Problems and Prospects of Geophysical Methods in Identifying Groundwater Potential Zones of Hard Rocks

The case studies of success and failed wells are taken up to identify the efficacy of the various geophysical techniques to identify the aquifers in the khondalitic formation, granitic formation and basaltic formation. Geophysical surveys were conducted at pairs of successful and failed wells covering all the three formations in such a way that the failed well and successful wells are only few metres apart and are in similar hydrogeologic setting. The comparison of geophysical signals have revealed that studying of coefficient of anisotropy is important by conducting radial vertical electrical soundings to identify the fracture distribution. To produce a good well yield fracture system must extend in all the four directions which is identified with high values of coefficient of anisotropy while the unidirectional fracture system may not produce the good well yield which is identified with less value of coefficient of anisotropy. Shallow Seismic Refraction method could not be of much help to find the fracture zones. Similarly Very Low Frequency electromagnetic method is of some use where inclined and nearly vertical fractures present.