Removal of trichloroethylene contamination from the subsurface: A comparative evaluation of different remediation strategies by means of numerical simulation

Abstract

DISCLAIMERThis document was prepared as an account of work sponsored by the United States Government. Neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any G_their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agencj thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California and shall not be used for advertising or product endorsement purposes.This report has been reproduced directly from the best available copy. water, many of these organics have large enough aqueous phase solubilities to significantly degrade the quality of groundwater with which they come in contact. In addition, many of these substances exhibit high vapor pressures, causing them to partition strongly into the gas phase in their surroundings. Because of these properties, a volatile organic compound (VOC), once introduced into the subsurface may be transported as a solute, a vapor, or as a constituent in a nonaqueous phase liquid (NAPL). This implies that at some sites, an adequate description of the migration of these contaminants in the subsurface would necessarily involve three phasesmgas, aqueous and NAPL. For example, to design an effective aquifer remediation scheme for a site where NAPL is present, it would be wrong to focus solely on the aqueous phase while ignoring either the gas phase or the NAPL phase.Equations governing multiphase fluid flow with interphase mass transfer in porous media have been presented in the literature, see for example Faust [1985], Abriola and Pinder [1985], Falta [1990]. Owing to the highly non-linear nature of these equations, they are not amenable to solution by analytical means. As a result, significant research effort has been directed toward the development of numerical simulators capable of solving the system of equations and modeling the behavior of NAPL contaminants in the subsurface under natural (ambient) conditions, as well as in response to various clean-up and treatment procedures.The capabilities and limitations of several of the numerical simulators reported in the litera-• ture have been reviewed and summarized by Falta [1990]. The interested reader should consult that reference. In the present work, we use a simulator developed by Falta et al. [1990a], known as "STMVOC," which models true three-phase flow in which NAPL, gas and aqueous phases can move in respon...