Around 1.5 million cubic metres - enough to fill 600 50m swimming pools - of soil will be excavated and cleaned where necessary. Soil washing machines at two remediation plants on the Olympic Park will wash, sieve and shake out pollutants including petrol, oil, tar and heavy metals such as arsenic and lead.

An additional soil washing machine has been ordered to help meet demand. In total approximately 750 tonnes of soil will be treated per day to help create the right ground levels across the Olympic Park.

Soil will be cut from areas that need to be lowered and used to fill others that need to be raised. For instance, some parts of the Olympic Stadium site will have to be lowered by nine metres while others areas need to be raised by five metres.

Nearly the entire 2.5 sq km site has been investigated and two-thirds of demolition has been completed.