I am retired, but during my working years I was asked to come up with some very crazy ideas to get the work done. So set my mind to the money pit and how I would go about getting to the bottom.
From the latest show on the History Channel that there are three flood tunnels and maybe more. The first thing that I would do is throw dye in the water see where it shows up on the beach. Then I would rent a ground sonar truck, like the ones oil companies use, to map the beaches where the tunnels are.
Once the tunnels were located, then I would bring a well drilling rig and sink a wells to hit the tunnels. Pump in cement and plug the tunnels. once the water was stopped then pump down the pit slowly to lessen the chance of a cave in.
A simple idea that I heard was done with the first tunnel with TNT. I have wondered why it was not used on the other ones.
When my nephew was working in the oil fields overseas. They would come in with maps that was made by ground sonar and they would show any tunnel or cave so that they could avoid drilling into them. Bad for the drill heads. Using ground sonar the whole island could be maps and show where the tunnel are and at what depth. It would take a few days at most and could be without digging. Just a truck driving around press a sensor onto the ground and thumping and record the echo. Once you know where the tunnels are, drilling a 6" water well hole and pumping in cenment to plug the tunnels Also it would show any chambers or any more flood tunnels that had not been tripped.
How did the builders of the money pit stop the water during construction? They build a tunnel underwater going into the island. How did they comtrol the water. If you map the tunnels with sonar you might find a gate or valve on each tunnel. That might tell us more about the builders.