There are parts of this country where the radon readings are higher than 4.0 p/c outside in the open air! Why would you want to waste your money doing anything? This is one of those issues where some of the DNR organizations have gone nuts to justify their own existence. If you want to play it ultra safe, first get retested. there are a lot of variations from test to test, and the next test may be negative. If you still feel the need to do something, go down to your local county extension office, they have several methods suggested to mitigate radon.