Much of the loose rubble at Ground Zero has been cleared away, leaving engineers with the fresh challenge of advising contractors how to prise away compacted steelwork.
An army of 90t 'ripper' machines has converged on the huge piles to claw out the crushed debris.
Once freed, the huge cranes will lift the heavy pieces onto lorries.
Engineers are also expected to provide solutions to lift out compacted rubble from the WTC's six storey basement within the next two weeks, said a Thornton Tomasetti spokesman.
Removing this rubble is complicated by the need to retain the slurry wall surrounding the basement.
At the moment compacted debris is thought to be holding this in place.
Collapse of the twin towers demolished floor slabs which had been supporting the basement wall - part of which keeps out the Hudson river (NCE 27 September).
Engineers are reported to be considering building a soil backfill ramp down to the basement to provide access for the rippers.