Utilities in many parts of the United States are challenged by compliance issues associated with the federal Radionuclide Rule, in large part due to the performance limitations associated with the existing approved analytical methods for radionuclides, such as gross alpha activity, radium-226 (226Ra), and radium-228 (228Ra).

Source:: http://www.wateronline.com/doc/awwa-releases-radionuclides-methods-guidance-0001?atc~c=771+s=773+r=001+l=a