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Advanced Tensionmeter for Vadose Zone Monitoring

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Tech ID: 2122
Project Overview
Fluid movement and contaminant transport in fractured rock is important at INEEL, Hanford, and Oak Ridge because the subsurface at those sites contains natural fractures. The fracture system and the flow characteristics must be understood before effective cleanup or stabilization can be accomplished. This project investigates and develops combinations of instruments, techniques, and tests to establish flow paths and transport mechanisms. It uses combinations of 'point' measurement technologies, including tensiometers, suction lysimeters, time domain reflectometry, thermistors, and miniature electrical resistivity probes. It uses slanted wells to intersect vertical fractures, video borehole scanning, and a new borehole instrumentation completion method using polyurethane foam. Data visualization and modeling are also employed.
Technology Description
For the suite of technologies developed jointly (Analog Site for Characterization of Contaminant Flow and Transport through Fractured Rock) and (Integrated Geophysical and Hydrological Characterization of Transport through Fractured Media), the estimate for savings is minimum of $1,000,000 per known contaminated site or waste burial site in or above fractured Rock (as compared to current costs). The savings are expected to result from improved design of containment or cleanup actions, and from improved performance assessment, the latter sometimes resulting in a decision requiring NO FURTHER ACTION. The Vadose Zone Monitoring Well (VMW) is a monitoring instrument used to measure the soil water potential (the affinity of water to soil) in sediments or rock between land surface and the water table. The VMW is a tensiometer that has been redesigned to provide soil water potential at any depth and in the process provides data that exhibits an order of magnitude less diurnal fluctuations than conventional tensiometers. Conventional tensiometers have been used for fifty years and are considered the most precise of the vadose zone instruments. However, they could not be used below a few meters below land surface and tend to have significant diurnal measurement fluctuations. The VMW can be used in many fields for practical applications including slope stability monitoring, water management for agriculture, and environmental monitoring as well as basic science to evaluate water movement in deep vadose zones. Soil water potential data is used to quantify the hydraulic gradient in the unsaturated zone to determine the rate and direction of water movement. This information is vitally important at waste disposal sites since nearly all waste is disposed above the water table and any leakage moves through the vadose zone prior to entering potable water supplies. Monitoring in the vadose zone using the VMW can then be used to forewarn water disposal site prior to contamination of water supplies when the problem has become acute. The VMW provides an elegant solution to the problem of obtaining water potential measurements at depths greater than a few meters. The configuration of the VMW also allows other vadose zone monitoring to be performed using the permanently installed portion of the well and then interchanging instruments including geophysical monitoring, moisture and gas sampling, temperature or thermocouple psychrometry.

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