CUBIC BLOCK Make 10 ft sided cubic block (1000 cu ft) of concrete, rebar, and sand, on a barge. Then use 2 barges and pulleys perhaps to drop such block 2000 ft (10 secs?), which might penetrate 100 ft(?) into muck. Drop it slightly off target, so that sub-mud surface conduit collapses shut. Water is non-compressible fluid, whereas gas in conduit is a compressible fluid. So the cubic block would push muck over into conduit, collapsing it.