Open Cut » Environment
The aim of this project was to evaluate geophysical methods for detecting the spatial distribution of major flow pathways and water tables within spoil piles, to support numerical predictions of spoil seepage volumes and quality. Geophysical methods are considered non-invasive alternatives for characterising and monitoring subsurface hydrogeology, particularly where multiple drill holes are required to capture heterogeneity and where ongoing issues exist with in-situ sensors.
Field based geophysics survey
Electrical Resistivity Tomography (ERT) was employed to characterise subsurface moisture distribution and oxidation zones within spoil piles. Findings indicate that spoil hydrology is strongly influenced by the original pit geometry and compacted layers formed during placement.
Spoil Characterisation
Sampling from drill cores was designed to obtain representative spoil materials from key hydrostratigraphic units within the backfilled open cut for subsequent laboratory characterisation.
Geophysics Laboratory tests and petrophysical model
Laboratory measurements allowed calibration of petrophysical relationships that translate geophysical properties into hydrogeological parameters such as water content and permeability. Spectral induced polarisation (SIP) was applied in the laboratory to measure the frequency-dependent electrical properties of selected spoil samples, providing insights for interpreting field-based ERT and IP data.
Numerical Modelling and Flow Pathway Analysis
The numerical model used TOUGH2 and TOUGHREACT to simulate coupled fluid flow and geochemical reactions in the backfilled spoil, allowing assessment of flow pathways, water table development, and contaminant migration.
Integration of results
The project did not attempt a quantitative integration of the geophysics-derived parameter distributions with the numerical model. Instead, the interpretations from ERT tomograms, borehole moisture distributions and pit topography were used to inform the conceptual model.