Magnetic resonance sounding (MRS) is distinguished from other geophysical tools used for ground water investigation by the fact that it measures a magnetic resonance signal generated directly from subsurface water molecules. An alternating current pulse energizes a wire loop on the ground surface and the MRS signal is generated; subsurface water is indicated, with a high degree of reliability, by nonzero amplitude readings. Measurements with varied pulse magnitudes then reveal the depth and thickness of water saturated layers. The hydraulic conductivity of aquifers can also be estimated using boreholes for calibration. MRS can be used for both predicting the yield of water supply wells and for interpolation between boreholes, thereby reducing the number of holes required for hydrogeological modeling. An example of the practical application of MRS combined with two-dimensional electrical imaging, in the Kerbernez and Kerien catchments area of France, demonstrates the efficiency of the technique.

At bioreactor landfills, biodegradation parameters are carefully controlled to achieve faster stabilization of the waste mass. For example, liquid (leachate) injection into the waste mass is used to increase waste moisture content and thereby enhance waste degradation. The objective of this study is to validate the use of non-intrusive two-dimensional electrical resistivity imaging (ERI) for monitoring a liquid injection system, and to determine the relationship between measured resistivity and water content variations in waste. Temporal variations of waste electrical resistivity, during leachate recirculation, are mainly linked to water and ionic content variations. Two-dimensional ERI monitoring was carried out at a municipal solid waste landfill using a multi-channel resistivity meter to follow transient resistivity variations during leachate recirculation in the waste mass. Resistivity variations mainly correspond to variations in water content, and to temperature variations resulting from the injection of cold leachate into the warm waste mass. Laboratory experiments can be used to calibrate water content variations in the waste as a function of variations in electrical resistivity. Although such an approach is realistic for short measurement periods (hours), it is not reliable over longer time periods (months) since other parameters, such as biodegradation of the waste, may also influence its electrical resistivity.

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The stream function described is employed for the presentation of 2D DC modeling results. The 2D model is understood as a 2D medium with linear current electrodes, oriented along the inhomogeneities' strike direction. In this case both the medium and the electric field depend on two space coordinates only. Modeling becomes much easier than considering point current electrodes, where the electrical field always is three-dimensional. Meanwhile the actual results of such modeling are qualitatively equivalent to 3D modeling with point electrodes, as long as the measurements are conducted across the objects. The classical modeling presentation is in apparent resistivity which reflects an electric field distribution on the earth's surface. Quite often the connection of measured anomalies with a geoelectrical model is rather complex (fig. 1, A and C). The visualization of DC current lines simplifies understanding of the electric field's structure. Current lines are used in almost each textbook, but a practical technique for their construction is usually not included. The evident way for drawing current-lines is the step by step continuation of a line from some point along the electric field direction. The practical realization of such approach is not trivial. For a 2D field it is possible to use the stream-function. This function is often used in EM field modeling [flux function, Berdichevsky, 1984]. A contour map of the streamfunction corresponds to the streamline distribution. Thus the problem of current streamlines' construction is reduced to the calculation of the streamfunction in the research area. This can be achieved by calculating secondary surface charges, which are determined at 2D modeling, using Fredholm's integral equation of the second type relatively of electric field [Escola, 1979].