According to the EPA (Environmental Protection Agency January is National Radon Month. The EPA and 8 other federal agencies have joined together to educate the public about the negative health effects to individuals caused by long term exposure to Radon.
What is Radon?
Radon is a radioactive gas that is released from the normal decay of uranium in rocks and soils and is found in nearly all soils in the United States.  Radon is invisible, colorless, odorless and tasteless and seeps up through the ground and diffuses into the air. We all breathe radon every day, usually at very low levels without serious negative effects.  However, it has been estimated that 1 in 15 American homes have high levels (above 4.0 pCi/L) of Radon.
Myth vs Fact
Is radon a health hazard?
Many people have dis-regarded the warnings about radon because most early testing was done on hard rock miners who were exposed to extremely high levels for long periods of time.
New studies performed on homeowners have confirmed Radon’s negative health affects. The most recent  residential case-controlled study’s results were published in 2000.   Radon is considered a Group A carcinogen which means it is known to cause cancer in humans with prolonged exposure.
Is radon a problem in Colorado?
It is estimated that nearly 1 out of every 15 homes in the US have elevated radon levels. The concentration of radon does vary by geographical area. 
The map to the right is the EPA Radon map of Colorado. As you can see the majority of Colorado is in Zone 1 which has the highest potential for predicted indoor averages over the EPA limit of 4.0 pCi/L. 
Should Homeowners Test for Radon?
In 2005 the Surgeon General released a National Health Advisory on Radon recommending testing of all homes. You can read that press release here:
What are dangerous levels of radon?
I have often heard that the levels considered dangerous are different in Canada and the US giving rise to questions about the validity of the problem.  The fact is that levels, at which mitigation is recommend, are very close and the recommendations are similar.  Testing in the US typically occurs during real estate transactions while in Canada they tend to be done by homeowners.
The US Environmental Protection Agency and Surgeon General recommend that people not have long term exposure in excess of 4.0 Pico Curies per liter (4.0 pCi/L).  In Canada the number is 5.4 pCi/L.
The following are the general recommendations of the EPA based on the results of short term radon testing. The amount of radon in the air is measured in “picocuries of radon per liter of air” or “pCi/L”.
  •  Short term testing with levels less than 4.0 pCi/L – The EPA does not recommend any follow up action or mitigation.
  • Short-term testing with levels near but not more than 4.0 pCi/L – A second short term test may be in order.  If you do a 2nd short-term test the 2 values should be averaged and if the average is LESS THAN 4 pCi/L no follow up action or mitigation is recommended.
  •  Short term testing with levels equal to or greater than 4.0 pCi/L- The EPA recommends mitigation to reduce radon levels.
In Canada the recommendations are slightly different.  Remedial measures are recommended in a dwelling whenever the average annual radon concentration exceeds 200 Bq/m3 (5.4 pCi/L).
  • Short term testing with levels less than 5.4 pCi/L – no mitigation necessary
  • Short term testing with levels between 5.4 pCi/L and 16 pCi/L – mitigate within 2 years
  • Short term testing with levels over 16 pCi/L – mitigate within 1 year.
What to do with the results.
If testing shows levels well above those listed above,  mitigation within the next year is strongly advised.  If your results fall below the levels listed above than no action is required.  If testing shows levels very near the 4.0 pCi/L level you may want to consider a few things before deciding when or if to mitigate.
  • Is anyone who will be living in the home a smoker?  The risk of contracting lung cancer rises significantly for smokers.
  •  How much time will family members spend at home? 16 or more hours in the home (including sleep) would be considered long term exposure.  Stay at home moms with young children will easily meet these times.
  • Do you have bedrooms or a home office in your basement? Radon concentrations tend to be greater on the lower levels of a home and testing should be performed in these areas. A person who sleeps or spends much of his/her waking hours in the basement is exposed to more risk than others who occupy higher levels in the same house.
  • How long will you live in your home? Consider the amount of time you expect to live in your home. Most of the studies and guidelines are based on a “lifetime” of exposure. Be aware that radon testing results may be an issue when trying to sell your home.
How radon is mitigated or reduced?
There are several methods that a contractor can use to lower the radon levels in your home.  Some techniques prevent radon from entering your home while others reduce the level after it has entered.  The type of radon reduction system that will work best for your home will depend on the foundation design of your home. (i.e. basement, slab-on-grade, crawlspace).
In houses with basement or slab-on-grade foundations, radon is usually reduced by one of four types of soil suction: subslab suction, drain tile suction, sump hole suction, or block wall suction.
The most common, and usually the most reliable, is the subslab suction technique.  Basically suction pipes are inserted through the floor slab into the soil underneath.  A radon vent fan connected to the suction pipe draws the radon gas from below the house and releases it into the outdoor air while creating a vacuum beneath the slab.  For a more detailed description of this an the other types of radon reduction techniques I recommend you download the EPA’s “Consumer’s Guide to Radon Reduction” 
All radon reduction techniques typically include sealing cracks and other openings in the foundation.  Sealing cracks helps limit the flow of radon into the home thereby improving the effectiveness of the other systems in place.  Please note that the EPA does not recommend the use of sealing alone to reduce radon. Tests have shown this is not an effective way to consistently reduce radon levels.
You can help in the reduction of radon levels in your home by opening windows, doors and vents on the lower floors in your home.  This mixes the outdoor and indoor air together effectively reducing radon levels in the home.  This should be regarded as a temporary radon reduction technique as radon levels will return to the previous levels when the doors and windows are closed not to mention the increased cost of re-conditioning the air. 
Radon Study (American Journal of Epidemiology  ) 
EPA’s “Consumer’s Guide to Radon Reduction”