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Site characterization is an essential initial step in determining the feasibility of remedial alternatives at hazardous waste sites. Physico-chemical and mineralogical characterization of U-contaminated soils in deeply weathered saprolite at Area 2 of the DOE Field Research Center (FRC) site, Oak Ridge, TN, was accomplished to examine the feasibility of bioremediation. Concentrations of U in soil-saprolite (up to 291 mg kg^-1 in oxalate-extractable Uo) were closely related to low pH (ca. 4-5), high effective cation exchange capacity without Ca (64.7-83.2 cmolc kg_1), amorphous Mn content (up to 9910 mg kg_1), and the decreased presence of relative clay mineral contents in the bulk samples (i.e., illite 2.5-12 wt. %, average 32 wt. %). The pH of the fill material ranged from 7.0 to 10.5, whereas the pH of the saprolite ranged from 4.5 to 8. Uranium concentration was highest (about 300 mg kg^-1) at around 6 m below land surface near the saprolite-fill interface. The pH of ground water at Area 2 tended to be between 6 and 7 with U concentrations of about 0.9 to 1.7 mg L^-1. These site specific characteristics of Area 2, which has lower U and nitrate con-tamination levels and more neutral ground water pH comparedmore » with FRC Areas 1 and 3 (ca. 5.5 and _4, respectively), indicate that with appropriate addition of electron donors and nutrients bioremediation of U by metal reducing microorganisms may be possible.« less

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 weatheredmore » 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.« less

Permeable reactive barriers (PRBs) of zero-valent iron (Fe{sup 0}) are increasingly being used to remediate contaminated ground water. Corrosion of Fe{sup 0} filings and the formation of precipitates can occur when the PRB material comes in contact with ground water and may reduce the lifespan and effectiveness of the barrier. At present, there are no routine procedures for preparing and analyzing the mineral precipitates from Fe{sup 0} PRB material. These procedures are needed because mineralogical composition of corrosion products used to interpret the barrier processes can change with iron oxidation and sample preparation. The objectives of this study were (i) to investigate a method of preparing Fe{sup 0} reactive barrier material for mineralogical analysis by X-ray diffraction (XRD), and (ii) to identify Fe mineral phases and rates of transformations induced by different mineralogical preparation techniques. Materials from an in situ Fe{sup 0} PRB were collected by undisturbed coring and processed for XRD analysis after different times since sampling for three size fractions and by various drying treatments. We found that whole-sample preparation for analysis was necessary because mineral precipitates occurred within the PRB material in different size fractions of the samples. Green rusts quickly disappeared from acetone-dried samples and weremore » not present in air-dried and oven-dried samples. Maghemite/magnetite content increased over time and in oven-dried samples, especially after heating to 105 C. We conclude that care must be taken during sample preparation of Fe{sup 0} PRB material, especially for detection of green rusts, to ensure accurate identification of minerals present within the barrier system.« less