The potential for human activities to adversely affect environment has become of increasing concern during the past two decades. Concomitantly, the transport and fate of contaminants in subsurface systems has become one of the major research areas in the environmental, hydrological, and Earth sciences. An understanding of how contaminants move in the subsurface is needed to evaluate the probability of contaminants associated with a chemical spill reaching an aquifer and contaminating groundwater. This knowledge is also required to develop and evaluate methods for cleaning up contaminated soils and aquifers. Just as importantly, knowledge of contaminant transport and fate is necessary to design ''pollution prevention'' strategies. A tremendous body of literature on contaminant transport has been generated in response to these needs. This literature consists primarily of results obtained by theoretical, experimental, and mathematical modeling based investigations and, to a much lesser extent, field experiments.

This paper consists of a brief review of some of the major aspects associated with the transport of reactive contaminants in heterogeneous subsurface environments. It begins with a review of basic concepts related to contaminant transport, followed by a discussion of the results obtained from some of the few well-controlled field experiments designed to investigate transport of reactive contaminants in the subsurface. Some of the major factors controlling contaminant transport will then be discussed, followed by a review of conceptual and mathematical approaches used to represent those factors in mathematical models. A brief overview of future needs and opportunities in contaminant transport will close the discussion. ¿ American Geophysical Union 1994