Modeling for determination of pre- and post remediation prediction of dissolved contaminant concentration downstream of NAPL source zones

摘要

Organic chemicals that are in the form of dense nonaqueous phase liquids (DNAPLs) exhibit complex flow and entrapment behavior in the subsurface. Because of concerns for groundwater contamination and the long-term costs of pump-and-treat schemes, interest has increased in the application of aggressive free-phase removal technologies. However, these technologies cannot completely remove DNAPLs, especially in heterogeneous aquifers. In managing source zones, decision tools are needed for the assessment of suitability of specific technology to a site and design remediation operations to achieve desired end-points. This paper presents the evaluation of an existing numerical model of multiphase flow and transport for its ability to conduct analysis on the expected solute concentrations downstream of NAPL source zones undergoing remediation. To be used as decision tools, such models should be able to capture the complex processes of mass transfer and mixing from entrapped NAPL sources undergoing remediation. Results from intermediate-scale laboratory experiments are used to evaluate the model to make necessary future improvements. Specifically, the ability of the model to predict downstream solute concentrations resulting from source removal using surfactants is investigated. Partitioning tracer techniques are used to determine the pre and post treatment saturations in the source zone. The ability of the model to simulate the partitioning behavior of tracers is also evaluated.