What is Vapor Intrusion? Should I Care?

Question:
Could you discuss the issues and health risks related to "vapor intrusion" of volatile organic chemicals into buildings from contaminated sites? What can a homeowner or purchaser do to find out if there is a vapor intrusion risk at home, schools, or day care centers?

Response:
“Vapor intrusion” (sometimes called “soil gas vapor intrusion”) is what happens when chemicals move from the ground or water into your home or other buildings. Chemicals that enter your home through the ground often belong to a class of chemicals called “volatile organic compounds” (VOCs), which as their name implies are volatile, and thus like to exist as a gas.

This property is important, allowing VOCs to move easily through openings that exist between the soil grains and thus to move from areas of high pressure to areas of low pressure. Since basements tend to be at lower pressure than the ground below, this pressure-related movement can cause VOCs to enter your home from the ground through openings or cracks in your foundation. Once inside, the VOCs can spread through out your home with the help of natural air flow, room or house fans, or other home ventilation devices. When this occurs, vapor intrusion can be an important source of indoor pollution in your home.

Whether vapor intrusion also presents additional health risks depends on many factors. For example, health risks will depend on the people that live or spend time in your home, as people have different responses to chemical exposures. Health risks will also depend on the type and amount of your chemical exposures, more precisely the specific VOCs that enter your home, their levels inside your home, and the length of time that the VOCs remain elevated.

Although other kinds of chemical spills, leaks or contamination can also lead to vapor intrusion in homes, the most common VOCs associated with vapor intrusion are gasoline-related, the result of spills or leaks from an underground storage tank at a gas station. For gasoline-related intrusions, VOCs of concern may include (but are certainly not limited to) benzene, toluene, xylenes, and styrenes. Exposures to these and other gasoline-relaed VOCs have been linked to a variety of adverse effects, including short term (and generally reversible) effects such as eye and respiratory irritation, headaches, and nausea, and long-term effects, such as cancer.

There are several ways to test if VOCs or other chemicals are entering your home through the ground. You can collect samples in the nearby ground (soil vapor samples), in the ground directly below your foundation (sub-slab vapor samples), in your indoor air, and in your outdoor air (for comparison). Samples in these different places should be collected at the same time, preferably during the heating season when the pressure difference between the ground and the basement should be highest. Similarly, indoor samples should be collected in the basement or first floor of the living space, since these are the areas in your home where the levels from vapor intrusions should be highest. Since there are many sources of VOCs inside your home and since indoor VOC concentrations can vary widely day-to-day, indoor sampling results may be more difficult to interpret than the soil and sub-slab sampling results, but interpretation of indoor sampling results will be easier with outdoor sampling data and information about your house, including its ventilation, characteristics, and other VOC sources.

Also, if you know that a nearby gas station, commercial or industrial facility or other site has had a spill or a leak of VOCs, you may want to call the owners, local government officials, or the people cleaning up the spill to see if any sampling is being performed to test for vapor intrusion and if so, to ask for testing to be performed at your home. The U.S. Environmental Protection Agency provides extensive technical guidance on vapor intrusion including “safe” levels of chemicals in groundwater and soil gas (See Draft Guidance at http://www.epa.gov/correctiveaction/eis/vapor.htm).

If tests show that chemicals are getting into your home through the ground, there are many possible solutions, including sealing cracks and openings in the foundation or installing a radon remediation system. Often, the costs of these solutions will be paid for by the person or company who allowed the chemicals to get into the ground.

Radon testing: What do the results mean?

Question:
I am selling my house and in this process, my house was tested for radon using a mail-in kit. The buyers got the radon results back and they show that my house is just below the EPA recommended limit. The buyers want me to install equipment to reduce radon in my home. I don't think that this is is necessary, because my radon levels were just below the limit. If radon levels are below the EPA limit, doesn't that mean that my radon levels are fine?

Response:
Radon is a naturally occurring gas that has been shown in research studies to cause lung cancer. People are exposed to radon primarily in their homes, as that is where people spend the majority of their time and that is where radon levels (in every day life) tend to be highest.

EPA recommends that people take steps to reduce radon levels in their home when levels are at or above 4 pCi/L. Since exposures to radon at even lower levels carry some risk of lung cancer, EPA recommends that people think about lowering their home's radon levels to even lower levels, or to 2 pCi/L. Lowering radon levels will be particularly important for areas where people spend time.

To know how your home fits within the EPA guidelines, you need to know the average radon levels in your home over a long time period, as EPA developed these guidelines based on life time exposures to radon. Since your radon levels were measured using a mail-in kit, my guess is that your radon test was performed over a couple of days. Your test results near the 4 pCi/L action level indicate that it is possible for your home to have long-term average radon levels that need remediation (or lowering).

Since your test results were just under the action level, however, it is not clear that you need to remediate. Radon levels vary over time -- for example higher indoor radon levels are generally found in winter. As a result, it is possible that long-term radon concentrations are lower than measured. To check, you can retest your home for radon, making sure to place the radon kit in the same place as before (usually the basement or first floor is recommended). You could estimate the long-term average radon level as the average of the two test results. It's far from perfect, but retesting will give you more information to decide what to do. If the second test result is much greater than the 4 pCi/L action level, for example, I would assume my radon levels were too high. If the retesting results were much lower, then I would assume that my radon levels were within the recommended levels. If the test results are again close to 4 pCi/L, then the decision is harder.

Alternatively or in addition, you could just propose a radon mitigation or reduction solution that you have installed or provide funds to cover the costs for installation. This might be the easiest and quickest way to reach a suitable resolution with the prospective buyers of your home. Some radon reduction fixes are relatively easy and inexpensive to do, while others are more labor-intensive and costly. EPA estimates that radon remediation ranges between $800-$2500.

EPA has a good website about radon for home buyers and seller (http://www.epa.gov/radon/realestate.html). This site contains pretty user-friendly information about radon, its health risks, measurement, and remedies. On this website, EPA mentions their video "Breathing Easy: What Home Buyers and Sellers Should Know About Radon", which you may find helpful. To get a free copy of this video, you can call 1-800-438-4318 and ask for video number EPA 402-V-02-003.