I believe you will have the least possible problems (legal and geological) if all you do is clean out the old pond.
If you have a solid tree for an anchor on one side, and a solid work place on the other, a dragline arrangement of cables and scoop can clean it while it is wet.
Bruce
If you have a solid tree for an anchor on one side, and a solid work place on the other, a dragline arrangement of cables and scoop can clean it while it is wet.
Bruce