1 g l
À1
. For water non-miscible hydrocarbons, their behavior in groundwater
mostly depends on their density (<1 floating and >1 sinking). By taking events
of pollution into account, the French commission for sustainable development has
distinguished hydrocarbons in four main categories (CGDD 2013): (1) Usual
hydrocarbons (gas, fuel oil) display a density below 1 and very low water
solubility, whereas gas is volatile and rather biodegradable, fuel oil is semivolatile and less biodegradable; (2) BTEX are hardly oxidizable monocyclic
aromatic VCs with density lower than 1 and a rather high solubility in pure
water ranging from 0.17 to 1.8 g l
À1 (log K ow between 2 and 3). (3) Polycyclic
aromatic hydrocarbons (PAHs) are compounds of a large family (hundreds of
compounds at least) made of fused aromatic rings that have densities higher than
1. They can have heteroatoms (O, N, S) within their rings that improve their
solubility in water. Nevertheless, their water solubility is very low for the most
usual molecules (log K ow > 4), except for naphthalene (C 10 H 8 ) that behaves
between PAHs and BTEX; it is considered as volatile and its solubility in pure
water is 32 mg l
À1 . They are very abundant in tars and are strongly adsorbed to
soils. (4) Halogenated compounds (mainly chlorinated and fluorinated ones)
which represent a large family with different behaviors: some of them are VCs
and display high solubility in water (e.g., up to 4.5 g l
À1 for trichloroethylene
(TCE) at room temperature, RT), while some others like polychlorinated benzene, PCBs and dioxins, are lipophilic, concentrate in sediments and behave more
like SVCs. All these compounds are poorly biodegradable because of their high
toxicity. However, the reductive dehalogenation is more and more used for in situ
remediation (Stroo et al. 2012). Because of their different behavior, these compounds must be considered individually when treatment is decided.
The reality of environmental pollutions is often much more complex, because of
the mixtures of substances and their interactions with the soil organic matter, but
their characteristics are often attenuated (Mulligan and Yong 2004; Fakour and Lin
2014). The effect of local conditions (e.g., pH, redox potential, permeability, ligand
concentrations) on contaminants mobility is difficult to predict. Knowing the speciation of MTEs and metalloids is critical in order to understand the mechanisms that
control their mobility. The determination of pollutant speciation is needed in order to
elaborate an accurate conceptual site model and suitable treatments. Therefore, the
measurement of leaching potentials for contaminants and the soil buffer capacity are
necessary before considering a treatment in order to, whenever it is required, make it
the least impacting and the most economic possible (Gillow and Hay 2016).
In conclusion, SL is of special interest to water-soluble, recalcitrant, and poorly
volatile contaminants. Therefore, it is often used for salts, usually without the need
for additives, unless a redox treatment would be more appropriate. Besides, the most
usual contaminants treated by leaching are metals in mono and divalent oxidation
states and low volatile and recalcitrant hydrocarbons (PAHs and low solubility
chlorinated compounds such as dioxins and PCBs); however, they mostly require
the use of additives in order to improve their water solubility (Sect. 1.3).
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
13
À1
. For water non-miscible hydrocarbons, their behavior in groundwater
mostly depends on their density (<1 floating and >1 sinking). By taking events
of pollution into account, the French commission for sustainable development has
distinguished hydrocarbons in four main categories (CGDD 2013): (1) Usual
hydrocarbons (gas, fuel oil) display a density below 1 and very low water
solubility, whereas gas is volatile and rather biodegradable, fuel oil is semivolatile and less biodegradable; (2) BTEX are hardly oxidizable monocyclic
aromatic VCs with density lower than 1 and a rather high solubility in pure
water ranging from 0.17 to 1.8 g l
À1 (log K ow between 2 and 3). (3) Polycyclic
aromatic hydrocarbons (PAHs) are compounds of a large family (hundreds of
compounds at least) made of fused aromatic rings that have densities higher than
1. They can have heteroatoms (O, N, S) within their rings that improve their
solubility in water. Nevertheless, their water solubility is very low for the most
usual molecules (log K ow > 4), except for naphthalene (C 10 H 8 ) that behaves
between PAHs and BTEX; it is considered as volatile and its solubility in pure
water is 32 mg l
À1 . They are very abundant in tars and are strongly adsorbed to
soils. (4) Halogenated compounds (mainly chlorinated and fluorinated ones)
which represent a large family with different behaviors: some of them are VCs
and display high solubility in water (e.g., up to 4.5 g l
À1 for trichloroethylene
(TCE) at room temperature, RT), while some others like polychlorinated benzene, PCBs and dioxins, are lipophilic, concentrate in sediments and behave more
like SVCs. All these compounds are poorly biodegradable because of their high
toxicity. However, the reductive dehalogenation is more and more used for in situ
remediation (Stroo et al. 2012). Because of their different behavior, these compounds must be considered individually when treatment is decided.
The reality of environmental pollutions is often much more complex, because of
the mixtures of substances and their interactions with the soil organic matter, but
their characteristics are often attenuated (Mulligan and Yong 2004; Fakour and Lin
2014). The effect of local conditions (e.g., pH, redox potential, permeability, ligand
concentrations) on contaminants mobility is difficult to predict. Knowing the speciation of MTEs and metalloids is critical in order to understand the mechanisms that
control their mobility. The determination of pollutant speciation is needed in order to
elaborate an accurate conceptual site model and suitable treatments. Therefore, the
measurement of leaching potentials for contaminants and the soil buffer capacity are
necessary before considering a treatment in order to, whenever it is required, make it
the least impacting and the most economic possible (Gillow and Hay 2016).
In conclusion, SL is of special interest to water-soluble, recalcitrant, and poorly
volatile contaminants. Therefore, it is often used for salts, usually without the need
for additives, unless a redox treatment would be more appropriate. Besides, the most
usual contaminants treated by leaching are metals in mono and divalent oxidation
states and low volatile and recalcitrant hydrocarbons (PAHs and low solubility
chlorinated compounds such as dioxins and PCBs); however, they mostly require
the use of additives in order to improve their water solubility (Sect. 1.3).
1 Contaminant Mobilization from Polluted Soils: Behavior and Reuse of Leaching. . .
13