Among the distinctive challenges presented by karst terrain are the size and spacing of the subsurface water channels, which—as compared to granular aquifers—can be relatively small and widely distributed.  These attributes make karst systems difficult targets for exploratory drillers.

One of the priorities for those dealing with karst systems, therefore, is the development of characterization technologies which are better suited to the particularities of this terrain.  This paper considers the results of recent efforts to apply Controlled Source-Frequency Domain Magnetics to the problem of karst characterization. 

The examined technique begins with the placement of electrodes into the ground water system associated with the project. The electrodes then charge the water with a low voltage, low amperage, audio frequency electrical current.  As the current forges a path through the features of the network, it emits a magnetic field that is characteristic of those features (Biot-Savart law). That field can be captured and analyzed at the surface by a specially tuned receiver. The measured magnetic field data are then processed, contoured, and correlated to other hydrogeologic data, resulting in enhanced definition of the ground water system in the study area. Because this characterization technique relies on electrical current as its subsurface tracer, it is not impeded by the dimensions and distribution of karst features.    

This paper will largely rely on information gained in a recent karst characterization case study from the upper Midwest.  It will detail both the theoretical science behind this technique and the lessons learned from its recent applications.