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Two-dimensional detection of underground contamination and buried objects using cross-well radar

Traditional approaches for locating and characterizing contaminated sites rely on invasive techniques which require drilling, testing, and sampling. These techniques provide the most direct access to the subsurface, but they are generally expensive and only provide measurements at points in a three dimensional surface. Furthermore, invasive techniques in polluted areas can promote further spread of contaminants. Development of non-invasive techniques that offer rapid and relatively inexpensive characterization is, therefore, necessary to detect and monitor plumes and sources of contaminants. Non-invasive techniques are also required for locating buried objects, such as landmines and unexploded ordnances. The use of cross well radar (CWR) as a non-invasive technique that has proven to be a reliable technology for detection of target objects that exhibit significant contrast of dielectric properties in saturated soils. Its application to detection of heterogeneously distributed phases in unsaturated soils under variable flow conditions has yet to be developed. This paper addresses the development of 2D flow and electromagnetic (EM) soilBed setup to further assess and enhance CWR technology for the detection of Dense Non-Aqueous Phase Liquids (DNAPLs) contamination and other target elements in variably-saturated soils subjected to transient flow conditions. Loop antennas have been developed and tested for this purpose. Transmission and reflection measurements are evaluated to determine the antenna's reliability and optimize their performance in the 2D electromagnetic field. The measurements indicate that a 2D EM boundary condition may be imposed by placing two parallel perfectly-reflecting metal plates along one of the dimensions of the soilBed setup. Transmission and reflection characteristics of the antennas vary with their method of construction. Results show a reliable and reproducible response from the loop antennas, but suggest some wave leakage and indicate that their design must be optimized. Measured variations in the transmission, reflection and impedance in the presence and absence of a buried object suggest that the 2D EM soilBed setup using loop antennas can be aplied to detect target elements in subsurface environments subjected to flow conditions. Future work addresses the assessment of CWR technology as a non-invasive method for detection and monitoring of heterogeneously-distributed target objects in subsurface environments.