Nonideal transport of contaminants in heterogeneous porous media: 8. Characterizing and modeling asymptotic contaminant-elution tailing for several soils and aquifer sediments.

Miscible-displacement experiments were conducted to characterize long-term, low-concentration elution tailing associated with sorption/desorption processes. A variety of soils and aquifer sediments, representing a range of particle-size distributions and organic-carbon contents, were employed, and trichloroethene (TCE) was used as the model organic compound. Trichloroethene transport exhibited extensive elution tailing for all media, with several hundred to several thousand pore volumes of water flushing required to reach the detection limit. The elution tailing was more extensive for the media with higher organic-carbon contents and associated retardation factors. However, when normalized by retardation, the extent of tailing did not correlate directly to organic-carbon content. These latter results suggest that differences in the geochemical nature of organic carbon (e.g., composition, structure) among the various media influenced observed behavior. A mathematical model incorporating nonlinear, rate-limited sorption/desorption described by a continuous-distribution function was used to successfully simulate trichloroethene transport, including the extensive elution tailing.