Characterization of Vadose Zone Sediment: Borehole 299-E33-45 Near BX-102 in the B-BX-BY Waste Management Area

Abstract

Executive SummaryThis report was revised in September 2008 to remove acid-extractable sodium data from Table 4.22. The data was removed due to potential contamination introduced during the acid extraction process. The remaining text is unchanged from the original report issued in 2002.The overall goal of the Tank Farm Vadose Zone Project, led by CH2M HILL Hanford Group, Inc., is to define risks from past and future single-shell tank farm activities. To meet this goal, CH2M HILL Hanford Group, Inc., asked scientists from Pacific Northwest National Laboratory to perform detailed analyses on vadose zone sediments from within Waste Management Area B-BX-BY. This report is the first in a series of four reports to present the results of these analyses. Specifically, this report contains all the geologic, geochemical, and selected physical characterization data collected on vadose zone sediment recovered from borehole 299-E33-45 installed northeast of tank BX-102.This report also presents interpretation of the data in the context of the sediment lithologies, the vertical extent of contamination, the migration potential of the contaminants, and the likely source of the contamination in the vadose zone, perched water and groundwater east of the BX tank farm. The information presented in this report supports the Waste Management Area B-BX-BY field investigation report prepared by CH2M HILL Hanford Group, Inc. (a) Overall, the analyses identified common ion exchange and heterogeneous (solid phase-liquid solute) precipitation reactions as two mechanisms that influence the distribution of contaminants within that portion of the vadose zone affected by tank liquor. Significant indications of caustic alteration of the sediment mineralogy or porosity were not observed, but slightly elevated pH values between the depths of 79 to 141 ft below ground surface (bgs) were observed. X-ray diffraction measurements indicate no evidence of mineral alteration or precipitation resulting from the interaction of the tank liquor with the sediment. However, no samples were studied by scanning electron microscopy, a more sensitive technique for searching for faint evidence of caustic attack.The analyses do not firmly suggest that the source of the contamination in the groundwater east of the BX tank farm is the 1951 overfill event at tank BX-102. However, evidence is convincing that the fluids from the overfill event are present in the vadose zone sediments at borehole 299-E33-45 to a depth of 170 ft bgs.The near horizontally bedded, northeasterly dipping sediment likely caused horizontal flow of the migrating contaminants. At borehole 299-E33-45, there are several fine-grained lenses within the Hanford H2 unit at 74.5, 120, and 167 ft bgs that likely cause some horizontal spreading of percolating fluids. The 21-ft thick Plio-Pleistocene fine-grained silt/clay unit is also an important horizontal flow conduit as evidenced by the perched water zone between 227 and 232 ft bgs.The following are the key findings of the detailed characterization o...

Influence of calcium on microbial reduction of solid phase uranium(VI)

“…This study demonstrated that calcium can significantly affect the rates of U(VI) dissolution, microbial reduction, and their coupling through aqueous U(VI) complexation reaction in bicarbonate solutions. Calcium is a common chemical component in groundwater and has a concentration range of 0.5-50 mmol/L and a medium of about 5 mmol/L in the Hanford porewater and groundwater (Serne et al, 2002). Speciation calculations and spectroscopic analyses indicated that either UO 2 (CO 3 ) 4À 3 or Ca 2 UO 2 (CO 3 ) 3 could dominate the aqueous U(VI) speciation depending on the chemical composition, pH, and calcium concentration in the Hanford pore and groundwaters (Dong et al, 2005;Wang et al, 2004).…”

Microscopic reactive diffusion of uranium in the contaminated sediments at Hanford, United States

“…This was the largest recorded single release of U(VI) to the subsurface at the Hanford site. Subsurface coring [ Serne et al , 2002] and U isotope analysis [ Christensen et al , 2004] revealed that the overfill event resulted in a large vadose plume that migrated to groundwater (250 m wide and 900 m long). Characterization of contaminated vadose zone sediments with X‐ray absorption spectroscopy, synchrotron X‐ray diffraction, laser induced fluorescence spectroscopy, and energy dispersive spectroscopy revealed that the sorbed uranium was hexavalent and precipitated as uranyl silicates, most likely as sodium boltwoodite [ Catalano et al , 2004; McKinley et al , 2006; Wang et al , 2005].…”

DOE FG02-03ER63557: Final Technical Report: Reactivity of Primary Soil Minerals and Secondary Precipitates Beneath Leaking Hanford Waste Tanks

“…The concentrations of uranium and silicon in the tank solution as well as those in contaminated and uncontaminated vadose zone sediments as determined via pore water analysis (7,8) are presented in Table 12. Uranium concentrations decrease from 10 -1 M in tank solutions to 1.910 -3 M in contaminated pore waters, but remain 10,000 times higher than background levels.…”

“…Table 12. Uranyl and aqueous silica concentrations for solutions relevant to Hanford vadose zone sediments (7,8). The pH of uncontaminated groundwater, though unreported, is likely to be near neutral to mildly basic.…”