Vertical electrical sounding (VES) resistivity survey technique to explore low salinity groundwater for tubewell installation in Chaj Doab

Groundwater quality is deteriorating due to ongoing heavy pumping of groundwater in Punjab, Pakistan. Geoelectrical resistivity survey technique was used to assess the potential of fresh water layer lying over the saline groundwater. A field survey was conducted during 2007-08 at three sites (i.e. Chak No. 52 (Chaj 1), Chak No. 100 (Chaj-2) and Chak No. 101 (Chaj-3) in Chaj Doab (land between river Jhelum and Chenab) during 2007-08. The resistivity meter (ABEM Terrameter SAS 4000, Sweden) was used to collect the vertical electrical sounding (VES) resistivity data at these three sites. For this purpose the Schlumberger electrode configuration was followed with half current electrode spacing (AB/2) ranging from 2 to 180 m and potential electrode (MN) from 1 to 40 m. The collected data were interpreted in terms of resistivity and corresponding thickness of various sub-surface layers using "Interpex IX1D" computer software and the outputs were verified using borehole data. The bore hole data of lithological and groundwater samples were collected from ground surface to 30 m depth with an interval of 1.5 m at these three sites. The correlation between VES and borehole data was found to be in close agreement with each other. The combination of VES data with borehole data provided useful information on subsurface hydrogeologic conditions. It was observed that geoelectrical resistivity of the layers containing groundwater ranged between 2.5 to 50.4 omega and VES criteria of fit groundwater quality for aquifer resistivity values of 45 omega was valid for the sites. The results also showed that effective depth of the current penetration ranged between 1/8 to 1/2 of outer current electrode spacing (AB/2). The results indicate that VES survey has the potential to identify the layer containing water and quality of groundwater depth and thickness for its development.