Geoelectric and Borehole Lithology Studies for Groundwater Investigation in Alluvial Aquifers of Munger District, Bihar

Geoelectric studies and borehole logs of Older and Younger Alluvium adjacent to Chhotanagpur plateau fringe area in the district of Munger, Bihar, indicate the presence of clay unit at many places near the surface and occasionally at depths. The clay unit does not occur as a continuous layer. This indicates that the aquifer, in general, is under unconfined condition Study of borehole logs and results obtained from interpretation of vertical electrical soundings are useful to find out potential groundwater bearing zones. A panel diagram has been prepared to understand the nature and disposition of the aquifer(s) and thereby hydrogeological framework prevailing in the area Based on comparison of interpreted sounding data and available borehole log information, resistivities of different lithological formations have also been determined. Layer parameters obtained from vertical electrical sounding( VES) studies corroborate the lithologs of the area Estimation of aquifer hydraulic properties using surface electrical resistivity method has also been attempted. For such estimation, hydraulic conductivities and transmissivities determined from pumping tests have been correlated with resistivities obtained from electrical soundings. Empincal relations between (i) aquifer electrical resistivity and aquifer hydraulic conductivity, (ii) aquifer resistivity and specific capacity and (iii) aquifer transverse resistance and transinissivity have been developed. All the relations thus developed can be used for estimation of hydraulic properties of the aquifer(s)of the study area. Using geoelectric data and applying Archle's equation, an estimation of the bulk porosity of the aquifer is done and it ranges from 0 295 to 0.477