Hydraulic tomography for characterizing subsurface heterogeneity in fractured rocks: implications for in-situ recovery mining

In-situ recovery (ISR) mining demands reliable forecasts of groundwater flow and solute transport, which are highly sensitive to subsurface heterogeneity. This study evaluated alternative modeling approaches for characterizing heterogeneity using data from Denison’s Wheeler River Property, Saskatchewan, Canada. Spatial distributions of hydraulic conductivity (K) and specific storage (Ss) were characterized using four modeling cases: a homogeneous case, a geology-based zonation case, and two hydraulic tomography (HT) cases. All models were calibrated against 17 cross-hole aquifer tests, with one HT model additionally constrained by long-term feasibility field test (FFT) responses. Estimated K and Ss fields from four cases were subsequently validated against independent tracer test data. Results revealed systematic improvements in predictive performance with increasing model complexity, with HT models reproduced observed hydraulic responses and breakthrough curves with higher fidelity. Incorporating FFT data further enhanced delineation of large-scale hydraulic connectivity and improved BTC prediction at the more distant extraction well. These findings underscore that treating K and Ss fields to be heterogeneous and accurately characterizing their spatial distributions are essential for realistic simulations of groundwater flow and solute transport in ISR operations. Overall, we conclude that HT is an effective approach to support ISR wellfield design, recovery optimization, and environmental protection.