HR: 11:50h
AN: H52D-07    [Abstracts]
TI: Impact of boundary conditions on tracer retention in discrete fracture networks
AU: * Frampton, A
EM: frampton@kth.se
AF: Royal Institute of Technology, Dept of Water Resources Engineering, Brinellv. 32, Stockholm, SE-10044 Sweden
AB: We study the impact of boundary conditions on transport of tracers subject to retention in discrete fracture networks. Coupled advection and retention are controlled by two correlated variables integrated along random trajectories: the water residence time τ , and the hydrodynamic retention parameter β . The effect of two types of injection modes for tracer transport are investigated within the framework of two-dimensional discrete fracture network simulations of fluid flow and particle advection. In addition to different injection modes, we consider two cases of aperture variability, corresponding to strong and weak heterogeneity in the flow velocities. Results show that both τ and β statistics are significantly altered depending on the choice of injection mode. In addition, the variation of these random variables is increased by several orders of magnitude as the variation in aperture is increased. We also study related segmentwise distributions, such as ξ and ζ which integrate to τ and β respectively. In particular, we analyse the asymptotic behaviour of the breakthrough distributions of these transport variables at constant control planes throughout the system. The value of the asymptotic slopes α can range from less than 1 (indicating anomalous transport) to greater than 2 (indicating Gaussian transport), and is strongly dependent on the type of injection mode. This impacts fundamental aspects of the class of distributions governing advective transport. Finally, we show implications of the injection modes for a few specific sorbing and decaying radionuclides, relevant for typical applications in crystalline rock. These new findings suggest that careful consideration of the type of boundary condition for transport in conjunction with the variation of fracture transmissivity should be made for more accurate transport simulations in discrete fracture networks.
DE: 1832 Groundwater transport
DE: 1847 Modeling
DE: 1869 Stochastic hydrology
SC: Hydrology [H]
MN: Fall Meeting 2005