I strongly recommend that you contact Joe Nermber with Amerispec. He is the local CREIA chapter president and a resident in the Agoura/Oak Park area. If anyone knows about this issue, he will be able to assist you. You can find him here on Trulia or his cell number is (818) 292-7242
I notice that you list yourself as a home seller. If you arent already working with someone regarding your plans to sell, please contact me directly.
This is an excellent question to be asking. I have included several links to government websites and reports to enable and empower you to obtain the answer(s) directly from the experts:
Radon is discussed in length here: http://www.americandreampropertyinspections.com/radon%20faq.htm
Good luck in your quest for answers. We can also refer you to companies that test radon and to devices that diminish the levels found in local homes.