water. Measurements of radon in air and water use were made in each of 119 houses before and after treatment. In two homes one measurement was unavailable; therefore, values for only 117 homes were used. In two of the communities, concentrations of radon in water were generally below 185,000 Bq m-3; thus, the increment of airborne radon was small and difficult to measure accurately. In addition, not all of the before-and-after measurements were made in comparable seasons, so there might be substantial errors in many of the measurements. However, in a number of the homes, the measurement after treatment of the water was higher than the measurement before the reduction in waterborne radon. It is possible to estimate the transfer coefficient from the before-and-after radon concentration measurements appropriately weighted for the measured water use. However, some of the values are negative and therefore invalid. To incorporate all of the data into the distribution of values, the measurements for each home were averaged. Examination of the transfer coefficient as a function of the radon concentration in water before treatment suggested that choosing homes where the untreated-water concentrations were greater than 81,000 Bq m-3 would avoid most of the invalid results. Use of this criterion resulted in 31 values, which included only three negative ones.

Lawrence and others (1992) made a series of measurements in 29 homes in Conifer, Colorado. The air volume of each home and the volume of water used were determined, and the air and water 222Rn concentrations were measured. However, ventilation rates were not measured, so the authors only estimated the minimum and maximum values of airborne radon resulting from release from the water used in the homes. Thus, minimum and maximum values of the transfer coefficients could be calculated from the results given in their paper. To use the resulting information in the overall distribution of measured transfer coefficients, a best estimate of the transfer coefficient was calculated by taking the square root of the product of the maximum and minimum values.

Chittaporn and Harley (1994) have measured the water-use contribution to airborne radon in an energy-efficient home in New Jersey. They estimate a transfer coefficient for the home at 1.7 × 10-5.

The resulting distribution of values of the measured transfer coefficient is shown in figure 3.1. The median is 4.5 × 10-5, and the average is 8.7 × 10-5 with a standard deviation of 1.2 × 10-4. When plotted on a logarithmic scale, the central portion of the distribution is fairly linear and thus the geometric properties have also been calculated. The geometric mean is 3.8 × 10-5 with a geometric standard deviation (GSD) of 3.3.

Modeling Of Transfer Coefficient

The model of Nazaroff and others (1987) is used here to estimate the central values of the distribution of transfer coefficient. As in that report, it is assumed that the underlying distributions of the house volumes, ventilation rates, water



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