Here's the problem:

I have a 30" by 30" square concrete slab (underground pillar) in my yard
that is several feet (or more) deep. It used to be the base for an old ham
radio antenna tower that neighbors say was 40 or 50 feet high. The concrete
base was put in by the former owners who are now deceased. It sticks up
about 1 inch above ground level and I want to get rid of it.

I want to either remove the concrete base entirely, or take off the top 4 to
6 inches so it will be below the ground level. I had a guy with a backhoe
try to remove it while he was taking out other concrete sidewalk slabs. He
said he couldn't get it to budge and said there is no way to know how deep
it goes. I watched him try grasping and hitting it with the backhoe scoop,
but nothing happened. It wouldn't break up, it wouldn't move, etc.

So, here's one goofy idea I was thinking about. If I made a little ridge
around the slab and poured some type of acid on it, would the acid eat away
at and/or dissolve the concrete? Anyone ever tried anything like this? Any
particular acid I should try if I am crazy enough to do this?

My other idea is to try drilling holes into the side of the pillar, about 6
inches below the top, then trying to hammer an iron wedge into the holes to
try to crack the top section off. I saw them doing something like this on a
TV show where they were cutting large slabs of marble. I have tried renting
a jack hammer in the past to get rid of solid concrete steps and the jack
hammer didn't do much because the concrete was so thick. So, I don't thin a
jack hammer would do much to this monster.

My last idea is to get someone else with a backhoe and get them to dig a
hole around two sides as deep as needed, then tip it over into the hole, and
re-fill the hole to bury the sucker. I wanted to get the guy I had there
(with the backhoe) to do that, but it was a real struggle trying to
communicate with him, so I gave up.

The bottom line is that I really like my acid idea, but I don't know if it
would work.