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Fractured aquifers impose challenges in predicting solute transport as the complex connectivity within discrete fracture networks, mass exchange between rock matrix and fractures and heterogeneous rock permeability should be considered. This research presents a holistic approach to characterize hydrogeologic features of fractured aquifers and to establish a predictive model for flow and transport processes. We focus on a field site located in the University of Minnesota, Twin Cities campus, which has been developed as a research and teaching facility for the purpose of improving our ability to predict groundwater flow and solute transport in fractured rock aquifers.
Tracer tests conducted at the site revealed a strong tailing with power law slopes of 1.1 and 1.29. Aquifer tests, borehole logging, Discrete Fracture Network (DFN) modeling, and Electrical Resistivity Tomography (ERT) were conducted to improve the subsurface characterization and assess the role of matrix and fractures on producing the anomalous solute transport observed in the breakthrough curves.
Ten injection tests were performed using three Multi-Level Hydraulic Packer and Port Systems (MHPS) that isolated the main Bedding Parallel Parting fracture (BPP) and measured water level responses with pressure transducers and Fiber-Optics pressure transducers. Subsurface parameters were estimated by using various pumping test analytical solutions for porous and fractured media.
These field data, and fracture statistics obtained from outcrops, were incorporated into a three dimensional Upscaled Discrete Fracture Matrix (UDFM) model to simulate flow and transport processes at the field site to reproduce the tracer tests. Achieving predictability, especially in late-time regimes, simulation results with sensitivity analysis suggests that high matrix permeability underpins the strong tailing.
Ongoing DFN simulation aims to assess the role of fractures on the anomalous solute transport and a Hydraulic Tomography inversion is planned to evaluate the connectivity and pathways across the site. Preliminary ERT results showed promise approach for tracking the injected water displacement and highlighting the water pathways in the fractured system.
| References | Wang, L., Yoon, S., Zheng, L., Wang, T., Chen, X., and Kang, P. K. (2023). Flux Exchange Between Fracture and Matrix Dictates Late-Time Tracer Tailing. Journal of Hydrology, Vol. 627, Part B. https://doi.org/10.1016/j.jhydrol.2023.130480; Yoon, S., Hyman, J. D., Han, W. S., and Kang, P. K. (2023). Effects of Dead-End Fractures on Non-Fickian Transport in Three-Dimensional Discrete Fracture Networks. Journal of Geophysical Research: Solid Earth, 128, e2023JB026648. https://doi.org/10.1029/2023JB026648 |
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| Country | United States |
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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