How to Read a Radon Test

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Radon is an invisible, odorless and tasteless gas that contributes to about 20,000 lung cancer deaths each year in the United States, according to the U.S. Environmental Protection Agency. It is produced when uranium, a naturally occurring element, decays in soil and water. Because radon in high concentrations poses a threat to human health, the EPA recommends that all people test their homes for it, and if levels are unsafe, to use radon reduction systems to reduce levels. Contractors reduce radon in the home by sucking it from the soil and venting it through pipes to dissipate safely outside. Radon in water can be mitigated by treating it with charcoal. In order to know how to proceed, you'll need to know how to read your radon test.


Step 1

Look at the air test number on your radon test result, which is measured in picocuries per liter of air (pCi/L). A picocurie is one-trillionth of a curie, a measurement unit of radioactivity. One curie is the amount of radiation given off by one gram of radium, and one picocurie per liter indicates 2.22 radioactive disintegrations per minute in one liter of air. If the radon test result number is 4 pCi/L or higher, you need to get a treatment system. If it is between 2 and 4, you might need to treat it, and should consult with a radon treatment service for details about your situation. If it is less than 2 and you tested in cold weather with the heat on, you should test again in three to five years; if it is less than 2 and you tested in warm weather, you should test once more during cold weather with the heat on. Radon may be higher during cold weather if your home is leaky, causing pressure inside to be lower than the pressure of radon in the soil below the home.


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Step 2

See the well water test number if you had that test performed as well. If the number is 10,000 pCi/L or higher, you need to get the water treated. If the number is between 4,000 and 10,000, you might need to get it treated. Consult with a radon treatment service for details for your particular situation. If the number is 4,000 or less, you should test again in three to five years. The main source of radon in homes is from the soil. In some areas, radon is present in high levels in drinking water, and radon from the water is emitted into the air. For every 10,000 pCi/L of radon in the water, 1 pCi/L will be emitted into the air.


Step 3

Notice a series of numbers arranged in a column that you read from left to right, and up and down, which list the radon level detected every hour during a test. If you see a "T" next to one of the hourly numbers, that signifies that the test device was moved, touched or bumped or that the reading was taken manually by touching a button. A "P" next to a number indicates that there was a power interruption during that hour of testing, which could mean that the radon-testing device was turned off or that there was a power failure.


You may be able to get a free or low-cost radon test through a state program. Go to the EPA’s State Radon Contact Information page and click on your state for details.


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