Interlaboratory Comparison of <sup>226</sup>Ra and <sup>228</sup>Ra Activity Concentrations in Groundwater and Surface Water
2022
David B. Levy
<sup>226</sup>Ra and <sup>228</sup>Ra are typically monitored for groundwater and surface water compliance at legacy U mining and milling sites. Groundwater monitoring results for combined Ra (<sup>226</sup>Ra + <sup>228</sup>Ra) reported by the existing contract laboratory at a former U mine and mill Site (Converse County, WY, USA) have been highly variable and with increasing trends at the Site compliance and background wells since the method was changed in 2005. Sample reanalysis has indicated poor reproducibility and significant analytical error in <sup>228</sup>Ra measurements. An interlaboratory comparison was conducted to evaluate the potential causes of the high variability and analytical error. Two different methods were used for <sup>226</sup>Ra (M903.0 and M903.1) and <sup>228</sup>Ra (M904.0 and Ra-05). <sup>226</sup>Ra results were less variable compared to <sup>228</sup>Ra, and <sup>228</sup>Ra data from the existing laboratory were qualified as estimated with high bias due to detection of <sup>228</sup>Ra in the field blank. Compliance with the <sup>226</sup>Ra + <sup>228</sup>Ra groundwater standard was either met or not met, depending on which laboratory conducted the analyses. Specific laboratory techniques, rather than the analytical method, are contributing to elevated <sup>228</sup>Ra values being reported. It was recommended that samples whose <sup>226</sup>Ra + <sup>228</sup>Ra results exceed the Site standard in the future be reanalyzed by the existing laboratory with a sample split also being sent to an outside laboratory for confirmatory analysis.
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