Just show in a long series pictures inscribed in granite a happy productive group of humans and animals, having offspring, eating/drinking/being merry, then show them digging and investigating the radioactive symbol. Then show a picture of the entire tribe being sick, showing the radioactive symptoms to humans/animals in pictures. Then show every life form obviously dead. Put that radioactive symbol all around, in the ground and at the entrance of the waste.
If an alien culture comes to investigate, it will probably be much more highly advanced so they will treat our warnings as "cute and endearing", as we treat a mouse warning us about an oncoming cat.
The only creatures who could be helped by this warning is humans (if we decline back into the stone age) or some other form of life that takes root on earth long after our ecosystem goes away. I think the whole issue is irrelevant. Just keep it contained and add pictures describing biological decay in the presence of this area.
If an alien culture comes to investigate, it will probably be much more highly advanced so they will treat our warnings as "cute and endearing", as we treat a mouse warning us about an oncoming cat.
The only creatures who could be helped by this warning is humans (if we decline back into the stone age) or some other form of life that takes root on earth long after our ecosystem goes away. I think the whole issue is irrelevant. Just keep it contained and add pictures describing biological decay in the presence of this area.