FinderKeeper, first off I have to say I don't know anything. A treasure hunter from Boston sent me info. that discribed seperate compartments at the bottom "dug" out in bed rock. I think this is true, I've got it some where. Anyway it occured to me that this was a powder magazine because of the seperate compartments. I thought there were 3 flood tunnels, am I wrong? Isn't that why the first shaft
flooded? The British Navy could bring the coconut fibers. You've got me on the carbon dateing. My thinking is, the flood tunnels were
dug in case it fell into enemy hands. You are right it could flood acidently and ruin the black powder; that's the crazyness of the whole project and I expect it was never used for that reason. Why fill it in? Maybe to save face----------I filled in a mine shaft, it goes fast.
Like I say, I realy don't know but, it strikes me as a typical goverment boondoggle. Tod R.