| Mapping the distribution, fractional amount and type of clay is important in understanding groundwater flow and contaminant transport. Clay minerals have distinctive surface electrical properties and large surface areas that lead to decreased electrical resistivity in soils containing them and to a distinctive frequency dependent complex resistivity known as induced polarization (IP). IP depends on the clay type, concentration, cation exchange capacity and other factors, which are the same as those controlling fluid and contaminant transport. Extraction of intrinsic clay properties from surface surveys would be valuable in all hydrological studies. It is known that surface measurements of IP using arrays of current and voltage electrodes can detect clays but there has been little work to determine whether surface data can be used quantitatively to map intrinsic properties.; The inversion of surface resistivity survey data for Cole-Cole parameters first requires an accurate representation of the do resistivity and IP distribution. To investigate the accuracy of modeling and inversion algorithms this study used a horizontal 3-D rectangular slab to represent a clay body. The analysis shows that for idealized clay bodies with a high contrast with their surroundings, IP interpretation requires full 3-D modeling, especially for the imaginary components. The traditional 2-D assumption is only useful for IP interpretation if the strike extent of the body is at least 20 times its cross-sectional dimension. Further, for practical detection, and recovery of intrinsic properties, the depth of the tabular clay body cannot exceed about three times its vertical dimension.; This model study indicates that at least for confined clay rich zones accurate IP surveys can yield the data to determine the intrinsic Cole-Cole parameters. In view of this result, it appears that a major study is warranted to establish what quantitative relationships exist between the Cole-Cole parameters and the required physical-hydrological properties of clays. (Abstract shortened by UMI.)... |
