David Lesher wrote:
How can you have a silo when the water table is a few feet below
ground level?
I thought the same thing, and apparently others did at the time, too.
Encyclopedia Astronautica says, "There was considerable concern about
building such a huge facility below the water table, but the 50 m depth
proved no problem for a competent caisson contractor."
(
http://www.astronautix.com/engines/aj2602.htm; thanks to Jeff for the
link.)