Radon comes from the natural decay of uranium in the soil. All rocks contain between 1 and 3 parts per million (ppm) of uranium – and the soil will have the same amount of uranium as the rocks inside.
Some rocks have higher than average uranium amounts, including pale volcanic rocks, granite, dark shales, sedimentary rocks with phosphate, and metamorphic rocks. Soils that contain these rocks could have as much as 100 ppm of uranium. In areas where these rocks are common, these homes tend to have higher levels of indoor radon.
However, just because a house is in a uranium-rich area does not always indicate high levels of home radon – it just happens to be more of a risk. A radon test can help you get much-needed peace of mind.