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NH DES Recommendations 2015

Radon in Your Home:

An Overview for New Hampshire Homeowners


Radon is a naturally occurring radioactive gas that is commonly found in bedrock and in water from bedrock (drilled) wells in New Hampshire. Radon gas is colorless, odorless, and tasteless. Radon gas finds its way into indoor air mainly by migrating from bedrock, through the soil, and into the home via cracks or other openings in the foundation. Radon from bedrock wells is released into indoor air during showering, dishwashing and doing laundry. Dug wells and point wells tend to have minimal to no radon. The amount of radon released from stone building materials such as a granite block founda- tions, fireplace materials, counter tops and floor or wall tiles is usually insignificant.


Exposure to radon poses an increased risk of developing certain types of cancer, primarily lung cancer and stomach cancer. Radon concentrations in both air and water are measured in picocuries per liter (pCi/L). A general rule of thumb is that for every 10,000 pCi/L of radon in a home’s water supply, the radon concentration in indoor air is increased by 1 pCi/L.


The increased risk of lung cancer is due to inhalation of radon-laden indoor air, including any radon en- tering the building through the water supply. (There is also an increased risk of stomach cancer due to ingesting radon in drinking water.) Any amount of radon in air or water increases one’s risk of lung can- cer; the greater the amount, the larger the risk. Radon is the leading environmental cause of cancer deaths in the U.S. and the leading cause of lung cancer in non-smokers. Exposure to the combination of radon gas and cigarette smoke creates a greater risk for lung cancer than either factor alone. Long-term exposure to radon leads to the deaths of an estimated 100 New Hampshire residents each year.


The main health risk associated with radon in water is from breathing radon released into indoor air. According to the National Academy of Sciences, 89 percent of the risk from radon in a home’s water supply is the increased lung cancer risk from inhalation of radon that the water adds to the air in the home, while the other 11 percent is due to other cancers, primarily stomach cancer, due to drinking the water. This risk estimate is based on the typical situation in which every 10,000 pCi/L of radon in water adds 1 pCi/L of radon to the air. For example, if a home using a bedrock well has 5,000 pCi/L of radon in water and detects 4 pCi/L of radon in the indoor air, then one would make the following calculations to estimate how much of the radon in the air is due to the presence of radon in the water supply, how much is due to natural background conditions, and how much is due to infiltration:


0.5 pCi/L from water (5,000 divided by 10,000)

0.4 pCi/L from “background” (outdoor air; see REDUCING HEALTH RISK below)

3.1 pCi/L from infiltration of high-radon air through the foundation (4.0 - 0.5 - 0.4 = 3.1)

4.0 pCi/L total radon in air Every home is different in terms of the relative contributions of air and water to the total radon risk, which is why NHDES recommends testing air and/or water according to the flow chart on page 4 and consulting with a certified radon mitigation provider and (if radon in water is a concern) with a radon-in- water treatment professional. However, in the example above and in most cases in New Hampshire in which total radon in the indoor air is elevated, infiltration of high-radon air through the foundation con- tributes more to the overall health risk than radon in the water supply, and addressing infiltration is usu- ally more cost-effective than treating the water. Nevertheless, it is quite common for water from bedrock wells in New Hampshire to have radon levels that pose a significant health risk (based on a lifetime of exposure) in comparison with other common drinking water contaminants.

NHDES’ Environmental Health Program considers the risk of one excess cancer case per one million people exposed over a projected 70-year lifetime to constitute a significant health risk. The U.S. Environmental Protection Agency (EPA) considers significant health risk to be in the range of one per million to 100 per million people exposed. At 2,000 pCi/L of radon in the water supply, the estimated contribution to radon in air is 0.2 pCi/L, and the associated estimated total (lung, stomach, etc.) increase in cancer deaths is 1,300 per million people exposed. There is no federal or state standard for radon in drinking water.

NHDES recommends that at 2,000 pCi/L or greater in water, homeowners should test the indoor air for radon and consult with radon miti- gation and water treatment providers on the advisability of taking measures to reduce their exposure to radon in air. In most cases, “mitigation” of radon in air by preventing infiltration of air through the foundation is more effective and less expensive than treatment to remove radon from water. In cases where radon in water is contributing significantly to radon in air, radon-in-water treatment may also be warranted. Accordingly,

NHDES recommends testing both air (if living space in the home is below the third floor) and water (if from a bedrock well). These results, reviewed with a certified radon mitigation provider, will help homeowners to make well-informed decisions about the best way to reduce their ex- posure.

REDUCING HEALTH RISK The U.S. Surgeon General and EPA recommend testing for radon in air in all living spaces below the third floor. The U.S. Congress has set a long-term goal that indoor air radon levels be no more than out- door levels, which average around 0.4 pCi/L. While this goal is not yet technologically achievable in all cases, radon in most homes today can be reduced to 2 pCi/L or below and EPA strongly recommends treatment when the radon indoor air concentration exceeds 4 pCi/L. Approximately 27,000 cancer deaths can be expected for every 1 million persons exposed for a “lifetime” (70 years) at 4 pCi/L. Radon miti-

gation is achieved mainly through reducing the passage of radon through foundations and, in some cas- es, treating bedrock well water to remove radon.

TESTING FOR RADON NHDES’ recommendations for testing and reducing exposure to radon are summarized in the flow chart on page 4 of this fact sheet. Testing for Radon in Air – Both short-term and long-term testing methods are available. For infor- mation on testing radon in air, please visit, call (800) 767- 7236, or search the internet for “USEPA Where Can I Get a Radon Test Kit?”

NHDES recommends us- ing nationally certified radon-in-air measurement providers. Certified radon service providers can be found at and

Testing Water for Radon – For an up-to-date list of New Hampshire-accredited laboratories that con- duct analyses for radon in water, visit the NHDES website, click on “A to Z LIST” in the up- per right or left corners, and select “L” and then “Laboratory Search.” On the “Accredited Laboratory Search” page, select “DRINKING WATER” for the Matrix, and for “Analyte” select “RADON,” and then click on “Submit Query.”

Radon concentrations in well water can vary substantially from one test to another. NHDES recommends at least two radon tests (at least one month apart when possible), prior to mak- ing any treatment decisions. Because radon is not the only potentially harmful radioactive substance com- monly found in New Hampshire well water, NHDES also recommends testing water from private bedrock wells for uranium and analytical gross alpha; some laboratories offer these tests as a package along with radon.

A well that has high levels of radon is more likely to have high levels of uranium and/or gross alpha. Radon Measurement and Mitigation Service Providers and Equipment Suppliers Since January 1, 2015, all radon-in-air mitigation designers and installers must be nationally certified to perform those services in New Hampshire. Certification is not required for radon-in-air testing or for radon-in-water treatment, but some radon-in-air testing providers are nationally certified. Certified radon service providers can be found at and

Suppliers of radon water treatment devices can be found on the internet and in the Yellow Pages under listings for “Water Treatment,” “Wa- ter Conditioning,” or “Radon Testing & Services.” ADDITIONAL RESOURCES • A Citizen’s Guide To Radon, The Guide to Protecting Yourself and Your Family From Radon (USEPA, 2012), available at • Information and publications about all aspects of radon at

• NHDES Fact Sheet ARD-EHP-22, “Radium, Radon, and Uranium: Health Information Summary,” available at • NHDES Fact Sheet GEO-2, “Radon in New Hampshire,” available at •

Risk Assessment of Radon in Drinking Water (National Academy of Sciences, 1999), available at

Note: During real estate sale or financing transactions, or at other times, parties may choose to test indoor air and water supply concurrently to save time.

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