Three‐Dimensional Analysis of Heat Tracer Transport With High‐Resolution Subsurface Heterogeneity Characterization in a Complex Aquifer System

Abstract

Accurate predictions of tracer transport in complex aquifer systems remain a formidable challenge, primarily owing to the spatial heterogeneity of hydraulic conductivity ( K ). Here, we conducted a forced‐gradient heat tracer test within a highly heterogeneous glaciofluvial deposit, injecting chilled water and monitoring temperature at depth‐specific ports, which revealed highly non‐uniform, three‐dimensional plume migration. To investigate whether such complex transport behavior can be reproduced with subsurface heterogeneity characterization approaches, we compared transport simulations based on several K representations: kriged and zonal K fields derived from direct‐push K logging, permeameter measurements, and pumping test data, as well as hydraulic tomography (HT) results, which utilized the geostatistical inverse modeling of head response data from multiple pumping tests to map K heterogeneity. Furthermore, we employed borehole nuclear magnetic resonance logging to estimate porosity distributions. We examined the impacts of porosity, mechanical heat dispersivity, and thermal conductivity on heat tracer transport. Results showed that K heterogeneity is the key factor governing the highly variable temperature breakthrough curves observed across the monitoring network. Simulations relying on spatial correlation of borehole data were insufficient to capture the three‐dimensional thermal patterns, whereas the HT‐based simulations reasonably reproduced the spatiotemporal evolution of the tracer plume and delineated the advection‐dominant regions, without site‐specific calibration to transport data. Our findings demonstrate that HT analysis provides a reliable basis for predicting heat tracer transport behavior in complex aquifer systems.