Plumbing – Why isn’t the sump pump kicking on

Well, if it's from the late 80s, then it shouldn't contain any PCBs.

That liquid is probably a dielectric oil with a high viscosity. That would explain why you were thinking it's a solid. They're non-conductive mineral oils and as oil does, it displaces water.

Treat it like a motor oil spill. Here's an MSDS sheet for Shell Morlina oil which is probably similar.

This should be a back flow-prevention measure, for flash flooding rains. I think your only good, but expensive ($1000), option would be to replace this setup with a Back-Flow Prevention Valve or Check Valve. Call the Builder or get a qualified Plumber...have them checkout your Water Supply Line too, that thing looks 100-years old. Otherwise, turn that corner into a closet or faux bookshelf.