A total of £12.7m has been spent on cleaning up toxic and radioactive waste on part of the Olympic site.
The contamination was found on the banks of the River Lea, in east London, when the site's previous owners left the land in July 2006.
An Environment Agency spokesman said the cost had come as "no great surprise" and had been budgeted for before the site was bought.
He said the site was going to be turned into a "magnificent asset for London."
According to the Olympic Delivery Authority (ODA), the site was identified as being heavily contaminated, through years of industrial use, during early investigations.
Tests by the Environment Agency detected vinyl chloride in the groundwater of the soil, which is a product of the break down of chlorinated chemicals.
An agency spokesman said the cost of clearing the waste was only a small part of a huge sum being spent on decontamination of the Olympic Park.
The ODA said the majority of the toxic waste had now been removed and cleaned and the clean-up of the groundwater was continuing.
As part of the process, more than 80% of previously contaminated soil that was excavated has been reused and more than 90% of demolition materials have been recycled or stored for reuse.
There is no suggestion that the company whose storage facility was previously on the site was in any way responsible for the contamination.