You post may be, and probably is, correct, but it doesn't really reflect what was being reported at the time. According to news reports at the time, as I remember them, the flooding was caused by the contractor drilling into the tunnel, and the flooding was stopped when concrete "plugs" were placed at the tunnel mouths.
In any event, 1,000's of us descended on a Metra system expecting maybe 100's of riders. Quite an afternoon.
I was back at work the next day, but places like Marshall Fields, Carson. Pirie Scott et al had flooding issues for quite awhile.
The part about the tunnels being "illegal" is partially true. They were initially approved to provide telecommunications, ie telegraph, phone, throughout the city. The builders just made 'em bigger, added rails, and became a big source of shipping for inner city stores/office buildings; goods in, trash out.