Determining and Modeling Mass-Transfer Rate Limitations in Heterogeneous Aquifers

Abstract

This work focuses on assessing mass-transfer rate limitations on the transport of aqueous phase volatile organic chemicals (VOCs) in real aquifer systems. The rate limiting mechanism is considered as diffusion through immobile regions of a porous medium, i.e., through intra-particle, intra-aggregate, intra-layer pores, or through a series of such zones. Sorption/desorption studies are reviewed for two experimental aquifers: the large-scale, relatively homogeneous Borden site, and the pilot-scale, relatively heterogeneous Moffett site. The flame-sealed ampule method, with accompanying intermittent purge, is discussed with respect to supplying diffusion rate parameters for homogeneous and heterogeneous solute transport models.