Creating the Olympic Park involves a major land remediation operation, coupled with landscaping and river works covering a 200ha dead zone along the banks of the river Lea. The huge park resulting will remain after the Games are over. It will be London's biggest, stretching from the Games site up the Lea valley northwards and south to the Thames.
Over the years the site earmarked for the Games has become a dumping ground for everything from Second World War demolition waste to old refrigerators. Some areas are polluted by dirty industries like soap manufacturing, forced out of central London in the 1960s.
There is also a disused gas works.
Demolition waste mountains distort the landscape, taking ground from 1.5m above ordnance datum to between 10m and 20m AOD. The River Lea itself also needs work.
Much of it has been canalised, with high sheet piled walls lining the banks making the waterway inaccessible from the landside.
The demolition waste mountains will be levelled and material redistributed around the site. 'These hills were not conducive to allowing pedestrian access to the site, ' says Buro Happold associate Mike Francescon.
Land reprofiling will be needed to give easy pedestrian and disabled access to the many footbridges required to connect the site to the surrounding area and transport links. Wherever possible, gradients will be limited to one in 30.
The aim is to minimise the export of contaminated material and maximise on-site treatment.
The sheer scale of the site makes this economically viable, says Francescon.
'On this site we have a lot of space and are looking to make a significant improvement on normal rates of dig and dump.'
As a result, all but the most contaminated soil will be treated on site through a combination of soil washing and bioremediation techniques.
Converting the unsympathetic, man-made banks of the River Lea into more a natural landscape is also a major aspect of the site preparation programme.
'There are a lot of hard edges, ' says Francescon, referring to the concrete and sheet piled retaining walls lining the river.
These will be demolished and replaced with landscaped riverbanks with gentler gradients.
Demolition will require care, not least because of the risk of unlocking underground contaminants and releasing them into the river. ' This problem will be dealt with partly by planting vegetation along the edge of the newly reprofiled river to soak up some pollutants. Heavy contamination will also be filtered out through permeable retention barriers inserted into the ground.