Widespread contamination of underground environments with dense non-aqueous phase liquids (DNAPLs) is of
great concern to the public, military, and industrial sectors. Proper management of contaminated sites requires
detection and monitoring of the contaminants, and accurate knowledge of their transport behavior in underground
environments. Over the last years we have done great efforts to develop and integrate technologies that serve to
locate contamination and monitor transport mechanism underground. In this paper, we describe a two-dimensional
multiphase flow experiment to develop and evaluate two modes of concurrent detection and monitoring
technologies: Cross Well Radar (CWR) and Image Analysis (IA). Loop antennas preset at specific locations in the
tank are used to evaluate wave scattering properties of the soil under different conditions, while color images are
acquired. The electromagnetic response in the CWR antennas and IA are used to establish the relation between
electrical soil properties variations and changes spatial and temporal mass of water and contaminants. The
technologies used in this research are both in development, but they can be successful tools for the detection,
monitoring and imagining of underground contaminants and process. Once develop, the technology may be applied
for detecting and monitoring other buried objects.
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.
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