three phases of its working life.

Overall, the site is essentially a lined pit that is first built, then filled and finally capped. Its design ensures that neither the liquid nor the gas produced by the waste escapes into the surroundings.

In the construction stage, a pit is dug into the natural rock. Its sides and base are lined with a layer of clay, on top of which a synthetic lining is laid. Drainage pipes are then installed along the bottom of the pit and connected to a drainage tank situated underground beside it.

Once the site is in use, household waste is delivered by lorry and tipped into the pit. Liquid from the waste runs into the pipes and drains into the tank, which gradually fills. When the pit can hold no more, it is sealed with a cap of clay, which is then covered with soil and grass to form a low mound. Finally, the methane given off by the rotting waste is collected through a gas pipe running up through the cap, while the liquid in the now-full tank is pumped out for treatment. Throughout, the lining prevents pollution from reaching the rock.