TRACER TECHNIQUES FOR CHARACTERIZATION OF AQUIFER AND CONTAMINANT HETEROGENEITY, AND REMEDIAL PERFORMANCE PREDICTION IN A LAGRANGIAN FRAMEWORK

The coupled use of nonreactive and reactive tracers to characterize aquifer heterogeneity and contaminant architecture is discussed, and parameters obtained from tracer tests are presented in a Lagrangian framework that can be used to predict remediation performance. Nonreactive tracers are commonly used to provide information about travel time distributions in hydrologic systems. Reactive tracers have more recently been introduced as a tool to quantify the amount of nonaqueous phase liquid (NAPL) contaminant present within the tracer swept volume. Our group has extended reactive tracer techniques to also characterize NAPL spatial distribution heterogeneity. By conceptualizing the flow field through an aquifer as a collection of streamtubes, the aquifer hydrodynamic heterogeneities may be characterized by a nonreactive tracer travel time distribution, and NAPL spatial distribution heterogeneity may be similarly described using reactive travel time distributions. The combined statistics of these distributions are used to derived a Lagrangian analytical solution for contaminant dissolution. Thus, performance of dissolution-based remedial techniques can be predicted (both in terms of breakthrough curves and mass reduction/flux reduction relationship) using parameters obtained from tracer tests. Illustrative applications are presented from numerical simulations of aqueous dissolution, and laboratory and field-scale experiments of surfactant-enhanced NAPL remediation.