Review of NAPL modeling approaches for remediation

Modeling the flow of nonaqueous phase liquids (NAPLs) involves the flow of two or more fluids through permeable media, referred to as multiphase flow modeling. This paper provides a review of multiphase modeling approaches and available codes, with particular emphasis on NAPL remediation technologies. Multiphase flow modeling has been used in the petroleum and geothermal fields for decades, but has been applied to environmental problems for about the last 10 years. Available multiphase flow models range from completely analytical solutions to numerical ones. These models vary in complexity from two-dimensional, interface models to three-dimensional, compositional models that account for partitioning for chemicals among different phases. Early applications of NAPL models primarily involved predicting free-phase product recovery of petroleum hydrocarbons or LNAPLs. More recently, NAPL models have been applied to a variety of emerging remedial options, including soil vapor extraction, surfactant-enhanced recovery, and thermal-enhanced recovery. Some of these model applications may be quite complex and have significant data requirements. Complete data sets for most NAPL-contaminated sites are not available, which along with inherent model complexity, makes application of these conceptual models difficult.