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Title: Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry

Journal Article · · Environmental Science and Technology
 [1];  [2];  [1];  [1];  [3];  [1];  [4];  [5];  [3];  [6];  [6];  [1]
  1. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL)
  2. SLAC National Accelerator Lab., Menlo Park, CA (United States). Stanford Synchrotron Radiation Lightsource (SSRL); Stanford Univ., CA (United States). Dept. of Environmental Earth System Science
  3. Stanford Univ., CA (United States). Dept. of Environmental Earth System Science
  4. Univ. de Lorraine, Vandœuvre-lès-Nancy (France)
  5. Stanford Univ., CA (United States). Dept. of Geological Sciences
  6. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Earth Sciences Division

The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. In conclusion, we show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

Research Organization:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
AC02-05CH11231
OSTI ID:
1471003
Journal Information:
Environmental Science and Technology, Vol. 50, Issue 1; ISSN 0013-936X
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 57 works
Citation information provided by
Web of Science

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Cited By (8)

Thermodynamically controlled preservation of organic carbon in floodplains journal May 2017
Uranium mobility and accumulation along the Rio Paguate, Jackpile Mine in Laguna Pueblo, NM journal January 2017
Evidence for Microbial Mediated NO3− Cycling Within Floodplain Sediments During Groundwater Fluctuations journal July 2019
Relations of Uranium Enrichment and Carbonaceous Debris within the Daying Uranium Deposit, Northern Ordos Basin journal January 2019
Abundance and Distribution of Microbial Cells and Viruses in an Alluvial Aquifer journal July 2017
Metatranscriptomic Analysis Reveals Unexpectedly Diverse Microbial Metabolism in a Biogeochemical Hot Spot in an Alluvial Aquifer journal January 2017
Paired RNA Radiocarbon and Sequencing Analyses Indicate the Importance of Autotrophy in a Shallow Alluvial Aquifer journal July 2019
Uranium(IV) adsorption by natural organic matter in anoxic sediments journal January 2017

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