If you notice of the color of the water...it is not only silt, but rust from the pipes themselves...
I have just rehabbed a water well on our farm that hadnt been in use for many years and it was the same color. plus metallic tasting...after two months of filtering to 20 microns, and many filter changes, the incoming water has finally cleared...the well casing pipe has cleared itself of loose rust particles and the years of sediments. There is new pvc pipe from the new pump to the house, so all rust came from the casings/sediment..
This is a well 180 foot deep with a 6 inch pipe...imagine how many years it would take to filter the amount of water in 10x before the pipes quit sloughing off rust particles...much less practical than just putting in a new liner and pumping...
Also...powdered bentonite clay is often used to repair leaking ponds, if placed in the 10x bore at the beginning of low tide, when water levels are sinking in the shaft, it would be drawn into water entry/exit points and seal them..just as it does in a pond
So there are many other schemes that could be used to get to the bottom of the hole...but wont be as it has already been explored and shown as nothing there of interest...
There is also better dive equipment that could be used, no tanks, air from above, that would extend dive periods dramatically...and be less cumbersome. Why are they not used? My theory is because they are not diving to the bottom of the hole at all...just down far enough to be unseen from above and provide the drama the show thrives on...Smoke and mirrors for the TV show.