No abstract

This work was supported by the Yucca Mountain Site Characterization Project Ofice as part of the Civilian Radioactive Waste Management Program of the US. Department of Energy. An Afirrnative ActionlEqual Opportunity Employer This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the Regents of the University qf Califarnia, the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the Regents of the University of California, the United States Government, or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reject those of the Regents of the University of California, the United States Government, or any agency there05 The Los Alamos National Laboratory strongly supports academicfieedom and a researcher's right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness. DISCLAIMER Portions of this document may be illegible electronic image products. Images are produced from the best available original document.

[1] If fluid is injected into joints in rock masses, the pressure required might result in changes in the joint space between rock blocks that accommodate the fluid transport. At one extreme, very low injection rate and pressure, the joint space is unaffected, and the fluid pressure follows the usual law of linear diffusion. At the opposite extreme, very high injection rates, as used, for example, during hydraulic fracturing, the pressure is so high as to overcome the original Earth stress holding the rock blocks in contact. They ''lift off,'' resulting in huge changes in joint space, and the flow equation then becomes so nonlinear that pressure pulses are no longer transmitted in a smooth, diffusive manner but more like a propagating shock wave. In between these extremes, at more modest pressure, the result is not liftoff, but nevertheless, the effective stress tending to close the joint space is reduced; this space dilates, and the effective permeability and storativity of the joint will increase. While the pressure wave will not propagate quite as sharply as it does for liftoff, nonlinearities greatly influence the results, exhibiting behavior far from that predicted by linear diffusion.

No abstract

A new numerical technique called the convolution-based particle tracking (CBPT) method is developed to simulate resident or flux-averaged solute concentrations in groundwater models. The method is valid for steady-state flow and linear transport processes such as sorption with a linear sorption isotherm and first-order decay. The CBPT method uses particle tracking to take advantage of the ability of particle-based approaches to maintain sharp fronts for advection-dominated transport problems common in groundwater modeling and because of the flexibility of the random walk method to simulate a wide range of possible forms of the dispersion tensor. Furthermore, the algorithm for carrying out the convolution and superposition calculation from particle tracking results is very efficient. We show that from a single particle tracking run, source term variability, sorption, and decay can all be simulated rapidly without rerunning the underlying transport model unless the flow field or dispersion parameters are changed. A series of verification simulations are presented to demonstrate the accuracy and efficiency of the CBPT method compared to more conventional particle tracking approaches.