Infiltration of Immiscible Contaminants in the Unsaturated Zone

The presence of a nonaqueous liquid phase in the subsurface often controls the rate and magnitude of ground‐water contamination. In addition, remediation efforts that do not directly address the nonaqueous phase material are unlikely to provide cost‐effective or timely solutions to the ground‐water contamination risk. Practical modeling tools that describe the fate and transport of a separate contaminant phase are described. Simple models such as those described are appropriate for regulatory development and preliminary site assessment and remediation planning. The current work is focused on the one‐dimensional infiltration of a nonaqueous phase liquid through an unsaturated zone initially at residual water saturation. Laboratory experiments examining the infiltration of the water immiscible organics, automatic transmission fluid and isooctane, were used to develop and validate the simple models of the infiltration process. The models described herein are applicable to large spills where the infiltration is essentially one‐dimensional and driven by gravity and capillary forces.