Adopted by Board of Directors on September 13, 2006

Radon is a colorless, odorless radioactive gas that comes from the natural breakdown of uranium in the soil or rock on which buildings are built. Radon can become trapped inside any type or size of building, leading to unsafe concentration levels.

The presence of radon in the indoor air has been proven to cause lung cancer. Extensive research shows that:


  • Any level of radon in the indoor air is expected to carry some risk of lung cancer (See Sources 1,2,3,4,5,6,7 at end of document)\
  • Air radon levels above 2 picoCuries per liter (pCi/L) have been found to lead to increased risk of lung cancer above background rates (See Sources 1,2,3,5,6)
  • Air radon levels of 4 pCi/L or above can be effectively reduced (See Sources 1,2,3,4,8)
  • Radon in well water increases the levels of radon in the indoor air (See Sources 1, 2, 3, 4, 5)
  • Significant risk reduction can be achieved by treating well-water with radon levels at or above 20,000 pCi/L. (See Sources 1,2,3,5,8)
  • Due to the varied pathways that radon takes to enter a structure, without conducting a radon test it is not possible to accurately predict whether or not a building has elevated radon levels, even if neighboring structures have elevated radon levels (See Sources 1, 2, 3)

Other factors:

  • Radon is the second leading cause of lung cancer in the U.S., and the number one leading cause of lung cancer among nonsmokers
  • Radon accounts for 10% of the lung cancer cases in nonsmoking men, and 20% of lung cancers in nonsmoking women. Smoking combined with radon creates especially high risk of lung cancer in both men and women.
  • Because of the types of rock and soils found in Maine, high radon concentrations are found throughout the state.
  • One in three Maine homes has air radon concentrations above 4 pCi/L, compared to one in fifteen nationally.
  • Radon gas can be found in all types and sizes of buildings
  • It is not possible to accurately predict if a site will cause a structure built on it to have elevated radon levels because one cannot predict the impact of site preparation on radon entry pathways, or the extent to which the structure itself will pull radon from the ground. (See Sources 1, 2, 3, 9, 12, 13)
  • Well-researched, usable guidance exists for the testing and mitigation of radon in well water and indoor air, as well as for radon resistant construction. (See Sources 10, 11, 12, 13) 

Because of the increased risk of lung cancer to Maine citizens from exposure to radon, the Maine Indoor Air Quality Council recommends the following.

1) All new building construction in Maine should include—at a minimum—a system for passive radon mitigation of radon with provisions for active system installation at a later date if needed.

2) All buildings in Maine (both new and existing construction) should be tested for radon in the indoor air. Mitigation efforts should be undertaken if results show the radon concentrations are at or exceed 4 pCi/L and should be considered if levels are between 2 pCi/L and 4pCi/L.

3) All buildings in Maine that have a well water source should have the water source tested for radon and mitigation efforts should be undertaken if radon concentrations in the water are at or exceed 20,000 pCi/L.

4) In order to have impact on public behavior regarding radon, a state-wide public education and communication program is necessary.


1. National Academy of Sciences’ (NAS) report on radon in indoor air, the Biological Effects of Ionizing Radiation (BEIR) VI Report (1999). 516 pages, ISBN number 0-309-056454-4.

2. National Academy of Sciences’ (NAS) report on radon in water: “Risk Assessment of Radon in Drinking Water”. 296 pages, ISBN number 0-309-06292-6.

3. U.S. Environmental Protection Agency: Risk Assessment for Radon, (EPA 402-R-03-003).

4. National Radon Health Advisory by the U.S. Surgeon General, Press release dated Thursday, January 13, 2005.

5. Iowa Radon Lung Cancer Study, Am J Epidemiology 2000; 151:1091-1102.

6. European Residential Radon Studies, Radon in Homes and Risk of Lung Cancer: Collaborative Analysis of Individual Data from 13 European Case-control Studies; S Darby, D Hill, A Auvinen, J M Barros-Dios, H Baysson, F Bochicchio, et al.; British Medical Journal, 2005 January 29, 330 (7485): 223.

7. Recommendations from the Clean Air Act Advisory Committee (PDF), July 21, 2005;

8. American Cancer Society: Radon Gas Confirmed as Second Largest Lung Cancer Risk, American Journal of Epidemiology (Vol. 151, No. 11).

9. The Maine Citizens Guide to Radon, July 2002, Maine Radon Hotline: 1-800-232-0842.

10. U.S. EPA Indoor Radon and Radon Decay Product Measurement Devise Protocols, EPA 402-R-92-004, July 1992 (revised).

11. Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings, Standard E2121-03, ASTM International, Technical committee E06.41 on Air Leakage and Ventilation Performance, 2005.

12. U.S. EPA guidance on Building Radon Out: A Step by Step Guide on How to Build Radon Resistant Homes, EPA/402-K-011-002, April 2001.

13. National Primary Drinking Water Regulations; Radon-222; Proposed Rule. Federal Register, November 2, 1999; .