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The City of Portland, Oregon

Portland Water Bureau

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Frequently Asked Questions about Radon in Portland's Drinking Water

Is Radon a concern in Portland’s drinking water system?

Radon in Portland’s drinking water does not pose a significant health concern. The risk associated with radon comes from long-term exposure to breathing air with high levels of radon, such as from indoor air where radon released from soils can accumulate. While drinking water can contribute a very small fraction to the amount of radon in indoor air, there are no known health effects connected with brief exposure to low levels of radon, similar to those found in Portland’s groundwater. Radon is rarely detected and only at extremely low levels from the Bull Run source.  The Bull Run supplies over 90 percent of Portland’s drinking water. Radon has been regularly detected in the Columbia South Shore Well Field, Portland’s back-up water source.  In Portland, groundwater is only used for brief periods of time, and is usually blended with water from the Bull Run. Based on the historical levels of radon in Portland’s drinking water, it is unlikely to contribute to adverse health effects. For more information visit

Does the Portland Water Bureau test for radon?

The Portland Water Bureau has been testing for radon in groundwater since 1989. Although not required by State or Federal regulation, Portland periodically tests for radon from the Bull Run, groundwater from the Columbia South Shore Well Field, and throughout the distribution system. Radon has rarely been detected, and even then, only at extremely low levels from the Bull Run. Levels at the Columbia South Shore Well Field have been consistent over this period, ranging from 131-390 pCi/L (picocuries per liter).  Although no standard has been adopted, the Environmental Protection Agency has proposed regulating radon in drinking water at 4,000 pCi/L. This level is approximately 10-30 times higher than what the Water Bureau has recorded from the Columbia South Shore Well Field. Further testing within the distribution system, which is representative of the water at customers’ taps, found lower levels of radon, from 34-140 pCi/L, indicating that radon naturally dissipates throughout the distribution system.

When tested, radon results are reported in the Annual Water Quality Report.

Are the radon levels in Portland’s groundwater above recommended levels?

There is no federal regulation for radon in indoor air or drinking water. The EPA has proposed to regulate radon in water, but since a major portion of the associated risk with radon is due to soil under homes, the EPA has not determined how regulating radon in drinking water would lower health risks. As with all carcinogens, the EPA has set a Maximum Contaminant Level Goal, or MCLG, of 0 pCi/L. This is below the average outdoor ambient radon level of about 0.4 pCi/L. 

How is radon in groundwater mitigated?

Radon in drinking water decreases due to natural decay and volatilization. This happens as water travels through conduits, pipes and storage tanks (both closed and open).

What can customers do to reduce exposure to radon?

Customers concerned about radon exposure are encouraged to test their home for radon. The EPA, Surgeon General, and the Oregon Health Authority all recommend testing your home for radon gas.  The American Lung Association of Oregon offers test kits at: And for more information on testing your home for radon gas, you can visit