To explain briefly.... the sump pump and basement slab are sealed completely and a vent pipe with a fan in installed. This creates a vacuum that draws the radon from beneath the slab and safely vents it out above the house to disburse outside. The radon is dangerous in concentrated levels such as you would find in a sealed up house but once it mixes with the outside air it does not create a danger.
A gauge is installed inside the house to monitor the vacuum.
This can be easily reduced by installing a radon remediation system. Check your purchase contract. If the seller agreed to the standard radon addendum, then they should fix this at their expense.
Tracey gives a great description of how these systems work. I find this costs anywhere from $800 to $1,000. I typically use Brenner Geo Tech - they are very reasonable and guarantee their work.
I just had a listing with high radon, and everyone we contacted was backed-up. Not sure why. So if this needs to be done prior to settlement, you should start making calls now