Evaluation of Vacuum-Enhanced SkimmingFor the Remediation of a Large LNAPL Plume

摘要

Vacuum-enhanced skimming utilizes a low vacuum to create a pressure gradient around a groundwater well,rninducing a vapor stream and light non-aqueous liquid (LNAPL) flow towards a recovery well. When thernLNAPL flows into the well, it is removed with LNAPL skimming pumps. The technology facilitates increasedrnLNAPL recovery with little or no groundwater being generated. A pilot study using vacuum-enhancedrnskimming was conducted at a former Department of Defense site. A skimming operation is currently in operationrnto remediate the LNAPL plume, which is estimated to be 1 to 1.5 million gallons. After conducting a pilotrnstudy, it was determined that this technology would be the best available technology for the full-scalernremediation of the LNAPL. The volatile nature of the LNAPL and the presence of a silt layer, located betweenrnthe LNAPL and the ground surface, prove to be an ideal condition to implement this technology. An internalrncombustion engine was utilized as a vacuum source and the vapor treatment method during the pilot study. Thernvacuum placed on the well is not only effective in increasing the free-phase LNAPL removal, but the inducedrnflow of air through the subsurface results in volatile organic compounds (VOC's) being volatilized andrntransported through the ground by the flowing air to the recovery well. The volatilization, or the mass transferrnfrom liquid to the gaseous phase, contributes to the mass removal of the LNAPL.rnThis paper focuses on the vacuum enhanced skimming pilot study, the evaluation of off-gas treatment options,rnand the challenges associated with the full-scale implementation of this technology.