Predicting indoor radon potential has gained in importance even asthe national radon programs began to wane. A cooperative study to produceradon potential maps was conducted by the Environmental Protection Agency(EPA), U.S. Geological Survey (USGS), Department of Energy (DOE), and LawrenceBerkeley Laboratory (LBL) with the latter taking the lead role. They developeda county-wide predictive model based dominantly on the National Uranium ResourceEvaluation (NURE) aerorad data and secondly on geology, both small-scale databases. However, that model breaks down in counties of complex geology anddoes not provide a means to evaluate the potential of an individual home orbuilding site. In this current study, soil-gas radon measurements on a largescale are shown to provide information for estimating radon potential at individualsites sort out the complex geology so that the small-scale prediction indexcan be validated. An example from Frederick County, Maryland indicates a positivecorrelation between indoor measurements and soil-gas data. The method doesnot rely on a single measurement, but a series that incorporate seasonal andmeteorological considerations.
An examination of year-long, in-home radon measurement in Colorado from commercial companies applying typical methods indicates
that considerable variation in precision exsts. This variation can have a substantial impact on any mitigation decisions,
either voluntary or mandated by law, especially regarding property sale or exchange. Both long-term exposure (nuclear track
greater than 90 days), and short-term (charcoal adsorption 4–7 days) exposure methods were used. In addition, periods of continuous
monitoring with a highly calibrated alpha-scintillometer took place for accuracy calibration. The results of duplicate commercial
analysis show that typical results are no better than ±25 percent with occasional outliers (up to 5 percent of all analyses)
well beyond that limit. Differential seasonal measurements (winter/summer) by short-term methods provide equivalent information
to single long-term measurements. Action levels in the U.S. for possible mitigation decisions should be selected so that they
consider the measurement variability; specifically, they should reflect a concentration range similar to that adopted by the
Authors:M. Lahti, L. Killoran, R. Holub, and G. Reimer
Measurement of soil-gas radon (Rn) concentration is an important parameter in estimating soil Rn potential for a building
site. Typically, field methods for grab samples (as contrasted with continuous flow systems) using a protable alpha-scintillometer
only considered222Rn (T1/2= 3.8 d) and ignored220Rn (T1/2=55 s). Now the calculation permits the determination of the concentrations of both isotopes with a single series of readings.
A sample is collected and within 1 minute is introduced into the counting system. A series of 1 minute counts begins immediately
and continues for 10 minutes. If high220Rn concentrations are present, there will be a rapid decay followed by a steady ingrowth of222Rn progeny. If very little220Rn is present, the ingrowth will be seen immediately. In either case, a non-linear least square fitting program from Statgraphics
is used to obtain both concentrations at time zero. When inexact timings ranging from 1 to 30 seconds were imposed on the
measured data, the method proved to be very robust; the biases did not exceed 15 percent.