According to the EPA about 21,000 people die each year from lung cancer caused by long term exposure to elevated levels of radon in their homes. Radon is the second leading cause of lung cancer in the general population, and is the leading cause of lung cancer in non-smokers. As radon gas is released from bedrock, it migrates upward through the soil and can seep into the basements of houses and other buildings through dirt floors, cracks in concrete, and floor drains. Radon has a tendency to accumulate in enclosed spaces such as buildings. Air pressure inside your home is usually lower than pressure in the soil around your home's foundation. Because of this difference in pressure, your home acts like a vacuum, drawing radon in through foundation cracks and other openings. Radon, in its natural state cannot be detected with human senses- you cannot see, taste or smell it. The only way to detect radon is to test.
Ambient levels of about 0.4 picocuries per liter, pCi/L, of radon are typically found in the outside air. EPA recommends mitigating radon if the results of one long-term test or the average of two short-term tests show radon levels of 4 pCi/L or higher. According to the EPA, radon levels in most homes can be reduced to 2 pCi/L or below using standard mitigation techniques. Short term radon testing kits consist of a container of granular activated charcoal. The charcoal absorbs the radon gas entering the canister from the surrounding air. At the end of the radon gas test period, typically 3-7 days the canister is sealed and sent to the laboratory in the pre-paid mailer for analysis. There are also 90 day test kits. I have been thinking of trying one of those this winter.
Radon mitigation takes one of two approaches either preventing the radon from entering the home or reducing the radon levels by dilution after the radon has entered the home. There are several techniques that can be used depending on the type of foundation the home has. It is better to prevent radon from entering the home in the first place so I will discuss the preferred methods of prevention. The type of foundation, construction materials and condition will determine the kind of radon reduction system that will work best. Homes are built with some kind of foundation- a basement, slab-on-grade, a crawlspace, or a combination of the three. It is common to have a basement under part of the home and to have a slab-on-grade or crawlspace under the rest of the home. In these situations a combination of radon reduction techniques may be needed to reduce radon levels to below 4 pCi/L, which the EPA says is a safe level, but be aware that there is a synergistic risk from active smoking and radon exposure that increases the risk of getting lung cancer.
Soil suction techniques are the preferred method of mitigation and prevents radon from entering your home by drawing the radon from below the home and venting it through a pipe(s) to the air above the home or outside the house where it is diluted by the ambient air. An effective method to reduce radon levels homes with crawl spaces is covering the dirt floor of the crawl space with a high-density plastic sheet. A vent pipe and fan are then installed and used to draw the radon from under the sheet and vent it to the outdoors. This is called sub-membrane suction, and according to the EPA when properly installed is the most effective way to reduce radon levels home with crawlspaces.
In homes with concrete slab foundations or basements, sub-slab depressurization is the most reliable radon reduction method. One or more suction pipes are inserted through the floor slab into the crushed rock or soil underneath the home and a fan is used to draw the radon from under the slab or basement floor to a roof or wall vent. It is possible, and in many cases preferable, to install the suction pipe under the slab by running the pipe on the outside of the house. Another variation is to use the drain tiles or perforated pipe that are installed in modern homes to keep basements dry. Suction on these tiles or pipes can be effective in reducing radon levels. This system is most effective if the drain tiles are on the inside of the footer, sealed beneath the floor and form a complete loop around the foundation of the building. In homes that have sump pumps the sump can be capped so that it can continue to drain water and serve as the location for a radon suction pipe. There are kits that can be purchased for capping the sump pump. It is important that the sump cover lid is readily removable for service of the sump pump.
There are several other techniques such as sealing cracks and passive methods that are often installed in new construction that are not as effective as active depressurization of the slab, basement or crawl space. As a temporary measure ventilation will reduce the radon levels by introducing more outside air, but it will increase your heating and cooling bills. After a mitigation system is installed do confirmation testing of radon levels before you make the last payment to the contractor to ensure that the mitigation system works. For more information of mitigation approaches and techniques see the EPA’s Consumer's Guide to Radon Reduction .