Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

R. L. Dhar ¹, N. S. Krishnamurthy ¹, B. A. Prakash ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad-500007, IN

Abstract

Geohydrological investigations including deep resistivity Schlumberger soundings were carried out to locate suitable drilling sites for groundwater expIoitation near Ramgarh, Alwar district, Rajasthan. The area under study appears to be a synclinal valley and is covered by a thick piIe of sediments comprising sand, silt, clay, gravel, pebble, kankar and scree underlain by rocks of Ajabgarb Group, which are exposed north-west of the area. The subsurface layer parameters obtained from the sounding interpretation have been presented in the form of fence diagrams and a geoelectric section. Characteristic resistivities of various litho-units were obtained by correlating the lithology of an existing tube well with the geoelectrical sounding data. The correlation indicated that there is very little resistivity contrast between water-bearing sandy layers and the kankar and clay beds. However, the kankar and clay beds are mostly confined to the top 20 m or so. Although occurrence of clay has not been reported in rocks of Ajabgarh Group except for thin lenses, the present investigations reveal a surprisingly low resistivity for the formation underlying the bedrock, which may be an indication of its saline and clayey nature. The possibility of an altered horizon in the bedrock comprising metasediment through lateral inflow of water cannot be ruIed out.

Keywords

Hydrogeology, Groundwater, Resistivity Sounding.

Full Text

     

Dewashish Kumar ¹, N. S. Krishnamurthy ¹, Shekeel Ahmed ¹, S. C. Jain ¹, R. L. Dhar ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Mise-a-la-masse technique has been applied to map water filled fracture1 struck in bore wells in a small watershed near Hyderabad. The area consists of hard crystalline rock mainly granite where groundwater is mostly tapped from iractured rock. In the watershed, 25 wells have been drilled fairly distributed over the area on the basis of results of Vertical Electrical Soundings (VES) to study the groundwater conditions in the weatheredffractured aquifer system. Mise-a-la-masse and Spontaneous Polarization (SP) investigations were carried out at five out of these 25 sites, to delineate the lateral extension of fractures. The anomalies are clearly indicative at four locations and some indication is seen at the fifth location. Two bore wells drilled on the basis of these results have encountered fractures at the same depth as at the experimental site. It is concluded that mise-a-la-masse technique supplemented with S.P. investigations could be helpful in delineating the extension of fractures.

Keywords

Mise-a-la-Masse, SP, Electrical Mapping, Fractures in Hard Rock, Maheshwaram Watershed, Andhra Pradesh.

Full Text