Application of electrical resistivity tomography, saline tracer and numerical studies to delineate preferential flow and transport paths in fractured granites

An accurate quantification of in situ heterogeneity and flow processes through fractured geologic media remains elusive for hydrog eologists due to the complexity involved in fracture characterization and its multi - scale behavior. In this research, we demonstrated the efficacy of tracer - ERT experiments coupled with numerical simulations in delineating heterogeneity and preferential fl ow paths of a fractured granite aquifer. A series of natural gradient saline tracer experiments were conducted from a depth window of 18 to 22 m in an injection well located inside IIT Hyderabad campus. Tracer migration was monitored in a time - lapse mode u sing two cross - sectional surface ERT profiles placed in the direction of flow gradient. ERT data quality was improved by considering stacking, reciprocal measurements, resolution indicators, and geophysical logs. The dynamic changes in sub - surface electric al properties inferred via resistivity anomalies were used to highlight preferential flow paths of the study area. Temporal changes in fluid resistivity, electrical resistivity, and tracer concentration were monitored along the vertical in an observation w ell located at 48 m to the north - east of injection well. ERT derived tracer break through curves were in agreement with geochemical sample measurements (R 2 =0.74). Fracture geometry and hydraulic properties derived from ERT and pumping tests were used to ev aluate two mathematical conceptualizations that are relevant to fractured aquifers. Results of numerical analysis conclude that, a dual continuum model that combines matrix and fracture systems through a flow exchange term has outperformed equivalent conti nuum model in reproducing tracer concentrations at the monitoring wells (evident by decrease in RMSE from 199 mg/l to 65 mg/l). A sensitivity analysis of the model parameters conclude that spatial variability in hydraulic conductivity, local - scale dispersi on, and flow exchange at fracture - matrix interface have a profound effect on model simulations