Theoretical study of the significance of nonequilibrium dissolution of nonaqueous phase liquids in subsurface systems

Abstract

The objective of this work is to assess the potential significance of deviations from local equilibrium for the exchange of mass between residual nonaqueous phase liquids and the aqueous phase in the saturated groundwater zone. A one‐dimensional convection‐dispersion mass balance equation incorporating a first‐order interphase mass transfer rate relationship and temporal changes in blob configuration is used to model this system. Analytical and numerical methods are employed to examine the steady state and transient behavior of the system under a variety of hypothetical aquifer conditions and pumping remediation schemes. Sensitivity of the model to several parameters including mass transfer coefficient, blob size and shape, and Darcy velocity is explored. Results of the theoretical assessment indicate that nonequilibrium effects could play a significant role in some contamination scenarios, primarily for large blob sizes and relatively high velocities. Design of soil flushing techniques will be impacted by these conclusions. Uncertainty in several parameter values used in this analysis indicate the need for further experimental investigation of this process.