This chapter reviews published transfer-coefficient measurements. In addition, it performs a distributional analysis in the same manner as Nazaroff and others (1987) and compares the results.

Measurements Of Transfer Coefficients

There are only a few measurements of transfer coefficients (from water to air) in the literature, and most of them refer to a limited number of geographic areas. Thus, there is considerable uncertainty in the extrapolation of the resulting distribution to the entire housing stock of the United States. The earliest reports of the measurements of the transfer coefficient were made by Gesell and Prichard (1980) and Castrèn and others (1980). They assumed that all the indoor radon was due to radon in the water, so the transfer coefficient was overestimated. Gesell and Prichard took measurements in apartments, where soil-derived radon is likely to contribute little to measured values. Castrèn's measurements, taken in houses in Finland, made the same assumption and are thus not likely to be useful. The actual values for the dwellings in Finland were not reported, and the data are no longer available (Castrèn, private communication, 1997).

McGregor and Gourgon (1980) measured Ca and Cw in six conventional residences, five trailers, and two schools in Nova Scotia, Canada. Only upper limits for the transfer coefficients can be estimated, because ventilation rates and water-use patterns were not determined. They found values of 0.032–0.24 × 10-4 for the trailers and 0.038–0.52 × 10-4 for the dwellings. The values are lower than many of the reported coefficients. Because the ventilation and water-use rates are not available, it is not possible to know whether the values are low as a result of high ventilation rates, low water use, or some combination of the two. Owing to the uncertainty in separating the contributions of soil gas and drinking water to the indoor radon concentrations, the transfer-coefficient values only for the five trailers have been included in the committee's estimated distribution of values.

During the late 1970s and throughout the 1980s, Hess and coworkers (1990; 1987b; 1987a; 1982) measured the transfer coefficients in a series of houses across Maine. In all, measurements were made in about 70 houses. They have used an approach that they term the ''burst method.'' Measurements are made during a 2-h period when a series of water-use activities are performed. The idea is to use as much water during this 2-h period as would typically be used over a 24-h period. Radon is also monitored over a second 24-h period during which the residents use water according to their normal daily routine. The water-use activities during the second 24-h period were recorded. Ventilation rates were also measured directly.

As part of a study of the effectiveness of radon-mitigation methods (Deb 1992), concentrations of radon in air and water were measured before and after the initiation of a water treatment to reduce the concentration of radon in the



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