This method allows long-term measurements, but the devices can be affected strongly by soil moisture. In the other method, a sample of soil air is collected from a probe driven into the ground, and the radon in the sample is measured by using electronic equipment. Radon levels vary widely in the top 2 to 3 feet of soil because of variations in soil moisture and the amount of radon that escapes to the atmosphere. Making measurements at 3 feet or deeper avoids many of the problems related to near-surface conditions, but it may be difficult in some soils. The best data on the physical properties of soils are in soil surveys published by the Soil Conservation Service of the U.S. Department of Agriculture in cooperation with state and county officials.
Soil surveys provide descriptions and maps of the soils that underlie the areas described.
Modern soil surveys include permeability data for the mapped soils at varying depths. In older soil reports, no permeability data are given, and soil names and statements regarding internal drainage must be used to estimate permeability. Indoor radon data Indoor radon has been measured in many houses, schools, and commercial buildings across the United States. For the most part, these measurements have been made by private homeowners using passive detection devices purchased at a nearby store, ordered by phone, or ordered through the mail. Radon concentrations in some homes and businesses are being measured by private companies as part of real estate transactions.