From the Curbed inbox:
From my window by the new Transbay Center I can see a lot of enormous holes in the ground. By my reckoning the total excavated earth would be enough to create another Rincon hill. So where does it all go? Endless trucks must take it... somewhere. The excavation for the new Transbay Transit Center recently wrapped up in February. After some major digging (complete with awesome woolly mammoth tooth find, among other cool things from the 1906 Earthquake and Gold Rush), the project removed about 640,000 cubic yards of soil. That's enough to fill 120 olympic sized swimming pools, and the new hole was big enough to hold 50,400 Mini Coopers and 2 Transamerica Pyramids laid end to end. So what happened to all that soil?
More than 60% of it was clean sandy soil that was sold for reuse on other construction projects. The rest, which included bay mud and soil with high clay content, went to clean landfills. Something like 99% of the concrete from the old Transbay Terminal demo was crushed and recycled, with some of it used on site to build up temporary roads and equipment pads. The demo also uncovered more than 2000 40' long Douglas Fir timber piles from the 1930s. They were able to pull the wood out intact and recycle it - some is being reused for woodwork in other buildings.