Hanford Site In South-central Washington Research Articles

An autotrophic H2 -oxidizing, nitrate-respiring, Tc(VII)-reducing Acidovorax sp. isolated from a subsurface oxic-anoxic transition zone.

Increasing concentrations of H2 with depth were observed across a geologic unconformity and associated redox transition zone in the subsurface at the Hanford Site in south-central Washington, USA. An opposing gradient characterized by decreasing O2 and nitrate concentrations was consistent with microbial-catalysed biogeochemical processes. Sterile sand was incubated in situ within a multilevel sampler placed across the redox transition zone to evaluate the potential for Tc(VII) reduction and for enrichment of H2 -oxidizing denitrifiers capable of reducing Tc(VII). H2 -driven TcO4 (-) reduction was detected in sand incubated at all depths but was strongest in material from a depth of 17.1 m. Acidovorax spp. were isolated from H2 -nitrate enrichments from colonized sand from 15.1 m, with one representative, strain JHL-9, subsequently characterized. JHL-9 grew on acetate with either O2 or nitrate as electron acceptor (data not shown) and on medium with bicarbonate, H2 and nitrate. JHL-9 also reduced pertechnetate (TcO4 (-) ) under denitrifying conditions with H2 as the electron donor. H2 -oxidizing Acidovorax spp. in the subsurface at Hanford and other locations may contribute to the maintenance of subsurface redox gradients and offer the potential for Tc(VII) reduction.

Mule deer antlers as biomonitors of strontium-90 on the Hanford Site

This study evaluated deer antlers as indicators of animal uptake of localized 90Sr contamination on the Hanford Site in south-central Washington. Levels of 90Sr were examined in 38 mule deer (Odocoileus hemionus hemionus) antler samples collected near and distant from previously active nuclear reactor facilities and from a reference site in central Oregon. Results showed that 90Sr concentrations in antlers collected near reactor facilities were significantly higher (P<0.001) than other Hanford samples. Reference samples contained nearly 5 times the levels of 90Sr compared with Hanford. Strontium-90 concentrations in deer antlers collected at the reference locations were higher than Hanford site deer, presumably because the deer inhabited mountain regions during the summer months that received more atmospheric fallout from historic weapons testing.

Time-dependent changes in viable numbers and activities of aerobic heterotrophic bacteria in subsurface samples

Vadose and saturated zone sediment cores from depths to 212 m were obtained from the U.S. Department of Energy's Hanford Site in south-central Washington by cable tool drilling, and volcanic ashfall tuff samples were obtained from tunnels 400 m beneath the surface of Rainier Mesa at DOE's Nevada Test Site (NTS) in southern Nevada. Numbers of viable aerobic heterotrophic bacteria were determined by plate counts and metabolic activities were determined by [ 14C]glucose radiorespirometry at t = 0 and at various post-sampling time points up to 154 d in order to assess the influence of sample storage on microbiological properties of subsurface samples. Increases in post-sampling populations of viable bacteria were observed in all samples, although the magnitude of the increase and time after sampling at which the maximum population size was reached varied with the sample type. The greatest post-sampling increases in viable counts and [ 14C]glucose mineralization occurred in a high-organic carbon lacustrine sediment. The population of aerobic heterotrophs increased from below detection at t = 0 to > 10 6 CFU g −1 after 139 d. Significant increases in culturable counts were shown to occur within 24 h for tuff samples from NTS. These results indicate that precautions are necessary in the post-drilling handling of subsurface sediments and rock for microbiological analysis. In addition, these results suggest that even low biomass subsurface environments may be readily stimulated for applications such as in situ bioremediation.

The use of batch tests as a screening tool for radionuclide sorption characterization studies, Hanford, Washington, U.S.A.

The U.S. Department of Energy was studying the feasibility of locating a high-level radioactive waste repository in basalt at the Hanford site in south-central Washington. This is a saturated site where ground water transport of radionuclides away from a repository is the mechanism for release to the accessible environment. Sorption as defined herein is the predominant means by which the movement of radionuclides are retarded in a ground water flow system. This work presents preliminary laboratory batch testing results in the context of the entire site system sorption characterization strategy. An anoxic experimental approach was used with basalt flow top core samples recovered from depths of 915 m (3000 ft) below the earth surface. The kinetics of sorption were relatively slow and increased in the order U<Se<Sr, Ra. Proportionate removal increased in the order Se<U<Sr<Ra. Freudlich isotherms were linear for Sr, U and Se over the concentrations tested. The batch results were helpful from a screening standpoint to indicate the direction of further testing, but were unsatisfactory by themselves to explain sorption behavior adequately.

Iodine in terrestrial wildlife on the U.S. department of energy's Hanford Site in southcentral Washington

Iodine-129 in controlled amounts has been released into the air from the operating chemical separations facilities on the Hanford Site. Small amounts of (129)I have accumulated in surface soils especially at locations near the chemical separations facilities. Enriched levels of (129)I also occur in the thyroid glands of mule deer (Odocoileus hemionus) residing on the Hanford Site.Stable iodine is present in low concentrations in Hanford Site soils and it is not avidly accumulated by wild plants. Soils at high elevations have greater concentrations of (127)I than low elevations soils. Mule deer thyroids had higher concentrations of stable iodine than the thyroids of black-tailed jackrabbits. Stable iodine in black-tailed jackrabbit thyroids varied with the season with maximal concentrations in summer.Iodine-131 has not been released into the air from operating chemical separations facilities for more than 10 yr. Because of its short half-life (131)I of Hanford Site origin has disappeared from the Hanford Site. In the event of a future restart of the chemical separations facilities black-tailed jackrabbits can be used as biological indicators of (131)I in the terrestrial environment of the Hanford Site.