Remediation and Management of Contaminated Soil - Sustainable Practices in Geoenvironmental Engineering - page 407

Activated carbon cells
or biofilters

Vacuum pump

Air-water separator

Contaminated air

SVE well

Entry ports to allow
air to be drawn into
soil

Air flow

Contaminant
plume

FIGURE 11.2
Schematic of a SVE process. (Adapted from Yong, R.N., Compatible Technology for Treatment and Rehabilitation of
Contaminated Sites , Nikken Sekkei Geotechnical Institute, Japan, NNGI Report No. 5, pp. 1-33, 1998.)

(vadose) zone soil remediation technology in which a vacuum is applied to the soil to
induce the controlled low of air and remove volatile and some semivolatile contaminants
from the soil (USEPA, 1997). The extracted vapor may then be treated to recover or destroy
the contaminants, depending on applicable regulations. The area of the extraction is called
the zone of inluence. Vertical extraction vents are typically implemented to depths of
greater than 1.5 meters up to as much as 91 meters. Horizontal extraction vents (trenches
or horizontal borings) can be used as warranted by contaminant zone geometry, drill rig
access, or other site-speciic factors.
The treatment is usually in situ for highly permeable soils. Groundwater levels may
require lowering to decrease the moisture content. The contaminants pass through the void
space in the soil by vaporization and are captured for further treatment on the soil surface
by condensation, combustion, oxidation, incineration, activated carbon absorption, or bio-
iltration. Field and pilot studies are usually necessary to determine the feasibility and sub-
sequently the design of the method as well as to obtain information necessary to design and
conigure the system. The process may be used in combination with other methods such a
bioremediation. A surface seal consisting of a geomembrane, concrete, or asphalt caps, or
natural materials such as clay or bentonite can be employed to control vapor low. Typically,
in situ SVE processes can require 1 to 3 years. Costs vary signiicantly between sites.

11.3.3 Fracturing

Fracturing differs from the method for extraction of oil or gas and is used to enhance the
eficiency of other in situ technologies in dificult conditions such as silts, clays, shale, and