HR: 0800h
AN: H31D-0446    [Abstracts]
TI: In Situ Gaseous Treatment and Reoxidation Studies - Implications for Vadose Zone Remediation
AU: * Zhong, L
EM: lirong.zhong@pnl.gov
AF: Pacific Northwest National Lab, Battelle Boulevard, MSIN: K-6-96 , Richland, WA 99354 United States
AU: Thornton, E C
EM: ed.thornton@pnl.gov
AF: Pacific Northwest National Lab, Battelle Boulevard, MSIN: K-6-96 , Richland, WA 99354 United States
AU: Oostrom, M
EM: mart.oostrom@pnl.gov
AF: Pacific Northwest National Lab, Battelle Boulevard, MSIN: K-6-96 , Richland, WA 99354 United States
AU: Deng, B
EM: DengB@missouri.edu
AF: University of Missouri -, Columbia, Columbia, MO 65211 United States
AB: The {\it In Situ} Gaseous Reduction (ISGR) approach has been developed by Pacific Northwest National Laboratory (PNNL) for vadose zone soil remediation. This technology uses diluted hydrogen sulfide gas (H$_{2}$S) as a reductant for immobilization of contaminants that show substantially lower mobility in their reduced forms, e.g., Tc, U, and Cr. The ISGR approach can be used to immobilize or stabilize pre-existing contaminants in the vadose zone by direct H$_{2}$S treatment. Alternatively, a permeable reactive barrier (PRB) could be generated by pumping a gaseous mixture of hydrogen sulfide diluted in nitrogen through an interval in the vadose zone to produce a layer of reduced sediment. Recent work directed towards development of the ISGR technology has focused on collection of laboratory data needed to support design and installation of a subsurface barrier. This has included conducting small and large scale column tests to determine the reaction characteristics between sediment and hydrogen sulfide gas mixtures and the rates of these reactions. During gaseous treatment, most of the hydrogen sulfide component is consumed in soil and results in the generation of FeS. This constituent is the active agent that maintains reducing conditions in the barrier needed for contaminant immobilization. Another aspect of current testing activities involves determining the reducing capacity of treated soil during reoxidation. This information is needed to assess the effectiveness and lifetime of the barrier. Initial testing activities have also been undertaken to assess the rate and extent of immobilization of Cr, Tc, and U and to evaluate the potential for remobilization of these contaminants as barrier reoxidation occurs. Barrier design and performance behavior is being supported by analytical and numerical modeling activities that utilize laboratory data regarding sediment treatment, roxidation, and contaminant immobilization processes as it becomes available.
DE: 1899 General or miscellaneous
DE: 1831 Groundwater quality
DE: 1875 Unsaturated zone
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting