The unprecedented clean-up began three years ago and has enabled construction to start on or ahead of schedule on all of the permanent Olympic Park venues.
The "big build" is now ramping up with venues coming out of the ground and work underway on 21 bridges, roads, a new energy centre and network and other infrastructure for the area in legacy.
ODA Director of Infrastructure and Utilities Simon Wright said: “Delivering one of the UK ’s most complex and greenest clean-up operations on time and on budget is a major milestone.
"It has ensured that the ‘big build’ is on track by creating, from mainly contaminated land, the foundation for the venues, parklands and homes that will transform this part of east London for the Games and legacy.
“We have worked closely with the regulatory bodies and local authorities while cleaning more than one million tonnes of contaminated material to protect the health and safety of the workforce, public and future generations that will live, work and play on and around the Olympic Park.”
Rosemary Redmond, the Environment Agency Olympic Delivery Project Manager, said: "The 2012 Olympic development is breathing new life into a part of East London that was blighted by fly-tipping, poor water quality and little public access.
"Throughout this exciting regeneration project we have worked closely with the ODA advising and regulating on a wide range of environmental issues including the site clean up, the removal of invasive species which prevented native wildlife thriving, and a facelift for the silted River Lea.
"We have set the highest environmental standards so the Olympic Park can provide the perfect backdrop for a ‘Green Games’ and provide a better place for Londoners in the decades to come after 2012."
The cleaning and clearing of the Olympic Park utilised sustainable techniques to recycle and reuse over 90 per cent of the demolition material and 80 per cent of soil on site, the ODA claimed.
This significantly reduced lorry journeys in the local area as only a minimal amount of contaminated material was taken to landfill sites.
Industrial contamination on site included oil, petrol, tar, cyanide, arsenic and lead as well as some very low level radioactive material.
In line with Environment Agency guidance a small amount of soil containing traces of this very low level radioactive material, classed as "exempt" under current environmental law, has been safely buried in a cell under a bridge embankment on site and is covered and capped on all sides.
This safe disposal has been approved by the Environment Agency and the legacy landowner the London Development Agency (LDA) and in no way poses a risk to the health of the workforce or public now or in the future, the ODA claimed.
Further small pockets of contaminated material already identified and arising during the ‘"big build" will be cleaned and reused on site wherever possible with minimal materials taken to registered landfills, such as the small amount (350 cubic metres) of non-hazardous soil containing traces of very low level radioactive materials which has already been safely disposed of off site.