Radon in well water around Duluth, MN

Who should be thinking about this

Radon in water is mainly a groundwater issue. Surface water has usually lost its radon to the air before it reaches a tap, and homes on Duluth's city system get water drawn from Lake Superior. If you are on a different public system, your supplier can tell you where the water comes from.

The homes to think about are the ones on private wells, which are common in the townships around Duluth and across rural St. Louis and Carlton counties. EPA has said radon in indoor air from the soil is by far the larger risk, so test your air first, and then test the water if you are on a well.

How to test a well

Water testing needs a sampling method that keeps the gas from escaping, so an ordinary water test kit is not enough. Contact a laboratory that offers a radon-in-water test and follow the instructions closely, including how to draw the sample and how quickly to send it back. The MDH Well Management program can point you toward labs and guidance.

There is no final federal limit for radon in drinking water. EPA proposed standards years ago and has not finalized them, so ask your lab or a water treatment professional how to interpret your result along with your air test.

Treatment options

If treatment makes sense, the system goes where water enters the house, so that all of the water is treated:

• Aeration bubbles air through the water and vents the released radon outdoors above the roofline. It is generally the more effective option at high levels.
• Granular activated carbon filters capture radon as water passes through. They cost less to buy, but the carbon can build up radioactivity over time, and the tank may need shielding and careful disposal.
• Faucet filters do not solve the problem, because most of the risk comes from radon released into the air throughout the home.

What to expect from a water treatment system

Treatment systems are installed at the point of entry, which is usually in the basement or utility area where the well line comes in. Aeration units take up some floor space, may need their own pump, and vent through a pipe to the outdoors, in much the same way a soil-gas system does. Carbon tanks are smaller and simpler, but ask how the tank will be handled when the carbon is spent, and whether the location keeps it away from where people spend time.

Ask for a follow-up water test after treatment begins, and repeat it on the schedule that your installer recommends. A water treatment contractor is often a different company from a radon air contractor, so check what license or qualifications apply to the work, and ask whether they have treated radon in water before. Other well-water issues, such as iron or bacteria, can affect which system is suitable, so a full water test is a useful place to start.

If you are buying a home with a well, it is sensible to test the water along with the air during the inspection period. Most ordinary well tests do not include radon, so you will have to ask for it specifically. Allow enough time for the sample to reach a laboratory and for the results to come back before your inspection deadline.

Air first, then water

If you get a high air test on a home with a well, have a contractor consider both sources. A radon-in-air system handles the soil gas beneath the foundation, while water treatment handles what comes through the plumbing. Treating one will not fix the other.

Common questions