First Radon test result ever! I have a question.

[Damien L.]

Hey guys!  Need a little bit of wisdom from the community.  Finally pulled the trigger on our first duplex and we are excited about that.  We are currently in the inspection phase.  We did a radon test during home inspection and got a result of 3.9 right under the 4.0 recommended limit at which you should act.  I did read the EPA guideline which says that if your first test comes close to four there is a 50% chance that your yearly limit is under 4.0.  I was thinking about asking the seller to put in a mitigation system but I feel like he may not feel obligated to do so.  Being under the recommended limit technically and after reading the guideline I feel like we don't have to put one in right away and I will probably retest next year to see where we are at.  What are your thoughts and recommendations?

Thanks!