Sustainable Water Management - Sustainable Practices in Geoenvironmental Engineering - page 92

additives include organic or inorganic acids, bases, water soluble solvents, complexing
agents, and surfactants. Removal eficiencies are related to, and affected by, soil pH, soil
type, cation exchange capacity, particle size, permeability, and the type of contaminants.
High soil permeabilities (greater than 1 × 10 −3 cm/s) are considered to be beneicial for
such procedures.
As an alternative to groundwater pumping, soil vapor extraction (SVE) (Figure 3.10) may
be utilized for the vaporization of volatile and semivolatile components in the unsaturated
zone (Yong, 1998; Rathfelder et al., 1991). Soil can be decontaminated by applying a vacuum
to pull the volatile emissions through the soil pore spaces. The air may be then treated at
the surface with activated carbon ilters, chemical oxidation, or bioilters. This technique
is applicable to highly permeable soils and volatile contaminants such as gasoline or sol-
vents. Other parameters such as the octanol-water coeficient, Henry's law constant and
solubility of the contaminant, and moisture and organic contents of the soil also affect the
removal eficiencies.
Volatile components can also be removed by air sparging. In this technique, bubbles of
air are injected into the groundwater to strip NAPLs and to add oxygen for in situ bioreme-
diation. It has been successfully used for dissolved hydrocarbon plumes (Bass et al., 2000).
Reduction of the NAPL zone may then allow natural attenuation processes to proceed.
Bioventing is a variation of this technique where lower aeration rates are used to promote
aerobic biodegradation instead of volatilization.

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 3.10
Schematic of a SVE process. A series of SVE wells can be introduced into the ground, connected in series or
in parallel. The number of SVE wells that can be introduced will depend on the capacity of the vacuum pump
system. (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.)