Must be doing to the bottom of the foundation.

They had to work in and out of the reinforcing metal rods that had been laid down in the bottom of the foundation trench.

Most important, Mr. Arad's original design did not provide access to structural remnants of the twin towers, like the perimeter column footings that can still be found at the bottom of the foundation.

A. Burying drainage tiles would be a good idea, but that means you would have to dig down to the bottom of the foundation wall and bury the tiles near the footing for them to be fully effective.