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