One of the most common mitigation techniques is ASD. With this process we drill a 3' hole in the foundation floor for the suction point with a Radon Fan on the exterior. Some homes do require two or more suction points.
HRV's are another method for radon mitigation. This works great for homes with stone foundations and/or dirt floors and crawlspaces.
Many newer homes from the early 2000's and on may have a passive system already. If the levels are still high we just need to install a fan in your attic.
One of the most common ways to remove radon from water is an aeration system like the bubble up. These systems are installed by your pressure tank and remove up to 99% of the radon.