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Mapping Radon Risks

Friday, October 28th by Tim Snyder


There's no shortage of maps that tell you how much radon exposure you're likely to face in different parts of the country. The map that's most frequently cited is produced by the Environmental Protection Agency.

The U.S. Geological Survey has its own version of a national radon map, using a blue, yellow and pink theme instead of the EPA's red, orange and yellow color scheme.

The Lawrence Berkeley National Laboratory also has a map.

There are even maps that predict radon exposure levels by county. Keep in mind, the EPA has labeled an action level for concentrations at or above 4.0 picocuries per liter. In Fairfield County, Connecticut where I live, the county map tells me that 30% of buildings will show radon levels above 4pCi/L; 26% will have radon levels between 2 and 3.9 pCi/L; and 45% will be under 2 pCi/L.

Maps Just Tell Part of the Story

It's good to know that radon is on the radar screen of at least several major government agencies and research organizations. The more we know about this radioactive, cancer-causing gas, the better. But it's important not to let map details lull us into a false sense of security. Here’s the caveat published by the EPA about their map, right at the top of their web page:

This map is not intended to be used to determine if a home in a given zone should be tested for radon. Homes with elevated levels of radon have been found in all three zones. All homes should be tested regardless of geographic location.

The Lawrence Berkeley Lab echoes this concern:

IMPORTANT: Radon concentrations are highly variable within a county, and in a given county some homes will have concentrations more than 5 times as high as the medians shown here!

Many Factors Determine Radon Exposure Levels

Since radon gas is emitted from rocks and soil, geological conditions play a significant role in the potential for radon exposure. But other factors can be just as or even more important. Ongoing radon research has shown that construction details are very important in determining the concentration of radon gas in indoor air.

For example, a building that has a dirt crawl space will be especially susceptible to radon gas emissions. With nothing covering the soil, there are no barriers to radon emissions. Likewise, a basement with an open sump pit is also providing an unobstructed pathway for radon. Even when a basement has a concrete floor, radon concentrations can be high, thanks to cracks in walls and floors, gaps around access holes for utility and plumbing lines, and radon in the water supply.

Good News Can Follow Bad News

The bottom line is that no matter what it says on a radon map or what radon exposure levels are detected in neighboring houses, it's crucial to have your own home and/or business tested. Since the test is inexpensive or even free in some areas (thanks to local promotions or programs), there's no reason not to do it.

If you get news of some pretty high levels, don't worry. There's good news too: A licensed radon specialist will be able to install an abatement system that exhausts radon gas harmlessly into the atmosphere. Even high radon concentrations can be reduced to negligible levels using well-established radon mitigation techniques.

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