A Field-Scale Reactive Transport Model for U(VI) Migration Influenced by Coupled Multirate Mass Transfer and Surface Complexation Reactions

Journal Article · Thu May 06 04:00:00 EDT 2010 · Water Resources Research, 46:Art. No. W05509

DOI:https://doi.org/10.1029/2009WR008168· OSTI ID:988635

Ma, Rui; Zheng, Chunmiao; Prommer, Henning; Greskowiak, Janek; Liu, Chongxuan; Zachara, John M; Rockhold, Mark L

A field-scale reactive transport model was developed that incorporates laboratory-characterized U(VI) surface complexation reactions (SCR) and multi-rate mass transfer processes, and field-measured hydrogeochemical conditions at Department of Energy, Hanford 300A site, Washington, where an Integrated Field Research Challenge project is ongoing. The model was used to assess the importance of multi-rate mass transfer processes on sorption-retarded U(VI) reactive transport at the 300A site and to evaluate the effect of variable geochemical conditions on U(VI) plume migration caused by dynamic river stage fluctuations at the east side of the site. Model simulations revealed a complex spatio-temporal variations of groundwater geochemistry that affects U(VI) speciation, adsorption, and plume migration. In general, the river water intrusion enhances uranium adsorption and lowers groundwater aqueous uranium concentration as a result of river water dilution that decreases aqueous carbonate concentration, which subsequently weakens aqueous U(VI)-carbonate complexation and enhances U(VI)-surface complexation. The simulations also found that SCR-retarded U migration becomes more dynamic and more in sync with the groundwater flow field when multi-rate mass transfer processes are involved. Strong U(VI) adsorption was simulated at the 300A site based on the field-measured hydrogeochemical conditions, suggesting a slow dissipation of U(VI) plume, a phenomenon consistent with the observation at the site. Uranium breakthrough curves at selected observation points and the mass changes over time in the simulation indicate that uranium adsorption/desorption never attains steady state as a result of both the highly dynamic flow field and the chemistry variations caused by river water intrusion. Thus, the multi-rate SCM model appears to be a crucial feature for future reactive transport simulations of uranium at the 300A site.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 988635
• Report Number(s): PNNL-SA-67581; KP1702030
• Journal Information: Water Resources Research, 46:Art. No. W05509, Journal Name: Water Resources Research, 46:Art. No. W05509 Vol. 46; ISSN WRERAQ; ISSN 0043-1397
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
BENCH-SCALE EXPERIMENTS
FLOW MODELS
GEOCHEMISTRY
GROUND WATER
HANFORD RESERVATION
HYDROLOGY
RADIONUCLIDE MIGRATION
SORPTION
URANIUM
URANIUM COMPLEXES
mass transfer
uranium
surface complexation
reactive transport
Hanford 300 Area