Identifying the sources of subsurface contamination at the Hanford Site in Washington using high-precision uranium isotopic measurements

被引:38
作者
Christensen, JN
Dresel, PE
Conrad, ME
Maher, K
Depaolo, DJ
机构
[1] Lawrence Berkeley Natl Lab, Ctr Isotope Geochem, Berkeley, CA 94720 USA
[2] Pacific NW Natl Lab, Richland, WA 99352 USA
[3] Univ Calif Berkeley, Dept Earth & Planetary Sci, Berkeley, CA 94720 USA
关键词
D O I
10.1021/es034700q
中图分类号
X [环境科学、安全科学];
学科分类号
08 ; 0830 ;
摘要
In the mid-1990s, a groundwater plume of uranium (U) was detected in monitoring wells in the B-BX-BY Waste Management Area at the Hanford Site in Washington. This area has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rod processing. Using multiple-collector ICP source magnetic sector mass spectrometry, high-precision uranium isotopic analyses were conducted of samples of vadose zone contamination and of groundwater. The isotope ratios U-236/U-238, U-234/U-238, and U-231/U-235 are used to distinguish contaminant sources. On the basis of the isotopic data, the source of the groundwater contamination appears to be related to a 1951 overflow event at tank BX-102 that spilled high-level U waste into the vadose zone. The U isotopic variation of the groundwater plume is a result of mixing between contaminant U from this spill and natural background U. Vadose zone U contamination at tank B-110 likely predates the recorded tank leak and can be ruled out as a significant source of groundwater contamination, based on the U isotopic composition. The locus of vadose zone contamination is displaced from the initial locus of groundwater contamination, indicating that lateral migration in the vadose zone was at least 8 times greater than vertical migration. The time evolution of the groundwater plume suggests an average U migration rate of similar to0.7-0.8 m/day showing slight retardation relative to a groundwater flow of similar to1 m/day.
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页码:3330 / 3337
页数:8
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