Radon is produced naturally underground in areas near uranium deposits. Most of the time they are in such small amounts that they can be ignored, but Kansas has

Radon is produced naturally underground in areas near uranium deposits. Most of the time they are in such small amounts that they can be ignored, but Kansas has a lot of Radon, (https://kansasradonprogram.org/county-map https://kansasradonprogram.org/county-map). Having such a deep set building would allow more of it to seep in and settle, and it is doubtful that there is any form of radon mitigation system built into the building. You might get lucky, the 4 ft of concrete might make a nigh impenetrable barrier, but the only way to know would be to test it.