(Johnson and Pankow 1992). The low interfacial tension between liquid chlorinated
solvent phase and water allows chlorinated solvent DNAPL to enter small fractures
and pore spaces, facilitating deep penetration into the subsurface (Johnson and
Pankow 1992). Alternatively, the unpredictable nature of DNAPL flow can cause
the solvent to continue migrating as a continuous body, or in thin “fingers” which
can lead to the collection of large amounts of solvent in “pools” on top of less
permeable layers (Johnson and Pankow 1992). The low solubility of COCs mean
that when a significant quantity of solvent is introduced into the environment, liquid
solvent will dissolve slowly and persist for decades or centuries (Johnson and
Pankow 1992). Moreover, most COCs exhibit low biologic and abiotic degradation
rates and can persist in the subsurface for extended periods of time.
Different remediation technologies are efficient to remove COCs pollution,
especially physical and thermal treatment methods. Pump-and-treat systems are
well developed and industrially applied in order to remove most pollutant, as the
technology was available and relatively fast and easy to operate (Colombano et al.
2010). However, “rebound” effect generally occurs at the end of the treatment, and
pump-and-treat technologies cannot achieve a complete remediation after many
years because of pollutant persistence (Travis and Doty 1990; Pankow and Cherry
1996). Thermal treatment and surfactant/foam flushing were thus proposed as
complementary techniques to reduce as low as possible residual saturations (Kingston et al. 2014; Pennell et al. 2014; Maire et al. 2018), before implementing more
costly remediation methods such as in situ remediation.
Development of in situ chemical processes, which involves the injection of a
chemical reagent directly in front of the pollution, has shown promising results for
the remediation of COCs pollution, for both source remediation and plume control
(McCarty 2010; Kueper et al. 2014). If in situ chemical oxidation (ISCO) has been
first applied for the remediation of chlorinated solvents, in situ chemical reduction
(ISCR) is more effective on highly chlorinated compounds, due to electron deficiency on carbon atoms (Brown 2010). ISCR is often presented as a more
environmental-friendly alternative than ISCO as it is less destructive with respect
to soil organic matter (Colombano et al. 2010).
This chapter describes the preliminary step concerning the implementation of in
situ chemical reduction technologies, with the presentation of the prerequisites
related to chlorinated solvent properties and transport/fate in soils and groundwater.
Discussions are essentially focused on the development and improvement of zerovalent iron-based particles for the chemical reduction of COCs, with kinetic and
degradation pathway approaches in order to highlight chemical reduction mechanisms. Effects of environmental conditions on degradation rate are then developed.
Finally, injection technologies and a case study are presented and discussed in
details.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
285
solvent phase and water allows chlorinated solvent DNAPL to enter small fractures
and pore spaces, facilitating deep penetration into the subsurface (Johnson and
Pankow 1992). Alternatively, the unpredictable nature of DNAPL flow can cause
the solvent to continue migrating as a continuous body, or in thin “fingers” which
can lead to the collection of large amounts of solvent in “pools” on top of less
permeable layers (Johnson and Pankow 1992). The low solubility of COCs mean
that when a significant quantity of solvent is introduced into the environment, liquid
solvent will dissolve slowly and persist for decades or centuries (Johnson and
Pankow 1992). Moreover, most COCs exhibit low biologic and abiotic degradation
rates and can persist in the subsurface for extended periods of time.
Different remediation technologies are efficient to remove COCs pollution,
especially physical and thermal treatment methods. Pump-and-treat systems are
well developed and industrially applied in order to remove most pollutant, as the
technology was available and relatively fast and easy to operate (Colombano et al.
2010). However, “rebound” effect generally occurs at the end of the treatment, and
pump-and-treat technologies cannot achieve a complete remediation after many
years because of pollutant persistence (Travis and Doty 1990; Pankow and Cherry
1996). Thermal treatment and surfactant/foam flushing were thus proposed as
complementary techniques to reduce as low as possible residual saturations (Kingston et al. 2014; Pennell et al. 2014; Maire et al. 2018), before implementing more
costly remediation methods such as in situ remediation.
Development of in situ chemical processes, which involves the injection of a
chemical reagent directly in front of the pollution, has shown promising results for
the remediation of COCs pollution, for both source remediation and plume control
(McCarty 2010; Kueper et al. 2014). If in situ chemical oxidation (ISCO) has been
first applied for the remediation of chlorinated solvents, in situ chemical reduction
(ISCR) is more effective on highly chlorinated compounds, due to electron deficiency on carbon atoms (Brown 2010). ISCR is often presented as a more
environmental-friendly alternative than ISCO as it is less destructive with respect
to soil organic matter (Colombano et al. 2010).
This chapter describes the preliminary step concerning the implementation of in
situ chemical reduction technologies, with the presentation of the prerequisites
related to chlorinated solvent properties and transport/fate in soils and groundwater.
Discussions are essentially focused on the development and improvement of zerovalent iron-based particles for the chemical reduction of COCs, with kinetic and
degradation pathway approaches in order to highlight chemical reduction mechanisms. Effects of environmental conditions on degradation rate are then developed.
Finally, injection technologies and a case study are presented and discussed in
details.
6 In Situ Chemical Reduction of Chlorinated Organic Compounds
285