Potentially buying a house (~30 years old) which currently has a radon mitigation system put in 2006. The current level post a recent radon test is 1.5 pci/L in basement. I know EPA recommends anything below pci/l 4, with recent updated saying (2 pci/l) being even better. As the house already has a radon mitigation system I was hoping levels would come in below 1 pci/L. Should I be concerned if we want to use basement in future ? Would appreciate any thoughts on anyone who has dealt with a radon mitigation system.