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Title: Uranium Bioreduction Rates across Scales: Biogeochemical Hot Moments and Hot Spots during a Biostimulation Experiment at Rifle, Colorado

We aim to understand the scale-dependent evolution of uranium bioreduction during a field experiment at a former uranium mill site near Rifle, Colorado. Acetate was injected to stimulate Fe-reducing bacteria (FeRB) and to immobilize aqueous U(VI) to insoluble U(IV). Bicarbonate was coinjected in half of the domain to mobilize sorbed U(VI). We used reactive transport modeling to integrate hydraulic and geochemical data and to quantify rates at the grid block (0.25 m) and experimental field scale (tens of meters). Although local rates varied by orders of magnitude in conjunction with biostimulation fronts propagating downstream, field-scale rates were dominated by those orders of magnitude higher rates at a few selected hot spots where Fe(III), U(VI), and FeRB were at their maxima in the vicinity of the injection wells. At particular locations, the hot moments with maximum rates negatively corresponded to their distance from the injection wells. Although bicarbonate injection enhanced local rates near the injection wells by a maximum of 39.4%, its effect at the field scale was limited to a maximum of 10.0%. We propose a rate-versus-measurement-length relationship (log R' = -0.63
Authors:
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Publication Date:
OSTI Identifier:
1168880
Report Number(s):
PNNL-SA-106276
KP1702030
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science & Technology, (17):10116-27
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
FEED MATERIALS PLANTS; SIMULATION; HYDRAULICS Uranium Bioreduction; uranium mill; Rifle, CO; modeling; hydraulic; geochemical