Geochemical, mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer

Journal Article · Wed Aug 01 00:00:00 EDT 2012 · Applied Geochemistry

DOI:https://doi.org/10.1016/j.apgeochem.2012.04.013· OSTI ID:1064451

Campbell, K. M. ^[1]; Kukkadapu, R. K. ^[2]; Qafoku, N. P. ^[2]; Peacock, A. D. ^[3]; Lesher, E. ^[4]; Williams, K. H. ^[5]; Bargar, J. R. ^[6]; Wilkins, M. J. ^[7]; Figueroa, L. ^[4]; Ranville, J. ^[4]; Davis, J. A. ^[8]; Long, P. E. ^[9]

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1. U.S. Geological Survey, Boulder, CO and Menlo Park, CA (United States); Laurence Berkeley National Laboratory
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
3. Haley and Aldrich, Oak Ridge, TN (United States)
4. Colorado School of Mines, Golden, CO (United States)
5. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
6. Stanford Synchrotron Radiation Lab., Menlo Park, CA (United States).
7. Univ. of California, Berkeley, CA (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
8. U.S. Geological Survey, Menlo Park, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
9. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO₄ reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.

• Research Organization: U.S. Geological Survey, Boulder, CO (United States)
• Sponsoring Organization: USDOE SC Office of Biological and Environmental Research (SC-23)
• DOE Contract Number: SC0000773
• OSTI ID: 1064451
• Report Number(s): DOE--SC0000773; PII: S0883292712001187
• Journal Information: Applied Geochemistry, Journal Name: Applied Geochemistry Journal Issue: 8 Vol. 27; ISSN 0883-2927
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
aquifer
contamination
uranium