It was surprising to see how big the crawlspace was underneath the old building.  I spoke with Dennis, and he said that they will remove the giant chunks of concrete, and pull up the footings.  Before they start on the new building's slab, they will excavate down to more compacted soil or bedrock, then bring in a new base of soil and compact that down.  After they have a solid base to work on, then they'll pour the new building's slab.