Contrasting Advective Spreading And Dispersive Mixing In Groundwater
Piscopo, Amy N 1 ; Mays, David C 2 ; Neupauer, Roseanna M 3
1 University of Colorado at Boulder
2 University of Colorado Denver
3 University of Colorado at Boulder
The lack of mixing in laminar flows is a fundamental problem when addressing groundwater contamination, and explains why active in-situ remediation is limited to a thin zone at the plume fringe. One common remediation design is to inject one or more reactants in a treatment solution into the aquifer to stimulate reactions to degrade the contaminant, coupled with extraction of water from another well to increase circulation. The degradation reactions occur at the plume fringe, which can be viewed as the material interface between the contaminated groundwater and the injected treatment solution of reactants, where the two solutions are blended. The term blended is used in this context rather than the term mixed in order to make the distinction between (1) advective spreading, also called stirring, and (2) dispersive mixing. In the case of pure advective spreading, the length of the material interface is a critical parameter in controlling the reaction rates. When the effect of dispersive mixing is considered in addition to advective stirring, the width of the interface grows due to molecular diffusion and mechanical dispersion, increasing blending, which is expected to affect the reaction rate. In this presentation, we describe a design for transient injection and extraction at wells installed near the contaminated site in order to elongate the material interface by advective stirring, or more specifically by stretching and folding the treatment solution. In particular, we compare the degree of blending caused by this transient injection and extraction with the degree of blending caused by dispersive mixing alone (Fig.1).