HR: 0800h
AN: H31D-0432    [Abstracts]
TI: Vadose Zone Characterization and Monitoring Beneath Waste Disposal Pits Using Horizontal Boreholes
AU: * McLin, S G
EM: sgm@lanl.gov
AF: Los Alamos National Laboratory, P.O. Box 1663 MS-K497, Los Alamos, NM 87545 United States
AU: Newman, B D
EM: bnewman@lanl.gov
AF: Los Alamos National Laboratory, P.O. Box 1663 MS-J495, Los ALamos, NM 87545 United States
AU: Broxton, D E
EM: broxton@lanl.gov
AF: Los Alamos National Laboratory, P.O. Box 1663 MS-T003, Los Alamos, NM 87545 United States
AB: Vadose zone characterization and monitoring immediately below landfills using horizontal boreholes is an emerging technology. However, this topic has received little attention in the peer-reviewed literature. The value of this approach is that activities are conducted below the waste, providing clear and rapid verification of containment. Here we report on two studies that examined the utility of horizontal boreholes for environmental characterization and monitoring under radioactive waste disposal pits. Both studies used core sample analyses to determine the presence of various radionuclides, organics, or metals. At one borehole site, water content and pore-water chloride concentrations were also used to interpret vadose zone behavior. At another site, we examined the feasibility of using flexible membrane liners in uncased boreholes for periodic monitoring. For this demonstration, these retrievable liners were air-injected into boreholes on multiple occasions carrying different combinations of environmental surveillance equipment. Instrument packages included a neutron logging device to measure volumetric water at regular intervals, high-absorbency collectors that wicked available water from borehole walls, or vent tubes that were used to measure air permeability and collect air samples. The flexible and retrievable liner system was an effective way to monitor water content and collect air permeability data. The high-absorbency collectors were efficient at extracting liquid water for contaminant analyses even at volumetric water contents below 10 percent, and revealed vapor-phase tritium migration at one disposal pit. Both demonstration studies proved that effective characterization and periodic monitoring in horizontal boreholes is both feasible and adaptable to many waste disposal problems and locations.
DE: 1866 Soil moisture
DE: 1875 Unsaturated zone
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting