Geochemical evolution of highly alkaline and saline tank waste plumes during seepage through vadose zone sediments
Leakage of highly saline and alkaline radioactive waste from storage tanks into underlying sediments is a serious environmental problem at the Hanford Site in Washington State. This study focuses on geochemical evolution of tank waste plumes resulting from interactions between the waste solution and sediment. A synthetic tank waste solution was infused into unsaturated Hanford sediment columns (0.2, 0.6, and 2 m) maintained at 70C to simulate the field contamination process. Spatially and temporally resolved geochemical profiles of the waste plume were obtained. Thorough OH neutralization (from an initial pH 14 down to 6.3) was observed. Three broad zones of pore solutions were identified to categorize the dominant geochemical reactions: the silicate dissolution zone (pH > 10), pH-neutralized zone (pH 10 to 6.5), and displaced native sediment pore water (pH 6.5 to 8). Elevated concentrations of Si, Fe, and K in plume fluids and their depleted concentrations in plume sediments reflected dissolution of primary minerals within the silicate dissolution zone. The very high Na concentrations in the waste solution resulted in rapid and complete cation exchange, reflected in high concentrations of Ca and Mg at the plume front. The plume-sediment profiles also showed deposition of hydrated solids and carbonates. Fair correspondence was obtained between these results and analyses of field borehole samples from a waste plume at the Hanford Site. Results of this study provide a well-defined framework for understanding waste plumes in the more complex field setting and for understanding geochemical factors controlling transport of contaminant species carried in waste solutions that leaked from single-shell storage tanks in the past.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 15007689
- Report Number(s):
- PNNL-SA-40820; GCACAK; 820101000; TRN: US0402285
- Journal Information:
- Geochimica et Cosmochimica Acta, Vol. 68, Issue 3; Other Information: PBD: 1 Feb 2004; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BOREHOLES
CARBONATES
CATIONS
CONTAMINATION
DEPOSITION
DISSOLUTION
LIQUID WASTES
PLUMES
RADIOACTIVE WASTES
SEDIMENTS
SILICATES
STORAGE
TANKS
WASTES
WATER
TANK WASTE
CAUSTIC FLUID INTERACTIONS WITH SEDIMENT
HANFORD LEAKS