Coupled Hydrological and Geochemical Studies on Uranium Plumes at Hanford Site: Reactions, Spatial Distributions, Speciation, and Future Mobility
EMSL Project ID
25656
Abstract
Massive quantities (exceeding 85 tons) of U currently reside in the Hanford vadose zone, and will threaten groundwater and the accessible environment for generations to come. Present insufficient knowledge of the current status and transport of the U contaminants make DOE's long-term stewardship and monitored natural attenuation strategies ambiguous. Many knowledge gaps remain to be filled. For instance, compositions of waste solutions initially entering the subsurface, their infiltration rates, the hierarchy of dominant reactions during seepage, current spatial distribution, speciation, and mobility are largely unknown. Gaining these understanding is extremely difficult because of the insufficient historical records, sediment heterogeneity, and the complexity of the strongly coupled hydrological and geochemical processes. This proposed investigation attempts to obtain a comprehensive understanding of the main geochemical reactions of U waste plumes, the related current U spatial distribution and speciation along the flow paths, and future mobilities for the varieties of U-containing waste streams that were discharged at the Hanford. In this project, tests are designed to determine U spatial distribution and chemical and mineralogical status along the plume paths at the time of contamination as well as upon later redistribution. We will simulate the waste solution seepage events in columns that are sectioned/profiled after plume migration to different distances. In this project, columns will be constructed from individual segments joined with quick-release sealed sleeves. Uncontaminated Hanford formation sediment at the field moisture content will be used to pack the columns. These columns will be packed homogeneously and vertically oriented. Columns simulating waste pond and crib seepage will be run at room temperature. The tank leak simulations will be run in hot-water baths up to 75°C. Synthetic waste solutions will be injected into the columns at the desired flow rate. When the effluent is just detected emerging at the outlet, flow will be terminated and the column segments will be immediately detached. The pore liquids will be immediately extracted by vacuum from each segment. The extracted segment liquids will be analyzed for their pH, electrical conductivity, turbidity, and their major ion chemistry (ICP and IC). U concentrations will be analyzed using a kinetic phosphorescence analyzer (KPA). The suspended colloids will be analyzed using SEM, TEM, and μ-XRD. U speciation will be determined by time-resolved laser fluorescence spectroscopy, and EXAFS spectroscopy if necessary and achievable.
This project is currently funded by the DOE ERSP program. The research team of this project includes Jiamin Wan, Tetsu Tokunaga, and Nicolas Spycher at Lawrence Berkeley national Laboratory (LBNL) and John Zachara, Zheming Wang, and James McKinley at PNNL. In this research, all the tasks involve batch and column work will be performed at LBNL. Small sets of samples will be packaged according to appropriate protocols (e.g. non-dispersible procedure for uranium analysis) and sent to EMSL for analysis. μ-XRD and EXAFS spectroscopy analysis of sorbed and precipitated U phases will be performed at other national facilities such as the PNC-CAT at Argonne National Laboratory or the Stanford Synchrotron Radiation Laboratory.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-05-25
End Date
2009-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Wan J, Y Kim, TK Tokunaga, Z Wang, S Dixit, CI Steefel, E Saiz, M Kunz, and N Tamura. 2009. "Spatially Resolved U(VI) Partitioning and Speciation: Implications for Plume Scale Behavior of Contaminant U in the Hanford Vadose Zone." Environmental Science & Technology 43(7):2247-2253.