Radon is a naturally occurring radioactive gas that comes from radium deposits in the earth's crust. If present in the soil under your home, it can get sucked into your house via the basement or crawl space.
Don't panic. It's fairly common and easy to get rid of.
CleanSpace® is a passive radon reduction system and method all by itself. If an "active" system needs to be installed, a fan can draw air from below the CleanSpace® and exhaust it outside above the highest eave. In this case, CleanSpace® represents the majority of the work and expense to get rid of the radon (if you have it), so it shouldn't cost much to add a fan and exhaust pipe.