This sounds like a reasonable approach. Considering the volume of high level wastes actually being produced, dry cask storage might be the best option if we want to always have "eyes on" the waste materials. Physical risk is a little higher above ground, but you always know exactly where it all is at all times and you can constantly measure it for safety. Shoving it 3 miles deep into the earth is very likely not going to be a problem for anyone, but you will always have some uncertainty around how it is behaving down there.