Abstract: Use of High-Vacuum Technology to Remediate Soils and Groundwater in Low-Permeability Formations

Steven P. Sittler, Mark D. Flavin

The combination of groundwater pump-and-treat with vapor extraction has been successfully practiced as an integrated remedial strategy in high-permeability geologic formations. However, the effectiveness of such systems can be severely restricted as formation permeability decreases. In silty clay, glacial till materials common throughout the upper midwest, conventional pump-and-treat/vapor extraction systems typically cannot produce sufficient groundwater recovery nor create adequate subsurface air flow to expedite site remediation. Remedial efforts are further hindered by the high adsorptive capacity of silts and clays, making removal of adsorbed organics more difficult.

The application of high vacuums, using liquid-ring pumps, has enabled successful remediation at sites that are not amenable to conventional groundwater pump-and-treat/vapor extraction techniques. High vacuums (25 in. of mercury vs. 1 to 5 in. for a conventional system) can be applied to a network of extraction wells to increase groundwater recovery rates and maximize subsurface air flow in these low-permeability formations, resulting in increased volatilization of organic compounds and increased mass removal rates. In addition, subsurface oxygen levels are also increased, enhancing naturally occurring biodegradation. Increased groundwater recovery rates under the influence of a vacuum also can create a larger capture zone for each individual extraction well, substantially increasing s te dewatering and aiding vapor extraction from previously saturated sediments. Since vapor extraction is much more efficient at mass removal of volatile organics than groundwater extraction, the added dewatering because of the high vacuum will increase overall contaminant removal and decrease remedial time.

AAPG Search and Discovery Article #90984©1994 AAPG Annual Convention, East Lansing, Michigan, September 18-20, 1994