Why Testing Radon in Water Matters

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There seems to be a lot of confusion when it comes to assessing radon risk factors in a home and what to do to correct any issues; especially when it comes to buying or selling a home with a well water system. This post will not be a technical writing; rather, a simple, straightforward attempt to remove any confusion and provide you with a protocol for properly assessing radon risks as it relates to radon in well water.

Radon Risk Sources

There are two main pathways for radon to enter a home with a well:

1. Through the soil

2. Through well water

In order to fully assess risk factors for a family, both the air and water should be tested as each source requires a separate mitigation system to protect families if necessary.

Please note: soil is the primary pathway for radon, not water.

Radon in Water

Radon is a naturally-occurring radioactive gas that may be found in drinking water, as well as indoor air. Over ninety-five percent (95%) of exposure to radon is from indoor air; and less than five percent (5%) is from water –- released from running water activities, such as bathing, showering, cooking, dishwashing, and laundering.

Key point: Radon particles are easily inhaled and deposited in the lungs where they can damage sensitive lung tissue—long-term inhalation may lead to lung cancer.

Lifetime health risk from ingestion is very low, relative to cost of remediation. Approx. only 20 of the 13,000 stomach cancer deaths each year may result from consuming water that contains radon.

Radon is released from the water into air when water is agitated or heated. As radon escapes from the water, it contributes to health risks within a home; adding to the contribution from the soil gas.

SafeWell--The Healthy Well Water Folks
Source: Certi.us

Assessing Radon in Water Risk Factors in a Home

As radon is released from the water it is “transferred” into the air. Many years ago, scientists created a calculation that for every 10,000 pCi/L of radon in a home’s water supply, 1 pCi/L of radon “may” be contributed to the home’s radon-in-air measurement when released from the water. This is known as the “transfer ratio.” The transfer ratio can vary widely from one home to another. The USEPA Action Level for radon in air is 4 pCi/L (the level you definitely want to take action).

We’ve completed 50-100 radon in air tests for our customers and have yet to see the 10,000pCi/L to 1pCi/L transfer ratio correlation. The results have been lower.

Please keep in mind that the transfer ratio is “potential,” and “may”  increase the overall average radon concentration in a conventional single family home. The transfer ratio is a metric to work off of but the interpretation of the real risks needs further assessment through additional radon in air testing in the upper levels of the home where the water is being released. The transfer ratio can vary widely from one home to another (e.g., depending on size, ventilation, insulation/tightness, hours of occupancy, etc.).

Key point: a radon in water test is an “indicator” test. Historical data for radon testing at a property for sale will be very helpful in determining the average radon in water level.

What Does The MassDEP Action Level Mean?

Here is where all the confusion lies when it comes to interpreting radon in water test results:

The MassDEP Action Level (which is really defined by the Office of Research and Standards–ORS) means in practice:

Exceedance of the 10,000pCi/L guideline indicates that indoor air sampling for radon should be completed mainly in the upper levels of the home where water is disbursed through cooking, dishwashing, laundering, or showering. Breaching the 10,000pCi/L level doesn’t necessarily mean that a radon in water mitigation system is warranted. Further testing is advised. This testing is in “addition” to the typical radon in air test completed by the home inspector in the basement.

If a radon in air mitigation system is already installed and working properly, identifying radon in water transfer risk factors is easier to assess due to the isolation technique of the soil gas variable being removed from the equation.

The radon in water test results need to be viewed in context and not in isolation and requires additional assessment to determine whether expensive mitigation is justified.

A six month radon in air test is the most accurate and preferred for assessing radon in air factors. Since there isn’t a six month window during a real estate transaction, a 48-hr test may be used and if the test results indicate 4 pCi/L or above, a second 48-hr test should be completed to validate the results taking the average of the two test results under consideration for corrective action.

If the test results come back lower than 4 pCi/L, monitoring radon in air and water is advised annually or every two years to ensure the level remains low and an opportunity exists to take action if the levels increase.

Here’s a quick example of assessing radon risks factors in a home:

The home inspector completes a radon in air test in the basement and the result is 5 pCi/L. SafeWell completes a radon in water test and the result is 25,000 pCi/L. Since the radon in water level is above the 10,000pCi/L MassDEP Action Level, an additional radon in air test needs to be completed in the upper levels of the home. After completing an air test in the upper levels of the home, the result is only 1.5 pCi/L.  Radon in air mitigation should be installed to address the soil gas contribution (the basement) first and radon in water should be monitored to make sure current levels remain low.

If the radon in air test results in the upper levels came back at 2.5pCi or higher, a second radon in air test should be completed to validate results and the average used for mitigation criteria. If the average of the two radon in air test results is 2.5 pCi/L or higher, radon in water mitigation may be necessary. The USEPA suggest that with radon levels between 2-4 pCi/L, you should consider correcting the issue, if 4 pCi/L and above, you definitely want to correct the issue. The World Health Organization believes the radon in air level should be 2.7 pCi/L or less. The goal is to get the level as close to zero as possible. The high the level, the higher the exposure rate and the higher the risk to damaging lung tissue leading which may lead to cancer.

Please note: always mitigate the highest source of radon in the house first. If the contribution from the radon in water is higher than the soil gas, mitigate the water first, and vice-versa.

In conclusion, a radon in water test is an “indicator” test that warrants additional radon in air testing if the 10,000 pCi/L “guideline” is breached. Having historical test results for radon in water is helpful in determining the average levels in the home, but radon in air testing is still required to assess the transfer ratio and health risks. All parties involved with a property transfer need more data in order to justify installing expensive treatment systems that may or may not be needed.

If you have any questions, you can contact our team by clicking here. We’re always happy to help.

To access and download a PDF of the radon in water testing protocol, click here.

Here is a direct link to the MassDEP Drinking Water Standards and Guidelines for radon in water advisement:


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