Assessment of the radon contribution from mining sites to the geogenic environment

An issue associated with NORM in mining areas is the mean radon exposure assignable to surface mining residues. Outdoor radon decay chain concentrations (at breathing height), compared with elevated indoor levels, are relatively low and they fluctuate widely with time and location. Differentiating a mining contribution to the geogenic radon exposure is a challenging metrological task, particularly in the later stages of remediation. The activity concentrations of radon decay chain members can be determined accurately with good time resolution down to low outdoor concentrations using (quasi-) continuous on-filter concentration measurements. Such measurements showed continuous diurnal concentration cycles ranging from a general minimum concentration to a widely varying maximum for different cycles. Correlation with chain activity ratios and diurnal wind velocity clarifies the build-up of concentrations near the ground during minimal vertical air exchange, above an otherwise generally low concentration over the height of the atmosphere. Ways of assessing radon exhalation and of the exhalation ratio 222Rn/220Rn are indicated, and these may provide a better measure for assessing possible mining influence on local radon exposure. (author)