Starfire tested all units for radon levels 2-3 years ago at HOA expense. Summit County provides free test kits, but these are not as precise as the machines that commercial companies use.
Some units already had radon mitigation systems in place that were effective. Others went ahead and installed mitigation units at owner expense - these are the external units that you may not like. I find the fan to be relatively quiet, but I don't sit right next to it.
I believe that Northstar installed similar systems (fans with external vents) on a building by building basis - the HOA paid for it because those buildings have subfloors that are common for all units in a building.
Aspire Property Inspections did the testing. We used All Colorado Radon Mitigation in Denver for the installations - they were good and reasonably priced - happy to provide more info