Page 168 - Materials Chemistry, Second Edition

5

Vadose Zone Soil Remediation

5.1 Introduction
After site assessment and remedial investigation, if compounds of concern
(COCs) in the subsurface at a site exceed the acceptable levels, remediation
and/or removal of the impacted soil would be required. Many remedial
technologies have been developed and utilized to remediate impacted soil.
These technologies can be categorized into physical, chemical, biological,
and thermal methods. The technologies can also be applied in situ and/or
ex situ. The remedial objective is to reduce the COC concentrations below
acceptable cleanup levels.
This chapter covers design calculations for some commonly used in situ
and ex situ soil remediation techniques. The technologies covered include
soil vapor extraction, soil washing, bioremediation, in situ chemical oxida-
tion, low-temperature thermal desorption, and thermal destruction.

5.2 Soil Vapor Extraction
5.2.1 Description of the Soil-Venting Process

Soil vapor extraction (SVE), also known as soil venting, in situ vacuum extrac-
tion, in situ volatilization, or soil vapor stripping, has become a very popu-
lar remediation technique for soil impacted by volatile organic compounds
(VOCs). The process strips volatile organic constituents from the impacted
soil by inducing an air flow through the impacted zone. The air flow is cre-
ated by a vacuum pump (often called a “blower”) through a single well or a
network of wells.
As the soil vapor is swept away from the void of the vadose zone, fresh air
is naturally (through passive venting wells or air infiltration) or mechani-
cally (through air-injection wells) introduced and refills the void. This flux
of the fresh air will (1) disrupt the existing partition of the COCs among the
void, soil moisture, and soil grain surface by promoting volatilization of the

151