Radiochemistry – Interpreting Your Test Results


This information is geared for the private well/home owner. The Safe Drinking Water Act (SDWA) regulations that govern radioactivity in drinking water do not apply to the individual well/home owner. Public water suppliers should contact the Wisconsin Department of Natural Resources for information regarding SDWA regulations.


Radon in Air


If your radon level is below 4 picocuries per liter (pCi/L), you do not need to take action. You may want to test again sometime in the future if your living patterns change, or if a lower level becomes occupied then test in that level.

If your radon level is 4 pCi/L or greater, use the following charts to determine what your test results mean. Depending upon the type of test you took, you should either test again or fix your home.


CHART 1: Radon Tests Conducted Outside a Real Estate Transaction

Type of Test If Radon Level is 4.0 pCi/L or Greater
Single short-term test less than 4 pCi/L No mitigation
Single short-term test between 4 and 10 pCi/L Test again using a long-term testing device* (Alpha-track detector)
Single short-term test above 10 pCi/L Repeat short-term test
Average of 2 short-term tests above 4 pCi/L Fix the home
Single long-term* test above 4 pCi/L Fix the home

*A long-term test is defined as a test lasting more than 90 days.


CHART 2: Radon Tests Conducted During a Real Estate Transaction (Buying or Selling a Home)

Type of Test If Radon Level is 4.0 pCi/L or Greater
Single ACTIVE short-term test (this test requires a machine) Fix the home
Average of 2 PASSIVE short-term tests* (these tests do not require a machine) Fix the home
Single long-term test** Fix the home

*Use two passive (simultaneous) short-term tests and average the results.

**A long-term test is defined as a test lasting more than 90 days.



If the radon level is 4.0 pCi/L or greater, you can call the Wisconsin Division of Public Health’s Radon Information Center (RIC) nearest you by dialing toll-free 888-569-7236.

Individuals at the RIC can give you more information, including a list of EPA approved radon contractors who can fix, or help you develop a plan for fixing, the radon problem. You may also call the Radon Fix-It Line at 800-767-7236.



Radon in Water


Radon in Water drafted Feb. 20, 2004, C. Weiffenbach, Wisconsin Department of Health Services

There is currently no U.S. EPA standard for radon in drinking water although regulation is called for in the 1996 amendments to the Safe Drinking Water Act. A few years ago, a 4000 pCi/L standard for radon in community supplies was proposed by EPA for states that undertake a suitable program for control of radon in air (like Wisconsin), but that regulation was not finalized. For the latest update on possible regulation, please see


Gross Alpha/Beta in Water


This screening test measures the total alpha and beta radioactivity in the sample. The test does not give any information about which radioactive isotopes are in the sample.

If your test result was less than the MDL (minimum detection limit), then you do not need take any action to treat your water if you are a private well owner. If your results were above the MDL and you would like help interpreting the results, please call the lab at 608-224-6227.


Radium 226 and 228 in Water


These are two naturally occurring isotopes that are sometimes present in well water. Radium analyses are usually only performed if the gross alpha/beta screening test is elevated. It is not possible to have radium 226 in the water without having an elevated gross alpha value. The current standard for municipal wells is that the sum of the radium 226 and 228 activity must be less than 5 pCi/L (picocuries per liter) to be in compliance with the Safe Drinking Water Act (SDWA).

If you are a private well owner and have an elevated radium level, please call the lab at 608-224-6227 for help interpreting the results.


Total Uranium in Water


Elevated uranium levels are sometimes found in private wells, primarily in the north central part of the state. The uranium result is the sum of the activities for all of the isotopes of uranium found in the water sample and is therefore reported as total uranium. The various isotopes of uranium are present on the Earth in specific ratios. However, these ratios may be altered in well waters due to a number of chemical and physical conditions that are present in the well. This condition is known as disequilibrium. The total uranium method as well as another technique called alpha spectroscopy accurately determine the uranium activity even if disequilibrium is present.

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