Groundwater investigations in parts of Alwar district, Rajasthan

Geohydrological investigations including deep resistivity Schlumberger soun dings were carried out to locate suitable drilling sites for groundwater ex ploitation near Ramgarh, Alwar district, Rajasthan. The area under study ap pears to be a synclinal valley and is covered by a thick pile of sediments comprising sand, silt, clay, gravel, pebble, kankar and scree underlain by rocks of Ajabgarh Group, which are exposed north-west of the area. The subs urface layer parameters obtained from the sounding interpretation have been presented in the form of fence diagrams and a geoelectric section. Charact eristic resistivities of various lithe-units were obtained by correlating t he lithology of an existing tube well with the geoelectrical sounding data. The correlation indicated that there is very little resistivity contrast b etween water-bearing sandy layers and the kankar and clay beds. However, th e 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 tenses, the present investigations reveal a surprisingly low resis tivity 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 ruled out.