I have no helpful information, but will comment anyway.
I think at 4 you should do another test to double check, levels can fluctuate.
We had to test for radon when we bought our place. I thought it was a law? Maybe it's a state law. I think our number was under 1 or maybe around 1. We never had it tested again, but we did some insane basement waterproofing which I have to believe helped.
Does this only really matter in houses with basements? The cabin has a space under the floor with the windows down there that are always open. Never had the cabin tested.
Jason if you want we can put peace and love in your signature.
"You just need to go at that shit wide open, hang on, and own it." —Camp