Ali Zafarani Subsurface Processes Group University of California, Irvine

1. Ali Zafarani Subsurface Processes Group University of California, Irvine A review on solute transport in single fractures: combined Experimental/ Computational modeling approach

2. 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 Why we are interested in subsurface contaminant transport?

3. Provide pathways for fluid flow • Large scale fracture networks • Reservoirs formed in fractured rocks • Fractures appear in many kinds of geological systems Importance of fractures in contaminant transport in subsurface environment

4. Advection • Transport of particle with the flow field • Dispersion (Effective Longitudinal Dispersion) • Molecular Diffusion • Taylor dispersion • Macro scale dispersion What are the Transport Mechanisms in fractured porous Media

5. 3-D Navier-Stokes Equation Formulation of advection and Fluid flow through a fracture Momentum Eq. Mass Conservation Inertial forces Viscous forces Pressure term Inertial<< viscous and pressure • 3-D Stokes Equation Changes in fracture aperture are smooth Normal velocity to fracture walls are negligible 3-D  2-D • 2-D Reynolds Equation

6. Molecular Diffusion • Fick’s first law of Diffusion • diffusive flux ~ spatial concentration gradient Diffusion Coefficient [L2/T] • Fick’s second law of Diffusion • Changes of concentration field with time

7. b Parabolic distribution of velocity in aperture ~ square mean velocity ~ Mean aperture size Taylor Dispersion V

8. Dispersion caused by variety of pathways Macrodispersion

9. Effective Longitudinal Dispersion

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

11. 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 Images provide detailed quantitative measurements Aperture (cm) 0 0.04 Entrapped nonaqueous phase 3 cm

12. Constant fracture aperture (smooth walls) Macro-scale dispersion is zero Taylor dispersion results the plume to be stretched in flow direction (DL,Taylor) Hele-shaw cell experiment and results

13. Aperture 0 0.24 mm Rough-walLed fracture (variable aperture) • Variable aperture field is measured by image system • Finger shaped forefront of solute plume shows the Macro-Dispersion 10 cm Simulation Experimental

14. Simulation and Experimental results match for Hele-Shaw cell Simulations underestimate dispersion in Rough-Walled cell Reynolds equation underestimates variations in velocity field Comparison of effective dispersion between experimental and simulation results

15. Network fracture simulation Scale dependent dispersion coefficients Future: Developing from single fracture to fracture network

16. Thank you for your attention!