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Scholarly Works (2 results)

  • Article
  • Peer Reviewed
Lawrence Berkeley National Laboratory (2008)

Processes of fluid flow and chemical transport through the vadose zone can be characterized through the isotopic systematics of natural soils, minerals, pore fluids and groundwater. In this contribution, we first review our research using measured isotopic variations, due both to natural and site related processes, of the elements H, O, N, Sr and U, to study the interconnection between vadose zone and groundwater contamination at the Hanford Site in south-central Washington. We follow this brief review with a presentation of new data pertaining to vadose zone and groundwater contamination in the WMA T-TX-TY vicinity. Uranium (U) isotopic data for the C3832 core (WMA TX) indicates the involvement of processed natural U fuel, and links the observed U contamination to the nearby single shelled tank TX-104. The data also precludes contamination from an early 1970 s TX-107 leak. In the case of the C4104 core (WMA T), the U isotopic data indicates a mixture of processed natural and enriched U fuels consistent with the major leak from T-106 in 1973. Uranium and Strontium isotopic data for the cores also provides direct evidence for chemical interaction between high-pH waste fluid and sediment. Isotopic data for groundwater nitrate contamination in the vicinity of WMA-T strongly suggests high-level tank waste (most likely from T-106) as the source of very high 99Tc concentrations recently observed at the NE corner of WMAT.

    Cover page: Isotopic Studies of Contaminant Transport at the Hanford Site, WA
    • Article
    LBL Publications (2005)
    A suite of isotopic measurements of vadose zone soil samples and groundwater has been successfully used to identify the sources of groundwater contamination at the Hanford site in south-central Washington. The isotopic composition of nitrate can be used to distinguish high-level tank waste (high d15N) and low-level process wastes (high d18O) from the relatively high background concentrations of nitrate in the groundwater at the site. The 87Sr/86Sr of strontium is typically elevated above background in areas where large volumes of water have been flushed through the vadose zone. Conversely, interaction between high-level caustic waste and feldspars in the vadose zone sediments releases low 87Sr/86Sr. Uranium isotope ratios (234U/238U, 235U/238U, 236U/238U) have been particularly useful for distinguishing different generations of nuclear fuel processing, allowing identification of waste in the vadose zone and groundwater derived from known or suspected leaks or spills. Data will be presented from a site adjacent to one of the high-level tank farms where multiple possible sources of contamination are suspected of causing high (and increasing) concentrations of 99Tc and nitrate in groundwater. The isotopic composition of nitrate from a multi-level well shows a clear example of vertical mixing of high nitrate, low-level waste with concentrated high-level waste. Sr and U isotope data are helping to define the possible source of the high-level and low-level waste components in the groundwater.
      Cover page: Isotope Tracking of Contaminant Movement in the Hanford Vadose Zone
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