Which is the best location for storing radioactive wastes? in the sand of a remote island in chambers carved into the rock of a mountain in the lava tubes of an active volcano in natural caverns formed by the action of a river

The answer is in chambers carved into the rock of a mountain. Radioactive waste should be well disposed where they are little to no anthropogenic activity that would uncover them. This is especially critical for high-level radioactive waste should be buried deep up to 2000 meters. While low-level radioactive waste can be buried 100 meters into the ground such as in sand, the risk is that it could contaminate the water table.