Understanding the Relationship between Gross Alpha/Beta and Radionuclide-Specific Testing in Drinking Water

During the initial screening of their water supplies for radioactivity, members of the public often have questions about high gross alpha/beta results, but there is not a specific radionuclide of concern identified. In an ongoing groundwater testing project in Whitehorse, Yukon, uranium concentrations that correspond to guidance levels (e.g., 20-30 μg L -1 ) were found to cause exceedances of the gross alpha screening criteria (e.g., 0.5 Bq L -1 ). Ninety-five percent of these samples were also observed to have a 234 U/ 238 Uactivity ratio >1, which puts caution in trying to apply a universal correction factor for the gross alpha activity. These results will help inform the next revision of Canada's drinking water guidelines for radiological parameters and the type of water testing considerations that could be communicated to the Canadian public.