The 12th International Conference on Environmental ... - Events

Abstracts Session 62-63
4) BIOAVAILABILITY OF MERCURY IN CONTAMINATED OAK RIDGE WATERSHED AND POTENTIAL
REMEDIATION OF RIVER/RUNOFF/STORM WATER BY AN AQUATIC PLANT - 16319
Yi Su, Fengxiang X. Han, Jian Chen, Yunju Xia, David L. Monts, Mississippi State University (USA)
Historically as part of its national security mission, the U.S. Department of Energys Y-12 National Security Facility in Oak
Ridge, TN, USA acquired a significant fraction of the worlds supply of elemental mercury. During the 1950s and 1960s, a large
amount of elemental mercury escaped confinement and is still present in the buildings and grounds of the Y-12 Facility and in the
Y-12 Watershed. Because of the adverse effects of elemental mercury and mercury compounds upon human health, the Oak Ridge
Site is engaged in an on-going effort to monitor and remediate the area. <strong>The</strong> main thrust of the Oak Ridge mercury remediation
effort is currently scheduled for implementation in FY09. In order to more cost effectively implement those extensive remediation
efforts, it is necessary now to obtain an improved understanding of the role that mercury and mercury compounds play in the Oak
Ridge ecosystem.
Most recently, concentrations of both total mercury and methylmercury in fish and water of lower East Fork Poplar Creek
(LEFPC) of Oak Ridge increased although the majority of mercury in the site is mercury sulfide. This drives the US DOE and the
Oak Ridge Site to study the long-term bioavailability of mercury and speciation at the site. <strong>The</strong> stability and bioavailability of mercury
sulfide as affected by various biogeochemical conditions presence of iron oxides have been studied. We examined the kinetic
rate of dissolution of cinnabar from Oak Ridge soils and possible mechanisms and pathways in triggering the most recent increase
of mercury solubility, bioavailability and mobility in Oak Ridge site. <strong>The</strong> effects of pH and chlorine on oxidative dissolution of
cinnabar from cinnabar-contaminated Oak Ridge soils will be discussed.
On the other hand, aquatic plants might be good candidate for phytoremediate contaminated waste water and phytofiltration of
collective storm water and surface runoff and river. Our greenhouse studies on uptake of Hg by water lettuce (Pistia stratiotes) show
that water lettuce is effectively removing Hg from water solution and Hg was mostly stored in roots. One day of growing could
remove 93-98% of Hg from water solutions. However, Hg shows acute toxicity to water lettuce as indicated by decreases in fresh
biomass and moisture contents.
5) REMEDIATION OF URANIUM- AND CHC-CONTAMINATED GROUNDWATER
ON A FORMER NUCLEAR FUEL-ELEMENT PRODUCTION SITE - 16244
Joerg Woerner, Sonja Margraf, RD Hanau (Germany)
Since July 2002 a pump & treat remedial action has been in operation for the extraction of Uranium- and CHC-compoundscontaminated
ground-water flowing below an industrial area used before as production site for nuclear fuel elements. So far about 17
kg Uranium and 22 kg CHC-compounds have been eliminated. As described earlier [1] two ground-water plumes have transported
the Uranium down-stream to locations where two main remediation wells are placed. <strong>The</strong>y show characteristic differences with
respect to their Uranium-nuclide vector. More than 220.000 m³ ground-water of the whole 350.000 m³ have been pumped therefrom.
Preferred ground-water paths cause blending the two plumes waters. <strong>The</strong> first plumes water characterized by decreasing Uranium-235
ratios is meanwhile dominated by the second plumes water of up to 85% in case of well W10. <strong>The</strong> overall activity of 122
MBq Uranium-235 has been extracted from the saturated zone with decreasing quantities. Only a small area remains where the first
plumes pure ground water will be extracted in future. Both target values of 20 ?g/l and 10 ?g/l for dissolved Uranium and CHCcompounds,
respectively, could not yet be reached for all remediation wells. In accordance to the 10?Sv-concept of radiation protection
the improvement of specific parameters will still be necessary in order
SESSION 63 - NATURAL ANALOGUES IN RADWASTE DISPOSAL - ANSWERING THE HARD QUESTIONS
1) IMPLICATIONS OF MICROBIAL REDOX CATALYSIS IN ANALOGUE SYSTEMS
FOR REPOSITORY SAFETY CASES - 16336
Julia M West, British Geological Survey (UK); Ian McKinley, McKinley Consulting (Switzerland);
Simcha Stroes-Gascoyne, AECL, Whiteshell Laboratories (Canada)
A detailed assessment of studies of oxidising redox fronts around fractures at depth in otherwise reducingenvironments suggests
that the usual explanation in terms of disturbances that have, in the past, resulted in deep penetration of oxidising water are
incompatible with observations. An alternative hypothesis involving microbial catalysis of kinetically hindered reactions involving
oxyanions such as sulphate or carbonate appears potentially more credible. Although still not always taken into account by the geochemical
community, the role of microbial metabolism on subsurface geochemistry is supported by the rapidly expanding database
on subsurface microbial populations. <strong>The</strong>se populations are demonstrated to be viable and, therefore, could potentially be active at
levels close to or below current detection limits (either continuously or intermittently) in deep geological systems. Indeed, inspection
of information available from several analogue studies or repository site characterisation programmes suggests that such activity
may explain some of the geochemical anomalies encountered.
This paper examines the current (indirect) evidence for microbial redox catalysis in relevant subsurface environments and considers
the implications that this would have for the development of site understanding and, in particular, the identification of factors
that may distinguish between different locations during site selection. Further, it examines the wider implications of more
extensive roles of microbes in repository systems on the overall post-closure safety case and the need for further focused analogue
studies to develop answers to these open questions.
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