Unsteady multiphase flow modeling of in-situ air sparging system in a variably saturated subsurface environment

In order to preserve groundwater resources from contamination by volatile organic compounds and to clean up sites contaminated with the compounds, we should understand fate and transport of contaminants in the subsurface systems and physicochemical processes involving remediation technologies. To enhance our understanding, numerical studies were performed on the following topics: (i) multiphase flow and contaminant transport in subsurface environments; (ii) biological transformations of contaminants; (iii) in-situ air sparging (IAS); and, thermal-enhanced venting (TEV). Among VOCs, trichloroethylene (TCE) is one of the most-frequently-detected chemicals in the contaminated groundwater. TCE and its daughter products (cis-1,2-dichloroethylene (cDCE) and vinyl chloride (VC)) are chosen as target contaminants.; The effect of the density-driven advection of gas phase, which is generated due to vaporization of high-molecular weight contaminants, on fate and transport of TCE was investigated under several environmental conditions. The density-driven advection accelerated TCE transport into the atmosphere and into the saturated-zone groundwater near a contaminant source area. Sequential biotransformations of TCE, cDCE, and VC are considered herein to examine the effect of biotransformations on multispecies transport.; As two remediation technologies, IAS and TEV were simulated to evaluate their remedial efficiency at contaminated subsurface domains. In IAS simulations done here, IAS using multiple-injection wells showed superior remedial performances over IAS using single-injection well. Under modeling conditions used here, TEV was effective to deliver thermal energy to contaminated zones.; For numerical studies, a three-dimensional finite-element-based numerical model, called TechFlowMP model, was developed.