The accompanying table gives the results of 48,000 short-term basement radon measurements in homes in Wisconsin, listed by county and zip code.
These are basement results. However, the U.S. EPA recommends testing the lowest lived-in levels of houses, not normally basements. The EPA guideline is 4 pCi/L for the radon exposures, as determined by year-average main floor measurements, unless the basement is lived-in significantly, more than seven hours per week, for example.
An estimate of the percentage of houses in a given zip code that are above the EPA guideline, as a main floor year-average radon level, can be made from the table’s fourth column (number of basements at greater that 10 pCi/L) divided by the second column (total number). This procedure is based on a study in which one-year follow-up measurements were done on the first floors in houses where basement 2-day screening levels were over 4 pCi/L in a 1987 Wisconsin-U.S.EPA random survey of 1100 houses. The study showed the year main floor radon test results ranged from 10% to 100% of the corresponding basement short-term results, with most clustered near the average, 40%. So basements over 10 pCi/L correspond, statistically in the table (though not for any particular house) to main-floor year averages over the EPA 4 pCi/L guideline. The more measurements there are in the table for a given zip code, the more representative this estimating procedure is.
Far more radon measurements than these listed have been made in the state. The data tabulated were obtained from some companies that sell radon detectors, and are not a random survey. None-the-less, the table indicates that elevated radon occurs in most regions of the state. Whether the chance of elevated radon is one per cent or twenty percent, the conclusion is the same: every home should be tested.
Wisconsin radon test results by County and Zip Code
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