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Ali Zafarani Subsurface Processes Group University of California, Irvine

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Groundwater is one of the main resources to provide water consumption needs Sources of pollution: Chemicals (detergents, petroleum, etc.), Radionuclides, Seawater, Pathogens Understanding the transport mechanisms of contaminants Designing infrastructures and hydrogeologic systems Designing remediation systems Estimate of damage

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Provide pathways for fluid flow Large scale fracture networks Reservoirs formed in fractured rocks Fractures appear in many kinds of geological systems

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Advection Transport of particle with the flow field Dispersion (Effective Longitudinal Dispersion) Molecular Diffusion Taylor dispersion Macro scale dispersion

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3-D Navier-Stokes Equation 3-D Stokes Equation 2-D Reynolds Equation Inertial<< viscous and pressure Changes in fracture aperture are smooth Normal velocity to fracture walls are negligible 3-D 2-D Inertial forces Viscous forces Pressure term Momentum Eq. Mass Conservation

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Fick’s first law of Diffusion diffusive flux ~ spatial concentration gradient Fick’s second law of Diffusion Changes of concentration field with time Diffusion Coefficient [L 2 /T]

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Parabolic distribution of velocity in aperture ~ square mean velocity ~ Mean aperture size b V

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Dispersion caused by variety of pathways

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CCD Camera Porous media cell Rotating stand Uniform light source Textured glass plates provide analog to fracture surfaces. Rotating test stand holding test cells and equipped with a high resolution 12-bit CCD camera (2048 x 3072 pixels) Fracture plate 3/4” flat glass No flow boundary Inlet manifold Aluminum frame Reference wedge Clear PVC gasket Confinement pressure inlet

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Measured light intensities are used to accurately quantify: Fracture aperture Solute concentrations at high resolutions over entire flow field. Measurements can be used to calculate Solute dispersion Aperture (cm) 0 0.04 Entrapped nonaqueous phase 3 cm

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Constant fracture aperture (smooth walls) Macro-scale dispersion is zero Taylor dispersion results the plume to be stretched in flow direction (D L,Taylor )

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Aperture 0 0.24 mm 10 cm Experimental Simulation Variable aperture field is measured by image system Finger shaped forefront of solute plume shows the Macro-Dispersion

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Simulation and Experimental results match for Hele-Shaw cell Simulations underestimate dispersion in Rough- Walled cell Reynolds equation underestimates variations in velocity field

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Network fracture simulation Scale dependent dispersion coefficients

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