Investigating the groundwater resources of weathered bedrock using an integrated geophysical approach

• Published in: Environmental earth sciences Vol. 82; no. 9; p. 213
• Main Authors: Hasan, Muhammad, Shang, Yanjun
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.05.2023; Springer Nature B.V
• Subjects: Aquifers; Bedrock; Biogeosciences; Boreholes; clay fraction; Earth and Environmental Science; Earth Sciences; electrical resistance; Electrical resistivity; Electrical studies; Electrode polarization; Electrodes; Environmental Science and Engineering; Fault lines; Fractures; Geochemistry; Geoelectricity; Geological faults; Geology; Geophysical exploration; Geophysical methods; geophysics; Groundwater; Groundwater flow; Groundwater resources; Hydraulic conductivity; Hydraulic properties; Hydrology/Water Resources; Induced polarization; Magnetic permeability; Magnetic surveys; Magnetic susceptibility; magnetism; Magnetometers; Methods; Original Article; Profile method (forecasting); Proton precession; Rock; Rocks; surveys; Terrestrial Pollution; Tomography; Transmissivity; Water resources; Self-potential; Fractures; Electrical resistivity tomography (ERT); Magnetic method; Weathered rock; Induced polarization
• ISSN: 1866-6280; 1866-6299
• DOI: 10.1007/s12665-023-10892-5

Groundwater occurs within fractures of crystalline hard-rock. Mostly, these fractures are covered by weathered rocks; therefore, delineation of their spatial position is a challenge task. Geophysical methods are widely used to obtain subsurface geological information in the weathered terrains. However, use of single geophysical method may be ambiguous to reliably assess the highly heterogeneous crystalline hard-rock. As part of an ongoing study to choose the most suitable methods towards this end, an incorporated study of electrical resistivity tomography (ERT), magnetic, vertical electrical sounding (VES), self-potential (SP), and induced polarization (IP) coupled with limited pumping/borehole tests was performed to assess the distinct geologic layers, to trace the main faults/fractures, to make a clear distinction between water and clay content, to identify groundwater flow, and to estimate groundwater yield of the fractured/weathered rock. ERT data were collected along four geophysical profiles using ABEM LUND Imaging System for 358 electrodes with 5 m electrode spacing. Magnetic survey along the same ERT profiles was performed using two G-856 proton precession magnetometers with 0.1 nT sensitivity to acquire 358 measurements with 5 m station interval. The Joint Profile Method JPM (ER-IP-SP) was performed for 87 electrodes using WDJD-4 with 10 m electrode spacing along two profiles. A two-layered subsurface model of weathered and unweathered rock was obtained by the incorporation of upfront boreholes with subsurface resistivity and magnetic susceptibility. Integration of ERT and magnetic models with JPM curves revealed several localized fractures/faults. Hydraulic properties specifically transmissivity and hydraulic conductivity obtained from geoelectrical resistivity data were used to estimate aquifer potential enclosed within the fractured/weathered rock. Integrated geophysical results are well correlated with borehole data. This study provides the best alternative of the costly traditional methods for more reliable evaluation of groundwater reserves in the heterogeneous settings.