(2-PHASE EXTRACTION Process)
The 2-PHASE EXTRACTION Process was developed as an alternative to conventional pump-and-treat technology, particularly in low conductivity formations such as silts and clays that are impacted by volatile organic compounds (VOC). 2-PHASE EXTRACTION uses a high-vacuum source applied to an extraction tube within a water well to increase groundwater removal rates (consequently the dissolved phase of contamination) and to volatilize and extract that portion of contaminant from the sorbed or free product phases. Vacuum lift of water is not a limiting factor in the application of the technology. Since a mixed vapor-liquid column is extracted from the well, the 2-PHASE EXTRACTION technology allows a single piece of equipment (a high vacuum source) to remove contaminants in both the liquid and vapor phases.
To extract both groundwater and soil vapor from a single extraction well, the 2-PHASE EXTRACTION process uses a vacuum pump to apply a high vacuum (generally 18 to 29 inches of mercury) through a central extraction tube, which extends down the well. Soil vapor drawn into the well by the vacuum provides for a high velocity vapor stream at the bottom tip of the extraction tube, which entrains the contaminated groundwater and lifts it to ground surface. As groundwater moves through the extraction system, as much as 95 percent of the VOCs in the water phase are transferred to the vapor phase. The vapor and water phases are then separated at the surface in a separator tank. The water phase requires only carbon polishing prior to discharge, provided that the compounds are adsorbable. With some compounds the water carbon treatment can be eliminated. The vapor phase is subjected to carbon treatment, bioremediation, resin regeneration, catalytic oxidation, or other vapor phase treatment (based on contaminant characteristics, mass loadings, and economics) prior to release to atmosphere.
A kick-start system can induce flow and help dewater the well. The flow of atmospheric air can be regulated by adjustment of the gate valve to: (1) optimize the air-to-water flow ratio to minimize water "slug" production at startup (the term slug refers to an irregular pulsation of water through the extraction tube which indicates irregular water flow); (2) maximize tube penetration into the saturated zone; and (3) maximize the groundwater flow rate by optimizing the applied vacuum to the well's annular space.
Typical installation activities require connection of a power supply, piping and vacuum system leveling, connection to the extraction well(s), and connection of vapor and liquid-phase discharge connections to the final treatment process(es).
This technology is designed to remove VOCs from groundwater and soils.
The Xerox 2-PHASE EXTRACTION process was accepted into the SITE Demonstration Program in summer 1994. The demonstration began in August 1994 at a contaminated groundwater site at McClellan Air Force Base in Sacramento, California and was completed in February 1995. The demonstration was conducted in support of the McClellan Public-Private Partnership coordinated by Clean Sites, Inc. Reports of the demonstration are in preparation.
The Xerox 2-PHASE EXTRACTION process is a patented technology. Six patents were issued from 1991-1995 and several patents are pending. The 2-PHASE EXTRACTION process technology is available under license and is being used extensively in the United States, Canada, South America, Great Britain, and Europe.
Results from the demonstration are detailed below:
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