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  • Journal of Environmental and Engineering Geophysics  (1)
Type of Medium
  • 1
    Language: English
    In: Journal of Environmental and Engineering Geophysics, 03/2004, Vol.9(1), pp.1-10
    Description: A series of laboratory experiments that measured electrical properties and permeability was performed on carefully characterized sand-clay mixtures. Different mixtures and configurations of quartz sand and 10% Na-montmorillonite clay were investigated using solutions of NaCl, CaCl sub(2), and deionized water. A sample containing 10% dispersed clay was also studied using fluids containing 20- and 500-ppm trichloroethylene (TCE). Each sample's electrical properties after fluid saturation were measured at frequencies between 10 super(-2)and 10 super(6)Hz by using the four-electrode method with Ag-AgCl inner electrodes at room temperature and 412 kPa confining pressure, which corresponds to a soil depth of 15-20 m. Our results show that adding TCE had a small effect on electrical resistivity: resistivity was greater at higher concentrations of TCE. The influence of TCE on electrical properties was most prominent in plots of loss tangent as a function of frequency. These plots showed that loss-tangent peaks occurred at ~200 Hz and that peak and peak frequency were smaller at higher concentrations of TCE. Additional experiments were performed on a sample that contained a distinct clay layer parallel to the current flow. The electrical properties of the sample were measured as it was saturated with deionized water and CaCl sub(2)solutions, and as an ethanol-water mixture (80:20) was flowed through the sample. Resistivity increased by about a factor of 4 as the ethanol mixture replaced the water solution. Nondestructive x-ray imaging of the sample at various stages of dewatering indicated a decrease in the thickness of the clay layer as more pore volumes of ethanol-water were flowed. Our results show that electrical measurements are useful tools for characterizing porous rocks and soils and that it is feasible to remotely detect the presence and follow the transport of contaminants such as TCE in the subsurface.
    Keywords: Scientific Research ; Soil Depth ; Clay ; Sand ; Electrodes ; Solvents ; Geophysics ; Trichloroethylene ; Ethanol ; General ; Electrical Properties;
    ISSN: 1083-1363
    E-ISSN: 1943-2658
    Source: CrossRef
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