Distribution of Uranium Contamination in Weathered Fractured Saprolite/Shale and Ground Water
- ORNL
The objective of this study was to determine how structure, stratigraphy, and weathering influence fate and transport of contaminants (particularly U) in the ground water and geologic material at the Department of Energy (DOE) Environmental Remediation Sciences Department (ERSD) Field Research Center (FRC). Several cores were collected near four former unlined adjoining waste disposal ponds. The cores were collected, described, analyzed for U, and compared with ground water geochemistry from surrounding multilevel wells. At some locations, acidic U-contaminated ground water was found to preferentially flow in small remnant fractures weathering the surrounding shale (nitric acid extractable U [U{sub NA}] usually < 50 mg kg{sup -1}) into thin (< 25 cm) Fe oxide-rich clayey seams that retain U (U{sub NA} 239 to 375 mg kg{sup -1}). However, greatest contaminant transport occurs in a 2 to 3 m thick more permeable stratigraphic transition zone located between two less permeable, and generally less contaminated zones consisting of (i) overlying unconsolidated saprolite (U{sub NA} < 0.01 to 200 mg kg{sup -1}) and (ii) underlying less-weathered bedrock (UNA generally < 0.01 to 7 mg kg{sup -1}). In this transition zone, acidic (pH < 4) U-enriched ground water (U of 38 mg L{sup -1}) has weathered away calcite veins resulting in greater porosity, higher hydraulic conductivity, and higher U contamination (U{sub NA} 106 to 745 mg kg{sup -1}) of the weathered interbedded shale and sandstone. These characteristics of the transition zone produce an interval with a high flux of contaminants that could be targeted for remediation.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 989668
- Journal Information:
- Journal of Environmental Quality, Vol. 35, Issue 1; ISSN 0047-2425
- Country of Publication:
- United States
- Language:
- English
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