(4) remediation costs. In this chapter, we present conventional technologies for free
product recovery from the practical and theoretical viewpoints: pump-and-treat,
skimming, bioslurping, and recovery trenches. This chapter describes the advantages
and limitations of these techniques, and discusses innovative technologies such as
thermal and chemical enhancement (i.e., surfactants), which aim to increase free
product recovery yields and rates.
Keywords Free product recovery · LNAPL · DNAPL · Remediation
2.1 Introduction
Non-Aqueous Phase Liquids (NAPLs) are liquid organic contaminants that are
poorly soluble in water. When present as free products, they migrate into soils and
groundwater as oily liquids. They can be divided into two classes (Mercer and
Cohen 1990; Lemière et al. 2008):
• Light NAPLs (LNAPLs) are lighter than water and therefore float on top of the
water table. LNAPLs include various classes of chemical compounds such as
monoaromatic compounds (benzene and toluene), fuels, oils, lubricants, crude
oil, and cyclohexane.
• Dense NAPLs (DNAPLs) are heavier than water. If the mass of contaminant is
sufficient, DNAPLs sink through the saturated zone and accumulate at the bottom
of the aquifer where their movement is dictated by gravity and heterogeneity: e.g.,
the topography of subsurface geological formations—specifically, the characteristics of layers and fractures—as well as groundwater flow direction. DNAPLs
include creosotes, chlorinated compounds, polycyclic aromatic hydrocarbons,
and coal tar.
These contaminants exist simultaneously in several phases (free product,
dissolved phase, and gaseous phase). The fundamental behavior mechanisms of
NAPL dissolved phase are the same as those of miscible contaminants (i.e., convection, dispersion, and diffusion). Thereby the overall behavior mechanisms depend on
the behavior laws of each phase (Mercer and Cohen 1990; Pankow and Cherry
1996). This is, therefore, a particularly complex situation where NAPL contamination leads to the formation of mixed contaminated phases (water, NAPL, air), each
with its own physical characteristics (density, viscosity, etc.). Each moving phase
conveys contaminants that can pass from one phase to another (by dissolution,
vaporization, or condensation), and can interact with the surrounding solid phases
(i.e., sorption–desorption) (Mercer and Cohen 1990; Cohen and Mercer 1993;
Huling and Weaver 1996).
The contaminant bulk forms a liquid phase distinct from the water phase; NAPL
fraction may be soluble and can dissolve in water (two-phase NAPL/water system).
In unsaturated zones, another phase exists as the gas phase (three-phase NAPL/
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S. Colombano et al.
product recovery from the practical and theoretical viewpoints: pump-and-treat,
skimming, bioslurping, and recovery trenches. This chapter describes the advantages
and limitations of these techniques, and discusses innovative technologies such as
thermal and chemical enhancement (i.e., surfactants), which aim to increase free
product recovery yields and rates.
Keywords Free product recovery · LNAPL · DNAPL · Remediation
2.1 Introduction
Non-Aqueous Phase Liquids (NAPLs) are liquid organic contaminants that are
poorly soluble in water. When present as free products, they migrate into soils and
groundwater as oily liquids. They can be divided into two classes (Mercer and
Cohen 1990; Lemière et al. 2008):
• Light NAPLs (LNAPLs) are lighter than water and therefore float on top of the
water table. LNAPLs include various classes of chemical compounds such as
monoaromatic compounds (benzene and toluene), fuels, oils, lubricants, crude
oil, and cyclohexane.
• Dense NAPLs (DNAPLs) are heavier than water. If the mass of contaminant is
sufficient, DNAPLs sink through the saturated zone and accumulate at the bottom
of the aquifer where their movement is dictated by gravity and heterogeneity: e.g.,
the topography of subsurface geological formations—specifically, the characteristics of layers and fractures—as well as groundwater flow direction. DNAPLs
include creosotes, chlorinated compounds, polycyclic aromatic hydrocarbons,
and coal tar.
These contaminants exist simultaneously in several phases (free product,
dissolved phase, and gaseous phase). The fundamental behavior mechanisms of
NAPL dissolved phase are the same as those of miscible contaminants (i.e., convection, dispersion, and diffusion). Thereby the overall behavior mechanisms depend on
the behavior laws of each phase (Mercer and Cohen 1990; Pankow and Cherry
1996). This is, therefore, a particularly complex situation where NAPL contamination leads to the formation of mixed contaminated phases (water, NAPL, air), each
with its own physical characteristics (density, viscosity, etc.). Each moving phase
conveys contaminants that can pass from one phase to another (by dissolution,
vaporization, or condensation), and can interact with the surrounding solid phases
(i.e., sorption–desorption) (Mercer and Cohen 1990; Cohen and Mercer 1993;
Huling and Weaver 1996).
The contaminant bulk forms a liquid phase distinct from the water phase; NAPL
fraction may be soluble and can dissolve in water (two-phase NAPL/water system).
In unsaturated zones, another phase exists as the gas phase (three-phase NAPL/
62
S. Colombano et al.