Optimizing groundwater quality exploration for irrigation water wells using geophysical technique in semi-arid irrigated area of Pakistan

Abstract

Geophysical method using vertical electrical sounding (VES) technique, in combination with borehole lithological data analysis was used to locate the subsurface layers containing good quality water in District Okara, Punjab Pakistan. Ten VES surveys (VES-1-10) were conducted by utilizing the Schlumberger electrode configuration. A calibrated model was developed for the study area by integrating the resistivity and lithological data. The model showed that the study area has three geoelectric layers below the water table with resistivities 50-100 Ω-m, 25-50 Ω-m and <25 Ω-m describing the good, marginal and poor quality water layers respectively. Integrated data analysis show that six sites (i.e., VES-1, VES-2, VES-3, VES-5, VES-7, & VES-10) have layers of good quality water at different depths. Out of these 6 sites, 3 sites (VES-3, VES-7 and VES-10) are suitable for installing the irrigation water wells in terms of water quality and potential while the remaining three sites (VES-1, VES-2 and VES-5) were not suitable due to shallow thickness of good quality aquifer. Three sites VES-3, VES-5 and VES-10 were selected for drilling in order to validate the modeled results, samples were collected from each 1.5–3.0 m depth for the laboratory analysis. The results showed that the resistivity data were in close agreement with the lithological data and VES-10 was most suitable for groundwater extraction. An Irrigation tube-well was installed at VES-10 and its quality was monitored for one year which showed successful supply of groundwater in terms of quality and potential.