The house that we tore down had a tested radon level in the basement of over 5 pCi/L, slightly above the recommended action level set forth by the EPA (4 pCi/L). Last week, I did a short-term (4-day) radon test and found out today that radon level was 1.1 during the time that I conducted the test. Apparently, it's not possible to get to 0, but given the sealed slab, vapor barrier, gravel bed with vented perforated pipe, and a vertical stack to the exterior - I though that we would.
At some point, I'll likely do a long-term radon test. Still, 1.1 is not at all bad. All the same, I'm hoping to get a better result in the future.