pressure. It results in high risk to enhance downward migration of DNAPLs
(Rathfelder et al. 2003). However, it can bring benefits when a trapped DNAPL
contamination is positioned above a compact and isotropic shallow substratum.
Thus, SF can also improve the recovery of pure NAPL, especially when using
dynamic GW recirculation (Potter and Killingstad 2016). Another way to enhance
NAPL recovery is by increasing the pressure gradient, also called viscous force,
within the porous network (Maire et al. 2015).
The behavior of chemical mixtures usually differs substantially from the one of
pure compounds. A well-known example is coal tars, that are mixtures of many
molecules with highly different water solubility and affinity for the solid phase. At
the tar/water interface, the least soluble compounds limit the availability of the others
(Birak and Miller 2009; Ranc et al. 2016).
1.2.2.2 Behavior of Dissolved Contaminants
This behavior concerns all contaminants, but this section focuses more especially on
MTEs ions. Several phenomena are involved which delay or speed up the transport
of contaminants in GW. These phenomena are adsorption, precipitation (before or
after a change of the oxidation state), (bio)transformation, colloidal transport, and
volatilization. Chemical speciation is a determining factor in these phenomena. So,
the chemical elements can be found in GW as free ions (e.g., Ca
2+ , Fe
2+ ), as
oxyanions when the oxidation state of MTEs is ! IV (e.g., CrO 4
À ) and as inorganic
complexes (e.g., (UO 2 ) 2 CO 3 (OH) 3
À ) or organic ones (e.g., Fe(CN) 6
3À
). Most of
MTEs are under the cationic form. These cations easily react with the negatively
charged soil phases; they can be precipitated by anions in the form of poorly soluble
complexes (e.g., sulfide, carbonates, humic acids (HA), aluminosilicates) or remain
dissolved as free ion or being stabilized in water in the form of charged complexes
(e.g., with fluvic acids (FA) or malate ligands). The formation of strong complexes
Fig. 1.8 Variations of residual saturations vs. capillary number [Adapted from Lake (1989)]
18
N. Fatin-Rouge
(Rathfelder et al. 2003). However, it can bring benefits when a trapped DNAPL
contamination is positioned above a compact and isotropic shallow substratum.
Thus, SF can also improve the recovery of pure NAPL, especially when using
dynamic GW recirculation (Potter and Killingstad 2016). Another way to enhance
NAPL recovery is by increasing the pressure gradient, also called viscous force,
within the porous network (Maire et al. 2015).
The behavior of chemical mixtures usually differs substantially from the one of
pure compounds. A well-known example is coal tars, that are mixtures of many
molecules with highly different water solubility and affinity for the solid phase. At
the tar/water interface, the least soluble compounds limit the availability of the others
(Birak and Miller 2009; Ranc et al. 2016).
1.2.2.2 Behavior of Dissolved Contaminants
This behavior concerns all contaminants, but this section focuses more especially on
MTEs ions. Several phenomena are involved which delay or speed up the transport
of contaminants in GW. These phenomena are adsorption, precipitation (before or
after a change of the oxidation state), (bio)transformation, colloidal transport, and
volatilization. Chemical speciation is a determining factor in these phenomena. So,
the chemical elements can be found in GW as free ions (e.g., Ca
2+ , Fe
2+ ), as
oxyanions when the oxidation state of MTEs is ! IV (e.g., CrO 4
À ) and as inorganic
complexes (e.g., (UO 2 ) 2 CO 3 (OH) 3
À ) or organic ones (e.g., Fe(CN) 6
3À
). Most of
MTEs are under the cationic form. These cations easily react with the negatively
charged soil phases; they can be precipitated by anions in the form of poorly soluble
complexes (e.g., sulfide, carbonates, humic acids (HA), aluminosilicates) or remain
dissolved as free ion or being stabilized in water in the form of charged complexes
(e.g., with fluvic acids (FA) or malate ligands). The formation of strong complexes
Fig. 1.8 Variations of residual saturations vs. capillary number [Adapted from Lake (1989)]
18
N. Fatin-Rouge