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

Journal Article · Wed May 23 00:00:00 EDT 2012 · Applied Geochemistry

DOI:https://doi.org/10.1016/j.apgeochem.2012.04.013· OSTI ID:1047358

Campbell, Kate M; Kukkadapu, Ravi K; Qafoku, Nikolla; Peacock, Aaron D; Lesher, E; Williams, Kenneth H; Bargar, John R; Wilkins, Michael J; Figueroa, Linda A; Ranville, James; Davis, James; Long, Philip E

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, we examined several cores from a region of naturally occurring reducing conditions in a uranium-contaminated aquifer (Rifle, CO). Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for uranium and iron content, oxidation state, and mineralogy, reduced sulfur phases, and solid phase organic carbon content using a suite of analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase uranium concentrations were higher in the naturally reduced zone, with a high proportion of the uranium present as reduced U(IV). The sediments were also elevated in reduced sulfur phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and sulfate reduction 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 concentration of solid phase organic carbon and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic carbon 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 carbon for maintaining reducing conditions and uranium immobilization.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1047358
• Report Number(s): PNNL-SA-85044; APPGEY; 34002; KP1704020; TRN: US201216%%217
• Journal Information: Applied Geochemistry, Vol. 27, Issue 8; ISSN 0883-2927
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
AQUIFERS
BIOMASS
CARBON
CORRELATIONS
GEOCHEMISTRY
IRON
METALS
MINERALOGY
NATURAL ATTENUATION
PERMEABILITY
POTENTIALS
RADIOISOTOPES
REDUCTION
REDUNDANCY
SEDIMENTS
SEMIMETALS
SIZE
SOLIDS
SULFATES
SULFUR
TRANSPORT
URANIUM
VALENCE
ZONES
Environmental Molecular Sciences Laboratory