STP1415: Water Potential Response in Fractured Basalt from Infiltration Events

    Hubbell, JM
    Advisory Scientist, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

    Mattson, ED
    Advisory Scientist, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

    Sisson, JB
    Consulting Scientist, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

    McElroy, DL
    Staff Scientist, Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID

    Pages: 19    Published: Jan 2002


    Abstract

    The detection of moisture movement in the vadose zone beneath hazardous waste disposal sites is important for monitoring and predicting contaminant transport in the subsurface. This study was conducted to determine if moisture movement could be detected from natural water infiltration in a dual porosity, fractured basalt at the Idaho National Engineering and Environmental Laboratory (INEEL). Episodic infiltration events were determined by examining long-term water potential over three and a half years. Water potential measurements were collected from 2 to over 30 m below land surface. Instruments were placed in both fractured and unfractured basalt media. Water potential measurements were within the tensiometric range, from approximately +100 to −250 cm of water. Typically, water potentials within the fractured basalt exhibited a near steady-state unit-gradient downward flux. However, episodic snowmelt infiltration events at land surface produced detectable changes in water potentials at depths to 15.5 m, in some cases within a few days of the infiltration events. Smaller infiltration events were difficult to distinguish due to fluctuations in water potential resulting from changes in barometric pressure. Water potential responses in boreholes varied both temporally and spatially during episodic infiltration events indicating preferential flow pathways through the fractured basalt. The results of this study indicate that water potential measurements can be used to detect and monitor deep infiltration events at waste disposal sites using tensiometers.

    Keywords:

    water potential, vadose zone, fractured rock, tensiometer, infiltration, percolation, recharge


    Paper ID: STP10618S

    Committee/Subcommittee: D18.02

    DOI: 10.1520/STP10618S


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