Monday, February 4, 2013

Radon in Your Home

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium, thorium, radium, and other radioactive elements that naturally occur in granites as well as some metamorphic and sedimentary rocks in soil, rock, and water and is widespread in the United States.  According to the U.S. Environmental Protection Agency, EPA, radon is the second leading cause of lung cancer in the general population, and estimated to cause about 21,000 lung cancer deaths per year making it the leading cause of lung cancer in non-smokers. Like all environmental pollutants, there is some uncertainty about the magnitude of radon health risks. However, because estimates of radon risks are based on studies of cancer in humans (underground miners) we know more about radon risks than risks from most other cancer-causing environmental risks.

Radon is a colorless, odorless, radioactive gas derived from the decay of radioactive elements that naturally occur in granites as well as some metamorphic and sedimentary rocks. 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. Although areas of the country where Uranium concentrations are higher are more likely to contain higher radon levels, radon is a house specific issue. Even in an area of low radon potential a house can have elevated radon while neighbors’ houses have low radon levels. Migration and concentration of radon varies considerably, and depends on the amount of radioactive material especially uranium in the bedrock, the moisture levels in the soil, groundwater circulation, and atmospheric pressure. Uranium, thorium, and radium can be highly mobile in groundwater and can move considerable distances and be re-deposited in soils.

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. 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.  Most people only test their home at purchase, but the It is a good idea to retest your home if you make any changes to the structure and every few years to be sure radon levels remain low. In addition, if a radon mitigation system is installed it is important to monitor the system and retest at least every two years to make sure the system is functioning.

Yellow is low radon potential, orange is moderate radon potential and dark orange is high radon potential from DMME VA
Professional radon testers and mitigation contractors operating in the Commonwealth of Virginia and many other states can be found on the websites of the National Radon Safety Board  and the National Environmental Health Association . Radon contractors are not specifically licensed in Virginia, but many states require radon professionals to be licensed, certified, or registered, and to install radon mitigation systems that meet state requirements. Check with your local building department or the state department of health for the local requirements in your area. In 1986, the Virginia Department of Health, VDH, conducted a survey of 800 homes throughout the state and found that about 12 % had radon levels above the EPA’s recommended action level of 4.pCi/L. It would be reasonable to assume that radon probably is a significant problem in land overlying the regions of uranium deposits in Pittsylvania County and other areas of the Piedmont.

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. According to the EPA 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.

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 .

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