Reactive tracer tests to predict dense nonaqueous phase liquid dissolution dynamics in laboratory flow chambers

Reactive tracer tests were conducted to evaluate the relationship between contaminant mass reduction, R-m, and flux reduction, R-j, in laboratory experiments with porous media contaminated with a dense nonaqueous phase liquid (DNAPL). The reduction in groundwater contaminant flux resulting from partial mass removal was obtained from continuous and pulsed cosolvent and surfactant flushing dissolution tests in laboratory flow chambers packed with heterogeneous porous media. Using the streamtubes concept, a Lagrangian analytical solution was applied to study the contaminant dissolution. The analytical solution was independently parametrized using nonreactive and reactive tracer tests and the predicted dissolution was compared to the observed data. Analytical solution parameters related to aquifer hydrodynamic heterogeneities were determined from a norreactive tracer, while those related to DNAPL spatial distribution heterogeneity were obtained from a reactive tracer. Reactive travel time variance, derived from this combination of tracers, was used to predict the relationship between R-m and R-j. Predictions based on the tracer tests closely matched measured dissolution data, suggesting that tracers can be used to characterize the DNAPL spatial distribution heterogeneity controlling the dissolution behavior. Experimental results demonstrated that increased reactive travel time variance led to greater flux reduction for a given partial mass removal.