Identification of water-bearing fractures in hard rock terrain by electrical conductivity logs, India

For the delineation of water-bearing fractures in hard rock areas, a new hydro-chemical technique has been developed which is based on electrical conductivity (EC) logs. The EC logs were carried out in experimental shallow bore wells (≈50 m) in three different parts of India. A sharp variation in EC was observed near water-bearing fractures in hard rock areas. To access applications of this technique, different locations in India were selected and experimental bore wells (≈50 m) were drilled. These were:

(1)	Maheswaram (30 km South of Hyderabad): nine shallow bore wells in a watershed of 60 km2 in granitic aquifers,
(2)	Wailpally (60 km East of Hyderabad): four shallow bore wells in a watershed of 50 km2 in granitic terrain.
(3)	Sadras (60 km SSW of Chennai): four shallow bore wells in a watershed 12 km2 in a charnokite aquifers.

Observations on EC logs were made at short intervals of 1.0 m from the water table (narrow spacing wherever required) until reaching the bottom of the wells. EC showed remarkable changes in value, which was attributed to the presence of water-bearing fractures in the hard rock areas. The results of this study are in good agreement with geophysical and geological findings. In addition to identifying the water-bearing fractures, the EC logs also provide various other hydrological and hydrochemical information, i.e., water table, total depth of the bore well, total dissolved solids (TDS), behavior of water–rock interaction, water quality, information about the chemistry of aquifers, etc.