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#### Use-Weighted Transfer Efficiency

The transfer efficiency is the fraction of the radon in the water that is released to the air during the activities that use water (showering, clothes-washing or dishwashing, and so on). The earliest values of the transfer efficiencies have been previously reported by EPA (Becker III and Lachajczyk 1984) and Nazaroff and others (1987). The transfer efficiency of showerheads has been measured by Fitzgerald and others (1997) and by Bernhardt and Hess (1996), who found values quite similar to those used by Nazaroff and others. The transfer efficiency for each activity was combined with the water use data to yield a use-weighted transfer coefficient. A geometric mean of 0.52 with a GSD of 1.3 was obtained.

#### Transfer-Coefficient Model Results

The new input values and the earlier values of Nazaroff and others are compared in table 3.1. Both the dwelling volume and the water use per occupant are greater in the committee's analysis. The transfer efficiency has remained essentially the same. The resulting geometric mean value of the transfer coefficient has risen to 0.55 × 10-4 with a GSD of 3.5. The arithmetic average transfer coefficient is estimated at 1.2 × 10-4, it is considerably higher than the geometric mean value because of the high degree of skewness of the distribution.

### Conclusions

There is reasonable agreement between the average value of the transfer coefficient estimated by the model and the value calculated from the measured data.

Table 3.1

Lognormal Distributions of Parameters in Transfer-Coefficient Calculation

 Nazaroff and others (Nazaroff and others 1987) Committee Parameter GeometricMean Geometric Standard Deviation Geometric Mean Geometric Standard Deviation Dwelling volume per occupant (m3 person-l) 99 1.9 115 2.0 Ventilation rate 0.68 2.0 0.77 or 1.07 2.3 Transfer efficiency water to air 0.55 1.1 0.52 1.3 Water use per capita (m3 person-1 h-l) 7.9 × 10-3 1.6 9.4 × 10-3 1.8 Geometric mean transfer coefficient 6.5 × 10-5 2.8 5.5 × 10-5 or 3.9 × l0-5 3.5

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