Optimizing exploration of quality groundwater through geophysical investigations in district Pakpattan, Punjab, Pakistan

Abstract

The geophysical method of investigation allied with borehole lithological logs was used integrally to explore promising zones of quality groundwater within district Pakpattan of Punjab province. Vertical electrical sounding technique of electrical resistivity survey (ERS) using Schlumberger electrode configuration was carried out to investigate subsurface hydrogeophysical conditions. In this alluvial Plain, ERS is the best tool for groundwater exploration. To achieve the target, thirty-one (31) vertical electrical soundings were conducted in the study area. A total of three (3) to five (5) geo-electric layers are identified through the software-based modeling along with the processed and interpreted resistivity data. The interpreted results decipher that the subsurface alluvial succession is primarily composed of clay, silt, sand, gravel, and some kankar inclusions. In terms of resistivity range, the study area is classified as very high (> 230 Ω-m), high (230–100 Ω-m), medium (< 100–40 Ω-m), low (< 40–20 Ω-m), and very low (< 20 Ω-m) resistivity zones. Below the water table, very low resistivity values are interpreted as unfit groundwater zones due to salinity and brackishness within thick segments mainly composed of sand and gravel. Low resistivity values are interpreted mainly as sand with admixture of fine silt and clay. The zones of low resistivity values are interpreted as groundwater with marginally fit condition. The zones of medium resistivity values are interpreted as the most promising zones of good-quality groundwater within sand-gravel strata with interbedded layers of fine silty clay/silt/clay. Moreover, below the water table, the zones of high and very high resistivities are also interpreted as the source of good quality groundwater. The 2D maps of the study area also lead to delineating fresh and saline groundwater zones. The saline zone appears at the depth of 50 m but the salinity increases rapidly with depth and goes on to replace the fresh groundwater as well. For irrigation and other industrial use, the optimizing site selection for water well installations is the key to a cost-effective approach and management of groundwater resources as well. To yield good-quality water, the locations of VES-1, 2, 6, 9–12, 14–17, and 21–31 are the most promising sites for installation of water wells at shallow depths. The water well can be installed within any suitable depth < 50 m. However, water turns to saline or marginally fit while depth increases. At VES-3, 4, 5, 7, 18, 19 and 20 the groundwater is expected to be marginally fit at even shallow depths. So, the water well installation at these sites would be optional and in only case of water shortage.