Radon in Colorado: County Zones and How to Test

EPA assigns radon zones to counties, not to whole states. On the EPA Map of Radon Zones, drawn in 1993 and not revised since, Colorado's 64 counties split 52 in Zone 1 (highest potential), 12 in Zone 2 (moderate) and 0 in Zone 3 (low). The zones describe predicted county averages, and EPA's own instruction is: "The map should not be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon."

Colorado has 52 Zone 1 counties on the 1993 EPA map: Adams County, Arapahoe County, Baca County, Bent County, Boulder County, Broomfield County, Chaffee County, Cheyenne County, Clear Creek County, Crowley County, Custer County, Delta County and more, all listed on this page. Zone 1 means EPA predicted a county average indoor screening level above 4 pCi/L; it is not a reading of any home.

No, and that answer is EPA's own. The map predicts county averages from 1993 data; it does not measure homes. EPA's words: "The map should not be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested for radon." A short-term test costs little and is the only way to know your own number.

EPA's numbers, quoted directly: "The EPA recommends homes be fixed if the radon level is 4 pCi/L (picocuries per liter) (150 becquerels per meter cubed (Bq/m3)) or more. Because there is no known safe level of exposure to radon, the EPA also recommends that Americans consider fixing their home for radon levels between 2 pCi/L and 4 pCi/L (75 - 150 Bq/m3)." This site adds no threshold of its own.

January is National Radon Action Month on EPA's calendar, and winter is the practical testing season everywhere, because short-term tests want closed-house conditions. EPA's test instructions: "Follow the instructions that come with your test kit. If you are doing a short-term test, close your windows and outside doors and keep them closed as much as possible during the test." Cold months are when windows and doors stay shut anyway, in Colorado as anywhere.

Here is EPA's answer, verbatim: "Radon is the number one cause of lung cancer among non-smokers, according to EPA estimates. Overall, radon is the second leading cause of lung cancer. Radon is responsible for about 21,000 lung cancer deaths every year. About 2,900 of these deaths occur among people who have never smoked." The EPA and the U.S. Surgeon General recommend testing every home. Read more at https://www.epa.gov/radon/health-risk-radon, and talk to your doctor about personal risk, particularly if you smoke.

Yes, as an interactive application rather than a downloadable dataset: Colorado Environmental Public Health Tracking, radon dataset publishes county average indoor radon values and the percent of tests over 4.0 pCi/L, in an interactive application, linked from this page at https://coepht.colorado.gov/radon-dataset-details.