Impact Assessment of Existing Vadose Zone Contamination at the Hanford Site SX Tank Farm

Khaleel, Raziuddin; White, Mark D.; Oostrom, Martinus; Wood, M.I.; Mann, F.M.; Kristofzski, J.G.

doi:10.2136/vzj2006.0176

Cited by 17 publications

(12 citation statements)

References 29 publications

(36 reference statements)

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“…Larger in-ground inventories of 99 Tc exist within Hanford's S-SX tank farm [$30 Ci;Khaleel et al (2007)] and the BC cribs [410 Ci; Serne and Mann, 2004;Kincaid et al, 2006;Rucker and Fink, 2007]. In the absence of barriers to prevent infiltration or as yet untried deep vadose zone remediation techniques, there is little to prevent this mobile 99 Tc from eventually entering Hanford's unconfined aquifer and traveling with groundwater that to the Columbia River.…”

Section: Environmental Implicationsmentioning

confidence: 99%

“…At the US Department of Energy's Hanford Site and other DOE sites across the US (Riley and Zachara, 1992) and at nuclear facilities world-wide, 99 Tc contamination is of particular concern because it can migrate rapidly with vadose zone water and groundwater as pertechnetate ½TcðVIIÞO 4 À (Evans et al, 2007;Zachara et al, 2007a). At Hanford, over 500 Ci of TcðVIIÞO 4 À released to the vadose zone in past site operations are forecast to be mobile in predominantly oxidizing groundwaters with eventual discharge to the Columbia River (Khaleel et al, 2007), making it one of the site's major risk-driving contaminants. The subsurface inventory and behavior of 99 Tc at Hanford, 0016-7037/$ -see front matter Ó 2009 Elsevier Ltd. All rights reserved.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Oxidative dissolution potential of biogenic and abiogenic TcO2 in subsurface sediments

Fredrickson

Zachara

Plymale

et al. 2009

Geochimica et Cosmochimica Acta

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Technetium-99 (Tc) is an important fission product contaminant associated with sites of nuclear fuels reprocessing and geologic nuclear waste disposal. Tc is highly mobile in its most oxidized state ½TcðVIIÞO 4 À and less mobile in the reduced form [Tc(IV)O 2 ÁnH 2 O]. Here we investigate the potential for oxidation of Tc(IV) that was heterogeneously reduced by reaction with biogenic Fe(II) in two sediments differing in mineralogy and aggregation state; unconsolidated Pliocene-age fluvial sediment from the upper Ringold (RG) Formation at the Hanford Site and a clay-rich saprolite from the Field Research Center (FRC) background site on the Oak Ridge Site. Both sediments contained Fe(III) and Mn(III/IV) as redox active phases, but FRC also contained mass-dominant Fe-phyllosilicates of different types. Shewanella putrefaciens CN32 reduced Mn(III/ IV) oxides and generated Fe(II) that was reactive with Tc(VII) in heat-killed, bioreduced sediment. After bioreduction and heat-killing, biogenic Fe(II) in the FRC exceeded that in RG by a factor of two. More rapid reduction rates were observed in the RG that had lower biogenic Fe(II), and less particle aggregation. EXAFS measurements indicated that the primary reduction product was a TcO 2 -like phase in both sediments. The biogenic redox product Tc(IV) oxidized rapidly and completely in RG when contacted with air. Oxidation, in contrast, was slow and incomplete in the FRC, in spite of similar molecular scale speciation of Tc compared to RG. X-ray microprobe, electron microprobe, X-ray absorption spectroscopy, and micro X-ray diffraction were applied to the whole sediment and isolated Tc-containing particles. These analyses revealed that non-oxidizable Tc(IV) in the FRC existed as complexes with octahedral Fe(III) within intra-grain domains of 50-100 lmsized, Fe-containing micas presumptively identified as celadonite. The markedly slower oxidation rates in FRC as compared to RG were attributed to mass-transfer-limited migration of O 2 into intra-aggregate and intraparticle domains where Tc(IV) existed; and the formation of unique, oxidation-resistant, intragrain Tc(IV)-Fe(III) molecular species.

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Section: Environmental Implicationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Oxidative dissolution potential of biogenic and abiogenic TcO2 in subsurface sediments

Fredrickson

Zachara

Plymale

et al. 2009

Geochimica et Cosmochimica Acta

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“…Its presence in the subsurface is largely a result of past disposal practices at nuclear reprocessing facilities, including the Hanford site in Washington State, USA, and elsewhere (Gee et al, 2007;Khaleel et al, 2007). The risk of unmitigated 99 Tc contamination is substantial because of its long half-life (2.1 Â 10 5 yr), relatively high fission yield, and high potential mobility in surface and groundwater.…”

Section: Introductionmentioning

confidence: 99%

Tc(VII) reduction kinetics by titanomagnetite (Fe3−xTixO4) nanoparticles

Liu

Pearce

Qafoku

et al. 2012

Geochimica et Cosmochimica Acta

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Technetium contamination remains a major environmental problem at nuclear reprocessing sites, such as at the Hanford nuclear reservation, Washington, USA. Here we investigate the heterogeneous reduction of the highly soluble pertechnetate anion [Tc(VII)O 4 À ] to sparingly soluble Tc(IV)-bearing solids by a novel and well-characterized set of mixed-valent titaniumdoped magnetite nanoparticles, structurally and chemically analogous to titanomagnetites naturally present in Hanford sediments. Titanomagnetite (Fe 3Àx Ti x O 4 ) nanoparticles (10-12 nm) with varying Ti content (0 6 x 6 0.53) were synthesized in aqueous suspension. Reaction with 10 and 30 lM Tc(VII) solution yielded fast exponentially decaying reduction kinetics with rates that increased with increasing solid-state Fe(II)/Fe(III) ratio in the nanoparticles, a characteristic systematically controlled by the Ti-content. Nanoparticles before and after reduction experiments and surface-associated products of Tc(VII) reduction were characterized using transmission electron microscopy (TEM), X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure spectroscopy (EXAFS), micro X-ray diffraction (l-XRD), X-ray absorption (XA) and X-ray magnetic circular dichroism (XMCD). A mechanistic reaction model was developed involving reduction of Tc(VII) to form Tc(IV)/Fe(III) solids by structural Fe(II) enriched at the nanoparticle surface, a reactive Fe(II) pool that during reaction is resupplied and sustained by outward migration of Fe(II) from the particle interior with concurrent inward migration of charge-balancing cationic vacancies in a ratio of 3:1. The reaction process was quantitatively linked to mass and electron balanced changes in the Fe 3Àx Ti x O 4 nanoparticles, and the accessibility of structural Fe(II) from these phases was determined.

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“…Understanding and characterizing the sources of these plumes will provide the basis to mitigate against future risk through placement of various flow barriers, whether physical (Khaleel et al, 2007) or hydrological (Oostrom et al, 2009, "Desiccation of Unsaturated Porous Media: Intermediate-Scale Experiments and Numerical Simulation"). The waste sites at Hanford, unfortunately, are difficult to characterize due to the obstructions posed by different types of infrastructure.…”

Section: Conlcusionsmentioning

confidence: 99%