R 325.10729 Radionuclides; compositing; substituting gross alpha for radium-226 or uranium.

Rule 729. (1) To fulfill quarterly monitoring requirements for gross alpha particle activity, radium-226, radium-228, or uranium, a supply may composite up to 4 consecutive quarterly samples from a single entry point if analysis is done within 1 year of the first sample. The department considers analytical results from the composited sample as the average analytical result to determine compliance with the MCLs and the future monitoring frequency. If the analytical result from the composited sample is more than half the MCL, then the department may direct the supply to take additional quarterly samples before allowing the supply to sample under a reduced monitoring schedule. (2) A gross alpha particle activity measurement may be substituted for the required radium-226 measurement if the measured gross alpha particle activity does not exceed 5 pCi/l. A gross alpha particle activity measurement may be substituted for the required uranium measurement if the measured gross alpha particle activity does not exceed 15 pCi/l. The gross alpha measurement shall have a confidence interval of 95% (1.65s, where s is the standard deviation of the net counting rate of the sample) for radium-226 and uranium. If a supply uses a gross alpha particle activity measurement instead of a radium- 226 or uranium measurement, or both, then the gross alpha particle activity analytical result shall be used to determine the future monitoring frequency for radium-226 or uranium, or both. If the gross alpha particle activity result is less than detection, then half the detection limit shall be used to determine compliance and the future monitoring frequency.