At Fort McHenry, there is a 90 foot deep well, created with "the best
available mining techniques" according to the original contract, and
had 12 foot cast iron barrel staves, tongue and groove, to keep out
the salty bay at about 40 feet. It was built just before the siege of
the fort and the burning of the White House (which I have learned was
for burning York in or near present Toronto, Canada) as the water
there could only last a day at a time and had to be brought in. That
feature as well as part of the well was excavated in 1978. I went into
the well, which was domed at top with two circular openings in the
dome for some sort of apparatus to bring the water up from depth at
the time it was unearthed, unknown. I've seen hollowed out logs used
in shallower wells, there's one in the Tuftonboro, NH History Museum.
There was some concern for the stability of its filling, and indeed if
it had been filled to the top, it was now about 5 feet lower, allowing
one to perhaps assume that no large timbers had been dropped into it
and the deposit had collapsed further, purposely filled in but not a
"jam".

I assume your well is not of the same construction. The experience I
have of this is only filmic. The WIlliamsburg films of the late 1970's
was it, actually discussed the benefit of inserting corrugated tubing,
like a large drainge pipe in sections connected to facilitate and
thereby making safer excavation in the bottom of the well(s) there, at
least one of the crew explained to the camera such, an improvement to
previous methods or lack of.

Another well excavated was full of clean gravel from the nearby
Dutchess Quarry to 11' from its top (with a "special" U-Haul double
cross handled post hole digger made from light tubing) and it was
finally excavated to the bottom by removing the soils around it,
creating a tower if you will of stone on the Hudson River terrace at
the former ferry landing to Marlboro, NY in Bowdoin Park, then chosen
site of the sewerage treatment plant. That is until it collapsed.
After it was cleared away the bottom was found to be clean except for
an aluminum pitcher.

Better found indoors than outdoors inadvertantly there has been some
talk of mandating well recording:

Seeking Abandoned Water Wells

Near Surface Geophysics - Seeking Abandoned Water Wells

One of the northern states in the US has a unique and very aggressive
environmental protection program, especially with regard to water well
management. Specifically, every property transaction that occurs in
the state requires a disclosure of wells on the property. For
properties with no well, then that is disclosed. For properties with a
well, the well status (in use, not in use, or sealed by a licensed
well contractor) and a rough sketch of the well location is required.

GEM Advanced Magnetometer and Gradiometer - Quantum E-News, Fall 2004.

Maybe someone can make a robotic claw and lift soils off the bottom?

George Myers