Radon is a naturally occurring radioactive gas that is invisible, odorless, and tasteless. It originates from the natural breakdown of uranium found in nearly all soils and rocks beneath the Earth’s surface. As uranium decays, it produces radon, which can then migrate into the air we breathe. Exposure to elevated levels of radon poses a public health risk, primarily increasing the likelihood of developing lung cancer.
The Nature and Origin of Radon
Radon is a product of the natural radioactive decay chain of uranium, an element present in varying amounts in most soils, rocks, and groundwater. Uranium undergoes transformations, producing radium, which then decays into radon gas. This gas is chemically inert but radioactive, continuously breaking down and emitting alpha particles.
Once formed underground, radon gas moves through pores and cracks in the soil and rock. It can then enter buildings through foundation openings like cracks in concrete slabs, floor drains, sump pits, or utility pipe penetrations. Once inside, the gas accumulates, particularly in basements or crawl spaces, where it becomes trapped and concentration increases. Any home, regardless of age, design, or foundation type, can experience elevated indoor radon levels.
Mapping High Radon States
Many US states experience elevated indoor radon levels due to specific geological conditions. The Environmental Protection Agency (EPA) designates “Radon Zones” to identify areas with greater potential for elevated indoor radon, with Zone 1 having the highest predicted average levels, exceeding 4 picocuries per liter (pCi/L). These levels are often linked to uranium-rich bedrock like granite, shale, and certain metamorphic rocks, or soil types that facilitate radon movement.
States with high average radon levels include Iowa, Pennsylvania, Illinois, Indiana, Wyoming, and Colorado. In Iowa, glacial activity left extensive uranium deposits in the soil, contributing to an average indoor radon level of 8.5 pCi/L, with all counties designated as Zone 1. Pennsylvania’s geology includes uranium-rich metamorphic rocks, particularly in areas like the Reading Prong, and black shales, leading to over 40% of homes exceeding the EPA’s action level.
Illinois and Indiana also present significant radon risks, with central and northern Illinois showing higher soil radon levels due to geological composition. Indiana has areas with both high and moderate potentials, influenced by local geology and soil permeability. In the western US, Colorado and Wyoming have elevated radon due to prevalent uranium deposits in granite and shale formations, especially in Colorado’s Front Range and Western Slope, and throughout all 23 counties in Wyoming. Parts of the Northeast, with high granite content, and the Appalachian regions, with uraniferous sediments and fractured bedrock, also report higher radon potential.
Reducing Radon Exposure
Protecting against radon exposure begins with testing, the only way to determine if elevated levels exist in a home. Homeowners can use various testing methods, including short-term kits for quick results over a few days, or long-term kits that measure radon for 90 days to a year. While short-term tests are useful for initial screening, long-term tests offer a more accurate average by accounting for seasonal fluctuations. If tests reveal indoor radon concentrations at or above 4 pCi/L, mitigation is recommended.
The most common and effective method for reducing radon is active soil depressurization, often implemented as sub-slab depressurization. This system involves installing a suction pipe through the foundation slab into the soil beneath, connected to a fan that continuously draws radon gas from below the house. The fan safely expels the gas into the outdoor air, preventing it from entering living spaces. Sealing cracks and other foundation openings complements these systems by preventing radon entry and improving overall system efficiency. For proper installation and optimal results, hiring qualified and certified radon mitigation professionals is important.