A simplified probabilistic approach to cover thickness design

Radon emissions from uranium mill tailings have long been recognized as a potential health hazard. As a result, the EPA established standards for the maximum average release rate for radon-222 of 20 picocuries per square meter per second, averaged over the entire tailings surface, for inactive uranium tailings impoundments. The management procedure suggested to reduce radon emissions of inactive mill tailings is to cover the tailings with earthen materials or a combination of earthen materials and cement, asphalt, etc. Recent research has shown that the variability of the parameters used in solving the radon emanation model may cause large variations in the results; however, how this variability might be included in an engineering analysis was not shown. Probability allows the variation of a parameter, both as a result of sampling and as a result of measurement, to be taken into account in the analyses and provides a method for interpreting the results. This paper introduces two simplified probability methods that may be used with the analytical approaches currently in use for determination of radon flux and optimal cover thickness