HR: 0800h
AN: H31D-0416    [Abstracts]
TI: Plutonium Particle Migration in the Shallow Vadose Zone: The Nevada Test Site as an Analog Site
AU: * Hunt, J R
EM: hunt@ce.berkeley.edu
AF: Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720-1710 United States
AU: Smith, D K
EM: smith24@llnl.gov
AF: Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551 United States
AB: The upper meter of the vadose zone in desert environments is the horizon where wastes have been released and human exposure is determined through dermal, inhalation, and food uptake pathways. This region is also characterized by numerous coupled processes that determine contaminant transport, including precipitation infiltration, evapotranspiration, daily and annual temperature cycling, dust resuspension, animal burrowing, and geochemical weathering reactions. While there is considerable interest in colloidal transport of minerals, pathogenic organisms, and contaminants in the vadose zone, there are limited field sites where the actual occurrence of contaminant migration can be quantified over the appropriate spatial and temporal scales of interest. At the US Department of Energy Nevada Test Site, there have been numerous releases of radionuclides since the 1950's that have become field-scale tracer tests. One series of tests was the four safety shots conducted in an alluvial valley of Area 11 in the 1950's. These experiments tested the ability of nuclear materials to survive chemical explosions without initiating fission reactions. Four above-ground tests were conducted and they released plutonium and uranium on the desert valley floor with only one of the tests undergoing some fission. Shortly after the tests, the sites were surveyed for radionuclide distribution on the land surface using aerial surveys and with depth. Additional studies were conducted in the 1970's to better understand the fate of plutonium in the desert that included studies of depth distribution and dust resuspension. More recently, plutonium particle distribution in the soil profile was detected using autoradiography. The results to date demonstrate the vertical migration of plutonium particles to depths in excess of 30 cm in this arid vadose zone. While plutonium migration at the Nevada Test Site has been and continues to be a concern, these field experiments have become analog sites for the release of radiological materials potentially important to consequence management investigations. In particular, these 50-year old experiments with long and detailed site investigations under relative undisturbed conditions offer insights into transport pathways that must be represented in simulation models that evaluate responses to radiological dispersal devices (RDDs). A compilation of the available site characterization data suggests additional experimental and modeling programs that can ultimately quantify the fate of contaminant particles released at the soil surface.
DE: 1803 Anthropogenic effects
DE: 1875 Unsaturated zone
DE: 1886 Weathering (1625)
DE: 1065 Trace elements (3670)
DE: 0305 Aerosols and particles (0345, 4801)
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting