The 13th International Conference on Environmental ... - Events

Abstracts
radioactive waste over more than three decades. <strong>The</strong> resulting groundwater plume contains multiple contaminants,
including nitrate, iodine-129, strontium-90, technetium-99, tritium, and uranium isotopes. Since 1991, groundwater near
the source area has been analyzed for evidence that plume acidity is naturally attenuating. Other biogeochemical
gradients are also being evaluated to determine natural waste site evolution and impacts from active remediation systems.
<strong>The</strong>se systems include a neutralization barrier to mitigate plume acidity and a biostimulation zone to enhance in situ
reductive metal precipitation. <strong>The</strong> influence of reactive facies on plume dynamics is also being examined using
geophysical tools to detect these subsurface zones of unique mineralogy, hydrology, and microbiology. Site
characterization data, plume dynamics, and contaminant behavior are incorporated into an evolving site conceptual model,
which serves as the foundation for reactive transport modeling. This unique approach for site assessment is expected to
improve the selection of remedial strategies and decision making for long-term environmental stewardship at SRS and
other sites. <strong>The</strong> work is complementary to the U.S. Environmental Protection Agency’s recent guidance on monitored
natural attenuation of inorganics.
3) 40260 – Current Mercury Distribution and Bioavailability in Floodplain Soils of Lower East Fork Popular
Creek, Oak Ridge, Tennessee, USA
Fengxiang X. Han, Yi Su, David L. Monts,� Mississippi State University (USA)
<strong>The</strong> objectives of this study were to investigate the current status of mercury distribution, speciation and
bioavailability in the floodplain soils of Lower East Fork Poplar Creek (LEFPC) after decades of US Department of
Energy’s remediation. Historically as part of its national security mission, the U.S. Department of Energy’s Y-12
National Security Facility in Oak Ridge, TN, USA acquired a significant fraction of the world’s supply of elemental
mercury. During the 1950s and 1960s, a large amount of elemental mercury escaped confinement and is still present in
the watershed surrounding the Y-12 facility. A series of remediation efforts have been deployed in the watersheds around
the Oak Ridge site during the following years. <strong>The</strong> sampling fields were located in a floodplain of LEFPC of Oak Ridge,
TN, USA. A series of surface soils (10-20 cm) were sampled from both wooded areas and wetland/grass land. Two 8x8
m fields were selected in the woodland. Five profiles each consisting of three layers were randomly taken from each field.
<strong>The</strong> three layers were the surface layer at 0-10cm, subsurface layer at 50-60 cm, and bottom layer at 100-110 cm. Soil in
both wood and wetland areas was well developed with a clear B horizon. <strong>The</strong> present study clearly shows that the total
mercury in floodplain soils of LEFPC significantly decreased after the series of remediation. This study confirmed the
long-term effectiveness of these remediation actions, especially after excavation of highly contaminated floodplain soils.
However, the average total mercury level of all soil samples collected are in the range of 50-80 mg/kg, still significantly
above toxic level (> 5mg/kg). Furthermore, contrary to conventional believing, the major mercury form in current soils of
this particular area of floodplain of LEFPC is mainly in non-cinnabar mercury bound in clay minerals (after decades of
remediation). <strong>The</strong> floodplains can act both as a medium-term sink and as long-term sources. Native North American
earthworms (Diplocardia spp.) and adjacent soils were taken from each spot in each field. Our results show strong linear
relationships between mercury concentrations in earthworms (both mature and immature groups) and non-cinnabar
mercury form, while cinnabar mercury is less bioavailable to native earthworms. Earthworms may be used as a potential
mercury ecological bioindicator (bio-marker) for demonstrating mercury bioavailability and ecotoxicity in the ecosystem.
<strong>The</strong> long-term stability, mobility and bioavailability of mercury contaminants in these floodplains still needs to be
monitored continuously and closely.
4) 40262 – Integrated Strategy to Address Hanford's Deep Vadose Zone Remediation Challenges
Mark B. Triplett, Mark D. Freshley, Michael J. Truex, Dawn Wellman, PNNL (USA);
Kurt D. Gerdes, Briant L. Charboneau, John G. Morse, Robert W. Lober, US DOE (USA);
Glen B. Chronister, CH2M Hill Plateau Remediation Company (USA)
A vast majority of Hanford’s remaining in-ground contaminants reside in the vadose zone of the 200 Area Central
Plateau, where reprocessing operations occurred. <strong>The</strong> vadose zone at this location is comprised of about 75 meters of
water-unsaturated, unconsolidated, stratified sediments above groundwater that discharges to the Columbia River.
Contaminants in this zone originated from intentional discharges to cribs, retention basins, and trenches, and from
unintended tank waste releases in the tank farms. <strong>The</strong> “deep vadose zone” is defined as the region below the practical
depth of surface remedy influence (e.g., excavation or surface barrier). At the Hanford Site, this region poses unique
challenges for characterization and remediation.
In 2008, the Department of Energy initiated a deep vadose zone treatability test to seek remedies for technetium-99
and uranium contamination. <strong>The</strong> treatability approach includes laboratory, modeling, and field tests building on previous
work at the Hanford Site. Initial laboratory and field tests for technetium-99 have focused on use of desiccation which
could be used in combination with an infiltration barrier to slow the transport of technetium-99 in the subsurface. For
uranium contamination, reactive gas technologies are being tested as one component of the overall treatability test
approach.
More recently, in recognition of the need for a broader strategy, the Department of Energy initiated an integrated
study of the deep vadose zone to establish a technical basis for addressing risk-driving contaminants and supporting
selection of remediation approaches for the deep vadose zone that are protective of groundwater. This is a cooperative
effort that combines the resources and contributions of research scientists, technology developers, and remediation
contractors.
50