Dual Phase Vacuum Extraction
http://en.wikipedia.org/wiki/Groundwater_remediation
http://www.cpeo.org/techtree/ttdescript/dualphex.htm
Dual-phase extraction (DPE), also known as multi-phase extraction, is a technology that
uses a high-vacuum system to remove both contaminated groundwater and soil vapor. In DPE systems a
high-vacuum extraction well is installed with its screened section in the zone
of contaminated soils and groundwater. Fluid/vapor extraction systems depress
the water table and water flows faster to the extraction well. DPE removes contaminants from above and below the water table. As the water table around
the well is lowered from pumping, unsaturated soil is exposed. This area,
called the capillary fringe, is often highly
contaminated, as it holds undissolved chemicals, chemicals that are lighter
than water, and vapors that have escaped from the dissolved groundwater below.
Contaminants in the newly exposed zone can be removed by vapor extraction. Once
above ground, the extracted vapors and liquid-phase organics and groundwater are separated and treated. Use of dual-phase
extraction with these technologies can shorten the cleanup time at a site, because the capillary fringe is often the most
contaminated area.
In DPE, gas and liquids are conveyed from the extraction well to
the surface in separate conduits by separate pumps or blowers. With a similar
technology called two-phase extraction (in 1997, EPA distinguished dual-phase
and two-phase extraction technologies), soil gas and liquid are conveyed from
the extraction well to the surface in the same conduit. A single vacuum source
(vacuum pump or blower) is used to extract both liquid and gaseous phases. This
latter version is used more often when fuel contamination is present.