| Note: This map
of elevated main floor year averages of radon is derived from
87,000
basement test results, obtained from companies
that sell radon detectors.
The conversion to the main-floor average mapped is based on a
random survey of 1100 houses, in which one-year follow-up measurements
were done on the first floors in 200 houses where basement 2-day
screening levels were over 4 pCi/L (picocuries per liter).
Year-average main-floor radon levels for individual houses were
typically 40% of the corresponding basement short-term levels.
They ranged from 10% to 100% of the basement short-term results, with
the distribution peaking at 40%, the average. For the map,
basements with short-term test results over 10 pCi/L were taken to
correspond statistically (though not for any particular house) to
main-floor year averages higher than the EPA 4 pCi/L guideline.
The more measurement results there are for a given zip code, the
better this estimating procedure is. |
