I have a concrete that is stuck underwater. The concrete piece is too heavy. I think that I could break it into small pieces with my pneumatic impact drill.
I do light underwater work as a part of my job. One thing I do is drill in rock underwater with a CP9 rock drill. This is a pneumatic tool but is designed to work both above and under water. It works great as long as it is properly lubed before and disassembled and lubed as soon as possible after the job is done.
I have no first hand experience of other tools, but according to a colleague it is perfectly fine to use more or less any pneumatic tools underwater, he often uses cheap ones and says that they do get the job done.
Edit: I have since I posted this answer used multiple cheap pneumatic tools underwater. I can report that I have had no problems at all in doing so, as long as the tool is disassembled within a day (preferrably ASAP) after being used and lubricated throughout.
As a salvage diver, I know that a pneumatic tool will work in the water.
The only difference between a $2,000 impact driver used at Haliburton and a $20 Harbor Freight 'wonder tool' is all that high precision stainless steel internal components (brass, bronze, stainless, etc.). With your $20 HF wonder tool, just make sure to soak it in MINERAL OIL after use (tap the air SLIGHTLY to fully lubricate everything)...and drain it well, with another 'tap' to clear it before re-entering the water...oh, and SALT WATER is HELL on pneumatics not specifically made for them.
ALL THAT SAID...be aware, HIGH AIR RATE pneumatics produce COPIOUS AMOUNTS of air bubbles!!! In doing so, you MIGHT not be able to see, during your process...this of course, is MOST PREVALENT on the most-dangerous tools, like die grinders, p-grinders, etc...and lowest on things like impact drills, wrenches or 'jaw cutters'.