How can you tell if an old water well has been filled in or just covered up?

We know this space used to hold a well, and I'm hoping they just covered it with concrete and it's hollow under the floor, but I don't know how to proceed, just start drilling? any other ideas?

frollard8 years ago
We happened into a old outhouse pit while trenching our back yard for a new gas line. I want to turn it into a geothermal/solar battery for heating cooling the house. Anyhoo - back to your question. How big a hole can you dig? We dug around the side of the concrete slab - and found the pit by 'drilling' thru the dirt at a 45 degree angle (since we didnt know why there was a slab buried 2 feet underground). A masonry drill bit with a hammerdrill should be able to get you thru the slab - what you find on the other side is the mystery!
Maybe it could be a secret pirate treasure cove, like in The Goonies :-P
maybe... we dropped a stone in and heard the thud...estimating its about 20 feet deep :D