Half crawlspace half concrete slab?? Any advice?

[Frank Z.]

Bought a house in probate recently for a good price. It appeared that about 30% of the crawlspace under the house was inaccessible. Theory was there was a hatch under the carpet somewhere that could get you in, but didn't know where. 

I have corrugated pipes that have rusted from the inside so there's very low water pressure in the bathrooms due to the rust buildup. Plumber recommended replacing them completely with PVC. Today I had a contractor try to cut a hole into the inaccessible crawlspace area but turns out there is no crawl space! 

The house was built in 1958 and after laying all the pipes for the two bathrooms, they filled that part of the house up with some dirt and poured concrete on top, then put the floors on top of that.

Has anyone else been in this kind of situation? Any recommendations would be most appreciated.

I spoke with a friend with a lot more experience in construction than I have and he suggested renting a jackhammer to bust all the concrete up, have the plumbers do what they have to do, and turn it into a crawlspace so it's accessible going forward.