I have seen several different threads where the solution to getting rid of unwanted ammunition is to throw it in a lake. I am glad some people think this way because I am in the process of cleaning out my garage and have some car batteries, motor oil, and paint to get rid of. No pesky environmental fees this time.
Sorry to hear about your basement. Modern cartridges can be exposed to water for quite some time without developing any problems. I have never had any soaked shotgun shells, but the rice trick might save them. You could try it and the before firing the ammo cut the end of one or two shells to see the state of the steel shot.