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Title: Electron Microbeam Investigation of Uranium-Contaminated Soils from Oak Ridge, TN, USA

Authors:
; ; ;
Publication Date:
Research Org.:
Subsurface Biogeochemical Research (SBR)
Sponsoring Org.:
USDOE Office of Science (SC), Biological and Environmental Research (BER)
OSTI Identifier:
1154298
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Science&Technology; Journal Volume: 40; Journal Issue: 7
Country of Publication:
United States
Language:
English

Citation Formats

Joanne E.,Stubbs, David C.,Elbert, David R.,Veblen, and Chen,Zhu. Electron Microbeam Investigation of Uranium-Contaminated Soils from Oak Ridge, TN, USA. United States: N. p., 2006. Web. doi:10.1021/es0518676.
Joanne E.,Stubbs, David C.,Elbert, David R.,Veblen, & Chen,Zhu. Electron Microbeam Investigation of Uranium-Contaminated Soils from Oak Ridge, TN, USA. United States. doi:10.1021/es0518676.
Joanne E.,Stubbs, David C.,Elbert, David R.,Veblen, and Chen,Zhu. Sat . "Electron Microbeam Investigation of Uranium-Contaminated Soils from Oak Ridge, TN, USA". United States. doi:10.1021/es0518676.
@article{osti_1154298,
title = {Electron Microbeam Investigation of Uranium-Contaminated Soils from Oak Ridge, TN, USA},
author = {Joanne E.,Stubbs and David C.,Elbert and David R.,Veblen and Chen,Zhu},
abstractNote = {},
doi = {10.1021/es0518676},
journal = {Environmental Science&Technology},
number = 7,
volume = 40,
place = {United States},
year = {Sat Apr 01 00:00:00 EST 2006},
month = {Sat Apr 01 00:00:00 EST 2006}
}
  • A field test on in situ subsurface bioremediation of uranium(VI) is underway at the Y-12 National Security Complex in the Oak Ridge Reservation, Oak Ridge, TN. Nitrate has a high concentration at the site, which prevents U(VI) reduction, and thus must be removed. An acidic-flush strategy for nitrate removal was proposed to create a treatment zone with low levels of accessible nitrate. The subsurface at the site contains highly interconnected fractures surrounded by matrix blocks of low permeability and high porosity and is therefore subject to preferential flow and matrix diffusion. To identify the heterogeneous mass transfer properties, we performedmore » a novel forced-gradient tracer test, which involved the addition of bromide, the displacement of nitrate, and the rebound of nitrate after completion of pumping. The simplest conceptualization consistent with the data is that the pore-space consists of a single mobile domain, as well as a fast and a slowly reacting immobile domain. The slowly reacting immobile domain (shale matrix) constitutes over 80% of the pore volume and acts as a long-term reservoir of nitrate. According to simulations, the nitrate stored in the slowly interacting immobile domain in the fast flow layer, at depths of about 12.2-13.7 m, will be reduced by an order of magnitude over a period of about a year. By contrast, the mobile domain rapidly responds to flushing, and a low average nitrate concentration can be maintained if the nitrate is removed as soon as it enters the mobile domain. A field-scale experiment in which the aquifer was flushed with acidic solution confirmed our understanding of the system. For the ongoing experiments on microbial U(VI) reduction, nitrate concentrations must be low in the mobile domain to ensure U(VI) reducing conditions. We therefore conclude that the nitrate leaching out of the immobile pore space must continuously be removed by in situ denitrification to maintain favorable conditions.« less
  • In support of environmental restoration projects at the Y-12 Facility in Oak Ridge, Tennessee, a series of bench-scale thermal desorption experiments were conducted on mercury contaminated soils from the Building 9201-2 basement. Due to the health concerns associated with the material handling of mercury contaminated soils, an in-situ thermal treatment method could provide significant advantages over conventional, ex-situ treatment methods. The primary objective for the experimental program was to determine if the soil could be heated to a temperature where the mercury contamination would be vaporized and purged to an offgas stream. A secondary objective of the treatability test wasmore » to capture the mercury in the offgas stream in order to complete a mass balance for each experiment. The mercury concentration in the untreated soil was approximately 6,700 mg/kg. The contaminated soil, in a simulated in-situ condition, was slowly heated over 24-hour and 72-hour time periods to a final treatment temperature of 900 F, with an air flow rate of 0.1 liters per minute per pound of test soil used to purge the test apparatus. The purged offgas was then routed to an offgas collection system where any organic material, elemental mercury and/or other mercury species were collected. The thermally treated soil samples were analyzed for residual mercury contamination. The test data showed that in-situ thermal desorption, at a temperature of 900 F, removed mercury from the soil at an average efficiency of approximately 99%. Residual mercury concentrations averaged 70 mg/kg. Analysis of the offgas provided an average mercury mass balance of 56 percent. Factors which may have influenced these recoveries include the formation of amalgams, chemical speciation, and equipment rinsate efficiencies.« less
  • In this paper, sediments were analyzed for total Hg concentration (THg) and isotopic composition from streams and rivers in the vicinity of the Y-12 National Security Complex (Y12) in Oak Ridge, TN (USA). In the stream directly draining Y12, where industrial releases of mercury (Hg) have been documented, high THg (3.26 to 60.1 μg/g) sediments had a distinct Hg isotopic composition (δ 202Hg of 0.02 ± 0.15‰ and Δ 199Hg of -0.07 ± 0.03‰; mean ± 1SD, n=12) compared to sediments from relatively uncontaminated streams in the region (δ 202Hg = -1.40 ± 0.06‰ and Δ 199Hg of –0.26 ±more » 0.03‰; mean ± 1SD, n=6). Additionally, several streams that are nearby but do not drain Y12 had sediments with intermediate THg (0.06 to 0.21 μg/g) and anomalous δ 202Hg (as low as -5.07‰). We suggest that the low δ 202Hg values in these sediments provide evidence for the contribution of an additional Hg source to sediments, possibly derived from atmospheric deposition. In sediments directly downstream of Y12 this third Hg source is not discernible and the Hg isotopic composition can be largely explained by the mixing of low THg sediments with high THg sediments contaminated by Y12 discharges.« less
  • A hydrologic, geochemical and microbial characterization of the Area 3 field site has been completed. The formation is fairly impermeable, but there is a region of adequate flow approximately 50 feet bgs. The experiment will be undertaken within that depth interval. Groundwater from that depth is highly acidic (pH 3.2), and has high levels of nitrate, aluminum, uranium, and other heavy metals, as well as volatile chlorinated solvents (VOCs). Accordingly, an aboveground treatment train has been designed to remove these contaminants. The train consists of a vacuum stripper to remove VOCs, two chemical precipitation steps to adjust pH and removemore » metals, and a fluidized bed bioreactor to remove nitrate. The aboveground system will be coupled to a belowground recirculation system. The belowground system will contain an outer recirculation cell and a nested inner recirculation cell: the outer cells will be continuously flushed with nitrate-free treated groundwater. The inner cell will receive periodic inputs of uranium, tracer, and electron donor. Removal of uranium will be determined by comparing loss rates of conservative tracer and uranium within the inner recirculation cell. Over the past year, a detailed workplan was developed and submitted for regulatory approval. The workplan was presented to the Field Research Advisory Panel (FRAP), and after some extensive revision, the FRAP authorized implementation. Detailed design drawings and numerical simulations of proposed experiments have been prepared. System components are being prefabricated as skid-mounted units in Michigan and will be shipped to Oak Ridge for assembly. One manuscript has been submitted to a peer reviewed journal. This paper describes a novel technique for inferring subsurface hydraulic conductivity values. Two posters on this project were presented at the March 2002 NABIR PI meeting. One poster was presented at the Annual conference of the American Society for Microbiology in Salt Lake City, UT in May 2002.« less
  • Bioremediation of uranium contaminated groundwater was tested by delivery of ethanol as an electron donor source to stimulate indigenous microbial bioactivity for reduction and immobilization of uranium in situ, followed by tests of stability of uranium sequestration in the bioreduced area via delivery of dissolved oxygen or nitrate at the US Department of energy's Integrated Field Research Challenge site located at Oak Ridge, Tennessee, USA. After long term treatment that spanned years, uranium in groundwater was reduced from 40-60 mg {center_dot} L{sup -1} to <0.03 mg {center_dot} L{sup -1}, below the USA EPA standard for drinking water. The bioreduced uraniummore » was stable under anaerobic or anoxic conditions, but addition of DO and nitrate to the bioreduced zone caused U remobilization. The change in the microbial community and functional microorganisms related to uranium reduction and oxidation were characterized. The delivery of ethanol as electron donor stimulated the activities of indigenous microorganisms for reduction of U(VI) to U(IV). Results indicated that the immobilized U could be partially remobilized by D0 and nitrate via microbial activity. An anoxic environmental condition without nitrate is essential to maintain the stability of bioreduced uranium.« less