Submitted to: Journal of Contaminant Hydrology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/10/2003
Publication Date: 9/10/2004
Citation: O'Carroll, D.M., Bradford, S.A., Abriola, L.M. Infiltration of PCE in a system containing spatial wettability variations. Journal of Contaminant Hydrology. 2004. 73:39-63. Interpretive Summary: Soil and groundwater in many regions of the United States are contaminated with organic liquid wastes such as oil, gas, and solvents. Knowledge of the processes that control organic liquid migration in the soil is needed to accurately assess contaminant extent and to develop efficient cleanup strategies. This manuscript reports on research designed to explore the role of soil texture (size) and composition (chemical properties) on organic liquid migration. The spatial configuration and rate of migration of the organic liquid was found to be highly dependent on soil-organic liquid interactions and the texture distribution. In soils with strong organic liquid interactions the organic liquid filled much the pore space and migrated at a slower rate, whereas in soils with minimal organic liquid interactions the organic liquid occurred at lower contents and migrated at a faster rate. A computer model developed by the authors accurately predicted organic-liquid migration when both the soil texture and composition were accurately accounted for in this model.
Technical Abstract: A two-dimensional infiltration experiment was conducted to investigate and quantify the effect of spatial wettability variations on DNAPL migration and entrapment in saturated sands. Visual observations of tetrachloroethylene (PCE) infiltration show that organic-wet sand lenses act as very effective capillary barriers, retaining PCE and inhibiting its downward migration. At the end of the PCE infiltration and redistribution event, high PCE saturations were present in the organic-wet lenses, whereas low residual PCE saturations were present in the exposed water-wet sands. A multiphase numerical simulator, previously modified to account for the influence of wettability variations on hydraulic property relations, was used to model this sand box experiment. The simulator incorporates wettability-modified van Genuchten and Brooks-Corey capillary pressure/saturation relationships as well as Burdine and Mualem relative permeability relationships. Although both relative permeability models were qualitatively able to predict the observed PCE retention in the organic-wet layers, simulations with the Mualem model failed to capture the observed rate of PCE migration. A traditional multiphase simulator, incorporating water-wet capillary retention relations, failed to predict both observed PCE pathways and retention behavior. This study illustrates the potential influence of subsurface wettability variations on DNAPL migration and entrapment and supports the use of modified capillary relations in conjunction with the Burdine model for multiphase migration predictions in chemically heterogeneous environments.