Electrokinetic sounding applied to well and borehole siting : an appraisal

This report is written to summarise the findings of project R6232 whose goal was to improve the assessment, development and management of water resources. The stated purpose was ‘to increase the success rate of well and borehole siting, in diverse hydrogeological environments, by assessing and developing a ‘new’ electrokinetic (EK) geophysical methodology’. With hindsight, the assessment and development requirements have proved to be far more intricate and involved than was originally envisaged. Simple hydrogeological questions (does the method work, or have any value?) have, of necessity, required detailed geophysical research. One of the reasons for the complexity stems from the technical platform used for the assessments. The EK instrument and procedures were purchased from a new company who had developed the world’s first commercial system for EK sounding. The claims made for the system were considerable; the available background to the methodology was minimal. In order to provide objectivity, it has been necessary to review and examine the physical theory alongside the measurement/processing techniques used. These developments had then to be assessed alongside the results of field experiments both in the UK and overseas. A second reason for the complexity has been the nature of the wavefields employed The two fields used are acoustic (source) and electromagnetic (received). Individually both fields are well-defined following established geophysical methodologies which routinely employ them. The EK method exploits subsurface coupling of these wavefields. Theoretical predictions concerning the nature of the fully-coupled wavefields are difficult and limited. To our knowledge there is only one recent paper (Mikhailov et al.,1997) that attempts to deal adequately and practically with the numerical simulation of electrokinetic signals observed in the field. Even this assessment is quite limited.