Ali Zafarani Subsurface Processes Group University of California, Irvine

 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

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

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

 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

 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]

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

 Dispersion caused by variety of pathways

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

 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) Entrapped nonaqueous phase 3 cm

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

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

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

 Network fracture simulation  Scale dependent dispersion coefficients