Successful Demonstration of Enhanced Soil Vapour Extraction

Researchers at Integrated Science & Technologies Inc. recently presented the findings from a field demonstration project that showed that enhanced soil vapour extraction significantly reduced the concentration of 1,4-Dioxane in soil.

1,4-Dioxane is often called simple dioxane because the other dioxane isomers (1,2- and 1,3-) are rarely encountered.  1,4-Dioxane is a synthetic industrial chemical that is completely miscible in water.  It is used as a solvent for a variety of applications.  1,4-Dioxane is a likely contaminant at many sites contaminated with certain chlorinated solvents (particularly 1,1,1-trichloroethane [TCA]) because of its widespread use as a stabilizer for chlorinated solvents

With respect to remediation, some 1,4-dioxane can be removed from pore water found in the vadose zone (unsaturated zone) in the subsurface by conventional soil vapor extraction (SVE), remediation is typically inefficient.  SVE extracts vapors from the soil above the water table by applying a vacuum to pull the vapors out.

SVE is inefficient at removing 1,4-dioxane from pore water in the subsurface vadose zone.  1,4-dioxane has a low Henry’s Law constant at ambient temperature.  This means that there is a low concentration of dissolved 1,4-dioxane gas proportional to its partial pressure in the gas phase.

To enhance the extraction for 1,4-dioxane in the subsurface, the researchers used heated air injection and more focused SVE extraction (XSVE).  The pilot teste was conducted at the former McClellan Air Force Base located in the North Highlands area of Sacramento County, 7 miles (11 km) northeast of Sacramento, California.

Soil Vapor Extraction unit at former McClellan Air Force Base, Calif. (U.S. Air Force Photo by Scott Johnston)

The pilot test consisted for four peripheral heated air injection wells of the XSVE system surrounded a 6.1 m x 6.1 m x 9.1 m deep treatment zone with a central vapor extraction well.

Soil temperature measurements were taken during the pilot test.  Soil temperatures reached as high as ~90°C near the injection wells after 14 months of operation and flushing of the treatment zone with ~20,000 pore volumes of injected air.  Results post treatment showed dioxane reductions of ~94% and ~45% decrease in soil moisture.  See additional information in slides at http://www.contaminantssummit.com/images/presentations/3_RobHinchee.pdf .