Determination of fracture apertures via calibration of three-dimensional discrete-fracture-network models: application t
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PAPER
Determination of fracture apertures via calibration of three-dimensional discrete-fracture-network models: application to Pahute Mesa, Nevada National Security Site, USA Hai V. Pham 1
&
Rishi Parashar 2 & Nicole Sund 2 & Karl Pohlmann 1
Received: 4 January 2020 / Accepted: 9 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The Pahute Mesa Corrective Action Unit on the Nevada National Security Site (USA) contains several fractured aquifers that can potentially provide high-permeability pathways for migration of radionuclides away from underground nuclear testing locations. Though geometric properties of fractures such as length and orientations, can generally be obtained by geophysical methods and borehole image analyses, their hydraulic properties (primarily influenced by their apertures) are often unknown or have a high degree of uncertainty. This study presents a novel approach to determine fracture apertures at a site by integrating numerical models of flow with data of certain geometrical fracture attributes and hydraulic response of the system because of long-term pumping. Discrete fracture network (DFN) models were used in this study to construct a three-dimensional (3-D) flow model for lava-flow aquifers of Western Pahute Mesa (WPM). Models built using a 3-D DFN code, dfnWorks, were calibrated to hydraulic drawdown observations recorded at the site of a forced-gradient experiment (BULLION FGE). Multiple conceptualizations of boundary conditions, fracture aperture distributions, and realizations of the fracture network were considered to simulate flow and migration of particles between an injection well and a pumping well. Calibrating the DFN flow models to hydraulic drawdown data constrained the ranges of aperture values and helped develop a realistic description of the properties of fractured rocks in WPM. The aperture values resulting from this study are expected to enhance understanding of radionuclide transport in WPM and support the development of large-scale flow and transport models. Keywords Groundwater flow . Numerical modeling . Fractured rocks . Fracture aperture . USA
Introduction Modeling flow and transport in fractured media is an important step in many geoscience and engineering applications, including hydrocarbon extraction, geologic carbon sequestration, aquifer storage and recovery, geothermal energy extraction, groundwater management, and radioactive and toxic industrial wastes (Bodvarsson et al. 1999; Barbier 2002; Berkowitz 2002; Lewicki et al. 2007; Tsang et al. 2008; Karra et al. 2015; Hyman and Jiménez-Martínez 2018).
* Hai V. Pham [email protected] 1
Division of Hydrologic Sciences, Desert Research Institute, Las Vegas, NV 89119, USA
2
Division of Hydrologic Sciences, Desert Research Institute, Reno, NV 89512, USA
Constructing models to study subsurface processes in fractured rocks is a formidable challenge as fractures are spatially discontinuous and exhibit strong multi-scale variability in geometric and hydraulic properties (de Dr
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