In 2000, the U.S. Environmental Protection Agency (USEPA) promulgated a revised final regulation for radionuclides in drinking water. Thisrule retained the maximum contaminant level (MCL) at 5 pCi/L for combined Ra226/Ra228 butrequires separate monitoring requirements for Ra228. Previously, analysis for Ra228 wasrequired only when Ra226 measurement was greater than 3 pCi/L.With the promulgation of the Radionuclide Rule and completion of the first round of requiredmonitoring, many utilities throughout the country who were previously in compliance havefound themselves now uncertain of their compliance status as a result of the added compliancemonitoring parameters. In some regions radionuclide activities from groundwater supplies at thesame site appear to vary by more than two fold over time. This may be due to natural variabilityin concentrations of some of the radionuclides, but it is also likely due to issues related to methodand laboratory variability. To address this issue MWH evaluated compliance data from anumber of utilities who have done repeat monitoring over time and then designed and conducteda blind interlaboratory evaluation of performance for routine samples among 5 multi-statecertified labs. This interlab study was designed to address both intralab variation among blindreplicate samples at levels near the MCL for radium 226, radium 228 and gross alpha activity,along with assessing laboratory precision and accuracy, and equally important, to examine theinterlab variability among well qualified laboratories for the same samples. Participatinglaboratories were not aware that the study was a blind proficiency test, so samples wereprocessed in the same way that normal compliance samples were processed. A total of 14samples were submitted to each laboratory in several discrete batches. Each batch consisted ofseveral replicates and also some Youden pairs to determine the single lab precision at applicableconcentration ranges for compliance assessment and historical data.Results of the interlab study demonstrate that while Radium-226 measurements appear to be bothaccurate and precise, even at low levels, radium-228 analysis and gross alpha is much lessrugged, resulting in potential false positives and false negatives for compliance determinations. Includes 8 references, tables, figures.
