Aquifer characterization using geophysical borehole-logging and hydrochemical techniques—a case study from Lahore, Pakistan

Abstract

Aquifer characterization is crucial, specifically in regions where it continuously depletes and deteriorates with time. This study deals with geophysical and hydrochemical borehole logging techniques to assess the lithology of the Lahore aquifer and its impact on groundwater chemistry. To execute this study, eight observatory wells were installed in the selected regions at 200 ft depth to run MGX-II logger. According to the results of the water samples collected from the boreholes the concentrations levels of majority of the physicochemical parameters are within allowable limits prescribed by the WHO except As, HCO₃ ^–, and TDS. Geochemical analysis indicate the existance of geogenic activities, resulting from the weathering of carbonate (calcite and dolomite) and silicate (quartz, feldspar, pyroxene, amphibole, mica, and olivine) minerals. The Gibbs plot and Pipper trilinear diagram revealed that Na⁺–HCO₃⁻, Ca²⁺–Na⁺–HCO₃⁻, and mixed Ca²⁺–Mg²⁺–HCO₃⁻ are the eminent soil and rock-weathering processes. The aquifer was efficiently delineated as unconsolidated sands, silt and clay particles based on the lithological logs and natural gamma-ray data showing a wide variation between 20.44 and 195.47 cps. The outcome of the multi-parameter probe revealed that the in situ measured temperature, thermal gradient, pressure, pH, and redox potential (Eh) varied between 12.1 and 22.5 °C, 0.004 –0.02 °C/ ft, 5.34–8.13 dbar, 6.7–8.7, and 112 to 232 DmV, indicating the anoxic condition in the Lahore aquifer respectively. This study successfully reveals the effectiveness of the combined use of advanced geophysical and hydrochemical borehole log measurements at the regional level.