This is a three-year experimental, theoretical and field study of convective instability and its role in solute mixing during mass transport. Instabilities can develop at different scales under a variety of geologic and hydrogeologic situations when more dense groundwater overlies less dense groundwater. The process mixes the two waters to reduce the density stratification. The specific objectives of the study are to describe the dynamics of instability development both conceptually and mathematically and to evaluate the potential for instability development to influence the chemical evolution of groundwater in large flow systems. The study includes both experiments and the evaluation of an actual groundwater system, the Milk River artesian aquifer, in which unstable mixing has a significant potential for influencing the chemical evolution of the water. The laboratory work will involve a series of precisely controlled and monitored flow tank studies designed to describe the dynamics of the mixing process. The field study will involve a detailed characterization of the geology and hydrogeology of the Milk River aquifer, followed by an evaluation with a variable density model. This study will contribute basic knowledge about a relatively unknown and poorly understood process. Previous studies show that mixing due to instability development can be more important than commonly realized. The work is of practical and academic importance to problems of solvent-enhanced oil recovery, chemical mixing in sedimentary basins and contaminant migration.
