How do you properly seal an old cast iron waste pipe? This pipe was
for
a septic system used before the home was connected to the town sewer.
Right now, the previous owners broke off the pipe at the wall and
filled it with expanding foam insulation. The problem is, we have had
a lot of rain and the water table is very high. The pipe is now
leaking water onto the basement floor. I probably can not cap the
pipe
because it is broken off and even with the wall. Any suggestions
would
be appreciated.

Well, really you ought to remove the thing entirely, but a short term
solution is one of those 4" rubber-plugs with metal plates on both
sides, and a bolt through the middle. You slide the whole plug into
the pipe, and crank the bolt tight, with pulls the plates together and
squeezes the rubber against the sides of the pipe. goedjn

But as soon as you can, replace the whole mess with 4" PVC, connected by
the 4" rubber pipe connectors that tighten with a screw driver. Iron
pipe is obsolete.