Updated: Feb 19, 2022
We are all interested in giving our clients the best value, so I regularly mention the lower risk of radon in homes without a basement. It is certainly true that radon tends to collect in basements, yet having just got a reading of 14.8 pico-Curies/liter in an on-slab home where an elderly woman with health problems was going to live, I'm going to change my tune. It's just not worth the risk to not test for radon.
Radon is odorless and colorless so maybe we take it for granted, yet the EPA has determined it is the second leading cause of lung cancer in the U.S. The good news is it's easy to test for; you can get a permanent monitor, like for carbon monoxide, another odorless, colorless gas; and relatively simple to get out of your house. See other posts with the RADON tag.
Red zones have a high potential and yellow a medium potential. DC has relatively low potential except near wooded areas.