Identifying the Sources of Subsurface Contamination at the Hanford Site in Washington using High-Precision Uranium Isotopic Measurements

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• 作者：John N. Christensen ; P. Evan Dresel ; Mark E. Conrad ; Kate Maher ; and Donald J. DePaolo
• 刊名：Environmental Science & Technology
• 出版年：2004
• 出版时间：June 15, 2004
• 年：2004
• 卷：38
• 期：12
• 页码：3330 - 3337
• 全文大小：172K
• 年卷期：v.38,no.12(June 15, 2004)
• ISSN：1520-5851

文摘

In the mid-1990s, a groundwater plume of uranium (U)was detected in monitoring wells in the B-BX-BY WasteManagement Area at the Hanford Site in Washington. Thisarea has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rodprocessing. Using multiple-collector ICP source magneticsector mass spectrometry, high-precision uraniumisotopic analyses were conducted of samples of vadosezone contamination and of groundwater. The isotope ratios²³⁶U/²³⁸U, ²³⁴U/²³⁸U, and ²³⁸U/²³⁵U are used to distinguishcontaminant sources. On the basis of the isotopic data, thesource of the groundwater contamination appears to berelated to a 1951 overflow event at tank BX-102 that spilledhigh-level U waste into the vadose zone. The U isotopicvariation of the groundwater plume is a result of mixingbetween contaminant U from this spill and naturalbackground U. Vadose zone U contamination at tankB-110 likely predates the recorded tank leak and can beruled out as a significant source of groundwatercontamination, based on the U isotopic composition. Thelocus of vadose zone contamination is displaced from theinitial locus of groundwater contamination, indicatingthat lateral migration in the vadose zone was at least 8times greater than vertical migration. The time evolution ofthe groundwater plume suggests an average U migrationrate of ~0.7-0.8 m/day showing slight retardation relative toa groundwater flow of ~1 m/day.