Unique applications of MMR to track preferential groundwater flow paths in dams, mines, environmental sites, and leach fields

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Groundwater systems have been notoriously di!cult to map with high degrees of accuracy. As a result, not only have traditional geophysical methods proven inaccurate for groundwater characterization work, but they are often costly in terms of time, money, and environmental trauma. 'is paper describes a unique application of magnetometric resistivity or MMR (Edwards and Nabighian, 1991) for groundwater mapping and modeling, which is high-speed, accurate, minimally invasive, and cost e#ective. 'is method has now been deployed at many di#erent sites all over the United States and in other countries like Canada, England, Peru, Sri Lanka, and Argentina. In 2007, the method was employed at 17 dams; some are large well-known structures in the United States. 'rough two case histories, this paper will assess the e#ectiveness of this methodology.

The application of our technology, as applied to groundwater characterization, is based on the principle that the naturally ionized groundwater is more conductive than the earthen materials in which it $ows through. 'is method relies on the measurement of three orthogonal components of the magnetic %eld to track the subsurface electric current distribution. We choose to operate at 380 Hz signal to maximize the coil magnetometer sensitivity, while neglecting ground induction in data processing and interpretation. 'e electric current injection electrodes are placed in direct contact with groundwater to preferentially introduce electric current to follow the water of interest. 'e measured components of the magnetic %eld, after removing the electric wire contributions, and correction for topography, are contoured, and interpreted in conjunction with other hydrogeologic data, resulting in enhanced de%nition of preferential groundwater $ owpaths. Resolution of the electric current $owpaths depends on spacing of the measurement stations and the depth of electric current $ow. Cultural features such as metallic pipes, guardrails, power lines, and any other long continuous conductors between the electrodes, often obscure the e#ectiveness of this method.

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