The Radionuclides rule was revised on December 8, 2003, for community public water systems (CWS). This rule covers both naturally occurring and man-made parameters. All CWSs are required to perform quarterly testing to satisfy the initial monitoring for gross alpha, radium-226, radium-228, and uranium. Compliance and future monitoring frequency will be based on the results of the annual average of this quarterly monitoring. CWSs utilizing a source of supply deemed as “vulnerable” are required to test for man-made parameters.