Answer:
This location was chosen because rock salt has qualities that can withstand the negative effects of nuclear waste and prevent it from causing any harm to the biosphere and all life in it.
Explanation
How to properly dispose of radioactive waste has always been a great problem due to its very high potential to negatively affect life in every form. There have been several kinds of research into the best ways to dispose of such waste. In times past, we have seen radioactive waste sealed up in drums and disposed of. These drums are not everlasting and can be subject to accidents, weakened by weather, etc thus creating a radioactive leak.
One of the results of the research was to store such waste away far below the ground where there are deposits of rock salt.
Radioactive waste generates tremendous amounts of heat if buried in ordinary underground sites and can contaminate underground water channels with radioactive poisoning. So if it were to be buried underground, it had to be in a site that is impregnable by water with very high resistance to heat.
It has been discovered that rock salt has very high boiling and melting points which are 1413 degrees Celsius and 807 degrees Celsius respectively. This makes the ancient bed of rock salt a preferred location by the US government for storing nuclear waste.
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