Jim Douglas, Jr.'' These proceedings reflect some of the thoughts expressed at the Oberwolfach Con ference on Porous Media held June 21-27, 1992, organized by Jim Douglas, Jr., Ulrich Hornung, and Cornelius J, van Duijn. Forty-five scientists attended the conference, and about thirty papers were presented. Fourteen manuscripts were submitted for the proceedings and are incorporated in this volume; they cover a number of aspects of flow and transport in porous media. Indeed, there are 223 individual references in the fourteen papers, but fewer than fifteen are cited in more than one paper. The papers appear in alphabetical order (on the basis of the first author). A brief introduction to each paper is given below. Allen and Curran consider a variety of questions related to the simulation of ground water contamination. Accurate water velocities are essential for acceptable results, and the authors apply mixed finite elements to the pressure equation to obtain these ve locities. Since fine grids are required to resolve heterogenei ties, standard iterative procedures are too slow for practical simulation; the authors introduce a parallelizable, multigrid-based it.erative scheme for the lowest order Raviart-Thomas mixed method. Contaminant transport is approximated through a finite element collocation procedure, and an alternating-direction, modified method of characteristics technique is employed to time-step the simulation. Computational experiments carried out on an nCube 2 computer.
