In a written answer to a question from shadow Olympics minister Hugh Robertson, Jowell said:
"Initial site investigation studies on the site of the Velopark were carried out throughout 2007 and continued into 2008, when the poor ground conditions were identified.
"As part of the review of the Masterplan for the Olympic Park, undertaken in 2007, the Velodrome was moved slightly to the west to help with the design and layout of the wider cycling facilities to be built in legacy. This movement exacerbated the ground conditions problem.
"The July 2008 London 2012 Olympic and Paralympic games update report identified a £40M cost pressure against other Olympic park venues, part of which was for the Velopark. The level of contamination on this site was more extensive than originally assessed and this contributed to the overall increase of £25M in the Velopark budget to £105M.
"Once the full extent of the ground conditions was known, design and ground modelling studies were undertaken which produced an accurate estimate of the potential costs," she said.
Jowell also confirmed that a legacy plan for the business park: "is currently being developed for the legacy use," but its 6,000-seat capacity would be retained.