6' radius, 10' deep hole
V=Pi*r(squared)*h
V=3.14*36*10
v= ~1130
It takes you quite some time to sift out of rusted metals, the rocks, and silt, and other debris. But with nothing else to do, the crew digs for six days and you use spells to help the process.
The gems you put aside, as the have to be appraised later. There are no art or collectibles, as the years of salt water would have destroyed them all.
It also appears that Dark Sea only kept gold and silver; there are no other precious metals. The silver all appears to be in bad shape. It has turned black.
You get a fair count on the gold; and the best estimates that you get are in the 25 million gold coin range. Give or take 2 million.