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Vacuum‐enhanced recovery of water and NAPL: Concept and field test
Many hydrocarbon‐contaminated soils contain nonaqueous phase liquid (NAPL) following releases from facilities such as underground storage tanks and pipelines. The recovery of free product by pumping from extraction wells or trenches is often an essential prerequisite step prior to further remedial actions. Vacuum‐enhanced NAPL recovery (sometimes referred to as dual‐phase extraction or bioslurping) has attracted recent attention because it offers a means to increase NAPL recovery rates compared with conventional methods, and to accomplish dewatering, while also facilitating vapor‐based unsaturated zone cleanup. A conceptual model is presented that recognizes the effects that vacuum‐enhanced recovery has on soil water and NAPL, with a focus on liquid residing at negative gage pressures and therefore lacking sufficient potential energy to flow into a conventional recovery well or trench. The imposition during vacuum‐enhanced recovery of subatmospheric pressures within the subsurface can reduce the required potential energy (i.e., the entry suction), allowing liquid to be extracted that hitherto had not been able to flow into the well; moreover, it induces both pneumatic and hydraulic gradients toward the vacuum source that increase the rate of water and NAPL recovery. This conceptual model was tested during a 3‐week‐long pilot study at a South Carolina industrial site at which diesel fuel had been discovered in a saprolite formation. During Phase 1 of the pilot study, conventional recovery (liquid only) was carried out from a well screened at the water table, while during Phase 2 dual‐phase extraction was performed at the same well. The application of 27 kPa vacuum resulted in an increase in NAPL recovery from negligible (Phase 1) to approximately 6.6 l/d (Phase 2), with a concurrent increase in water recovery from approximately 190 to 760 l/ d. Neutron moisture probe observations revealed that vadose‐zone liquids underwent redistribution toward the extraction well in response to the onset of Phase 2, also in accordance with the conceptual model. An understanding of soil physical relationships is crucial to the successful application of these and other in situ soil remediation technologies.
Vacuum‐enhanced recovery of water and NAPL: Concept and field test
Many hydrocarbon‐contaminated soils contain nonaqueous phase liquid (NAPL) following releases from facilities such as underground storage tanks and pipelines. The recovery of free product by pumping from extraction wells or trenches is often an essential prerequisite step prior to further remedial actions. Vacuum‐enhanced NAPL recovery (sometimes referred to as dual‐phase extraction or bioslurping) has attracted recent attention because it offers a means to increase NAPL recovery rates compared with conventional methods, and to accomplish dewatering, while also facilitating vapor‐based unsaturated zone cleanup. A conceptual model is presented that recognizes the effects that vacuum‐enhanced recovery has on soil water and NAPL, with a focus on liquid residing at negative gage pressures and therefore lacking sufficient potential energy to flow into a conventional recovery well or trench. The imposition during vacuum‐enhanced recovery of subatmospheric pressures within the subsurface can reduce the required potential energy (i.e., the entry suction), allowing liquid to be extracted that hitherto had not been able to flow into the well; moreover, it induces both pneumatic and hydraulic gradients toward the vacuum source that increase the rate of water and NAPL recovery. This conceptual model was tested during a 3‐week‐long pilot study at a South Carolina industrial site at which diesel fuel had been discovered in a saprolite formation. During Phase 1 of the pilot study, conventional recovery (liquid only) was carried out from a well screened at the water table, while during Phase 2 dual‐phase extraction was performed at the same well. The application of 27 kPa vacuum resulted in an increase in NAPL recovery from negligible (Phase 1) to approximately 6.6 l/d (Phase 2), with a concurrent increase in water recovery from approximately 190 to 760 l/ d. Neutron moisture probe observations revealed that vadose‐zone liquids underwent redistribution toward the extraction well in response to the onset of Phase 2, also in accordance with the conceptual model. An understanding of soil physical relationships is crucial to the successful application of these and other in situ soil remediation technologies.
Vacuum‐enhanced recovery of water and NAPL: Concept and field test
Baker, Ralph S. (author) / Bierschenk, John (author)
Journal of Soil Contamination ; 4 ; 57-76
1995-01-01
20 pages
Article (Journal)
Electronic Resource
Unknown
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