Had a similar problem in KC, 5 year old house. There is a debate over it's danger, however, we learned that many mortgage companies won't extend a mortgage if the Radon level is too high. Worst case scenario is about a $1-2 thousand fix which includes drilling a hole in the basement floor and running a 4" PVC pipe through the roof. A pump is attached and constantly moves the radon from under the house. Other fixes might be filling cracks in basement floor, covering crawl spacy with poly, being sure the sump pump has a SEALED cover also be sure the sump isn't being drained into the house sewer line as the radon will be sent throughout the house) Hope this helps.