Relevance of radon progeny measurements for the assessment of inhalation doses in groundwater utilities

The high radon concentrations measured in the indoor air of groundwater facilities and the prevalence of the problem have been known for several years. Unlike in other workplaces, in groundwater plants, radon is released into the air from the water treatment processes. During the measurements of this study, the average radon concentrations varied from 500 to 8800 Bq m-3. In addition, the indoor air of the treatment plants is filtered and there are no significant internal aerosol sources. However, only a few published studies on groundwater plants have investigated the properties of the radon progeny aerosol, such as the equilibrium factor (F) or the size distribution of the aerosol, which are important for assessing the dose received by workers. Moreover, the International Commission on Radiological Protection has not provided generic aerosol parameter values for dose assessment in groundwater treatment facilities. In this study, radon and radon progeny measurements were carried out at three groundwater plants. The results indicate surprisingly high unattached fractions (fp = 0.27-0.58), suggesting a low aerosol concentration in indoor air. The corresponding F values were 0.09-0.42, well below those measured in previous studies. Based on a comparison of the effective dose rate calculations, either the determination of the fp or, with certain limitations, the measurement of radon is recommended. Dose rate calculation based on the potential alpha energy concentration alone proved unreliable.