The heating pipe is getting close to the soil stack. Close, but no cigar. Let's try that again.
Removing the old layers exposed a bit of a structural problem in the corner. This part of the house is sinking and some of the interior brick has fallen into a hole. I think at one time, someone exposed this and just ignored it. We fixed it. These old beach houses are notorious for having sandy foundations and some of the more unlucky ones were built over underground ravines and flood regularly.
Above the window:
Fixing the hole:
Tearing up some of the subfloor to get at the pipes. The white pipe is the exhaust for the basement bathroom.